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Author(s): Henrik Degel, Elena Fedotova, Igor Karpushevskiy, Ain Lankov, Niklas Larson, Juha Lilja, Jukka Pönni, Krzysztof Radtke, Paco Rodriguez-Tress, Beata Schmidt, Elor Sepp, Vladimir Severin, Ivo Sics, Vaishav Soni, Marijus Spegys, Guntars Strods & Andrés Velasco Title: Baltic International Fish Survey Working Group (WGBIFS) Year: 2019 Version: Published version Copyright: The Author(s) 2019 Rights: CC BY-NC 4.0 Rights url: http://creativecommons.org/licenses/by-nc/4.0/ Please cite the original version: ICES. 2019. Working Group on Baltic International Fish Survey (WGBIFS). ICES Scientific Reports. 1:37. 79 pp. http://doi.org/10.17895/ices.pub.5378 ICES SCIENTIFIC REPORTS RAPPORTS SCIENTIFIQUES DU CIEM ICES INTERNATIONAL COUNCIL FOR THE EXPLORATION OF THE SEA CIEM COUNSEIL INTERNATIONAL POUR L’EXPLORATION DE LA MER WORKING GROUP ON BALTIC INTERNATIONAL FISH SURVEY (WGBIFS) VOLUME 1 | ISSUE 37 International Council for the Exploration of the Sea Conseil International pour l’Exploration de la Mer H.C. Andersens Boulevard 44-46 DK-1553 Copenhagen V Denmark Telephone (+45) 33 38 67 00 Telefax (+45) 33 93 42 15 www.ices.dk info@ices.dk The material in this report may be reused for non-commercial purposes using the recommended cita- tion. ICES may only grant usage rights of information, data, images, graphs, etc. of which it has owner- ship. For other third-party material cited in this report, you must contact the original copyright holder for permission. For citation of datasets or use of data to be included in other databases, please refer to the latest ICES data policy on ICES website. All extracts must be acknowledged. For other reproduction requests please contact the General Secretary. This document is the product of an expert group under the auspices of the International Council for the Exploration of the Sea and does not necessarily represent the view of the Council. ISSN number: 2618-1371 I © 2019 International Council for the Exploration of the Sea ICES Scientific Reports Volume 1 | Issue 37 WORKING GROUP ON BALTIC INTERNATIONAL FISH SURVEY (WGBIFS) Recommended format for purpose of citation: ICES. 2019. Working Group on Baltic International Fish Survey (WGBIFS). ICES Scientific Reports. 1:37. 79 pp. http://doi.org/10.17895/ices.pub.5378 Editors Olavi Kaljuste Authors Henrik Degel • Elena Fedotova • Igor Karpushevskiy • Ain Lankov • Niklas Larson • Juha Lilja • Jukka Pönni • Krzysztof Radtke • Paco Rodriguez-Tress • Beata Schmidt • Elor Sepp • Vladimir Severin • Ivo Sics • Vaishav Soni • Marijus Spegys • Guntars Strods • Andrés Velasco ICES | WGBIFS 2019 | I Contents i Executive summary .......................................................................................................................iv 1 Expert group information .............................................................................................................. v 2 Terms of References ...................................................................................................................... 1 3 Summary of the Work Plan for Year 2 ........................................................................................... 3 4 List of outcomes and achievements of the WG in this delivery period ......................................... 4 5 Progress report on ToRs and Work Plan........................................................................................ 5 5.1 ToR a) Combine and analyse the results of spring (BASS) and autumn (BIAS) 2018 acoustic surveys and report to WGBFAS ................................................................. 5 5.2 ToR b) Update the BIAS and BASS hydro-acoustic databases and ICES database for acoustic-trawl surveys ................................................................................................ 5 5.3 ToR c) Plan and decide on acoustic surveys to be conducted in autumn 2019 and spring 2019-2020 ............................................................................................................. 6 5.4 ToR d) Discuss the results from BITS surveys performed in autumn 2018 and spring 2019 and evaluate the characteristics of TVL and TVS standard gears used in BITS .............................................................................................................................. 6 5.5 ToR e) Plan and decide on demersal trawl surveys and experiments to be conducted in autumn 2019 and spring 2020, and update, and correct the Tow- Database and DATRAS ..................................................................................................... 7 5.6 ToR f) Conduct analyses related to the improvement of quality of acoustic indices and estimation of the uncertainty in the BIAS and BASS surveys ........................ 7 5.7 ToR g) Update on progress in development of the StoX software and implementation of it for the calculation of WGBIFS acoustic stock estimates, based on the IBAS methodology and data from ICES acoustic-trawl survey database........................................................................................................................... 7 5.8 ToR h) Define methods for the appropriate processing of the survey data and output products from the BITS survey to deliver input-data for calculation of the Baltic LFI and MML indicators .......................................................................................... 8 5.9 ToR i) Coordinate the marine litter-sampling programme within the Baltic International Trawl Survey and registering the data in the ICES database...................... 8 5.10 ToR j) Agree a standard pelagic trawl gear used in BIAS and BASS surveys .................... 9 5.11 ToR k) Review and update the International Baltic Acoustic Surveys (IBAS) manual and address methodological question raised at the last review of the SISP................................................................................................................................... 9 5.12 ToR l) Review and update the Baltic International Trawl Survey (BITS) manual and address methodological question raised at the last review of the SISP ................... 9 6 Inquiries Besides of the Fixed ToRs ............................................................................................. 10 6.1 Adopt the ICES metadata convention for processed acoustic data and the ICES data portal for acoustic trawl surveys (WGFAST request) ............................................. 10 6.2 Adopt the ‘WKMATCH 2012 maturity scale revised’ and approve the implementation plan (presented in chapter 7). Approval should be sent to WGBIOP. (WKASMSF request) ....................................................................................... 10 6.3 Update their manuals with the correct references and include or update the conversion table for the national maturity scales. (WKASMSF request) ....................... 10 6.4 Collect, count, and report litter data according to the two guidance documents produced by WGML-2018. a) Distribution of the manual on sampling, identification and registration of sea floor litter caught in bottom trawl surveys. b) Distribution of the document on suggestions for quality assurance/quality control measures for studies on micro litter. (WGML request)..................................... 10 ii | ICES SCIENTIFIC REPORTS 1: 37 | ICES 6.5 Follow Litter Data Collection Guidelines by WGML. a) Seafloor litter data requested via DATRAS b) All microplastic data requested via DOME c) Other litter data requested via DOME. (WGML request) ........................................................ 11 6.6 Contact ICES Data Centre with data reporting issues (accessions@ices.dk). (WGML request) ............................................................................................................ 11 6.7 National submitters to correct historic data. (WGML request) ..................................... 11 6.8 WGBIOP recommends the collection of gonad samples (images of gonads and gonads for histology) during regular sampling to ensure a basic set of samples is available for maturity exchanges and workshops. This will be followed up with an email with a protocol with instructions on how to collect the samples. (WGBIOP request) .......................................................................................................... 11 6.9 The IBPCluB recommends the Baltic International Fish Survey Working Group (WGBIFS) to evaluate whether the annual variation in the predicted average TS density patterns in different water depths impact the survey numbers that are used in the Gulf of Bothnia herring stock assessments. (IBPCluB request) ................... 12 6.10 Conduct data cleaning and provide algorithms for estimating missing values of variables needed for the calculation of swept area for the period 2000 to present (for WGBIFS) and for the period after 2014 (for IBTSWG if necessary e.g. in case of vessel changes or changes of trawl netting material). (WKSABI request) .......................................................................................................................... 12 6.11 Encourage survey participants to continue collecting door and wing spread data (ideally both variables on each tow but preferably at least door spread) during NS-IBTS, NeAtl-IBTS and BITS. (WKSABI request) .......................................................... 12 6.12 Identify other variables than swept area which are potentially important for improving survey estimates (e.g. bottom current speed and direction in areas with strong tides, wind speed and direction in shallow waters). (WKSABI request) .......................................................................................................................... 13 6.13 Submit size category information for Marine Litter in all cases in future surveys. (WKSABI request) ........................................................................................................... 13 7 Revisions to the work plan and justification ............................................................................... 14 8 Next meeting ............................................................................................................................... 15 Annex: ToR a) Combine and analyse the results of spring (BASS) and autumn (BIAS) 2018 acoustic surveys and report to WGBFAS ................................................................................................................. 16 5.1.1. Combined results of the Baltic International Acoustic Survey (BIAS) ................................ 16 5.1.1.1. Area under investigation and overlapping areas............................................................ 16 5.1.1.2. Total results .................................................................................................................... 18 5.1.1.3. Area corrected data ........................................................................................................ 29 5.1.1.4. Tuning fleets for WGBFAS .............................................................................................. 30 5.1.1.4.1. Herring in the ICES Subdivisions 25–29 ....................................................................... 30 5.1.1.4.2. Sprat in the ICES Subdivisions 22–29 ........................................................................... 32 5.1.1.4.3. Herring in the ICES Subdivision 30 ............................................................................... 34 5.1.2. Combined results of the Baltic Acoustic Spring Survey (BASS) .......................................... 36 5.1.2.1. Area under investigation and overlapping areas............................................................ 36 5.1.2.2. Combined results and area corrected data .................................................................... 37 5.1.2.2.1. Sprat in the ICES Subdivisions 24 – 28 ......................................................................... 39 Annex: ToR b) Update the BIAS and BASS hydroacoustic databases and ICES database for acoustic-trawl surveys .............................................................................................................................. 41 5.2 ToR b) Update the BIAS and BASS hydroacoustic databases and ICES database for acoustic-trawl surveys ................................................................................................... 41 Annex: ToR c) Plan and decide on acoustic surveys to be conducted in autumn 2019 and spring 2019-2020 ................................................................................................................................................. 42 5.3.1. Planned acoustic survey activities ..................................................................................... 42 ICES | WGBIFS 2019 | III Annex: ToR d) Discuss the results from BITS surveys performed in autumn 2018 and spring 2019 and evaluate the characteristics of TVL and TVS standard gears used in BITS ......................................... 46 5.4.1 BITS 4th quarter 2018 .................................................................................................... 46 5.4.2 BITS 1st quarter 2019 ...................................................................................................... 46 5.4.3 Standard fishing-gear checking ...................................................................................... 47 Annex: ToR e) Plan and decide on demersal trawl surveys and experiments to be conducted in autumn 2019 and spring 2020, and update, and correct the Tow-Database and DATRAS ...................... 49 5.5.1. Plan and decide on demersal trawl surveys and experiments .......................................... 49 5.5.2. Update and correct the Tow-Database .......................................................................... 50 5.5.3. Reworking of the Database of Trawl Surveys (DATRAS) ................................................ 50 Annex: ToR f) Conduct analyses related to the improvement of quality of acoustic indices and estimation of the uncertainty in the BIAS and BASS surveys ................................................................... 51 Annex: ToR g) Update on progress in development of the StoX software and implementation of it for the calculation of WGBIFS acoustic stock estimates, based on the IBAS methodology and data from ICES acoustic-trawl survey database ................................................................................................ 56 Annex: ToR h) Define methods for the appropriate processing of the survey data and output products from the BITS survey to deliver input-data for calculation of the Baltic LFI and MML indicators .................................................................................................................................................. 57 Annex: ToR i) Coordinate the marine litter-sampling programme within the Baltic International Trawl Survey and registering the data in the ICES database .................................................................... 62 Annex 1: List of Participants .......................................................................................................... 64 Annex 2: Terms of reference for the next meeting .................................................................... 66 Annex 3: Agenda of WGBIFS 2019 ................................................................................................ 70 Annex 4: Recommendations ......................................................................................................... 73 Annex 5: Action List ...................................................................................................................... 74 Annex 6: Standard and Cruise Reports of BITS surveys at the WGBIFS 2019 annual meeting ....................................................................................................................................... 77 Annex 7: Cruise reports of acoustic surveys BASS and BIAS in 2018 ............................................ 158 Annex 8: List of presentations made at the WGBIFS 2019 meeting ............................................. 428 IV | ICES SCIENTIFIC REPORTS 1:37 | ICES i Executive summary The International Council for the Exploration of the Sea (ICES) Baltic International Fish Sur-vey Working Group (WGBIFS) met in the Marine Research Institute, Klaipeda University in Kaipeda, Lithuania, on 25–29 March 2019. A total of 21 participants, representing all countries around the Baltic Sea, attended in the meeting (see Annex 1). Olavi Kaljuste, Sweden chaired the group. The main aim of the WGBIFS is the planning, coordination, and implementation of demersal trawl surveys and hydroacoustic surveys in the Baltic Sea. It compiles results from, coordinates and plans the schedule for the Baltic International Acoustic Survey (BIAS), the Baltic Acoustic Spring Survey (BASS), and the Baltic International trawl Surveys (BITS) in the 1st and 4th quarter on an annual basis. The group provides the herring, sprat and cod abundance indices for the Baltic Fisheries Assessment Working Group (WGBFAS) to use as tuning fleets. The common sur- vey manuals are also updated according to decisions made during the meeting. Survey results from 2018 and the first half of 2019 were compiled. The schedule for surveys in the second half of 2019 and the first half of 2020 were planned and coordinated. All Baltic fish stocks assessment relevant surveys were internationally coordinated. The area coverage and the number of control hauls in the BASS and in the BIAS in 2018 were considered to be appropriate for the calculation of tuning indices and the data can be used for the assessment of Baltic herring and sprat stocks. The number of valid hauls accomplished dur- ing the 4th quarter 2018 and 1st quarter 2019 BITS were considered by the group as appropriate for tuning series and the data can be used for the assessment of Baltic and Kattegat cod and flatfish stocks. Data from the recent BITS has been uploaded to ICES DATRAS database. Tow-Database which allows planning the spatial distribution of hauls in the areas, where the seabed is suit-able for safety trawling, was corrected and updated. Access-databases for aggregated acoustic data were updated. ICES database of acoustic-trawl surveys for disaggregated data was updated as well. All countries also registered collected litter materials to the DATRAS database. Inquiries from other ICES expert groups were discussed and addressed. ICES | WGBIFS 2019 | V 1 Expert group information Expert group name Baltic International Fish Survey Working Group (WGBIFS) Expert group cycle Multiannual fixed term Year cycle started 2018 Reporting year in cycle 2/3 Chair(s) Olavi Kaljuste, Sweden Meeting venue(s) and dates 24-28 March 2018, Lyngby, Denmark 25-29 March 2019, Klaipeda, Lithuania ICES | WGBIFS 2019 | 1 2 Terms of References TOR Description Background Science plan codes Du- ra- tion Expected delivera- bles a Combine and analyse the re- sults of spring and autumn acoustic surveys and experi- ments Acoustic surveys provide im- portant fishery-independent stock estimates for Baltic herring and sprat stocks 3.1 annu- ally Year 1, 2 and 3 Updated acoustic tuning index for WGBFAS b Update the BIAS and BASS hydroacoustic databases and ICES database for acoustic- trawl surveys The aim of BIAS and BASS data- bases is to store the aggregated data. The aim of ICES database is to ensure that the standardized and quality-controlled scrutinized data from the acoustic-trawl sur- veys will be stored centrally in a safe way and enables easy access to the data, which will facilitate usage for many different analyses by a wider range of users. 3.1 annu- ally Year 1, 2 and 3 Updated databases with acoustic and biotic data for WGBIFS c Coordinate and plan acoustic surveys including any experi- ments to be conducted Acoustic surveys provide im- portant fishery-independent stock estimates for Baltic herring and sprat stocks 3.1 annu- ally Year 1, 2 and 3 Finalized planning for the surveys for WGBIFS d Discuss the BITS surveys re- sults and evaluate the char- acteristics of TVL and TVS standard gears used in BITS Demersal trawl surveys provide important fishery-independent stock estimates for Baltic cod and flatfish stocks 3.1 annu- ally Year 1, 2 and 3 Updated BITS data in DATRAS database for ICES Data Centre and WGBFAS e Coordinate and plan demer- sal trawl surveys and experi- ments to be conducted, and update and correct the Tow Database Demersal trawl surveys provide important fishery-independent stock estimates for Baltic cod and flatfish stocks 3.1 annu- ally Year 1, 2 and 3 Finalized planning for the surveys for WGBIFS, updated and corrected Tow Database f Conduct analyses related to the improvement of quality of acoustic indices and esti- mation of the uncertainty in the BIAS and BASS surveys Acoustic surveys provide im- portant fishery-independent stock estimates for Baltic herring and sprat stocks 3.1, 3.2, 3.3 Year 1-3 Improved quality of acoustic indices with es- timates of the uncer- tainty for WGBFAS g Update on progress in devel- opment of the StoX software and implementation of it for the calculation of WGBIFS acoustic stock estimates, based on the IBAS methodol- ogy and data from ICES acoustic-trawl survey data- base StoX software produces fish abundance estimations in a trans- parent and reproducible way. Planned development of the StoX post-processing program should allow implication this software by WGBIFS using the acoustic and bi- otic data from ICES database for acoustic-trawl surveys. 3.1, 3.2 Year 1-3 Improved transparency and reproducibility of acoustic indices, im- proved pace of work on the level of national data compilation and verification 2 | ICES Scientific Reports 1:37 | ICES Comparisons will be performed to validate whether the StoX soft- ware provides us similar results as the current IBAS calculation method in order to allow WGBIFS to use it as a new standard tool for the calculation of annual BIAS and BASS survey estimates. h Define methods for the ap- propriate processing of the survey data and output prod- ucts from the BITS survey to deliver input-data for calcula- tion of the Baltic LFI and MML indicators. The ground trawl surveys provide important fishery-independent stock estimates for Baltic cod and flatfish stocks and can be a source of the ecosystem indicators, re- cently requested by different sci- entific organizations 3.1, 3.2 Year 1, 2 and 3 Improvement the scien- tific knowledge about the demersal/benthic components (mostly fish) in the Baltic Sea i Coordinate the marine litter- sampling programme within the Baltic International Trawl Survey and registering the data in the ICES database. Collected and registered infor- mation about the marine litter (mostly anthropogenic origin), oc- casionally appeared in the ground trawl fish control-catches, are ad- ditional source of data about pre- sent ecological status of marine seabed in investigated areas of the Baltic. 3.1 annu- ally Year 1, 2 and 3 Coordinated the marine litter sampling pro- gramme in the Baltic In- ternational Trawl Survey (BITS). j Agree a standard pelagic trawl gear used in BIAS and BASS surveys Acoustic surveys provide im- portant fishery-independent esti- mates for Baltic herring and sprat stocks size and possible uncer- tainties, which result from, e.g. different type of fishing gears ap- plied for fish control-catches, should be eliminated. 3.1, 3.2 Year 1-3 Agreement on the standard pelagic fishing gear which will be used in the BIAS and BASS surveys k Review and update the Inter- national Baltic Acoustic Sur- veys (IBAS) manual and ad- dress methodological ques- tion raised at the last review of the SISP Acoustic surveys provide im- portant fishery-independent stock estimates for Baltic herring and sprat stocks 3.1, 3.2 Year 3 Updated IBAS manual for WGBIFS (SISP 8) l Review and update the Baltic International Trawl Survey (BITS) manual and address methodological question raised at the last review of the SISP Demersal trawl surveys provide important fishery-independent stock estimates for Baltic cod and flatfish stocks 3.1, 3.2 Year 3 Updated BITS manual for WGBIFS (SISP 7) ICES | WGBIFS 2019 | 3 3 Summary of the Work Plan for Year 2 • Combined survey results from 2018 and the first quarter of 2019 and updated tuning indices for WGBFAS (ToR a and d). • Updated databases with acoustic and biotic data (ToR b). • Finalized coordination and planning for the BASS, BIAS and BITS surveys in 2019 and first half of 2020, updated and corrected Tow Database (ToR c and e). • Progress in estimation of the uncertainty in the BIAS and BASS surveys (ToR f). • Progress towards a comparison exercise to validate the StoX software in order to allow WGBIFS to use it as a new standard tool for the calculation of annual BIAS and BASS survey estimates (ToR g). • Progress in delivering input-data for the calculation of the Baltic LFI and MML indicators (ToR h). • Coordinated marine litter sampling programme in the BITS surveys and registered data in the ICES database (ToR i). • Progress towards an agreement in the standard pelagic fishing gear to be used in the BIAS and BASS surveys (ToR j). • Progress in review and update procedure of the IBAS and BITS manuals (ToR k and l). 4 | ICES Scientific Reports 1:37 | ICES 4 List of outcomes and achievements of the WG in this delivery period Indices for the pelagic and demersal fish stocks in the Baltic Sea from annual surveys as fishery- independent data for analytical assessment purposes in WGBFAS: • Calculated BASS tuning fleet index for Baltic sprat in SDs 24–26 and 28.2 (abundance per age in the age groups 1-8+). • Calculated BIAS tuning fleet index for Baltic sprat in SDs 22–29 (abundance per age in the age groups 1-8+). • Calculated BIAS tuning fleet index for Baltic sprat recruitment in SDs 22–29 (abundance at age 0). • Calculated BIAS tuning fleet index for Baltic herring in SDs 25–29 (abundance per age in the age groups 1-8+). • Calculated BIAS tuning fleet index for Baltic herring recruitment in SDs 25–29 (abun- dance at age 0). • Calculated BIAS tuning fleet index for Baltic herring in SD 30 (abundance per age in the age groups 0-8+). • Uploaded data from the 4th quarter 2018 and the 1st quarter 2019 BITS surveys to the DATRAS data base to be used for the calculation of survey indices for the relevant cod and flatfish stocks Other survey-derived products: • Maps of BASS and BIAS area coverage in 2018. • Geographical distribution maps of sprat abundance in the Baltic Sea (May-June 2018; BASS surveys). • Geographical distribution maps of sprat, herring and cod abundance in the Baltic Sea (September-October 2018; BIAS surveys). • Updated Access-databases for aggregated acoustic data (BASS_DB.mdb and BIAS_DB.mdb). • Updated ICES database of acoustic-trawl surveys for disaggregated data. • Updated and corrected the Tow-Database which allows planning the spatial distribution of hauls in the areas, where the seabed is suitable for safety trawling. Other outcomes and achievements: • Agreed plans (time and spatial coverage by countries) for the next standard acoustic sur- veys. • Agreed plans (time and number of planned stations by countries) for BITS surveys to be conducted in autumn 2019 and spring 2020. • 5 recommendations (Annex 4) was made to ICES Data Centre and to other ICES working groups. • Action list (Annex 5) for WGBIFS members was updated. ICES | WGBIFS 2019 | 5 5 Progress report on ToRs and Work Plan 5.1 ToR a) Combine and analyse the results of spring (BASS) and autumn (BIAS) 2018 acoustic surveys and report to WGBFAS In September – October 2018 six research vessels (representing seven national research institutes) participated in the accomplishment of autumn acoustic survey (BIAS). The survey was con- ducted in the ICES Subdivisions 21-32 (excl. ICES SD 31) however, some Subdivisions were only partly covered. Russia did not participate in 2018 BIAS. Echointegration was recorded at totally of 5967 NM linear distance moreover, 218 and 246 catch and hydrological stations, respectively were inspected too. Totally, three statistical ICES-rectangles were controlled by more than one country. The extended reports from BIAS 2018 cruises are available in Annex 7. The whole time- series of the area-corrected BIAS survey data of sprat and herring are presented in Annex ToR a. In May 2018, three research vessels participated in the accomplishment of five spring acoustic surveys (German, Latvian-Polish, Estonian-Polish, Polish and Lithuanian BASS survey; Annex ToR a). The BASS 2018 survey was realised in the ICES Subdivisions 24-32 (excl. ICES SD 30, 31). It should be underlined that the ICES SD 29 was monitored with acoustic-trawl investigations only in the southern and middle parts moreover, only one ICES rectangle (47H3) was inspected in the ICES Subdivision 32. The part of ICES SD 26 (the ICES rect. 39H0) was not investigated as Russia did not take part in BASS 2018 cruises. Overall 54 the ICES rectangles were covered with acoustic-biotic monitoring, what is comparable with 96.5% of area coverage. Four ICES rectan- gles were inspected by two countries. Echointegration was recorded at totally of 3321 NM linear distance moreover, 124 and 319 catch and hydrological stations, respectively were inspected too. The extended reports from the above-mentioned BASS cruises are presented in Annex 7. The complete time-series of the area-corrected BASS sprat abundance is given in Annex ToR a. The area coverage and the number of control hauls in the BASS and BIAS surveys in 2018 were considered to be appropriate for the calculation of tuning indices and the data can be used for the assessment of Baltic herring and sprat stocks. 5.2 ToR b) Update the BIAS and BASS hydro-acoustic databases and ICES database for acoustic-trawl surveys An error was discovered shortly before WGBIFS 2019 meeting in the queries that calculate her- ring and sprat biomass per ICES Sub-division. The algorithms in both queries were corrected just before the meeting (see Annex ToR b). Few errors in reported cod abundance in some rectangles were found during the WGBIFS 2019 meeting. All values of cod abundance were checked and corrected. Shortly after meeting the faulty query was corrected and improved BIAS_DB.mdl access-database was uploaded into the folder “Data” of the WGBIFS 2019 SharePoint. A marginal change in BASS time series was done during the WGBIFS 2019 meeting. The value for sprat age 1 in 2002 was changed from 27412.12 to 27412.11. After validation, the aggregated data from BIAS and BASS surveys from 2018 were added to the BIAS_DB.mdb and the BASS_DB.mdb Access-databases, respectively. The updated versions of the databases are located in the folder “Data” of the ICES WGBIFS 2019 SharePoint site. 6 | ICES Scientific Reports 1:37 | ICES The disaggregated data from BIAS and BASS surveys were also uploaded to the recently created ICES data base for acoustic-trawl data (http://ices.dk/marine-data/data-portals/Pages/acous- tic.aspx). 5.3 ToR c) Plan and decide on acoustic surveys to be conducted in autumn 2019 and spring 2019-2020 All the Baltic Sea countries intend to take part in the autumn BIAS acoustic surveys and experi- ments in 2019. Cooperation between Germany and Denmark, Latvia and Poland and Estonia and Poland in the BIAS survey realisation is planned. Germany, Lithuania, Poland and the joint Lat- vian-Polish and Estonian-Polish BASS surveys will be continued in May 2019-2020 too. Russia is not planning to participate in these BASS surveys. There is also an intention to conduct a Latvian- Estonian survey on the Gulf of Riga in July 2019 and 2020. The list of participating research ves- sels and initially planned periods of particular surveys are given in Annex ToR c. 5.4 ToR d) Discuss the results from BITS surveys performed in au- tumn 2018 and spring 2019 and evaluate the characteristics of TVL and TVS standard gears used in BITS During the BITS-Q4/2018 surveys the level of realized valid ground trawl hauls represented 102% of the total planned catch-stations (see Annex ToR d). The survey was accomplished by Denmark, Germany, Sweden, Poland, Estonia, Latvia and Lithuania in the ICES Subdivisions 20- 29. Russia did not participate in BITS-Q4/2018 survey. The coverage in all Sub-divisions and all depth strata is in general quite good. In SD 24, the achieved number of hauls is smaller than planned due to the trawling restrictions enforced by the Swedish military. The differences in numbers of planned and index-valid fishing stations for each monitored ICES subdivision is pre- sented in the Annex ToR d. The coverage by depth stratum is as follows (depth stratum, coverage in %): 1, 100; 2, 83.6; 3, 94.5; 4, 117.8; 5, 131.3 and 6, 128.6. The lower coverage in depth strata 2 and 3 is due to the restrictions enforced by the Swedish military. In the 1st quarter 2019 the areas coverage with designated catch-stations was on similar level than in 2018, i.e. 97 % (Annex ToR d). The BITS Q1 2019 surveys were realized by Denmark, Germany, Sweden, Poland, Latvia and Lithuania in the ICES Subdivisions 22-28. Russia did not participate in BITS-Q1/2019 survey. The coverage with control-hauls by the depth stratum is as follow (depth stratum, coverage in %): 1, 100; 2, 95.5; 3, 92.6; 4, 101.9; 5, 81.1; 6, 162.5. The depth stratum 2 and 3 has significantly lower coverage because of the stations in the south-eastern Swedish waters which were not performed due to abrupt termination of the survey resulting from sickness on board of the RV „Solea“. The number of valid hauls accomplished during the BITS-Q4/2018 and BITS-Q1/2019 were con- sidered by WGBIFS 2019 as appropriate for tuning series (e.g. CPUE indices) and the data can be used for the assessment of Baltic and Kattegat cod and flatfish stocks. Standard reports from participating countries giving overviews of the BITS Q4 2018 and BITS Q1 2019 results can be found in Annex 6. NB! Due to a technical mistake, all standard reports from BITS-Q4/2017 cruises in the Annex 6 of the WGBIFS 2018 report were incorrectly dated to 2018. ICES | WGBIFS 2019 | 7 WGBIFS has implemented a complete and smaller scale measurement of the technical parame- ters of the exploited demersal trawls (type TV-3L and TV-3S) as a standard procedure. The com- plete measurement procedure has to be performed at least once a year by each country involved in the BITS surveys realization. The smaller scale measurement procedure should be made prior to each BITS survey. Standard protocols with the results of these measurements from all coun- tries are available in the WGBIFS SharePoint. 5.5 ToR e) Plan and decide on demersal trawl surveys and experi- ments to be conducted in autumn 2019 and spring 2020, and update, and correct the Tow-Database and DATRAS The most of the WGBIFS member countries, who intend to participate in the BITS-Q4/2019 and BITS-Q1/2020 surveys, have nearly the same plans regarding the numbers of hauls as in the pre- vious years. The total number of stations committed by the countries and available is given in the Annex ToR e. According to preliminary information, Russia is not planning to participate in the BITS surveys in autumn 2019 and in spring 2020. Since other ICES member countries will not be able to get permission to work in the EEZ of Russia, the negative effect on the quality of the survey results based on BITS survey would be eminent. Two hauls were deleted from the Tow-Database. For four tracks the depth were adjusted, for six tracks the positions were adjusted and one new track was added to the database. During the WGBIFS 2019, meeting no any essential changes of the data in the Database of Trawl Surveys (DATRAS) was made. 5.6 ToR f) Conduct analyses related to the improvement of quality of acoustic indices and estimation of the uncertainty in the BIAS and BASS surveys At the WGBIFS meeting 2016 it was decided that a bootstrap method should be used to present the survey sampling variance. That method was based on recalculations of the survey results by resampling of acoustic data and trawl hauls. On the Workshop on Sampling Design and Opti- mization (WKSDO) in Lysekil, Sweden in 2016, the method was discussed with Jon Helge Vølstad and Mary Christman and they suggested to do a bootstrap on the survey results from the covered area. At 2017 year’s WGBIFS meeting the two bootstrapping methods were dis- cussed and it was decided that WGBIFS should move forward and try to evaluate the results from the bootstrap method recommended at WKSDO. This evaluation will be presented in the final report of the Baltic International Fish Survey Working Group in 2020. In the Annex ToR f is presented an example about the estimation of the uncertainties in the acoustic survey estimates using the bootstrap method. 5.7 ToR g) Update on progress in development of the StoX soft- ware and implementation of it for the calculation of WGBIFS acoustic stock estimates, based on the IBAS methodology and data from ICES acoustic-trawl survey database During the WGBIFS 2018 meeting a StoX task sub-group was created for the implementation of the StoX software for the calculation of WGBIFS acoustic stock estimates. 8 | ICES Scientific Reports 1:37 | ICES StoX task sub-group organized a net-meeting together with StoX developers on 13th of September 2018 to go through the fish abundance index calculation procedure in the StoX software using the BIAS data from 2017. The main goal for this net-meeting was to learn the standard analysis procedure in StoX (using IBAS calculation standards). Some issues with the BIAS 2017 data, with data uploading, deletion and downloading in the ICES database for acoustic trawl surveys and with StoX software were discovered before and during that meeting. Several of them were solved due to the meeting time and the rest was solved afterwards. During the WGBIFS 2019 meeting a WebEX-meeting was held together with StoX developers to discuss the issues related to the progress in development of the StoX software and implementa- tion of it for the calculation of WGBIFS acoustic stock estimates. During this meeting it was demonstrated that the latest version of StoX software is able to perform the calculation procedure according to IBAS methods. It was decided that members of WGBIFS StoX task sub-group will: • analyse their national survey data with StoX software and compare the results with their official results, • organize a meeting together with StoX developers in beginning of November 2019 to set up the final herring and sprat abundance index calculation procedures in the StoX soft- ware. 5.8 ToR h) Define methods for the appropriate processing of the survey data and output products from the BITS survey to de- liver input-data for calculation of the Baltic LFI and MML indi- cators The large fish indicator (LFI) is an important community indicator that integrates different stocks in a unique regional indicator. The LFI is one of the DCF indicators and is used by OSPAR in the Ecological Quality Objective (EcoQO), by HELCOM as a useful indicator of biodiversity, related to the food webs MSFD descriptor D4 and used in ICES Advice. LFIs may also be used in the future as a standard product in the ICES Ecosystem Overviews and will be calculated every year. ICES Data Centre request of the outlier-rechecking in DATRAS was addressed by the national data submitters of BITS in 2018 as the first step in the process of developing Large Fish Indicator (LFI) for the Baltic Sea. ICES Workshop on methods to develop swept-area based effort indexes (WKSABI) was held in January 2019. WGBIFS was represented there by Henrik Degel, who was also co-chair of that workshop. One of the goals of that workshop was to define and describe a size-based indicator based on the swept-area index. During the workshop, the nature of the gaps of knowledge were discussed and number recommendations (four of them to WGBIFS) were formulated. These rec- ommendations were addressed during the WGBIFS 2019 meeting and are summarized in chap- ters 6.10-6.13. 5.9 ToR i) Coordinate the marine litter-sampling programme within the Baltic International Trawl Survey and registering the data in the ICES database Collected and registered information about marine litter is an important source of knowledge regarding current ecological status of marine seabed in investigated areas of the Baltic. Almost all countries, who realized the BITS-Q4/2018 and BITS-Q1/2019 surveys and submitted the data, ICES | WGBIFS 2019 | 9 have also registered collected litter materials into the DATRAS Litter database. Only two coun- tries had not yet done so. Following the WGML request, WGBIFS adopted proposed rules (checklist) for formatting and reporting of litter data (see Annex ToR i). 5.10 ToR j) Agree a standard pelagic trawl gear used in BIAS and BASS surveys During the WGBIFS 2018 meeting a WebEX-meeting was held with two representatives of WGFTFB to discuss the issues related to survey gear standardization. Based on the discussions, the needs for the possible standard pelagic trawl gear where identified and the next steps in the gear standardisation process were agreed. It was decided that Haraldur Einarsson and Daniel Stepputtis will present the topic briefly at WGFTFB meeting in June 2018 to ask gear technolo- gists for their participation. During the WGBIFS 2019 meeting, there was no new information about this ToR available and therefore this issue was not discussed there. WGBIFS will wait the response from the WGFTFB to make a final decision about the survey gear standardization in 2020. 5.11 ToR k) Review and update the International Baltic Acoustic Sur- veys (IBAS) manual and address methodological question raised at the last review of the SISP The IBAS manual was reviewed during the WGBIFS 2019 meeting and several suggestions about the possible changes and corrections were listed. The updated manual will be presented as an Addendum to the final report of the Baltic International Fish Survey Working Group in 2020. 5.12 ToR l) Review and update the Baltic International Trawl Survey (BITS) manual and address methodological question raised at the last review of the SISP The BITS manual was reviewed during the WGBIFS 2019 meeting and several suggestions about the possible changes and corrections were listed. The updated manual will be presented as an Addendum to the final report of the Baltic International Fish Survey Working Group in 2020. 10 | ICES Scientific Reports 1:37 | ICES 6 Inquiries Besides of the Fixed ToRs 6.1 Adopt the ICES metadata convention for processed acoustic data and the ICES data portal for acoustic trawl surveys (WGFAST request) WGBIFS found that we have already adopted the recommendation from WGFAST. Currently, WGBIFS coordinated acoustics surveys BASS and BIAS have already started to upload it into ICES Acoustic database, where the acoustic part of the format is based on the SISP 4 – A metadata convention for processed acoustic data from active acoustic systems developed by the ICES Working Group on Fisheries Acoustics, Science and Technology (WGFAST), while the biotic part of the format is based on the ICES Database of Trawl Surveys (DATRAS). Before the ICES Acous- tic database, WGBIFS have not had a common database for disaggregated acoustic data. 6.2 Adopt the ‘WKMATCH 2012 maturity scale revised’ and ap- prove the implementation plan (presented in chapter 7). Ap- proval should be sent to WGBIOP. (WKASMSF request) WGBIFS discussed this request during the meeting. As each of the National laboratories has their own scale to determine maturity, it was decided to continue report the original maturity scale data to the ICES databases in order to minimize the risk of conversion errors and to keep the historic national data series. The group decided to provide ICES with the conversion tables of the national maturity scales. In most situations it is very easy to convert maturity data from na- tional scale to the ICES scale. 6.3 Update their manuals with the correct references and include or update the conversion table for the national maturity scales. (WKASMSF request) WGBIFS is currently reviewing the manual and this review will also update the conversion table for the national maturity scales. The updated manual will be presented as an Addendum to the final report of the Baltic International Fish Survey Working Group in 2020. 6.4 Collect, count, and report litter data according to the two guid- ance documents produced by WGML-2018. a) Distribution of the manual on sampling, identification and registration of sea floor litter caught in bottom trawl surveys. b) Distribution of the document on suggestions for quality assurance/quality control measures for studies on micro litter. (WGML request) WGBIFS has communicated this request to the relevant national data submitters. WGBIFS is cur- rently reviewing the BITS manual and this review will also update the marine litter sampling, identification and registration instructions there. The updated manual will be presented as an Addendum to the final report of the Baltic International Fish Survey Working Group in 2020. None of the countries participating in BITS has so far reported collection of samples for micro ICES | WGBIFS 2019 | 11 litter identification. However, during the process of reviewing the BITS manual, also guidance for the micro litter studies will be added. 6.5 Follow Litter Data Collection Guidelines by WGML. a) Seafloor litter data requested via DATRAS b) All microplastic data re- quested via DOME c) Other litter data requested via DOME. (WGML request) WGML addressed this request to relevant national data submitters associated with WGBIFS. WGBIFS has communicated this request to the relevant national data submitters. 6.6 Contact ICES Data Centre with data reporting issues (acces- sions@ices.dk). (WGML request) WGML addressed this request to relevant national data submitters associated with WGBIFS. WGBIFS has communicated this request to the relevant national data submitters. 6.7 National submitters to correct historic data. (WGML request) WGML addressed this request to relevant national data submitters associated with WGBIFS. WGBIFS has communicated this request to the relevant national data submitters. 6.8 WGBIOP recommends the collection of gonad samples (images of gonads and gonads for histology) during regular sampling to ensure a basic set of samples is available for maturity ex- changes and workshops. This will be followed up with an email with a protocol with instructions on how to collect the sam- ples. (WGBIOP request) Similarly to WGIPS, also WGBIFS recognises the potential importance of the collection of such samples and the benefits of the availability of such a library of samples. Through the maturity estimation exchanges and workshops it would possible lead to an improvement of the assess- ments of stocks surveyed by WGBIFS coordinated surveys. Although, sometimes additional per- son might be required in the surveys to collect these samples, but unfortunately not all vessels have vacancies on board. More detailed instructions on number of gonad samples required per survey, area, species, sex, maturity stage, season and year would be necessary. Additionally, before any sampling will be initiated by the national institutions, it must be clarified, who will be responsible for the coordination of this sampling, where and how the samples will be stored and how curated. 12 | ICES Scientific Reports 1:37 | ICES 6.9 The IBPCluB recommends the Baltic International Fish Survey Working Group (WGBIFS) to evaluate whether the annual vari- ation in the predicted average TS density patterns in different water depths impact the survey numbers that are used in the Gulf of Bothnia herring stock assessments. (IBPCluB request) The acoustic sub-group of the WGBIFS tried to figure out the meaning of this recommendation. It was not totally understood, which parameters were used behind the functions (Figure 2, in ICES IBPCluB report 2018). Therefore, the average TS predictions by depth layer should be se- lected from small subareas that have more or less equal water depths. By this way it would be easier to quantify whether or not these vertical patterns have an impact on abundance indices of Bothnian Sea herring. 6.10 Conduct data cleaning and provide algorithms for estimating missing values of variables needed for the calculation of swept area for the period 2000 to present (for WGBIFS) and for the period after 2014 (for IBTSWG if necessary e.g. in case of vessel changes or changes of trawl netting material). (WKSABI re- quest) WGBIFS found that particularly for the door spread, it is necessary to establish an algorithm for filling in data gaps. Unfortunately, the group had no time during the meeting to decide on which algorithms would be the most appropriate model to use for that purpose. It was agreed that the work should be done intersessionally before the next meeting. 6.11 Encourage survey participants to continue collecting door and wing spread data (ideally both variables on each tow but pref- erably at least door spread) during NS-IBTS, NeAtl-IBTS and BITS. (WKSABI request) Based on the data uploaded to DATRAS the status of upload of variables related to swept area estimates (Haul duration, Trawling speed, Distance, Door spread, Wing spread) were investi- gated. The upload format (exchange format) includes all relevant variables for calculating the swept area estimate. Not all variables are mandatory and therefore data gaps for the calculation of the swept area exists. Furthermore, scrutinizing the swept area relevant data reveals some errors in the data already entered in DATRAS. The errors include upload of invalid fixed constant values (not observed), and probably erroneous values. The data gaps are due to lack of availability of gear geometry monitoring devices on the research vessels and to less extent omission to upload- ing certain variables even though the values are recorded during the survey. Nevertheless, al- most complete data series are available from three countries (Denmark, Germany and Sweden) operating in Sub-division 22- 26 (western Baltic). Initiatives between ICES and the countries involved to BITS to correct the errors and to investi- gate if additional values are available for filling data gaps have been initiated and it is expected that the data are updated in due time before the next survey working group (WGBIFS) meeting in March 2020. ICES | WGBIFS 2019 | 13 All countries were encouraged to submit as many data as possible for all the swept area relevant variables even though they not all are categorized as mandatory in the DATRAS exchange for- mat. 6.12 Identify other variables than swept area which are potentially important for improving survey estimates (e.g. bottom current speed and direction in areas with strong tides, wind speed and direction in shallow waters). (WKSABI request) Considering the complex environmental situation caused by the fluctuating hydrographic con- ditions in the Baltic Sea due to the fluctuating inflow of new salty water from the North Sea, the group found that linking the catch results to the CTD profiles potentially was the most important element in order to improve the survey estimates. Therefore, it was stressed out that the link to the CTD station number always should be filled in in the HH-record in the DATRAS exchange format. A check showed that this parameter almost always has been filled in by all countries in the past. 6.13 Submit size category information for Marine Litter in all cases in future surveys. (WKSABI request) WGBIFS has communicated this request to the relevant national data submitters. WGBIFS is cur- rently reviewing the manual and this review will also update the marine litter reporting instruc- tions there. The updated manual will be presented as an Addendum to the final report of the Baltic International Fish Survey Working Group in 2020. 14 | ICES Scientific Reports 1:37 | ICES 7 Revisions to the work plan and justification No changes in ToRs have been proposed. Not any significant revisions to the work plan were made. ICES | WGBIFS 2019 | 15 8 Next meeting There was one proposal for the venue of the next WGBIFS meeting, i.e. Cadiz, Spain. Majority of WGBIFS members supported the idea to organize the next meeting at the University of Cadiz in the period of 30 March – 3 April 2020. 16 | ICES Scientific Reports 1:37 | ICES Annex: ToR a) Combine and analyse the results of spring (BASS) and autumn (BIAS) 2018 acoustic sur- veys and report to WGBFAS 5.1.1. Combined results of the Baltic International Acoustic Survey (BIAS) In September - October 2018, the following acoustic surveys were conducted in the ICES Subdi- visions 21-32 (excl. ICES SD 31) however, in some subdivisions only in parts: 5.1.1.1. Area under investigation and overlapping areas Each the ICES statistical rectangle of the area under investigation was allocated to one country during the WGBIFS meeting in 2005. Thus each country has a mandatory responsible area, where the acoustic transects of length about 60 NM per 1000 NM2 area and at least two fish catch-sta- tions should be performed. However, it is allowed for all nations to cover also other areas, the results from the responsible country are used if these data are available. Totally, three statistical ICES rectangles were inspected by more than one country during BIAS cruises in 2018 (Fig. 5.1.1.1.1), precisely the following rectangles: - 38G4 by GER and POL, - 39G5 by SWE and POL, - 40G7 by SWE and POL. The Figure 5.1.1.1.1 illustrates that the coverage of the Baltic Sea during the BIAS-2018 survey, was only slightly less as it was planned during the WGBIFS 2018 meeting. The part of ICES SD 26 (the ICES rct.39H0 ) was not investigated as Russia did not take part in BIAS 2018 cruises. The part of ICES SD 32 (the ICES rct. 48H3, 48H4) and 29 (the ICES rct. 47H0, 48H0,48H1, 48H2) were designed to Finland and were only investigated acoustically, without any biological sampling, as the weather condition prevented to perform any pelagic trawl. During the meeting the calcu- lations for rectangles 47H0, 48H1, 48H1, 48H2, 48H3 and 48H4 ware performed using Sweden ICES | WGBIFS 2019 | 17 and Estonian biological data from neighbouring rectangles. For rectangle 48H4, that was inves- tigated by Estonia during BIAS 2018 cruise in half, the fish abundance and fish mean weight were calculated based on Finish acoustic data and Estonian trawl data (the data for rectangle 41H4 reported by Estonia in BAD1 format were not included into the BIAS_DB.mdb access-da- tabase). Investigations in the eastern part of the ICES SD 32 (the Russian zone) were not planned and remain not realised. Additionally, the Estonian-Latvian acoustic survey in the Gulf of Riga was conducted in July- August 2018, as was planned during WGBIFS 2018 meeting. The survey results from the recent years are accessible at the national level, however, were not uploaded to the WGBIFS database. Figure 5.1.1.1.1. Map of the BIAS survey conducted in September-October 2018. Various colours indicate the countries, which covered specific ICES rectangles and delivered data to BIAS-database, thus was responsible for this rectangle. Dot with different colour within a rectangle explain additional data in BIAS-database partly or totally covered by other coun- tries. 18 | ICES Scientific Reports 1:37 | ICES 5.1.1.2. Total results Geographical distribution of herring, sprat and cod abundance in the Baltic Sea, accordingly to the ICES rectangles inspected in September-October 2018 is illustrated in Figures 5.1.1.2.1 - 5.1.1.2.5. Figure 5.1.1.2.1. The abundance of herring (age 1+) per ICES rectangles monitored in September-October 2018 (the area of circles indicates estimated numbers of specimens x10^6 in given rectangle). ICES | WGBIFS 2019 | 19 Figure 5.1.1.2.2. The abundance of herring (age 0) per ICES rectangles monitored in September-October 2018 (the area of circles indicates estimated numbers of specimens x10^6 in given rectangle). 20 | ICES Scientific Reports 1:37 | ICES Figure 5.1.1.2.3. The abundance of sprat (age 1+) per ICES rectangles monitored in September-October 2018 (the area of circles indicates estimated numbers of specimens x10^6 in given rectangle). ICES | WGBIFS 2019 | 21 Figure 5.1.1.2.4. The abundance of sprat (age 0) per ICES rectangles monitored in September-October 2018 (the area of circles indicates estimated numbers of specimens x10^6 in given rectangle). 22 | ICES Scientific Reports 1:37 | ICES Figure 5.1.1.2.5. The abundance of cod (age 1+) per the ICES rectangles monitored in September-October 2018 (the area of circles indicates estimated numbers of specimens x10^6 in given rectangle). The fish abundance estimates, which are based on the BIAS survey in September-October 2018, are presented per the ICES rectangles and age groups and are specified in Tables 5.1.1.2.1, 5.1.1.2.2 and 5.1.1.2.3 for herring, sprat and cod, respectively. In addition, the abundance esti- mates for herring and sprat aggregated per ICES subdivisions and fish age groups are presented in Tables 5.1.1.2.4 and 5.1.1.2.5. The highest herring (age 1+) stock abundance was observed in the eastern part of the ICES SD 29 and western part of the ICES SD 32 (the Gulf of Finland), Fig. 5.1.1.2.1. Somewhat lower, however also significant abundance of herring stock was assessed in the ICES SDs 26 and 28. Herring (age 1+) was distributed in all except one (the ICES rec. 44H1) inspected areas of the Baltic, however with various abundances. The highest concentration of YOY herring (age group 0, year-class 2018) was detected in the ICES rectangle 50G8 (south part of the Bothnian Sea; Fig. 5.1.1.2.4). Somewhat smaller 0-age group herring concentration was detected in the north part of the ICES SD 30 (the Bothnian Sea) and the ICES SDs 21, 22 and 23. YOY herring occurred also in others inspected waters of the Baltic, however on the very low level (Fig. 5.1.1.2.2). ICES | WGBIFS 2019 | 23 The highest sprat (age 1+) stock abundance was observed in the eastern Baltic, particularly in the ICES SDs 29 and 32 (the western part of the Gulf of Finland), the north part of the ICES SD 26 (the Estonian coast) and the east part of the ICES SD 26 (the Lithuanian inshore waters) (Fig. 5.1.1.2.3). The highest concentration of YOY sprat (year-class 2018) was detected in the ICES SDs 29, 28 and 26. YOY sprat was distributed in all ICES subdivisions except the ICES SD 30, where occurred only in two ICES rectangles (50G8 and 51G8) on the very low level (Fig. 5.1.1.2.4). The highest cod stock abundance (age 1+) was detected in the ICES rectangle 40H0 (the Lithua- nian inshore waters), Fig. 5.1.1.2.5. Cod with low abundance was detected in many others areas of the Baltic, with exception of the ICES SDs 31 and 32 and inspected part of the ICES SD 21. It should be underlined that cod stock abundance was several times lower than herring and sprat stocks abundance. 24 | ICES Scientific Reports 1:37 | ICES Table 5.1.1.2.1. Estimated numbers (millions) of herring in September-October 2018, by ICES rectangles, accordingly to age groups. ICES | WGBIFS 2019 | 25 Continued Table 5.1.1.2.1. Estimated numbers (millions) of herring in September-October 2018, by ICES rectangles, accordingly to age groups. 26 | ICES Scientific Reports 1:37 | ICES Table 5.1.1.2.2. Estimated numbers (millions) of sprat in September-October 2018, by ICES rectangles, accordingly to age groups. YEAR SD RECT total age 0 age 1 age 2 age 3 age 4 age 5 age 6 age 7 age 8+ 2018 21 41G0 5.10 0.00 2.13 1.27 1.36 0.23 0.11 0.00 0.00 0.00 2018 21 41G1 266.97 0.00 107.64 44.24 63.62 40.74 9.80 0.00 0.93 0.00 2018 21 41G2 100.66 2.76 95.15 2.15 0.48 0.07 0.05 0.00 0.00 0.00 2018 21 42G1 114.47 0.00 104.95 6.08 2.18 0.80 0.30 0.00 0.16 0.00 2018 21 42G2 257.49 1.29 152.89 23.71 45.14 27.57 6.89 0.00 0.00 0.00 2018 21 43G1 121.81 0.33 114.65 5.68 0.70 0.36 0.09 0.00 0.00 0.00 2018 21 43G2 95.81 0.44 90.48 4.09 0.51 0.23 0.06 0.00 0.00 0.00 2018 22 37G0 87.83 10.27 16.12 38.92 9.98 11.65 0.73 0.00 0.16 0.00 2018 22 37G1 139.15 54.51 35.43 23.55 6.59 10.20 6.22 0.00 2.65 0.00 2018 22 38G0 248.67 113.11 30.40 65.46 17.48 20.42 1.42 0.00 0.38 0.00 2018 22 38G1 69.41 69.22 0.19 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2018 22 39F9 15.89 0.96 4.49 6.65 1.65 1.99 0.15 0.00 0.00 0.00 2018 22 39G0 17.81 1.08 5.03 7.45 1.85 2.23 0.17 0.00 0.00 0.00 2018 22 39G1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2018 22 40F9 18.02 10.98 0.50 3.57 1.36 1.41 0.20 0.00 0.00 0.00 2018 22 40G0 90.12 54.89 2.52 17.83 6.82 7.04 1.02 0.00 0.00 0.00 2018 22 40G1 9.05 0.00 0.00 5.11 1.97 1.97 0.00 0.00 0.00 0.00 2018 22 41G0 0.85 0.00 0.33 0.34 0.09 0.09 0.00 0.00 0.00 0.00 2018 23 39G2 5.50 0.62 2.10 1.67 0.58 0.45 0.07 0.01 0.00 0.00 2018 23 40G2 139.56 121.04 12.10 2.49 0.53 3.08 0.16 0.16 0.00 0.00 2018 23 41G2 45.29 43.45 1.66 0.14 0.01 0.03 0.00 0.00 0.00 0.00 2018 24 37G2 110.30 6.77 48.04 32.96 11.35 9.36 1.23 0.51 0.04 0.04 2018 24 37G3 77.75 55.46 18.62 2.35 0.66 0.56 0.07 0.03 0.00 0.00 2018 24 37G4 74.30 13.82 18.71 20.54 10.18 8.71 1.48 0.74 0.06 0.06 2018 24 38G2 173.22 83.98 47.88 25.98 8.21 6.65 0.13 0.39 0.00 0.00 2018 24 38G3 539.87 134.72 208.91 117.87 39.73 32.26 4.41 1.69 0.14 0.14 2018 24 38G4 929.16 172.82 233.97 256.83 127.34 108.95 18.48 9.21 0.78 0.78 2018 24 39G2 150.15 16.43 48.30 46.34 19.52 15.70 2.77 0.91 0.09 0.09 2018 24 39G3 397.32 46.02 136.02 124.09 45.14 37.11 6.27 2.21 0.23 0.23 2018 24 39G4 429.29 70.30 117.64 120.44 58.06 49.78 7.97 4.64 0.23 0.23 2018 25 37G5 396.91 253.90 25.32 29.50 44.21 34.22 6.98 2.70 0.00 0.07 2018 25 38G5 125.19 5.39 4.87 22.54 42.42 35.96 11.01 2.86 0.07 0.07 2018 25 38G6 851.30 491.71 31.73 83.70 125.24 96.75 14.81 6.79 0.40 0.16 2018 25 38G7 306.86 86.89 39.37 51.50 65.64 53.72 7.05 2.69 0.00 0.00 2018 25 39G4 394.20 2.15 6.46 58.59 15.51 235.66 50.41 0.00 25.42 0.00 2018 25 39G5 1 628.09 157.92 118.54 76.97 258.07 645.60 158.47 89.22 8.48 114.81 2018 25 39G6 562.08 10.40 18.30 116.88 201.60 166.49 33.63 13.54 0.77 0.46 2018 25 39G7 555.81 57.11 89.95 124.81 152.65 110.59 13.11 7.44 0.10 0.07 2018 25 40G4 1 407.15 73.83 60.88 33.53 254.06 699.50 93.74 163.38 0.00 28.23 2018 25 40G5 2 206.37 12.11 137.77 266.61 839.70 372.26 11.99 334.27 185.86 45.79 2018 25 40G6 1 455.62 98.33 22.78 113.02 141.60 767.02 103.48 127.40 82.00 0.00 2018 25 40G7 790.32 157.49 62.55 43.40 71.70 366.84 32.35 48.15 7.85 0.00 2018 25 41G6 740.64 140.45 24.27 22.58 129.76 352.69 51.08 6.60 13.21 0.00 2018 25 41G7 3 324.11 360.86 175.86 197.67 773.13 1 353.05 336.34 68.43 29.38 29.38 2018 26 37G8 861.71 242.23 389.36 119.33 84.98 25.61 0.20 0.00 0.00 0.00 2018 26 37G9 3 032.91 583.06 1 337.51 534.61 412.61 158.76 4.95 0.00 1.42 0.00 2018 26 38G8 2 710.35 352.99 853.09 588.18 623.65 271.99 15.43 2.35 2.67 0.00 2018 26 38G9 2 158.15 270.10 317.05 356.45 700.72 443.55 53.70 3.00 13.60 0.00 2018 26 39G8 2 350.13 752.56 272.61 421.27 581.55 292.89 23.53 0.42 5.30 0.00 2018 26 39G9 628.77 33.77 72.38 159.57 231.18 118.69 10.73 0.28 2.17 0.00 2018 26 40G8 303.87 45.34 19.13 51.63 107.73 68.24 9.15 0.66 2.00 0.00 2018 26 40G9 57.45 1.96 3.92 20.19 16.29 10.95 1.79 1.64 0.43 0.29 2018 26 40H0 15 322.31 1 313.54 6 946.86 5 560.41 1 120.63 376.12 4.76 0.00 0.00 0.00 2018 26 41G8 2 212.21 665.50 200.51 149.76 136.03 935.44 43.60 48.22 22.70 10.45 2018 26 41G9 1 149.56 72.69 239.35 130.75 103.00 414.43 115.04 39.20 13.26 21.84 2018 26 41H0 2 240.96 177.83 575.17 287.98 339.63 657.87 70.15 60.40 35.52 36.42 2018 27 42G6 34.46 5.74 2.15 0.00 10.41 10.62 2.44 0.86 1.54 0.68 2018 27 42G7 2 073.53 499.27 154.33 158.75 277.11 906.60 45.56 0.00 9.76 22.18 2018 27 43G7 483.24 115.97 8.00 23.89 92.38 197.61 5.42 32.46 0.00 7.51 2018 27 44G7 1 003.65 128.66 154.76 183.00 43.59 484.09 9.55 0.00 0.00 0.00 2018 27 44G8 77.26 24.88 6.55 0.00 1.57 20.69 8.38 0.00 9.17 6.02 2018 27 45G7 419.61 209.16 58.55 13.54 6.98 125.99 1.51 1.98 0.95 0.95 2018 27 45G8 763.66 116.21 145.68 73.57 67.25 258.33 44.24 37.91 18.92 1.56 2018 27 46G8 128.33 56.17 14.22 1.85 7.25 28.90 9.88 4.09 2.31 3.66 ICES | WGBIFS 2019 | 27 Continued Table 5.1.1.2.2. Estimated numbers (millions) of sprat in September-October 2018, by ICES rectangles, accordingly to age groups. YEAR SD RECT total age 0 age 1 age 2 age 3 age 4 age 5 age 6 age 7 age 8+ 2018 28_2 42G8 854.58 245.47 241.60 0.00 50.09 277.19 32.34 6.20 0.00 1.68 2018 28_2 42G9 2 734.15 86.94 482.26 288.97 231.15 973.26 128.22 243.45 114.82 185.08 2018 28_2 42H0 454.78 44.04 86.18 59.03 36.97 162.35 19.65 26.94 7.34 12.28 2018 28_2 43G8 962.49 84.51 136.16 32.87 146.49 511.76 29.11 0.00 0.00 21.60 2018 28_2 43G9 2 335.88 374.45 314.64 0.00 195.96 1 123.09 199.73 22.88 40.38 64.76 2018 28_2 43H0 274.90 8.17 92.54 24.50 21.77 78.93 10.89 21.77 10.89 5.44 2018 28_2 43H1 443.65 0.00 158.43 58.12 47.52 169.03 0.00 0.00 5.28 5.28 2018 28_2 44G9 1 043.51 600.07 47.70 99.51 58.68 225.36 6.21 2.74 2.74 0.51 2018 28_2 44H0 2 362.80 543.00 575.96 200.73 234.16 575.96 116.14 46.67 23.51 46.67 2018 28_2 44H1 1 636.12 239.62 490.45 198.06 145.46 510.01 8.26 8.26 18.00 18.00 2018 28_2 45G9 4 297.98 430.66 376.25 73.74 802.83 2 069.23 391.06 81.62 50.39 22.21 2018 28_2 45H0 2 977.40 83.73 212.44 726.46 168.92 623.28 828.64 197.09 52.29 84.54 2018 28_2 45H1 8 626.16 1 043.35 1 389.67 2 228.28 512.87 1 548.47 1 412.38 277.68 81.76 131.70 2018 29 46G9 930.62 441.14 122.39 77.70 134.20 125.95 13.58 3.28 10.30 2.07 2018 29 46H0 5 661.10 1 390.75 1 705.63 187.53 693.19 1 449.91 86.94 60.22 20.07 66.86 2018 29 46H1 3 614.63 9.87 711.21 481.23 274.96 1 098.38 779.15 197.32 33.12 29.39 2018 29 46H2 648.47 1.77 127.59 86.33 49.33 197.05 139.78 35.40 5.94 5.27 2018 29 47G9 2 790.66 941.20 233.44 70.36 375.59 738.99 333.07 8.46 0.00 89.55 2018 29 47H0 4 685.70 975.05 1 050.87 444.96 553.66 1 092.06 426.43 83.64 26.21 32.82 2018 29 47H1 2 932.40 305.36 772.39 423.30 165.56 650.22 487.04 102.35 14.00 12.17 2018 29 47H2 1 145.59 75.75 212.69 130.99 81.77 291.25 238.38 72.40 21.05 21.31 2018 29 48G9 556.26 54.53 166.73 41.27 25.86 142.43 108.35 7.51 8.35 1.21 2018 29 48H0 1 432.58 233.14 312.61 163.89 109.02 333.17 221.10 38.52 5.12 16.01 2018 29 48H1 3 606.11 375.52 949.85 520.55 203.60 799.61 598.93 125.86 17.22 14.97 2018 29 48H2 3 512.70 232.28 652.18 401.67 250.72 893.06 730.93 222.00 64.54 65.33 2018 29 49G9 136.43 18.58 35.28 9.15 5.54 33.73 27.48 2.46 3.15 1.07 2018 30 50G7 8.65 0.00 1.55 0.91 0.45 1.25 3.52 0.19 0.20 0.58 2018 30 50G8 106.44 6.74 27.00 9.62 4.32 12.83 37.75 1.88 2.21 4.08 2018 30 50G9 3.78 0.00 0.01 0.19 0.16 0.64 1.97 0.12 0.24 0.46 2018 30 50H0 80.69 0.00 6.54 6.05 3.83 12.64 37.81 2.56 3.85 7.41 2018 30 51G7 11.40 0.00 1.81 1.02 0.64 1.88 5.45 0.08 0.15 0.36 2018 30 51G8 20.22 0.65 0.97 1.55 0.89 2.93 9.18 0.73 1.10 2.23 2018 30 51G9 6.81 0.00 0.63 0.60 0.36 1.09 3.19 0.19 0.26 0.50 2018 30 51H0 74.95 0.00 3.61 4.93 3.46 12.30 36.63 2.28 3.76 7.98 2018 30 52G7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2018 30 52G8 12.11 0.00 0.94 0.53 0.42 1.41 4.92 0.57 0.95 2.37 2018 30 52G9 40.54 0.00 1.02 1.47 1.38 5.73 19.35 1.95 3.40 6.24 2018 30 52H0 9.21 0.00 0.36 0.75 0.54 1.58 4.84 0.23 0.34 0.57 2018 30 53G8 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2018 30 53G9 71.51 0.00 3.71 4.57 3.20 10.75 33.42 2.70 4.34 8.82 2018 30 53H0 81.56 0.00 4.62 5.65 3.89 12.70 38.94 2.76 4.34 8.65 2018 30 54G8 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2018 30 54G9 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2018 30 54H0 118.75 0.00 7.13 6.09 4.76 17.78 56.24 4.24 7.27 15.25 2018 30 55G9 1.47 0.00 0.00 0.05 0.05 0.28 0.83 0.05 0.09 0.13 2018 30 55H0 203.71 0.00 43.51 21.61 10.88 28.48 82.64 3.82 3.86 8.91 2018 32 47H3 1 598.38 45.60 587.64 261.54 67.95 471.59 122.71 7.65 10.06 23.64 2018 32 48H3 5 984.80 170.76 2 200.27 979.29 254.43 1 765.77 459.46 28.66 37.66 88.51 2018 32 48H4 8 362.66 179.96 3 482.39 1 176.26 365.85 2 336.59 645.57 23.11 48.73 104.20 2018 32 48H5 776.11 20.14 252.20 96.86 39.26 245.92 80.40 7.46 8.42 25.45 2018 32 48H6 3 666.17 55.07 1 880.60 495.60 117.20 817.62 223.47 10.92 22.43 43.27 2018 32 48H7 1 149.80 13.29 380.13 118.71 51.48 362.34 141.55 14.96 19.78 47.56 28 | ICES Scientific Reports 1:37 | ICES Table 5.1.1.2.3. Estimated numbers (millions) of cod in September-October 2005-2018, by ICES rectangles. Note: During WGBIFS meeting in 2019 errors in reported cod abundances in some rectangles were found and corrected - red coloured numbers. ICES | WGBIFS 2019 | 29 Table 5.1.1.2.4. Estimated numbers (millions) of herring by ICES subdivisions, accordingly to age groups; September-Oc- tober 2018. Table 5.1.1.2.5. Estimated numbers (millions) of sprat by ICES subdivisions, accordingly to age groups; September-Octo- ber 2018. 5.1.1.3. Area corrected data During WGBIFS meeting in 2006 possible improvement of presenting the results from acoustic surveys was discussed, and correction factor for each ICES subdivision and year was introduced because of the coverage of the investigated area differed in the years. This factor is the proportion between the total area of the ICES subdivision that are presented in the IBAS Manual (see Ad- dendum 2) and the area of the ICES rectangles, which was covered during the survey. Some disagreements appeared about appropriate area of the ICES Subdivision 28. It was agreed that the Gulf of Riga (the ICES Subdivision 28_1) must be excluded from the total area. All other the ICES subdivisions kept their areas from the a.-m. Manual. The area corrected abundance estimates for herring and sprat per the ICES subdivisions and age groups are summarized in Tables 5.1.1.3.1 and 5.1.1.3.2, respectively. Biomass for herring and sprat per the ICES subdivisions and age groups are summarized in Tables 5.1.1.3.3 and 5.1.1.3.4, respectively. Table 5.1.1.3.1. Area corrected numbers (millions) of herring by ICES subdivisions and age groups (September-October 2018). YEAR Sub_Div 0 1 2 3 4 5 6 7 8 2018 21 4.82 667.89 87.22 113.99 70.00 17.30 0.00 1.09 0.00 2018 22 315.02 95.01 168.88 47.79 57.00 9.91 0.00 3.19 0.00 2018 23 165.11 15.86 4.30 1.12 3.56 0.23 0.17 0.00 0.00 2018 24 600.32 878.09 747.40 320.19 269.08 42.81 20.33 1.57 1.57 2018 25 1 908.55 818.64 1 241.31 3 115.28 5 290.37 924.44 873.48 353.54 219.05 2018 26 4 511.57 11 226.94 8 380.12 4 457.99 3 774.53 353.02 156.17 99.05 69.00 2018 27 1 156.06 544.24 454.58 506.53 2 032.84 126.97 77.30 42.64 42.56 2018 28_2 3 784.02 4 604.26 3 990.25 2 652.87 8 847.93 3 182.61 935.31 407.40 599.75 2018 29 5 054.95 7 052.87 3 038.95 2 923.01 7 845.80 4 191.15 959.41 229.07 358.03 2018 30 7.39 103.40 65.57 39.25 124.29 376.67 24.34 36.36 74.54 2018 32 484.81 8 783.23 3 128.26 896.16 5 999.83 1 673.16 92.76 147.08 332.62 YEAR Sub_Div AREA_CORR_FACTOR AGE 0 AGE 1 AGE 2 AGE 3 AGE 4 AGE 5 AGE 6 AGE 7 AGE 8+ 2018 21 1.22 1 303.63 293.78 48.93 8.07 2.79 1.91 0.00 0.00 0.00 2018 22 1.02 973.20 48.76 12.74 2.33 2.38 0.17 0.00 0.00 0.00 2018 23 1.00 488.74 10.37 2.19 1.17 3.25 1.08 0.27 0.00 0.04 2018 24 1.00 758.30 134.92 50.55 111.51 200.70 91.88 29.97 12.59 15.74 2018 25 1.03 192.53 702.51 788.28 995.91 4 375.66 946.67 471.16 150.26 88.44 2018 26 1.10 360.97 1 682.44 1 163.99 1 935.89 4 325.16 1 988.15 1 664.61 533.80 618.81 2018 27 1.23 255.78 394.75 1 246.64 1 117.62 3 015.60 436.31 38.05 39.62 0.00 2018 28_2 1.01 500.36 846.47 2 627.72 1 855.86 8 623.94 1 341.64 1 633.31 767.90 363.68 2018 29 1.04 742.82 2 679.70 3 258.86 2 502.61 6 322.29 893.07 818.25 524.56 240.25 2018 30 1.08 5 817.77 2 994.51 3 937.75 2 243.29 2 878.45 886.53 719.35 388.13 1 326.35 2018 32 1.71 472.09 4 206.75 6 470.68 6 609.51 5 717.81 2 486.78 1 419.57 251.63 0.00 30 | ICES Scientific Reports 1:37 | ICES Table 5.1.1.3.2. Area corrected numbers (millions) of sprat by ICES subdivisions and age groups (September-October 2018). Table 5.1.1.3.3. Estimated biomass (in tons) of herring in September-October 2018. Table 5.1.1.3.4. Estimated biomass (in tons) of sprat in September-October 2018. 5.1.1.4. Tuning fleets for WGBFAS 5.1.1.4.1. Herring in the ICES Subdivisions 25–29 The tuning fleet for assessment of the Central Baltic herring (CBH) abundance in the ICES Sub- divisions 25-29 per age groups and years 1991-2018 (BIAS) is presented in Figure 5.1.1.4.1.1, with inclusion of the data from the ICES SD 29N. The area corrected combined results (for age 1+ CBH) of the above-mentioned ICES subdivisions are presented in Table 5.1.1.4.1.1. The recruit- ment index for herring (age 0) in the ICES Subdivisions 25-29 is presented in Table 5.1.1.4.1.2. YEAR Sub_Div AREA_CORR_FACTOR AGE 0 AGE 1 AGE 2 AGE 3 AGE 4 AGE 5 AGE 6 AGE 7 AGE 8+ 2018 21 1.22 5.86 812.69 106.13 138.70 85.18 21.05 0.00 1.33 0.00 2018 22 1.02 321.52 96.97 172.36 48.78 58.18 10.11 0.00 3.26 0.00 2018 23 1.00 165.11 15.86 4.30 1.12 3.56 0.23 0.17 0.00 0.00 2018 24 1.00 600.32 878.09 747.40 320.19 269.08 42.81 20.33 1.57 1.57 2018 25 1.03 1 969.60 844.83 1 281.02 3 214.94 5 459.60 954.01 901.42 364.85 226.06 2018 26 1.10 4 973.17 12 375.60 9 237.51 4 914.10 4 160.71 389.14 172.15 109.19 76.06 2018 27 1.23 1 422.80 669.81 559.47 623.41 2 501.89 156.27 95.14 52.48 52.38 2018 28_2 1.01 3 833.61 4 664.61 4 042.56 2 687.64 8 963.90 3 224.32 947.56 412.74 607.61 2018 29 1.04 5 255.83 7 333.15 3 159.72 3 039.17 8 157.59 4 357.71 997.53 238.18 372.26 2018 30 1.08 7.99 111.76 70.87 42.42 134.34 407.12 26.31 39.30 80.56 2018 32 1.71 829.53 15 028.33 5 352.54 1 533.36 10 265.86 2 862.82 158.72 251.65 569.12 YEAR Sub_Div AREA_CORR_FACTOR AGE 0 AGE 1 AGE 2 AGE 3 AGE 4 AGE 5 AGE 6 AGE 7 AGE 8+ 2018 21 1.22 18.78 10 287.58 1 871.72 2 695.19 1 747.14 426.72 31.34 2018 22 1.02 1 807.19 1 251.33 2 657.64 806.89 961.69 213.20 66.74 2018 23 1.00 911.39 180.80 68.49 18.16 68.09 5.17 4.18 2018 24 1.00 2 857.88 10 098.51 10 741.72 5 078.44 4 308.36 744.92 367.28 31.04 31.04 2018 25 1.03 8 448.19 7 639.69 14 862.95 39 981.30 70 552.12 13 688.57 13 980.69 5 532.22 3 670.61 2018 26 1.10 20 489.69 99 322.51 92 682.40 54 738.29 47 482.16 4 896.05 2 229.69 1 414.01 1 005.27 2018 27 1.23 5 242.93 5 493.54 5 622.43 6 713.57 27 986.56 1 928.01 1 202.77 678.76 676.57 2018 28_2 1.01 14 451.33 36 577.22 35 721.70 25 361.83 90 558.85 34 321.34 10 988.18 5 102.99 7 500.65 2018 29 1.04 20 316.34 55 870.53 25 451.69 29 418.47 76 134.85 42 947.05 10 451.26 2 727.20 4 478.95 2018 30 1.08 26.10 1 095.02 826.35 534.04 1 728.69 5 327.05 369.70 580.26 1 218.44 2018 32 1.71 3 407.69 103 899.87 41 440.63 13 307.16 88 839.71 26 431.43 1 762.10 2 553.79 6 133.45 YEAR Sub_Div AREA_CORR_FACTOR AGE 0 AGE 1 AGE 2 AGE 3 AGE 4 AGE 5 AGE 6 AGE 7 AGE 8+ 2018 21 1.22 17 241.47 14 916.27 3 486.61 677.22 235.38 203.87 2018 22 1.02 11 105.72 1 834.04 838.72 122.46 83.37 9.02 2018 23 1.00 5 353.25 424.01 114.68 49.26 122.14 37.02 11.89 2.37 2018 24 1.00 8 994.67 4 547.02 2 534.31 5 822.11 8 618.27 5 575.64 1 964.90 830.31 1 095.47 2018 25 1.03 2 117.85 17 589.89 23 787.08 41 044.89 159 329.00 47 170.64 23 919.83 8 907.41 5 029.43 2018 26 1.10 3 050.90 37 565.17 30 998.19 59 479.38 144 809.67 78 008.39 74 361.60 27 942.02 36 016.60 2018 27 1.23 1 123.88 5 731.24 24 848.92 28 055.85 80 837.01 14 171.91 1 362.55 1 539.09 2018 28_2 1.01 2 071.75 12 768.93 52 837.34 46 514.22 230 220.52 43 146.92 52 111.98 27 380.04 15 281.95 2018 29 1.04 2 808.41 35 398.66 58 737.54 52 127.93 137 894.74 21 193.17 20 014.48 12 834.82 7 111.37 2018 30 1.08 29 489.95 44 237.92 91 285.82 59 071.60 83 224.41 27 117.64 22 642.45 14 018.84 58 382.62 2018 32 1.71 1 841.32 45 704.28 106 544.64 126 920.66 115 835.80 55 186.37 34 641.65 7 061.56 ICES | WGBIFS 2019 | 31 Figure 5.1.1.4.1.1. Autumn (BIAS) tuning fleet index (abundance per age groups and years 1991-2018) for herring in the ICES Subdivisions 25-29. Table 5.1.1.4.1.1. Whole time-series of tuning indices. Autumn acoustic (BIAS) tuning fleet index (numbers in millions) for the Central Baltic herring (the ICES Subdivisions 25–27, 28.2 and 29, including the existing data of the ICES SD 29 North). Note: The coverage of the ICES Subdivision 29N was very inconsistent until 2007. In the years, 1993, 1995 and 1997 the total coverage was very poor. It is recommended that these data should not be used. YEAR HER_TOTAL_age1_8 HER_AGE1 HER_AGE2 HER_AGE3 HER_AGE4 HER_AGE5 HER_AGE6 HER_AGEHER_AGE8+ 1991 59 944.22 6 942.71 20 002.43 11 963.95 4 148.43 9 642.76 2 511.21 2280.03 2452.71 1992 45 994.83 7 416.92 9 155.99 13 177.55 7 156.18 4 107.91 2 273.74 1539.52 1167.03 1993 28 396.39 709.95 4 539.70 6 809.39 7 830.70 3 619.01 2 054.43 1089.66 1743.56 1994 57 157.97 3 924.41 11 881.25 20 303.84 11 526.53 5 653.24 2 098.90 940.75 829.04 1995 28 048.83 4 663.87 2 235.90 4 464.12 5 908.26 5 286.76 3 156.91 1503.95 829.06 1996 43 944.57 3 985.13 13 761.96 9 989.35 7 360.96 4 532.76 2 358.59 1178.87 776.94 1997 15 438.37 1 447.81 1 544.65 5 182.71 3 237.17 2 156.86 1 091.15 466.71 311.32 1998 24 922.96 4 285.08 2 170.72 6 617.17 6 520.67 2 584.07 1 523.58 791.27 430.41 1999 20 511.86 1 754.15 4 741.92 3 193.65 4 251.46 3 679.73 1 427.81 833.2 629.96 2000 40 924.36 10 151.18 2 560.04 9 873.66 4 837.59 5 200.35 3 234.04 3006.83 2060.67 2001 24 300.57 4 028.51 8 194.34 3 286.15 4 660.79 1 567.36 1 238.05 861.26 464.12 2002 20 672.28 2 686.92 4 242.02 6 508.41 2 842.26 2 326.29 869.78 741.28 455.3 2003 49 161.77 16 704.18 9 115.70 10 643.33 6 689.95 2 319.57 1 777.96 755.07 1156 2004 34 519.87 4 913.56 13 229.49 6 788.89 4 672.24 2 500.08 1 132.10 603.52 679.98 2005 41 760.33 1 920.24 8 250.78 15 344.88 7 123.19 4 355.80 2 540.70 1095.95 1128.8 2006 62 514.29 7 316.60 8 059.84 12 700.27 21 120.77 7 336.31 3 068.12 1700.65 1211.72 2007 29 634.05 5 400.70 6 587.26 2 974.88 4 191.03 7 092.91 1 696.87 882.93 807.46 2008 35 039.19 6 841.54 6 822.40 7 588.80 3 612.67 4 926.52 3 563.14 877.07 807.05 2009 38 653.24 6 408.78 12 141.39 6 820.28 5 551.44 2 058.64 2 969.48 2089.22 614 2010 37 891.76 3 829.47 8 278.75 12 047.60 5 006.24 3 542.80 1 684.71 1901.9 1600.3 2011 44 141.66 2 338.71 5 667.81 10 992.95 12 668.94 5 525.30 3 257.40 1448.43 2242.12 2012 51 695.69 14 947.97 3 630.05 7 544.67 9 345.39 9 199.52 2 684.65 2 261.89 2 081.55 2013 46 887.63 6 895.68 9 160.08 3 855.08 6 934.01 7 127.08 7 272.45 2 154.28 3 488.96 2014 59 146.09 5 086.33 10 113.93 15 408.71 5 916.49 7 369.87 6 664.24 4 933.46 3 653.07 2015 95 183.53 36 179.38 9 812.43 15 272.96 15 548.98 5 486.39 4 873.36 3 648.14 4 361.89 2016 58 119.58 6 830.44 27 754.78 7 212.29 7 276.68 4 049.76 2 031.87 1 493.15 1 470.62 2017 41 451.96 4 453.61 5 361.84 20 366.65 3 944.99 3 662.63 1 823.71 628.36 1 210.17 2018 64 020.47 6 305.87 9 085.50 8 407.90 26 662.65 5 605.86 4 625.38 2 016.15 1 311.18 32 | ICES Scientific Reports 1:37 | ICES Table 5.1.1.4.1.2. Autumn acoustic (BIAS) recruitment index (age 0; numbers in millions) for the Central Baltic herring (the ICES Subdivisions 25-27, 28.2 and 29, including the existing data of the ICES SD 29 North). Note: The coverage of the ICES Subdivision 29N has been very inconsistent until 2007. In the years, 1993, 1995 and 1997 the total coverage was very poor. It is recommended that these data should not be used. 5.1.1.4.2. Sprat in the ICES Subdivisions 22–29 The tuning fleet for assessment of sprat abundance in the ICES Subdivisions 22-29 per age groups and years 1991-2018 (BIAS) is presented in Figure 5.1.1.4.2.1. The area corrected combined results (for age 1+ sprat) of the above-mentioned ICES subdivisions are presented in Table 5.1.1.4.2.1. The recruitment index for sprat (age 0) in the ICES Subdivisions 22-29 is presented in Table 5.1.1.4.2.2. YEAR HER_AGE0 1991 13 732.73 1992 1 607.67 1993 1 297.73 1994 6 122.03 1995 1 356.71 1996 336.39 1997 4 050.41 1998 507.52 1999 2 591.05 2000 1 318.96 2001 2 122.76 2002 16 046.38 2003 9 066.54 2004 1 586.72 2005 5 567.63 2006 1 990.13 2007 12 197.22 2008 8 673.16 2009 3 365.99 2010 1 177.97 2011 10 098.28 2012 11 140.63 2013 3 068.44 2014 35 060.67 2015 7 661.72 2016 2 956.58 2017 7 183.88 2018 2 052.46 ICES | WGBIFS 2019 | 33 Figure 5.1.1.4.2.1. Autumn (BIAS) tuning fleet index (abundance per age groups and years 1991-2018) for sprat in the ICES Subdivisions 22-29. Table 5.1.1.4.2.1 Whole time-series of tuning indices. Autumn acoustic (BIAS) tuning fleet index (numbers in millions) for Baltic sprat (the ICES Subdivisions 22–29). Note: In the years, 1993, 1995 and 1997 the coverage was very poor. It is recommended that these data should not be used. YEAR SPR_TOTAL_age 1_8 SPR_AGE1 SPR_AGE2 SPR_AGE3 SPR_AGE4 SPR_AGE5 SPR_AGE6 SPR_AGE7 SPR_AGE8 1991 149 058.78 46 487.55 40 298.51 43 681.07 2 743.40 8 923.78 1 850.70 1 956.55 3117.22 1992 102 482.10 36 519.48 26 991.22 24 050.54 9 289.37 1 920.67 2 436.59 714.03 560.2 1993 98 533.51 30 598.67 30 890.12 16 143.51 12 681.94 4 602.94 989.26 1 451.80 1175.27 1994 137 290.10 12 531.57 44 587.69 43 274.48 17 271.54 11 924.82 5 111.65 1 028.95 1559.41 1995 231 515.93 133 193.30 16 471.15 39 297.74 22 146.93 11 336.09 5 565.78 2 104.11 1400.83 1996 268 983.16 69 994.44 130 760.26 20 797.14 23 240.90 12 777.76 6 405.11 3 696.69 1310.87 1997 143 508.24 9 279.48 57 189.82 56 067.88 8 711.23 7 627.08 2 577.01 1 638.94 416.8 1998 229 727.74 100 615.48 21 975.06 55 422.01 36 291.46 8 055.62 4 734.54 1 623.02 1010.56 1999 195 727.24 4 892.39 90 049.98 15 989.26 35 716.70 38 820.46 5 230.64 3 289.62 1738.19 2000 153 298.39 58 702.70 5 284.94 49 634.73 5 676.06 13 932.76 15 834.60 1 554.39 2678.2 2001 107 308.72 12 047.44 35 686.65 6 927.47 30 236.94 4 028.43 9 605.64 6 369.57 2406.58 2002 118 874.55 31 208.71 14 414.86 36 762.80 5 733.13 18 735.12 2 638.09 5 036.99 4344.84 2003 213 176.57 99 128.90 32 269.59 24 035.40 23 198.49 8 015.62 13 163.37 4 830.62 8534.58 2004 199 357.55 119 497.31 47 026.76 11 638.43 7 928.99 4 875.78 2 449.65 2 388.71 3551.91 2005 204 805.07 7 082.11 125 148.06 48 723.56 10 035.20 5 115.68 3 010.70 2 364.40 3325.36 2006 201 584.17 36 531.26 11 773.53 103 289.44 32 411.85 7 937.24 4 582.91 2 110.57 2947.37 2007 120 744.73 51 888.04 21 665.20 8 174.54 26 102.00 9 800.35 1 066.69 470.39 1577.52 2008 127 064.04 28 804.63 45 117.75 20 134.34 5 350.44 18 819.87 5 678.43 1 241.37 1917.21 2009 145 140.98 77 342.78 25 333.42 20 839.86 6 546.99 4 667.38 7 023.48 2 011.35 1375.72 2010 88 295.36 12 048.42 51 771.79 10 275.01 6 594.51 1 880.19 1 951.11 2 591.36 1182.97 2011 99 587.07 20 620.08 11 656.53 43 356.67 9 989.74 6 746.61 2 614.83 1 794.67 2807.94 2012 90 590.08 40 515.77 16 525.13 7 935.32 18 412.56 3 494.33 1 732.67 606.20 1368.12 2013 71 926.85 19 407.84 20 363.57 11 448.00 5 683.54 11 219.11 1 771.30 759.48 1274.02 2014 40 768.24 10 447.80 8 623.21 9 735.00 4 695.08 2 033.89 3 778.55 681.04 773.67 2015 158 980.65 99 618.14 17 315.45 19 727.94 11 041.13 3 426.39 3 552.12 2 771.69 1 527.78 2016 142 927.58 20 593.04 80 929.70 24 268.59 9 416.64 3 774.99 1 496.16 1 196.02 1 252.44 2017 166 670.25 30 170.75 33 936.85 78 088.23 13 673.42 6 371.96 2 680.92 822.75 925.38 2018 105 294.21 26 878.92 19 204.34 14 849.34 29 574.50 9 134.61 3 134.31 1 182.26 1 335.94 34 | ICES Scientific Reports 1:37 | ICES Table 5.1.1.4.2.2. Autumn acoustic (BIAS) recruitment index (age 0; numbers in millions) for sprat (the ICES Subdivisions 22-29). Note: In the years, 1993, 1995 and 1997 the coverage was very poor. It is recommended that these data should not be used. 5.1.1.4.3. Herring in the ICES Subdivision 30 The results from 2012 survey are not consistent with the results from other years due to lower area coverage than normally. In 2012, Sweden could not support the funding for the BIAS survey in the Bothnian Sea and therefore the coverage of the ICES SD 30 was based on the Finnish data only, which resulted in half of the normal effort. In 2013, Finland installed fishing equipment and the Simrad EK-60 echosounder into the R/V “Aranda” and used the vessel in order to cover all required ICES rectangles in the Bothnian Sea. In 2014-2018, the distance of the acoustic tran- sects and the numbers of realized fish control-hauls were done almost as planned. In 2018, the Finnish BIAS survey was realised on board of the r/v “Aranda”. Tuning fleet data from the October 1991, 2000, 2007-2018 BIAS surveys are accessible for the assessment of the Gulf of Bothnian herring stock (the ICES Subdivisions 30-31), the area corrected combined results are presented in Table 5.1.1.4.3.1 and Figure 5.1.1.4.3.1. YEAR SPR_AGE0 1991 59 472.84 1992 48 035.33 1993 5 173.57 1994 64 092.10 1995 44 364.82 1996 3 841.55 1997 45 947.64 1998 1 279.14 1999 33 320.45 2000 4 601.26 2001 12 000.66 2002 79 550.86 2003 146 334.99 2004 3 562.32 2005 41 862.94 2006 66 125.22 2007 17 821.04 2008 115 698.22 2009 12 798.16 2010 41 158.22 2011 45 186.05 2012 33 653.39 2013 24 694.37 2014 162 714.99 2015 36 900.25 2016 30 765.04 2017 78 166.60 2018 18 541.96 ICES | WGBIFS 2019 | 35 Figure 5.1.1.4.3.1. Autumn (BIAS) tuning fleet index (abundance per age groups and years 1999-2000 and 2007-2018) for herring in the ICES Subdivision 30. Table 5.1.1.4.3.1. Correction factor and area corrected numbers (millions) of herring per age groups in the ICES Subdivi- sion 30 (1999, 2000, 2007-2018). YEAR AREA_CORR_FACTOR age 0 age 1 age 2 age 3 age 4 age 5 age 6 age 7 age 8+ 1999 1.28 100.45 187.68 561.32 252.25 228.34 252.55 140.65 156.24 188.65 2000 1.06 104.19 3 846.00 928.57 1 794.16 4 429.95 2 048.50 2 704.11 4 361.30 8 552.91 2007 1.06 442.53 5 670.78 4 916.19 1 845.69 1 507.59 5 254.43 1 441.11 826.08 2 347.95 2008 1.2 859.15 2 669.79 4 846.31 3 386.30 1 649.49 1 825.30 3 344.39 1 265.96 3 049.00 2009 1.06 679.46 3 573.39 5 089.63 5 558.51 2 438.03 1 282.91 1 518.46 3 615.98 3 757.41 2010 1.06 452.73 3 989.84 6 534.82 3 500.95 3 535.59 1 576.84 982.35 891.26 4 479.00 2011 1.06 2 041.68 3 699.81 6 100.51 7 384.00 3 086.23 3 133.75 1 442.21 641.73 3 870.69 2012 1.08 1 402.04 11 647.55 3 841.53 3 108.94 2 733.63 1 868.14 1 693.16 987.30 2 494.57 2013 1.11 8 358.81 3 306.48 6 645.52 2 843.18 3 486.22 3 386.11 1 434.66 1 771.46 3 946.95 2014 1.08 22 393.65 9 007.65 6 686.09 4 905.35 2 234.93 2 126.82 1 691.66 1 550.85 3 642.34 2015 1.21 8 949.47 17 996.57 8 079.44 4 637.48 3 507.45 1 844.19 1 681.52 1 331.19 4 362.95 2016 1.07 516.11 2461.71 7523.15 3435.98 2143.38 1348.59 656.18 754.88 2257.24 2017 1.08 1210.64 7469.92 4502.78 7473.83 2398.53 1427.02 940.46 446.82 1765.08 2018 1.08 5 817.77 2 994.51 3 937.75 2 243.29 2 878.45 886.53 719.35 388.13 1 326.35 36 | ICES Scientific Reports 1:37 | ICES 5.1.2. Combined results of the Baltic Acoustic Spring Survey (BASS) In May–June 2018, the following acoustic surveys were conducted: 5.1.2.1. Area under investigation and overlapping areas The BASS surveys were realised in May 2018 by the above-mentioned five countries in the ICES Subdivisions 24-32 (excl. ICES SD 30, 31) however, in some ICES subdivisions only fragmentary (Fig. 5.1.2.1.1). The area coverage of the Baltic Sea with the BASS/2018 survey was very broad and 96.5% of planned area was monitored with acoustic and trawling. The ICES SD 29 was mon- itored with acoustic-trawl investigations in the southern and middle parts moreover, only one the ICES rectangle 47H3 was inspected in the ICES Subdivision 32. The part of ICES SD 26 (the ICES rct.39H0 ) was not investigated as Russia did not take part in BASS 2018 cruises. In May 2018, overall 54 the ICES rectangles were covered with acoustic-biotic monitoring. Four ICES rectangles were inspected by two countries (i.e. 42G9, 43G9, 44G9 and 46H0). Echointegration was recorded at totally of 3321 NM linear distance moreover, 124 and 319 catch and hydrological stations, respectively were inspected too. The estimated numbers of sprat per age groups and the ICES rectangles are presented in Table 5.1.2.2.1. The geographical distribution of sprat abun- dance is demonstrated in Figure 5.1.2.1.2. Because of relatively small portion of herring (<10%) in comparison with sprat (>86%) in most of areas monitored during the BASS 2018 surveys only the distribution of sprat is further examined. It should be mentioned, that in some ICES rectan- gles the great share of abundance of stickback were observed e.g. in rect. 41G6 its numerical contribution to the total abundance was above 97%. ICES | WGBIFS 2019 | 37 Figure 5.1.2.1.1. Map of the BASS survey conducted in May 2018. Various colours indicate the countries, which covered specific ICES rectangles and delivered data to the BASS-database, thus was responsible for this rectangle. Dot with dif- ferent colour within a rectangle explain additional data in the BASS-database partly or totally covered by other countries. 5.1.2.2. Combined results and area corrected data The geographical distribution of the sprat abundance per ICES rectangles monitored in May 2018 is demonstrated in Figure 5.1.2.2.1. The Baltic sprat stock abundance estimates per ICES rectan- gles and ICES subdivisions according to age groups are presented in Tables 5.1.2.2.1 and 5.1.2.2.2. During the WGBIFS 2006 meeting possible improvement of the results from acoustic surveys was discussed, and a correction factor for each ICES subdivision and year was introduced be- cause of the coverage of the investigated areas differed in the years. This factor is the proportion to the total area of the ICES subdivision (see the IBAS Manual) and the area of rectangles covered during the survey. The correction factors, calculated by ICES subdivisions for 2016 are included. In May 2018 sprat was very widely distributed in the Baltic Sea, it occurred in the each monitored ICES rectangle (Fig. 5.1.2.2.1). The highest sprat (age 1+) stock abundance was observed in the ICES SD 26 (the Gdansk Basin) and in the eastern part of the ICES SD 25. 38 | ICES Scientific Reports 1:37 | ICES Figure 5.1.2.2.1. The abundance of sprat per ICES rectangles monitored in May 2018 (the area of circles indicates esti- mated numbers of specimens x10^6 in given rectangle). ICES | WGBIFS 2019 | 39 Table 5.1.2.2.1. Estimated abundance (millions) of sprat in May 2018 per age groups and the ICES-rectangles in given ICES subdivisions. Table 5.1.2.2.2. Estimated numbers of sprat (millions) by ICES subdivisions, according to age groups (May 2018). 5.1.2.2.1. Sprat in the ICES Subdivisions 24 – 28 Tuning Fleets for WGBFAS The area corrected abundance estimates for sprat per ICES subdivision are summarized in Table 5.1.2.2.1.1. The corresponding biomass estimates of sprat are given in the Table 5.1.2.2.1.2. The complete time-series (2001 - 2018) of the area-corrected sprat abundance in the ICES Subdivisions 24, 25 26 and 28_2 is given in the Table 5.1.2.2.1.3. ANNUS SD RECT total age 1 age 2 age 3 age 4 age 5 age 6 age 7 age 8+ 2018 24 38G2 1 343.73 387.92 471.53 277.23 185.77 14.15 3.58 3.26 0.29 2018 24 38G3 2 507.89 31.63 778.72 915.67 673.54 73.87 19.89 14.57 2018 24 38G4 1 383.06 233.90 485.99 374.00 258.21 21.21 5.15 4.15 0.45 2018 24 39G2 337.69 45.61 141.11 84.61 58.87 4.82 1.39 1.22 0.06 2018 24 39G3 534.59 27.89 221.38 159.19 113.72 8.42 2.18 1.81 2018 24 39G4 509.90 55.32 209.86 140.11 94.43 6.73 1.85 1.52 0.08 2018 25 37G5 619.73 8.40 32.41 49.53 346.07 111.25 47.87 19.33 4.86 2018 25 38G5 1 867.26 79.58 125.52 273.23 1 137.36 178.63 42.61 24.16 6.16 2018 25 38G6 1 809.04 74.43 229.09 1 153.22 235.14 67.07 38.77 11.33 2018 25 38G7 824.88 1.98 29.13 94.47 514.14 120.67 39.48 19.36 5.65 2018 25 39G4 382.45 59.51 30.48 66.70 172.72 38.92 4.66 9.46 2018 25 39G5 4 452.59 178.64 553.13 1 011.88 2 370.75 279.30 26.22 32.67 2018 25 39G6 5 799.38 856.87 953.41 992.47 2 746.92 186.97 34.59 22.01 6.14 2018 25 39G7 9 450.20 3 545.88 1 663.11 1 185.35 2 937.51 111.54 2.16 4.10 0.54 2018 25 40G4 328.72 73.79 29.32 58.94 133.36 29.19 1.70 2.42 2018 25 40G5 1 110.05 41.53 129.61 249.75 593.48 78.01 7.20 10.47 2018 25 40G6 3 972.91 258.69 532.54 951.27 2 029.48 165.76 16.01 19.16 2018 25 40G7 7 280.05 1 058.16 950.40 1 476.25 3 331.69 392.33 34.69 36.53 2018 25 41G6 218.63 20.45 46.31 60.51 87.18 3.70 0.24 0.24 2018 25 41G7 922.45 42.47 104.47 203.53 500.82 53.13 8.39 9.64 2018 26 37G8 679.34 189.76 85.80 177.68 209.10 15.69 1.14 0.16 2018 26 37G9 951.96 199.33 118.66 262.61 340.46 27.54 2.65 0.72 2018 26 38G8 4 352.00 407.63 570.86 1 430.58 1 784.72 143.07 13.41 1.75 2018 26 38G9 3 559.97 471.31 382.04 1 062.57 1 484.12 138.78 17.18 3.97 2018 26 39G8 12 303.66 2 000.00 1 256.07 3 800.47 4 782.26 407.39 49.51 7.96 2018 26 39G9 19 423.58 1 893.01 2 398.25 6 366.34 8 010.92 661.01 82.88 11.18 2018 26 40G8 12 015.43 447.15 2 293.62 3 856.53 4 947.24 416.17 49.88 4.84 2018 26 40G9 6 730.63 667.68 815.29 1 058.02 2 151.72 1 299.46 531.27 149.00 58.18 2018 26 40H0 8 202.82 3 580.06 620.73 1 033.78 1 699.39 616.24 327.27 257.43 67.91 2018 26 41G8 6 458.11 135.68 1 502.48 1 957.80 2 728.56 119.28 14.31 2018 26 41G9 7 216.64 1 219.27 1 202.41 980.60 3 379.61 147.33 102.03 41.13 144.26 2018 26 41H0 2 490.29 234.00 201.61 420.47 1 338.75 102.14 100.04 30.52 62.75 2018 27 45G8 2 244.93 321.88 553.80 639.89 685.57 35.52 5.84 1.62 0.81 2018 27 46G8 2 001.68 230.54 520.12 579.68 632.78 31.37 3.90 1.16 2.13 2018 28_2 42G8 3 411.91 179.81 528.51 718.25 1 879.39 55.43 32.39 8.10 10.03 2018 28_2 42G9 5 148.83 294.55 1 166.45 934.99 2 711.94 19.41 14.33 3.58 3.58 2018 28_2 42H0 2 942.57 1 107.97 258.29 297.16 1 080.33 92.71 64.22 28.94 12.94 2018 28_2 43G9 1 476.79 64.98 355.90 267.18 782.03 4.28 1.62 0.40 0.40 2018 28_2 43H0 3 685.60 444.71 481.20 652.05 1 727.62 189.65 72.57 59.72 58.09 2018 28_2 43H1 474.20 400.18 6.94 13.88 41.64 9.25 2.31 2018 28_2 44G9 1 776.52 141.38 438.51 300.38 888.72 4.69 1.52 0.38 0.94 2018 28_2 44H0 2 123.49 792.46 333.93 159.71 723.73 35.70 26.23 10.25 41.49 2018 28_2 44H1 1 584.07 982.88 90.93 165.16 279.91 8.73 24.58 16.70 15.18 2018 28_2 45G9 1 699.73 104.98 398.18 313.87 874.35 5.57 1.47 0.37 0.94 2018 28_2 45H0 1 923.68 789.66 225.77 173.75 628.54 41.11 21.75 20.47 22.62 2018 28_2 45H1 2 518.60 1 579.24 178.66 146.03 517.82 37.16 16.58 18.45 24.66 2018 29 46G9 1 646.50 110.17 261.13 442.30 786.21 35.29 4.73 6.32 0.35 2018 29 46H0 1 803.95 149.07 248.32 448.61 883.68 51.08 11.59 9.94 1.66 2018 29 46H1 1 632.31 562.89 82.44 115.42 645.19 76.27 49.83 46.39 53.87 2018 29 47G9 3 862.17 537.65 550.57 937.13 1 708.13 92.73 17.16 17.37 1.43 2018 29 47H0 3 051.62 194.98 429.77 826.95 1 460.71 100.99 17.21 18.88 2.13 2018 29 47H1 2 483.92 974.69 156.70 173.67 1 016.36 72.99 29.14 28.08 32.30 2018 29 47H2 1 426.33 403.34 70.17 107.67 636.92 64.94 45.58 45.59 52.12 2018 32 47H3 715.55 134.71 63.32 81.86 326.46 34.62 21.49 23.59 29.51 ANNUS Sub_Div AGE1 AGE2 AGE3 AGE4 AGE5 AGE6 AGE7 AGE8 2018 24 782.27 2 308.59 1 950.81 1 384.54 129.20 34.04 26.53 0.88 2018 25 6 225.95 5 254.28 6 902.97 18 054.70 1 984.54 332.89 248.31 34.69 2018 26 11 444.89 11 447.81 22 407.45 32 856.85 4 094.11 1 277.25 508.65 347.42 2018 27 552.42 1 073.92 1 219.57 1 318.35 66.89 9.74 2.78 2.94 2018 28_2 6 882.80 4 463.27 4 142.41 12 136.03 503.69 279.56 167.36 190.87 2018 29 2 932.79 1 799.10 3 051.75 7 137.20 494.29 175.24 172.58 143.86 2018 32 134.71 63.32 81.86 326.46 34.62 21.49 23.59 29.51 40 | ICES Scientific Reports 1:37 | ICES Figure 5.1.2.2.1.1. Spring (BASS) tuning fleet index (abundance per age groups and years 2001-2018) for sprat in the ICES Subdivisions 24, 25, 26 and 28_2. Table 5.1.2.2.1.1. Area corrected numbers (millions) of sprat by ICES subdivisions and age groups (May 2018). Table 5.1.2.2.1.2. Corrected sprat biomass (in tonnes) according to ICES subdivisions and age groups (May 2018). Table 5.1.2.2.1.3. Whole time-series of tuning indices. Spring acoustic (BASS) tuning fleet index (numbers in millions) for Baltic sprat (the ICES Subdivisions 24, 25, 26 and 28_2). Note: In year 2016, the coverage was very poor. It is recommended that these data should not be used. ANNUS Sub_Div AREA_CORR_FACTOR AGE1 AGE2 AGE3 AGE4 AGE5 AGE6 AGE7 AGE8+ 2018 24 1.28 1 000.42 2 952.39 2 494.83 1 770.65 165.23 43.53 33.93 1.13 2018 25 1.03 6 425.11 5 422.35 7 123.79 18 632.25 2 048.02 343.54 256.26 35.80 2018 26 1.10 12 615.85 12 619.07 24 700.02 36 218.52 4 512.99 1 407.93 560.69 382.97 2018 27 4.25 2 347.12 4 562.87 5 181.71 5 601.40 284.20 41.38 11.81 12.49 2018 28_2 1.04 7 167.48 4 647.87 4 313.74 12 637.97 524.52 291.13 174.28 198.77 2018 29 1.61 4 727.15 2 899.84 4 918.89 11 503.94 796.71 282.46 278.16 231.88 2018 32 13.98 1 883.56 885.29 1 144.51 4 564.56 484.05 300.50 329.83 412.65 ANNUS Sub_Div AREA_CORR_FACTOR AGE1 AGE2 AGE3 AGE4 AGE5 AGE6 AGE7 AGE8+ 2018 24 1.28 6297.44 38656.60 39374.79 29414.42 3396.03 944.95 725.38 26.73 2018 25 1.03 25805.37 47652.23 72789.50 205456.56 27662.64 5386.29 3915.84 554.50 2018 26 1.10 41616.92 97613.52 218057.54 335556.43 45433.64 15700.74 6287.84 4488.02 2018 27 4.25 7262.21 34408.34 45836.04 51228.21 3337.94 534.09 160.99 179.22 2018 28_2 1.04 22644.63 35848.13 37571.23 109105.11 5487.79 3141.76 1870.57 2183.61 2018 29 1.61 13469.76 21927.00 41234.91 95341.51 8249.62 3111.92 2942.51 2438.26 2018 32 13.98 4888.13 6806.75 8754.52 36960.98 4823.56 3001.34 2843.83 4386.84 ANNUS SPR_TOTAL SPR_AGE1 SPR_AGE2 SPR_AGE3 SPR_AGE4 SPR_AGE5 SPR_AGE6 SPR_AGE7 SPR_AGE8 2001 109 404.16 8 225.02 35 734.86 12 970.86 37 327.77 5 384.44 4 635.49 4 526.01 599.71 2002 125 782.95 27 412.11 18 982.00 36 813.57 19 044.89 14 758.59 2 517.12 3 669.81 2 584.85 2003 84 986.61 26 468.98 16 471.45 8 422.95 15 532.70 5 653.45 7 169.73 1 660.01 3 607.34 2004 258 606.73 136 162.06 65 565.92 15 783.74 11 042.29 12 655.24 3 270.65 7 805.79 6 321.05 2005 134 373.52 4 358.61 88 829.99 23 556.64 7 258.25 3 516.63 2 780.51 1 829.96 2 242.94 2006 130 287.13 13 416.63 7 980.49 76 703.20 21 045.81 5 701.71 1 970.41 1 525.76 1 943.11 2007 132 637.19 51 568.74 28 713.21 6 377.16 36 006.21 7 480.56 1 261.14 532.65 697.52 2008 102 722.51 9 029.20 40 269.65 20 164.14 5 627.08 21 187.94 4 209.97 757.16 1 477.38 2009 139 641.22 39 412.17 26 701.03 36 255.42 10 548.51 6 312.12 14 106.27 5 341.22 964.48 2010 112 784.60 9 387.20 58 680.01 15 199.18 15 963.48 5 061.93 1 653.59 5 566.35 1 272.87 2011 128 153.97 18 091.69 6 790.99 66 159.99 16 689.00 10 564.65 4 076.69 2 399.13 3 381.83 2012 107 660.52 22 699.62 22 079.78 11 274.09 35 541.24 7 515.42 5 024.69 1 367.20 2 158.48 2013 111 418.65 24 876.63 35 333.30 18 392.57 11 357.94 14 959.37 3 385.50 2 163.71 949.62 2014 76 549.35 10 144.65 26 906.62 19 857.10 7 457.71 6 098.20 3 810.12 1 217.38 1 057.57 2015 160 548.72 70 752.42 24 659.60 29 744.21 18 934.79 8 080.81 4 074.30 2 581.47 1 721.12 2016 108 392.40 15 554.71 75 824.12 9 121.48 3 989.53 1 894.54 791.08 513.72 703.20 2017 233 353.41 32 701.04 36 291.63 132 939.42 20 629.89 6 790.33 2 249.57 809.40 942.12 2018 171 723.01 27 208.85 25 641.68 38 632.38 69 259.39 7 250.77 2 086.13 1 025.15 618.66 ICES | WGBIFS 2019 | 41 Annex: ToR b) Update the BIAS and BASS hydroa- coustic databases and ICES database for acoustic- trawl surveys 5.2 ToR b) Update the BIAS and BASS hydroacoustic databases and ICES database for acoustic-trawl surveys After validation, the international data from the Baltic International Acoustic Survey (BIAS) and the Baltic Acoustic Spring Survey (BASS) curried out in 2018 were added to the BIAS_DB.mdb and the BASS_DB.mdb access-databases, respectively. These databases also include queries with the used algorithms for creation of report tables and calculation of the different tuning fleets. The updated versions of the databases are located in the folder “Data” of the ICES WGBIFS 2019 SharePoint. Before the WGBIFS 2019 meeting the errors in BIAS_DB.mdl access-database in queries 149_B_Report_SD_AREA_COR and 649_B_Report_SD_AREA_COR were found. In query 149_B_Report_SD_AREA_COR (which calculates corrected SPRAT biomass per SD) the herring mean weights were used in calculations and vice versa, in query 649_B_Report_SD_AREA_COR (which calculates corrected HERRING biomass per SD) the sprat mean weights were used. The algorithms in both queries were corrected just before the meeting. Errors in reported cod abundance in some rectangles were found during WGBIFS-2019 meeting (Table 5.1.1.2.3 calculated by query ‘902_Report_COD per_rect’ in BIAS_DB.mdl access-data- base). All values of cod abundance were checked and corrected – all corrected values are marked by red in table 5.1.1.2.3 in this report). Shortly after meeting the algorithm in query ‘902_Re- port_COD per_rect’ was corrected and improved BIAS_DB.mdl access-database was uploaded in the folder “Data” of the ICES WGBIFS 2019 SharePoint. In Table 5, there has been found one inconsistency with table generated by BASS_DB.mdl access-databases (query 110). The value for sprat age 1 in 2002 reported in Table 5 in WGBIFS 2018 report was 27412.12 and it changed to 27412.11 in this report. The results of the next international acoustic surveys (BIAS, BASS) should be summarized in table format according the IBAS Manual and latest one month before the next year meeting up- loaded to the ICES WGBIFS-SharePoint. O. Kaljuste and N. Larson from Sweden were assigned as the above-mentioned (BAD1) acoustic-trawl data coordinators, responsible to control that the acoustic survey results are uploaded in the right format to the SharePoint of WGBIFS. Moreover, B. Schmidt from Poland was assigned as the manager of the BIAS and BASS databases for aggre- gated data (BIAS_DB.mdb and BASS_DB.mdb). B. Schmidt in cooperation with particular na- tional submitters will check the integrated data for errors and preliminary analysis will be per- formed in order to present the data to the WGBIFS meeting for further evaluations and discus- sion. If the countries do not submit the data to database manager in the agreed time, this work cannot be done during the WGBIFS annual meeting with the required quality. Additionally, before the next WGBIFS meeting the acoustic-trawl data from BIAS and BASS sur- veys should be uploaded also to the database for Acoustic trawl surveys in the ICES data portal (http://ices.dk/marine-data/data-portals/Pages/acoustic.aspx). Furthermore, O. Kaljuste (Swe- den) and J. Lilja (Finland) were assigned as the data coordinators of the acoustic-trawl data in the ICES data portal. 42 | ICES Scientific Reports 1:37 | ICES Annex: ToR c) Plan and decide on acoustic surveys to be conducted in autumn 2019 and spring 2019- 2020 5.3.1. Planned acoustic survey activities All the Baltic Sea countries intend to take part in the autumn BIAS acoustic surveys and experi- ments in 2019 (Fig. 5.3.2). Germany, Lithuania, Poland, Latvia and Estonia intend to take part in the BASS surveys in May 2019 and 2020 (Figs. 5.3.1 and 5.3.3). Russia is not planning to partici- pate in these BASS surveys. There is also an intention to conduct a Latvian/Estonian survey on the Gulf of Riga in July 2019 and 2020. The list of participating research vessels and initially planned periods of particular surveys are given in the following tables: BASS/2019 surveys Vessel Country Area of Investigation (ICES Subdivisions) (Preliminary) Period of In- vestigations Dura- tion (Days) Solea Germany 24, 25, 26, 27, 28 (part), 29S 03-28.05.2019 25 Baltica Latvia/Poland 26N, 28 (part) 18-25.05.2019 8 Baltica Estonia/Poland 28N, 29E 26-31.05.2019 6 unknown Lithuania 26 (the Lithuanian EEZ) 07-08.05.2019 2 Baltica Poland 24 (part), 25, 26 (in the Polish EEZ) 02-13.05.2019 13 BIAS/2019 surveys Vessel Country Area of Investigation (ICES Subdivisions) (Preliminary) Period of Investigations Duration (Days) Solea Germany 21, 22, 23, 24 01-21.10.2019 21 unknown Lithuania 26 (the Lithuanian EEZ) 08-09.10.2019 2 Baltica Latvia/Poland 26N, 28 (part) 11-20.10.2019 10 Baltica Poland 24(part), 25, 26 (in the Polish EEZ) 15-30.09.2019 16 Svea Sweden 25, 26, 27, 28, 29 Calibration: 22-28.10.2019 Survey: 01-20.10.2019 7 20 Baltica Estonia/Poland 28N, 29E, 32S 21-31.10.2019 11 Aranda Finland 29N, 30, 32N 25.09.- 09.10.2019 14 AtlantNIRO or Atlantida Russia 26 (the Russian EEZ) 04-18.10.2019 15 ICES | WGBIFS 2019 | 43 BASS/2020 surveys Vessel Country Area of Investigation (ICES Subdivisions) (Preliminary) Pe- riod of Investiga- tions Duration (Days) Solea Germany 24, 25, 26, 27, 28 (part), 29S May 2020 25 Baltica Poland 24(part), 25, 26 (in the Polish EEZ) May 2020 13 Baltica Estonia/Poland 28N, 29 May 2020 6 Baltica Latvia/Poland 26(part), 28(part) May 2020 9 unknown Lithuania 26 (the Lithuanian EEZ) May 2020 2 44 | ICES Scientific Reports 1:37 | ICES ICES | WGBIFS 2019 | 45 Figures 5.3.1–5.3.3. The planned coverage of the Baltic Sea and the assignment of the national/joint acoustic surveys to the ICES rectangles during the May 2019, September/October-2019 and May 2020 surveys (from top to bottom). Base colours of rectangles indicate the country or joint survey, which is responsible for given ICES-rectangle. Coloured dots indicate overlapping coverage by other countries (sometimes only parts of rectangle are covered). 46 | ICES Scientific Reports 1:37 | ICES Annex: ToR d) Discuss the results from BITS surveys performed in autumn 2018 and spring 2019 and evaluate the characteristics of TVL and TVS stand- ard gears used in BITS 5.4.1 BITS 4th quarter 2018 During quarter 4th BITS in 2018, the level of realized valid hauls represented 102% of the total planned stations (Figure 5.4.1.1). The number of hauls is above the mean historical level. In SD 24 the sampling was influenced by the restrictions enforced by the Swedish military. The coverage by depth stratum is as follows (depth stratum, coverage in %): 1, 100; 2, 83.6; 3, 94.5; 4, 117.8; 5, 131.3 and 6, 128.6). Again, the lower coverage in depth strata 2 and 3 were in- duced by the restrictions by the Swedish military preventing sampling in south-eastern part of Swedish waters. Russia did not perform neither the spring survey 2019 nor the autumn survey 2018 in the Russian EEZ of the ICES Subdivision 26 due to problems with financing research vessel. The number of valid hauls was considered by WGBIFS as appropriate for tuning series and it is recommended that the data are used for the assessment of Baltic and Kattegat cod and flatfish stocks. Figure 5.4.1.1. Comparison of the planned and the index-valid fishing stations by ICES Subdivisions and depth layers dur- ing BITS 4th quarter 2018. 5.4.2 BITS 1st quarter 2019 The overall coverage in this quarter is 97% (Figure 5.4.2.1). The coverage by depth stratum is (depth stratum, coverage %): 1, 100; 2, 95.5; 3, 92.6; 4, 101.9; 5, 81.1; 6, 162.5. The depth stratum 2 ICES | WGBIFS 2019 | 47 and 3 has significantly lower coverage because of the stations in the south-eastern Swedish wa- ters which were not performed due to abrupt termination of the survey resulting from sickness on board of the RV „Solea“. The number of valid hauls accomplished during the BITS-Q1/2019 was considered by WGBIFS 2019 as appropriate for tuning series (e.g. CPUE indices) and the data can be used for the assess- ment of Baltic and Kattegat cod and flatfish stocks. Figure 5.4.2.1. Comparison of the planned and the index-valid fishing stations by ICES Sub-divisions and depth layers during BITS 1q 2019. 5.4.3 Standard fishing-gear checking WGBIFS has implemented a complete and accurate measurement of technical parameters (the geometry, mesh sizes, rope lengths of the trawl, etc.) of the exploited demersal trawls (type TV- 3L and TV-3S) as a standard procedure. This procedure has to be performed at least once a year by each country involved in the BITS surveys realization. In addition, prior to each BITS survey, also a smaller scale measurement of the trawl should be made. All the measurements should follow the Manual of the construction and use of the International Standard Trawl for the Baltic Demersal Surveys. It is recommended that the measurements of TV-3L and TV-3S trawl technical parameters is done by professional experts in fishing gear technology or experienced crew mem- bers. Results of the measurements must be uploaded to the WGBIFS SharePoint using the stand- ard protocols. Four reports, covering the trawls type TV-3S and TV-3L, were submitted by na- tional laboratories to WGBIFS 2019. Poland has not made measurements of standard gear pa- rameters due to time constrains resulting from the very intensive sea exploitation of the RV “Bal- tica” in different projects. The same refers to Latvia as the fishing gear and vessel is chartered by the Latvian Institute BIOR. Presented reports did not show any values, which were outside of the acceptable percentage deviation from the standard reference values of the two trawls. All reports can be found in WGBIFS SharePoint. One example of filled report of the standard bottom fishing gear-checking is given below in Table 5.4.3.1. 48 | ICES Scientific Reports 1:37 | ICES Table 5.4.3.1. Results of the Lithuanian (FV “LBB-1010”) bottom, standard fishing gear-checking exercise. Table 2. Check list for trawl and for frame ropes of trawl Country: Year: Quarter: Date: Remarks: Tag no. TV3-520 # Trawl no./name: LTU 2018 4 06.11.2018 1B1 8,22 120 69 8,2 120 120 68,3 0,0 -0,2 1A1 8,10 200 41 8 200 200 40,0 0,0 -1,2 1A2 8,10 200 41 8 200 200 40,0 0,0 -1,2 1B2 8,22 120 69 8,2 120 120 68,3 0,0 -0,2 1C1 8,28 120 69 8,2 120 120 68,3 0,0 -1,0 1C2 8,28 120 69 8,2 120 120 68,3 0,0 -1,0 2B1 2,04 80 26 2,05 80 80 25,6 0,0 0,5 2A 2,04 120 17 2 120 120 16,7 0,0 -2,0 2B2 2,04 80 26 2,05 80 80 25,6 0,0 0,5 2C1 2,12 80 27 2,1 80 80 26,3 0,0 -0,9 2C2 2,12 80 27 2,1 80 80 26,3 0,0 -0,9 3B1 1,96 80 25 2 80 80 25,0 0,0 2,0 3A 1,96 80 25 1,95 80 80 24,4 0,0 -0,5 3B2 1,96 80 25 2 80 80 25,0 0,0 2,0 3C 2,12 80 27 2,1 80 80 26,3 0,0 -0,9 4B1 7,92 80 99 7,8 80 80 97,5 0,0 -1,5 4A 7,92 80 99 7,8 80 80 97,5 0,0 -1,5 4B2 7,92 80 99 7,9 79 79 100,0 -1,3 1,0 4C 8,00 80 100 8 82 82 97,6 2,5 -2,4 5B1 3,96 80 50 3,95 80 80 49,4 0,0 -1,3 5A 3,96 80 50 3,95 80 80 49,4 0,0 -1,3 5B2 3,96 80 50 3,95 80 80 49,4 0,0 -1,3 5C 4,00 80 50 3,92 80 80 49,0 0,0 -2,0 6B1 3,92 80 50 3,9 80 80 48,8 0,0 -2,5 6A 3,92 80 50 3,9 81 81 48,1 1,3 -3,7 6B2 3,92 80 50 3,9 80 80 48,8 0,0 -2,5 6C 3,96 80 50 4 82 82 48,8 2,5 -2,4 40 20 20 20 Standard TV3-520 # Head line extension Port. 3,00 3 Head line extension Stbd. 3,00 3,00 Head line wing section Port. 12,68 12,7 Head line wing section Stbd. 12,68 12,70 Head line bosom section 2,80 2,8 Fishing line extension Port. 0,80 0,8 Type of fishing gear: TV3-520 # Fishing line extension Stbd. 0,80 0,8 Nation: LTU Fishing line wing section Port. 14,41 14,4 Date of measurements: Fishing line wing section Stbd. 14,41 14,4 Name of operators: Marijus Spegys Fishing line bosom section 2,80 2,8 Lower wing line Port. 3,73 3,7 Comments concerning the use: Lower wing line Stbd. 3,73 3,7 Upper wing line Port. 3,83 3,8 Upper wing line Stbd. 3,80 3,8 20.02.2018 Number of realized hauls: 6 Manual TV3-520 # page 43 Remarks C h e c k l i s t f o r t r a w l T V 3 -520 # Check list for frame ropes of trawl TV3-520 # Relative error [%]Tag no. TV3-520 # - Mean mesh opening in codend (OMEGA mesh gauge): mm (n, n, n, n, n, n, n, n, n, n) Standard 6 Codend 3 4 5 1 2 Measured distance [m] Mesh size [mm] Number of meshes RemarksManual TV3-520 # page 42Section Measured distance [m] Mesh size [mm] Mesh size Number of meshes Mesh size [mm] Number of meshes Measured distance [m] ICES | WGBIFS 2019 | 49 Annex: ToR e) Plan and decide on demersal trawl surveys and experiments to be conducted in au- tumn 2019 and spring 2020, and update, and cor- rect the Tow-Database and DATRAS 5.5.1. Plan and decide on demersal trawl surveys and experiments The most of the participating institutes plan the same numbers of hauls during BITS surveys in autumn 2019 and spring 2020 as in the year before. The total number of stations committed by the countries and available is given in Table 5.5.1.1. Table 5.5.1.1. Total numbers of catch-stations planned by particular country during BITS in au- tumn 2019 and spring 2020. COUNTRY VESSEL NUMBER OF PLANNED STATIONS IN AU- TUMN NUMBER OF PLANNED STATIONS IN SPRING 2019 2020 Denmark Havfisken 21 21 Total 21 21 21 Germany Solea 57 60 Denmark Havfisken 27 27 Poland Baltica 3 5 Total 22 + 24 87 92 Denmark Dana 55 55 Estonia Commercial vessel 5* 0 Finland Aranda 0 0 Latvia Chartered vessel 25 25 Lithuania Chartered vessel 6 6 Poland Baltica 57 64 Russia Atlantniro/Atlantida 0 0 Sweden Svea 50 50 Total 25 - 28 198 200 Total 22 - 28 285 292 * Only in Estonian EEZ. WGBIFS acknowledges that Russia re-established its participation in BITS surveys in 2020. How- ever, according to preliminary information from the Member Country, the participation of Rus- 50 | ICES Scientific Reports 1:37 | ICES sia in the BITS surveys in spring 2020 cannot be confirmed yet. Since other ICES Member Coun- tries will not be able to get permission to work in the EEZ of Russia, the negative effect on the quality of the survey results based on BITS survey would be eminent. 5.5.2. Update and correct the Tow-Database Feedbacks of the recent BITS surveys (Q4 2018 and Q1 2019) were used to update the Tow-Data- base (TD). Changes of the TD structure were not proposed. The current used structure of the TD was described in the WGBIFS 2005 report and in the BITS Manual. The following changes have been made to the TD based on input from users: • One haul was deleted from the database because it was situated in a dumping area. • Another haul was deleted because it was identical to another haul in TD. • In four tracks the depth were adjusted • In six tracks the positions were adjusted. • One new track was added to the database. Furthermore, the TD is still subject to continuous clean-up of the structure and minor mistakes discovered during working with the database. More than 95% of the stations, which are stored in the Tow Database, have already successfully been used at least one time. On the other hand, trawls were damaged at stations, which were already successfully used at least one time. Those hauls were further used in the Tow Database, but the datasets are marked. The stations are deleted if similar problems were found during the next surveys. It is necessary that all countries submit the feedback according to the instructions given in the action list (Annex 5). The structure of required feedback is demonstrated in Table 8.1.1 in the WGBIFS 2014 report. 5.5.3. Reworking of the Database of Trawl Surveys (DATRAS) During the WGBIFS 2019, meeting no any essential changes of the data in the Database of Trawl Surveys (DATRAS) was made. ICES | WGBIFS 2019 | 51 Annex: ToR f) Conduct analyses related to the improvement of quality of acoustic indices and estimation of the uncertainty in the BIAS and BASS surveys At the WGBIFS meeting 2016 it was decided that a bootstrap method should be used to present the survey sampling variance. The method was based on recalculations of the survey results by resampling of acoustic data and trawl hauls. On the workshop WKSDO "Workshop on Sampling Design and Optimization" in Lysekil, Sweden, the method was discussed with Jon Helge Vølstad and Mary Christman and they suggested to do a bootstrap on the survey results from the covered area. At 2017 year’s WGBIFS meeting the two bootstrapping methods was discussed and it was decided that WGBIFS should at first move forward and try to evaluate the results from the boot- strap method recommended at WKSDO. Below are the figures (5.6.1-5.6.8) produced at the WGBIFS meeting in Klaipeda 2019, which are based on the BIAS and BASS 2018 survey data. 52 | ICES Scientific Reports 1:37 | ICES Figure 5.6.1 Histogram of bootstrap of mean sA value for BIAS 2018. Blue line is the original result from the survey. Figure 5.6.2 Histogram of bootstrap of sum of total numbers of fish for BIAS 2018. Blue line is the original result from the survey. ICES | WGBIFS 2019 | 53 Figure 5.6.3 Histogram of bootstrap of Herring numbers for BIAS 2018. Blue line is the original result from the survey. Figure 5.6.4 Histogram of bootstrap of Sprat numbers for BIAS 2018. Blue line is the original result from the survey. 54 | ICES Scientific Reports 1:37 | ICES Figure 5.6.5 Histogram of bootstrap of mean sA value for BASS 2018. Blue line is the original result from the survey. Figure 5.6.6 Histogram of bootstrap of sum of total numbers of fish for BASS 2018. Blue line is the original result from the survey. ICES | WGBIFS 2019 | 55 Figure 5.6.7 Histogram of bootstrap of Herring numbers for BASS 2018. Blue line is the original result from the survey. Figure 5.6.8 Histogram of bootstrap of Sprat numbers for BASS 2018. Blue line is the original result from the survey. 56 | ICES Scientific Reports 1:37 | ICES Annex: ToR g) Update on progress in development of the StoX software and implementation of it for the calculation of WGBIFS acoustic stock estimates, based on the IBAS methodology and data from ICES acoustic-trawl survey database During the WGBIFS 2018 meeting a StoX task sub-group was created containing Juha Lilja (Fin- land), Olavi Kaljuste (Sweden), Elor Sepp (Estonia), Niklas Larson (Sweden), Paco Rodriguez- Tress (Germany) and Beata Schmidt (Poland) as contact persons for the implementation of the StoX software for the calculation of WGBIFS acoustic stock estimates. StoX task sub-group organized a net-meeting together with StoX developers on 13th of September 2018 to go through the fish abundance index calculation procedure in the StoX software using the BIAS data from 2017. The main goal for this net-meeting was to learn the standard analysis procedure in StoX (using IBAS calculation standards). Some issues with the BIAS 2017 data (up- loaded to the ICES database for acoustic trawl surveys) were discovered before that meeting. Several of them were solved due to the meeting time and the rest was solved afterwards. There were also some issues with data uploading, deletion and downloading in the ICES database for acoustic trawl surveys. These were solved by ICES Data Centre. Additionally, it was discovered that StoX software did not allow to use data from 9 surveys in one project. StoX developers promised to solve that problem with the next version of StoX software. During the WGBIFS 2019 meeting a WebEX-meeting was held with Espen Johnsen and Atle Tot- land to discuss the issues related to the progress in development of the StoX software and im- plementation of it for the calculation of WGBIFS acoustic stock estimates, based on the IBAS methodology and data from ICES acoustic-trawl survey database. During this meeting it was demonstrated that the latest version of StoX software is able to perform the calculation procedure according to IBAS methods based on the BIAS 2017 data downloaded from the ICES database for acoustic trawl surveys. During the discussions a problem was raised that some countries perform biological sampling during the surveys and are unable to measure fish individual weights with sufficient accuracy. Therefore, they are measuring mean weights for all length-classes in each haul instead. In the standard IBAS calculation procedure these mean weights are then used instead of the individual weights. The current biotic data format of ICES database for acoustic trawl surveys does not allow to upload these values and therefore they are also not incorporated into StoX calculations. WGBIFS recommends to ICES Data Centre to add a new field into the biotic data format of ICES data base for acoustic survey data. This new field would specify whether the values given in the “BiologyIn-dividualWeight” field are measured as individual weights or as mean weights of current length-class. It was decided that StoX task sub-group members will analyse their national survey data with StoX software using the BIAS data from 2017, compare the results with their official results and contact the developers of StoX if necessary to solve the problems with abundance index calcula- tion procedure in the StoX software. StoX task sub-group decided additionally to organize a meeting together with StoX developers in beginning of November 2019 to set up the final herring and sprat abundance index calculation procedures in the StoX software using the BIAS and BASS data from 2017. ICES | WGBIFS 2019 | 57 Annex: ToR h) Define methods for the appropriate processing of the survey data and output products from the BITS survey to deliver input-data for calcu- lation of the Baltic LFI and MML indicators Vaishav Soni (ICES Data Centre) and Henrik Degel (member of WGBIFS, co-chair of WKSABI) participated in Workshop on methods to develop swept-area based effort indexes (WKSABI) in January 2019. The goals of WKSABI were: 1) Adopt and agree on an effort estimate based in trawl swept-area, valid for all surveys available in DATRAS, independent of ecoregion and survey a. a) to check and validate the calculations of missing data of the variables related to the swept-area effort estimates submitted by the different countries and sur- veys; b. propose common strategies to reduce missing data in the crucial variables c. define common calculations, when possible, across surveys and countries, …. e. BITS and NeAtl IBTS: Define by survey the first possible year for which the re- quired data checking and interpolation of missing values can be done with a reasonable effort and draft a realistic time line to finish this task; (From 2000) 2) Define and describe i) a size-based indicator, and ii) a marine litter indicator based on this swept-area index. During the workshop, the nature of these gaps of knowledge were discussed and none of these ToRs were fully accomplished, but instead they became recommendations, most of them for the survey groups (WGBIFS, IBTSWG and WGBEAM), but also for the Marine Litter Working Group (WGML). Recommendation: Encourage survey participants to continue collecting door and wing spread data (ideally both variables on each tow but preferably at least door spread). As shown in Figure 1, five out of 8 countries submitting data to BITS in DATRAS have never reported DoorSpread, due to lack of the adequate equipment for this measurement. 58 | ICES Scientific Reports 1:37 | ICES Figure 5.8.1 Proportion of missing values for DoorSpread in BITS 2000:2018 by country. Given the wide interest of achieving a swept-area calculation also for BITS survey (this calcula- tion is already existing and available for WGBEAM and NS-IBTS, not free of issues), it would be desirable to prioritize in the national institutions the need of this kind of equipment, or alterna- tive solutions. Recommendation: Conduct data cleaning and provide algorithms for estimating missing values of variables needed for the calculation of swept area for the period 2000 to present (for WGBIFS). During WKSABI, it was agreed with one of the chairs (Henrik Degel, also member of WGBIFS), that the missing data calculation algorithms could only be required to those countries with the adequate equipment of measuring DoorSpread and/or WingSpread, i.e. Denmark, Sweden and Germany. These 3 countries, in the near future will have to commit to send to the DATRAS Administration the adequate algorithms for each of these variables: DoorSpread, WingSpread and Distance, the most important for the swept-area calculation. For helping them out, they have as reference, the work done by IBTSWG http://www.ices.dk/marine-data/Documents/DATRAS/NS-IBTS_swept_area_km2_algo- rithms.pdf DATRAS Administration, also during WKSABI, agreed on developing a submission tool for these algorithms, in order to facilitate the submission process, the calculations and also to keep record of the different algorithms provided (they can change due to changes in boats, gears, etc.). ICES | WGBIFS 2019 | 59 Action point for ICES Data Centre: Provide gear geometry plots (with confidence intervals) for NS- IBTS, NeAtl-IBTS and BITS in cooperation with area coordinators for identifying limits of values of door spread, wing spread and vertical net opening for submission of survey data to DATRAS During 2018, ICES Data Centre has detected a large amount of data outliers, which would greatly compromise the swept-area calculation. In order to avoid this, the definition of ranges for several variables is requested to the group, in order to fix these ranges in the submission. As guidance, plots of the variables of interest for BITS 2000:2018 are provided: 60 | ICES Scientific Reports 1:37 | ICES Figure 5.8.2 Data distribution of DoorSpread in BITS 2000:2018 by country. Figure 5.8.4 Data distribution of Distance in BITS 2000:2018 by country. ICES | WGBIFS 2019 | 61 The goal of the request would be to provide ICES data centre with a table similar to this: Variable Upper limit Lower limit Door Spread Wing Spread Netopening Haul duration Ground speed Distance Other recommendations: Submit size category information for Marine Litter in all cases in future surveys Identify other variables than swept-area, which are potentially important for improving survey estimates (e.g. bottom current speed and direction in areas with strong tides, wind speed and direction in shallow waters) This recommendation to WGBIODIV: Provide survey specific species list and lists of missing/additional data such as length-weight relationships to be collected from surveys for the calculation of MSFD indicators to the respective survey groups. could not be communicated before WGBIODIV 2019 so, in order to avoid wasting one whole year of data, we fast-tracked this recommendation to the survey groups. For the indexes calcu- lation, length-weight relationships should be collected at least for standard species. 62 | ICES Scientific Reports 1:37 | ICES Annex: ToR i) Coordinate the marine litter-sampling programme within the Baltic International Trawl Survey and registering the data in the ICES data- base The WGBIFS at the meeting in 2014 agreed on systematically monitoring and reporting the find- ings of marine litter (anthropogenic origin), occurred in the bottom trawl during the BITS sur- veys. Submission of the marine litter data from the BITS surveys into DATRAS is uploaded rou- tinely and fully functional. The Group inspected marine litter data submission status for 2018. All countries participating in BITS-Q1/2018 surveys submitted the data, while the litter data from BITS-Q4/2018 has not been uploaded yet by Denmark and Lithuania. Marine litter data is up- loaded in the format C-TS-REV of the DATRAS Litter database (Table 5.2.2.1 in the BITS Manual 2017). Following the WGML request to verify application of guidances in marine litter data collection, the WGBIFS inspected BITS countries for the application of proposed rules specified in litter data formatting and reporting rules (checklist) for DATRAS presented in WGML report 2018 (Table 5.7.1). Survey across the WGBIFS countries clearly indicated full applicability of the rules by countries. The guidance for reporting litter data from environmental (DOME) surveys in the Northeast Atlantic has not been inspected by the WGBIFS as none of the Baltic countries partic- ipated in these surveys. None of the Baltic countries has reported collecting samples for micro- plastic identification. Marine litter data submitters will transfer data using the DATRAS Trawl litter standard format, implementing ICES vocabulary and classification coding (Tables 5.2.2.1 and 5.2.2.2 in the Manual for the Baltic International Trawls Surveys (BITS). Series of ICES Survey Protocols SISP7 – BITS. 95 pp. http://doi.org/10.17895/ices.pub.2883), described in the suitable manual, or via the Litter Reporting Format (ERF3.2; vide Annex 12), downloadable here: http://www.ices.dk/marine- data/data-portals/Pages/DATRAS-Docs.aspx. References ICES. 2018. Interim Report of the Working Group on Marine Litter (WGML), 23-27 April, 2018, ICES Headquarters, Copenhagen, Denmark. ICES CM 2018/HAPISG:10. 90 pp. ICES | WGBIFS 2019 | 63 Table 5.7.1. Litter data formatting and reporting rules (checklist). (ICES 2018). Rule DATRAS Litter submission files should contain only 1 type of records – LT (Litter) The files should use extension csv (or txt) Each of the submitted files must contain unique key fields: survey, country, ship, gear, year, and quarter. Submissions with these key values will overwrite the previously submitted data, which also means that partial data submissions are not allowed. Reported key fields must have previously submitted ‘parent’ HH records. Each record should be reported in a separate row, while fields within a record should be separated by commas. Objects belonging to the same subcategory A1 etc. and size might be reported on the same row. Remove header lines before submitting your files Fields should be reported in a specific order identified in http://datsu.ices.dk/web/selRep.aspx?Dataset=122 Empty fields are not allowed. Report -9 instead For numbers requiring decimals, report with decimal points, not decimal commas Codes can be found in the respective code lists in ICES vocabulary at vocab.ices .dk. If additional codes are required, contact accessions@ices.dk Hauls with 0 litter must be reported. For reporting zero litter catches, report LTREF = RECO-LT, PARAM = LT-TOT, UnitItem = items/haul, LT_Items = 0 Litter categories in hauls with litter should only be based on the LTREF = C-TS-REV Litter size categories should be reported on CEFAS litter size categories. The field LT_Items should be used for reporting the number of litter items of the same type/category. Preferably, items should be weighed individually. If the items are weighed together, the total weight for (multiple) items of the same litter type/category should be reported in the LT_Weight field. More details about counting and weighing litter can be found in Seafloor Litter Data Collection Guidelines (WGML, Annex 9c, 2018). Field LTPRP allows simultaneous reporting of several codes, which should be separated with ~. No other fields allow the reporting of multiple codes Submit data online at https://datras.ices.dk/Data%20submission/Default.aspx by following the instructions on the screen for the dataset “Litter data from DATRAS trawl surveys” Contact accessions@ices.dk for log-in or any additional information 64 | ICES Scientific Reports 1:37 | ICES Annex 1: List of Participants Name Address Telephone E-mail Degel Henrik (part time) Danish Technical University, National Institute of Aquatic Resources, Sec- tion for Fisheries Advice, Copenha- gen, Denmark +45 33963386 or +45 21314880 hd@aqua.dtu.dk Fedotova Elena Marine Research Institute, Klaipeda University, Universiteto ave. 17, LT- 92294 Klaipeda, Lithuania jelena.fedotova@apc.ku.lt Johnsen Espen (part time as chair-invited ex- pert via WebEx) Institute of Marine Research, Bergen, Norway +47 906 06 394 espen.johnsen@imr.no Kaljuste Olavi (chair) Swedish University of Agricultural Sciences, Department of Aquatic Re- sources, Institute of Coastal Re- search, Skolgatan 6, SE-74242 Öregrund, Sweden +46 761 268 071 olavi.kaljuste@slu.se Karpushevskiy Igor AtlantNIRO, 5 Dmitry Donskogo Street, RU-236000 Kaliningrad, Rus- sian Federation +7 4012 925 568 karpushevskiy@at- lantniro.ru Lankov Ain University of Tartu, Estonian Marine institute, Vana-Sauga 28, 80031 Pärnu, Estonia +372 4433800 ain.lankov@ut.ee Larson Niklas Swedish University of Agricultural Sciences, Department of Aquatic Re- sources, Institute of Marine Re- search, Turistgatan 5, SE- 453 30 Lysekil, Sweden +46 70 3034773 niklas.larson@slu.se Lilja Juha Natural Resources Institute Finland (Luke), Natural Resources and Bi- oproduction, Survontie 9A, FI-40500 Jyväskylä, Finland +358 295 327 525 juha.lilja@luke.fi Pönni Jukka Natural Resources Institute Finland (Luke), Natural Resources and Bi- oproduction; Latokartanonkaari 9, FI- 00790 Helsinki, Finland +358 29 532 7894 jukka.ponni@luke.fi Radtke Krzysztof National Marine Fisheries Research Institute, ul. Kollataja 1, 81-332 Gdy- nia, Poland radtke@mir.gdynia.pl Rodriguez-Tress Paco Thünen-Institute of Baltic Sea Fisher- ies, Alter Hafen Süd 2, D-18069 Ros- tock, Germany paco.rodriguez- tress@thuenen.de ICES | WGBIFS 2019 | 65 Name Address Telephone E-mail Schmidt Beata National Marine Fisheries Research Institute, ul. Kollataja 1, 81-332 Gdy- nia, Poland bschmidt@mir.gdynia.pl Sepp Elor Estonian Marine Institute, University of Tartu, 14 Mäealuse Street, EE-126 18 Tallinn, Estonia Center of Lake Peipsi Fisheries +372 521 7789 elor.sepp@ut.ee Severin Vladimir AtlantNIRO, 5 Dmitry Donskogo Street, RU-236000 Kaliningrad, Rus- sian Federation +74012 925 564 vseverin@gmail.com severin@atlantniro.ru Sics Ivo Institute of Food Safety, Animal Health and Environment (BIOR), Fish Resources Research Department; Daugavgrivas Str. 8, LV-1048 Riga, Latvia +371 7610 776 ivo.sics@bior.lv Soni Vaishav (part time as ICES staff) International Council for the Explora- tion of the Sea, Data Center, H.C. An- dersens Boulevard 44-46, 1553 Co- penhagen V, Denmark +45 33386737 vaishav.soni@ices.dk Spegys Marijus Marine Research Institute, Klaipeda University, Universiteto ave. 17, LT- 92294 Klaipeda, Lithuania marijus.spegys@apc.ku.lt Strods Guntars Institute of Food Safety, Animal Health and Environment (BIOR), Fish Resources Research Department; Daugavgrivas Str. 8, LV-1048 Riga, Latvia +371 7613 775 guntars.strods@bior.lv Storr-Paulsen Marie (part time via WebEx) Danish Technical University, National Institute of Aquatic Resources, Sec- tion for Fisheries Advice, Copenha- gen, Denmark msp@aqua.dtu.dk Totland Atle (part time as chair-invited expert via WebEx) Institute of Marine Research, Bergen, Norway +47 480 62 529 atle.totland@imr.no Velasco Andrés Thünen-Institute of Baltic Sea Fisher- ies, Alter Hafen Süd 2, D-18069 Ros- tock, Germany +49 381 811 6123 andres.ve- lasco@thuenen.de 66 | ICES Scientific Reports 1:37 | ICES Annex 2: Terms of reference for the next meeting The Baltic International Fish Survey Working Group (WGBIFS), chaired by Olavi Kaljuste, Sweden, will meet to work on ToRs and generate deliverables as listed in the table below. Meeting dates Venue Reporting details Comments (change in Chair, etc.) Year 2018 24–28 March 2018 Lyngby-Copenhagen, Denmark The first interim report by 15 May 2018 to, SCICOM and ACOM Olavi Kaljuste ap- pointed as chair Year 2019 25–29 March 2019 Klaipeda, Lithuania The second interim report by 15 May 2019 to SCICOM and ACOM Year 2020 30 March-03 April 2020 Cadiz, Spain Final report by 15 May 2020 to SCICOM and ACOM ToR descriptors TOR Description Background Science plan topics addressed dura- tion Expected delivera- bles a Combine and analyse the results of spring and au- tumn acoustic surveys and experiments Acoustic surveys provide im- portant fishery-independent stock estimates for Baltic her- ring and sprat stocks 1 Year 1, 2 and 3 Updated acoustic tun- ing index for WGBFAS b Update the BIAS and BASS hydroacoustic databases and ICES database for acoustic-trawl surveys The aim of BIAS and BASS da- tabases is to store the aggre- gated data. The aim of ICES da- tabase is to ensure that the standardized and quality-con- trolled scrutinized data from the acoustic-trawl surveys will be stored centrally in a safe way and enables easy access to the data, which will facilitate usage for many different anal- yses by a wider range of users. 31 Year 1, 2 and 3 Updated databases with acoustic and bio- tic data for WGBIFS c Plan and decide on acous- tic surveys and experi- ments to be conducted Acoustic surveys provide im- portant fishery-independent stock estimates for Baltic her- ring and sprat stocks 27 Year 1, 2 and 3 Finalized planning for the surveys for WGBIFS d Discuss the results BITS sur- veys and evaluate the char- acteristics of TVL and TVS standard gears used in BITS Demersal trawl surveys pro- vide important fishery-inde- pendent stock estimates for Baltic cod and flatfish stocks 1 Year 1, 2 and 3 Updated BITS data in DATRAS database for ICES Data Centre and WGBFAS e Plan and decide on demer- sal trawl surveys and exper- iments to be conducted, and update and correct the Tow Database Demersal trawl surveys pro- vide important fishery-inde- pendent stock estimates for Baltic cod and flatfish stocks 27 Year 1, 2 and 3 Finalized planning for the surveys for WGBIFS, updated and corrected Tow Data- base ICES | WGBIFS 2019 | 67 f Analyses related to the im- provement of quality of acoustic indices and esti- mation of the uncertainty in the BIAS and BASS sur- veys Acoustic surveys provide im- portant fishery-independent stock estimates for Baltic her- ring and sprat stocks 31 Year 1, 2 and 3 Improved quality of acoustic indices with estimates of the uncer- tainty for WGBFAS g Review the progress in de- velopment of the StoX soft- ware and implementation of it for the calculation of WGBIFS acoustic stock esti- mates, based on the IBAS methodology and data from ICES acoustic-trawl survey database StoX software produces fish abundance estimations in a transparent and reproducible way. Planned development of the StoX post-processing program should allow implication this software by WGBIFS using the acoustic and biotic data from ICES database for acoustic- trawl surveys. Exercises will be performed to validate whether the StoX soft- ware provides us similar re- sults as the current IBAS calcu- lation method in order to allow WGBIFS to use it as a new standard tool for the calcula- tion of annual BIAS and BASS survey estimates. 31 Year 1, 2 and 3 Improved transparency and reproducibility of acoustic indices, im- proved pace of work on the level of national data compilation and verification h Define methods for the ap- propriate processing of the survey data and output products from the BITS sur- vey to deliver input-data for calculation of the Baltic LFI and MML indicators. The ground trawl surveys pro- vide important fishery-inde- pendent stock estimates for Baltic cod and flatfish stocks and can be a source of the eco- system indicators, recently re- quested by different scientific organizations 9, 31 Year 1, 2 and 3 Improvement the sci- entific knowledge about the demer- sal/benthic compo- nents (mostly fish) in the Baltic Sea i Coordinate the marine lit- ter-sampling programme within the Baltic Interna- tional Trawl Survey and registering the data in the ICES database. Collected and registered infor- mation about the marine litter (mostly anthropogenic origin), occasionally appeared in the ground trawl fish control- catches, are additional source of data about present ecologi- cal status of marine seabed in investigated areas of the Baltic. 1 Year 1, 2 and 3 Coordinated the ma- rine litter sampling programme in the Bal- tic International Trawl Survey (BITS). j An attempt to make stand- ardization of the pelagic fishing gear used in BIAS and BASS surveys Acoustic surveys provide im- portant fishery-independent estimates for Baltic herring and sprat stocks size and possi- ble uncertainties, which result from, e.g. different type of fishing gears applied for fish control-catches, should be eliminated 31 Year 1, 2 and 3 Agreement on the standard pelagic fish- ing gear which will be used in the BIAS and BASS surveys k Review and update the In- ternational Baltic Acoustic Surveys (IBAS) manual and address methodological Acoustic surveys provide im- portant fishery-independent 31 Year 3 Updated IBAS manual for WGBIFS (SISP 8) 68 | ICES Scientific Reports 1:37 | ICES question raised at the last review of the SISP stock estimates for Baltic her- ring and sprat stocks l Review and update the Bal- tic International Trawl Sur- vey (BITS) manual and ad- dress methodological ques- tion raised at the last re- view of the SISP Demersal trawl surveys pro- vide important fishery-inde- pendent stock estimates for Baltic cod and flatfish stocks 31 Year 3 Updated BITS manual for WGBIFS (SISP 7) Summary of the Work Plan Year 1 Compilation the survey results from 2017 and the first quarter of 2018 and reporting to WGBFAS. Coordination and planning the schedule for surveys in 2018 and first half of 2019. Review the development and validation progress of the StoX software. Coordinate the marine litter-sampling programme in the BITS surveys and regis- tering the data in the ICES database. Define methods for the appropriate processing of the survey data and output products from the BITS survey to deliver input-data for calculation of the Baltic LFI and MML indicators. The approach to designing the standard pelagic fishing gear used in BIAS and BASS surveys. Year 2 Compilation the survey results from 2018 and first quarter of 2019 and reporting to WGBFAS. Coordination and planning the schedule for surveys in 2019 and first half of 2020. Review the development and validation progress of the StoX software. Coordinate the marine litter-sampling programme in the BITS surveys and regis- tering the data in the ICES database. Define methods for the appropriate processing of the survey data and output products from the BITS survey to deliver input-data for calculation of the Baltic LFI and MML indicators. The approach to designing the standard pelagic fishing gear used in BIAS and BASS surveys. Year 3 Compilation the survey results from 2019 and first quarter of 2020 and reporting to WGBFAS. Coordination and planning the schedule for surveys 2020 and first half of 2021. Implementation of the StoX software linked with the ICES acoustic-trawl survey database for the calculation of stock estimates for Baltic herring and sprat. Coordinate the marine litter-sampling programme in the BITS surveys and registering the data in the ICES data- base. An attempt to calculate the LFI and MML indicators based on the Baltic research surveys (e.g. BITS). Re- viewing and updating the BITS and IBAS survey manuals according to SISP standards. Final decision concerning the possible implementation of the standard pelagic fishing gear for control-catches in BIAS and BASS surveys and assignment of the intercalibration exercises between the new and old fishing gears. Supporting information Priority The scientific surveys coordinated by this Group provide major fishery-independent tuning information for the assessment of several fish stocks in the Baltic Sea. Consequently, these activities are considered to have a very high priority. Resource requirements The research programmes which provide the main input to this group are already under- way, and resources are already committed. The additional resource required to undertake additional activities in the framework of this group is negligible. Participants The Group is normally attended by about 25 members and guests. Secretariat facilities None. Financial No financial implications. Linkages to ACOM and groups under ACOM The survey data are prime inputs to the assessments of Baltic herring, sprat, cod and flat- fish stocks carried out by WGBFAS. Linked to ACOM through the quality of stock assess- ments and management advice. Linkages to other commit- tees or groups There is a very close working relationship with WGBFAS. It is also relevant to the SSGESST and WGFAST. ICES | WGBIFS 2019 | 69 Linkages to other organi- zations No direct linkage to other organizations. 70 | ICES Scientific Reports 1:37 | ICES Annex 3: Agenda of WGBIFS 2019 Introduction 1. Opening of the meeting (25.03 2019 at 10:00) • Welcome and introduction (presentation made by chair) • Households remarks (info from local organizers of the meeting, Marijus Spegys and Jūranda Savukynienė) 2. Adoption of the agenda and organization of the meeting • Discussion and adoption of the agenda • Allocation of tasks between participants • Presentation of time schedule Acoustic surveys and data 3. Combine and analyse the results of spring and autumn 2018 acoustic surveys and exper- iments and report to WGBFAS. (ToR a) • Status of BIAS and BASS standard survey reports. 4. Update the BIAS and BASS hydroacoustic databases and ICES database for acoustic- trawl surveys. (ToR b) 5. Plan and decide on acoustic surveys and experiments to be conducted in autumn 2019 and spring 2020. (ToR c) 6. Analyses related to the improvement of quality of acoustic indices and estimation of the uncertainty in the BIAS and BASS surveys. (ToR f) 7. Review the progress in development of the StoX software and implementation of it for the calculation of WGBIFS acoustic stock estimates, based on the IBAS methodology and data from ICES acoustic-trawl survey database. (ToR g) 8. An attempt to make standardization of the pelagic fishing gear used in BIAS and BASS surveys. (ToR j) 9. Review and update the International Baltic Acoustic Surveys (IBAS) manual and address methodological question raised at the last review of the SISP. (ToR k) Bottom trawl surveys and data 10. Discuss the results from BITS surveys performed in autumn 2018 and spring 2019 and evaluate the characteristics of TVL and TVS standard gears used in BITS. (ToR d) • Status of BITS standard and extended survey reports. 11. Plan and decide on demersal trawl surveys and experiments to be conducted in autumn 2019 and spring 2020, and update and correct the Tow Database. (ToR e) 12. Define methods for the appropriate processing of the survey data and output products from the BITS survey to deliver input-data for calculation of the Baltic LFI and MML indicators. (ToR h) ICES | WGBIFS 2019 | 71 13. Coordinate the marine litter-sampling programme within the Baltic International Trawl Survey and registering the data in the ICES database. (ToR i) 14. Review and update the Baltic International Trawl Survey (BITS) manual and address methodological question raised at the last review of the SISP. (ToR l) Inquiries besides of the fixed ToRs 15. 15. Recommendations from other Expert Groups 15.1. Adopt the ICES metadata convention for processed acoustic data and the ICES data portal for acoustic trawl surveys. (Rec. by WGFAST) 15.2. Adopt the ‘WKMATCH 2012 maturity scale revised’ and approve the implementation plan (presented in chapter 7). Approval should be sent to WGBIOP. (Rec. by WKASMSF) 15.3. Update their manuals with the correct references and include or update the conversion table for the national maturity scales. (Rec. by WKASMSF) 15.4. Collect, count, and report litter data according to the two guidance documents produced by WGML-2018. a) Distribution of the manual on sampling, identification and registra- tion of sea floor litter caught in bottom trawl surveys. b) Distribution of the document on suggestions for quality assurance/quality control measures for studies on micro litter. (Rec. by WGML) 15.5. Follow Litter Data Collection Guidelines by WGML. a) Seafloor litter data requested via DATRAS b) All microplastic data requested via DOME c) Other litter data requested via DOME. (Rec. by WGML) 15.6. Contact ICES Data Centre with data reporting issues (accessions@ices.dk). (Rec. by WGML) 15.7. National submitters to correct historic data. (Rec. by WGML) 15.8. WGBIOP recommends the collection of gonad samples (images of gonads and gonads for histology) during regular sampling to ensure a basic set of samples is available for ma- turity exchanges and workshops. This will be followed up with an email with a protocol with instructions on how to collect the samples. (Rec. by WGBIOP) 15.9. The IBPCluB recommends the Baltic International Fish Survey Working Group (WGBIFS) to evaluate whether the annual variation in the predicted average TS density patterns in different water depths impact the survey numbers that are used in the Gulf of Bothnia herring stock assessments. (Rec. by IBPCluB) 15.10. Conduct data cleaning and provide algorithms for estimating missing values of variables needed for the calculation of swept area for the period 2000 to present (for WGBIFS) and for the period after 2014 (for IBTSWG if necessary e.g. in case of vessel changes or changes of trawl netting material). (Rec. by WKSABI) 15.11. Encourage survey participants to continue collecting door and wing spread data (ideally both variables on each tow but preferably at least door spread) during NS-IBTS, NeAtl- IBTS and BITS. (Rec. by WKSABI) 15.12. Identify other variables than swept area which are potentially important for improving survey estimates (e.g. bottom current speed and direction in areas with strong tides, wind speed and direction in shallow waters). (Rec. by WKSABI) 72 | ICES Scientific Reports 1:37 | ICES 15.13. Submit size category information for Marine Litter in all cases in future surveys. (Rec. by WKSABI) Final issues 16. Going through the recommendations 17. Going through the action plan 18. Selection of time and venue for the next meeting Closing of the meeting (29.03.2019 at 13:30). ICES | WGBIFS 2019 | 73 Annex 4: Recommendations Recommendation Responsible Deadline Recipients Section from report this relates to WGBIFS recommends that, the BIAS- dataset, including the valid data from 2018 can be used in the assessment of the CBH (herring) and sprat stocks in the Baltic Sea with the restriction that the years 1993, 1995 and 1997 are ex- cluded from the index series. WGBIFS Before WGBFAS 2019 meeting. WGBFAS Annex ToR a), chapter 5.1.1.4. WGBIFS recommends that, the current BIAS index series can be used in as- sessment of the Gulf of Bothnia her- ring stock size with the restriction that the year 1999 is excluded from the da- taset. The abundance indices for age groups 0 and 1 should be handled with caution. WGBIFS Before WGBFAS 2019 meeting. WGBFAS Annex ToR a), chapter 5.1.1.4. WGBIFS recommends that, the BASS- dataset can be used in the assessment of sprat stock in the Baltic Sea with re- striction that the year 2016 is ex- cluded from the dataset. WGBIFS Before WGBFAS 2019 meeting. WGBFAS Annex ToR a), chapter 5.1.2.2.1. WGBIFS recommends that the data obtained and uploaded to DATRAS for both the 4th quarter 2018 and the 1st quarter 2019 BITS are used for calcu- lating survey indices for the relevant cod and flatfish stocks. WGBIFS Before WGBFAS 2019 meeting. WGBFAS Annex ToR d), chapter 5.4.1 and 5.4.2. WGBIFS recommends to ICES Data Centre to add a new field into the bio- tic data format of ICES data base for acoustic survey data. This new field would specify whether the values given in the “BiologyIndividualWeight” field are measured as individual weights or as mean weights of current length-class. This would allow coun- tries, which perform biological sam- pling during the surveys and are una- ble to measure fish individual weights with sufficient accuracy, to upload measured mean weight at length in- formation into the data base. WGBIFS As soon as possi- ble ICES Data Centre Annex ToR g), chapter 5.7 74 | ICES Scientific Reports 1:37 | ICES Annex 5: Action List 1) The feedback of the recent catch-stations realized in the framework of BITS surveys should be submitted to Henrik Degel (Denmark; e-mail: hd@aqua.dtu.dk), using the proposed standard format (Annex ToR e, Ch. 5.5.2.2; WGBIFS 2016 Report) not later than 20 December (autumn survey) and immediately after winter-spring survey. The above-mentioned Danish delegate is a coordinator of the reprogrammed Tow-Database, responsible for storage old control-hauls loca- tion with remarks concern realization - and for planning new catch-stations distribution for the next BITS surveys. All problems with realization of designated single control-hauls or part (whole) of survey should be promptly transferred (by e-mail or mobile phone) to H. Degel with c/c to the WGBIFS chair. The updated version of the trawl data base will be made available after submission the full set of data from the current BITS surveys by all countries. 2) Olavi Kaljuste (Sweden) and Juha Lilja (Finland) were assigned as coordinators of acoustic- trawl (IBAS) surveys, responsible among-others for controlling that the acoustic surveys results are uploaded in the right format. Beata Schmidt (Poland; e-mail: bschmidt@mir.gdynia.pl) was assigned as the coordinator of BIAS and BASS national databases aggregated data uploading and compilation to international level, moreover she is responsible also for all kind of input data preparation, before and during the ongoing WGBIFS meeting. The recently collected aggregated acoustic-trawl surveys (BASS, BIAS) data (in already agreed Excel format) should be uploaded to the latest WGBIFS SharePoint site at least one month before beginning of the annual WGBIFS meeting. At the same time, the latest disaggregated acoustic and biotic data from national BASS and BIAS surveys should also be uploaded to the new database for acoustic trawl surveys at the ICES Data Centre (http://ices.dk/marine-data/data-portals/Pages/acoustic.aspx), using the ICES acoustic data format. 3) Directly, after each BITS survey finalization, national submitters of data linked with monitor- ing of the marine litter from seabed should be uploaded to the DATRAS database (the ICES Data Center). The upload data format is described in the manual accessible at the ICES web page: http://www.ices.dk/marine-data/data-portals/Pages/DATRAS-Docs.aspx. 4) WGBIFS suggested performing in every year, as obligatory - the technical checking of standard parameters, i.e. measurements of the TV-3 ground trawl elements. The measurements results should be reported to next WGBIFS meeting, using the agreed format of protocols. 5) It’s important for precise values of the LFI and MML indicators to inspect that both doors and wingspread indices are included in DATRAS uploads. This should be analyzed by all WGBIFS members involved in the BITS surveys accomplishment. This information will facilitate the abil- ity calculate the swept area, one of the much needed parameter in calculation of the a.-m. indi- cators. Therefore, WGBIFS suggest that all vessels involved in the BITS surveys realization should to have possibly soon suitable equipment (sensors on the trawl wings) for measuring horizontal and vertical trawl opening during fishing. 6) For action during the next WGBIFS meeting (March 2020) it was suggested to make regular consistency analyses to the age matrixes of the indices produced by the regular research surveys, for the use of WGBFAS 7) WGBIFS StoX task sub-group [including Juha Lilja (Finland), Olavi Kaljuste (Sweden), Elor Sepp (Estonia), Niklas Larson (Sweden), Paco Rodriguez-Tress (Germany) and Beata Schmidt (Poland)] will: ICES | WGBIFS 2019 | 75 • analyse their national survey data with StoX software using the BIAS data from 2017, compare the results with their official results and contact the developers of StoX if nec- essary to solve the problems with abundance index calculation procedure in the StoX software; • organize a net-meeting together with StoX developers in beginning of November 2019 to set up the final herring and sprat abundance index calculation procedures in the StoX software using the BIAS and BASS data from 2017. 8) WGBIFS recommends national laboratories to collect, whenever possible, the data requested by WKQUAD: 1. Collect data during both calm weather and in inclement weather. Use the opportunity of inclement weather to collect data along a transect in opposite headings (i.e. with and against the seas). The objectives of collecting data along a transect in inclement weather are to: a) characterize the vessel motion, b) characterize the seabed backscatter, and c) characterize the backscatter by your target species. One can characterize the vessel motion in a fairly short time, but to characterize the seabed and fish backscatter with enough data to compare to the same stretch of transect in good weather will take longer - i.e., in good weather you can cover 10 nmi in an hour, but in inclement weather one may only be able to cover 2-3 nmi. The safety of the vessel and comfort of crew/scientist should also be taken into consideration. It is recommended that the data in inclement weather are collected at least dur- ing one hour in one heading of the transect. If there is a need to steam longer along a transect, then one should do that. 2. Compile seabed substrate maps and data for the survey area. These may be useful for decoupling substrate effects from noise or attenuation effects on data quality when the seabed backscatter is used as a diagnostic. Any quality information is useful. Even publicly-available seabed classification data are useful. 3. Compile information on transducer location and vessel trim, and collect vessel motion (pitch, roll, heave) data at a sampling rate of at least twice the frequency of the vessel motion (<1/2 the period), i.e. Nyquist sampling rate. A typical rate is 3 Hz. 4. Collect meteorological data, e.g. windspeed and direction, swell, sea state, wave height during the surveys. 5. Collect passive data during inclement weather. Transient and impulse noise will ap- pear in passive data. Compare noise values between good and bad data. The objective is to measure and monitor the background, transient, and impulse noise as weather conditions deteriorate. Ideally this should be done at survey speed, but if that is not possible, then slower speeds can be informative. If the survey protocols specify a minimum speed, then speeds below that are not as useful. 76 | ICES Scientific Reports 1:37 | ICES It is recommended that the passive data in inclement weather are collected at least during one hour per one data sample. If there is a need to steam longer along a transect, then one should do that. 9) WGBIFS recommends national laboratories to collect of gonad samples (images of gonads and gonads for histology) during regular sampling; the data requested by WGBIOP. That’s potential importance of the collection gonad samples (images of gonads and gonads for histology) and the benefits the other availability of such a library of samples would have for maturity exchanges and workshops. This will be fol- lowed up with an email with a protocol with instructions on how to collect the samples 10) WGBIFS recommends to adopt the ‘WKMATCH 2012 maturity scale revised’ update the conversion tables and update surveys manual (Rec. by WKASMSF). ICES | WGBIFS 2019 | 77 Annex 6: Standard and Cruise Reports of BITS surveys at the WGBIFS 2019 annual meeting Please see Annex 6 below. Annex 6: Standard and Cruise Reports of BITS surveys at the WGBIFS 2019 annual meeting Note: Authors are fully responsible for quality of the prepared text and all kind of pre- sented data. I List of standard reports:  1. BITS 2018 Quarter 4 Standard Report of Lithuania;  2. BITS 2018 Quarter 4 Standard Report of Germany;  3. BITS 2018 Quarter 4 Standard Report of Estonia;  4. BITS 2018 Quarter 4 Standard Report of Poland;  5. BITS 2018 Quarter 4 Standard Report of Latvia;  6. BITS 2018 Quarter 4 Standard Report of Denmark  7. BITS 2018 Quarter 4 Standard Report of Sweden;  8. BITS 2018 Quarter 1 Standard Report of Germany;  9. BITS 2018 Quarter 1 Standard Report of Poland;  10. BITS 2018 Quarter 1 Standard Report of Latvia;  11. BITS 2018 Quarter 1 Standard Report of Lithuania;  12. BITS 2018 Quarter 1 Standard Report of Denmark  13. BITS 2018 Quarter 1 Standard Report of Sweden II List of cruise reports:  1. BITS 2018 Quarter 4 Cruise Report of Latvia.  2. BITS 2018 Quarter 4 Cruise Report of Poland.  3. BITS 2018 Quarter 4 Cruise Report of Germany  4. BITS 2018 Quarter 4 Cruise Report of Lithuania  5. BITS 2018 Quarter 1 Cruise Report of Poland 78 ICES | WGBIFS 2019 NATION: LITHUANIA VESSEL: LBB-1010 Survey: BITS2018Q4 Dates: 08th – 09th November 2018 Cruise Gear details: The small (520#) standard TV3 trawl was used. Notes from survey (e.g. problems, additional work etc.): Survey made with Lithuania commercial fishery vessel LBB-1010. Total 6 fishing hauls was performed. Additional comments: ICES SUB- DIVISIO NS GEAR (TVL, TVS) DEPTH STRATA (2–6) NUMBER OF HAULS PLANED NUMBER OF VALID HAULS REALIZED USING “STANDARD” GROUND GEAR NUMBER OF VALID HAULS REALIZED USING ROCK HOPPERS NUMBER OF ASSUMED ZERO- CATCH HAULS NUMBER OF REPLACE- MENT HAULS NUMBER OF INVALID HAULS % STATION S FISHED 26 TVS 2 1 1 - - - - 100 26 TVS 3 5 5 - 1 - - 100 NUMBER OF BIOLOGICAL SAMPLES (MATURITY AND AGE MATERIAL, *MATURITY ONLY): SPECIES LENGTH AGE Clupea harengus 607 Gadus morhua 1009 293 Myoxocephalus scorpius 46 Osmerus eperlanus 5 Platichthys flesus 394 229 Pleuronectes platessa 14 14 Sprattus sprattus 12 ICES | WGBIFS 2019 79 NATION: GERMANY VESSEL: FRV “SOLEA” Survey: BITS 2018, quarter 4 Dates: 8th – 25 th November 2018 Cruise Gear details: The small (520#) standard TV3 trawl was used. All Tow Database stations were fished without rock-hoppers. The construction of the trawl follows the specifications in the manual. Notes from survey (e.g. problems, additional work etc.): A total of 52 fishing hauls and 52 hydrographical stations were performed. 4 stations in Swedish territorial waters were not allowed to carry out. The survey had three days daowntime due to bad weather. Additional comments: ICES SUB- DIVISIONS GEAR (TVL, TVS) DEPTH STRATA (1–3) NUMBER OF HAULS PLANED NUMBER OF VALID HAULS REALIZED USING “STANDARD” GROUND GEAR NUMBER OF VALID HAULS REALIZED USING ROCK HOPPERS NUMBER OF ASSUMED ZERO- CATCH HAULS NUMBER OF REPLACE- MENT HAULS NUMBER OF INVALID HAULS % STATION S FISHED 22 TVS 1 2 2 - - - 100 22 TVS 2 12 12 - - - 100 24 TVS 1 8 8 - - - 95 24 TVS 2 13 10 - 1 - 77 24 TVS 3 22 20 - 1 - 91 NUMBER OF BIOLOGICAL SAMPLES (MATURITY AND AGE MATERIAL, *MATURITY ONLY): SPECIES LENGTH AGE Gadus morhua 4047 787 Platichthys flesus 4859 574 Pleuronectes platessa 6602 831 Limanda limanda 4666 594 Psetta maxima 216 211 Scophthalmus rhombus 34 34 Clupea harengus 4423 - Sprattus sprattus 4736 - 80 ICES | WGBIFS 2019 NATION: ESTONIA VESSEL: CEV Survey: BITS18IVQRT Dates: 18-21 November 2018 Cruise Gear details: The small (530) standard TV3 trawl was used. The construction of the trawl follows the specifications in the manual. Notes from survey (e.g. problems, additional work etc.): The survey was carried out as planned. Survey started late evening of 19 November 2018 from the Port of Haapsalu , steaming to the Sub-division 28-2. The weather conditions were good: light NE-E wind. Therefore, it was possible to carry out all 5 assigned for Estonia trawl hauls on November, 20th, as planned. Since the weather forecast for next days was bad, it was decided to continue with the rest of survey in the Sub-division 29. So, after accomplishing the planned work in Sub-division 28-2, the vessel steamed to Sub-division 29, where all planned additional 5 hauls were performed. The survey was finished in early hours of 21 November 2018 in the Port of Haapsalu. No technical problems were observed during the survey this year. All catches were analysed at the Pärnu field station of the Estonian Marine Institute. ICES SUB- DIVISIONS GEAR (TVL,TV S) DEPTH STRATA (1–6) NUMBER OF HAULS PLANED NUMBER OF VALID HAULS REALIZED USING “STANDARD” GROUND GEAR NUMBER OF VALID HAULS REALIZED USING ROCK HOPPERS NUMBER OF ASSUMED ZERO-CATCH HAULS NUMBER OF REPLACEMENT HAULS NUMBER OF INVALID HAULS % STATIONS FISHED 28 TVS 3 2 2 0 0 0 0 100 28 TVS 4 3 3 0 0 0 0 100 28 TVS 5 0 0 0 0 0 0 Na 29 TVS 2 1 1 0 0 0 0 100 29 TVS 3 3 3 0 0 0 0 100 29 TVS 4 1 1 0 0 0 0 100 29 TVS 5 0 0 0 0 0 0 Na NUMBER OF BIOLOGICAL SAMPLES (MATURITY AND AGE MATERIAL, *MATURITY ONLY): SPECIES AGE LENGTH Gadus morhua 39 39 Sprattus sprattus 0 414 Clupea harengus 0 386 Platichthys flesus 434 808 ICES | WGBIFS 2019 81 Approximate positions of realised hauls during Estonian BITS survey in 4 QRT 2018 Estonian BITS IV Quarter 2018: Overview of catches. 2018 Catches, kg 1 2 3 4 5 6 7 8 9 10 Haul ID. 28030 28029 28192 28191 28061 2902 2901 2903 2904 2905 Sd 28 28 28 28 28 29 29 29 29 29 Depth, m 50 59 67 71 71 74 47 46 38 42 Date 20.11.2018 20.11.2018 20.11.2018 20.11.2018 20.11.2018 20.11.2018 20.11.2018 20.11.2018 20.11.2018 20.11.2018 Coordinates 5755_2135 5755_2131 5759_2117 5802_2106 5828_2135 5835_2133 5837_2151 5837_2152 2834_2154 5839_2201 Total Clupea harengus 1,46 0,42 0,03 0,08 7,75 0,25 3,86 1,52 0,38 0,30 16,05 Sprattus sprattus 0,16 0,12 0,01 0,05 11,59 1,64 0,45 1,52 0,12 0,03 15,67 Platichthys flesus 34,33 16,65 0,19 0,09 0,24 11,49 10,13 11,19 12,99 97,3 Gadus morhua 0,85 1,79 1,28 4 Osmerus eperlanus 0,12 0,01 0,02 1,89 1,56 2,26 1,07 7 Scophthalmus maximus 0,193 0,099 0,292 Neogobius melanostomus 0,197 0,05 0,05 0,08 0,03 0,12 0,52 Gobius sp. 0,03 0,02 0,13 0,03 0,20 Gasterosteus aculeatus 0,002 0,01 0,02 0,002 0,007 0,003 0,003 0,05 Pungitius pungitius 0 Myoxocephalus scorpius 0,473 0,82 0,26 0,36 0,28 0,37 2,56 Zoarces viviparus 0,041 0,004 0,03 0,14 0,17 0,38 Cyclopterus lumpus 0,299 0,30 Myxocephalys quadricornis 0,21 0,18 0,47 0,86 Taurulus bubalis 0 Lumpenus lampretaeformis 0 Enchelyopus cimbrius 0,042 0,042 37,92 19,89 0,29 0,23 19,61 13,40 6,70 16,88 14,61 15,55 145,1 82 ICES | WGBIFS 2019 1 NATION: POLAND VESSEL: RV “BALTICA” Survey: BITS-Q4/2018 Dates: 14/11-03/12/2018 Cruise No. 22/2018/MIR Gear details: The standard rigging cod ground trawl type TV-3#930, with 10-mm mesh bar length in the codend was applied for fish control-catches realisation. The construction of the trawl follows the specifications in the manual. Notes from survey (e.g. problems, additional work etc.): According to the WGBIFS recent (March 2018) recommendations, the vessel “Baltica” was designated to cover in November/December 2018 survey, the Polish part of ICES Sub-divisions 24, 25 and 26 with 3, 21 and 18, respectively randomly selected bottom control-hauls and also in Swedish EEZ to cover Swedish part of ICES Sub-division 25 with 12 control-hauls. The R/V Baltica realized 54 of the 60 planned hauls for this survey. Due to the ships technical problems with engine the cruise was shortened by two days and six hauls planned in Gdańsk Bay was not realized (No 26007, 26277, 26267, 26183, 26270, 26131). Totally, 54 fish catch-stations can be accepted as representative. Due to stormy weather, rocky bottom and large fish concentrations observed in echosounder – 5 and 6 hauls was shortened to 20 min and 15 min, respectively. Every control-haul was preceded by the seawater temperature, salinity and oxygen content measurements, made continuously from the sea-surface to a bottom. Overall, 54 fish catch-stations starting positions and 26 standard hydrographic stations were controlled by the SeaBird SBE 911 CTD-probe combined with the rosette sampler (the bathometer rosette). Oxygen content was determined by the standard Winkler’s method. Additional comments: ICES SUB- DIVISIONS GEAR (TVL, TVS) DEPTH STRATA (2– 6) NUMBER OF HAULS PLANED NUMBER OF VALID HAULS REALIZED USING “STANDARD” GROUND GEAR NUMBER OF VALID HAULS REALIZED USING ROCK HOPPERS NUMBER OF ASSUMED ZERO- CATCH HAULS NUMBER OF REPLACE- MENT HAULS NUMBER OF INVALID HAULS % STATIONS FISHED 24 TVL 2 1 1 0 0 0 0 100 24 TVL 3 2 2 0 0 0 0 100 25 TVL 2 13 13 0 0 0 0 100 25 TVL 3 12 12 0 0 0 0 100 25 TVL 4 6 6 0 0 0 0 100 25 TVL 5 2 2 0 0 0 0 100 26 TVL 2 7 4 0 0 0 0 57 26 TVL 3 7 6 0 0 0 0 86 26 TVL 4 3 1 0 0 0 0 33 26 TVL 5 6 6 0 0 0 0 100 26 TVL 6 1 1 0 0 0 0 100 NUMBER OF BIOLOGICAL SAMPLES (MATURITY AND AGE MATERIAL, *MATURITY ONLY): SPECIES (LATIN NAME) Length Age and maturity Neogobius melanostomus 1 Pomatoschistus minutus 1 Mullus surmuletus 1 Pungitius pungitius 1 Gasterosteus aculeatus 4 Hyperoplus lanceolatus 148 2 Gadus morhua 4339 435 Pleuronectes platessa 565 455 Myoxocephalus scorpius 173 5 Agonus cataphractus 3 Lampetra fluviatilis 4 Enchelyopus cimbrius 288 17 Alosa fallax 17 Engraulis encrasicolus 4 Scophthalmus maximus 22 22 ICES | WGBIFS 2019 83 2 Platichthys flesus 3413 776 Osmerus eperlanus 451 4 Sprattus sprattus 6551 584 Clupea harengus 8066 1105 Cyclopterus lumpus 4 Zoarces viviparus 10 Merlangius merlangus 36 Crosses – fish control stations, red dots – hydrological stations, green line – hydrological profile. 84 ICES | WGBIFS 2019 1 NATION: LATVIA VESSEL: RV “BALTICA” Survey: BITS-Q4/2018 Dates: 11-21/12/2018 Cruise No. 2/2018 Gear details: The hard bottom ground-rope (rockhopper) trawl, type TV-3#930 (with 10-mm mesh bar length in the codend) was applied for fish catches. The construction of the trawl follows the specifications in the manual. Notes from survey (e.g. problems, additional work etc.): The original surveys plan provided that 24 control-hauls will be realized in the Latvian EEZ (9 trawls in SD 26, 15 trawls in SD 28) and 1 control-hauls in the Lithuania EEZ (SD 26). Five additional trawls were planned in the SD 26 (5 trawls in the Lithuanian EEZ). The r.v.“Baltica” realized 31 bottom trawl control-hauls including the Latvian territorial waters (Fig.1). Trawl with track number 28084 was not in the correct depth zone as it was indicated in track database. This track with number 28084 was realized. Later, new track position in this area were find within correct depth zone. Information about new track will be sent to track database administrator. Fifteen catch-stations were only initiated by hydrological parameters measurement and due to very low oxygen concentration (below 0.5 ml/l) near bottom, fishing was omitted. Five additional trawls were realized in the Lithuanian EEZ (SD 26). All trawl catches were performed in the daylight. The hard bottom ground-rope (rockhopper) trawl, type TV-3#930 (with 10-mm mesh bar length in the codend) was applied for fish catches. The standard trawling duration was 30 minutes. The mean speed of vessel while trawling was 3.0 knots. However, in the case of 5 hauls, their duration was shortened to 15-20 minutes, due to dense clupeids concentrations observed on the echosounder or bad fishing ground. The length measurements in the 1.0-cm classes were realised for all 945 cod and 1519 flounder. Length measurements in the 0.5-cm classes were realized for 1653 herring and 1580 sprat. In total, 457 cod and 409 flounder individuals were taken for biological analysis. Stomachs from the 350 cod were taken for investigation of cod feeding. Acoustic data, i.e. the echo-integration records (SA = NASCs; Nautical Area Scattering (Strength) Coefficient) were collected with the EK-60 scientific echosounder during fishing operations and on the distances between consecutive hauls. Echo-sounding data collected during the BITS survey were delivered to the Latvian researchers for further analysis. Directly before every haul, the seawater temperature, salinity and oxygen content were measured continuously from the sea surface to a bottom. The seawater samples were taken also at the standard HELCOM stations. Totally, 36 hydrological stations were inspected with the Neil-Brown CTD-probe combined with the rosette sampler (the bathometer rosette). Oxygen content was determined by the standard Winkler’s method. Meteorological observations of wind velocity and directions and the sea state were realized at the actual geographic position of each control-haul. Additional comments: ICES SUB- DIVISIONS GEAR (TVL, TVS) DEPTH STRATA (2–6) NUMBER OF HAULS PLANED NUMBER OF VALID HAULS REALIZED USING “STANDARD” GROUND GEAR NUMBER OF VALID HAULS REALIZED USING ROCK HOPPERS NUMBER OF ASSUMED ZERO- CATCH HAULS NUMBER OF REPLACE- MENT HAULS NUMBER OF INVALID HAULS % STATIONS FISHED 26 TVL 3 3 3 100 26 TVL 4 1 1 100 26 TVL 5 3 1 2 100 26 TVL 6 3 3 100 28 TVL 2 4 2 50 28 TVL 3 2 4 150 28 TVL 4 3 2 1 100 28 TVL 5 5 6 120 28 TVL 6 1 0 ICES | WGBIFS 2019 85 2 NUMBER OF BIOLOGICAL SAMPLES (MATURITY AND AGE MATERIAL, *MATURITY ONLY): SPECIES LENGTH AGE Clupea harengus 1653 0 Sprattus sprattus 1580 0 Platichthys flesus 1519 409 Gadus morhua 945 457 Myoxocephalus scorpius 87 0 Zoarces viviparus 22 0 Osmerus eperlanus 19 0 Hyperoplus lanceolatus 11 0 Cyclopterus lumpus 5 0 Gasterosteus aculeatus 4 0 Scophthalmus maximus 1 0 Pleuronectes platessa 1 0 Alosa alosa 1 0 Lumpenus lampretaeformis 1 0 86 ICES | WGBIFS 2019 3 Figure 1. Location of the realized fish control-hauls (marked with red dots) and the HELCOM standard hydrological stations (marked with black triangles), green lines - national fishing zone borders. ICES | WGBIFS 2019 87 Nation: Denmark Vessel: Survey: BITS Dates: Gear details: Notes from survey (e.g. problems, additional work ICES Sub-Divisions and Depth stratum Gear Number of hauls planed Number of valid hauls realized using “Standard” ground gear Number of valid hauls realized using Rock-hoppers Number of assumed zero- catch hauls Number of replacement hauls Number of invalid hauls Coverage (%) (TVL,TVS) 25 TVL 2 TVL 1 1 0 0 0 0 100.0 3 TVL 21 15 0 0 0 1 71.4 4 TVL 20 23 0 4 0 0 135.0 5 TVL 12 16 0 4 0 0 166.7 6 TVL 0 1 24 TVL 3 TVL 1 1 0 0 0 0 100.0 55 57 0 8 0 1 118.2 Species Age Species Age Clupea harengus Gadus morhua Sprattus sprattus 01/11-18/11 - 2018 Dana Number of biological samples (maturity and age material, Cruise The big (#920) standard TV3 trawl is used. The construction of the trawl follows the specifications in the manual. No rock hopper was used Stomack sampling from cod, plankton fishing during night. 88 ICES | WGBIFS 2019 NATION: SWEDEN VESSEL: RV “DANA” Survey: BITS Q4 2018 Dates: 19-28 November 2018 Cruise Gear details: The large (930#) standard TV3 trawl was used. No tows are done with the rock hopper ground gear on harder ground stations. The trawl construction is according to the specification in the BITS manual. Notes from survey (e.g. problems, additional work etc.): 30 stations were allocated, 28 of these were trawled. Six hauls were cancelled in SD 27 and two in SD 28 because the Swedish Armed Forces (SAF) did not grant us permission. Six of those could be replaced. Two complementary haul, not included here. Four hauls in SD 27 and 28 had oxygen deficiency. Additional comments: Depth strata 2 SD 25 where planned 3 hauls but only two where made due to close proximity to next haul, (cluster haul), 1 additional haul where made in depth strata 3. Depth strata 4 and 5 in SD 28 deviates because one haul is randomized as depth layer 5 but in reality is in dl 4. ICES SUB- DIVISIO NS GEAR (TVL, TVS) DEPTH STRATA (2–6) NUMBER OF HAULS PLANNED NUMBER OF VALID HAULS REALIZED USING “STANDARD ” GROUND GEAR NUMBER OF VALID HAULS REALIZED USING ROCK HOPPERS NUMBER OF ASSUMED ZERO- CATCH HAULS NUMBER OF REPLACE -MENT HAULS NUMBER OF INVALID HAULS STATIONS FISHED % REMARKS 25 TVL 2 3 2 - 0 0 0 66 2 25 TVL 3 7 8 - 0 2 0 114 2 27 TVL 3 1 1 - 0 0 0 100 27 TVL 4 5 5 - 2 2 0 100 27 TVL 6 2 2 - 2 2 0 100 28 TVL 3 3 3 - 0 0 0 100 28 TVL 4 3 4 - 0 0 0 125 28 TVL 5 4 3 - 2 0 0 75 Remark 1. The % number deviates from 100 because we were prohibited by Swedish Armed Forces to visit some of the stations. Remark 2. The % number deviates from 100 because we don’t have any replacement stations at that depth and area. ICES | WGBIFS 2019 89 NUMBER OF BIOLOGICAL SAMPLES (MATURITY AND AGE MATERIAL, *MATURITY ONLY): Specname sci. Lenght Age Stomachs Agonus cataphractus 1 Anguilla anguilla 1 Clupea harengus 6 478 Cyclopterus lumpus 15 Enchelyopus cimbrius 29 Gadus morhua 3 897 490 101 Gasterosteus aculeatus 120 Hyperoplus lanceolatus 1 Limanda limanda 51 Lumpenus lampretaeformis 7 Merlangius merlangus 24 Myoxocephalus quadricornis 452 Myoxocephalus scorpius 437 Osmerus eperlanus 4 Platichthys flesus 2 839 788 - Pleuronectes platessa 495 Pollachius virens 1 Pomatoschistus 5 Saduria entomon 26 Sander lucioperca 1 Scophthalmus maximus 75 Sprattus sprattus 4 676 Trachurus trachurus 1 Zoarces viviparus 160 90 ICES | WGBIFS 2019 NATION: GERMANY VESSEL: FRV “SOLEA” Survey: BITS 2019, quarter 1 Dates: 16 th February to 1st March, 4th to 12th March 2019 Cruise Gear details: The small (520#) standard TV3 trawl was used. All Tow Database stations wre fished without rock-hoppers. The construction of the trawl follows the specifications in the manual. Notes from survey (e.g. problems, additional work etc.): A total 48 fishing hauls and 48 hydrographical stations were performed. Technical problems, bad weather and sickness caused 9 days downtime. Fishing activities had to be interrupted 3 days before the end of the cruise because of a highly contagious norovirus, which have teared through the vessel. Therefore was not possible to carry out 8 of 10 planned stations (2 of them were prohibited by the armed forces) in Swedish waters. Additional comments: ICES SUB- DIVISIONS GEAR (TVL, TVS) DEPTH STRATA (1–3) NUMBER OF HAULS PLANED NUMBER OF VALID HAULS REALIZED USING “STANDARD” GROUND GEAR NUMBER OF VALID HAULS REALIZED USING ROCK HOPPERS NUMBER OF ASSUMED ZERO- CATCH HAULS NUMBER OF REPLACE- MENT HAULS NUMBER OF INVALID HAULS % STATIONS FISHED 22 TVS 1 2 2 - 1 - 100 22 TVS 2 13 13 - - 1 100 24 TVS 1 8 8 - - - 100 24 TVS 2 15 10 - - - 67 24 TVS 3 21 15 - 1 - 71 NUMBER OF BIOLOGICAL SAMPLES (MATURITY AND AGE MATERIAL, *MATURITY ONLY): SPECIES LENGTH AGE Gadus morhua 7872 1084 Platichthys flesus 2756 652 Pleuronectes platessa 4763 843 Limanda limanda 3405 609 Psetta maxima 156 154 Scophthalmus rhombus 198 17 Clupea harengus 2935 - Sprattus sprattus 3810 - ICES | WGBIFS 2019 91 1 NATION: POLAND VESSEL: RV “BALTICA” Survey: BITS-Q1/2019 Dates: 12/02-06/03/2019 Cruise No. 3/2018/MIR Gear details: The standard rigging cod ground trawl type TV-3#930, with 10-mm mesh bar length in the codend was applied for fish control-catches realisation. The construction of the trawl follows the specifications in the manual. Notes from survey (e.g. problems, additional work etc.): According to the WGBIFS recent (March 2018) recommendations, the vessel “Baltica” was designated to cover parts of the ICES Sub-divisions 24, 25 and 26 with 5, 29 and 22, respectively randomly selected bottom control-hauls, and also in Swedish EEZ to cover Swedish part of ICES Sub-division 25 and 26 with 4 and 9 control-hauls, respectively. The R/V Baltica realized 71 of the 69 planned hauls for this survey. Two hauls (ICES no 26020 and ICES no 26224) were considered as „Invalid” due to technical problems associated with gear performance observed during trawling. Both hauls were repeated successfully in the places as assigned in the survey plan. One haul (ICES no 26221) was not realized due to oxygen level on the bottom below 0.5 ml/l. Totally, all the 69 fish catch-stations can be accepted as representative. Due to stormy weather, rocky bottom and large fish concentrations observed in echosounder – 1 and 11 hauls were shortened to 10 min and 20 min, respectively. Haul No. 26221 was classified as “no oxygen”. Every control-haul was preceded by the seawater temperature, salinity and oxygen content measurements, made continuously from the sea-surface to a bottom. Overall, 69 fish catch-stations starting positions and 28 standard hydrographic stations were controlled by the SeaBird SBE 911 CTD-probe combined with the rosette sampler (the bathometer rosette). Oxygen content was determined by the standard Winkler’s method. Additional comments: ICES SUB- DIVISIONS GEAR (TVL, TVS) DEPTH STRATA (2– 6) NUMBER OF HAULS PLANED NUMBER OF VALID HAULS REALIZED USING “STANDARD” GROUND GEAR NUMBER OF VALID HAULS REALIZED USING ROCK HOPPERS NUMBER OF ASSUMED ZERO- CATCH HAULS NUMBER OF REPLACE- MENT HAULS NUMBER OF INVALID HAULS % STATIONS FISHED 24 TVL 2 3 3 0 0 0 0 100 24 TVL 3 2 2 0 0 0 0 100 25 TVL 2 13 13 0 2 0 0 100 25 TVL 3 11 11 0 2 0 0 100 25 TVL 4 7 7 0 0 0 0 100 25 TVL 5 2 2 0 0 0 0 100 26 TVL 2 9 9 0 0 0 0 100 26 TVL 3 7 7 0 0 0 0 100 26 TVL 4 6 6 0 0 0 0 100 26 TVL 5 6 6 0 0 0 0 100 26 TVL 6 3 3 0 1 0 0 100 NUMBER OF BIOLOGICAL SAMPLES (MATURITY AND AGE MATERIAL, *MATURITY ONLY): SPECIES (LATIN NAME) Length Age and maturity Neogobius melanostomus 2 Pomatoschistus minutus 2 Pomatoschistus microps 2 Vimba vimba 1 Gasterosteus aculeatus 15 Pollachius virens 1 1 Hyperoplus lanceolatus 9 Gadus morhua 14349 800 Pleuronectes platessa 1726 742 Gymnocephalus cernuus 2 92 ICES | WGBIFS 2019 2 Myoxocephalus scorpius 884 16 Agonus cataphractus 2 Salmo salar 1 1 Enchelyopus cimbrius 261 30 Scophthalmus rhombus 1 1 Perca fluviatilis 3 Trachurus trachurus 5 1 Alosa fallax 25 1 Scophthalmus maximus 75 75 Platichthys flesus 8234 983 Osmerus eperlanus 18 Sprattus sprattus 6028 548 Clupea harengus 9362 1045 Cyclopterus lumpus 45 4 Ammodytes tobianus 2 Zoarces viviparus 93 Merlangius merlangus 19 2 Crosses – fish control stations, red dots – hydrological stations, green line – hydrological profile. ICES | WGBIFS 2019 93 1 NATION: LATVIA VESSEL: RV “BALTICA” Survey: BITS-Q1/2019 Dates: 13-21/03/2019 Cruise No. 1/2019 Gear details: The hard bottom ground-rope (rockhopper) trawl, type TV-3#930 (with 10-mm mesh bar length in the codend) was applied for fish catches. The construction of the trawl follows the specifications in the manual. Notes from survey (e.g. problems, additional work etc.): The original surveys plan provided that 24 control-hauls will be realized in the Latvian EEZ (all trawls in SD 28) and 3 control-hauls in the Estonian EEZ (SD 26). Five additional trawls were planned in the SD 26, in the Latvian EEZ. The r.v.“Baltica” realized 30 bottom trawl control-hauls including the Latvian territorial waters (Fig.1). Trawls with track number 28086, 28088, 28193 were not in the correct depth zone as it was indicated in track database. These tracks were realized. Information about correct depths for these trawls will be sent to track database administrator. Five catch-stations were only initiated by hydrological parameters measurement and due to very low oxygen concentration (below 0.5 ml/l) near bottom, fishing was omitted. Three additional trawls were realized in the Latvian EEZ (SD 26). All trawl catches were performed in the daylight. The hard bottom ground-rope (rockhopper) trawl, type TV-3#930 (with 10-mm mesh bar length in the codend) was applied for fish catches. The standard trawling duration was 30 minutes. The mean speed of vessel while trawling was 3.0 knots. However, in the case of 9 hauls, their duration was shortened to 15-20 minutes, due to dense clupeids concentrations observed on the echosounder or bad weather for trawling. The length measurements in the 1.0-cm classes were realised for all 503 cod and 5244 flounder. Length measurements in the 0.5-cm classes were realized for 2431 herring and 2510 sprat. In total, 352 cod and 446 flounder individuals were taken for biological analysis. Stomachs from the 237 cod were taken for investigation of cod feeding. Acoustic data, i.e. the echo-integration records (SA = NASCs; Nautical Area Scattering (Strength) Coefficient) were collected with the EK-60 scientific echosounder during fishing operations and on the distances between consecutive hauls. Echo-sounding data collected during the BITS survey were delivered to the Latvian researchers for further analysis. Directly before every haul, the seawater temperature, salinity and oxygen content were measured continuously from the sea surface to a bottom. The seawater samples were taken also at the standard HELCOM stations. Totally, 36 hydrological stations were inspected with the Neil-Brown CTD-probe combined with the rosette sampler (the bathometer rosette). Oxygen content was determined by the standard Winkler’s method. Meteorological observations of wind velocity and directions and the sea state were realized at the actual geographic position of each control-haul. Ichthyoplankton samples were collected in 10 stations. Additional comments: During the survey 1 working day were lost due to the bad weather. ICES SUB- DIVISIONS GEAR (TVL, TVS) DEPTH STRATA (2–6) NUMBER OF HAULS PLANED NUMBER OF VALID HAULS REALIZED USING “STANDARD” GROUND GEAR NUMBER OF VALID HAULS REALIZED USING ROCK HOPPERS NUMBER OF ASSUMED ZERO- CATCH HAULS NUMBER OF REPLACE- MENT HAULS NUMBER OF INVALID HAULS % STATION S FISHED 26 TVL 2 26 TVL 5 26 TVL 6 28 TVL 2 6 6 100 28 TVL 3 7 6 85.7 28 TVL 4 6 7 116.7 28 TVL 5 7 3 3 85.7 28 TVL 6 1 2 200 94 ICES | WGBIFS 2019 2 Figure 1. Location of the realized fish control-hauls (marked with red dots) and the HELCOM standard hydrological stations (marked with black triangles), green lines - national fishing zone borders. ICES | WGBIFS 2019 95 3 NUMBER OF BIOLOGICAL SAMPLES (MATURITY AND AGE MATERIAL, *MATURITY ONLY): SPECIES LENGTH AGE PLATICHTHYS FLESUS 5244 446 SPRATTUS SPRATTUS 2510 CLUPEA HARENGUS 2431 GADUS MORHUA 503 352 MYOXOCEPHALUS SCORPIUS 491 ZOARCES VIVIPARUS 87 OSMERUS EPERLANUS 61 GASTEROSTEUS ACULEATUS 24 CYCLOPTERUS LUMPUS 23 POMATOSCHISTUS MINUTUS 13 SCOPHTHALMUS MAXIMUS 12 ENCHELYOPUS CIMBRIUS 5 LUMPENUS LAMPRETAEFORMIS 3 GASTEROSTEUS PUNGITIUS 2 HYPEROPLUS LANCEOLATUS 2 NEOGOBIUS MELANOSTOMUS 2 PLEURONECTES PLATESSA 1 TRIGLOPSIS QUADRICORNIS 1 96 ICES | WGBIFS 2019 NATION: LITHUANIA VESSEL: LBB-1032 Survey: BITS2019Q1 Dates: 21th – 25th February 2019 Cruise Gear details: The small (520#) standard TV3 trawl was used. Notes from survey (e.g. problems, additional work etc.): Survey made with Lithuania commercial fishery vessel LBB-1032. Total 6 fishing hauls was performed. First three hauls was made November 21 and last three November 25. Additional comments: ICES SUB- DIVISIO NS GEAR (TVL, TVS) DEPTH STRATA (2–6) NUMBER OF HAULS PLANED NUMBER OF VALID HAULS REALIZED USING “STANDARD” GROUND GEAR NUMBER OF VALID HAULS REALIZED USING ROCK HOPPERS NUMBER OF ASSUMED ZERO- CATCH HAULS NUMBER OF REPLACE- MENT HAULS NUMBER OF INVALID HAULS % STATION S FISHED 26 TVS 2 3 3 - - - - 100 26 TVS 3 3 3 - - - - 100 NUMBER OF BIOLOGICAL SAMPLES (MATURITY AND AGE MATERIAL, *MATURITY ONLY): SPECIES LENGTH AGE Alosa fallax 2 Clupea harengus 1068 Cyclopterus lumpus 1 Enchelyopus cimbrius 1 Gadus morhua 1183 162 Myoxocephalus scorpius 130 Osmerus eperlanus 2 Platichthys flesus 768 335 Pleuronectes platessa 7 7 Psetta maxima 6 6 Sprattus sprattus 143 ICES | WGBIFS 2019 97 Nation: Denmark Vessel: Survey: BITS Dates: Gear details: Notes from survey (e.g. problems, additional work ICES Sub-Divisions and Depth stratum Gear Number of hauls planed Number of valid hauls realized using “Standard” ground gear Number of valid hauls realized using Rock-hoppers Number of assumed zero- catch hauls Number of replacement hauls Number of invalid hauls Coverage (%) (TVL,TVS) 25 TVL 2 TVL 1 1 3 TVL 20 22 0 0 0 0 110.0 4 TVL 20 20 0 0 0 0 100.0 5 TVL 14 8 0 0 0 0 57.1 6 TVL 0 3 0 0 0 0 #DIV/0! 54 53 0 0 0 0 98.1 Species Age Species Age Clupea harengus Gadus morhua Sprattus sprattus 11/3-26/3 - 2019 Dana Number of biological samples (maturity and age material, *maturity only): Cruise The big (#920) standard TV3 trawl is used. The construction of the trawl follows the specifications in the manual. No rock hopper was used Stomack sampling from cod, plankton fishing during night. 98 ICES | WGBIFS 2019 NATION: SWEDEN VESSEL: RV “DANA” Survey: BITS Q1 2019 Dates: 28 February - 10 Mars 2019 Cruise Gear details: The large (930#) standard TV3 trawl was used. No tows are done with the rock hopper ground gear on harder ground stations. The trawl construction is according to the specification in the BITS manual. Notes from survey (e.g. problems, additional work etc.): 50 stations were randomly allocated, whereof 32 were trawled. One invalid haul this time. Seven hauls in SD 26 and 27 had oxygen deficiency. Additional comments: The Swedish Armed Forces forbade nine stations. We could replace six stations this year. ICES SUB- DIVISIO NS GEAR (TVL, TVS) DEPTH STRATA (2–6) NUMBER OF HAULS PLANNED NUMBER OF VALID HAULS REALIZED USING “STANDARD” GROUND GEAR NUMBER OF VALID HAULS REALIZED USING ROCK HOPPERS NUMBER OF ASSUMED ZERO- CATCH HAULS NUMBER OF REPLACE- MENT HAULS NUMBER OF INVALID HAULS STATIONS FISHED % 25 TVL 2 3 3 - 0 0 0 100 25 TVL 3 17 16 - 0 6 1 100 25 TVL 4 3 3 - 0 0 0 100 26 TVL 3 2 1 - 0 0 0 50 26 TVL 4 2 3 - 0 1 0 150 26 TVL 5 3 3 0 0 0 100 26 TVL 6 4 0 - 4 0 0 100 27 TVL 3 2 0 - 0 0 0 0 27 TVL 4 7 5 - 2 2 0 100 27 TVL 5 1 0 - 1 0 0 100 28 TVL 3 2 2 - 0 0 0 100 28 TVL 4 1 0 - 0 0 0 0 28 TVL 5 4 4 - 0 0 0 100 Remark. Stations fished shows a low percentage mostly because of the Swedish armed forces prohibition. ICES | WGBIFS 2019 99 NUMBER OF BIOLOGICAL SAMPLES (MATURITY AND AGE MATERIAL, *MATURITY ONLY): Specname sci. Lenght Age Stomach Agonus cataphractus 1 Alosa fallax 1 Ammodytes tobianus 1 Aphia minuta 43 Clupea harengus 51 197 Cyclopterus lumpus 9 Enchelyopus cimbrius 8 Eutrigla gurnardus 1 Gadus morhua 7 854 704 691 Gasterosteus aculeatus 267 Hyperoplus lanceolatus 1 Limanda limanda 63 Lumpenus lampretaeformis 1 Merlangius merlangus 699 Myoxocephalus quadricornis 119 Myoxocephalus scorpius 179 Osmerus eperlanus 2 Platichthys flesus 5 970 Pleuronectes platessa 1 939 Pollachius virens 76 100 ICES | WGBIFS 2019 1 Institute of Food Safety, Animal Health and Environment (BIOR), Riga, Latvia National Marine Fisheries Research Institute (NMFRI), Gdynia, Poland THE CRUISE REPORT FROM THE JOINT LATVIAN-POLISH BITS 4Q SURVEY ON THE POLISH R.V. “BALTICA” IN THE CENTRAL-EASTERN BALTIC (11-21 December 2018) by Ivo Sics*, Radosław Zaporowski** and Lena Szymanek ** * Institute of Food Safety, Animal Health and Environment (BIOR), Riga, Latvia ** National Marine Fisheries Research Institute (NMFRI), Gdynia, Poland Gdynia - Riga, January 2019 ICES | WGBIFS 2019 101 2 Introduction The joint Latvian-Polish BITS survey, conducted in the period of 11-21.12.2018 on the r.v. “Baltica”, was based on the agreement between the Institute of Food Safety, Animal Health and Environment (BIOR) in Riga and the National Marine Fisheries Research Institute (NMFRI) in Gdynia. The joint Latvian-Polish BITS 4Q survey was conducted in the Latvian and Lithuanian EEZs (the ICES Sub-divisions 26 and 28). It was part of the Baltic International Trawl Survey (BITS) programme, which was coordinated by the ICES Baltic International Fish Survey Working Group (WGBIFS) (Anon. 2018). The main aims of reported cruise were: 1. Collecting materials to investigate the distribution, abundance and biological structure of cod stock. 2. Determine distribution and abundance of cod recruits. Estimates of year – class strength of cod. 3. Collecting materials to investigate the distribution abundance and biological structure of flounder stock. 4. Collect data on cod feeding. 5. Analysis of the hydro-meteorological conditions (seawater temperature, salinity, oxygen content, air temperature, atmospheric pressure, wind velocity and directions) in the ICES Sub-divisions 26N and 28. 6. Acoustical data recording during trawling and on the distance between consecutive catch- stations. 7. A collection of information about marine litter. MATERIALS AND METHODS Personnel The BITS Q4 - 2018 survey scientific staff was composed of nine persons, i.e.: Radosław Zaporowski, NMFRI, Poland - cruise leader, Bartłomiej Nurek, NMFRI, Poland - acoustician, Lena Szymanek, NMFRI, Poland - hydrologist, Władysław Gaweł, NMFRI, Poland - ichthyologist, Ivo Šics, BIOR, Latvia – scientific leader, Janis Aizups, BIOR, Latvia - ichthyologist, Guntars Strods, BIOR, Latvia - ichthyologist, Laura Briekmane, BIOR, Latvia – ichthyologist, Janis Gruduls, BIOR, Latvia – ichthyologist. Narrative The reported survey research tasks realisation took place during the period of 11-21 December 2018 and overall eleven full days was devoted to survey plan accomplishment. The 102 ICES | WGBIFS 2019 3 at sea investigations were conducted within the Latvian and Lithuanian EEZs (the ICES Sub- divisions 26 and 28) moreover, inside the Latvian territorial waters not shallower than 20 m (the ICES Sub-division 28). The vessel left the Gdynia port (Poland) on 11.12.2018 at 00.05 o’clock and was navigated towards the south-western corner of the Latvian EEZs (Fig. 1). The direct at sea inestigations began on 11.12.2018 and ended on 19.12.2018. Due to the very bad weather forecast, in 19.12.2018 the ship left the working area and began return journey to home port. On 21.12.2018 r.v. “Baltica” returned to homeport. Survey design and realization The original survey plan provided that 24 control-hauls will be realized in the Latvian EEZ (9 trawls in SD 26, 15 trawls in SD 28) and 1 control-hauls in the Lithuania EEZ (SD 26). Five additional trawls were planned in the SD 26 (5 trawls in the Lithuanian EEZ). The r.v. “Baltica” realized 31 bottom trawl control-hauls including the Latvian territorial waters (Fig.1). Trawl with track number 28084 was not in the correct depth zone as it was indicated in track database. This track with number 28084 was realized however with new track position in this area which was found within correct depth zone. Supplementary information on new track will be sent to track database administrator. Fifteen catch-stations were only initiated by hydrological parameters measurement and due to very low oxygen content (below 0.5 ml/l) near bottom, fishing was omitted. Five additional trawls were realized in the Lithuanian EEZ (SD 26). All trawl catches were performed in the daylight. The hard bottom ground-rope (rockhopper) trawl, type TV-3#930 (with 10-mm mesh bar length in the codend) was applied for fish catches. The standard trawling duration was 30 minutes. The mean speed of vessel while trawling was 3.0 knots. However, in the case of 5 hauls, their duration was shortened to 15-20 minutes, due to dense clupeids concentrations observed on the echosounder or bad fishing ground. The length measurements in the 1.0-cm classes were realised for all 945 cod and 1519 flounder. Length measurements in the 0.5-cm classes were realized for 1653 herring and 1580 sprat. In total, 457 cod and 409 flounder individuals were taken for biological analysis. Stomachs from the 350 cod were taken for investigation of cod feeding. Acoustic data, i.e. the echo-integration records (SA = NASCs; Nautical Area Scattering (Strength) Coefficient) were collected with the EK-60 scientific echosounder during fishing operations and on the routes between consecutive hauls. Echo-sounding data collected during the BITS survey were delivered to the Latvian researchers for further analysis. Directly before every haul, the seawater temperature, salinity and oxygen content were measured continuously from the sea surface to bottom. The seawater samples were taken also at the standard HELCOM stations. Totally, 36 hydrological stations were inspected with the automatic CTD probe SeaBird 911 combined with the rosette sampler (the bathometer rosette). Oxygen content was determined by the standard Winkler’s method. Meteorological observations of wind velocity and directions and the sea state were conducted at the actual geographic position of each control-haul. Results Fish catches and biological data The control-catches basic results collected in December 2018 during the Latvian-Polish BITS- 4Q survey are presented in Table 1. Overall, 14 fish species were recognised in hauls performed in the central-eastern Baltic. Herring dominated by mass in the ICES Sub-division 26 with the average share of 49.6%. Sprat was the next species most frequently represented in terms of ICES | WGBIFS 2019 103 4 mass, i.e. 42.9%. The share of cod and flounder in control-catches made up in the ICES SD 26 - 6.3 and 1.0%, respectively. By-catch of other fishes was insignificant. Herring dominated by mass in the ICES Sub-division 28 with the average share of 63.1%. Flounder was the next species most frequently represented in terms of mass, i.e. 21.6%. Sprat was the third species most frequently represented in terms of mass in the ICES SD 28 (12.1%). The share of cod in control-catches made up 2.3% in the ICES SD 28. By-catch of other fishes was insignificant. The mean CPUE for all species in ICES SD 26 amounted 160.6 kg/h, and in this 395.4, 355.1, 45.2 and 6.8 kg/h were for herring, sprat, cod and flounder, respectively. The mean CPUE for all species in SD 28 amounted to 65.6 kg/h, and in this 275.0, 64.7, 96.6 and 10.7 kg/h were for herring, sprat, flounder and cod, respectively. Total catch of fish and the number of realized hauls in the Latvian and Lithuanian EEZs, during reported BITS survey is presented in the text-table below: EEZ Number of hauls Total catch (kg) Cod Herring Sprat Flounder Others Latvian 25 56.1 1771.0 643.9 366.4 16.3 Lithuanian 6 138.6 497.4 612.3 17.7 0.2 The length distributions of cod, flounder, herring and sprat, according to the ICES Sub- divisions 26 and 28 are illustrated in Figures 2-5 and Tables 3-6. Cod The total length of cod in scrutinized samples from the ICES Sub-division 26 ranged from 14 to 47 cm and specimens from the length classes of 22 - 36 cm dominated in catches.. In total 732 cod was measured from hauls in ICES Sub-division 26. The total length of cod in scrutinized samples from the ICES Sub-division 28 ranged from 15 to 42 cm and specimens from the length classes of 19 - 32 cm dominated in catches (Fig. 2, Table 3). In total 213 cod was measured from hauls in ICES Sub-division 28. Flounder The total length of flounder in samples from the ICES Sub-division 26 ranged from 19 to 33 cm. . In total 144 flounder was measured from hauls in ICES Sub-division 26. The total length of flounder in scrutinized samples from the ICES Sub-division 28 ranged from 12 to 35 cm and specimens from the length classes of 12 - 35 cm dominated in catches (Fig. 3, Table 4). Herring The length range of herring collected in samples from the ICES Sub-divisions 26 was 12-25 cm, and specimens from the length classes of 15-22 cm were most the frequently represented (Fig. 4, Table 5). The length range of herring collected in samples from the ICES Sub-divisions 28 was 9-26 cm, and specimens from the length classes of 15-22 cm were the most frequently represented (Fig. 4, Table 5). 104 ICES | WGBIFS 2019 5 Sprat The length range of collected sprat was 7-14.5 cm. The length frequency apexes of 7.5-9.5 cm and 10-13.5 cm were characteristically for sprat samples from the ICES Sub-division 26 and the length frequency apexes of 7.0-9.0 cm and 10.0-12.5 cm were clearly visible for sprat samples from the ICES Sub-division 28 (Fig. 5, Table 6). Hydrological situation in December 2018 Graphic illustration of the main hydrological parameters is shown in the figures 7 and 8. Hydrological parameters were measured at each trawling (31) and hydrological stations (5) (Fig. 1). Measurements were conducted with the CTD SeaBird 911-probe combined with the rosette sampler. Oxygen content was determined by the standard Winkler’s method. The CTD data were aggregated to the 1-m depth strata. The oxygen samples were taken every 10 meters. The salinity parameter was presented in Practical Salinity Unit (PSU). Meteorological parameters were measured by MicroStep-MIS AMS 111 automatic weather station. The most frequent winds (Fig. 6) were observed from directions: ENE and NE. The average (10 min) wind speed varied from 1.0 m/s to 12.5 m/s (wind gusts up to 24.7 m/s). The air temperature ranged from -1.6 °C to 6.2 °C, and average temperature was 2.2°C. The seawater temperature in the surface layer varied from 5.31 to 7.15 °C. The lowest values were observed at the vicinity of the trawl no. 9, while the warmest surface water was at the hydrological station 46. The average value equalled 6.54°C. The average surface salinity was 7.29 PSU. The minimum value was 7.05 PSU (trawl no. 9) and maximum 7.41 PSU (trawl no. 27). The highest oxygen content in surface layer was 8.40 ml/l (trawl no. 6), while the lowest one 7.07 ml/l (trawl no. 15A). Mean value of dissolved oxygen equalled 7.96 ml/l. Near - bottom water layer conditions are presented in Fig. 7. Water temperature varied from 5.14 °C (trawl no. 26) to 9.39 °C (hydrological station 43). The mean value calculated for the whole area covered during the cruise was 6.43 °C. The average salinity in the close-to-the- bottom water layers was 9.98 PSU. The highest value was measured at the hydrological station 43 (13.88 PSU). The lowest one was 7.26 PSU (trawl no. 3). The dissolved oxygen varied from 0.00 ml/l (hydrological station 37) to 8.07 ml/l (trawl no. 10).The mean value was 2.56 ml/l. In comparison to March 2018, the thickness of the low oxygen layer (less than 2 m/l) significantly increased. Currently, the hypoxia zone begins at about 70 m, which could be spotted in the vertical diagram of parameters from deepest hydrological station (37) (Fig. 8) Oxygen content in this water layer very quickly reaches a value close to zero, indicating anoxia- like state. The consequence of this is the increase of the spatial extent of the anoxic zone. ICES | WGBIFS 2019 105 6 Figure 1. Locations of the fish bottom control catches and hydrological stations during the survey (December 2018). 7 Table 1. Catch results from the Latvian-Polish BITS 4Q survey; r.v. "Baltica", 11-21 December 2018 Haul number Date of catch EEZ ICES rectangle ICES SD Depth to the bottom [m] The ship's course during fishing [°] Geographical position of the catch station Time of Haul duration [ min.] Total catch all species CPUE [kg/0.5h] CATCH of particular fish species [kg] start end shutting net pulling up net latitude 00°00' N longitude 00°00' E latitude 00°00' N longitude 00°00'E Sprat Herring Cod Flounder Others 1 2018-12-12 LAT 43H0 28 95 000 57°20.4 20°35.6 57°20.4 20°35.6 07:35 07:40 5 0 0 0 0 0 0 0 2 2018-12-12 LAT 43H0 28 62 115 57°20.3 20°54.3 57°19.4 20°56.8 09:50 10:20 30 296.331 296.331 6.963 279.367 6.675 3.21 0.116 3 2018-12-12 LAT 43H1 28 63 210 57°22.1 21°14.6 57°22.6 21°14.0 12:35 12:50 15 142.003 284.006 58.017 52.134 3.6 27.64 0.612 4 2018-12-13 LAT 43H0 28 77 220 57°13.4 20°43.6 57°13.4 20°43.6 07:50 07:55 5 0 0 0 0 0 0 0 5 2018-12-13 LAT 43H0 28 84 220 57°12.3 20°40.4 57°12.3 20°40.4 08:20 08:25 5 0 0 0 0 0 0 0 6 2018-12-13 LAT 43H0 28 95 190 57°10.5 20°35.2 57°10.5 20°35.2 09:05 09:10 5 0 0 0 0 0 0 0 7 2018-12-13 LAT 43H0 28 86 308 57°01.9 20°22.2 57°01.9 20°22.2 10:45 10:50 5 0 0 0 0 0 0 0 8 2018-12-13 LAT 43H0 28 86 090 57°02.8 20°36.9 57°02.8 20°36.9 11:25 11:30 5 0 0 0 0 0 0 0 9 2018-12-14 LAT 43H1 28 31 200 57°03.3 21°01.7 57°01.9 21°00.6 08:20 08:50 30 166.498 166.498 37.262 85.324 3.23 39.7 0.982 10 2018-12-14 LAT 43H0 28 29 195 57°02.5 20°59.9 57°01.0 20°59.0 09:30 10:00 30 115.526 115.526 23.188 69.671 3.141 18.83 0.696 11 2018-12-14 LAT 42H0 28 40 225 56°39.0 20°44.9 56°37.9 20°43.1 13:30 14:00 30 494.405 494.405 30.263 438.567 6.95 18.54 0.085 12 2018-12-15 LAT 42H0 28 41 225 56°38.8 20°44.9 56°37.8 20°43.0 08:20 08:50 30 202.59 202.59 27.392 109.009 9.48 53.2 3.509 13 2018-12-15 LAT 42H0 28 40 045 56°36.9 20°41.6 56°38.0 20°43.2 09:30 10:00 30 66.043 66.043 2.983 7.12 2.205 51.78 1.955 14 2018-12-15 LAT 42H0 28 49 210 56°38.4 20°39.3 56°37.2 20°37.7 10:50 11:20 30 177.66 177.66 14.824 6.681 3.74 145.66 6.755 15 2018-12-15 LAT 42H0 28 91 210 56°36.0 20°20.3 56°36.0 20°20.3 12:55 13:00 5 0 0 0 0 0 0 0 15A 2018-12-15 LAT 42H0 28 116 000 56°36.2 20°15.7 56°36.2 20°15.7 13:40 13:45 5 0 0 0 0 0 0 0 16 2018-12-16 LAT 41H0 26 88 055 56°28.9 20°07.9 56°28.9 20°07.9 07:50 07:55 5 0 0 0 0 0 0 0 17 2018-12-16 LAT 41H0 26 83 215 56°26.0 20°05.0 56°26.0 20°05.0 08:40 08:45 5 0 0 0 0 0 0 0 18 2018-12-16 LAT 41H0 26 77 30 56°23.5 20°05.5 56°24.7 20°06.3 10:20 10:50 30 302.835 302.835 99.532 196.988 1.65 4.665 0 19 2018-12-16 LAT 41G9 26 110 275 56°22.8 19°42.4 56°22.8 19°42.4 13:00 13:05 5 0 0 0 0 0 0 0 20 2018-12-16 LAT 41G9 26 102 195 56°12.0 19°27.1 56°12.0 19°27.1 15:50 15:55 5 0 0 0 0 0 0 0 21 2018-12-17 LAT 41G9 26 83 025 56°21.1 19°51.2 56°22.4 19°52.6 08:30 09:00 30 145.798 145.798 70.43 69.57 4.425 1.37 0.003 22 2018-12-17 LAT 41G9 26 107 250 56°18.0 19°31.5 56°18.0 19°31.5 10:35 10:40 5 0 0 0 0 0 0 0 23 2018-12-17 LAT 41G9 26 58 180 56°07.8 19°50.4 56°10.0 19°50.4 12:40 13:00 20 397.563 596.3445 242.6 152.12 1.203 0.99 0.65 24 2018-12-17 LAT 41G9 26 55 260 56°04.1 19°46.2 56°04.1 19°44.5 14:10 14:30 20 346.444 519.666 30.492 304.458 9.77 0.835 0.889 25 2018-12-18 LIT 40H0 26 51 305 55°47.5 20°22.6 55°48.4 20°20.5 08:20 08:50 30 190.929 190.929 0.896 81.914 92.64 15.31 0.169 26 2018-12-18 LIT 40H0 26 62 170 55°46.0 20°13.6 55°45.1 20°13.3 10:00 10:20 20 373.214 559.821 197.039 154.611 21.42 0.144 0 27 2018-12-18 LIT 40H0 26 71 225 55°39.5 20°16.5 55°38.9 20°15.3 11:45 12:05 20 389.8 584.7 259.86 110.59 17.59 1.76 0 28 2018-12-18 LIT 40H0 26 75 185 55°38.6 20°09.4 55°37.2 20°09.4 13:25 13:55 30 312.23 312.23 154.478 150.322 6.99 0.44 0 29 2018-12-19 LIT 40G9 26 79 030 55°40.1 19°58.6 55°40.1 19°58.6 07:55 08:00 5 0 0 0 0 0 0 0 30 2018-12-19 LIT 40H0 26 71 035 55°44.1 20°03.6 55°44.1 20°03.6 08:45 08:50 5 0 0 0 0 0 0 0 ICES | WGBIFS 2019 107 8 Table 2. Number of fish biologically analysed during the BITS 4Q survey; r.v. "Baltica" (11-21 December 2018). Species Number of samples Number of fish measured analyzed stomach samples SD 26 SD 28 Total SD 26 SD 28 Total SD 26 SD 28 Total SD 26 SD 28 Total Cod 8 8 16 481 7 488 251 206 457 192 158 350 Flounder 8 8 16 29 1081 1110 115 294 409 Herring 8 8 16 825 828 1653 Sprat 8 8 16 766 814 1580 Turbot 0 1 1 0 1 1 Eelpout 0 4 4 0 22 22 Snake Blenny 1 0 1 1 0 1 Greater Sandeel 0 2 2 0 11 11 Smelt 1 5 6 1 18 19 Three-spined Stickleback 1 2 3 1 3 4 Lumpfish 1 3 4 1 4 5 Sea Scorpion 2 6 8 9 78 87 Plaice 1 0 1 1 0 1 Twaite Shad 1 0 1 1 0 1 Total 40 55 95 2116 2867 4983 366 500 866 192 158 350 SD 26; 14; 0,14SD 26; 15; 0SD 26; 17; 0SD 26; 18; 0 SD 26; 19; 0,41 SD 26; 20; 1,37 SD 26; 21; 2,19 SD 26; 22; 5,19 SD 26; 23; 7,38 SD 26; 24; 9,43 SD 26; 25; 6,97 SD 26; 26; 9,97 SD 26; 27; 8,2SD 26; 28; 7,92 SD 26; 29; 6,69 SD 26; 30; 5,19 SD 26; 31; 6,97 SD 26; 32; 3,28 SD 26; 33; 4,64 SD 26; 34; 3,55 SD 26; 35; 2,46 SD 26; 36; 3,14 SD 26; 37; 0,68 SD 26; 38; 1,23 SD 26; 39; 0,41 SD 26; 40; 1,09 SD 26; 41; 0,272S 26; 44; 0,145647SD 28; 14; 0 SD 28; 15; 0,94SD 28; 17; 0,94 SD 28; 18; 1,41 SD 28; 19; 3,76 SD 28; 20; 3,29 SD 28; 21; 7,51 8 6 SD 28; 23; 9,86 SD 28; 24; 6,57 SD 28; 25; 8,92 SD 28; 26; 11,27 SD 28; 27; 6,1 SD 28; 28; 7,04 SD 28; 29; 3,76 SD 28; 30; 2,35 SD 28; 31; 5,16SD 28; 32; 5,16 SD 28; 33; 0 SD 28; 34; 1,41 SD 28; 35; 1,88 SD 28; 36; 1,41 SD 28; 37; 2,82 SD 28; 38; 1,41 8; ; , 7012 SD 28; 44; 0567Total; 14; 0,11Total; 15; 0,21Total; 7; 0,21 Total; 18; 0,32 Total; 19; 1,16 Total; 20; 1,8 Total; 21; 3,39 Total; 22; 5,19 Total; 23; 7,94 Total; 24; 8,78 Total; 25; 7,41 Total; 26; 10,26 Total; 27; 7,72Total; 28; 7,72 Total; 29; 6,03 Total; 30; 4,55 Total; 31; 6,56 Total; 32; 3,7Total; 33; ,6 Total; 34; 3,07 Total; 35; 2,33 Total; 36; 2,75 Total; 37; 1,16Total; 38; 1,27 Total; 39; 0,42 Total; 40; 0,95 Total 32Total 1t l; ; , Fr e q u e n cy ( % ) Length class (cm) Fig. 2. Length frequency of cod from Sub-Divisions 26 and 28 in the control catches during the r/v "Baltica" BITS survey, 11-21 December 2018 SD 26 SD 28 Total 108 ICES | WGBIFS 2019 9 SD 26; 12; 0SD 26; 13; 0SD 26; 15; 0SD 26; 16; 0SD 2 ; 17; 0SD 26; 18; 0 SD 26; 19; 0,69 SD 26; 20; 2,78 SD 26; 21; 4,86 SD 26; 22; 9,03 SD 26; 23; 15,28 SD 26; 24; 22,22 SD 26; 25; 11,81 SD 26; 26; 15,97 SD 26; 27; 6,25 SD 26; 28; 3,47 SD 26; 29; 2,78 SD 26; 30; 0,69 SD 26; 31; 2,08 ; 2; , SD 26; 33; 1,39 SD 26; 34; 058 ,078 ,07SD 28; 15; 0,44 SD 28; 16; 1,24 SD 28; 17; 2,76 SD 28; 18; 8,22 SD 28; 19; 9,53 SD 28; 20; 11,49 SD 28; 21; 13,24 SD 28; 22; 12,07 SD 28; 23; 10,47 SD 28; 24; 8,36 SD 28; 25; 6,98 SD 28; 26; 5,53 SD 28; 27; 2,47SD 28; 28; 2,18SD 28; 29; 1,89 8; 0; ,53 SD 28; 31; 0,36 ; ; ,513 29S 28; 34; 0,155Total; 1 ; 0,07Total; 13; 0,07Total; 15; 0,39 Total; 16; 1,12 Total; 17; 2,5 Total; 18; 7,44 Total; 19; 8,69 Total; 20; 10,66 Total; 21; 12,44 Total; 22; 11,78 Total; 23; 10,93 Total; 24; 9,68 Total; 25; 7,44 Total; 26; 6,52 Total; 27; 2,83Total; 8; 2,3Total; 29; 1,97Total; 30; 1,45 Total 3t lTotal 3 Fr e q u e n cy ( % ) Length class (cm) Fig. 3. Length frequency of flounder from Sub-Divisions 26 and 28 in the control catches during the r/v "Baltica" BITS survey, 11-21 December 2018 SD 26 SD 28 Total SD 26; 9; 0SD 26; 10; 0SD 26; 12; 0,12SD 26; 3; 0,12 SD 26; 14; 0,97 SD 26; 15; 4 SD 26; 16; 14,06 SD 26; 17; 28,61 SD 26; 18; 22,06 SD 26; 19; 13,45 SD 26; 20; 8,61 SD 26; 21; 4,24 SD 26; 22; 1,94 SD 26; 23; 0,97 ; 4; ,73SD 26; 25; 0,12SD 26; 26; 08 ,128 ,SD 28; 12; 0,6 SD 28; 13; 1,93 SD 28; 14; 6,16 SD 28; 15; 17,87 SD 28; 16; 26,81 SD 28; 17; 23,67 SD 28; 18; 12,44 SD 28; 19; 6,04 SD 28; 20; 1,69SD 28; 21; 1,33SD 28; 22; 0,6 8; 3; ,3648 56Total; 9; 0,06Total; 10; 0,06Total; 12; 0,36 Total; 13; 1,03 Total; 14; 3,57 Total; 15; 10,95 Total; 16; 20,45 Total; 17; 26,13 Total; 18; 17,24 Total; 19; 9,74 Total; 20; 5,14 Total; 21; 2,78 Total; 22; 1,27Total 23 0 67t l 4 42Total 06 Fr e q u e n cy ( % ) Length class (cm) Fig. 4. Length frequency of herring from Sub-Divisions 26 and 28 in the control catches during the r/v "Baltica" BITS survey, 11-21 December 2018 SD 26 SD 28 Total SD 26; 7; 0SD 26; 7,5; 0,26 SD 26; 8; 6,4SD 26; 8,5; 5,87 SD 26; 9; 3,79 SD 26; 9,5; 2,09SD 26; 10; 2,48 SD 26; 10,5; 7,05 SD 26; 11; 11,88 SD 26; 11,5; 15,54 SD 26; 12; 23,63 SD 26; 12,5; 12,79 SD 26; 13; 6,27 SD 26; 13,5; 1,44 SD 26; 14; 0,52SD 26; 14,5; 0 SD 28; 7; 1,11 SD 28; 7,5; 15,85 SD 28; 8; 28,13 SD 28; 8,5; 14,13 SD 28; 9; 4,91 S 8; , ; 1,84 SD 28; 10; 3,44 SD 28; 10,5; 8,6SD 28; 11; 8,23 SD 28; 11,5; 7,13 SD 28; 12; 4,05 SD 28; 12,5; 1,72 8 3 49SD 28; 13,5; 0,25SD 28; 14 4, ,12Total; 7; 0,57 Total; 7,5; 8,29 Total; 8; 17,59 Total; 8,5; 10,13 Total; 9; 4,37 Total; 9,5; 1,96 Total; 10; 2,97 Total; 10,5; 7,85 Total; 11; 10 Total; 11,5; 11,2 Total; 12; 13,54 Total; 12,5; 7,09 Total; 13; 3,29 Total; 13,5; 0,82Total; 14Total; ; 06 Fr e q u e n cy ( % ) Length class (cm) Fig. 5. Length frequency of sprat from Sub-Divisions 26 and 28 in the control catches during the r/v "Baltica" BITS survey, 11-21 December 2018 SD 26 SD 28 Total ICES | WGBIFS 2019 109 10 Table 3. Cod length measurements by consecutive hauls in the r.v. “Baltica” Latvian - Polish BITS 4Q survey (11-21 December 2018); specimens grouped by 1 cm length classes. Table 4. Flounder length measurements by consecutive hauls in the r.v. “Baltica” Latvian - Polish BITS 4Q survey (11 - 21 March 2018); specimens grouped by 1 cm length classes. Haul no SD 14 15 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 44 45 46 47 Sum 2 28 1 3 3 5 3 3 3 1 3 2 1 3 1 1 1 1 1 36 3 28 1 2 1 2 1 3 1 3 2 5 3 1 2 2 29 9 28 2 2 1 2 1 2 1 2 1 1 15 10 28 1 1 4 2 2 2 1 13 11 28 2 3 1 3 2 3 7 1 3 1 1 1 1 1 2 1 1 34 12 28 2 2 1 5 4 4 4 6 2 1 1 2 3 1 2 1 1 1 1 1 45 13 28 1 1 4 1 1 1 1 1 1 12 14 28 1 1 2 3 5 2 1 1 6 4 1 1 1 29 18 26 1 1 2 2 6 21 26 1 1 5 7 3 2 2 2 2 4 1 1 31 23 26 1 2 1 1 1 6 24 26 2 1 5 6 8 4 8 12 4 4 1 3 1 1 1 1 62 25 26 1 1 5 7 18 21 31 27 36 30 32 32 25 38 15 24 17 10 17 4 6 2 4 1 2 1 1 408 26 26 3 2 4 10 17 6 12 14 10 9 7 6 2 4 3 2 2 1 2 116 27 26 1 2 5 6 5 5 8 7 1 2 4 4 4 4 2 2 2 1 1 1 2 69 28 26 1 3 6 3 4 1 3 3 3 1 2 1 1 1 1 34 SD 26 1 3 10 16 38 54 69 51 73 60 58 49 38 51 24 34 26 18 23 5 9 3 8 2 2 1 1 2 3 732 SD 28 2 2 3 8 7 16 11 21 14 19 24 13 15 8 5 11 11 3 4 3 6 3 1 1 1 1 213 Total 1 2 2 3 11 17 32 49 75 83 70 97 73 73 57 43 62 35 34 29 22 26 11 12 4 9 3 3 1 1 2 3 945 cm_group 110 ICES | WGBIFS 2019 11 Table 5. Herring length measurements by consecutive hauls in the r.v. “Baltica” Latvian-Polish BITS 4Q survey (11- 21 December 2018); specimens grouped by 0.5 cm length classes. Table 6. Sprat length measurements by consecutive hauls in the r.v. “Baltica” Latvian-Polish BITS 4Q survey (11- 21 December 2018); specimens grouped by 0.5 cm length classes. Haul no SD 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 Sum 2 28 2 6 10 10 3 5 17 16 15 7 3 2 96 3 28 7 18 13 11 5 4 11 20 12 5 1 107 9 28 1 22 41 16 3 1 1 4 6 4 3 1 103 10 28 1 18 29 15 3 1 2 4 4 15 6 3 1 102 11 28 10 39 22 4 2 5 7 3 3 2 2 1 100 12 28 1 4 29 26 4 2 6 12 7 7 3 2 1 104 13 28 6 19 25 6 2 5 15 11 2 7 2 1 101 14 28 47 42 7 3 1 1 101 18 26 4 4 4 5 7 9 16 14 25 9 3 1 101 21 26 3 3 2 1 12 13 16 31 14 6 1 102 23 26 12 10 8 2 2 10 17 21 17 6 3 1 109 24 26 1 3 2 1 4 6 14 19 27 16 6 1 2 102 25 26 1 10 2 1 2 2 6 3 2 6 35 26 26 8 5 3 2 2 5 8 17 29 18 11 1 1 110 27 26 1 11 12 4 3 2 7 18 15 16 9 5 1 104 28 26 3 6 4 1 1 3 5 15 30 23 12 103 SD 26 2 49 45 29 16 19 54 91 119 181 98 48 11 4 766 SD 28 9 129 229 115 40 15 28 70 67 58 33 14 4 2 1 814 Total 9 131 278 160 69 31 47 124 158 177 214 112 52 13 4 1 1580 cm_group Haul no SD 9.5 10 12 12.5 13 13.5 14 14.5 15 15.5 16 16.5 17 17.5 18 18.5 19 19.5 20 20.5 21 21.5 22 22.5 23 23.5 24 24.5 25 26 Sum 2 28 1 1 1 3 4 13 13 14 13 15 6 7 8 1 1 1 2 104 3 28 1 3 4 5 12 17 8 20 11 8 1 6 2 1 1 1 1 102 9 28 3 1 5 4 12 15 10 12 7 7 7 5 3 1 2 2 2 1 1 1 1 1 103 10 28 1 5 4 6 8 6 13 15 18 12 7 3 3 1 2 1 105 11 28 1 1 5 6 12 14 10 19 17 8 3 3 1 1 1 1 1 104 12 28 1 1 2 2 5 10 15 19 16 7 13 2 5 2 2 1 1 1 105 13 28 1 2 5 2 6 6 12 13 11 18 11 1 4 7 1 1 1 1 103 14 28 2 3 13 17 13 17 18 5 5 6 2 1 102 18 26 2 2 5 4 16 16 13 13 7 9 8 7 2 1 1 106 21 26 1 2 2 9 18 17 16 8 10 4 5 3 4 2 1 102 23 26 1 1 1 7 16 21 10 15 6 10 3 5 2 4 2 1 105 24 26 2 3 2 10 13 12 14 12 9 3 9 2 4 1 5 1 102 25 26 1 3 10 4 11 19 12 6 9 6 2 3 3 4 1 3 1 1 1 1 101 26 26 1 2 6 8 15 13 19 5 6 6 6 9 1 1 2 1 1 102 27 26 2 8 5 19 13 14 11 9 8 3 3 2 3 2 1 103 28 26 1 3 4 4 12 13 17 10 12 6 8 3 2 3 1 2 1 2 104 SD 26 1 1 4 4 7 26 37 79 133 103 114 68 71 40 46 25 23 12 10 6 6 2 5 1 1 825 SD 28 1 1 3 2 7 9 24 27 56 92 107 115 107 89 70 33 32 18 8 6 6 5 3 2 1 2 1 1 828 Total 1 1 3 3 8 9 28 31 63 118 144 194 240 192 184 101 103 58 54 31 29 17 13 8 7 4 6 1 1 1 1653 cm_group ICES | WGBIFS 2019 111 12 Figure 6. Changes of the main meteorological parameters (December 2018). 112 ICES | WGBIFS 2019 13 Figure 7. Distribution of the seawater temperature, salinity and oxygen content in the near bottom waters (December 2018). ICES | WGBIFS 2019 113 14 Figure 8.Vertical distribution of the seawater temperature, salinity and oxygen content at the hydrological profile 37 (December 2018). 0 25 50 75 100 125 150 175 200 225 250 0 2 4 6 8 10 12 14 Temperature [°C] Salinity [PSU] Oxygen content [ml/l] 114 ICES | WGBIFS 2019 CRUISE REPORT FROM THE POLISH R/V BALTICA BITS 4Q 2018 SURVEY IN THE SOUTHERN BALTIC (14 November - 01 December 2018) by Krzysztof Radtke and Tycjan Wodzinowski Gdynia, 15 January 2019 ICES | WGBIFS 2019 115 INTRODUCTION Since 1995, the permanent participation of Polish R/V Baltica operated by the National Marine Fisheries Research Institute (NMFRI) in Gdynia, has taken place in autumn and winter Baltic International Trawl Surveys (BITS-4Q and BITS-1Q) realised in the southern Baltic. In March 2000 when the research standard fishing gear in the Baltic Sea - the cod bottom trawl type TV-3, has been applied by the vessels assigned to the BITS surveys realization, the principal methods of investigations within BITS-4Q ground-trawl surveys designated to particular national labora- tories, including the NMFRI were designed and co-ordinated by the Baltic International Fish Survey Working Group (WGBIFS; Anon. 2018). The main aim of the BITS-4Q survey planned in autumn 2018 was to monitor abundance and spatial distribution of the main demersal fish spe- cies and to some extent also clupeids in the bottom zone of the Baltic, taking into account hydro- logical parameters. The R/V Baltica BITS-4Q 2018 survey, which was realized in the Polish part of the ICES Sub-divisions 24, 25, 26 and Swedish part of the ICES Sub-division 25, was aimed at:  determination of the spatial distribution of cod, flounder, herring and sprat in the near bottom zone of the southern and central Baltic during autumn 2018 applying method of random selection of control-hauls,  estimation of the fishing efficiency, i.e. catch per unit effort (CPUE), the share of particu- lar species in total mass of bottom control-catches,  collecting biological samples of dominated fish for the determination of the age-length- mass relationship, sex, sexual maturation, feeding conditions and externally visible dis- eases,  analysis of the vertical and horizontal changes of the basic hydrological parameters (tem- perature, salinity, oxygen content) in the areas of fish catches and in neighbouring stand- ard hydrological stations. MATERIAL AND METHODS The above purposes of the November 2018 BITS 4Q survey aboard of R/V Baltica were realized by the NMFRI nine members of scientific team, with Krzysztof Radtke as a cruise leader. The scientific team was also composed of seven ichthyologists including technicians, responsible for determination of fish species composition of catches, fish biological analyses and data pro- cessing and one hydrologist, responsible for seawater sampling and analysing as well as for me- teorogical monitoring. Narrative The reported Polish ground-trawl survey on board of R/V Baltica, marked with the number 22/2018/MIR took place during the period of 14.11-01.12.2018 within the framework of the IC- ES Baltic International Trawl Surveys (BITS) long-term programme (Anon. 2018) and the Polish Fisheries Data Collection Programme for 2018. The vessel left the port of Gdynia on 14.11.2018 in the morning and at sea investigations began in the eastern part of the Gulf of Gdańsk (Fig. 1, Tab. 1). During the period of 21-24.11. 2018, the investigations were conducted in Swedish wa- ters. The survey ended on 01.12.2018 (morning) in Gdynia harbour. The R/V Baltica operated mostly in the Polish EEZ. Overall, eighteen days were utilized for fulfilling the BITS_4Q survey purposes including time spent for the vessel translocation from the Gdynia port to research area and in the final phase of the survey, a return way to the vessel home-port. The vessel technical fault resulting from failure of the engine cooling system was the reason of two days earlier sur- vey termination than the planned schedule. 116 ICES | WGBIFS 2019 Survey design and realization – sampling description According to the WGBIFS plan, the Polish vessel was recommended to cover in Novem- ber/December 2018 survey, the Polish part of ICES Sub-divisions 24, 25 and 26 with 3, 21 and 18, respectively randomly selected bottom control-hauls. and also in Swedish EEZ to cover Swedish part of ICES Sub-division 25 with 12 control-hauls. The R/V Baltica realized 54 of the 60 planned hauls for this survey. Due to the ships technical problems with engine, six hauls planned in Gdańsk Bay was not realized. It can be concluded that the hauls realized could be accepted as fully representative from the technical point of view (Fig. 1, Table 1) taking into account gear performance during hauls. Trawling was done with the standard rigging ground trawl type TV-3#930 (without bobbins and additional chains connected to the footrope), with 10-mm mesh bar length in the codend. A standard vertical fish-sounder monitored the trawling depth. Usually a 5-7 m vertical net opening was achieved, which was monitored by the net echosounder. The catch stations were located on the depth range from 23 to 102 m. Fish control-hauls were conducted at the daylight only, lasting maximum 30 minutes, at 3.0 knots vessel speed. Each control-catch was sorted out for the determination of the species composition. Mean CPUE of each fish species and their average share in mass of catches were calculated. From each catch station, representative samples of dominated fishes were collected to determine age-length-mass relationships, sex, sexual maturation, feeding conditions, externally visible diseases and addi- tionally stomach samples for food composition estimation of cod were collected for further ex- aminations in the Institute. In the case of cod, flounder, turbot and plaice all the caught specimens were taken for total length and mass measurements. In the case of clupeids, the representative sub-samples of these fish were investigated. Overall, 4339 cod, 3413 flounder, 565 plaice, 22 turbot, 6551 sprat and 8066 herring were taken for the length and mass determination. In total, 435, 776, 455, 22, 584 and 1105, individuals of the above-mentioned species were aged. Biological analyses of fishes were performed directly on board of surveying vessel, according to standard methodological procedures. The length of 35 cm, 23 cm (ICES SD 25) and 21 cm (ICES SD 26), 16 cm and 10 cm was taken into account as a separation (protective) length between juvenile and commercial size of cod, flounder (differed by the ICES Sub-divisions), herring and sprat, respectively. Externally visible diseases of fish’s skin and their vertebral column anomalies were monitored for 4339 cod, 3413 flounder, 565 plaice, 6551 sprat and 8066 herring. Data on patho- logical symptoms were registered based on the visual inspection of fish taken to the length measurements. Every control-haul was preceded by the measurements of basic hydrological parameters continuously from the sea surface to the bottom. Overall, 80 hydrological stations (including hydrographic standard stations) were inspected with the automatic CTD probe SeaBird 911 combined with the rosette sampler (the bathometer rosette). Oxygen content was determined using the standard Winkler’s method. The seawater temperature and salinity row data was ag- gregated to the 1-m depth stratum while oxygen content was aggregated to the 10-m intervals. Temperature, salinity and oxygen content was the source of information on abiotic factors poten- tially influencing fish spatial distribution. Distribution of all hydrological stations inspected by the R/V Baltica in November 2018 is presented in Figure 1. RESULTS Fish catches and biological data Twenty two species were recognized in 54 scrutinized bottom catches (Table 1). Only two fish species – red mullet and European anchovy represent fish species permanently inhabit- ing Atlantic Ocean. Cod, herring, flounder and sprat were the most frequently occurring fish species in the catches - 96%, 91%, 81% and 79% of hauls, respectively (Table 1). Cod, flounder, herring, and ICES | WGBIFS 2019 117 sprat dominated also with respect to mass of catch (kg) and efficiency (CPUE). By-catch of other fish species was insignificant. Cod catches were generally low. The highest average cod CPUE has been recorded in ICES SD 24 – 57 kg/1h (Fig. 2). Lower result of CPUE was observed in ICES SD 25 (48 kg/1h) and in ICES SD 26 – 30 kg/1h. In the same cruise from November 2017 r., CPUEs of cod in ICES SDs 24, 25 and 26 were markedly higher and amounted to 121, 143 and 244 kg/1h of cod, respectively. Sprat, out of all fish species found in catches, predominated in terms of CPUE in ICES SDs 24, 25 and 26, respectively - 92, 189 and 114 kg/1h. In the last year's survey, the sprat CPUEs were significantly lower - 0.7, 107 and 11.7 kg/1h respectively. The highest CPUE of herring was obtained in ICES SD 25 – 185 kg/1h. However, in IC- ES SDs 24 and 26 CPUEs of herring were markedly higher and amounted to 72 and 78 kg/1h, respectively. In comparison with the November 2017 cruise, the current year CPUEs were higher (by 50 kg/1h on average) in ICES SD 25 but in ICES SDs 24 and 26 lower CPUEs were noted – by 20 and 34 kg/1h, respectively. CPUEs in ICES SDs 24 and 25 were characterized by the lowest values among the four fish species reported. The CPUEs in above mentioned SDs amounted to 51 and 15 kg/1h. The CPUE of flounder in ICES SD 26 amounted to 101 kg/1h and it was the second largest CPUE in this SD (higher for sprat, but lower for herring and cod). In comparison with the November 2017 cruise, the average CPUEs obtained this year were higher in ICES SDs 26 and 24 by 4 and 39 kg/1h, respectively, while in ICES SD 25 the CPUE this year was lower by 7 kg/1h. Length distributions of main fish species according to the ICES Sub-divisions are illus- trated in Figure 3. Similarly as in the cruise in November 2017, in the cruise of the current year, there was a slight variation in the length of cod in ICES SDs 25 and 26. In the ICES SD 25 there was a clearly marked single peak of cod frequency, which amounted 9.2%, and corresponded to length class 27 cm. Two cod length fractions in cod length distribution curve from ICES SD 24 were distinguished. Those with smaller sizes were concentrated around 17-19 cm length classes and larger cods, clustered around 31-37 cm length classes. Cod length distribution in ICES SD 24 indicated a smaller share of cod in the range of 20-29 cm length classes than in ICES SDs 25 and 26, and for the 31-39 cm length classes, the share of cod in the ICES SD 24 was larger. The curves of the length distributions of herring in ICES SDs 25 and 26 indicate the occurrence of two fish length fractions of this species in these SDs. Herring of smaller sizes in ICES SDs 25 and 26 contained fish with a range of length classes of 9.5-15 cm and 8.5-14 cm, respectively. Fish above the upper limit of the selected length ranges formed a larger size fish fraction. For herring from the ICES SD 24, three length fractions have been found. The smallest herring, in the range of length classes - 11.5-15 cm, herring with medium length - 16-20.5 cm and herring of the largest length - 21-28 cm. The length distribution of herring indicates that the fish of this species inhabiting in ICES SD 24 consisted of the most favourable length distribution, because the share of fish from the largest length classes - 21-28 cm was the highest. In the length distributions of sprat obtained in the three ICES SDs investigated, there were found two peaks in each of length distributions observed. The first peak in length distribu- tion curve (from the beginning of the horizontal axis on the chart) in ICES SDs 24, 25 and 26, corresponded to length classes - 9.5 cm (17.3%), 9.5 cm (14.0%) and 8.5 cm (7.2%), respective- ly. The second peak in the length distribution curve corresponded - in the above mentioned Sub- divisions - to the following length classes - 13.5 cm (16.5%), 12.5 cm (16.9%) and 12.0 cm (19.4%). Sprat of the most favourable length distribution for commercially fishery was observed in ICES SD 24. The smallest flounder were found in ICES SD 26 (modal length – 19-20 cm). In ICES SD 24 higher share of larger flounder was observed than in ICES SD 26. However, the highest share of larger flounder was noted in ICES SD 25. Length distribution of flounder in ICES SD 24 was 118 ICES | WGBIFS 2019 characterized by well distinguished peak of frequency (18%), which corresponded to length class 25 cm. Figure 4 shows the numerical shares of the undersized fish fractions of cod, herring, sprat and flounder. In cod catches from ICES SDs 25 and 26 the undersized fraction of cod prevailed markedly. Their numerical share in the above-mentioned ICES SDs was 86.4% and 72.8%, re- spectively. In ICES SD 24 the share of undersized fish amounted to 63.7%. In the same cruise in November 2017, the share of undersized cod was lower and amounted to 81.6%, 69% and 37%, respectively. The total share of undersized cod from the last survey was very high and amounted to 82.1%. Numerical share of undersized herring decreased westward. The share of the under- sized fraction in ICES SDs 26, 25 and 24 amounted to 37.2%, 11.0% and 9.8%, respectively. The largest share of undersized sprat was observed in samples form ICES SD 25 (27.3%). Un- dersized sprat share in ICES SD 26 amounted to 21.7%, while in ICES SD 24 to 19.2%. The share of undersized flounder was low in ICES SDs 24 and 25 – 8.5% and 6.6%, respectively. In ICES SD 26 the undersized fraction of flounder was markedly higher and amounted to 54.1%. Mean length (l.t.) and mean mass of sprat, herring, cod and flounder calculated for the whole survey and separately for ICES SDs 24, 25 and 26 are presented in the text table below (in parenthesis are shown parameters from November 2017 cruise): ICES Sub- division para- meter sprat herring cod flounder 24 mean length [cm] 12.1 (9.4) 20.2 (19.4) 31.6 (31.4) 26.3 (24.6) 25 11.5 (10.6) 18.7 (18.2) 29.3 (31.0) 28.0 (27.3) 26 11.4 (11.4) 17.0 (16.2) 31.0 (30.5) 21.0 (21.5) whole survey 11.5 (10.7) 18.3 (17.7) 29.8 (30.9) 23.4 (24.6) 24 mean mass [g] 12.1 (5.3) 55.6 (45.5) 318.0 (316.7) 203.8 (157.9) 25 10.1 (8.1) 40.0 (39.7) 232.8 (298.3) 257.2 (222.2) 26 9.3 (9.9) 31.7 (30.6) 277.0 (302.4) 109.9 (119.8) whole survey 9.9 (8.4) 38.7 (37.7) 247.3 (300.2) 158.0 (173.3) The measurement of the length of the main fish species was accompanied by a macro- scopic analysis of the presence of symptoms of visible diseases of fish’s skin, i.e. anatomopatho- logical changes (Fig. 5). The highest prevalence of fish with externally visible pathological changes was recorded for cod (3.3%) and flounder (21%). With regard to cod, there was a slight increase in the share of cod with diseases compared to the results obtained in the cruise in 2017 (2.8%). The share of herring and sprat with observed pathological symptoms was insignificant and amounted to 0.33% and 0.031% respectively. Hydrological situation in the southern Baltic In the near-bottom water layer (Fig. 6) temperatures in the range from 12.08°C to 5.13°C were noted. The lowest temperature was noted in the control haul no 19, while the highest in hydrological station no 15. The highest salinity was recorded in hydrological station no 16 (Bornholm Deep) (17.87 on the PSU scale). In hydrological station IBY5, monitored permanently during BITS surveys in Bornholm Basin, the salininy at the bottom was 17.86 on the PSU scale. Salinity measured in Gdańsk Deep amounted to 13.78 in hydrological station (G2). The lowest oxygen content in the water was noted on the hydrological station IBY5 (1.48 ml/l), while in the neighbouring hydrological station no 16 oxygen was 0.91 ml/l. In Gdańsk Deep the oxygen content noted in hydrological station G2 was 1.72 ml/l. Surface water temperature fluctuated from 11.11°C to 6.74°C (Fig. 7). The lowest temperature was recorded in control haul no 53, and the highest in hydrological station no 76. Mean value of the surface water temperature was 9.32°C. The average salinity of surface water was 7.48 on the PSU scale. The lowest value - 7.04, was recorded in the control haul no 15. The ICES | WGBIFS 2019 119 highest salinity was recorded in the haul no 39 (7.85 on the PSU scale). Mean oxygen content was 7.52 ml/l. The highest level of oxygen was registered in control haul no. 45 (7.86 ml/l). The lowest oxygen level was recorded in the control haul no. 12 (7.21 ml/l). CONCLUSIONS The data collected during Polish BITS-4Q 2018 survey is considered as representative, taking into account the degree of the survey plan realization, and therefore can be used by the ICES Baltic International Fish Survey Working Group (WGBIFS) and the Baltic Fisheries Assessment Working Group (WGBFAS) for evaluation of fish species abundance and their distribution. The survey data collected during the survey is stored in the international DATRAS database publicly available and managed by the ICES Secretariat. References: ICES. 2018. Report of the Baltic International Fish Survey Working Group (WGBIFS). ICES WGBIFS report 2018. 24-28 March 2018. Lyngby, Copenhagen, Denmark.380 pp. 120 ICES | WGBIFS 2019 Fig. 1. Location of fish control-hauls (black crosses) and hydrological standard stations (red dots) realised during the r/v Baltica BITS-4Q survey (14.11-01.12. 2018). (green solid line indi- cates hydrological research profile). ICES | WGBIFS 2019 121 Fig. 2. Mean share in mass of control hauls (A), and mean CPUE (B) of dominant fish species, and share of cod (C) in particular catches conducted during r/v Baltica BITS-4Q survey (14.11- 01.12. 2018). 122 ICES | WGBIFS 2019 Fig. 3. Length distributions of cod, herring, sprat and flounder in samples from fish control hauls conducted during r/v Baltica BITS-4Q survey (14.11-01.12. 2018). ICES | WGBIFS 2019 123 Fig. 4. Mean numerical share (in %) of undersized fish species in samples from fish control hauls conducted during r/v Baltica BITS-4Q survey (14.11-01.12. 2018). Fig. 5. Mean prevalence (in %-indiv.) of fish with externally visible diseases in samples from fish control hauls conducted during r/v Baltica BITS-4Q survey (14.11-01.12. 2018). 124 ICES | WGBIFS 2019 Tab. 1. Number of fish species individuals measured and aged during r/v Baltica BITS-4Q sur- vey (14.11-01.12. 2018). 26 ICES 25 ICES 24 ICES total 26 ICES 25 ICES 24 ICES total Sub-division Sub-division Sub-division Sub-division Sub-division Sub-division Round goby 0 0 1 1 0 0 0 0 Sand goby 0 0 1 1 0 0 0 0 Red mullet 0 1 0 1 0 0 0 0 Ninespine stickleback 0 1 0 1 0 0 0 0 Three-spined stickleback 0 4 0 4 0 0 0 0 Greater sandeel 0 144 4 148 2 0 0 2 Cod 267 3160 912 4339 151 154 130 435 Plaice 129 234 202 565 137 209 109 455 Short-horn scorpion 1 146 26 173 5 0 0 5 Hooknose 0 2 1 3 0 0 0 0 River lamprey 0 0 4 4 0 0 0 0 Fourbeard rockling 2 185 101 288 0 17 0 17 Twaite shad 0 1 16 17 0 0 0 0 Anchovy 0 4 0 4 0 0 0 0 Turbot 3 16 3 22 3 16 3 22 Flounder 317 912 2184 3413 355 266 155 776 Smelt 0 1 450 451 4 0 0 4 Sprat 416 3365 2770 6551 200 284 100 584 Baltic herring 549 5232 2285 8066 351 611 143 1105 Lumpfish 1 3 0 4 0 0 0 0 Eelpout 0 2 8 10 0 0 0 0 Whiting 34 1 1 36 0 0 0 0 TOTAL 1719 13414 8969 24102 1208 1557 640 3405 Species name Number of fish mesured (l.t) Numer of fish aged and weighed (g) ICES | WGBIFS 2019 125 Tab. 2. Fish control-hauls data obtained during r/v Baltica BITS-4Q survey (14.11-01.12. 2018). Haul Haul ICES ICES Trawling Trawling number number Catch rectangle Sub-division depth duration Total according to according to date [m] szerokość długość szerokość długość shooting hauling up [min] catch Cod Herring Sprat Flounder Plaice Turbot Hooknose Eelpout Fourbeard Three-spined Lumpfish Short-horn Round Sand Smelt Twaite Whiting Greater Ninespine Anchovy Red River survey order ICES (N) (E) (N) (E) net net [kg] rockling stickleback scorpion goby goby shad sandeel stickleback mullet lamprey database 1 26169 2018-11-14 38G8 26 33 54°46.4' 18°41.5' 54°47.5' 18°40.4' 12:55 13:25 30 88.938 12.8 61.086 3.726 10.53 0.188 0.109 0.167 0.275 0.057 2 26019 2018-11-14 38G8 26 48 54°53.5' 18°37.7' 54°54.8' 18°36.9' 14:50 15:20 30 62.356 5.221 31.289 1.131 23.32 0.705 0.622 0.068 3 26099 2018-11-15 39G8 26 86 55°27.9' 18°19.5' 55°27' 18°21.8' 07:32 08:02 30 85.66 76.54 5.918 2.132 0.129 0.941 4 26212 2018-11-15 40G8 26 92 55°34.6' 18°23.8' 55°35.9' 18°22.8' 09:45 10:15 30 11.017 8.94 0.977 1.1 5 26290 2018-11-15 40G8 26 87 55°36.1' 18°58.6' 55°34.7' 18°59.2' 14:30 15:00 30 6.641 1.02 5.314 0.307 6 26107 2018-11-16 40G8 26 87 55°30.5' 18°59.6' 55°29.8' 18°59.6' 07:30 07:45 15 9.745 2.495 7.25 7 26045 2018-11-16 39G9 26 82 55°16.4' 19°5.1' 55°14.9' 19°5.6' 10:16 10:46 30 187.634 7.915 117.4 61.94 0.379 8 26091 2018-11-16 39G9 26 93 55°7.2' 19°4.3' 55°7.2' 19°1.9' 12:30 13;00 30 9.577 1.735 1.291 6.42 0.131 9 26257 2018-11-16 38G9 26 102 54°57.2' 19°2.5' 54°55.8' 19°2.7' 14:41 15:11 30 6.121 2.88 1.229 1.901 0.111 10 26261 2018-11-17 37G9 26 53 54°25.7' 19°18.2' 54°25.5' 19°15.7' 07:35 08:05 30 292.907 19.4 86.029 54.429 126.16 1.614 1.885 0.34 0.002 2.946 0.102 11 26163 2018-11-17 37G9 26 43 54°24.9' 19°18.3' 54°24.9' 19°16.6' 09:35 09:55 20 418.573 39.28 47.58 137.114 181.27 4.963 0.033 0.072 0.269 0.372 6.804 0.688 0.128 12 26216 2018-11-17 37G9 26 37 54°24.2' 19°16.2' 54°24.4' 19°18.5' 11:41 12:11 30 849.538 20.18 83.684 561.691 177.07 2.221 0.235 0.281 2.317 1.669 0.19 13 26191 2018-11-17 38G9 26 88 54°38.1' 19°18.4' 54°39.4' 19°18' 14:15 15:15 30 11.066 6.52 2.309 1.833 0.373 0.03 0.001 14 26289 2018-11-18 37G9 26 55 54°26.5' 19°5.9' 54°26.2' 19°8.2' 07:32 08:02 30 205.878 11.69 48.994 32.841 93.6 2.158 3.095 13.5 15 26014 2018-11-18 37G9 26 52 54°26.3' 19°3.1' 54°26.2' 19°4.7' 09:17 09:37 20 167.738 6.82 45.585 7.822 97.63 0.762 0.068 3.779 5.133 0.139 16 26220 2018-11-18 37G9 26 44 54°25.3' 19°4.8' 54°25.3' 19°2.3' 10:45 11:15 30 268.714 8.354 113.649 67.432 31.02 0.579 0.131 0.701 46.47 0.26 0.118 17 25339 2018-11-20 39G7 25 87 55°15.8' 17°23.4' 55°15.9' 17°20.9' 08:00 08:30 30 74.823 53.93 6.701 1.004 6.071 3.691 3.426 18 25463 2018-11-20 39G7 25 91 55°14.1' 17°18.1' 55°14.2' 17°15.7' 10:00 10:30 30 55.187 33.9 5.132 0.104 2.855 3.886 9.15 0.16 19 25084 2018-11-20 39G7 25 60 55°23.7' 17°23.5' 55°23.2' 17°21.1' 12:50 13:20 30 101.635 53.21 41.634 5.241 0.702 0.155 0.693 20 25455 2018-11-20 39G7 25 44 55°27.3' 17°15.8' 55°26.7' 17°13.3' 14:27 14:57 30 172.744 11.535 129.965 20.529 8.514 0.285 0.529 1.387 21 25250 2018-11-21 39G7 25 68 55°24.2' 17°34.2' 55°24.1' 17°31.8' 07:50 08:20 30 399.75 92.08 296.235 0.282 8.491 0.868 1.6 0.194 22 25030 2018-11-21 39G7 25 42 55°29.4' 17°30.7' 55°28.9' 17°28.3' 09:55 10:25 30 424.266 113.78 266.403 28.165 11.46 0.137 1.291 3.03 23 25136 2018-11-21 40G7 25 58 55°46.8' 17°42.1' 55°47.5' 17°41.7' 13:45 14:00 15 464.86 0.469 464.391 24 25309 2018-11-21 40G7 25 60 55°50.7' 17°41.6' 55°51.3' 17°40.8' 15:00 15:15 15 215.167 21.87 190.519 2 0.778 25 25038 2018-11-22 41G7 25 52 56°9' 17°45.8' 56°8.9' 17°44.5' 07:50 08:05 15 324.152 1.755 315.1 0.672 0.601 0.034 5.99 26 25410 2018-11-22 41G7 25 64 56°3.4' 17°45' 56°4.7' 17°46.1' 09:31 10:01 30 76.016 12.681 58.109 3.122 1.733 0.2 0.171 27 25504 2018-11-22 41G7 25 64 56°4.7' 17°45.9' 56°3.4' 17°45' 11:05 11:35 30 70.696 13 49.56 6.588 0.931 0.339 0.002 0.274 0.002 28 25461 2018-11-22 41G7 25 41 56°4.3' 17°22.7' 56°4.9' 17°25.1' 13:46 14:16 30 244.694 5.96 224.29 11.42 0.747 2.277 29 25403 2018-11-23 40G6 25 53 55°52' 16°26.8' 55°51.9' 16°29.3' 08:00 08:30 30 180.771 4.37 83.202 90.135 2.084 0.197 0.565 0.017 0.201 30 25462 2018-11-23 40G6 25 55 55°46' 16°39.8' 55°46.7' 16°38.6' 10:22 10:42 20 492.944 2.795 86.682 403.209 0.258 31 25505 2018-11-23 40G6 25 53 55°43.5' 16°40.5' 55°43.9' 16°42' 12:00 12:20 20 160.06 18.93 54.664 85.596 0.49 0.38 32 25509 2018-11-23 40G6 25 53 55°44' 16°42.3' 55°43.5' 16°40.1' 12:50 13:20 30 921.402 4.595 69.097 845.444 1.482 0.722 0.062 33 25450 2018-11-23 40G6 25 62 55°40.6' 16°32.4' 55°41.4' 16°34.4' 14:40 15:10 30 39.678 1.63 4.18 33.52 0.345 0.003 34 25389 2018-11-24 40G6 25 54 55°35.6' 16°40' 55°37.1' 16°40.9' 07:50 08:20 30 148.077 62.48 80.713 1.91 1.606 1.159 0.209 35 25080 2018-11-24 39G6 25 54 55°24.6' 16°45.8' 55°25.1' 16°48.1' 10:30 11:00 30 133.315 10.77 87.873 32.937 0.348 0.035 1.352 36 25081 2018-11-24 39G6 25 56 55°24.3' 16°51.6' 55°24.6' 16°54' 11:45 12:15 30 93.495 8.47 71.369 8.331 1.375 3.95 37 24055 2018-11-25 38G4 24 36 54°34' 14°43.6' 54°33.6' 14°46' 08:01 08:31 30 108.441 20.29 41.32 39.57 6.93 0.214 0.11 0.007 38 24150 2018-11-25 38G4 24 47 54°36.9' 14°48.4' 54°36.8' 14°50.8' 09:45 10:15 30 228.428 42.43 52.945 98.165 28.32 2.402 1.073 0.448 2.645 39 24162 2018-11-25 38G4 24 55 54°42' 14°54.8' 54°40.8' 14°53.5' 12:10 12:40 30 96.563 22.19 13.203 40.052 7.936 8.103 0.223 4.856 40 25008 2018-11-26 37G5 25 30 54°23' 15°37.1' 54°23' 15°34.6' 08:00 08:30 30 98.494 16.36 59.76 17.1 3.154 0.699 0.01 1.396 0.015 41 25009 2018-11-26 37G5 25 30 54°22.9' 15°46.3' 54°22.8' 15°43.7' 10:00 10:30 30 11.09 2.395 4.96 2.845 0.268 0.523 0.083 0.016 42 25011 2018-11-26 37G6 25 27 54°24.5' 16°1.3' 54°24.4' 16°0.1' 12:25 12:40 15 6.839 2.39 2.856 0.658 0.506 0.429 43 25010 2018-11-26 37G6 25 28 54°25.6' 16°0.5' 54°25.9' 16°1.6' 13:17 13:32 15 22.211 18.795 2.409 0.639 0.23 0.126 0.012 44 25042 2018-11-26 38G6 25 46 54°32.3' 16°0' 54°33.8' 16°0' 14:51 15:21 30 96.625 53.02 32.547 1.995 6.365 1.751 0.947 45 25013 2018-11-27 38G6 25 33 54°38.6' 16°22.1' 54°39.2' 16°24.4' 07:55 08:25 30 134.232 50.48 59.701 2.151 16.635 4.365 0.757 0.036 0.107 46 25014 2018-11-27 38G6 25 28 54°40.6' 16°35.3' 54°41.3' 16°37.5' 09:37 10:07 30 37.412 4.145 8.858 0.086 20.02 2.573 0.309 1.126 0.243 0.052 47 25016 2018-11-27 38G6 25 31 54°44.8' 16°49.5' 54°45.7' 16°51.3' 11:30 12:00 30 310.341 26.63 34.995 226.57 16.695 4.609 0.688 0.023 0.131 48 25017 2018-11-27 38G6 25 29 54°44.7' 16°53.5' 54°45.9' 16°55.1' 13:00 13:30 30 248.692 12.405 61.179 146.898 25.915 1.277 0.574 0.321 0.123 49 25004 2018-11-27 38G6 25 23 54°52.4' 16°43.2' 54°52.3' 16°40.8' 15:00 15:30 30 35.209 3.535 17.71 12.69 1.132 0.142 50 25364 2018-11-28 39G7 25 33 55°0' 17°27.7' 54°59.9' 17°25.2' 08:00 08:30 30 85.307 4.98 53.41 24.82 1.905 0.192 51 25022 2018-11-28 38G7 25 27 54°57.4' 17°24.9' 54°57.2' 17°22.3' 09:21 09:51 30 10.743 1.765 0.056 7.618 0.64 0.209 0.455 52 25024 2018-11-28 38G7 25 24 54°51.2' 17°28.4' 54°51.3' 17°30.8' 11:15 11:45 30 54.271 11.03 21.37 18.06 0.321 0.514 2.976 53 26274 2018-11-29 38G8 26 24 54°54.2' 18°13.3' 54°54' 18°10.4' 07:56 08:26 30 37.841 21.62 15.493 0.15 0.435 0.058 0.085 54 26005 2018-11-29 38G8 26 23 54°53.9' 18°12.9' 54°53.9' 18°11.1' 09:21 09:41 20 9.45 1.7 7.75 Time ofGeographical position of the catch-station start/shoot end Weight of the catch by fish species [kg] 126 ICES | WGBIFS 2019 Fig. 6. Horizontal distribution of the seawater temperature, salinity and oxygen content in the near bottom layer during r/v Baltica BITS-4Q survey (14.11-01.12. 2018). ICES | WGBIFS 2019 127 Fig. 7. Vertical distribution of the seawater temperaturę, salinity and oxygen content along the hydrological research profile during r/v Baltica BITS-4Q survey (14.11-01.12. 2018). 128 ICES | WGBIFS 2019 Verteiler: Deutscher Fischerei-Verband e. V., Hamburg BLE, Hamburg Leibniz-Institut für Ostseeforschung Schiffsführung FFS „Solea“ Doggerbank GmbH BMELV, Ref. 614 Mecklenburger Hochseefischerei Sassnitz TI, Präsidialbüro (M. Welling) Kutter- und Küstenfisch Sassnitz TI, OF TI Landesverband der Kutter- und Küstenfischer TI, FOE Sassnitzer Seefischer TI, SF Deutsche Fischfang Union Cuxhaven TI, FIZ Fahrtteilnehmer Eurobaltic Mukran Verantw. Seeeinsatzplanung, Herr Dr. Rohlf BFEL Hamburg, FB Fischqualität IFM-GEOMAR, Kiel Institut für Fischerei der Landesforschungsanstalt LA für Landwirtschaft, Lebensmittels. u. Fischerei BSH, Hamburg Institute of Baltic Sea Fisheries Alter Hafen Süd 2, 18069 Rostock Phone: +49 381 8116123 Fax: + 49 381 8116199 Date: 21/01/2019 Mail andres.velasco@thuenen.de Cruise report Cruise number 756 FRV „SOLEA“ 08/11/ - 25/11/2018 Baltic International Trawl Autumn Survey (BITS) in the Arkona Sea, Mecklenburg- and Kiel Bight (ICES SD 24+22) Scientist in charge: Dr. A. Velasco 1. Summary The 756th cruise of the FRV “SOLEA” is the 37st November survey since 1981. It was part of the Baltic International Trawl Survey (BITS) which was coordinated by ICES WGBIFS. The main objective of the survey was the estimation of fishery independent stock indices for both Baltic cod stocks, flounder and other flat fish. In total 52 fishery and 52 hydrography stations were carried out. A preliminary analysis of the survey results suggests a weak year class of cod in 2018 as compared with the previous year class 2017 (recruits at length range 10- 25 cm). The proportion of cod between 26-40 cm was lower in all depth layers as compared to the previous year, with exception of the depth layer of 10–39 m in SD 24. The abundance of flounder as compared to the previous year decreased in SD 22 and in SD 24. The oxygen concentration close to the bottom was above 2.1 ml/l. ICES | WGBIFS 2019 129 2 2. Research programme The cruise took place from 08th until 25th November 2018. Corresponding to the recommendations of the WGBIFS in 2007, the survey of the FRV “SOLEA” covered the subdivisions 22 and 24 (Figure 1). The following stock assessment objectives were covered during the survey:  Collecting data for assessing stock indices, the structure and recruitment of the stocks, especially for cod and flatfish  Monitoring the composition of fish species in the western Baltic Sea  Collecting samples of cod and flounder for biological investigations (i.e. sex, maturity, fecundity, age)  Monitoring the actual hydrographical situation in the survey area 3. Narrative The internationally coordinated trawl survey is planned as a Stratified Random Survey where ICES subdivisions and depth layers are used as strata. A total of 59 stations (45 in subdivision 24 and 14 in subdivision 22) were planned for the German part of the survey which covered the southern part of ICES subdivision 22 and subdivision 24 in total. The haul positions were selected from the TOW Database by the coordinator of the BITS surveys (ICES 2008, WGBIFS report as reference). 52 fishing stations were realized and can be used for stock assessment. The fishing hauls were carried out between 7:00 and 15:00 UTC (8:00 and 16:00 local time). The positions of the trawl hauls are shown in Figure 1. 11 fishing hauls and 14 hydrographic stations were done in subdivision 22, and 38 fishing hauls and 38 hydrographical stations were realized in subdivision 24. Fig. 1 Stations of the 756th FRV “SOLEA” cruise (Ocean Data View, R. Schlitzer, www.awi- bremerhaven.de/GEO/ODV) 130 ICES | WGBIFS 2019 3 The numbers of fishing hauls and hydrographic stations by subdivision and 10 m depth layers are given in Table 1. The 14 hauls in subdivision 22 were located at depths from 10 m to 29 m and 20 of 38 hauls in subdivision 24 between 40 and 59 m. Tab. 1 Sampling intensity (evaluated fishing stations) 1 [10-19] 3.2 2 2 2 [20-29] 20.6 12 12 1 [10-19] 12.2 8 8 8.3 6 6 5.4 4 4 28.3 18 18 3.1 2 2 Area Stations Subdivision Stratum Depth [m] Total trawl distance [sm] 22 24 Fishing [n] Hydrography [n] 2 [20-39] 3 [40-59] Trawling was done with the standard BITS trawl “TV3 520#“. The stretched mesh size in the codend was 20 mm. The duration of each haul was 30 minutes at a velocity of 3 kn as required in the BITS manual. The total catch of a haul was analysed to determine species composition in weight and number as well as the length distribution of all species. Subsamples of cod, flounder, plaice, dab and turbot were investigated concerning sex, maturity and age. Vertical profiles of the hydrographical parameters temperature, salinity and oxygen were sampled from the surface to the bottom immediately after every fishing haul with a CTDO probe (Sea Bird 19 +). 4. Preliminary results 4.1. Biological data In total 787 cod, 574 flounder, 831 plaice, 594 dab, 211 turbot and 34 brill were collected for measuring length, weight, sex, maturity and age. The total catches and numbers of length samples of cod and flounder are given in Table 2 by subdivision and depth stratum. Tab. 2 Numbers of length measurements of cod and flounder by depth stratum and ICES subdivision 22 10-29 23.7 82 59.5 197 10-19 275.5 742 260.7 1063 20-39 1642.6 3269 636.6 2675 40-59 1578.2 4157 731.5 3256 Area Sample Cod Flounder 24 Weight [kg] Number [n] Subdivision Depth [m] Weight [kg] Number [n] ICES | WGBIFS 2019 131 4 22 10-29 468.3 2253 809.9 8176 10-19 83.2 349 100.3 761 20-39 172.0 988 75.6 603 40-59 1935.3 10045 44.2 273 24 Subdivision Depth [m] Weight [kg] Number [n] Weight [kg] Number [n] Sample Plaice Dab Area The mean catch per hour (CPUE) was 86,8 kg of cod and 41,6 kg of flounder. In general the catch composition was dominated by cod and flounder. However, plaice and dab were also abundant in the catches. The mean fraction of cod biomass in the hauls was 32,7 % and mean fraction of flounder, plaice and dab was 15,7 %, 24,7 % and 9,6 %, respectively. sprat and herring represented 6.5 % of the total biomass in mean. The highest abundances in weight and number of cod and flounder were observed in subdivision 24 in depths between 20 - 59 m. Mean CPUE of cod and flounder are given in Table 3 by subdivision and depth stratum. Tab. 3 Mean CPUE of cod and flounder and average individual weights by sub- division and depth 22 10-29 1 3 288.7 14 2.5 8 302.1 14 10-19 22.5 61 371.3 8 21.3 87 245.3 8 20-39 119.6 238 502.5 10 46.3 195 238 10 40-59 50.3 132 379.6 20 23.3 104 224.7 20 22 10-29 19.7 95 207.9 14 34.1 345 99.1 14 10-19 6.8 29 238.4 8 8.2 62 131.9 8 20-39 12.5 72 174.1 10 5.5 44 125.4 10 40-59 61.7 320 192.7 20 1.4 9 162.3 20 Cod Flounder Average Weight [g] Stations [n] Average Weight [g] Subdivision Stations [n] Subdivision Depth [m] Area Catch Area Dab Weight [kg/sm] Number [n/sm] 24 Weight [kg/sm] Number [n/sm] Average Weight [g] Catch Plaice 24 Weight [kg/sm] Number [n/sm] Average Weight [g] Stations [n] Stations [n] Depth [m] Weight [kg/sm] Number [n/sm] The frequencies of cod grouped by subdivision and depth strata are presented in Figures 2 to 4. Noteworthy is the low abundance of young cod ranging in length from 10 to 25 cm in the subdivisions 24 and 22. The length range 26–40 cm of cod recruits compared to the previous year has significantly decreased in all depths layers in the subdivisions 24 and 22 with exception of the depth layer 10-39 m in subdivision 24 (Table 4 and Figures 2 to 4). 132 ICES | WGBIFS 2019 5 Fig. 2 Length frequencies of cod in number per mile in depth strata 10 m to 29 m in SD 22 2018 (line) and 2017 (bars), (14 Hauls) Fig. 3 Length frequencies of cod in number per mile in depth strata 10 m to 39 m in SD 24 2018 (line) and 2017 (bars), (18 Hauls) Fig. 4 Length frequencies of cod in number per mile in depth strata 40 m to 59 m in SD 24 2018 (line) and 2017 (bars), (20 Hauls) ICES | WGBIFS 2019 133 6 Tab. 4 Recruitment of length groups of the year 2018 in comparison to the previous year Catch 22 10-29 21 1 23,7 10-19 396 32 12.2 20-39 2448 178 13.7 40-59 2951 94 31.4 22 - 24 10-59 5816 72 81.1 22 10-29 48 2 23.7 10-19 209 17 12.2 20-39 150 11 13.7 40-59 571 18 31.4 22 - 24 10-59 978 12 81.1 Catch 22 10-29 147 9 16.4 10-19 342 29 12.0 20-39 2288 139 16.5 40-59 6878 190 36.1 22 - 24 10-59 9655 119 80.9 22 10-29 668 41 16.4 10-19 74 6 12.0 20-39 1041 63 16.5 40-59 842 23 36.1 22 - 24 10-59 2625 32 80.9 10 - 25 Trawl distance [sm] Number/ Mile [n/sm] Area 2018 Number [n] 24 Depth [m] 24 Subdivision Length range [cm] 2017 Subdivision Depth [m] Length range [cm] Number [n] Number/ Mile [n/sm] Trawl distance [sm] 24 24 26 - 40 10 - 25 26 - 40 Area Under the assumption that the survey covered all nursery grounds of cod, a weak year class 2018 (top table) compared to the year class 2017 (table below) can be assumed. 4.2 Hydrographical data Figure 5 shows the distribution of temperature, salinity and oxygen near the bottom and at the surface in the covered area. The hydrography was characterised by typical autumn conditions with surface temperatures between 7.7 °C and 11.4 °C. The salinity of the surface water decreased from 20.3 to 7.3 from west to east. The lowest temperature value was found in front of Møn at 7.7 °C. The salinity above the permanent halocline at a water depth of 23.6 m south of Bornholm was approx. 7.7 The salinity increased below the halocline at a depth of 45 m in the Arkona Basin up to 20.1 The oxygen concentration close to the bottom was between 2.1-11.8 ml/l. 134 ICES | WGBIFS 2019 7 Fig. 5 Hydrography of the survey near the bottom (left) and at the surface (right) 5. Participants A. Velasco TI-OF Scientist in charge C. Albrecht TI-OF Technician S. Dressler TI-OF Technician S. Winning TI-OF Student helper R. Wiechert TI-OF Technician R. Klinger University of Hamburg Ph. D. Student S. Eskildsen DTU Aqua, DK Technician M. Bächtiger University of Hamburg Student helper ICES | WGBIFS 2019 135 8 6. Acknowledgements I would like to express my gratitude to Captain Koops and his crew on the FRV "Solea" for their good cooperation. sgd. Scientist in charge 136 ICES | WGBIFS 2019 Lithuania BITS Q4 2018 cruise report Marijus Špėgys 1. INTRODUCTION The cruise of the FV “LBB-100” was part of the Baltic International Trawl Survey (BITS), which is coordinated by ICES WGBIFS. The main objective of the survey is the estimation of fishery independent stock indices of both Baltic cod stocks, of flounder and other flat fish. The following further objectives were covered during the survey: Collecting data for assessing stock indices, the structure and recruitment of the stocks especially for cod and flatfish. Monitoring the composition of fish species in the South-Eastern Baltic Sea Collecting length samples for all species. Collecting samples of cod and flounder for biological investigations (i.e., sex, maturity, age). Collecting litters from trawl. 2 METHODS 2.1 Personnel Marijus Špegys, Marine research institute, Klaipeda University - cruise leader; Deividas Norkus, Marine research institute, Klaipeda University –fish sampling. 2.2 Description The cruise took place two days (08-09 November 2018). FV “LBB-1010” has covered the Sub-division 26 in Lithuanian EEZ. 2.3 Survey design and realization The international coordinate trawl survey is planned as Stratified Random Survey where ICES subdivisions and depth layers are used as strata. A total of 6 stations were planned for the Lithuania part of the survey, which realize complete accordance with the agreements of WGBIFS during the meeting in 2017. The hauls' positions were selected from the TOW Database by the coordinator of the BITS surveys (ICES 2017, WGBIFS report as reference). All 6 fishing stations were successfully realized. The fishing hauls were realized in the daylight, between 8:15 and 16:50 local time. Trawling was done with the standard trawl “TV3/520#“. The stretched mesh size in the codend was 20 mm. The duration of the hauls was 30 minutes and the velocity was 3 knots. The total catch of each haul was analysed to determine the species' composition in weight and number as well as the distribution of length among all species. Sub-samples of cod, flounder were investigated concerning sex, maturity and age. Surface temperature and salinity were immediately sampled after every fishing hauls. ICES | WGBIFS 2019 137 Figure 1. Trawl hauls position of C/V “LBB -1010” in BITS 2018 m. Q4 survey The length measurements in the 1.0 cm classes was realised for cod, flounder and turbot, subsample were taken for biological analysis to laboratory. The length measurements in the 0.5 cm classes was realised of herring and sprat. All information about haul and catches are shown in table 1 and table 2. Table 1. Haul information from the Lithuania BITS Q4 survey with the TV3/520# bottom trawl Haul number according to TD data The ICES rectangle (subdivision) Trawling depth (m) Geographical position of catch station Surface temperature Surface salinity Bot. Tempe- rature Bot. salinity 00.00 N 00.00 E 00.00 E 00.00 N 26052 40H0 (26) 60 55.50 20.62 55.48 20.65 7,7 6,4 7,3 7,3 26193 40H0 (26) 70 55.67 20.28 55.65 20.25 6,6 6,7 7,3 7,3 26058 40H0 (26) 72 55.67 20.30 55.64 20.32 6,5 6,1 7,3 7,3 26206 40H0 (26) 56 55.76 20.33 55.74 20.33 7,0 6,8 7,3 7,3 26158 40H0 (26) 60 55.87 20.10 55.88 20.07 7,8 7,6 7,3 7,3 26057 40G9 (26) 75 55.72 19.97 55.72 20.01 8,0 7,2 7,3 7,3 138 ICES | WGBIFS 2019 Table 2 Fish catches results from the Lithuania BITS 2018 4Q survey with the TV3/520# bottom trawl Haul number according to TD data Catch date The ICES rectangle (subdivision) Trawling depth (m) Total CPUE (kg/h) CPUE per species (kg/h) Cod Flounder Place Herring Others 26153 2018-11-08 40H0(26) 64 366.9 240.0 106.0 4.1 16.3 16.7 26052 2018-11-08 40H0(26) 66 3.2 0 3.2 0 0 0 26060 2018-11-08 40H0(26) 76 0 0 0 0 0 0 26205 2018-11-09 40H0(26) 54 64.7 40.0 5.3 0 0.9 19.4 26134 2018-11-09 40H0(26) 36 338.3 206.0 32.0 0 87.5 22.7 26011 2018-11-09 40G9(26) 34 0.6 4 0 0 0 0.2 Mean 81.1 24.4 0.7 17.5 5.3 3. RESULTS In total 1009 cods, 394 flounders, 14 places, 607 herrings and 63 other species were collected for measuring and from that measurement sample 287 cods and 229 flounders and 14 place were collected for weight, sex, maturity and age. Numbers of biological samples by haul given in Table 3. Cod from the length classes range of 22-39 dominated in samples. The fish with this length range constituted about 92.9% of all measured cod (Fig. 1). Moreover, 82.6% of all measured cods were undersized individuals (less than 35 cm). The total length of flounder ranged from 11 to 37 cm, with dominating length classes of 20-33 cm. The fish with this length range constituted about 82.4% of all measured flounder. The total length of herring ranged from 8 to 30.0 cm. Herring from the length classes of 16.5-24 was dominated in samples and constituted about 64.5% of all measured herring (Fig. 3). The length distributions of cod, flounder, herring and sprat, according to the ICES Sub-divisions 26 are shown in Figures 1-3. Table 3. Biological samples of all hauls from the Lithuania BITS 2018 Q4 survey Haul number Catch date The ICES rectangle and subdivision Trawling depth (m) Numbers of biological samples Length Age, sex, maturity Cod Flounder Place Herring Sprat Cod Flounder 1 24.02.2015 40H0 (26) 58.2 524 321 14 224 3 226 189 2 24.02.2015 40H0 (26) 63.1 - 9 - - - - 1 3 24.02.2015 40G9 (26) 65.8 - - - - - - - 4 25.02.2015 40H0 (26) 49.9 64 10 - 11 - - 8 5 25.02.2015 40H0 (26) 37.3 420 54 - 372 - 16 31 6 25.02.2015 40H0 (26) 29.6 1 - - - 9 45 - Sum 1009 394 14 607 12 287 229 ICES | WGBIFS 2019 139 0 2 4 6 8 10 12 14 5 11 14 17 20 23 26 29 32 35 38 41 44 47 50 53 59 F r e q u e n c y , % Length, cm Figure 2. Cod length distribution from Lithuania BITS 2018 Q4 survey 0 2 4 6 8 10 12 9 11 13 15 17 19 21 23 25 27 29 31 33 35 38 F r e q u e n c y , % Length, cm Figure 3. Flounder length distribution from Lithuania BITS 2018. 4Q survey 140 ICES | WGBIFS 2019 02 4 6 8 10 12 14 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 F r e q u e n c y , % Length, cm Figure 4. Herring length distribution from Lithuania BITS 2018 m. Q4 survey ICES | WGBIFS 2019 141 CRUISE REPORT FROM THE POLISH R/V BALTICA BITS 1Q 2019 SURVEY IN THE SOUTHERN BALTIC (12 February - 07 March 2019) by Krzysztof Radtke and Tycjan Wodzinowski Gdynia, 21 March 2019 142 ICES | WGBIFS 2019 INTRODUCTION Since 1995, the permanent participation of Polish R/V Baltica operated by the National Marine Fisheries Research Institute (NMFRI) in Gdynia, has taken place in autumn and winter Baltic International Trawl Surveys (BITS-4Q and BITS-1Q) realised in the southern Baltic. In March 2000 when the research standard fishing gear in the Baltic Sea - the cod bottom trawl type TV-3, has been applied by the vessels assigned to the BITS surveys realization, the principal methods of investigations within BITS-1Q ground-trawl surveys designated to particular national labora- tories, including the NMFRI were designed and co-ordinated by the Baltic International Fish Survey Working Group (WGBIFS; Anon. 2018). The main aim of the BITS-1Q survey planned in winter 2019 was to monitor abundance and spatial distribution of the main demersal fish spe- cies and to some extent also clupeids in the bottom zone of the Baltic, taking into account hydro- logical parameters. The R/V Baltica BITS-1Q 2019 survey, which was realized in the Polish part of the ICES Sub-divisions 24, 25, 26 and Swedish part of the ICES Sub-divisions 25 and 26, was aimed at:  determination of the spatial distribution of cod, flounder, herring and sprat in the near bottom zone of the southern and central Baltic during winter 2019 applying method of random selection of control-hauls,  estimation of the fishing efficiency, i.e. catch per unit effort (CPUE), the share of particu- lar species in total mass of bottom control-catches,  collecting biological samples of dominated fish for the determination of the age-length- mass relationship, sex, sexual maturation, feeding conditions and externally visible dis- eases,  analysis of the vertical and horizontal changes of the basic hydrological parameters (tem- perature, salinity, oxygen content) in the areas of fish catches and in neighbouring stand- ard hydrological stations. MATERIAL AND METHODS The above purposes of the February/March 2019 BITS 1Q survey aboard of R/V Baltica were realized by the NMFRI nine members of scientific team, with Krzysztof Radtke as a cruise lead- er. The scientific team was also composed of seven ichthyologists including technicians, respon- sible for determination of fish species composition of catches, fish biological analyses and data processing and one hydrologist, responsible for seawater sampling and analysing as well as for meteorological monitoring. Narrative The reported Polish ground-trawl survey on board of R/V Baltica, marked with the number 3/2019/MIR took place during the period of 12.02-07.03.2019 within the framework of the ICES Baltic International Trawl Surveys (BITS) long-term programme (Anon. 2018) and the Polish Fisheries Data Collection Programme for 2019. The vessel left the port of Gdynia on 12.02.2019 in the morning and at sea investigations began in the southern part of the Gulf of Gdańsk (Fig. 1, Tab. 1). During the period of 01-06.03. 2019, the investigations were conducted in Swedish wa- ters. The survey ended on 07.03.2019 (morning) in Gdynia harbour. The R/V Baltica operated mostly in the Polish EEZ. Overall, 24 days were utilized for fulfilling the BITS 1Q survey pur- poses including time spent for the vessel translocation from the Gdynia port to research area and in the final phase of the survey, a return way to the vessel home-port. ICES | WGBIFS 2019 143 Survey design and realization – sampling description According to the WGBIFS plan, the Polish vessel was recommended to cover in February/March 2019 survey, the Polish part of ICES Sub-divisions 24, 25 and 26 with 5, 29 and 22, respectively randomly selected bottom control-hauls, and also in Swedish EEZ to cover Swedish part of ICES Sub-division 25 and 26 with 4 and 9 control-hauls, respectively. The R/V Baltica realized 71 of the 69 planned hauls for this survey. Two hauls (no 12 - ICES no 26020 and no 67 – ICES no 26224, see Table 3) were considered as „Invalid” due to technical problems associated with gear performance observed during trawling. Both hauls were repeated successfully in the places as assigned in the survey plan. One haul (no 70 – ICES no 26221) was not realized due to oxygen level on the bottom below 0.5 ml/l. The haul has a status „No oxygen” and the catch result is considered as „zero catch haul”. Finally, it can be concluded that the hauls realized during the survey correspond to the plan and could be therefore accepted as fully representative from the technical point of view (Fig. 1, Table 1) taking into account gear performance during hauls. Trawling was done with the standard rigging ground trawl type TV-3#930 (without bobbins and additional chains connected to the footrope), with 10-mm mesh bar length in the codend. A standard vertical fish-sounder was used to monitor the trawling depth. Usually a 6-7 m vertical net opening was achieved, which was monitored by the net echosounder. The catch stations were located on the depth range from 19 to 113 m. Fish control-hauls were conducted at the daylight only, lasting maximum 30 minutes, at 3.0 knots vessel speed. Each control-catch was sorted out for the determination of the species composition. Mean CPUE of each fish species and their average share in mass of catches was calculated. From each catch station, representative samples of dominated fishes were collected to determine age-length-mass relationships, sex, sexual maturation, feeding conditions, externally visible diseases and addi- tionally stomach samples for food composition estimation of cod were collected for further ex- aminations in the Institute. In the case of cod, turbot and plaice all the caught specimens were taken for total length and mass measurements. In the case of clupeids and flounder, the representative sub-samples of these fish species were investigated. Overall, 14349 cod, 8234 flounder, 1726 plaice, 75 turbot, 6028 sprat and 9362 herring were taken for the length and mass determination. In total, 800, 983, 742, 75, 548 and 1045 individuals of the above-mentioned species were aged. Biological analyses of fishes were performed directly on board of surveying vessel, according to standard methodologi- cal procedures. The length of 35 cm, 23 cm (ICES SD 25) and 21 cm (ICES SD 26), 16 cm and 10 cm was taken into account as a separation (protective) length between juvenile and commer- cial size of cod, flounder (differed by the ICES Sub-divisions), herring and sprat, respectively. Externally visible diseases of fish’s skin and their vertebral column anomalies were monitored for 14349 cod, 8234 flounder, 1726 plaice, 6028 sprat and 9362 herring. Data on pathological symptoms were registered based on the visual inspection of fish taken for length measurements. Every control-haul was preceded by the measurements of basic hydrological parameters continuously from the sea surface to the bottom. Overall, 97 hydrological stations (including hydrographic standard stations) were inspected with the automatic CTD probe SeaBird 911 combined with the rosette sampler (the bathometer rosette). Oxygen content was determined using the standard Winkler’s method. The seawater temperature and salinity row data was ag- gregated to the 1-m depth stratum while oxygen content was aggregated to the 10-m intervals. Temperature, salinity and oxygen content was the source of information on abiotic factors poten- tially influencing fish spatial distribution. Distribution of all hydrological stations inspected by the R/V Baltica in February/March 2019 is presented in Figure 1. 144 ICES | WGBIFS 2019 RESULTS Fish catches and biological data In total, twenty seven species were recognized in 69 scrutinized valid bottom catches (Table 1). Only two fish species – horse mackerel and saithe represent fish species permanently inhabiting Atlantic Ocean. The frequency of the most important commercial species occurrence in the hauls - floun- der, cod, herring and sprat was - 98%, 93%, 84% and 65% of the hauls, respectively (Table 1). Cod, flounder, herring, and sprat dominated also with respect to mass of catch (kg) and efficien- cy (CPUE). By-catch of other fish species was insignificant. The average CPUEs of cod in ICES SDs 25 and 26 were lower than the CPUE of herring and sprat in the same SDs, but were higher than flounder CPUE (Fig. 2). In ICES SD 24 cod CPUE was only lower than herring CPUE. The highest cod average CPUE was noted in ICES SD 25 – 134,6 kg/1h. Markedly lower CPUE results were obtained in ICES SDs 26 and 24 – 93.3 and 78.6 kg/1h. Similarly to February 2018 r. cruise, cod CPUE in ICES SD 25 was compa- rable with the CPUE obtained in the current survey - 144 kg/1h. However in ICES SDs 26 and 24 in 2018, the CPUEs of cod were markedly lower than in the current cruise, and amounted to 44 and 21 kg/1h, respectively. Herring definitely dominated among all the fish species in respect of CPUE. The CPUEs of herring were high and in ICES SDs 24, 25 and 26 amounted to 173.2, 347.6 and 344 kg/1h, respectively. During the last year’s survey, much lower herring CPUEs were obtained - 13, 197 and 214 kg/1h, respectively. The highest sprat CPUE was obtained in ICES SD 26 – 251.7 kg/1h. Whereas in ICES SDs 24 and 25 the sprat CPUEs were considerably lower and amounted to 28.9 and 142.7 kg/1h, respectively. In comparison with the cruise from February 2018, the CPUEs in the current year were much higher in ICES SDs 25 and 26. Sprat CPUEs in 2018 amounted to 45 and 98 kg/1h, respectively. Sprat did not occur in ICES SD 24 in February 2018. Flounder CPUEs in ICES SDs 25 and 26 were marked by the lowest values as compared to the CPUEs obtained for four important commercial species. Flounder CPUE amounted to 80.3 and 89.1 kg/1h, respectively in ICES SDs 25 and 26. Flounder CPUE in ICES SD 24 was 41,3 kg/1h and it was the third in row CPUE value in that ICES SD (higher than for sprat, lower than for herring and cod). As compared to the cruise from February 2018, the average CPUEs obtained in the current year were lower in ICES SDs 26 and 25, respectively by 25.9 and 20.7 kg/1h, while in the ICES SD 24 flounder CPUE was higher by 16.3 kg/1h. Length distributions of main fish species according to the ICES Sub-divisions are illus- trated in Figure 3. The curves of cod length distributions for all the ICES SDs were very similar, what indicates low cod length variety observed in all the three ICES SDs in the area of investiga- tion. In respect of cod length distribution in ICES SD 26, slight shift of the length distribution curve to the left along the horizontal axis was noted as compared to length distribution curves from ICES SDs 25 and 24, what indicates that slightly higher share of smaller cod inhabited in that ICES SD. However there was only slightly difference between these ICES SDs. Length dis- tributions clearly indicate that the area of investigation was occupied by the cod from the range of length classes 18-43 cm. Number of cod below the length of 20 cm was very low (probably mostly 2018 year-class). Small cod was most numerous in ICES SD 24. In the length distribution curve of cod in ICES SD 25 there was clearly distinguished single peak corresponding to length class 27 cm (9,4%) (similarly as in the cruise from November 2018). Peak in length distribution curve in ICES SD 26 corresponded to length class 24 cm (7,8%), while in ICES SD 25 the peak corresponded to length class 30 cm (9,3%). Three herring length fractions in herring length distribution curve from ICES SD 24 were distinguished. Small size herring (12,5-16 cm), medium size herring (6,5-20,5 cm) and largest size herring (21-30,5 cm). Herring length distribution curves form ICES SDs 25 and 26 were of very similar shape. It indicates that the length of herring in these ICES SDs was homogeneous. ICES | WGBIFS 2019 145 Also, in ICES SDs 25 and 26 clearly distinguished single peak in each of the length distributions was observed, corresponding to length class 18.5 cm (10.3%) and to 18 cm (8.5%), respectively. Sprat length distribution curve in ICES SD 26 indicates that two sprat length fractions in- habited the ICES SD mentioned. Smaller size sprat (7.0-9.5 cm) and the larger sprat (10.0-14.5 cm). Sprat length distributions indicate relatively high variety of the fish length with respect to ICES SD. The smallest size sprat was caught in ICES SD 26. Towards west (ICES SDs 25 and 24) the length od sprat was smaller. Sprat of the most favourable length distribution for commer- cial fishery was observed in ICES SD 24. Flounder of the smallest length was observed in ICES SD 26 (length classes – 18-20 cm, were the most abundant - 8% on average per length class). Slightly higher share of larger floun- der (above 26 cm) was observed in ICES SD 25 than in ICES SD 24. Below the length of 26 cm the share of flounder in the length classes was in ICES SD 25 lower than in ICES SD 24. A clearly distinguished single peak corresponding to length class 27 cm (11%) was observed in flounder length distribution in ICES SD 25. Figure 4 shows the numerical shares of the undersized fish fractions of cod, herring, sprat and flounder. In cod catches from ICES SDs 25 and 26 the undersized fraction of cod prevailed markedly. Their numerical share in the above-mentioned ICES SDs was 82.8%, 84.3% and 87.4%, respectively. In the same cruise in February 2018, the share of undersized cod was lower and amounted to 81.6%, 69% and 37%, respectively. The total share of undersized cod from the last survey was very high and amounted to 85.4%. Numerical share of undersized herring de- creased westward. The share of the undersized fraction in ICES SDs 26, 25 and 24 amounted to 14.6%, 6.0% and 4.6%, respectively. The largest share of undersized sprat was observed in sam- ples from ICES SD 26 (25.6%). The share in ICES SD 25 was 1.9%, while in ICES SD 24 un- dersized sprat was not observed. Flounder undersized share was the highest in the ICES SD 26 (57.4%). The share of undersized flounder in the ICES SDs 25 and 24 was 10.9% and 20.4%, respectively. Mean length (l.t.) and mean mass of sprat, herring, cod and flounder calculated for the whole cruise and separately for ICES SDs 24, 25 and 26 are presented in the text table below (in parenthesis are shown parameters from February 2018 cruise): ICES Sub- division para- meter sprat herring cod flounder 24 mean length [cm] 13,7 () 20,9 (23,9) 29,8 (36,5) 26,1 (21,6) 25 12,3 (12,5) 19,6 (18,6) 29,8 (28,9) 27,4 (27,4) 26 10,9 (11,0) 18,8 (17,4) 28,3 (31,3) 20,6 (20,7) whole cruise 11,5 (12,0) 19,3 (18,4) 29,2 (29,2) 22,7 (23,6) 24 mean mass [g] 15,4 () 59,9 (101,3) 272,5 (451,5) 188,1 (110,3) 25 12,9 (11,9) 63,4 (42,1) 267,3 (254,0) 230,8 (265,5) 26 7,8 (8,1) 40,3 (34,4) 236,1 (344,4) 105,8 (121,3) whole cruise 9,7 (10,6) 52,9 (41,8) 255,4 (267,1) 143,3 (180,4) The measurement of the length of the main fish species was accompanied by a macro- scopic analysis of the presence of symptoms of visible diseases of fish’s skin, i.e. anatomopatho- logical changes (Fig. 5). The highest prevalence of fish with externally visible pathological changes was recorded for flounder (2.2%) and for cod (1.6%). With regard to cod a decrease in share of individuals with visible diseases was noted during the current survey as compared to February 2018 cruise - 2,8%. The share of herring and sprat with observed pathological symp- toms was very low and amounted to 0.34% and 0.017% in the whole area investigated. 146 ICES | WGBIFS 2019 Hydrological situation in the southern Baltic In the near-bottom water layer (Fig. 6) temperatures in the range from 9.51°C to 2.58°C were noted. The lowest temperature was noted in the control haul no 16, while the highest in hydrological station no 6. The highest salinity was recorded in hydrological station no IBY5 (Bornholm Deep) (17.32 on the PSU scale). The station IBY5 is monitored permanently during BITS surveys in Bornholm Basin. Salinity measured in Gdańsk Deep amounted to 13.11 in hy- drological station (G2). The lowest oxygen content in the water was noted on the hydrological station Gt1 (0.12 ml/l. In the Gdańsk Deep (G2) the oxygen content noted in hydrological station G2 was 1.25 ml/l and in the hydrological station IBY5 the content amounted to 2.16 ml/l. Surface water temperature fluctuated from 3.94 to 2.58°C (Fig. 7). The lowest tempera- ture was recorded in control haul no. 33, and the highest in control haul no 16. Mean value of the surface water temperature was 3.58°C. The average salinity of surface water was 7.58 on the PSU scale. The lowest value - 6.41 was recorded in the control haul no 9. The highest salinity was recorded in the haul no 37 (8.16 on the PSU scale). Mean oxygen content was 8.74 ml/l. The highest level of oxygen was registered in control haul no 21 (9.216 ml/l). The lowest oxygen level was recorded in the hydrological station no Gt1 (8.46 ml/l). CONCLUSIONS The data collected during Polish BITS-1Q 2019 cruise is considered as representative, taking into account the degree of the survey plan realization, and therefore can be used by the ICES Baltic International Fish Survey Working Group (WGBIFS) and the Baltic Fisheries As- sessment Working Group (WGBFAS) for evaluation of fish species abundance and their distri- bution. The survey data collected during the survey is stored in the international DATRAS data- base publicly available and managed by the ICES Secretariat. References: ICES. 2018. Report of the Baltic International Fish Survey Working Group (WGBIFS). ICES WGBIFS report 2018. 24-28 March 2018. Lyngby, Copenhagen, Denmark.380 pp. ICES | WGBIFS 2019 147 Fig. 1. Location of fish control-hauls (black crosses) and hydrological standard stations (red dots) realised during the r/v Baltica BITS-1Q cruise (12.02-07.03. 2019 r.). (green solid line in- dicates hydrological research profile). 148 ICES | WGBIFS 2019 Fig. 2. Mean share in mass of control hauls (A), and mean CPUE (B) of dominant fish species, and share of cod (C) in particular catches conducted during r/v Baltica BITS-1Q cruise (12.02- 07.03. 2019 r.). ICES | WGBIFS 2019 149 Fig. 3. Length distributions of cod, herring, sprat and flounder in samples from fish control hauls conducted during r/v Baltica BITS-1Q cruise (12.02-07.03. 2019 r.). (red horizontal lines indicate minimum landing size). 150 ICES | WGBIFS 2019 Fig. 4. Mean numerical share (in %) of undersized fish species in samples from fish control hauls conducted during r/v Baltica BITS-1Q cruise (12.02-07.03. 2019 r.). Fig. 5. Mean prevalence (in %-indiv.) of fish with externally visible diseases in samples from fish control hauls conducted during r/v Baltica BITS-1Q cruise (12.02-07.03. 2019 r.). ICES | WGBIFS 2019 151 Tab. 1. Number of fish species individuals measured and aged during r/v Baltica BITS-1Q cruise (12.02-07.03. 2019 r.). 26 ICES 25 ICES 24 ICES total 26 ICES 25 ICES 24 ICES total Sub-division Sub-division Sub-division Sub-division Sub-division Sub-division Round goby 2 0 0 2 0 0 0 0 Sand goby 2 0 0 2 0 0 0 0 Common goby 2 0 0 2 0 0 0 0 Vimba bream 1 0 0 1 0 0 0 0 Three-spined stickleback 15 0 0 15 0 0 0 0 Saithe 0 1 0 1 0 1 0 1 Greater sandeel 4 5 0 9 0 0 0 0 Cod 5577 8051 721 14349 233 382 185 800 Plaice 293 1164 269 1726 198 335 209 742 Ruffe 2 0 0 2 0 0 0 0 Short-horn scorpion 380 456 48 884 0 16 0 16 Hooknose 0 2 0 2 0 0 0 0 Atlantic salmon 0 1 0 1 0 1 0 1 Fourbeard rockling 33 228 0 261 0 30 0 30 Brill 0 1 0 1 0 1 0 1 European perch 3 0 0 3 0 0 0 0 Atlantic horse mackerel 0 2 3 5 0 1 0 1 Twaite shad 24 1 0 25 0 1 0 1 Turbot 35 30 10 75 35 30 10 75 Flounder 5623 2194 417 8234 453 307 223 983 Smelt 18 0 0 18 0 0 0 0 Sprat 3792 2063 173 6028 251 235 62 548 Baltic herring 4169 4478 715 9362 388 508 149 1045 Lumpfish 19 25 1 45 0 4 0 4 Small sandeel 2 0 0 2 0 0 0 0 Eelpout 92 1 0 93 0 0 0 0 Whiting 0 10 9 19 0 2 0 2 TOTAL 20088 18713 2366 41167 1558 1854 838 4250 Species name Number of fish mesured (l.t) Numer of fish aged and weighed (g) 152 ICES | WGBIFS 2019 Tab. 2. Fish control-hauls data obtained during r/v Baltica BITS-1Q cruise (12.02-07.03. 2019 r.) (Hauls no. 1-35) lack of oxygen in the bottom -> haul not performed (no oxygen haul) Haul Haul ICES ICES Trawling Trawling number number Catch rectangle Sub-division depth duration Total according to according to date [m] szerokość długość szerokość długość shooting hauling up [min] catch Cod Herring Sprat Flounder Plaice Turbot Hooknose Eelpout Fourbeard Three-spined Lumpfish Short-horn Round Sand Smelt Twaite Whiting Greater Common Perch Small Atlantic Brill Horse Saithe Ruffe Vimba survey order ICES (N) (E) (N) (E) net net [kg] rockling stickleback scorpion goby goby shad sandeel goby sandeel salmon mackerel bream database 1 26264 2019-2-12 37G9 26 43 54°25.4' 19°2.9' 54°25.2' 19°4.7' 12:43 13:03 20 527.008 0.710 91.710 372.489 59.450 0.157 0.040 0.924 1.483 0.003 0.042 2 26282 2019-2-13 37G9 26 41 54°25.1' 19°3.1' 54°25.1' 19°5.1' 07:41 08:01 20 752.398 2.013 549.065 160.746 35.860 0.176 0.582 0.032 0.856 2.129 0.851 0.053 0.001 0.034 3 26265 2019-2-13 37G9 26 48 54°26' 19°4.4' 54°26' 19°6.3' 10:43 11:03 20 138.020 1.675 20.468 21.969 90.600 1.217 0.389 0.393 1.116 0.027 0.166 4 26256 2019-2-13 37G9 26 65 54°27.3' 19°13.5' 54°27' 19°16.3' 15:04 15:34 30 712.162 47.390 449.421 85.849 122.060 3.453 0.343 2.044 0.139 1.431 0.032 5 26217 2019-2-14 37G9 26 41 54°24.5' 19°11.6' 54°24.5' 19°13.4' 07:43 08:03 20 491.595 20.780 322.442 69.148 76.960 0.793 0.499 0.891 0.034 0.048 6 26163 2019-2-14 37G9 26 41 54°24.5' 19°15.9' 54°24.8' 19°18.6' 11:12 11:42 30 144.923 14.460 125.810 2.040 0.796 0.244 1.549 0.024 7 26001 2019-2-14 37G9 26 24 54°22.9' 19°13.3' 54°23.2' 19°15.8' 13:10 13:40 30 78.697 2.870 17.040 0.026 56.090 0.208 1.720 0.006 0.180 0.511 0.046 8 26263 2019-2-14 37G9 26 32 54°24' 19°3' 54°24.2' 19°1.3' 15:21 15:41 20 222.673 0.373 182.457 0.528 38.380 0.201 0.052 0.200 0.004 0.478 9 26219 2019-2-14 37G9 26 33 54°24.5' 19°0.7' 54°24.5' 19°2.4' 16:10 16:30 20 149.959 3.210 124.751 0.373 20.340 0.023 0.280 0.002 0.855 0.055 0.070 10 26269 2019-2-15 38G9 26 82 54°36' 19°10.1' 54°36.2' 19°12.5' 07:42 08:12 30 107.535 9.740 38.184 37.383 21.230 0.299 0.640 0.059 11 26287 2019-2-15 38G9 26 80 54°34.8' 19°10.5' 54°34.8' 19°12.9' 09:28 09:58 30 195.523 12.027 141.983 23.267 16.920 0.626 0.575 0.125 12 26020 2019-2-15 38G8 26 47 54°45.8' 18°43.2' 54°46.4' 18°43' 13:11 13:26 15 Haul technically unsuccessful (haul repeated) 13 26020 2019-2-15 38G8 26 49 54°47.9' 18°42.3' 54°46.8' 18°42.8' 14:13 14:33 20 623.401 19.060 468.549 56.946 72.651 4.845 0.333 0.333 0.684 14 26183 2019-2-16 38G8 26 31 54°52.5' 18°33.8' 54°51.4' 18°35.7' 07:34 08:04 30 184.363 13.190 137.490 30.970 2.234 0.174 0.305 15 26007 2019-2-16 38G8 26 30 54°51.4' 18°34.6' 54°50.3' 18°36.4' 09:35 10:05 30 71.604 17.987 25.901 0.048 23.560 2.108 0.152 1.515 0.333 16 26266 2019-2-16 38G8 26 19 54°49.9' 18°30.4' 54°48.6' 18°32' 11:47 12:17 30 37.428 1.854 15.010 0.160 18.190 0.938 1.231 0.002 0.019 0.024 17 26274 2019-2-16 38G8 26 22 54°53.6' 18°11.5' 54°53.8' 18°14.1' 14:34 15:04 30 84.307 67.310 1.737 14.410 0.324 0.466 0.060 18 25024 2019-2-17 38G7 25 23 54°50.7' 17°29' 54°50.9' 17°31.7' 07:29 07:59 30 41.560 8.015 15.637 11.368 1.471 0.359 4.710 19 25022 2019-2-17 38G7 25 27 54°57.1' 17°22.8' 54°57.3' 17°25.6' 09:40 10:10 30 18.921 10.306 0.315 4.010 2.888 0.252 0.712 0.438 20 25364 2019-2-17 38G7 25 31 54°59.8' 17°23.2' 54°59.9' 17°26' 11:19 11:49 30 16.850 9.886 2.676 2.847 0.232 1.209 21 25004 2019-2-17 38G6 25 20 54°52.7' 16°41.7' 54°52.5' 16°39.2' 15:35 16:05 30 5.770 1.007 3.107 0.598 0.208 0.618 0.232 22 25016 2019-2-18 38G6 25 30 54°45' 16°49.7' 54°46' 16°51.4' 07:32 08:02 30 269.553 19.292 246.299 0.400 1.526 1.320 0.389 0.327 23 25017 2019-2-18 38G6 25 28 54°44.4' 16°52.1' 54°43.8' 16°49.6' 10:11 10:41 30 11.292 5.385 0.843 2.771 1.729 0.564 24 25014 2019-2-18 38G6 25 29 54°41.5' 16°38' 54°41' 16°35.6' 12:03 12:33 30 15.077 7.936 2.486 3.391 0.352 0.861 0.051 25 25013 2019-2-18 38G6 25 32 54°39.2' 16°24.8' 54°38.5' 16°22.5' 13:51 14:21 30 27.028 12.572 8.134 1.905 3.432 0.401 0.544 0.040 26 25052 2019-2-18 38G6 25 48 54°37.7' 16°3.8' 54°36.9' 16°2.9' 16:08 16:28 20 188.986 16.980 147.852 3.719 17.000 3.435 27 25008 2019-2-19 37G5 25 30 54°23' 15°35' 54°23' 15°37.6' 07:32 08:02 30 37.762 1.048 8.592 0.028 6.259 15.115 0.035 0.200 6.465 0.020 28 25009 2019-2-19 37G5 25 30 54°22.7' 15°43.8' 54°23' 15°46.3' 08:57 09:27 30 21.057 0.278 4.105 10.781 0.023 0.260 5.610 29 25011 2019-2-19 37G5 25 27 54°24.1' 15°59.5' 54°24.5' 16°2' 11:20 11:50 30 14.930 4.287 2.677 4.399 0.266 0.952 2.349 30 25010 2019-2-19 37G6 25 28 54°25.4' 16°0.1' 54°26.1' 16°2.5' 12:43 13:13 30 25.069 5.440 8.716 2.306 7.192 0.230 0.339 0.703 0.143 31 25049 2019-2-19 38G5 25 56 54°32.1' 15°45.6' 54°32.1' 15°48.2' 15:33 16:03 30 217.936 87.770 28.746 74.658 21.304 3.193 2.265 32 25042 2019-2-20 38G5 25 53 54°31.6' 15°50.8' 54°31.4' 15°53.4' 12:20 12:50 30 380.224 31.700 303.410 29.339 13.931 1.832 0.012 33 24162 2019-2-21 38G4 24 53 54°40.9' 14°49.5' 54°40.7' 14°52.3' 07:41 08:11 30 353.891 80.210 140.866 71.794 55.990 2.040 1.008 1.940 0.043 34 24150 2019-2-21 38G4 24 47 54°37.6' 14°44.8' 54°37.5' 14°47.5' 15:09 15:39 30 244.112 87.740 131.510 18.315 6.093 0.252 0.196 0.006 35 24055 2019-2-22 38G4 24 36 54°33.4' 14°47.3' 54°33.7' 14°44.8' 07:44 08:14 30 197.791 11.460 152.397 0.433 16.275 14.182 0.666 2.378 Time ofGeographical position of the catch-station start/shoot end Weight of the catch by fish species [kg] ICES | WGBIFS 2019 153 Tab. 2. Fish control-hauls data obtained during r/v Baltica BITS-1Q cruise (12.02-07.03. 2019 r.) (Hauls no. 36-71) lack of oxygen in the bottom -> haul not performed (no oxygen haul) Haul Haul ICES ICES Trawling Trawling number number Catch rectangle Sub-division depth duration Total according to according to date [m] szerokość długość szerokość długość shooting hauling up [min] catch Cod Herring Sprat Flounder Plaice Turbot Hooknose Eelpout Fourbeard Three-spined Lumpfish Short-horn Round Sand Smelt Twaite Whiting Greater Common Perch Small Atlantic Brill Horse Saithe Ruffe Vimba survey order ICES (N) (E) (N) (E) net net [kg] rockling stickleback scorpion goby goby shad sandeel goby sandeel salmon mackerel bream 36 24295 2019-2-22 38G4 24 32 54°33.9' 14°43.3' 54°34.3' 14°40.8' 10:03 10:33 30 32.512 4.115 8.227 0.090 9.251 7.653 0.671 0.387 2.118 37 24004 2019-2-22 37G4 24 21 54°28.4' 14°48.6' 54°29' 14°46.1' 13:17 13:47 30 27.085 12.978 3.391 8.400 0.449 1.867 38 25080 2019-2-23 39G6 25 54 55°24.5' 16°45.2' 55°25' 16°47.5' 12:30 13:00 30 205.283 48.980 142.299 0.867 5.347 2.824 0.196 4.770 39 25229 2019-2-24 39G6 25 75 55°16.7' 16°51.4' 55°16.6' 16°54.1' 09:05 09:35 30 642.619 408.880 26.894 45.958 147.500 10.495 2.384 0.407 0.086 0.015 40 25081 2019-2-24 39G6 25 59 55°23.8' 16°47.6' 55°24' 16°50.2' 15:51 16:11 30 320.664 35.650 273.176 0.379 8.800 1.457 0.390 0.812 41 25247 2019-2-25 39G7 25 69 55°20.8' 17°9.2' 55°20.8' 17°11.8' 07:43 08:13 30 385.499 68.490 226.994 12.754 69.190 7.080 0.677 0.314 42 25231 2019-2-25 39G7 25 74 55°19.8' 17°17.9' 55°19.7' 17°20.6' 10:08 10:38 30 736.684 252.470 252.969 147.631 71.050 11.691 0.873 43 25232 2019-2-25 39G7 25 75 55°19.1' 17°16.1' 55°18.9' 17°18.6' 12:58 13:28 30 631.179 189.270 141.186 210.314 78.460 11.040 0.909 44 25463 2019-2-25 39G7 25 91 55°14.3' 17°15.3' 55°14.5' 17°17.9' 15:45 16:15 30 521.150 156.420 337.760 4.826 22.010 0.134 45 25339 2019-2-26 39G7 25 87 55°15.8' 17°18.8' 55°15.9' 17°21.5' 07:46 08:16 30 614.599 172.480 4.176 50.501 359.930 7.265 19.500 0.319 0.029 0.399 46 25248 2019-2-26 39G7 25 73 55°21.6' 17°24.9' 55°21.6' 17°26.7' 11:42 12:02 20 569.592 121.740 34.622 356.858 51.330 4.384 0.658 47 25084 2019-2-26 39G7 25 64 55°22.9' 17°21.5' 55°23' 17°24.1' 13:23 13:53 30 66.869 21.650 17.570 0.151 24.760 0.477 0.141 2.120 48 25455 2019-2-26 39G7 25 48 55°26.1' 17°13.2' 55°26.6' 17°15.7' 15:30 16:00 30 143.469 88.610 38.940 4.676 1.566 1.680 0.345 7.652 49 25030 2019-2-27 39G7 25 41 55°28.7' 17°26.8' 55°29.1' 17°29.3' 07:42 08:12 30 913.738 21.760 874.890 3.843 2.144 1.692 0.669 8.740 50 25107 2019-2-27 40G7 25 47 55°31' 17°33.8' 55°31.8' 17°36.2' 09:25 09:55 30 1530.814 1.125 452.479 1067.443 2.150 0.267 1.805 0.145 5.400 51 25380 2019-2-27 40G7 25 40 55°37' 17°35.7' 55°38.2' 17°37.4' 11:43 12:13 30 124.383 2.455 111.055 0.423 4.630 1.070 4.750 52 26050 2019-2-27 40G8 26 70 55°38.8' 18°3.7' 55°38.9' 18°4.7' 14:36 14:46 10 783.166 2.425 353.190 421.000 6.551 53 26110 2019-2-28 40G8 26 93 55°36.3' 18°22.4' 55°34.9' 18°23.6' 07:55 08:25 30 5.433 4.050 1.383 54 26164 2019-2-28 40G8 26 88 55°32.3' 18°31.9' 55°31' 18°33.2' 09:48 10:18 30 399.603 284.450 16.360 2.315 95.360 1.014 0.104 55 26286 2019-2-28 40G8 26 98 55°37.7' 18°30.3' 55°37.8' 18°33' 13:41 14:11 30 109.059 77.51 7.22 23.91 0.419 56 26055 2019-3-1 40G8 26 65 55°47.9' 18°6.4' 55°47.3' 18°5.1' 07:49 08:09 20 453.87 28.54 356.849 57.626 10.66 0.195 57 25161 2019-3-1 40G7 25 62 55°53.3' 17°42.4' 55°52.5' 17°44.6' 11:19 11:49 30 502.822 62.4 284.893 152.327 2.518 0.131 0.553 58 25410 2019-3-1 41G7 25 63 56°2.4' 17°44.5' 56°0.9' 17°44.8' 13:56 14:26 30 692.961 267.84 411.108 11.633 1.327 0.753 0.300 59 25038 2019-3-1 41G7 25 52 56°8.9' 17°44.1' 56°8.6' 17°41.5' 16:00 16:30 30 1553.427 4.981 1485.89 7.957 15.59 0.229 0.280 38.500 60 25167 2019-3-2 41G7 25 49 56°16' 17°57.3' 56°16' 18°0' 07:42 08:12 30 136.868 4.931 96.841 0.798 4.536 0.060 0.732 28.970 61 26170 2019-3-2 41G8 26 71 56°10.6' 18°21' 56°11.7' 18°23' 10:28 10:58 30 547.510 486.49 12.552 22.208 26.26 62 26069 2019-3-3 41G8 26 74 56°11.7' 18°25.4' 56°12.5' 18°26.6' 07:45 08:05 20 200.248 173.21 3.875 23.16 0.003 63 26124 2019-3-3 41G8 26 81 56°14.5' 18°29.6' 56°15.8' 18°30.9' 09:49 10:19 30 1366.800 9.47 9.53 1276.933 70.78 0.001 0.086 64 26141 2019-3-4 41G8 26 84 56°18.1' 18°32.8' 56°19.3' 18°34.5' 07:23 07:53 30 11.052 0.307 10.27 0.463 0.012 65 26074 2019-3-4 41G8 26 75 56°23.1' 18°35.2' 56°24.3' 18°36.8' 09:01 09:31 30 101.605 11.652 73.976 15.97 0.007 66 26013 2019-3-4 41G8 26 44 56°22.2' 18°29.4' 56°23.5' 18°30.7' 11:16 11:46 30 296.729 7.761 212.13 17.44 0.755 0.392 1.480 56.770 0.001 67 26224 2019-3-4 41G8 26 37 56°22.3' 18°27.4' 56°22.4' 18°27.5' 13:05 13:07 2 Haul technically unsuccessful (haul repeated) 68 26224 2019-3-4 41G8 26 37 56°22.2' 18°27.3' 56°23.4' 18°28.6' 13:42 14:12 30 44.098 2.955 1.425 19.98 0.758 18.980 69 26225 2019-3-4 41G8 26 42 56°18.9' 18°23.5' 56°20.1' 18°25.2' 15:45 16:15 30 62.094 3.43 1.541 16.19 0.515 0.628 39.790 70 26221 2019-3-6 40G8 26 112 55°55' 18°35.4' 07:35 71 26138 2019-3-6 40G8 26 113 55°53.3' 18°46.3' 55°53.5' 18°43.8' 09:43 10:13 30 8.237 5.875 2.362 Geographical position of the catch-station Time of Weight of the catch by fish species [kg] start/shoot end 154 ICES | WGBIFS 2019 Fig. 6. Horizontal distribution of the seawater temperature, salinity and oxygen content in the near bottom layer during r/v Baltica BITS-1Q cruise (12.02-07.03. 2019 r.). ICES | WGBIFS 2019 155 Fig. 7. Vertical distribution of the seawater temperature, salinity and oxygen content along the hydrological research profile during r/v Baltica BITS-1Q cruise (12.02-07.03. 2019 r.). 156 ICES | WGBIFS 2019 Annex 7: Cruise reports of acoustic surveys BASS and BIAS in 2018 Please see Annex 7 below. ICES | WGBIFS 2019 157 Annex 7: Cruise reports of BASS and BIAS surveys at the WGBIFS 2019 meeting Note: Authors are fully responsible for quality of the prepared text and all kind of pre- sented data. List of cruise reports:  1. Cruise Report of Germany BASS 2018;  2. Cruise Report of Poland BASS 2018;  3. Cruise Report of Lithuania BASS 2018;  4. Cruise Report of Estonia-Poland joint BASS 2018;  5. Cruise Report of Latvia-Poland joint BASS 2018;  6. Cruise Report of Germany BIAS 2018.  7. Cruise Report of Germany BIAS 2018_Summary Table.  8. Cruise Report of Poland joint BIAS 2018;  9. Cruise Report of Lithuania BIAS 2018  10. Cruise Report of Estonia-Poland joint BIAS 2018;  11. Cruise Report of Finland BIAS 2018;  12. Cruise Report of Sweden BIAS 2018;  13. Cruise Report of Latvia BIAS 2018; 158 ICES | WGBIFS 2019 Alter Hafen Süd 2, 18069 Rostock 13.03.2019 E-Mail: paco.rodriguez-tress@thuenen.de Cruise Report FRV ”Solea II” Cruise 747 30.04. – 25.05.2018 Hydroacoustic survey for the assessment of small pelagics in the Baltic Sea Scientist in charge: Paco Rodriguez-Tress (TI-OF) Federal Research Institute for Rural Areas, Forestry and Fisheries Thünen-Institute of Baltic Sea Fisheries Thünen-Institute of Sea Fisheries ICES | WGBIFS 2019 159 2 Summary 1. Introduction ..................................................................................................................................... 3 2. Cruise narrative and methods .......................................................................................................... 3 2.1. Narrative .................................................................................................................................. 3 2.2. Hydrography ............................................................................................................................ 3 2.3. Echosounder calibration and hydroacoustic sampling ............................................................ 4 2.4. Biological sampling ................................................................................................................. 4 2.5. Data analysis ............................................................................................................................ 5 3. Survey results .................................................................................................................................. 6 3.1. Hydrographic data ................................................................................................................... 6 3.2. Acoustic data ........................................................................................................................... 7 3.3. Biological data ......................................................................................................................... 7 3.4. Abundance Estimate ................................................................................................................ 7 4. Survey participants .......................................................................................................................... 8 5. Acknowledgement ........................................................................................................................... 8 6. Literature ......................................................................................................................................... 8 7. Tables .............................................................................................................................................. 9 8. Figures ........................................................................................................................................... 13 160 ICES | WGBIFS 2019 3 1. Introduction Cruise no. 747 of the FRV “Solea II” was conducted as part of the annual ICES Baltic International Acoustic Spring Survey (BASS). The main objective of this hydroacoustic survey is the yearly assessment of small pelagic fishes stock, especially sprat, in the Baltic proper. BASS is co-ordinated at the international level by the ICES Baltic International Fish Survey Working Group (WGBIFS) where timing, surveying area and the principal methods of investigations are discussed and decided. German investigation area in 2018 covered ICES subdivisions 24, 25, 26, 27, 28 and 29 (see Figure 1). Other areas in the Baltic Sea were covered by Estonia, Latvia, Lithuania, Estonia, Poland and Russia. Altogether 1212nmi of valid hydroacoustic transect were recorded and 60 control fishing hauls were carried out during the survey. In addition to the BASS the last days of the cruise, from the 21th to the 24 th May, were used to conduct hydroacoustic experiments in the Bornholm Basin with the aim to recorded additional wideband acoustic signature of clupeids and cod and to study their diel vertical migration. 2. Cruise narrative and methods 2.1. Narrative The scientific gear was loaded on the FRV “Solea II” the 25th April in the harbour of Rostock Marienhe (Germany). Cruise started the 30 th April after the ship left Rostock in the morning. Due to good weather conditions the 30 th April, the day was used to calibrate the echosounder in front of Kühlungsborn, Germany. Acoustic recording for the BASS started in the morning of the 1 st May after reaching the area of investigation in ICES subdivision 24. The Trawl-Eye sensor mounted on the haul broke down the 2 nd May. Fishing operations were stopped for the day as it proved too difficult to target fish in the water column without the system. Hydroacoustic data were still gathered for the day but the ship steamed to the harbour of Sassnitz (Germany) in the evening for technical assistance. The Trawl-Eye system from the FRV “Clupea” was retrieved and installed on the net the 3rd May in the morning and fishing tests were done in the afternoon in the Arkona area. The survey was resumed the 4 th May in the morning and, although one of the two pelagic nets broke while fishing the 7 th , it continued uninterrupted until the 16 th May. Due to the long-time at sea a two days break was done the 17 th and 18 th May in the harbour of Visby, Gotland. The BASS ended the 20 th May in the afternoon north west of Gotland in SD 27. The last days of the cruise were then used to collect wideband echo data of monospecific fish schools and study their diel vertical migration in the Bornholm Basin from the 21 th to the 24 th in the evening, after what the ship steamed back to Rostock. The cruise ended the 25 th May after a total of 17 days of hydroacoustic survey and 3 days of experiments when scientists disembarked in the morning in the harbour of Marienhe, Rostock. Despite some technical difficulties at the beginning of the cruise the good weather conditions allowed to fulfil the main objectives of the survey. 2.2. Hydrography A Seabird-CTD-probe equipped with a carousel water sampler and oxygen sensor was used for hydrographical measurements. Vertical profiles were taken on a fixed station grid along the track. ICES | WGBIFS 2019 161 4 Additional CTD casts were done after or before each trawl if distance from the planned station was high enough (ca. 5 nmi). The profiles covered the entire water column to about 2 m above the sea bottom except on the deepest station were the cable length of the ship was limited to ~320m. Water samples were taken once per day from different depths to check the oxygen data by Winkler titration and to collect reference salinity samples. The hydrological raw data were aggregated to 1 m depth strata. Altogether 237 CTD casts were performed during the cruise following this methodology. 2.3. Echosounder calibration and hydroacoustic sampling The Solea II is equipped with four Simrad EK80 wideband echosounders (34-45, 45-90, 90-160 and 160-260 kHz). Although the BASS was done with a narrowband, 38 kHz frequency setting (pulse length = 1024 µs; pingrate = 500 ms) each transducer were calibrated at a pulse length of 1024, 512 and 256 µs in narrow and broadband mode. Calibration procedure itself was carried out as described in the “Manual for International Baltic Acoustic Surveys (IBAS)” (ICES 2017). In addition to the standard recording at 38 kHz along the transects, the echosounder was set in frequency modulated (FM) mode with a frequency band ranging from 34 to 260 kHz while fishing to gather fish-frequency response data of the catches. As this setting is non-standard for this survey these wideband acoustic data were discarded from the final analysis for the BASS. The acoustic and ichthyologic sampling stratification was based on ICES statistical rectangles (0.5 degree in latitude and 1 degree in longitude). The daily surveyed distance amounted to approximately 90-100 nautical miles with an objective of 60 nautical miles per statistical rectangle. In general each ICES-rectangle was covered with two parallel transects spaced by a maximum of 15-18 nm whenever possible. Ship’s speed was 10 knots during acoustic measurements while fishing operation were conducted at 3 to 3.5 knots. The standard acoustic investigations and the fishing hauls were carried out at daylight from 4:00 - 19:00 UTC (6:00 and 21:00 local time; see Table 1). The survey covered the whole subdivision 24 except the rectangle 37G4 where time constraint, shallow depth restricting fishing operation and partial cover by the Polish EEZ didn’t allow any investigation (see Figure 1). With the exception of rectangle 43G8 (SD 28) -where fishing license were not granted- all rectangles assigned to German investigation in subdivisions 25 to 29 were covered by hydroacoustic transects. For some rectangles, due to time or spatial constrain the total hydroacoustic track length was however lower than the recommended 60 nautical miles (see Table 2). Absence of licence delivery for some specific planned station in the Swedish EEZ by authorities also forced some track changes, especially in rectangle 42G8 (SD 28) were transect was reduced. In total, out of 1521 nmi long acoustic track 1212 nmi were deemed valid and used in the further biomass estimation analysis. 2.4. Biological sampling Trawling was done with the pelagic gear “PSN388” in the midwater as well as near the bottom to identify the echo signals. The aim was to conduct at least two fishing hauls per ICES statistical rectangle. The trawling time lasted usually 30 minutes at a speed of 3 to 3.5 knots. The fishing time was however decreased in case of abundant catch observed with the Trawl Eye net-probe. In accordance to the IBAS manual cod end inlets with stretched 20 mm mesh sizes in Subdivision 24 and 12 mm in Subdivision 25 to 28 were used. While this setting was respected for most of the survey, net 162 ICES | WGBIFS 2019 5 damage and replacement the 6 th May (haul n°12) forced to revert back to a 20 mm codend for the day although still fishing in SD 25 (stations concerned: haul n°13, 14 and 15). The 12 mm codend was then available again for fishing the 7 th May for the rest of the survey. The trawling depth and the net opening were controlled by a Scanmar-net-probe. Generally the net opening was of ca. 8 m under usual operation. The trawl depth (headrope below the surface) was chosen regarding highest density of fish on the echogram and ranged from 10 m to 75 m. The bottom depth at the trawling positions varied from 21 m to 445 m. Samples were taken from each haul in order to determine the length and weight distribution of fish. Sub-samples of cod, herring and sprat were done to investigate sex, maturity and age of the catches. Samples of whole fishes and parts of different organs/tissues were also taken for later investigations in the laboratory. Detailed biological analyses were made according to the standard procedure (i.e. sex, maturity, otolith dissection). In total 60 standard hauls (59 valid) were carried out for the BASS: Subdivision Hauls (n) 24 8 25 19 26 4 27 8 28 13 29 8 Altogether 39816 fish were measured and 1962 additional fish (773 sprats and 1189 herrings) were sampled for further age determination 2.5. Data analysis The pelagic target species sprat and herring are usually distributed in mixed layers and in combination with other species so that the echo integration readings cannot be allocated directly to a single species. Therefore, the species composition used for the conversion of echo integrals into fish abundance was based on trawl catch results accordingly. For each rectangle the species composition and length distribution was determined as the unweighted mean of all trawl results in this rectangle. In case of missing hauls within an individual ICES rectangle (due to gear problems or other limitations), hauls results from neighbouring rectangles was used. From these distributions, the mean acoustic cross section σ was calculated according to the following target strength-length (TS) relations:  Clupeids/Gasterosteus aculeatus: TS = 20 log L (cm) - 71.2 (ICES 1983)  Gadoids: TS = 20 log L (cm) - 67.5 (Foote et al. 1986) The total number of fish (total N) in one rectangle was estimated as the product of the mean nautical area backscattering coefficient (i.e. echo integral) (Sa in m²/n.mi.²) and the rectangle area (n.mi.²), divided by the corresponding mean cross section. The total number of fish was separated into herring, sprat and cod according to the mean catch composition. In accordance with the guidelines in the ‘Manual for the Baltic International Acoustic Surveys (ICES 2017)’, the further calculation was performed in the following way: ICES | WGBIFS 2019 163 6 Species with an overall mean contribution to all sampled hauls of less than one percent are excluded from further total species frequency calculation. Fish species considered in this report are thus (see results for catch statistics):  Clupea harengus  Gadus morhua  Gasterosteus aculeatus  Sprattus sprattus Hauls with low level of catch and/or non-representative species compositions were excluded from analysis. This includes the following hauls:  Haul n°11; 40G4/SD25: only 0.4 kg catch  Haul n°12; 39G5/SD25: codend damaged while fishing Although haul n°13, 14 and 15 were performed with bigger mesh size that recommended by the IBAS manual for subdivision 25 it was decided to keep the catch data from these hauls for the further analysis as no obvious effect on the species and length composition was observed. Usage of neighbouring trawl information for investigated rectangles which contain only one or no haul:  Haul n°3: 39G3/SD24 for 38G2/SD24  Haul n°3: 39G3/SD24 for 39G2/SD24  Haul n°4: 38G3/SD24 for 39G3/SD24  Haul n°6: 38G4/SD24 for 39G4/SD24  Haul n°8: 39G4/SD24 for 39G4/SD25  Haul n°8: 40G4/SD25 for 39G4/SD25 Final results will be compared to those of the BASS 2017 or other previous surveys when relevant. 3. Survey results 3.1. Hydrographic data Measurements showed a regular stratification of the water column during the survey. Temperature, Salinity and Oxygen profile are represented in Figure 2. Seawater temperature ranged from 14.9 °C at the surface to 2.0°C (recorded at 22.5 m depth). At the deepest CTD recording of the survey (309.5 m) temperature was measured at 6.3°C. Overall intermediate water masses (depth ranging from 6.5 to 74.0 m) presented temperature below 4°C, which is considered as a temperature threshold limit for the distribution of sprat in the water column, while higher temperature were recorded above and below this stratum. Measured salinity ranged from 5.2 psu at the surface layer up to a maximum of 17.9 psu at the bottom of the Bornholm. Regarding oxygen, concentration ranged from 5 to 13 mL.L -1 in the intermediate water mass and dropped below 1 mL.L -1 under this layer. Overall hypoxic conditions (<1.4 mL.L -1 , ~30% atmospheric saturation) were observed below 70 m depth all along the survey. No fish echoes were usually observed under these conditions (Figure 3). 164 ICES | WGBIFS 2019 7 3.2. Acoustic data The basic hydroacoustic results are given in Table 3 (survey area, mean Sa, mean scattering cross section σ, estimated total number of fish and percentage of herring and sprat per rectangle). The valid measured cruise track reached a distance of 1212 nautical miles. Overall mean NASC recorded through the survey is lower than previous year with a mean NASC of 439.2 m²/nm² versus 597.6 m²/nm² in 2017 were a similar ICES rectangles were covered. On an ICES subdivision scale the mean NASC per subdivision were comparable to those recorded in the past 10 years with the exception of SD26 were values were the highest of the decade (Figure 4). Mean NASC recorded in the subdivision SD26 were also relatively high in 2017. Map of the echo distributions (Figure 5) shows heterogeneous fish concentration along the hydroacoustic track. 3.3. Biological data Catch statistics per fishing hauls and species and subdivision are presented in Table 4 and Table 5 respectively. Overall 9 fish species were recorded in 60 pelagic trawl hauls. Dismissing the invalid hauls, the CPUE ranged from 3.2 to 394.7 kg/0.5h. The mean CPUE reached 76.7 kg/0.5h, which is sensibly lower than the value calculated in the 2017 survey (286.7 kg/0.5h) but could be due to the difference in fishing gear. In terms of weight, catch was dominated by sprat (77.9%) followed by herring (17.1%) and stickleback (3.8%). Those three species were caught on the majority of the trawls through the survey, in respectively 55, 55 and 47 hauls. The numbers and biomass of species other than herring, sprat and stickleback was negligible. Figure 6 show the length frequency distribution for sprat and herring per subdivision in 2017 and 2018. Overall, with the exception of herring in SD 24, length distribution of clupeids tended to be bigger than observed during the BASS 2017. Age distribution per length class is presented in Figure 7. Final age distribution by subdivision for 2018 (Figure 8) was calculated according to the minimum effort method by multiplying the length frequency distribution with the age distribution per length class as recommended in the IBAS Manual (2017: eq 5.3.1). As shown in Figure 8, for both sprat and herring and with the exception of SD 24, most of the individuals were in the 4 years age class. Incoming year class represented by 1 year old individuals was mostly comparable or lower (especially for sprat) in 2018 compared to 2017. 3.4. Abundance Estimate The calculated abundance in number and weight of sprat and herring per rectangle and subdivision is presented in Table 6. Estimated abundances in all overlapping rectangle for herring and sprat are lower in 2018 compared to 2017 with respectively 3.99*10 9 versus 7.11*10 9 herrings (-44%) and 59.87*10 9 versus 85.38*10 9 sprats (-30%). Estimated biomass is also lower in 2018 for herring with 111.60*10 3 tonnes versus 170.18 *10 3 tonnes estimated in 2017 (-34%). Estimated biomass of sprat was again lower in 2018 with 661.62*10 3 tonnes versus 725.91*10 3 tonnes in 2017(-8%). Year Species n total (million) total biomass (tonne) 2017 Clupea Harengus 7106.8 170178.1 2018 3990.1 111596.0 2017 Sprattus sprattus 85382.7 725911.0 2018 59867.5 661615.2 ICES | WGBIFS 2019 165 8 4. Survey participants Name Function Institution P. Rodriguez-Tress Scientist in charge TI-OF B. Lüdke Acoustics TI-SF L. Wietrzinsky Fishery biology TI-OF K. Shöps Fishery biology TI-OF M. Bächtiger Fishery biology TI-OF (student assistant) N. Köstner Fishery biology TI-OF (student assistant) S. Winning Fishery biology TI-OF (student assistant) 5. Acknowledgement We hereby thank all participants, the crew of FRV “Solea” and Captain V. Koops for their outstanding cooperation and commitment. 6. Literature ICES 1983: Report of the Planning Group on ICES co-ordinated herring and sprat acoustic surveys. ICES CM 1983/H:12. ICES. 2017. Manual for the International Baltic Acoustic Surveys (IBAS). Series of ICES Survey Protocols SISP 8 - IBAS. 47 pp. http://doi.org/10.17895/ices.pub.3368 Foote, K.G., Aglen, A. and Nakken, O. 1986. Measurement of fish target strength with a split-beam echosounder. Journal of the Acoustical Society of America, 80(2): 612-621. 166 ICES | WGBIFS 2019 9 7. Tables Table 1: FRV “Solea” cruise 747/2018 BASS: Start and end time of hydroacoustic recording during the cruise. Date recording start time (UTC) recording end time (UTC) Date recording start time (UTC) recording end time (UTC) 01.05.2018 04:10 16:40 11.05.2018 04:13 18:15 02.05.2018 04:12 17:21 12.05.2018 04:36 18:10 04.05.2018 04:00 16:40 13.05.2018 04:19 17:31 05.05.2018 04:10 17:56 14.05.2018 04:01 18:44 06.05.2018 04:04 17:30 15.05.2018 04:03 17:22 07.05.2018 04:01 18:25 16.05.2018 04:06 18:53 08.05.2018 04:01 17:55 19.05.2018 04:17 17:36 09.05.2018 04:04 18:49 20.05.2018 04:08 11:49 10.05.2018 04:03 18:34 Table 2: FRV “Solea” cruise 747/2018 BASS: Hydroacoustic track length per ICES rectangle. Subdivision ICES rectangle Valid acoustic track length (nmi) Subdivision ICES rectangle Valid acoustic track length (nmi) 24 37G4 0 25 41G7 69 24 38G2 17 26 40G8* 21 24 38G3 46 26 41G8 54 24 38G4 58 27 42G7* 2 24 39G2 15 27 45G8 43 24 39G3 68 27 46G8 39 24 39G4 28 28 42G8 56 25 38G5* 10 28 42G9 42 25 39G4 21 28 43G8 0 25 39G5 44 28 43G9 61 25 39G6* 29 28 44G9 56 25 40G4 44 28 45G9 38 25 40G5 54 29 46G9 44 25 40G6 53 29 46H0 22 25 40G7 58 29 47G9 45 25 41G6 51 29 47H0 24 *ICES rectangle not assigned to German investigation ICES | WGBIFS 2019 167 10 Table 3: FRV “Solea” cruise 747/2018 BASS: Survey statistics of the cruise Subdivision Rectangle area (nmi²) Sa (m²/nmi²) sigma (m²) (*10e-4) n total (million) Clupea harengus (%) Sprattus sprattus (%) Gadus morhua (%) 24 38G2 832.9 270.6 1.612 1398.15 3.75 96.11 0.110 24 38G3 865.7 532.9 1.824 2529.22 0.84 99.16 0.000 24 38G4 1034.8 225.1 1.639 1421.19 2.68 97.32 0.000 24 39G2 406.1 146.9 1.699 351.12 3.77 96.18 0.030 24 39G3 765.0 125.4 1.754 546.92 2.20 97.74 0.030 24 39G4 524.8 164.3 1.647 523.52 2.60 97.40 0.000 25 39G4 287.3 350.3 1.961 513.21 25.39 74.61 0.000 25 39G5 979.0 695.5 1.521 4476.62 0.24 99.46 0.290 25 40G4 677.2 236.0 1.260 1268.40 24.23 25.92 0.000 25 40G5 1012.9 186.9 1.116 1696.33 1.12 65.44 0.050 25 40G6 1013.0 689.7 1.341 5210.03 4.93 76.25 0.270 25 40G7 1013.0 995.3 1.365 7386.36 0.23 98.56 0.000 25 41G6 764.4 510.3 0.370 10542.52 0.48 2.07 0.000 25 41G7 1000.0 218.2 0.724 3013.81 0.04 30.61 0.000 26 41G8 1000.0 826.9 1.272 6500.78 0.08 99.34 0.040 27 45G8 947.2 395.5 1.257 2980.25 13.59 75.33 0.020 27 46G8 884.8 494.2 1.504 2907.36 28.92 68.85 0.050 28 42G8 945.4 526.2 1.097 4534.81 0.75 75.24 0.020 28 42G9 986.9 659.7 1.237 5263.20 0.90 97.83 0.040 28 43G9 973.7 213.3 1.289 1611.25 5.09 91.66 0.110 28 44G9 876.6 259.7 1.188 1916.27 2.65 92.71 0.030 28 45G9 924.5 262.3 1.304 1859.63 7.54 91.40 0.080 29 46G9 933.8 285.6 1.369 1948.08 15.12 84.52 0.010 29 46H0 933.8 278.6 1.289 2018.28 10.31 89.38 0.000 29 47G9 876.2 605.9 1.224 4337.33 9.94 89.04 0.010 29 47H0 920.3 527.3 1.362 3562.95 14.28 85.65 0.010 168 ICES | WGBIFS 2019 11 Table 4: FRV “Solea” cruise 747/2018 BASS: Catch statistics per fishing haul. Haul n° Catch weight (kg) Fish number (n) CPUE (kg/0.5 hr) Haul n° Catch weight (kg) Fish number (n) CPUE (kg/0.5 hr) 1 8.0 605 8.0 31 38.2 4345 57.3 2 10.9 730 10.9 32 90.5 10768 135.8 3 31.5 1822 31.5 33 10.8 1600 11.2 4 87.0 5611 87.0 34 12.6 1738 13.0 5 78.0 4517 78.0 35 33.2 3974 41.5 6 5.3 390 5.3 36 48.1 5798 48.1 7 139.5 9749 139.5 37 43.6 5173 43.6 8 10.7 830 10.7 38 54.0 6113 55.8 9 73.7 3054 73.7 39 50.0 5620 51.8 10 13.2 10168 13.2 40 36.8 3734 36.8 11* 0.4 290 0.4 41 39.2 5090 49.1 12* 141.4 14047 176.8 42 49.1 5886 50.8 13 357.1 32901 357.1 43 147.5 16859 147.5 14 72.5 5887 108.7 44 30.2 2995 31.2 15 9.1 6581 9.1 45 62.7 6537 62.7 16 83.5 7838 167.0 46 105.2 10407 166.1 17 66.4 5525 99.6 47 127.3 13111 131.7 18 112.2 10056 168.3 48 71.7 9328 86.1 19 263.1 26645 394.7 49 127.2 13524 200.8 20 33.7 19368 33.7 50 124.1 11563 128.4 21 3.2 1504 3.2 51 93.0 9625 93.0 22 21.1 7895 21.1 52 220.8 24095 220.8 23 12.1 1186 10.6 53 113.9 12231 117.8 24 56.4 4690 56.4 54 34.3 4720 34.3 25 52.7 21334 52.7 55 118.0 11182 122.1 26 13.3 5963 13.3 56 66.0 6453 68.3 27 24.9 2792 24.9 57 53.2 5527 55.0 28 28.1 3405 28.1 58 89.0 7257 92.0 29 44.1 4826 44.1 59 166.3 12611 172.0 30 46.2 5484 69.3 60 86.9 9536 89.9 * invalid haul ICES | WGBIFS 2019 169 12 Table 5: FRV “Solea” cruise 747/2018 BASS: Catch statistics per species. Species No. of hauls with the species No. Of length measurements No. Of individaul measurements Total catch (kg) Percent of total catch weight Overall mean contribution to all sampled hauls (%) CLUPEA HARENGUS 55 11302 1180 705.259 16.68 6.88 GADUS MORHUA 31 202 186 39.794 0.94 0.1 GASTEROSTEUS ACULEATUS 47 2769 0 141.699 3.35 17.26 HYPEROPLUS LANCEOLATUS 2 2 0 0.033 0 0.02 MERLANGIUS MERLANGUS 6 16 0 3.471 0.08 0.18 PLATICHTHYS FLESUS 18 31 0 4.724 0.11 0.03 RHINONEMUS CIMBRIUS 1 1 0 0.155 0 0.01 SCOMBER SCOMBRUS 1 3 0 0.608 0.01 0.01 SPRATTUS SPRATTUS 55 24932 754 3333.344 78.82 83.74 Table 6: FRV “Solea” cruise 747/2018 BASS: Total number and biomass of sprat and herring per rectangle. Subdivision ICES rectangle n herring (million) Herring biomass (tonne) n sprat (million) Sprat biomass (tonne) 24 38G2 52.49 3467.23 1343.73 22836.69 24 38G3 21.35 1397.46 2507.89 42257.95 24 38G4 37.88 1597.12 1383.06 23975.35 24 39G2 13.23 824.59 337.69 5772.39 24 39G3 12.04 816.81 534.59 8726.80 24 39G4 13.56 598.23 509.90 8761.99 25 39G4 130.10 4917.94 382.45 4600.33 25 39G5 10.88 441.29 4452.59 52241.60 25 40G4 306.89 10824.01 328.72 3817.85 25 40G5 19.03 647.97 1110.05 13089.08 25 40G6 256.60 8814.85 3972.91 44882.53 25 40G7 16.63 584.40 7280.05 81494.96 25 41G6 50.40 1682.48 218.63 2434.60 25 41G7 1.14 53.66 922.45 10647.71 26 41G8 5.12 195.06 6458.11 56088.69 27 45G8 404.90 10438.32 2244.93 22645.73 27 46G8 840.84 21867.10 2001.68 20352.08 28 42G8 33.92 1013.05 3411.91 35987.12 28 42G9 47.29 1310.05 5148.83 53116.62 28 43G9 81.95 2250.45 1476.79 15157.40 28 44G9 50.80 1398.97 1776.52 18307.04 28 45G9 140.21 3688.05 1699.73 17415.86 29 46G9 294.63 6988.26 1646.50 15359.79 29 46H0 208.07 4649.58 1803.95 16950.37 29 47G9 431.19 9622.54 3862.17 35971.29 29 47H0 508.94 11506.50 3051.62 28723.37 170 ICES | WGBIFS 2019 13 8. Figures Figure 1: FRV "Solea" cruise 747/2018 BASS: Hydroacoustic track (purple line) and fishing hauls (red line) done during the BASS survey 2018. ICES | WGBIFS 2019 171 14 Figure 2: FRV "Solea" cruise 747/2018: Temperature (upper right panel), oxgen (middle right panel) and salinity (lower right panel) interpolated from CTD casts along a south/west - north/east transect as shown in the left panel (red line). CTD casts coordinates are display as blue dots on the map in the left panel. 172 ICES | WGBIFS 2019 15 Figure 3: FRV "Solea" cruise 747/2018: Vertical distribution of salinity, temperature and oxygen related to the echogram of fish (blue clouds). ICES | WGBIFS 2019 173 16 Figure 4 : FRV "Solea" cruise 747/2018: Mean NASC calculated per year and per subdivision (red bar correspond to 2018). 174 ICES | WGBIFS 2019 17 Figure 5: FRV "Solea" cruise 747/2018 BASS: hydroacoustic results: NASC (m²/nm²) per 1 nmi recorded during the survey. ICES | WGBIFS 2019 175 18 Figure 6: FRV "Solea" cruise 747/2018 BASS: Herring and sprat length distribution measured per ICES subdivision during BASS 2017 (black line) and BASS 2018 (bars). 176 ICES | WGBIFS 2019 19 Figure 7: FRV "Solea" cruise 747/2018 BASS: Age distribution per length class, species and subdivision for 2018. ICES | WGBIFS 2019 177 20 Figure 8: FRV "Solea" cruise 747/2018 BASS: Calculated age class distribution per species and subdivision in 2018. 178 ICES | WGBIFS 2019 1 Working paper on the WGBIFS meeting in Klaipeda (Lithuania) 25-29.03.2019 Research report from the Polish part of the Baltic Acoustic Spring Survey on board of the r.v. “Baltica” (02-13.05.2018) Beata Schmidt and Włodzimierz Grygiel National Marine Fisheries Research Institute, Gdynia (Poland) INTRODUCTION The autumn acoustic-biotic surveys in the Baltic were realised much early back in time and most frequently, than the May acoustic surveys. The acoustic surveys in October has been carried out in the Baltic Proper since 1978, however on the very beginning as the Swedish-German (GDR) cruise, not fully coordinated by the ICES (Håkansson et al. 1979, Hagström et al. 1989). The spring acoustic-biotic survey in Baltic proper was inaugurated in May 1978 by the Latvian-German (GDR) scientific team on board of the r.v. “Zvezda Baltiki” (Shvetsov et al. 1986, 1992). In the next several years, both countries dominated in accomplishment of May acoustic surveys. The initial Polish acoustic survey in the southern Baltic was conducted in July 1981, on board of the r.v. “Profesor Siedlecki” (Orłowski 1982, 1991). In October 1982, the National Marine Fisheries Research Institute (NMFRI) began simultaneous the acoustic, biological and fisheries investigations of herring and sprat stocks size and distribution, mostly in the southern Baltic (Grzebielec et al. 1995). The above-mentioned survey can be accepted as the beginning of somewhat regular autumn acoustic surveys in the Polish EEZ. The above-mentioned Polish research institute began the spring acoustic surveys in May 1983 (Elwertowski and Orłowski 1984, Elwertowski et al. 1984). In the 1980s, the NMFRI contribution to those surveys was limited to chartering of commercial stern cutter the m/t “HEL-100”, which was designated for fish control-hauls realization. Moreover, the NMFRI delegates participated in several acoustic surveys on board of the Swedish r.v. “Argos” (Hagström et al. 1989). Sporadically, also the Polish r.v. “Profesor Siedlecki” participated in the Baltic acoustic surveys (May 1985, October 1989 and 1990). In the 1980s and at the beginning of 1990s, the ICES Planning Group for Hydroacoustic Surveys in the Baltic with close cooperation of the ICES Working Group on Assessment of Pelagic Stocks in the Baltic were responsible for logistically coordination of international acoustic surveys (Anon. 1991a) and implementation of collected international data to the final assessment of Baltic sprat and herring stocks biomass (Anon. 1991b). Since 1994, the permanent participation of the Polish r.v. "Baltica", managed by the NMFRI in Gdynia, has took place in the framework of the ICES Baltic International Acoustic Surveys (BIAS) long-term programme. Poland join again the international spring acoustic-biotic surveys relatively late in time, i.e. in May 2017 (Kruk et al. 2018). The reported May/2018 survey is the second in order Polish survey realised in the framework of the Baltic Acoustic Spring Survey programme (BASS). The ICES Baltic International Fish Survey Working Group (WGBIFS) coordinates methods of investigations, timing of surveys, spatial allocation of vessels and general pattern of pelagic control-hauls distribution in the Baltic, regarding both types of acoustic surveys, i.e. BASS and BIAS. The above-mentioned working group is also responsible for the compilation of international results needed for assessment of clupeids stocks size in the Baltic. The set of input data and recommendations are next transferred to the ICES Baltic Fisheries Assessment Working Group [WGBFAS] for final evaluation of fish stocks size. The reported Polish BASS/2018 survey was conducted on board of the r.v. “Baltica” inside the Polish EEZ, in the period of 02-13 May 2018. The survey was focused on monitoring of clupeids and cod spatial-seasonal distribution in pelagic zone of the southern Baltic (parts of the ICES Subdivisions 25 and 26), giving high priority to assessment of sprat spawning stock size and distribution. The BASS survey was carried out in the season of herring initial phase of intensive feeding and sprat and cod spawning time in the southern Baltic. ICES | WGBIFS 2019 179 2 The acoustic system EK60 SIMRAD with the new determined calibration parameters were applied to completing the BASS survey tasks. The Polish Fisheries Data Collection Programme for 2018 and the European Union (the Commission Regulations Nos. 1639/2001, 1581/2005, 665/2008, 1078/2008, 2008/949/EC, 2010/93/EU) financially and logistically supported the Polish BASS survey marked with internal No. 7/2018/MIR-PIB. The WGBFAS will use recently collected the BASS data for tuning clupeids stock biomass assessment and spatial distribution based on the data from commercial catches. The acoustic estimates are, until present time, the commercial fishery independent source of input data available to the WGBFAS. The main goal of current paper is a brief description of result of analysis focused on sprat, herring and cod stocks size changes and their spatial distribution as well as the CPUE variation within the Polish part of the southern Baltic at spring 2018. Moreover, the paper contains description of sprat, herring and cod some biological parameters variation. The principal hydrological parameters fluctuation in the water column of the southern Baltic are also described. MATERIAL AND METHODS Research team personnel The main research tasks of the Polish BASS/2018 survey on board of the r.v. "Baltica" were realized by the NMFRI (Gdynia) nine members of the scientific team, with Kordian Trela as a cruise leader. The group of researchers was composed of: Beata Schmidt – hydroacoustician, Julia Gutkowska – intern, sprat analyses, Grzegorz Modrzejewski – technician, sprat analyses, Wojciech Deluga – technician, herring analyses, Stanisław Trella - technician, herring analyses, Zuzanna Mirny - ichthyologist, cod and other fish species analyses, Ireneusz Wybierala – technician, cod and other fish species analyses, Anetta Ameryk – hydrologist. The course of the cruise The r.v. “Baltica” left the Gdynia port on 02.05.2018 at 06:00 a.m. and was navigated in the south-eastern direction, where at the mouth of the Vistula River a successful calibration of the acoustic system SIMRAD EK60, installed on the vessel, was carried out. On 02.05.2018 at the evening, the ship was directed to the start point of a planned acoustic transects above the Gdansk Deep (Fig. 2). The acoustic integration started on the 3rd of May 2018 at about 7 a.m. and it finished on the 12th May 2018 in west part of Polish EEZ. The r.v. “Baltica” returned to the Gdynia port on the 13th of May 2018 around 9 a.m. Any strong winds and the stormy days not appeared during reported BASS survey. Survey design and realization – sampling description The ICES statistical rectangles, designated by the ICES-WGBIFS as mandatory to Poland, were full covered with the standard acoustic-biotic researches (Fig. 2). However, because of very limited survey time, the echosounding could not be performed in the 38G4 ICES rectangle (ICES SD 24), which as optional was allocated to Poland (ICES, 2018). The SIMRAD EK-60 version 2.2.0, a split beam scientific echosounder, linked with the GPT transceivers, operating at 38 and 120 kHz frequencies, as in the previous years, was used in the recent Polish BASS 2018 survey. Calibration of the vessel’s acoustic system was performed on 02nd of May 2018 at following location: λ = 019°11.8'E and φ = 54°27.6'N over seabed depth of 65 m (Fig. 2). The echosounder calibration was performed as described in Simrad (2012) using copper spheres of diameters 60mm and 23mm for 38kHz and 120kHz frequency respectively as reference targets. Calibration results obtained in May 2018 were considered as good for 38 kHz 180 ICES | WGBIFS 2019 3 (RMS=0.18) and acceptable for 120 kHz (RMS=0.38). Resulting transducer parameters were applied for consecutive data-collection and post-processing of hydroacoustic survey data. Calibration results for the 38 kHz transducer are given in Fig. 1. The acoustic sampling was performed along the pre-selected acoustic transects on the distance of 734 NM. The echo-integration data were collected in a daytime regime at the ship speed of 7 kn. Because of historical comparability of data, pre-selected echo-integration transects were planned in a similar pattern as was in the recent years, i.e. since the autumn 2013 BIAS survey, when transects were reshaped comparing with the period of 2009-2012. A fragment of shallow southern parts of the Polish marine waters was omitted from the investigations. The settings of the hydroacoustic equipment were as described in the IBAS Manual (ICES, 2017). The post processing of the stored raw data was done using the Echoview software (www.echoview.com). Only 38 kHz transmitter’s data were taken into further processing because that frequency is recommended for fish trace recording. In the first step of acoustic data checking, all visible interferences from the sea surface turbulences and bottom structures visible on echogram were excluded from further analysis. The minimum threshold on mean volume backscattering strength Sv was set to -60 dB. Calculation of parameter SA [m 2NM-2] (hereinafter called NASC) for 1 nautical mile elementary standard distance units (ESDUs) was carried out by integrating Sv values (in linear domain) from 10 m below the surface to about 0.5 m over the seafloor and then averaged it within 1 NM interval. Than the mean NASC (Nautical Area Scattering Coefficient) per ICES rectangles were calculated. Overall 25 catch-stations (11 in the ICES SD 25 and 14 in the ICES SD 26) were conducted by the r.v. “Baltica” in spring of 2018 (Fig. 2, Table 3), using the herring small-meshed pelagic trawl type WP53/64x4, with 6 mm mesh bar length in the codend (Table 3). All control-catches were accepted as representative from technical point of view. The trawling depth was chosen in accordance with echo distribution on the echogram. Because of a relatively high vertical opening (up to 20 m) of applied a pelagic trawl and the technical-acoustics disturbances from a set vessel- trawl, the areas shallower as 30-m were not controlled with the catch-stations. The trawling time for most hauls was 30 minutes, however it was shortened when echogram and net-sounder indicated large concentration of fishes in the area of operating a fishing gear. In the cases of two- layer fish concentrations appearing, the net was used for 15 minutes in each layer. The mean speed of surveying vessel during trawling was ranged from 3.1 to 3.5 knots. Fish catches were localized on the depth ranged from 6 to 70 m from the sea surface (position of the headrope). Depth to the bottom at trawling positions varied from 35 to 110 m. Fish caught in each control-haul was separated by species and weighted. The results of catch per unit effort of dominated fish species and their average share in the r/v “Baltica” pelagic catches are presented in Table 3 and Figs. 5-7. The samples for sprat, herring and cod were taken for length and mass measurements and ageing. Fish total length distribution (Fig. 8) and the mean mass were determined at the 0.5-cm classes - in the case of clupeids and 1-cm classes in the case of cod. The numerical share of juvenile, undersized (below minimum landing/protective size) sprat, herring and cod in samples was determined (Table 4) based on fish length distribution results. For sprat the minimum commercial size (the separate length) is equal to 10.0 cm, for herring is equal to 16.0 cm and for cod is 35.0 cm. Detailed ichthyological analyses were made according to standard procedures (Anon., 2012), directly on board of surveying vessel. Overall, 25, 25 and 13 samples were taken for the length and mass determination of sprat, herring and cod, respectively. Totally, the length and mass were measured for 5318 sprat, 1285 herring and 545 cod individuals. Respectively, 598, 583 and 129 individuals of the above-mentioned species were biologically analysed (sex, maturity, stomach fullness and age). Before each haul and at the standard hydrological stations located within the Polish EEZ, the seawater temperature, salinity and oxygen content were measured continuously from the sea surface to the seabed. Totally, 39 hydrological stations were inspected using the CTD IDRONAUT probe combined with the rosette sampler. Oxygen content was determined by the standard Winkler’s method. The hydrological row data, aggregated to the 1-m depth stratums, were ICES | WGBIFS 2019 181 4 information source about the abiotic factors potentially influencing fish’s spatial distribution. The basic meteorological parameters i.e. air temperature, air pressure, wind direction and force, and sea state were registered at the each catch-station location with the automatic station MILOS 500. Data analysis Due to herring and sprat normally cannot be distinguished from other species by visual inspection of the echogram, species composition and fish length distributions from trawl catch results are used to aid acoustic species identification. Such data analysis is sectioned according to the ICES statistical rectangles. For each rectangular, based on trawl results performed within, the share of all fish species numbers and its length distribution, as the unweighted mean, were calculated. Our intention was to carry out at least two control-hauls per ICES rectangle, according to the guidelines in the “SISP Manual of International Baltic Acoustic Surveys (IBAS)” (ICES, 2017). However, during BASS cruise in 2018, in rectangles 37G5, 39G9 and 37G8 only one haul per rectangle was performed. In such cases, the haul made in an adjacent rectangular in similar hydrology condition and resulted with similar species share and length distribution were included into analysis in given rectangle. In this way, haul No. 5 and haul No. 10 were included into analysis in ICES rectangles 37G8 and 39G9 respectively. However analysis in ICES rectangle 37G5 were based on only one haul (the nearest haul in 38G5 rectangle were performed in different hydrological condition, and was assumed as unrepresentative for shallow 37G5 ICES rectangle). In case when the mean numerical share of sprat herring and cod in ICES rectangle exceeded 99%, other species were excluded from further calculations. Based on species distributions the mean acoustic cross section  was calculated according to the following target strength-length (TS) relation: TS References Clupeoids = 20 log L (cm) - 71.2 ICES 1983 Gadoids = 20 log L (cm) - 67.5 Foote et al. 1986 The total number of fish in each the ICES rectangle was estimated as a product of the mean NASCs from scrutinized acoustic data and a rectangle area, divided by the corresponding mean acoustic cross-section . Clupeids abundance was separated as sprat or herring according to their mean share in control-catches of given the ICES rectangle. RESULTS Acoustic results The spatial distribution of mean NASC values (5 NM intervals), predominantly derived from clupeids, measured on hydroacoustic transects during BASS 2018 survey is presented on Fig. 3. The highest NASC values were recorded in SD26 (in the Gdańsk Deep and the southern part of the Gotland Deep ), and in the area of the Slupsk Furrow in SD25. Overall NASC values recorded in the Polish EEZ during BASS 2018 survey remains at a similar level as recorded during BASS 2017 cruise (Kruk et al., 2018). However differences in mean NASC values on ICES subdivisions and rectangles scales exist (Tables 1, 2). The mean NASC values per ICES subdivisions presented in Table 1 were calculated with use of areas of ICES rectangles as weight. Also for comparison reasons, presented mean NASC for in the ICES SD25 (BASS 2017) was calculated without the ICES rectangles 39G5 and 40G7, because in May 2018 mentioned rectangles were acoustically not inspected. In 2018, the mean NASC values in SD25 increased by about 50% comparing to 2017, while in SD26 it decreased by about 20%. Similar to 2017, during BASS 2018 survey, the highest NASC values were recorded in SD26, in waters with a depth above 50 m - in rectangles 39G9, 40G8 and 39G8 – where mean NASC values per rectangle reached the value 2408.6, 1506.2 182 ICES | WGBIFS 2019 5 and 1477.1 m2NM- 2 respectively. The highest NASC value per 1 NM equal to 6148 m2NM-2 was recorded in rectangle 39G8 (Fig. 4). The high integration values were also obtained for the southern part of the Gulf of Gdansk (rectangles 37G8 and 37G9). In SD25, comparing to previous year, the highest increase in the NASC value was recorded in the shallow waters, i.e. in rectangle 38G7 – five-fold increase in NASC value, and in rectangle 38G6 – two-fold increase. Fish catches, biological parameters and stocks size In May 2018, overall, nine fish species were recorded in 25 scrutinized pelagic control- hauls taking place in the Polish parts of the ICES Subdivisions 25 and 26 (Table 3, Fig. 2). Totally, 9467.4 kg of fish in 25 hauls were caught, and the mean share of sprat, herring, cod and all other species was adequately, 95.5: 2.5: 1.8 and 0.2%. Sprat distinctly dominated by mass in control- hauls, and herring as well as cod can be considered as a significant bycatch in accomplished hauls (Table 3, Figs. 5-7). From the remaining fish species only flounder with total catch of 15.1 kg in the entire study area was remarkable as component of bycatch. Sprat and herring occurred in each pelagic control-haul and cod in 52% of hauls number. Any sea-mammals and any sea-birds wasn’t detected in the control-catches. In the ICES Subdivision 26, sprat was dominated by the total mass (4862.9 kg), the mean CPUE (1144.4 kg h-1) and the mean share (97%) in 14 hauls realised inside the Polish part of the mentioned subdivision. The above-mentioned exploitation parameters were somewhat lower for sprat caught in the ICES Subdivision 25, where amounted 4178.4 kg, 782.8 kg·h-1 and 94%, respectively in 11 hauls. Sprat highest CPUE was obtained in a few single research catches conducted, e.g.: on the border between the Gulf of Gdansk and the Gdansk Deep (3742.4 kg h-1), in the south-western part of the Gulf of Gdansk (2158.9 kg h-1), on the border between the Gdansk Deep and the Gotland Deep (2338.0 kg h-1), and in the Slupsk Furrow (2592.9 and 2098.8 kg h-1). The total weight of catches, mean CPUE and a mean share of herring in hauls made at the same period in inspected the Polish part of the ICES Subdivision 25 was higher than in the ICES Subdivision 26. In the ICES SD25 values of above parameters was as follow: 170.3 kg, 31.1 kg h- 1 and 3.8%, whereas in the ICES SD26 was: 64.1 kg; 14.4 kg·h-1 and 1.3%. The CPUE of herring was relatively high in the limited number of hauls, i.e. eastward from the Bornholm Deep (139.8 and 52.8 kg h-1) and in eastern part of the Gdansk Deep (50.0 kg h-1). The mean share of cod in mass of the pelagic trawl control-catches conducted in the ICES SD25 was a bit higher than in the ICES SD26, where amounted 2.1 and 1.7%, respectively. The results of sprat, herring and cod some biological features investigations in May 2018 are presented in Figure 8 and Tables 4, 8, 11, 14. The total length of species dominated in control- hauls conducted in the all investigated areas ranged as follows:  sprat – 7.0 ÷ 15.5 cm (avg. l.t. = 11.6 cm, avg. W = 9.3 g),  herring – 9.0 ÷ 27.0 cm (avg. l.t. = 17.3 cm, avg. W = 32.8 g),  cod – 18.0 ÷ 59.0 cm (avg. l.t. = 32.0 cm, avg. W = 320.5 g). The bimodal shape of length distribution curve for sprat in May 2017 was very similar to this one originated from May 2018 however, slightly difference between the ICES Subdivisions 25 and 26 is visible (Fig. 8). The main frequency apex is distinguished for adults, commercially sized fish collected in the ICES SD25, i.e. from the length classes of 11.5-cm (May 2017) and 12.5-cm (May 2018). In the length distribution of sprat originated from catches in the ICES SD26, in both BASS surveys prevailed specimens from the same 11.5-cm class. In the case of May 2017 and samples from the ICES SD26, the second, minor frequency apex representing young, undersized specimens is visible for fish from the length class of 8.5-9.0 cm, and in the case of May 2018 and both the ICES SDs - from length class 8.0-cm. In the recent BASS survey, the mean numerical share of undersized sprat (<10.0 cm length) was somewhat similar in the ICES Subdivisions 25 and 26, and amounted 10.7 and 14.5%, on average (Table 4). In the previous BASS (2017) survey bycatch of undersized sprat was 1.4 and 10.5%, respectively in the ICES SDs 25 and 26. The mean share of undersized sprat in the entire study area was 12.6 and 5.7% respectively, in May 2018 and 2017. ICES | WGBIFS 2019 183 6 For herring the multimodal shape of length distribution curve was characteristic for May 2017 and 2018 as well as for both the ICES SDs (Fig. 8). In May 2017 dominated herring from the length classes of 22.0 and 16.0-16.5 cm adequately, in the ICES Subdivisions 25 and 26. In herring samples from May 2018, young undersized specimens, from the length classes of 13.0 and 12.0 cm prevailed by numbers respectively, in the ICES SDs 25 and 26. The mean numerical share of undersized herring (<16.0 cm length) in samples collected in May 2018 was practically the same in the ICES SDs 25 and 26, i.e. amounted of 42.5 and 42.3% (Table 4). In May 2017, values of mentioned parameter were much lower and amounted 9.9 and 26.6% on average, respectively in the ICES SDs 25 and 26. The length distribution curve for cod sampled in the ICES SD25 differed very much between May 2017 and May 2018 (Fig. 8). For the previous survey, with approximation it was one frequency apex appeared in the length classes of 35-36 cm, and in May 2018, two maximums of numerical share were visible, i.e. in 23 and 34 cm length classes. In the case of cod caught in the ICES SD26 only data from May 2018 were representative for preparation of the length distribution curve. In the recent BASS survey in mentioned subdivision, specimens from the length class 27 cm dominated by numerical share in samples. The mean bycatch of undersized cod (<35 cm length) in samples collected in May 2018 was 85 and 77% respectively, in the ICES SDs 25 and 26 (Table 4). For comparison, in samples originated from the ICES SD 25 and May 2017 the numerical share of undersized cod was 44%, on average. Data reflects changes of the mean weight of sprat, herring and cod per age groups according to inspected ICES rectangles are presented in Tables 8, 11 and 14. The basic data evaluated in May 2018, including data on Baltic sprat, herring and cod stocks total abundance and biomass per age groups and the ICES rectangles, adequately to echosounding under frequency of 38 kHz are given in Tables 6, 7, 9, 10, 12 and 13. The above- mentioned materials are strongly linked with data on BASS/2018 cruise statistics and average NASC values for acoustically covered ICES rectangles, within the Polish EEZ (Table 5).The mean surface biomass density of sprat, herring and cod, per the ICES rectangles located within the Polish marine waters is reflected in Figures 11 and 12. The abundance of above-mentioned species per age groups, according to inspected in May 2017 and 2018 the Polish parts of the ICES Subdivisions 25 and 26 is demonstrated in Figure 10. In May 2018, the highest mean surface biomass density of sprat stock was estimated for the ICES rectangles: 39G9, 40G8 and 39G8, where amounted: 161.3; 100.7 and 98.9 t NM-2, respectively (Fig. 11). The maximum of sprat surface biomass density was obtained in the Gdansk Deep and southern part of the Gotland Deep. In contrast, the minimum values of this parameter were noticed in the south-western parts of investigated the Polish marine waters. The recent pattern of sprat surface biomass density distribution per ICES rectangles can be considered as almost a mirror picture from May 2017 (Fig. 11). In May 2017 and May 2018 the mean biomass density of sprat in the ICES SD25 was 27.6 and 35.8 t NM-2, respectively and in the ICES SD26 it was 134.4 and 92.6 t NM-2 (Fig. 9). In May 2018, the highest mean surface biomass density of herring stock was estimated for the ICES rectangles: 39G9 (3.0 t NM-2), 38G6 (3.0 t NM-2), 39G6 (2.1 t NM-2) and 38G7 (2.1 t NM-2) – located adequately, in small eastern part of the Gdansk Deep and in middle part of the Polish marine waters, with the exception of the Slupsk Furrow (Fig. 11). The recent pattern of herring surface biomass density distribution per ICES rectangles can be considered as very different from May 2017. The maximum of herring stock biomass density in May was obtained in the ICES rectangles 39G6 (23.6 t NM-2) and 39G5 (5.4 t NM-2), located eastward from the Bornholm (Fig. 11). In May 2017 and May 2018 the mean biomass density of herring in the ICES SD25 was 6.3 and 1.6 t NM-2, respectively and in the ICES SD26 it was 1.2 and 1.7 t NM-2 (Fig. 9). By contrast to sprat, in May 2018 herring mean biomass density was significantly lower, e.g. in the ICES Subdivisions 25 and 26 by 22- and 55-times, respectively. Results of the acoustic-biotic monitoring in the Polish marine waters indicate on very different geographical distribution of Baltic cod biomass in May 2017 and May 2018. In May 2018, the highest mean biomass surface density was estimated for the ICES rectangles: 38G9 (12.7 184 ICES | WGBIFS 2019 7 t NM-2), 38G8 (3.9 t NM-2) and 39G9 (2.4 t NM-2) – located in the Gulf of Gdansk Deep (Fig. 12). In others more northern and western ICES rectangles the mean biomass surface density of cod was fluctuated from 0.5 to 1.1 t NM-2. However, in five ICES rectangles, namely: 37G5, 37G8, 37G9, 38G6 and 38G7 – located in the southern part of the Polish EEZ (in the vicinity of seacoast), appearance of cod was not detected (Tables 3, 13, Fig 12). The biomass density of Baltic cod in scrutinized a part of the ICES Subdivision 26 was higher than in the ICES Subdivision 25, and amounted 3.7 and 0.6 t NM-2, on average (Fig. 9). In May 2017 high biomass surface density of cod stock was estimated only for a small part of the ICES rectangle 39G5 (Fig. 12). Cod resources were patchy distributed inside the Polish marine waters and in nine others ICES rectangles biomass of cod was equal to zero (Fig. 12, Table 11). In May 2017 the mean biomass density of cod in scrutinized parts of the ICES Subdivisions 25 and 26 was much lower than in May 2018 and at nearly the same level, i.e. ≤0.03 t NM-2 (Fig. 9). In May 2018, the total biomass (B1), the mean surface biomass density (B2) and abundance (A) of dominants significantly differed between fish species and the ICES subdivisions: parameter sprat herring cod ICES SD25 B1 (tons) 183847.9 7963.7 3246.7 B2 (t NM-2) 35.76 1.55 0.63 A (·106 indiv.) 20370.5 272.4 10.3 ICES SD26 B1 (tons) 448599.0 8194.4 17719.4 B2 (t NM-2) 92.58 1.69 3.66 A (·106 indiv.) 53285.9 234.7 46.6 The above listed data indicate that the centre of fish resources temporal distribution in the Polish EEZ, during reported the BASS/2018 survey, in the case of sprat and cod was located adequately, in the northern and southern parts of Gdansk Basin, but in the case of herring - in middle part of the southern Baltic (Figs. 11, 12). Position of sprat as pronounced dominant regarding stock size (abundance, biomass), during the May 2018 survey is not questionable in the case of Polish marine waters. Meteorological and hydrological characteristics of the southern Baltic Changes of the main meteorological parameters – wind velocity and direction, and air temperature in consecutive days of the Polish BASS survey carried out in 2018 are illustrated in Figure 13. The air temperature during reported survey varied from 4 to 15°C (avg. was 9.2°C). The wind force changed from 1 to 5°B, and winds from the east direction were prevailed. During fishing operations prevail the light wind (3°B) mostly from north directions (Table 15). The strongest wind directions, occurred during fishing operations, were from east. The main hydrological parameters at the depths of fish pelagic catches (Table 15), i.e. in the range of 14-78 m (with 18 m vertical net opening on average) changed in the relatively broad ranges. The seawater temperature fluctuated from 2.7 to 7.4°C (the mean was 4.7°C), salinity from 7.4 to 12.7 PSU (the mean was 8.70 PSU) and oxygen content from 0.9 to 8.9 ml/l (the mean was 5.9). Horizontal distribution of the seawater temperature, salinity and oxygen content in the near bottom zone of the southern Baltic (within the Polish waters) is illustrated in Fig. 14. The temperature in near bottom layer was changing horizontally within the range of 3.1-7.6°C and the average was 5.7°C. The lowest seawater temperature was recorded at the catch-station No. 12 (westward from the Gulf of Gdansk) and the highest at the catch-station No. 22, i.e. eastern part of the Bornholm Basin (Fig. 1). Salinity in the bottom waters varied from 7.5 PSU – noticed at the catch-stations No. 5 and 6 (south part of the Gdansk Gulf), to the maximum of 16.9 PSU - appeared ICES | WGBIFS 2019 185 8 at the hydrographical station No. IBY5 (the Bornholm Basin). Oxygen content near bottom of deep waters varied from 0.09 ml l-1 – measured at the catch-station No. 2 (the Gdansk Deep) to the maximum of 9.3 ml l-1 – calculated at the hydrographical station No. 61 (the mean was 4.3 ml l-1). The vertical distribution of the seawater temperature, salinity and oxygen content, along the hydrological research profile determined in the southern Baltic in May 2018 is presented on Fig. 15. During the survey period, the waters with oxygen content below 2 ml l-1 occurred at depth just below 60m at the Bornholm Basin and the Gdansk Deep. This hypoxic waters were in coincide with waters with salinity above 11 PSU what caused unfavorable conditions for effective reproduction of the Eastern Baltic cod. CONCLUSION The ICES Baltic International Fish Survey Working Group and the Baltic Fisheries Assessment Working Group for the Baltic clupeids and cod stocks size analysis and their spatial distribution characteristics can apply the Polish BASS-2018 survey data obtained by the r.v. “Baltica” scientific team. Results presented in this paper can be considered as representative for the Polish part of the southern Baltic, namely for the ICES Sub-divisions 25 and 26. The basic acoustic, fisheries, biological and hydrological data collected during reported survey will be stored in the ICES Data-Center international databases, managed by the ICES Secretariat and designated experts from WGBIFS. 186 ICES | WGBIFS 2019 9 References: Anon. 1991a. Report of the Planning Group for Hydroacoustic Surveys in the Baltic. ICES CM 1991/J:28. Anon. 1991b. Report of the Working Group on Assessment of Pelagic Stocks in the Baltic. ICES CM 1991/Assess:18. Anon., 2012. Manual for International Baltic Acoustic Surveys (IBAS). Version 1.01, 30-03-2012 Helsinki, Finland; ICES Addendum 2: WGBIFS Manual for Baltic Acoustic Surveys, Version 1.01; 24 pp. Elwertowski, J., Orłowski A., 1984. Composition, distribution and biomass of juvenile sprat in May 1983 in the Southern Baltic. Bulletin of the Sea Fish. Inst., Gdynia, 3-6 (83/86); 5-13. Elwertowski, J., Orłowski A., Richert S., 1984. Badania oceanograficzno-rybackie południowego Bałtyku prowadzone w maju 1983 r. na r.v. Profesor Siedlecki. Bulletin of the Sea Fish. Inst., Gdynia, 1-2; 3- 15. Foote, K.G., Aglen, A. and Nakken, O. (1986) Measurement of fish target strength with a split-beam echosounder. Journal of the Acoustical Society of America, 80(2): 612-621. Grzebielec, R., A. Paciorkowski, M. Wyszyński, W. Grygiel 1995. Polish hydroacoustic assessment survey of herring, sprat and cod stocks in ICES Subdivisions 25 and 26 of the Baltic conducted in October 1994. ICES C.M. 1995/J:18, B.F.C.; 24 pp. Hagström, O., L-E. Palmén, N. Håkansson, D. Kästner, H. Bremer-Rothbart, W. Grygiel, M. Wyszyński 1989. Acoustic estimates of the herring and the sprat stocks in the Baltic Proper, October 1988. ICES C.M. 1989/J:26, B.F.C.; 9 pp. Håkansson, N., Kollberg, S., Falk, U., Goetze, E., Rechlin, O. 1979. A hydroacoustic and trawl survey of herring and sprat of the Baltic proper in October 1978. Fischerei-Forschung, 17(2); 7-23. ICES. 1983. Report of the Planning Group on ICES coordinated herring and sprat acoustic surveys. ICES Document CM 1983/H:12. ICES. 2017, SISP Manual of International Baltic Acoustic Surveys (IBAS). Series of ICES Survey Protocols SISP 8 – IBAS. 47pp. ICES. 2018, Report of the Baltic International Fish Survey Working Group (WGBIFS) 24-28 March 2018 Lyngby, Copenhagen, Denmark; ICES CM 2018/EOSG:6. Kruk, G., B. Schmidt, T. Wodzinowski 2018. Research report from the Polish part of the Baltic Acoustic Spring Survey on board of the r.v. “Baltica” (02-13.05.2017). Working paper, WGBIFS meeting in Lyngby, 24-28.03.2018; 28 pp. Orłowski, A. 1982. Zasoby ryb polskiej strefy Bałtyku oszacowane metodą hydroakustyczna podczas rejsu r.v. „Profesor siedlecki” w roku 1981. Biuletyn Mor. Inst. Ryb., Gdynia, 1-6 (69-74); 23-28. Orłowski, A. 1991. Hydroacoustic surveys of fish distribution in relation to environment. Acta Ichthyol. Pisc., Szczecin, XXI; 181-192. Shvetsov, F., V. Baturin, E. Goetze, R. Oeberst, D. Kästner 1986. Preliminary results of a joint hydroacoustic sprat survey by the USSR and GDR in Baltic in May 1986. ICES C.M. 1986/J:15, B.F.C. Shvetsov, F., W. Grygiel, M. Fetter, V. Chervontsev, A. Rudneva 1992. Distribution and size of herring and sprat stocks in the Baltic Proper, determined by the acoustic method (October, 1991). ICES C.M. 1992/J:8, B.F.C.; 10 pp. Simrad. 2012. Simrad EK60, Reference Manual, release 2.4.X. Kongsberg Maritime AS; 256 pp. Trella K., Schmidt B., Wodzinowski T., Ameryk A., Sprawozdanie z rejsu badawczego typu BASS, nr 7/2018/MIR-PIB na statku r.v. Baltica (GDY100) w dniach 02-13.05.2018 r., MIR-PIB, Gdynia; 24pp., (mimeo). ICES | WGBIFS 2019 187 10 Table 1. Weighted mean NASC values (m2·NM-2) for the Polish parts of the ICES SDs 25 and 26, calculated with use of areas of ICES rectangles as weight, for BASS 2017 and 2018 cruises (note: for comparison reasons, presented mean NASC for in the ICES SD 25 (BASS 2017) was calculated without the ICES rectangles 39G5 and 40G7, because in May 2018 mentioned rectangles were acoustically not inspected). Table 2. Average NASC values (m2·NM-2) for the acoustically covered ICES rectangles, within the Polish EEZ, in 2017 and 2018 BASS cruises (the NASC values from 2017 from Kruk et al., 2018 ). 25 375.7 565.9 26 1850.3 1457.4 ICES SDs < NASC > BASS 2017 < NASC > BASS 2018 25 37G5 642.2 329.8 162.0 25 38G5 1035.7 531.1 292.7 25 38G6 940.2 148.1 339.3 25 38G7 471.7 61.1 305.9 25 39G6 1026.0 407.3 751.7 25 39G7 1026.0 569.0 1009.0 26 37G8 86.0 1229.5 904.4 26 37G9 151.6 368.3 750.6 26 38G8 624.6 1145.4 907.3 26 38G9 918.2 2246.4 580.2 26 39G8 1026.0 895.9 1477.1 26 39G9 1026.0 3633.7 2408.6 26 40G8 1013.0 1360.8 1506.2 ICES SDs ICES rectangles Area [NM2] < NASC > BASS 2017 < NASC > BASS 2018 188 ICES | WGBIFS 2019 11 Table 3. Fish control-catches data from the Polish BASS survey conducted on board of the r.v. “Baltica” in May 2018. Table 4. The mean numerical share of young, undersized fishes per ICES SDs (the Polish BASS/2018 and BASS/2017). min max min max 1 03.05.2018 39G9 26 55.10'1 019.04'8 55.10'2 019.04'8 275 88 89 64 67 18-20 8.15 30 1 579.42 1 520.164 23.610 34.180 1.460 0.005 2 03.05.2018 38G9 26 54.55'5 019.08'8 54.55'5 019.06'5 260 103 104 40 42 16-17 11.55 30 625.22 623.780 1.260 0.180 3 03.05.2018 38G9 26 54.39'6 019.14'6 54.39'1 019.12'3 255 88 90 65 68 18 15.35 30 136.39 73.120 8.160 51.600 3.514 4 03.05.2018 37G9 26 54.29'2 019.10'7 54.28'0 019.12'7 130 68 70 20 25 18 18.30 30 54.90 53.140 1.760 0.000 5 04.05.2018 37G9 26 54.25'4 019.19'6 54.26'8 019.18'7 340 47 60 25 37 18 9.25 30 436.84 432.660 4.180 6 04.05.2018 37G8 26 54.27'5 018.54'9 54.28'2 018.54'3 335 49 59 29 34 16 12.50 15 2 175.33 2 158.920 16.360 0.050 7 04.05.2018 38G8 26 54.37'2 018.59'3 54.38'1 018.58'9 340 79 79 40 40 18 16.15 15 937.14 933.320 2.720 1.096 8 05.05.2018 40G8 26 55.35'1 018.58'6 55.35'7 018.58'0 330 86 86 60 64 18 10.10 15 1 740.18 1 679.600 49.960 5.184 5.432 9 05.05.2018 40G8 26 55.51'7 018.45'1 55.51'8 018.46'5 80 110 115 62 65 18 14.40 15 2 447.81 2 338.000 9.840 86.684 12.652 0.630 10 06.05.2018 39G8 26 55.11'5 018.40'4 55.12'9 018.40'7 5 88 88 68 68 18 7.30 30 743.59 726.980 15.540 1.072 0.000 11 06.05.2018 38G8 26 54.58'3 018.40'8 54.57'8 018.41'7 130 92 92 70 70 17 10.45 15 537.26 451.760 18.720 63.816 2.960 12 06.05.2018 39G8 26 55.01'7 018.20'0 55.02'3 018.20'0 360 52 62 30 40 18 16.05 15 3 782.48 3 742.400 40.080 13 06.05.2018 39G8 26 55.20'4 018.20'0 55.21'2 018.19'9 360 80 82 30 40 18 19.10 15 572.56 570.600 1.960 14 07.05.2018 40G8 26 55.37'4 018.25'9 55.38'0 018.25'0 340 93 94 60 60 18 7.50 15 735.78 717.440 7.720 2.632 7.708 0.280 15 07.05.2018 38G7 25 54.58'4 017.54'4 54.59'2 017.57'0 65 22 24 6 9 14 18.50 30 348.69 324.420 23.080 0.077 1.110 16 08.05.2018 39G7 25 55.18'7 017.43'0 55.18'8 017.44'4 80 78 80 55 58 18 9.20 15 511.67 507.160 2.440 1.656 0.412 17 08.05.2018 39G7 25 55.14'5 017.18'6 55.14'7 017.16'2 280 91 92 69 70 18 14.25 30 2 687.72 2 592.910 17.310 75.018 1.546 0.450 0.484 18 08.05.2018 38G7 25 54.57'6 017.20'7 54.58'5 017.22'9 60 27 28 10 12 14 18.30 30 41.35 37.180 4.152 0.020 19 09.05..2018 39G6 25 55.17'4 016.40'9 55.17'5 016.43'4 80 73 76 50 52 18 14.00 30 2 111.19 2 098.768 11.720 0.702 20 09.05..2018 38G6 25 54.47'3 016.52'8 54.47'1 016.50'3 260 30 33 13 15 13 19.40 30 167.28 127.428 39.852 21 10.05.2018 38G6 25 54.43'2 016.19'1 54.43'4 016.16'6 280 36 36 15 15 18 8.10 30 164.48 162.020 2.460 22 10.05.2018 39G6 25 55.06'8 016.18'5 55.06'6 016.15'7 265 72 78 50 53 18 12.45 30 1 496.69 1 310.450 139.790 38.316 6.628 1.505 23 11.05.2018 38G5 25 54.52'8 015.58'3 54.54'1 015.58'3 10-15 66 68 44 48 18 7.20 30 732.62 617.200 52.780 60.122 1.884 0.632 24 11.05.2018 37G5 25 54.23'8 015.45'3 54.23'9 015.48'0 90 35 36 18 18 13 13.05 30 97.23 96.920 0.305 25 11.05.2018 38G5 25 54.36'1 015.20'8 54.36'2 015.23'2 85 58 59 38 38 18 18.05 30 791.35 735.920 37.886 7.396 0.190 fourbeard rockling latitude N longitude E Depth to the bottom [m] Headrope depth from the sea surface [m] sprat The ship's course during fishing [°] Trawling duration [min] CPUE of particular fish speciesVertical net opening [m] CPUE of all species [kg·h-1] herring cod flounder three spine stickleback greater sand-eel Atlantic mackerel whiting Date of catch Haul number ICES SDs start Geographical position of the catch-station end ICES rectangles latitude N longitude E Local time of shutting net SD25 SD26 Mean SD25 SD26 Mean sprat < 10 cm 1.4 10.5 5.7 10.7 14.5 12.8 herring < 16 cm 9.9 26.6 14.8 42.5 42.3 42.4 cod < 35 cm 43.8 ­ 43.5 84.9 76.8 81.5 Mean share in % numbers Mean share in % numbersSpecies Fish length BASS 2017 BASS 2018 ICES | WGBIFS 2019 189 12 Table 5. Cruise statistics of the Polish BASS survey on board of the r.v. “Baltica”, 02-13.05.2018. sprat herring cod total sprat herring cod 25 37G5 34 1.68 162.0 642.2 99.8 0.2 0.0 620.8 619.7 1.1 0.0 25 38G5 70 1.59 292.7 1035.7 98.2 1.6 0.2 1902.4 1867.3 31.4 3.8 25 38G6 55 1.66 339.3 940.2 94.0 6.0 0.0 1925.0 1809.0 115.9 0.0 25 38G7 31 1.67 305.9 471.7 95.4 4.6 0.0 864.8 824.9 39.9 0.0 25 39G6 87 1.31 751.7 1026 98.7 1.2 0.1 5876.1 5799.4 73.1 3.7 25 39G7 89 1.09 1009.0 1026 99.9 0.1 0.0 9464.1 9450.2 11.0 2.9 Sum SD25 366 20653.2 20370.5 272.4 10.3 26 37G8 8 1.14 904.4 86 99.3 0.7 0.0 683.9 679.3 4.5 0.0 26 37G9 28 1.18 750.6 151.6 98.9 1.1 0.0 962.1 952.0 10.1 0.0 26 38G8 58 1.29 907.3 624.6 99.4 0.4 0.2 4378.3 4352.0 18.9 7.4 26 38G9 45 1.47 580.9 918.2 98.1 1.1 0.8 3627.8 3560.0 39.5 28.3 26 39G8 88 1.23 1477.1 1026 99.6 0.4 0.0 12357.7 12303.7 53.9 0.1 26 39G9 27 1.27 2408.6 1026 99.6 0.4 0.0 19500.1 19423.6 70.1 6.4 26 40G8 92 1.27 1506.2 1013 99.7 0.3 0.0 12057.4 12015.4 37.6 4.4 Sum SD26 346 53567.2 53285.9 234.7 46.6 Area [NM2] ICES rectangles ICES SDs EDSU [NM] <σ> [m2·10-4] < SA > [m2·NM-2] species composition [%] Abundance · 106 190 ICES | WGBIFS 2019 13 Table 6. Abundance of sprat (in millions of individuals) per age groups, ICES rectangles and ICES SDs, estimated using acoustic method, based on data collected during the Polish BASS survey on board of the r.v. “Baltica”, 02-13.05.2018. Table 7. Biomass of sprat (in tons) per age groups, ICES rectangles and ICES SDs, estimated using acoustic method, based on data collected during the Polish BASS survey on board of the r.v. “Baltica”, 02-13.05.2018. ICES SDs ICES rectangles Age 1 Age 2 Age 3 Age 4 Age 5 Age 6 Age 7 Age 8+ Total sprat abundance [mln indiv.] 25 37G5 8.4 32.4 49.5 346.1 111.3 47.9 19.3 4.9 619.7 25 38G5 79.6 125.5 273.2 1137.4 178.6 42.6 24.2 6.2 1867.3 25 38G6 0.0 74.4 229.1 1153.2 235.1 67.1 38.8 11.3 1809.0 25 38G7 2.0 29.1 94.5 514.1 120.7 39.5 19.4 5.6 824.9 25 39G6 856.9 953.4 992.5 2746.9 187.0 34.6 22.0 6.1 5799.4 25 39G7 3545.9 1663.1 1185.3 2937.5 111.5 2.2 4.1 0.5 9450.2 Sum SD25 4492.7 2878.0 2824.1 8835.2 944.2 233.8 127.7 34.7 20370.5 26 37G8 189.8 85.8 177.7 209.1 15.7 1.1 0.2 0.0 679.3 26 37G9 199.3 118.7 262.6 340.5 27.5 2.6 0.7 0.0 952.0 26 38G8 407.6 570.9 1430.6 1784.7 143.1 13.4 1.7 0.0 4352.0 26 38G9 471.3 382.0 1062.6 1484.1 138.8 17.2 4.0 0.0 3560.0 26 39G8 2000.0 1256.1 3800.5 4782.3 407.4 49.5 8.0 0.0 12303.7 26 39G9 1893.0 2398.3 6366.3 8010.9 661.0 82.9 11.2 0.0 19423.6 26 40G8 447.2 2293.6 3856.5 4947.2 416.2 49.9 4.8 0.0 12015.4 Sum SD26 5608.2 7105.3 16956.8 21558.8 1809.6 216.6 30.6 0.0 53285.9 ICES SDs ICES rectangles Age 1 Age 2 Age 3 Age 4 Age 5 Age 6 Age 7 Age 8+ Total sprat biomass [t] 25 37G5 50.4 285.8 579.6 4648.9 1694.7 779.4 304.1 75.3 8418.3 25 38G5 303.4 1222.6 2974.1 13658.9 2501.7 679.7 365.4 94.9 21800.8 25 38G6 0.0 793.1 2605.2 14548.8 3378.6 1065.8 593.1 175.1 23159.6 25 38G7 6.8 312.9 1082.5 6607.4 1770.4 628.4 295.8 86.9 10791.1 25 39G6 3133.6 8172.3 9731.8 28398.3 2467.2 551.6 338.3 97.1 52890.2 25 39G7 12042.3 13308.2 11213.3 28845.0 1281.4 32.4 57.3 8.1 66787.9 Sum SD25 15536.5 24094.9 28186.4 96707.3 13094.0 3737.4 1954.1 537.3 183847.9 26 37G8 698.9 616.7 1580.2 1927.9 161.0 13.7 2.0 0.0 5000.3 26 37G9 674.3 907.5 2343.4 3171.8 283.5 32.7 9.3 0.0 7422.5 26 38G8 1375.6 4463.1 12806.5 16641.0 1485.9 173.1 22.5 0.0 36967.8 26 38G9 1478.4 3034.8 9652.2 14307.6 1490.3 219.1 51.3 0.0 30233.8 26 39G8 6345.1 9845.0 34477.9 45700.9 4327.0 632.8 102.7 0.0 101431.3 26 39G9 5930.3 18829.7 57170.8 75458.5 6916.3 1078.8 144.2 0.0 165528.6 26 40G8 1568.4 17398.9 33269.1 44759.8 4292.1 664.1 62.4 0.0 102014.7 Sum SD26 18071.1 55095.8 151300.1 201967.4 18956.0 2814.2 394.4 0.0 448599.0 ICES | WGBIFS 2019 191 14 Table 8. Mean weight of sprat (in grams) per age groups, ICES rectangles and ICES SDs, based on data collected during the Polish BASS survey on board of the r.v. “Baltica”, 02-13.05.2018. Table 9. Abundance of herring (in millions of individuals) per age groups, ICES rectangles and ICES SDs, estimated using acoustic method, based on data collected during the Polish BASS survey on board of the r.v. “Baltica”, 02-13.05.2018. ICES SDs ICES rectangles Age 1 Age 2 Age 3 Age 4 Age 5 Age 6 Age 7 Age 8+ Mean W sprat [g] 25 37G5 6.01 8.82 11.70 13.43 15.23 16.28 15.73 15.49 13.58 25 38G5 3.81 9.74 10.88 12.01 14.00 15.95 15.13 15.39 11.68 25 38G6 ­ 10.66 11.37 12.62 14.37 15.89 15.30 15.45 12.80 25 38G7 3.41 10.74 11.46 12.85 14.67 15.92 15.28 15.38 13.08 25 39G6 3.66 8.57 9.81 10.34 13.20 15.95 15.37 15.80 9.12 25 39G7 3.40 8.00 9.46 9.82 11.49 15.01 13.98 15.01 7.07 MW SD25 3.46 8.37 9.98 10.95 13.87 15.99 15.30 15.49 9.03 26 37G8 3.68 7.19 8.89 9.22 10.26 12.00 12.90 ­ 7.36 26 37G9 3.38 7.65 8.92 9.32 10.30 12.34 12.90 ­ 7.80 26 38G8 3.37 7.82 8.95 9.32 10.39 12.91 12.90 ­ 8.49 26 38G9 3.14 7.94 9.08 9.64 10.74 12.75 12.90 ­ 8.49 26 39G8 3.17 7.84 9.07 9.56 10.62 12.78 12.90 ­ 8.24 26 39G9 3.13 7.85 8.98 9.42 10.46 13.02 12.90 ­ 8.52 26 40G8 3.51 7.59 8.63 9.05 10.31 13.32 12.90 ­ 8.49 MW SD26 3.22 7.75 8.92 9.37 10.47 12.99 12.90 ­ 8.42 ICES SDs ICES rectangles Age 1 Age 2 Age 3 Age 4 Age 5 Age 6 Age 7 Age 8+ Total herring abundance [mln indiv.] 25 37G5 0.9 0.0 0.0 0.0 0.0 0.2 0.0 0.0 1.1 25 38G5 2.6 4.2 6.5 4.5 3.9 4.5 1.5 3.7 31.4 25 38G6 78.6 9.1 11.1 5.3 4.1 5.4 1.0 1.4 115.9 25 38G7 23.5 5.0 5.0 2.3 1.5 2.1 0.2 0.2 39.9 25 39G6 40.4 4.3 7.9 5.9 4.1 5.5 1.9 3.0 73.1 25 39G7 1.7 3.2 3.7 0.5 0.7 1.1 0.1 0.1 11.0 Sum SD25 147.7 25.8 34.3 18.5 14.3 18.8 4.7 8.4 272.4 26 37G8 4.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.5 26 37G9 8.5 0.2 0.2 0.2 0.2 0.2 0.1 0.4 10.1 26 38G8 7.3 1.3 1.3 2.8 1.2 0.8 0.8 3.3 18.9 26 38G9 15.6 1.5 4.1 5.2 4.7 1.6 1.5 5.3 39.5 26 39G8 20.8 4.0 8.1 7.9 3.2 2.6 1.2 6.0 53.9 26 39G9 6.2 5.5 11.2 13.6 7.3 3.4 6.6 16.2 70.1 26 40G8 0.0 5.8 10.0 10.4 3.5 2.7 1.4 3.7 37.6 Sum SD26 62.9 18.5 35.0 40.2 20.1 11.3 11.7 34.9 234.7 192 ICES | WGBIFS 2019 15 Table 10. Biomass of herring (in tons) per age groups, ICES rectangles and ICES SDs, estimated using acoustic method, based on data collected during the Polish BASS survey on board of the r.v. “Baltica”, 02-13.05.2018. Table 11. Mean weight of herring (in grams) per age groups, ICES rectangles and ICES SDs, based on data collected during the Polish BASS survey on board of the r.v. “Baltica”, 02-13.05.2018. ICES SDs ICES rectangles Age 1 Age 2 Age 3 Age 4 Age 5 Age 6 Age 7 Age 8+ Total herring biomass [t] 25 37G5 15.0 0.0 0.0 0.0 0.0 11.9 0.0 0.0 27.0 25 38G5 38.3 169.4 311.5 235.8 209.3 255.4 98.9 258.2 1576.8 25 38G6 1197.6 342.3 457.0 246.4 196.3 265.3 61.7 90.3 2856.7 25 38G7 327.0 179.6 187.4 100.9 67.6 92.1 14.3 12.8 981.8 25 39G6 436.4 172.4 377.2 318.7 223.2 304.1 116.7 192.4 2141.1 25 39G7 33.0 108.9 130.5 23.8 29.7 44.3 3.8 6.4 380.2 Sum SD25 2047.3 972.5 1463.7 925.5 726.1 973.1 295.4 560.1 7963.7 26 37G8 41.3 0.5 0.7 0.0 1.7 0.0 0.7 0.0 44.9 26 37G9 77.9 4.2 6.8 9.6 8.1 9.3 7.0 27.9 150.7 26 38G8 67.9 32.3 47.3 94.2 49.7 44.3 52.4 206.7 594.9 26 38G9 185.1 54.5 160.5 207.6 189.1 83.7 78.3 336.7 1295.6 26 39G8 239.5 103.5 238.6 294.2 141.6 134.2 71.6 383.7 1606.8 26 39G9 75.8 174.3 425.4 501.0 316.5 182.8 367.4 1066.6 3109.9 26 40G8 0.0 145.8 327.7 360.3 158.6 125.3 69.6 204.2 1391.6 Sum SD26 687.5 515.0 1207.0 1466.9 865.4 579.7 647.0 2225.9 8194.4 ICES SDs ICES rectangles Age 1 Age 2 Age 3 Age 4 Age 5 Age 6 Age 7 Age 8+ Mean W sprat [g] 25 37G5 6.01 8.82 11.70 13.43 15.23 16.28 15.73 15.49 13.58 25 38G5 3.81 9.74 10.88 12.01 14.00 15.95 15.13 15.39 11.68 25 38G6 ­ 10.66 11.37 12.62 14.37 15.89 15.30 15.45 12.80 25 38G7 3.41 10.74 11.46 12.85 14.67 15.92 15.28 15.38 13.08 25 39G6 3.66 8.57 9.81 10.34 13.20 15.95 15.37 15.80 9.12 25 39G7 3.40 8.00 9.46 9.82 11.49 15.01 13.98 15.01 7.07 MW SD25 3.46 8.37 9.98 10.95 13.87 15.99 15.30 15.49 9.03 26 37G8 3.68 7.19 8.89 9.22 10.26 12.00 12.90 ­ 7.36 26 37G9 3.38 7.65 8.92 9.32 10.30 12.34 12.90 ­ 7.80 26 38G8 3.37 7.82 8.95 9.32 10.39 12.91 12.90 ­ 8.49 26 38G9 3.14 7.94 9.08 9.64 10.74 12.75 12.90 ­ 8.49 26 39G8 3.17 7.84 9.07 9.56 10.62 12.78 12.90 ­ 8.24 26 39G9 3.13 7.85 8.98 9.42 10.46 13.02 12.90 ­ 8.52 26 40G8 3.51 7.59 8.63 9.05 10.31 13.32 12.90 ­ 8.49 MW SD26 3.22 7.75 8.92 9.37 10.47 12.99 12.90 ­ 8.42 ICES | WGBIFS 2019 193 16 Table 12. Abundance of cod (in millions of individuals) per age groups, ICES rectangles and ICES SDs, estimated using acoustic method, based on data collected during the Polish BASS survey on board of the r.v. “Baltica”, 02-13.05.2018. Table 13. Biomass of cod (in tons) per age groups, ICES rectangles and ICES SDs, estimated using acoustic method, based on data collected during the Polish BASS survey on board of the r.v. “Baltica”, 02-13.05.2018. ICES SDs ICES rectangles Age 1 Age 2 Age 3 Age 4 Age 5 Age 6 Age 7 Age 8+ Total cod abundance [mln indiv.] 25 37G5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 25 38G5 0.0 1.1 2.1 0.4 0.2 0.0 0.0 0.0 3.8 25 38G6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 25 38G7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 25 39G6 0.0 1.1 2.4 0.1 0.0 0.0 0.0 0.0 3.7 25 39G7 0.0 0.4 1.6 0.7 0.1 0.0 0.0 0.0 2.9 Sum SD25 0.0 2.5 6.1 1.3 0.3 0.0 0.0 0.0 10.3 26 37G8 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 26 37G9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 26 38G8 0.0 2.8 2.0 1.5 1.1 0.0 0.0 0.0 7.4 26 38G9 0.0 9.7 7.6 5.4 3.9 1.2 0.4 0.0 28.3 26 39G8 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.1 26 39G9 0.0 1.6 1.5 2.9 0.2 0.1 0.0 0.0 6.4 26 40G8 0.1 2.6 0.7 0.4 0.4 0.1 0.0 0.0 4.4 Sum SD26 0.1 16.8 11.9 10.3 5.6 1.4 0.4 0.0 46.6 ICES SDs ICES rectangles Age 1 Age 2 Age 3 Age 4 Age 5 Age 6 Age 7 Age 8+ Total cod biomass [t] 25 37G5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 25 38G5 0.00 168.41 641.16 247.40 102.84 2.44 0.00 0.00 1162.25 25 38G6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 25 38G7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 25 39G6 0.00 126.20 809.30 56.87 25.96 0.00 0.00 0.00 1018.33 25 39G7 0.00 0.00 624.02 343.51 90.88 7.70 0.00 0.00 1066.12 Sum SD25 0.00 294.62 2074.48 647.77 219.68 10.14 0.00 0.00 3246.69 26 37G8 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 26 37G9 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 26 38G8 2.61 458.01 510.97 717.05 718.13 19.87 0.00 0.00 2426.65 26 38G9 0.00 1714.22 2258.23 3012.51 2966.85 923.48 779.77 0.00 11655.05 26 39G8 0.00 0.00 10.16 40.62 0.00 0.00 0.00 0.00 50.78 26 39G9 0.88 258.10 544.61 1472.71 134.95 68.43 0.00 0.00 2479.68 26 40G8 6.53 336.46 211.40 202.50 283.98 66.41 0.00 0.00 1107.28 Sum SD26 10.02 2766.79 3535.36 5445.39 4103.90 1078.19 779.77 0.00 17719.43 194 ICES | WGBIFS 2019 17 Table 14. Mean weight of cod (in grams) per age groups, ICES rectangles and ICES SDs, based on data collected during the Polish BASS survey on board of the r.v. “Baltica”, 02-13.05.2018. Table 15. Values of the basic meteorological and hydrological parameters recorded in May 2018 at the positions of the r.v. "Baltica" fish control catches (Trella et al., 2018). ICES SDs ICES rectangles Age 1 Age 2 Age 3 Age 4 Age 5 Age 6 Age 7 Age 8+ Mean W cod [g] 25 37G5 ­ ­ ­ ­ ­ ­ ­ ­ 25 38G5 ­ 152.9 310.9 550.3 618.2 683.0 ­ ­ 307.22 25 38G6 ­ ­ ­ ­ ­ ­ ­ ­ 25 38G7 ­ ­ ­ ­ ­ ­ ­ ­ 25 39G6 ­ 117.7 332.5 478.7 852.1 ­ ­ ­ 278.55 25 39G7 ­ 139.7 383.5 461.8 671.5 683.0 ­ ­ 388.09 MW SD25 136.1 338.8 493.6 661.4 683.0 319.6 26 37G8 ­ ­ ­ ­ ­ ­ ­ ­ 26 37G9 ­ ­ ­ ­ ­ ­ ­ ­ 26 38G8 82.6 164.6 260.7 466.0 661.6 628.6 ­ ­ 326.63 26 38G9 ­ 176.2 296.3 560.1 758.8 751.7 1735.0 ­ 411.63 26 39G8 ­ ­ 499.5 499.5 ­ ­ ­ ­ 499.50 26 39G9 82.6 157.5 355.1 503.7 623.5 1071.4 ­ ­ 388.26 26 40G8 82.6 127.2 287.1 486.8 662.5 856.6 ­ ­ 252.61 MW SD26 82.6 185.3 472.5 589.4 766.5 776.6 434.1 Air temperature [°C] Wind direction Wind force [B] sea state Temperature [°C] Salinity [PSU] Oxygen [ml·l-1] 1 2018-05-03 8.15 5.0 E 5 3 6.4 10.7 1.3 74 2 2018-05-03 11.55 8.0 E 5 4 3.0 7.5 8.5 50 3 2018-05-03 15.35 9.5 NW 3 2 5.4 9.4 2.1 75 4 2018-05-03 18.30 7.5 NW 3 2 4.3 7.4 8.7 31 5 2018-05-04 9.25 7.0 NW 3 2 4.4 7.5 8.6 40 6 2018-05-04 12.50 9.0 NNW 3 2 3.9 7.4 8.4 40 7 2018-05-04 16.15 7.0 N 3 2 4.0 7.5 8.7 40 8 2018-05-05 10.10 8.0 NW 1 1 5.9 10.5 2.2 71 9 2018-05-05 14.40 7.0 NW 2 1 5.3 9.6 0.9 72 10 2018-05-06 7.30 7.0 SW 2 1 6.0 10.7 3.2 77 11 2018-05-06 10.45 11.0 SW 2 1 6.0 10.8 2.8 78 12 2018-05-06 16.05 10.0 W 2 1 3.4 7.5 8.7 40 13 2018-05-06 19.10 7.0 W 2 1 3.4 7.5 8.6 44 14 2018-05-07 7.50 8.0 SW 2 1 3.2 7.6 2.8 69 15 2018-05-07 18.50 11.0 SW 1 1 6.1 7.6 8.6 14 16 2018-05-08 9.20 11.0 E 2 1 3.1 7.9 7.1 65 17 2018-05-08 14.25 10.5 NE 3 1 7.4 12.6 1.9 78 18 2018-05-08 18.30 10.0 NE 3 1 5.2 7.6 8.8 18 19 2018-05-09 14.00 10.0 ENE 3 2 3.3 8.7 6.2 60 20 2018-05-09 19.40 12.0 E 5 3 5.7 7.6 8.1 20 21 2018-05-10 8.10 12.0 E 4 2 5.0 7.6 8.4 24 22 2018-05-10 12.45 13.0 E 3 2 6.3 12.7 1.1 60 23 2018-05-11 7.20 11.0 E 2 1 2.7 8.6 5.5 55 24 2018-05-11 13.05 11.0 WSW 3 1 5.0 7.6 8.9 25 25 2018-05-11 18.05 11.0 W 3 2 3.3 7.7 7.4 47 Depth of measurement [m] * data of the mean depth of the fish control-catches (in the middle of trawl vertical opening) Haul no Date of catch Haul start time Hydrological parameters *Meteorological parameters ICES | WGBIFS 2019 195 18 Fig. 1. R.v. “Baltica” cruise BASS 2018: Simrad EK60 calibration report (38 kHz transducer). 196 ICES | WGBIFS 2019 19 Fig. 2. Location of realized investigations during the Polish BASS survey on board of the r.v. “Baltica”, 02–13.05.2018. ICES | WGBIFS 2019 197 20 Fig. 3. Cruise track (thin dashed line) and the mean NASC (5 NM intervals, bubbles) recorded during BASS 2018 cruise. Fig. 4. An example of an echogram analysis for 232th mile of the integration, NASC = 6148 (ICES rectangle 39G8, bottom depth 91 m; 06.05.2018). 198 ICES | WGBIFS 2019 21 Fig. 5. CPUE [kg h -1 ] of fish species per single pelagic hauls conducted in the Polish EEZ (BASS/2018 survey). Fig. 6. Mean CPUE [kg h-1] per fish species and the ICES SDs (the Polish BASS/2018 survey). total sprat herring cod others 0 500 1000 1500 C P U E [ k g h - 1 ] SD 25 SD 26 mean ICES | WGBIFS 2019 199 22 Fig. 7. Share (%) of sprat, herring, cod and other fishes in the mass of total catches per the ICES SDs (the Polish BASS/2018). 200 ICES | WGBIFS 2019 23 Fig. 8. Length distribution of sprat, herring and cod in samples taken from the control-catches conducted during the Polish BASS/2017 and BASS/2018 surveys. COD; May 2018 0 1 2 3 4 5 6 7 8 9 1 7 ,0 1 9 ,0 2 1 ,0 2 3 ,0 2 5 ,0 2 7 ,0 2 9 ,0 3 1 ,0 3 3 ,0 3 5 ,0 3 7 ,0 3 9 ,0 4 1 ,0 4 3 ,0 4 5 ,0 4 7 ,0 4 9 ,0 5 1 ,0 5 3 ,0 5 5 ,0 5 7 ,0 5 9 ,0 Length classes [cm] N u m er ic al s h ar e [% ] ICES SD 25, n = 311 ICES SD 26, n = 233 HERRING; May 2018 0 2 4 6 8 10 12 14 16 8 ,0 9 ,0 1 0 ,0 1 1 ,0 1 2 ,0 1 3 ,0 1 4 ,0 1 5 ,0 1 6 ,0 1 7 ,0 1 8 ,0 1 9 ,0 2 0 ,0 2 1 ,0 2 2 ,0 2 3 ,0 2 4 ,0 2 5 ,0 2 6 ,0 2 7 ,0 2 8 ,0 Length classes [cm] N u m er ic al s h ar e [% ] ICES SD 25, n = 904 ICES SD 26, n = 381 SPRAT; May 2018 0 4 8 12 16 20 24 28 32 6,0 7,0 8,0 9,0 10,0 11,0 12,0 13,0 14,0 15,0 16,0 Length classes [cm] N u m er ic al s h ar e [% ] ICES SD 25, n = 2322 ICES SD 26, n = 2996 COD; May 2017 0 2 4 6 8 10 12 1 7 ,0 1 9 ,0 2 1 ,0 2 3 ,0 2 5 ,0 2 7 ,0 2 9 ,0 3 1 ,0 3 3 ,0 3 5 ,0 3 7 ,0 3 9 ,0 4 1 ,0 4 3 ,0 4 5 ,0 4 7 ,0 4 9 ,0 5 1 ,0 5 3 ,0 5 5 ,0 5 7 ,0 5 9 ,0 Length classes [cm] N u m er ic al s h ar e [% ] ICES SD 25, n = 441 HERRING; May 2017 0 1 2 3 4 5 6 7 8 9 10 8 ,0 9 ,0 1 0 ,0 1 1 ,0 1 2 ,0 1 3 ,0 1 4 ,0 1 5 ,0 1 6 ,0 1 7 ,0 1 8 ,0 1 9 ,0 2 0 ,0 2 1 ,0 2 2 ,0 2 3 ,0 2 4 ,0 2 5 ,0 2 6 ,0 2 7 ,0 2 8 ,0 Length classes [cm] N u m er ic al s h ar e [% ] ICES SD 25, n = 1498 ICES SD 26, n = 616 SPRAT; May 2017 0 4 8 12 16 20 24 28 32 6,0 7,0 8,0 9,0 10,0 11,0 12,0 13,0 14,0 15,0 16,0 Length classes [cm] N u m er ic al s h ar e [% ] ICES SD 25, n = 3157 ICES SD 26, n = 3063 ICES | WGBIFS 2019 201 24 Fig. 9. Mean biomass density in the ICES Subdivisions 25 and 26 in the Polish BASS 2017 and 2018 for the three major fish species (note: for comparison reasons, presented biomass density in SD 25 for 2017 were calculated without the ICES rectangles 39G5 and 40G7, because in 2018 mentioned rectangles were acoustically not inspected). 0 10 20 30 40 b io m a s s d e n s it y [ t N M -2 ] sprat herring cod 27.58 35.76 6.25 1.55 0.01 0.63 Subdivision 25 2017 2018 0 50 100 150 b io m a s s d e n s it y [ t N M -2 ] sprat herring cod 134.37 92.58 1.17 1.69 0.03 3.66 Subdivision 26 2017 2018 202 ICES | WGBIFS 2019 25 Fig. 10. Abundance of sprat, herring and cod stocks per age groups, according to the ICES Subdivisions 25 and 26, based on data from the Polish BASS surveys in 2017 and 2018 (note: in set of data from 2017, the ICES rectangles 39G5 and 40G7 are not included, because in 2018 mentioned rectangles were acoustically not inspected). ICES | WGBIFS 2019 203 26 Fig. 11. Biomass surface density of sprat and herring [t·NM-2] in ICES rectangles, estimated using acoustic method, and based on data collected during the Polish BASS 2017 and 2018 surveys. 204 ICES | WGBIFS 2019 27 Fig. 12. Biomass surface density of cod [t·NM-2] in ICES rectangles, estimated using acoustic method, and based on data collected during the Polish BASS 2017 and 2018 surveys. ICES | WGBIFS 2019 205 28 Fig. 13. Changes of meteorological parameters during consecutive days of the Polish BASS survey in May 2018 (fig. Wodzinowski cit. in Trella et al., 2018). 206 ICES | WGBIFS 2019 29 Fig. 14. Horizontal distribution of the seawater temperature, salinity and oxygen content in the near seabed layer of the southern Baltic in May 2018 (fig. Wodzinowski cit. in Trella et al., 2018). ICES | WGBIFS 2019 207 30 Fig. 15. Vertical distribution of the seawater temperature, salinity and oxygen content, along the hydrological research profile determined in the southern Baltic (May 2018); X- and Y-axes reflects distance (in kilometres) and depth (in meters) from the sea surface to the seabed, respectively (fig. Wodzinowski cit. in Trella et al., 2018). 208 ICES | WGBIFS 2019 Fisheries Service under the Ministry of Agriculture of Republic of Lithuania, Fishery Research and Science State RESEARCH REPORT FROM THE BALTIC ACOUSTIC SPRING SURVEY (BASS) IN THE ICES SUBDIVISION 26 (LITHUANIAN EXCLUSIVE ECONOMIC ZONE) OF THE BALTIC SEA (Vessel “DARIUS”; 08.05 - 09.05.2018) Klaipeda, May, 2018 Lithuania ICES | WGBIFS 2019 209 2 1 INTRODUCTION The main objective is to assess clupeids resources in the Baltic Sea. The Lithuanian survey is coordinated within the frame of the Baltic International Spring Survey (BASS). The reported acoustic survey is conducted to supply the ICES Baltic Fisheries Assessment Working Group (WGBFAS) and the Fisheries Service under the Ministry of Agriculture of Republic of Lithuania with an index value for the stock size of herring and sprat in parts of the ICES subdivision (SD) 26 (Lithuanian Exclusive Economic Zone). 2 METHODS 2.1 Participants M. Špegys Fisheries Service under the Ministry of Agriculture of The Republic of Lithuania; Division of Fishery Research and Science, Klaipeda – cruise leader and acoustics; J. Fedotova D. Tarvydiene Fisheries Service under the Ministry of Agriculture of The Republic of Lithuania; Division of Fishery Research and Science, Klaipeda - scientific leader and fish sampling Fisheries Service under the Ministry of Agriculture of The Republic of Lithuania; Division of Fishery Research and Science, Klaipeda - fish sampling 2.2 Narrative The cruise of BASS survey took place from 08-th to 09-th of May 2018. The cruise was intended to cover parts of ICES subdivisions (SD) 26, constituting the Lithuanian Exclusive Economic zone in 40H0 and 40G9 rectangles. 2.3 Survey design The statistical rectangles were used as strata (ICES 2016). The area is limited by the 20 m depth line. The scheme of transects is defined as the regular. The average speed of a vessel for the period of acoustic survey was 8 knots. The average speed of the vessel with a trawl was 2.8 knots. Duration of trawling was 30 minutes. The survey was conducted in the daytime from 08.00 up to 20.00. The survey area was 1520 nm2 and the distance used for acoustic estimates was 125 nm. The entire cruise track with positions of the trawling is shown in Fig. 1. 2.4 Calibration 210 ICES | WGBIFS 2019 3 The SIMRAD EK60 echo sounder with split beam transducer ES38 - 12 was calibrated (10 of May 2017) at the site of 30 m depth, located 3.5 nm northwest of Klaipeda harbour according to the BIAS manual (ICES 2016). Sv correction after calibration was set to 21.94 dB. THE RESULTS OF CALIBRATION PROCEDURE FOR EK60 SCIENTIFIC ECHOSOUNDER Date: 28.04.2014 Place : near Klaipeda port Type of transducer Split – beam for 38 kHz Gain (38 kHz) 21.94 dB Athw. Angle Sens 12.5 Along. Angle Sens 12.5 Athw. Beam Angle 12.06 Along. Beam Angle 11.96 Athw. Offset Angle 0.08 Along. Offset Angle -0.15 SA Correction (38 kHz) -0.18 dB 2.5 Acoustic data collection The acoustic sampling was performed around the clock. The main pelagic species of interest were herring and sprat. The SIMRAD EK60 echo sounder with hull mounted 38 kHz transducer ES38-12 was used during the cruise. The specific settings of the hydro acoustic equipment were used as described in the BIAS manual (ICES 2016). The post-processing of the stored echo signals was made using the Sonar4 (Balk & Lindem, 2005). The mean volume back scattering values Sv, were integrated over 1 nm intervals, from 10 m below the surface 1 m to the bottom. Contributions from air bubbles, bottom structures and noise scattering layers were removed from the echogram using Sonar4. 2.6 Biological data – fishing stations All trawling was done with the pelagic gear in the midwater as well as near the bottom. The mesh size in the codend was 10 mm. The intention was to carry out at least two hauls per ICES statistical rectangle. The trawling depth was chosen by the echogram, in accordance to the characteristic of echo records from the fish. Normally, the trawl had vertical opening of about 12 m. The trawling time lasted 30 minutes. From each haul sub-samples were taken to determine length and weight composition of fish. Samples of herring and sprat were analyzed for further investigations on the board of vessel (i.e. sex, maturity, age). 2.7 Data analysis The pelagic target species sprat and herring are usually distributed in mixed layers in combination with other species, so that it is impossible to allocate the integrator readings to a single species. Therefore, the species composition was based on the trawl catch results. For each rectangle the species composition and length distribution were determined as the mean - weighted of all trawl results in this rectangle. From these distributions the mean acoustic cross section  was calculated according to the following target strength-length (TS) relationships: Clupeoids TS = 20 log L (cm) - 71.2 (ICES 1983/H:12) Gadoids TS = 20 log L (cm) - 67.5 (Foote et al. 1986) ICES | WGBIFS 2019 211 4 The total number of fish (total N) in one rectangle was estimated as the product of the mean area scattering cross section (Sa) and the rectangle area, divided by the corresponding mean cross section (). The total numbers were separated into herring and sprat according to the mean catch composition. 3 RESULTS 3.1 Biological data 517 herrings and 1870 sprats were measured and 260 herrings and 538 sprats were aged in 6 trawl hauls (Fig. 1) The results of the catch composition are presented in Table 1. In all catch compositions sprat was dominated (from 60% to 99%). The length distributions of herring and sprat of the May 2018 were presented in Fig.2 and Fig.3. In the 40H0 ICES rectangle in herring catches were dominated by 10-12 cm length classes and 88.1% of them were 2017 herring generation. In other rectangle (40G9) dominated 4-year fish (Table 10, 12). Sprat dominated by 8.0 cm length class in 40H0 ICES rectangle (43.6%). And 67% of sprats dominated by 10.0 – 11.0 cm length classes in 40G 9 rectangle witch age were 3-5 years old fishes. 3.2 Acoustic data The survey statistics concerning the survey area, the mean Sa, the mean scattering cross section , the estimated total number of fish, the percentages of herring, sprat per rectangle are shown in Table 2-14. 3.3 Abundance estimates Vessel “Darius” survey statistics (aggregated data for herring and sprat), included the total abundance of herrings and sprats are presented in Tables 2-4. The estimated age composition of sprat and herring are given in Tables 5, 10. The estimated number sprat and herring by age group and rectangle are given in Table 6, 11. The estimates of sprat and herring biomass by age group and rectangle are summarised in Table 7, 12. The corresponding mean weights and mean length by age group and rectangle for each species are shown in Table 8-9 and 13-14. The herring stock was estimated to be 108.6·106 fishes or about 2066 tonnes. The estimated sprat stock was 14933.4·106 fish or 112633 tonnes. 3.4. Hydrographic data Hydrographic data by hauls presented in the Table 15. The seawater temperature was 12.5 ºC in the surface layer in the first haul. Water temperature in others hauls was from 7 to 14 ºC. Differences between the first haul and others caused by wind direction. Wind direction was nord-east in the first half day of cruise. Later wind direction changed to east. There was no thermocline in 2018 of May 212 ICES | WGBIFS 2019 5 (Table.15). Salinity was about 6.7 ‰ in all hauls and depts. The oxygen-condition was excellent in all hauls and depts. 4 REFERENCES Balk, H. & Lindem, T. 2005. Sonar4, Sonar5 and Sonar6 post processing systems, operator manual version 5.9.6. Norway: Balk and Lindem. pp. 1-381 ICES 1983. Report of the Planning Group on ICES co-ordinated herring and sprat acoustic surveys. ICES CM 1983/H:12. ICES 2016. Manual for the international acoustic survey (BIFS). CM2003/G:05 Ref.: D, H; Appendix 9, Annex 3 Foote, K.G., Aglen, A. & Nakken, O. 1986. Measurement of fish target strength with a split-beam echosounder. J.Acoust.Soc.Am. 80(2):612-621. ICES | WGBIFS 2019 213 6 Figure1 The survey grid ant trawl hauls position of R/V “Darius” 08-09 May 2018 Table 1 Catch composition (kg/1hour) per haul (R/V "Darius", 08-09.05.2018) ICES subdivision 26 Haul No 1 2 3 4 5 6 Date 2018.05.08 2018.05.08 2017.05.08 2018.05.09 2018.05.09 2018.05.09 Validity Valid Valid Valid Valid Valid Valid Species/ICES rectangle 40H0 40H0 40G9 40G9 40G9 40H0 Clupea hrengus 1.5 0.68 8.67 1.26 2.0 17.6 Sprattus spratus 23.9 480.0 300.0 200 4.4 52.7 Gasterosteus aculeatus 0.035 0.32 0.01 Gadus morhua 0.9 Total 25.4 480.68 308.71 201.58 7.3 70.3 214 ICES | WGBIFS 2019 7 0 5 10 15 20 25 30 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 % Length, cm 40H0 Mean length: 10.0 cm 0 5 10 15 20 25 30 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 % Length, cm 40G9 Mean legth: 11,06 cm Figure 3 Length distribution of sprat (%) (R/V "Darius", 08-09.05.2018) 0 10 20 30 40 9 10 11 12 13 14 15 16 17 18 19 20 21 22 % Length, cm 40H0 Mean length: 12,03 cm 0 10 20 30 40 9 10 11 12 13 14 15 16 17 18 19 20 21 22 % Length, cm 40G9 Mean length: 16,22cm Figure 2. Length composition of herring (%) (R/V "Darius", 08-09.05.2018) Table 2 R/V "DARIUS" survey statistics (abundance of herring and sprat), 08-09.05.2018 ICES | WGBIFS 2019 215 8 ICES SD 26 ICES Area ρ Abundance, mln Biomass, tonn Rect. nm^2 mln/nm2 N sum N her N spr W sum W her W spr 40H0 1012.1 8.16 8261.8 59.0 8202.8 54886 678 54208 40G9 1013.0 6.69 6780.2 49.6 6730.6 59813 1388 58426 Table 3 R/V "DARIUS" survey statistics (aggregated data of herring and sprat), 08-09.05.2018 ICES SD 26 ICES No Herring Sprat SA TS calc. Rect. trawl L, cm w, g Numb.,% L, cm w, g Numb.,% m2/nm2 dB 40H0 1,2,6 12.03 11.49 0.71 10.05 6.61 99.29 809.6 -51.0 40G9 3,4,5 16.22 27.99 0.73 11.12 8.68 99.27 803.6 -50.2 Table 4 R/V "DARIUS" survey statistics (herring and sprat), 08-09.05.2018 ICES SD 26 ICES Rect. Area nm2 SA m2/nm2 σ *10^4 nm2 Abundance, mln Species composition (%) herring sprat 40H0 1012 809.6 0.99174 8261.8 0.71 99.29 40G9 1013 803.6 1.20062 6780.2 0.73 99.27 Table 5 R/V "Darius" estimated age composition (%) of sprat, 08-09.05.2018 SD 26 Rect. Age Total 0 1 2 3 4 5 6 7 8 40H0 100.0 0.0 43.6 7.6 12.6 20.7 7.5 4.0 3.1 0.8 40G9 100.0 0.0 9.9 12.1 15.7 32.0 19.3 7.9 2.2 0.9 Table 6 R/V "Darius" estimated number (millions) of sprat, 08-09.05.2018 SD 26 Rect. Age Total 0 1 2 3 4 5 6 7 8 40H0 8202.8 3580.1 620.7 1033.8 1699.4 616.2 327.3 257.4 67.9 40G9 6730.6 667.7 815.3 1058.0 2151.7 1299.5 531.3 149.0 58.2 Table 7 R/V "Darius" estimated biomass (in tons) of sprat, 08-09.05.2018 SD 26 Rect. Age Total 0 1 2 3 4 5 6 7 8 40H0 54208 12332 4775 8573 15268 5984 3452 2890 934 40G9 58426 2189 6434 9205 20103 12447 5714 1672 662 Table 8 R/V "Darius" estimated mean weights (g) of sprat, -08-09.05.2018 SD 26 Rect. Age Mean 0 1 2 3 4 5 6 7 8 40H0 6.61 3.4 7.7 8.3 9.0 9.7 10.5 11.2 13.8 40G9 8.68 3.28 7.89 8.70 9.34 9.58 10.75 11.22 11.38 Table 9 R/V "Darius" estimated mean length (cm) of sprat, 08-09.05.2018 SD 26 Rect. Age Mean 0 1 2 3 4 5 6 7 8 40H0 10.0 8.1 10.5 10.8 11.1 11.5 11.9 12.2 13.4 40G9 11.1 8.0 10.5 10.9 11.2 11.4 11.9 12.1 12.2 Table 10 R/V "Darius" estimated age composition (%) of herring, 08-09.05.2018 216 ICES | WGBIFS 2019 9 SD 26 Rect. Age Total 0 1 2 3 4 5 6 7 8 40H0 100.0 0.0 88.1 2.6 3.6 5.0 0.3 0.3 0.0 0.0 40G9 100.0 0.0 0.0 6.6 19.0 65.3 8.2 0.5 0.5 0.0 Table 11 R/V "Darius" estimated number (millions) of herring, 08-09.05.2018 SD 26 Rect. Age Total 0 1 2 3 4 5 6 7 8 40H0 59.0 52.0 1.6 2.1 2.9 0.2 0.2 40G9 49.6 3.2 9.4 32.4 4.1 0.2 0.2 Table 12 R/V "Darius" estimated biomass (in tons) of herring, 08-09.05.2018 SD Rect. Age Total 0 1 2 3 4 5 6 7 8 26 40H0 678 498.3 29.6 54.7 81.1 6.4 7.8 40G9 1388 63.1 251.8 919.8 138.6 5.3 8.8 Table 13 R/V "Darius" estimated mean weights (g) of herring, 08-09.05.2018 SD Rect. Age Total 0 1 2 3 4 5 6 7 8 26 40H0 11.5 9.6 19.0 25.5 27.8 33.0 40.1 40G9 28.0 19.4 26.7 28.4 34.1 23.1 38.2 Table 14 R/V "Darius" estimated mean length (cm) of herring, 08-09.05.2018 SD Rect. Age Total 0 1 2 3 4 5 6 7 8 26 40H0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 40G9 16.2 16.2 16.2 16.2 16.2 16.2 16.2 16.2 16.2 16.2 Table 15. The values of hydrological parameters registered at the catching depth in the Baltic Sea ICES SD from the Lithuanian BISS survey conducted by r/v "Darius" in the period of 08-09.05.2018 Haul number Date of catch Mean trawling depth, m Hydrological parameters Temperature, °C Salinity, ‰ Oxygen, ml/l 1 2018.05.08 32 11.1 6.7 7.4 2 2018.05.08 52 9.5 6.6 7.7 3 2018.05.08 56 7.4 6.7 8.1 4 2018.05.09 72 8.1 6.7 7.9 5 2018.05.09 76 8.4 6.7 7.9 6 2018.05.09 40 14.4 6.7 6.9 Average 60.7 ICES | WGBIFS 2019 217 1 REPORT FROM THE JOINT ESTONIAN-POLISH BASS 2018 CONDUCTED BY THE R.V. “BALTICA” IN THE NORTH-EASTERN BALTIC SEA (26-31 May 2018) by Miroslaw Wyszynski*, Ain Lankov**, Elor Sepp**, Andrus Hallang** and Tycjan Wodzinowski* * National Marine Fisheries Research Institute, Gdynia (Poland) ** University of Tartu, Estonian Marine Institute, Tallinn (Estonia) Introduction The recent joint Estonian-Polish Baltic Acoustic Spring Survey (BASS), marked with the number 8/2018/NMFRI/TUEMI was based on the procurement contract between the University of Tartu/Estonian Marine Institute in Tallinn and the National Marine Fisheries Research Institute in Gdynia. The survey was conducted in the Estonian EEZ (the ICES Sub- divisions 28.2, 29 and 32 West). The Estonian Data Collection Program for 2018 and the European Union (the Commission regulations Nos. 665/2008, 199/2008 and 2010/93/EU financially supported the EST-POL BASS 2018. Timing, surveying area in the North-eastern Baltic Sea and the principal methods of investigations concerns the above mentioned survey were designed and coordinated by the ICES WGBIFS (ICES 2018¹). The main aims of the reported cruise were:  to provide the echo-integration and to collect the acoustic data along the planed transects in the north-eastern Baltic Sea,  to conduct the fish pelagic control-catches in the fish concentration locations,  to collect ichthyological samples specially for herring and sprat,  to provide hydrological monitoring (water temperature, salinity and oxygen content) at the catch locations. Personnel The EST-POL BASS 2018 scientific staff was composed of 7 persons: Miroslaw Wyszynski (NMFRI, Gdynia – Poland) – survey leader Bartlomiej Nurek (NMFRI, Gdynia – Poland) – acoustician Tycjan Wodzinowski (NMFRI, Gdynia – Poland) – hydrologist Ain Lankov (TUEMI, Tallinn - Estonia) – Estonian scientific staff leader Andrus Hallang (TUEMI, Tallinn - Estonia) – ichthyologist Elor Sepp (TUEMI, Tallinn - Estonia) – acoustician Timo Arula (TUEMI, Tallinn - Estonia) – ichthyologist 1) ICES 2018. Report of the Baltic International Fish Survey Working Group (WGBIFS). ICES CM 2018/EOSG: 6. 218 ICES | WGBIFS 2019 2 Narrative The reported survey took place during the period of 26-31 May 2018. The at sea researches (echo-integration, fish control catches, hydrological and plankton stations) were conducted aboard r.v. “Baltica” within Estonian EEZ (the ICES Sub-divisions 28.2, 29 and 32 West), moreover inside the territorial waters of this country not shallower than 20 m depth. The survey started from the Ventspils port (Latvia) on 25.05.2018 after the midday and was navigated in the North-eastern direction to the entering point of planed acoustic transect at the geographical position 5917’N 02223’E on May 26 (Fig. 1). The at sea researches were ended on 30.05.2018 before the midday in the port of Ventspils (Latvia). Then the r.v. “Baltica” started its journey to the home-port in Gdynia (Poland), reaching it on 31.05.2018 afternoon. Survey design and realization The r.v. “Baltica” realized 392 Nm echo-integration transect and 15 fish control- catches (Fig. 1). All planed ICES rectangles were covered with acoustic transect and control catches. All control catches were performed in the daylight (between 07:40 am. and 17:50 p.m.) using the pelagic trawl type WP 53/64x4 (with 6 mm mesh bar length in the codend). The hauls trawling duration was varied from 15 to 30 minutes due to different fish densities observed on the net-sounder monitor. The mean speed of vessel while providing echo- integration was 8.0 knots, but in case of trawling was 3.0 knots. Overall, 4 hauls were conducted in SD 28.2, 8 hauls in SD 29 and 3 hauls in SD 32. The length measurements (in 0.5 cm classes) were realized for totally 3470 sprat and 3840 herring individuals. Totally, 409 sprat and 836 herring individuals were taken for biological analysis. Acoustic data were collected using the EK-60 echo-sounder equipped with “Echo- view V4.10” software for the data analysis. The acoustic equipment was calibrated at sea in the Gulf of Gdansk before the survey, according to the methodology described in the IBAS manual (ICES. 2015). The basic acoustic and biological data collected during recently carried out BASS were delivered to the TUEMI laboratories for further elaboration. Next they will be stored in the BASS_DB.mdb and the new acoustic data base WKBIFS-ACOU in the accepted CSV or XML formats, managed by ICES. The rosette sampler with connected CTD IDRONAUT probe were used for hydrological sampling, Data analysis The MYRIAX “EchoView v.4.10” software was used for the analysis of the acoustic data. The total number of fish in each the ICES rectangle was estimated as a product of the mean NASCs from scrutinized acoustic data and a rectangle area, divided by corresponding mean acoustic cross-section (σ) which is based on the trawl catch results. The abundance of clupeids was separated into sprat and herring according to the mean catch composition. Mean target strength (TS) – one of the principal acoustic parameter – of clupeids was calculated according to following formula: TS = 20 log L – 71.2 ICES | WGBIFS 2019 219 3 Due to fortunate weather conditions, all transects and planned trawls were conducted according to the plan. Catch results and fish measurements Overall, 9 fish species were recognized in hauls performed at the North-eastern Baltic Sea (SDs 28.2, 29 and 32 West) in May 2018. Sprat was prevailing species by mass in the total catch with the mean share amounted 62.6 % (especially high in SD 28.2 – 67.8%, but lowest in SD 29 – 54.5%). The rest 7 species (cod, flounder, three spine stickleback, smelt, lumpfish, lesser sandeel and fourbeard rockling) represented only about 0.75% of the total mass in average. The detailed catch and CPUE results are presented in the Table 1 and Fig. 2. The biological sampling is shown in Table 2. Mean CPUE for all species in the investigated area in May 2018 amounted 619.6 kg/h (comparing to 630.6 and 670.0 kg/h in the same period in 2017 and 2016 respectively). The highest CPUEs for sprat and herring was noted in SD 28.2. The mean CPUEs of sprat were as follow: 710.7 kg/h in ICES SD 28.2, 237.2 kg/h in SD 29 and 359.0 kg/h in SD 32. The mean CPUEs in case of herring were: 323.7, 190.2 and 173.3 kg/h in SDs 28.2, 29 and 32 respectively. Cod and three-spine stickleback prevailed among other species in bycatch with mean CPUEs 2.8 and 1.0 kg/h for all investigated area respectively. The length distributions of sprat, herring and three spine stickleback according to the ICES Sub-divisions 28.2, 29 and 32 are shown on Fig. 3-5. The sprat length distribution curves represent similar bimodal character in three investigated SDs. First frequency pick representing sprat generation born in 2017 take place on 7.5-8 cm length classes. The comparably high quantity of this generation was observed in Sub-division 28.2 only. The second pick representing adult sprat placed on 11 cm length class. The length distribution curves by Sub-divisions in case of herring show generally also two frequency picks – first one at 9 cm length class, second one at 14.5-15.5 cm length classes. The first pick shows low quantity of herring generation born in 2017 in both SDs 29 and 32, except slightly better quantity in SD 28.2. The length distribution of three spine stickleback was in range 4-8 cm with modal frequency at 6-6.5 cm length classes, taking into advice all investigated area. The length range of cod was between 17 and 46 cm with modal frequency at 23 cm length class. Acoustic results The survey statistics concerning the survey area, the mean NASC, the mean sigma, the estimated total number of fish, the percentages of herring and sprat per ICES statistical rectangles are presented in Table 3. Fish abundances were almost 50% lower than in 2017, with highest differences in open sea and northern areas. Abundance and biomass estimates The estimated abundances of herring and sprat by age group and Sub-division/ICES statistical rectangle are given in Table 4. The estimated biomass by age group and Sub- division/ICES statistical rectangle is shown in Table 5. Corresponding mean weights by age group and Sub-division/ICES statistical rectangle are summarized in Table 6. 220 ICES | WGBIFS 2019 4 Sprat abundance was two times lower compared to previous year and concentrations were evenly distributed through survey area. Average weights were similar with the 2017 results. Abundance of herring was about 20% lower compared to previous survey, but average weights were slightly higher. Meteorological and hydrological characteristics. The 15 control catches stations were inspected with the CTD-probe combined with the rosette sampler. Oxygen content was determined by the standard Winkler’s method. The CTD row data aggregated to the 1-m depth stratum. The Oxygen probes ware taken on every 10 meters, and on the catch depth. Changes of the main meteorological parameters during the joint EST-POL BASS conducted in May 2018 are presented at the Fig. 6. The wind force varied from 1°B to 4°B and average was 2.8°B The most often wind direction was ENE. The air temperature ranged from 13.0 °C to 18.0 °C, and average temperature was 14.7 °C. The seawater temperature in the sea water surface layers (Fig. 7) varied from 11,30 to 14.08°C (the mean was 12.97°C). The lowest surface temperatures were recorded at the haul 10. The highest ones were noticed at the haul 11. The minimum value of salinity in Practical Salinity Unit (PSU) was 5.46 at the haul 4 in the surface layer. The maximum was 7.07 PSU at the haul 15. The mean value of salinity was 6,38 PSU. The oxygen content in the surface layers of investigated the research area varied in the range of 8.09 ml/l (haul 8) - 9.43 ml/l (haul 7). The mean value of surface water oxygen content was 8.97 ml/l. The temperature at the control catch depth (Fig. 8) was changing in the range from 2.60 (haul 8) to 5.49 °C (haul 3), the mean was 4.78 °C. Salinity haul waters varied from 7.28 (haul 8) to 9.83 PSU (haul 3), and the mean was 9.04 PSU. Oxygen content varied from 1.05 ml/l (haul 6) to 6.89 ml/l (haul 8), the mean was 2.03 ml/l. The temperature of near bottom (Fig. 9) layer was changing in the range of 4.24 (haul 8) to 6.32 °C (haul 9), the mean was 5.90 °C. Salinity in the bottom waters varied from 8.46 to 11.58 PSU, and the mean was 10.80 PSU. The low values of salinity was at the haul 8. The highest values of salinity were noticed at the haul 9. Oxygen content varied from 0.00 ml/l to 4.96 ml/l (the mean was 0.71 ml/l). The zero values of this parameter were noticed at the hauls: 1, 2, 3 and 4. The vertical distributions of the seawater temperature, salinity and oxygen content along the hydrological profile during the joint EST-POL BASS (May 2018) are presented on the Fig. 10. The vertical hydrological profile at the one of the deepest measuring points (haul 9 start location) during EST-POL BASS in May 2018 is shown on the Fig. 11. The values of the meteorological and hydrological parameters recorded at the start positions of the r.v. “Baltica” fish control catches during the joint EST-POL BASS conducted in May 2018 are presented in the Tab. 7. ICES | WGBIFS 2019 221 5 The final report from the EST-POL BASS 2018 will be presented at the meeting of the ICES Baltic International Fish Survey Working Group (WGBIFS) at March 25-29, 2019 in Klaipeda (Lithuania). Fig. 1. Acoustic transects and pelagic fish control catches with connected hydrological stations realised during the joint EST-POL BASS (May 2018). 222 ICES | WGBIFS 2019 6 Table 1. Catch results during joint Estonian-Polish BASS conducted by r.v. “Baltica” in the Estonian EEZ in May 2018. Haul no Date ICES ICES Haul Total catch CPUE rectangle Sub-division latitude longitude latitude longitude start end duration [kg] [kg/h] sprat herring cod flounder lesser lumpfish fourbeard three-spined smelt (SD) 00°00.0'N00°00.0'E00°00.0'N00°00.0'E [min] sand eel rockling stickleback 1 2018-05-26 47H2 29 59°20.0' 22°51.9' 59°20.0' 22°54.8' 07:40 08:00 20 165,886 497,658 100,290 64,839 0,226 0,150 0,381 2 2018-05-26 47H3 32 59°27.7' 23°20.3' 59°27.8' 23°21.7' 11:15 11:30 15 227,415 909,660 159,580 67,376 0,255 0,204 3 2018-05-26 47H3 32 59°26.0' 23°39.4' 59°26.3' 23°40.3' 13:35 13:55 20 121,557 364,671 76,452 43,290 0,837 0,036 0,942 4 2018-05-26 48H4 32 59°33.9' 24°10.1' 59°34.1' 24°07.1' 17:00 17:30 30 166,300 332,600 104,669 60,267 0,017 1,347 5 2018-05-27 47H2 29 59°17.1' 22°23.1' 59°17.2' 22°20.4' 08:15 08:35 20 273,988 821,964 153,786 119,350 0,688 0,164 6 2018-05-27 47H1 29 59°16.6' 21°43.4' 59°16.2' 21°42.0' 11:30 11:45 15 74,737 298,948 48,931 24,777 0,577 0,452 7 2018-05-27 47H1 29 59°07.3' 21°15.6' 59°06.7' 21°16.5' 14:30 14:45 15 106,040 424,160 40,629 64,144 0,920 0,011 0,336 8 2018-05-27 46H1 29 58°53.8' 21°37.9' 58°52.8' 21°39.5' 17:20 17:50 30 34,181 68,362 20,579 12,584 0,161 0,857 9 2018-05-28 46H0 29 58°50.1' 20°44.6' 58°50.1' 20°44.6' 08:00 08:15 15 95,187 380,748 32,580 61,993 0,204 0,163 0,247 10 2018-05-28 46H0 29 58°37.8' 20°31.4' 58°37.6' 20°33.2' 10:55 11:15 20 46,024 138,072 23,748 20,266 1,231 0,153 0,626 11 2018-05-28 46H1 29 58°38.0' 21°22.8' 58°38.0' 21°25.7' 15:10 15:40 30 410,126 820,252 267,240 139,781 1,861 0,265 0,612 0,367 12 2018-05-28 45H1 28 58°23.1' 21°16.6' 58°23.0' 21°15.0' 19:20 19:40 30 122,597 245,194 76,458 43,828 1,802 0,255 0,254 13 2018-05-29 45H0 28 58°22.9' 20°36.2' 58°23.0' 20°34.0' 08:50 09:10 20 25,045 75,134 11,300 10,260 2,864 0,085 0,001 0,535 14 2018-05-29 45H0 28 58°04.8' 20°28.5' 58°04.8' 20°31.6' 12:35 13:05 30 375,684 751,368 225,200 145,351 4,432 0,552 0,149 15 2018-05-29 45H1 28 58°04.0' 21°00.3' 58°03.2' 21°00.5' 15:45 16:00 15 773,807 3095,228 551,450 221,462 0,206 0,071 0,618 Total 28 1297,133 1048,962 864,408 420,901 9,304 0,963 0,001 1,556 catch 29 1206,169 435,113 687,783 507,734 5,707 0,581 0,011 0,161 3,444 0,748 [kg] 32 515,272 538,980 340,701 170,933 1,092 0,257 2,289 Sum 3018,574 619,58 1892,892 1099,568 16,103 1,544 0,011 0,161 0,001 5,257 3,037 Catch per species [kg] Geographical position Time start end ICES | WGBIFS 2019 223 7 0 500 1000 1500 2000 2500 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 C PU E [k g/ h] Haul No sprat herring others Fig. 2. CPUE values (kg/h) of sprat and herring in particular pelagic fish control catches during the joint EST-POL BASS in the North-eastern Baltic Sea (Sub-divisions 28.2, 29 and 32), May 2018. 224 ICES | WGBIFS 2019 8 Table. 2. Biological sampling in the r.v.”Baltica” joint EST-POL BASS in May 2018. SD 28.2 SPRAT HERRING COD FLOUNDER LUMPFISH THREE SPINED SMELT FOURBEARD LESSER TOTAL STICKLEBACK ROCKLING SANDEEL Samples measurements 4 4 4 4 4 1 21 taken analyses 4 4 8 Fish measured 905 1047 50 9 95 1 2107 Fish analysed 129 302 431 SD 29 SPRAT HERRING COD FLOUNDER LUMPFISH THREE SPINED SMELT FOURBEARD LESSER TOTAL STICKLEBACK ROCKLING SANDEEL Samples measurements 8 8 7 4 1 8 2 1 39 taken analyses 8 8 16 Fish measured 1873 1992 29 4 1 325 6 1 4231 Fish analysed 153 317 470 SD 32 SPRAT HERRING COD FLOUNDER LUMPFISH THREE SPINED SMELT FOURBEARD LESSER TOTAL STICKLEBACK ROCKLING SANDEEL Samples measurements 3 3 2 3 2 13 taken analyses 3 3 6 Fish measured 692 801 4 17 24 1538 Fish analysed 127 217 344 SUM SPRAT HERRING COD FLOUNDER LUMPFISH THREE SPINED SMELT FOURBEARD LESSER TOTAL STICKLEBACK ROCKLING SANDEEL Samples measurements 15 15 13 8 1 15 4 1 1 73 taken analyses 15 15 30 Fish measured 3470 3840 83 13 1 437 30 1 1 7876 Fish analysed 409 836 1245 0 4 8 12 16 20 24 28 32 6, 5 7, 0 7, 5 8, 0 8, 5 9, 0 9, 5 10 ,0 10 ,5 11 ,0 11 ,5 12 ,0 12 ,5 13 ,0 13 ,5 14 ,0 L,cm SD 28.2 SD 29 SD 32 Fig. 3. Sprat length distributions from the control catches conducted by the r.v. “Baltica” during joint EST-POL BASS in the SDs 28.2, 29 and 32 (May 2018). ICES | WGBIFS 2019 225 9 0 2 4 6 8 10 12 14 16 18 Fr eq ue nc y, % L, cm SD 28.2 SD 29 SD 32 Fig. 4. Herring length distributions from the control catches conducted by the r.v. “Baltica” during joint EST-POL BASS in the SDs 28.2, 29 and 32 (May 2018). 0 4 8 12 16 20 24 28 32 36 40 44 48 52 4 4,5 5 5,5 6 6,5 7 7,5 8 L,cm SD 28.2 SD 29 SD 32 Fig. 5. Three spined stickleback length distributions from the control catches conducted by the r.v. “Baltica” during joint EST-POL BASS in the SDs 28.2, 29 and 32 (May 2018). 226 ICES | WGBIFS 2019 10 Table 3. The BASS survey basic biological and acoustic data concerning the clupeid stocks inhabiting the north- eastern Baltic Sea in May 2018. Area [NM2] Share [%-indiv.] Total abundance [x106] Abundance density [106/NM2] NASC [m2/NM2] σ [cm²] ICES Sub-div. ICES rectangle herring sprat 28 45H0 947.2 15.9 80.0 2404.71 2.539 312.9 1.233 28 45H1 827.1 12.0 87.6 2876.44 3.478 352.9 1.015 29 46H0 933.8 28.6 68.1 1855.21 1.987 264.8 1.333 29 46H1 921.5 15.3 79.4 2055.89 2.231 267.5 1.199 29 47H1 920.3 24.3 73.9 3361.61 3.653 468.5 1.283 29 47H2 793.9 19.6 79.9 1785.54 2.249 296.1 1.316 32 47H3 536.2 16.5 83.0 862.41 1.608 209.4 1.302 Average 18.9 78.8 2.535 310.3 1.240 Total 5880 15201 ICES | WGBIFS 2019 227 11 Table 4. Abundance (in 106 indiv.) of herring and sprat per age groups according to the ICES rectangles and Sub-divisions of the north-eastern Baltic in May 2018. ICES ICES rectangle HERRING – age groups Sub- div. 1 2 3 4 5 6 7 8+ total 28 45H0 42 18 18 152 18 63 55 17 383 28 45H1 104 13 14 111 13 42 35 12 344 total 146 31 31 263 32 106 90 28 727 29 46H0 89 38 37 190 29 89 28 31 531 29 46H1 21 30 35 150 13 42 11 11 314 29 47H1 11 117 86 390 37 119 28 29 817 29 47H2 9 39 40 173 18 50 12 11 350 total 131 224 197 903 97 300 78 82 2012 32 47H3 9 12 20 56 22 15 5 3 143 total 9 12 20 56 22 15 5 3 143 Grand total 285 268 248 1221 151 421 173 113 2881 228 ICES | WGBIFS 2019 12 Table 4. Continued ICES ICES rectangle SPRAT – age groups Sub- div. 1 2 3 4 5 6 7 8+ total 28 45H0 790 226 174 629 41 22 20 23 1924 28 45H1 1579 179 146 518 37 17 18 25 2519 total 2369 404 320 1146 78 38 39 47 4442 29 46H0 489 94 94 498 41 16 15 17 1263 29 46H1 563 82 115 645 76 50 46 54 1632 29 47H1 975 157 174 1016 73 29 28 32 2484 29 47H2 403 70 108 637 65 46 46 52 1426 total 2429 403 491 2796 255 140 135 156 6806 32 47H3 135 63 82 326 35 21 24 30 716 total 135 63 82 326 35 21 24 30 716 Grand total 4933 871 892 4269 368 200 198 232 11964 ICES | WGBIFS 2019 229 13 Table 5. Biomass (in tons) of herring and sprat per age groups according to the ICES rectangles and Sub-divisions of the north-eastern Baltic in May 2018. ICES ICES rectangle HERRING – age groups Sub-div. 1 2 3 4 5 6 7 8+ total 28 45H0 251 259 352 3195 473 1731 1680 640 8580 28 45H1 581 178 271 2330 344 1177 1092 453 6426 total 832 436 623 5525 817 2908 2772 1094 15006 29 46H0 492 460 514 4184 539 1835 1711 671 10406 29 46H1 129 358 410 3324 224 793 618 293 6149 29 47H1 89 1477 1011 8188 641 2165 1838 457 15866 29 47H2 61 447 474 3739 315 926 676 186 6824 total 771 2742 2409 19435 1719 5718 4843 1608 39245 32 47H3 43 221 181 1473 102 318 204 27 2568 total 43 221 181 1473 102 318 204 27 2568 Grand total 1646 3399 3212 26433 2638 8944 7819 2729 56819 230 ICES | WGBIFS 2019 14 Table 5. Continued ICES ICES rectangle SPRAT – age groups Sub-div. 1 2 3 4 5 6 7 8+ total 28 45H0 2504 1654 1389 4893 411 227 206 240 11523 28 45H1 5049 1364 1221 4192 380 175 187 279 12845 total 7553 3017 2610 9085 790 401 393 518 24368 29 46H0 1469 654 727 3921 370 176 157 183 7657 29 46H1 1682 615 955 5383 735 538 475 563 10945 29 47H1 2747 1111 1352 7897 649 317 288 340 14701 29 47H2 972 500 867 5087 606 485 460 536 9513 total 6870 2881 3900 22287 2360 1515 1379 1623 42816 32 47H3 350 487 626 2643 345 215 203 314 5183 total 350 487 626 2643 345 215 203 314 5183 Grand total 14773 6385 7136 34016 3495 2131 1976 2455 72367 ICES | WGBIFS 2019 231 15 Table 6. Mean weight (in grams) of herring and sprat per age groups, according to the ICES rectangles of the north-eastern Baltic in May 2018. ICES ICES rectangle HERRING – age groups Sub-div. 1 2 3 4 5 6 7 8+ avg. 28 45H0 6.05 14.24 20.07 21.03 25.59 27.26 30.54 38.55 22.42 28 45H1 5.57 13.60 20.07 21.02 25.82 27.76 31.23 38.78 18.67 29 46H0 5.52 12.06 13.95 22.01 18.56 20.72 61.38 21.58 19.60 29 46H1 6.00 12.00 11.74 22.16 16.88 18.70 58.30 25.64 19.58 29 47H1 8.08 12.59 11.81 21.02 17.17 18.19 65.50 15.79 19.42 29 47H2 6.83 11.41 11.91 21.63 18.01 18.49 58.45 17.72 19.48 32 47H3 5.00 17.70 8.98 26.35 4.55 21.31 40.61 8.64 18.02 232 ICES | WGBIFS 2019 16 Table 6, Continue ICES ICES rectangle SPRAT – age groups Sub-div, 1 2 3 4 5 6 7 8+ avg. 28 45H0 3.17 7.32 8.00 7.79 9.99 10.42 10.06 10.59 5.99 28 45H1 3.20 7.63 8.36 8.10 10.21 10.53 10.12 11.31 5.10 29 46H0 3.01 6.95 7.73 7.88 9.06 11.17 10.28 10.64 6.06 29 46H1 2.99 7.46 8.27 8.34 9.64 10.80 10.23 10.45 6.71 29 47H1 2.82 7.09 7.78 7.77 8.90 10.87 10.25 10.54 5.92 29 47H2 2.41 7.13 8.05 7.99 9.33 10.64 10.09 10.29 6.67 32 47H3 2.60 7.69 7.65 8.10 9.96 9.99 8.62 10.63 7.24 ICES | WGBIFS 2019 233 17 Fig. 6. Changes of the main meteorological parameters during the joint EST-POL BASS conducted in May 2018 (A and B – wind direction and velocity, C – air temperature). 234 ICES | WGBIFS 2019 18 Fig. 7. Horizontal distribution of the seawater temperature, salinity and oxygen content in the surface waters during the joint EST-POL BASS (May 2018) ICES | WGBIFS 2019 235 19 Fig. 8. Horizontal distribution of the seawater temperature, salinity and oxygen content on the control catch depth during the joint EST-POL BASS (May 2018) 236 ICES | WGBIFS 2019 20 Fig. 9. Horizontal distribution of the seawater temperature, salinity and oxygen content in the near bottom waters during the joint EST-POL BASS (May 2018). ICES | WGBIFS 2019 237 21 Fig. 10. Vertical distribution of the seawater temperature, salinity and oxygen content along the hydrological profile during the joint EST-POL BASS (May 2018). 238 ICES | WGBIFS 2019 22 8,80 8,86 8,23 7,74 5,15 1,340,91 0,10 0,00 0,00 0,00 0,11 0,09 0 25 50 75 100 125 0 2 4 6 8 10 12 14 temperature [°C] salinity PSU oxygen content [ml/l] Fig. 11. Vertical hydrological profile at the haul 9 start location during EST-POL BASS (May 2018). ICES | WGBIFS 2019 239 23 Table 7. Values of the basic meteorological and hydrological parameters recorded in May 2018 at the start positions of the r.v. “Baltica” fish control catches during joint EST-POL BASS. Number Date of haul of catch wind wind force sea state air temper. atmospheric temperature salinity oxygen direction [°B] [°C] pressure [hP] [°C] [PSU] [ml/l] 1 26-05-2018 E 2 1 13 1029 5,46 9,81 1,24 2 26-05-2018 E 2 1 14 1029 4,95 9,13 1,21 3 26-05-2018 NE 2 1 14 1029 5,49 9,83 1,36 4 26-05-2018 changeable 2 1 16 1028 5,26 9,56 2,03 5 27-05-2018 N 3 2 14 1027 5,30 9,61 1,43 6 27-05-2018 NE 4 2 15 1029 5,40 9,68 1,05 7 27-05-2018 NE 4 2 15 1030 5,33 9,58 1,13 8 27-05-2018 N 4 2 14 1029 2,60 7,28 6,89 9 28-05-2018 ENE 3 2 15 1031 4,84 8,88 1,34 10 28-05-2018 ENE 3 2 14 1031 4,65 8,65 1,28 11 28-05-2018 changeable 2 1 16 1030 4,62 8,69 1,34 12 28-05-2018 NNE 3 1 13 1030 4,94 8,98 1,46 13 29-05-2018 changeable 2 1 15 1026 5,47 9,72 1,14 14 29-05-2018 changeable 2 1 16 1025 3,93 8,17 3,92 15 29-05-2018 ENE 3 1 17 1024 3,44 8,05 3,68 Mean > 2,9 1,4 15,8 1101,9 5,12 9,69 2,18 * data at the mean depth of the fish control catch Meteorological parameters Hydrological parameters* 240 ICES | WGBIFS 2019 Institute of Food Safety, Animal Health and Environment – BIOR, Riga (Latvia) National Marine Fisheries Research Institute – NMFRI, Gdynia (Poland) THE CRUISE REPORT FROM THE JOINT LATVIAN-POLISH BALTIC ACOUSTIC SPRING SURVEY – BASS 2018 ON THE R/V “BALTICA” IN THE ICES SUBDIVISIONS 26N AND 28.2 OF THE BALTIC SEA (18-25 MAY 2018) Working paper on the WGBIFS meeting in Klaipeda, Lithuania, 25-29.03.2019 •FAUSTS SVECOVS•MIROSLAW WYSZYNSKI•TYCJAN WODZINOWSKI•BARTLOMIEJ NUREK• •GUNTARS STRODS•ANDREJS MAKARCUKS•ALLA VINGOVATOVA•GUNTA RUBENE• •LAURA BRIEKMANE•VADIMS CERVONCEVS• BIOR: Fausts Svecovs, Guntars Strods, Andrejs Makarcuks, Alla Vingovatova, Gunta Rubene, Ivars Putnis, Vadims Cervoncevs Fausts.Svecovs@bior.lv; Guntars.Strods@bior.lv NMFRI: Miroslaw Wyszynski, Tycjan Wodzinowski, Bartlomiej Nurek mwyszynski@mir.gdynia.pl; twodzinowski@mir.gdynia.pl Riga – Gdynia, March 2019 ICES | WGBIFS 2019 241 CONTENTS INTRODUCTION 3 1. MATERIALS AND METHODS 4 1.1. Personnel assignment 4 1.2. Survey description 4 1.3. Survey methods and performance 4 1.3.1. Acoustical and trawling methods 4 1.3.2. Biological sampling 5 1.3.2. Hydrological and meteorological observations 5 2. RESULTS 5 2.1. Biological data 5 2.1.1. Catch statistics 5 2.1.2. Acoustical and biological estimates 6 2.1.3. Ichthyoplankton estimates 7 2.1.4. Zooplankton estimates 7 2.2. Meteorological and hydrological data 8 2.2.1. Weather conditions 8 2.2.2. Hydrology of the Gotland Deep 8 3. DISCUSSION 8 REFERENCES 9 ANNEX. TABLES AND FIGURES 11 242 ICES | WGBIFS 2019 INTRODUCTION More less regular acoustic estimations of pelagic fish stocks in the Baltic Sea initiated by BaltNIIRH (now BIOR) and Institute für Hochseefischerei in Rostock (GDR) was performed since 1983, but the first scattered surveys was made since 1977 [Shvetsov 1983, Hoziosky et al. 1987, Shvetsov et al. 1988]. Several years in May (2005-2008) BIOR as assignee of BaltNIIRH, LatFRI and LatFRA cooperated with Polish NMFRI (former SFI) in Gdynia, but before – in 2003- 2004 with AtlantNIRO in Kaliningrad, Russia. In 2009 due to collapse of Latvian economy the survey was not performed. In 2010 we resumed our international cooperation in the fisheries research, but this time on the Lithuanian r/v “Darius” board. The collaboration lasted for three years till the 2012. In May 2013 The Latvian Baltic Acoustic Spring Survey (BASS) in the ICES Sub-divisions 26N and 28 was conducted on Latvian commercial fishing vessel “Ulrika” with which crew and the owners cooperation in research for pelagic fish distribution and feeding conditions in the recent decade has developed a very close and productive. Due to BONUS EEIG project INSPIRE (INSPIRE) funding historically the first Latvian-Estonian joint BASS in the ICES Sub-divisions 26N, 28 29 and 32W in May 2014 was conducted on the Latvian commercial fishing vessel “Ulrika” and in May 2015 the same survey was performed, too [Svecovs et al., 2015, 2016]. In May 2016 we renew cooperation with Polish NMFRI. This was the 7th joint Latvian-Polish Baltic Acoustic Spring Survey (BASS) in the ICES Sub-divisions 26N and 28.2 conducted by the r/v “Baltica” in May 2018. The reported survey was organized on the basis of the public procurement contract No. BIOR 2018/3/AK/EJZF from 14 February 2018 between the Institute of Food Safety, Animal Health and Environment (BIOR) from Riga and the National Marine Fisheries Research Institute (NMFRI) from Gdynia. The vessel was operated within the Latvian, Swedish and Estonian EEZs (ICES Sub-divisions 26N and 28.2). The “Latvian National Fisheries Data Collection Program, 2018” in accordance with the EU Commission Regulations No. 1639/2001, 1581/2004, 665/2008, 1078/2008 and 199/2008 was partly subsidized this survey. These investigations were coordinated by the ICES Baltic International Fish Survey Working Group (WGBIFS) [ICES 2018]. Pelagic research catches carried out during the acoustic survey are the information source, independent from topical preferences in fishery, about quantitative changes in a process of clupeids geographical and bathymetrical distribution in the Baltic Sea. The data from hydrological measurements are the information source about abiotic environmental factors (seawater temperature, salinity, oxygen content) influencing sprat and herring spatial distribution. Echo-integration results along the pre-selected tracks are the basic materials for fish stock biomass calculations. The ICES Baltic Fisheries Assessment Working Group (WGBFAS) applies the BASS data for clupeids (specially sprat and herring) stock biomass assessment and spatial distribution updating. The basic acoustic and biological data collected during recently carried out survey will be stored in the BASS_DB.mdb and the new acoustic data base WKBIFS-ACOU in the accepted CSV or XML formats, managed by ICES. The main aims of cruise were: • to collect the echo-integration data for the estimation of the clupeids stocks biomass and abundance in the central-eastern Baltic; • to collect materials from the fish control catches for investigations of the Baltic sprat, and in lesser degree herring, spawning stocks spatial distribution in the offshore waters of Latvia, Estonia and Sweden, moreover for analyses of the age-length structure and recruiting year-class strength of these fishes populations; • to collect sprat and herring stomachs samples for feeding condition and food components analyses; • to analyze the vertical and horizontal changes of the basic hydrological parameters (temperature, salinity and oxygen content) at the trawling positions and at the standard HELCOM hydrological stations; • to collect the zooplankton and ichthyoplankton samples at the referring area. ICES | WGBIFS 2019 243 1. MATERIALS AND METHODS 1.1. PERSONNEL ASSIGNMENT The scientific staff – seven persons: F. Svecovs, (BIOR, Riga – Latvia) – scientific staff leader, acoustic team; M. Wyszynski (NMFRI, Gdynia – Poland) – cruise leader, fish sampling team; T. Wodzinowski (NMFRI, Gdynia – Poland) – hydrologist, hydrology team; B. Nurek (NMFRI, Gdynia – Poland) – acoustician, acoustic team; G. Strods (BIOR, Riga – Latvia) – ichthyologist, acoustic and fish sampling team; V. Cervoncevs (BIOR, Riga – Latvia) – ichthyologist, fish sampling team; L. Briekmane (BIOR, Riga – Latvia) – ichthyologist, fish sampling team; A. Makarcuks (BIOR, Riga – Latvia) – hydrobiologist, hydrobiology and fish sampling team. 1.2. SURVEY DESCRIPTION The reported survey took place during the period of 18-25 May 2018 (8 working days at sea in accordance with Latvian-Polish survey plan). The at sea researches were conducted within Latvian and Swedish EEZs (the ICES Sub- divisions 26N and 28.2), moreover inside the Latvian territorial waters not shallower than 20 m. The vessel left the Gdynia port (Poland) on 17.05.2018 at 08:00 o’clock p.m. and was navigated in the north direction to the echo-integration start point at the geographical position 56°07’N 019°00’E. The direct at sea researches began on 18.05.2018 after midday. The survey ended on 25.05.2018 before midday in the port Ventspils (Latvia). 1.3. SURVEY METHODS AND PERFORMANCE 1.3.1. ACOUSTICAL AND TRAWLING METHODS Acoustic data were collected with the SIMRAD EK-60 38 kHz and 120 kHz two frequency split beam scientific echo- sounder equipped with “EchoView Version 7.10” software for the data analysis. These data collected during the described here BASS were delivered to the Latvian researchers for further elaboration. The survey echo-integration tracks were planned in the similar pattern as in the previous years, due to historical comparability of the data. Overall 585 nautical miles long survey tracks was observed and recorded with hydroacoustic equipment. The final pattern of transects was covered with a relatively good density. The area covered in May 2018 was 1953.3 nm2 in the northern part of the ICES Sub-division 26 and 7874.9 nm2 in Sub-division 28.2, totally 9828.2 nm2 (Fig. 1). The pre-selection of the pelagic fish catches based on the ICES statistical rectangle area (with range of 0.5 degree in latitude and 1 degree in longitude) and the present density pattern of vertical distribution of clupeids along a transect. The intention was to carry out at least two control hauls per the ICES statistical rectangle [ICES 2003]. The water depth range-layer with sufficient for fish oxygen content (minimum 1.0÷2.0 ml/l) were taken into account in the process of the hauls distribution. Survey was performed in accordance to “SISP Manual of International Baltic Acoustic Surveys (IBAS)” [ICES 2014]. The r/v “Baltica” realized 19 fish control-catches (Tab. 1). All catches were performed in the daylight between 07:20 and 19:30 (GMT+01:00; UTC+02:00) using the pelagic trawl type WP 53/64x4 (with 6 mm mesh bar length in the codend). The standard trawling duration was 30 minutes, but two hauls was shortened to 20 minutes and three hauls to 15 minutes, according to higher power of the echo-integration. The mean speed of vessel while trawling was 3.1 knots. Overall, 3 hauls were conducted in SD 26N and 16 hauls in SD 28.2. Totally 14 hauls were performed in the Latvian EEZ and 5 hauls in Swedish EEZ 244 ICES | WGBIFS 2019 1.3.2. BIOLOGICAL SAMPLING All biological material of fish collected in the survey is presented in Table 2. The length measurements (in 0.5 cm length classes) were realized for 3893 sprat, 2856 herring, 534 cod and 223 flounder individuals. In total, 1712 sprat and 1578 herring individuals were taken for biological analysis. Detailed ichthyologic analyses were made according to standard procedures, directly on board of surveying vessel. Due to herring and sprat normally cannot be distinguished from other species by visual inspection of the echogram species composition and fish length distributions were based on trawl catch results. Mean target strength of fish was calculated according to the following formulas [Foote et al. 1986, ICES 1983, 2014]: for clupeids: TS = 20logL-71.2; for gadoids: TS = 20logL-67.5; cross section σ = 4π10a/10×Lb/10. The total number of fish in each ICES rectangle was estimated as a product of the mean area scattering cross-section – NASC (SA) and the rectangle area, divided by corresponding mean acoustic cross-section. Fish abundance was separated into different species according to the mean catch composition in the given rectangle. Ichthyoplankton and zooplankton samples were collected at the positions of the hydrological stations or after trawling. Totally 23 ichthyoplankton and zooplankton stations were realized (Fig. 2) and 46 and 38 samples were taken accordingly. Ichthyoplankton was collected with IKS-80 net (mouth opening 0.5 m2, mesh size 500 μm). This net was towed vertically from the depths 150 or from the bottom in case of lesser depth, to the water surface with speed of 0.4 m/s. Zooplankton was collected with Judday net (mouth opening 0.1 m2, mesh size 160 μm). This net was towed vertically from the depths 50 and 100, or from the bottom in case of lesser depth, to the water surface with speed of 0.4 m/s. Low speed of lifting allowed preventing all plankton objects from destroying by mechanic forces. All samples were conserved in 2.5% unbuffered formaldehyde solution with sea water and processed during the year. 1.3.2. HYDROLOGICAL AND METEOROLOGICAL OBSERVATIONS The measurements of the basic hydrological parameters were realized in the period of 18-25 May 2018, totally at 23 stations, int. al. at 19 fish catch-station (Fig. 2). Hydrological stations were inspected with the IDRONAUT CTD- probe combined with the rosette sampler (the bathometer rosette). Oxygen content was determined by the standard Winkler’s method. The hydrological row data, originated from measuring realized from the sea surface layer up to the bottom, were aggregated to the 1-m depth stratums, were information source about the abiotic factors potentially influencing fishes spatial distribution. The oxygen probes ware taken on every 10 meters. The salinity parameter was presented in Practical Salinity Unit (PSU). Meteorological observations of air temperature, wind velocity and directions and atmospheric pressure were realized at the actual geographic position of each control-haul and in every 10 minutes interval over the whole survey. The automatic meteorological station type “Milosz” was applied for measurements of the above-mentioned parameters. The values of meteorological and hydrological parameters registered at trawling stations are aggregated in Table 3. 2. RESULTS 2.1. BIOLOGICAL DATA 2.1.1. CATCH STATISTICS Overall, 7 fish species were recognized in hauls performed in the Central-eastern Baltic Sea in May 2018. Sprat was dominating species by mass in the both ICES Sub-divisions 26N and 28.2 (83.4 and 76.9 % respectively). The share of the herring constitutes 15.2 and 21.4 % respectively. The rest 5 species represented 1.7 % (in this 1.3 % belonging to cod) of the total mass in average for all investigated area. Mean CPUE in BASS 2018 for all species in the investigated area amounted 1253.7 kg/h (comparing to 1436.4 and 1404.7 kg/h in 2017 and 2016 respectively). The mean CPUEs of sprat were: 1353.4 kg/h in ICES SD 26N, and 910.5 ICES | WGBIFS 2019 245 kg/h in SD 28.2. The mean CPUEs of herring were as follow: in SD 26N – 246.5 kg/h and 253.5 kg/h in SD 28.2. The CPUE values by particular haul for herring and sprat and are presented at the Fig. 2. The highest CPUE values for sprat were noted from the Central-western part of SD 28.2 to the Northern part of SD 26. The good CPUEs for herring were distributed more in Central part of SD 28.2 and partly in Northern SD 26. 2.1.2. ACOUSTICAL AND BIOLOGICAL ESTIMATES The basic acoustic and biological data (surveyed area statistics, mean NASC, the mean scattering cross-section, the total number of fish, percentages of herring and sprat) per ICES rectangles and the estimated abundance and biomass of sprat and herring per above mentioned rectangles, collected in May 2018, are given in Table 5. The characteristics of the pelagic fish stock are aggregated in Table 6 for sprat and Table 7 for herring. The geographical distributions of NASC, sprat and herring stock densities in the central-eastern Baltic Sea in May 2018 are shown in Figures 5, 6 and 7 respectively. The pelagic fish stock was represented mostly by sprat – 93.8 %, in comparison – 71.5% in 2013, 86.8 % in 2014, 88.2 % in 2015 and 92.9 % in 2016 and 94.1 % in 2017. Herring was represented as 6.2 %, 28.5 % in 2013, 13.2 % in 2014, 11.8 % in 2015, 7.1 % in 2016 and 5.9 % in 2017. The highest sprat stock density 108.8 n×106/nm2 according to acoustic estimates were recorded in ICES rectangle 41G9 of the ICES Sub-division 26. The highest average abundance 7.2 n×106/nm2 and biomass of the sprat stock were recorded in the southern part of investigated area in ICES rectangle 41G9. The distribution of the high density sprat concentrations in May 2018 had different pattern as in May 2017 and more-less copy distribution in previous years [Hoziosky et al. 1988, Shvetsov et al. 1988, 1989, 1992, 2002, Svecovs 2016]. The herring stock density was significantly lower in comparison to sprat stock density. The highest density value was 9.7 n×106/nm2 and noted in ICES rectangle 43H1 in central part of the investigated area in Sub-division 28.2 and was on the same level as in 2015 were highest density values was not over 10.2 n×106/nm2 in rectangle 44H0, in 2013 it was 8.8 n×106/nm2 in rectangle 44H0, in 2014 values over 10.0 n×106/nm2 were recorded in two rectangles 43H0 and 45H0, in 2016 the highest density 18.1 n×106/nm2 was recorded in rectangle 42G9 in central part of estimated aquatory and in May 2017 the highest density 26.1 n×106/nm2 was recorded in rectangle 44H0 in northern part of estimated aquatory. Comparison of the acoustic results from May of 2005-2016 indicated that investigated sprat stock abundance and biomass had decreasing tendency, but herring stock had a slight increase. In 2017 both of sprat and herring stocks had decreased in numbers, but in biomass herring stock had significantly increased. In 2018 sprat stock had significant decrease, but herring stock significant increase in abundance. The geographical distribution of main sprat stock shows different pattern as in years 2005-2016 and 2018 and 2017 when stock was less scattered with two large and dense concentrations of high abundance [Svecovs et al. 2010, 2011, 2012, 2013, 2014, 2015, 2016]. The mean length and mean weight distributions of dominant fish species (sprat and herring) by hauls and rectangles in the ICES Sub-divisions 26 and 28 are shown in Figures 8 and 9 respectively. The total length and mean weight in control hauls of sprat, herring and cod ranged as follows: • sprat – 7.0÷14.0 cm (average TL = 10.8 cm), 1.9÷15.4 g (average W = 7.1 g); • herring – 8.0÷24.0 cm (average TL = 16.3 cm), 3.4÷66.2 g (average W = 26.4 g); The sprat length distribution curves have a bimodal character for both above mentioned Sub-divisions. First length frequency pick takes place at 8.5 and 8 cm length classes in SDs 26 and 28.2 respectively, with considerably higher frequency values in SD 28.2 comparing to data from 2017. It represents sprat generation born in 2017. The second higher one at length classes 12 cm (SD 26) and 11 cm (SD 28.2) represents adult sprat. The herring length distribution curves have a similar multimodal character in both Sub-divisions 26N and 28.2. The highest picks of frequency belong to length classes 17 and 16 cm respectively. The fish representing 8-13 cm length range belonging to the herring generation born in 2017 characterized by very low frequency in both above mentioned SDs. The cod and flounder abundance in the pelagic control catches was considerably higher, comparing to the data from the recent years. Cod from SD 26 characterized by fish length range 18-43 cm, with modal frequency value at 35 cm length class. But in SD 28.2 its length range was 15-53 cm, and modal frequency values at 22-24 cm length classes. Flounder appearance was more abundant in the catches in SD 28.2. Its length ranged from 18 to 34 cm, with modal frequency values at 23-26 cm length classes. Comparably higher appearance of bottom fish species, like cod and 246 ICES | WGBIFS 2019 flounder in pelagic zone of SDs 26N and 28.2 during the BASS 2018 survey was impacted by low water oxygenation below 70 m depth coming to the oxygen value of 0 ml/l. The data related to cod aggregated in Table 8, length distributions of cod and flounder shown in Figures 10 and 11. 2.1.3. ICHTHYOPLANKTON ESTIMATES Totally 46 ichthyoplankton samples collected at 23 station positions during BASS on RV “Baltica”, including 23 samples collected in vertical hauls with IKS-80 net and 23 samples from horizontal hauls on water surface during 10 minutes. The number of sprat eggs and larvae in ICES SD 26 and 28 are aggregated in Table 9. Sprat eggs and larvae prevailed in the ichthyoplankton in May 2018. The average numbers of sprat eggs in the investigated region were above the corresponding average values for the previous years. Sprat eggs were more abundant in the southern and central parts of the Gotland Basin. Amount of eggs of sprat as usual increased towards the greater depths near the center of the basin. Amount of sprat larvae was below the average values for the previous years. Most of the larvae were sampled in the vertical hauls. They also were more numerous over the bigger depths and in the southern part of the Gotland Basin. There amount gradually decreased towards the northern areas. Sprat larvae in the water surface layer were not numerous in all the parts of the Gotland Basin with maximal abundance in the central part of the Gotland Basin. This must be the evidence that the spawning of sprat this year has started moderately early. This year there were fewer larvae of flounder compared with the years 2015-2017. All the larvae were collected on the water surface. They were more abundant in the central part of the Gotland Basin. The hydrological conditions in the Gotland Basin in 2018 were very bad for the survival of eggs of cod and four- bearded rockling. As a result only one egg and no larvae of cod were found. No rockling eggs and larvae were registered for the first time in recent years. Rather many herring larvae were sampled in the shallow waters close to the shoreline to the north from Liepaja. Biodiversity in the ichthyoplankton was on the low level – one egg of cod and also some larvae of flounder, herring and sand-eel were found in May, apart from those of sprat. 2.1.4. ZOOPLANKTON ESTIMATES The calculated average number and average biomass of zooplankton organisms in 0-100 m water column per volume unit from 38 samples taken in 23 stations are aggregated in Table 10. In May 2018 in the Baltic Sea the estimated zooplankton biomass was lower in comparison to 2017. Total zooplankton biomass in 2017 was 243.72 mg/m3, but in May 2018 194.20 mg/m3. The most part of the biomass (37.42 %) was made from small rotatories and copepods (42.99 %), the residual part was made from cladocers (3.80 %) and other planktonic organisms (15.79 %). The dominance of rotatorians in the spring season in the Baltic Sea creates favorable feeding conditions for larvae and smaller groups of pelagic fish species. Amount of them in 2017 and 2018 on average was significantly higher than in 2014 and the long-term average. Overall, the biomass of Temora longicornis, taking the top rank among copepods, has the same biomass as in May 2016. Pseudocalanus sp. and Acartia spp. biomass had decreased in comparison to 2016, but is higher than in 2014. In 2017 increased average biomass of rotatorians Synchaeta spp. and Polychaeta worms and still remains the same in May 2018. In 2017 and 2018 had increased the role of above mentioned copepods in all aquatory. In deep stations has dramatically decreased estimated quantity and biomass of Centropages hamatus – approximately by 3 times than was stated in 2016. In the upper layer (0-50 m) of water column the dominant object of zooplankton was rotatorians Synchaeta spp. and cladocerans Evadne spp. Biomass of Evadne spp. was at lower level than in 2016 and almost close to the level of long-term average. Overall, the favorable feeding conditions in May 2018 as in 2017 formed in the upper water column of the investigated area. ICES | WGBIFS 2019 247 2.2. METEOROLOGICAL AND HYDROLOGICAL DATA 2.2.1. WEATHER CONDITIONS Changes of the main meteorological parameters during joint LAT-POL BASS in May 2017 are shown at the Figure 12. The wind force varied from 2°B to 7°B and average was 3.6°B. The most often wind direction was from North direction. The air temperature ranged from 9.0 °C to 15.0 °C, and average temperature was 11.2 °C. 2.2.2. HYDROLOGY OF THE GOTLAND DEEP The seawater temperature in the surface layers (Fig. 13) varied from 7.42 to 13.74°C (the mean was 10.34°C). The lowest surface temperatures were recorded at the station T06. The highest ones were noticed at the haul 15 station. The minimum value of salinity in Practical Salinity Unit (PSU) was 6.70 at the station 00 in the surface layer. The maximum was 7.39 PSU at the haul 3 station. The mean value of salinity was 7.18 PSU. The oxygen content in the surface layers of investigated the research area varied in the range of 8.27 ml/l (haul 6) - 9.73 ml/l (haul 10). The mean value of surface water oxygen content was 9.02 ml/l. The temperature at the depth layer of hauls was changing (Fig. 14) in the range from 3.01 (haul 7) to 5.57 °C (haul 9), the mean was 4.50 °C. Salinity haul waters varied from 7.39 (haul 12) to 9.94 PSU (haul 9), and the mean was 8.78 PSU. Oxygen content varied from 0.50 ml/l (haul 9) to 8.67 ml/l (haul 7), the mean was 4.01 ml/l. The temperature of near bottom (Fig.15.) layer was changing in the range of 2.89 (station 00) – 7.09 °C (station 46), the mean was 5.77 °C. Salinity in the bottom waters varied from 7.45 to 13.29 PSU, and the mean was 10.90 PSU. The low values of salinity were at the haul 6 station. The highest values of salinity were noticed at the station 37. Oxygen content varied from 0.00 ml/l to 8.12 ml/l (the mean was 1.74 ml/l). The zero values of this parameter were noticed at the station 37, haul stations 8 and 9. The vertical distributions of the main hydrological parameters (sea water temperature, salinity and oxygen content) at the vertical hydrological profile at the deepest station (Haul 14 / station 37) in the Southern Gotland Deep measured during the LAT-POL BASS in May 2018 are presented at the Fig. 16, as well as at the hydrological profile of the Gotland Deep is shown at Fig. 17. Values of the basic meteorological and hydrological parameters recorded at the mean depth layer of fish control catches are presented at the table 3. 3. DISCUSSION The data of the Latvian-Polish BASS in the 2nd quarter of 2018 were considered by the ICES BIFS Working Group as representative for the central-eastern Baltic for the estimation of abundance and spatial distribution of pelagic fishes (herring and sprat) recruiting year classes and were provided to the Baltic Fisheries Assessment Working Group (WGBFAS) as the input data for fish stocks resources calculation. The acoustic, catch, biological and hydrological data, collected during reported survey were uploaded to the BAD1 and to the emerging international databases managed by the ICES Secretariat. The collected data shows that sprat population in ICES SD 26N and 28.2 till the 2014 had overall decreasing tendency of abundance, but since 2015 is increasing due to very abundant sprat generation of 2014. The mean length and weight of adult sprat had the same tendency to abundance. The geographical distribution of sprat densities in the May 2018 had different pattern as in 2017 and shows smaller aggregations with high densities. The overall estimated good feeding conditions should ensure increasing of individual fish body condition and young fish surviving of pelagic fish species in future. 248 ICES | WGBIFS 2019 REFERENCES Foote, K., Aglen, G. and Nakken, O. 1986. Measurement of fish target strength with split-beam echosounder. J. Acoust. Soc. Am. 80; 612-621. Grygiel, W. 2006. Polish-Latvian co-operation in biological and acoustic investigations of fish andenvironment of the Baltic Sea (May, October 2005). Wiadomości Rybackie, No. 1-2 (149), edited by the Sea Fisheries Institute, Gdynia; 14-17. Grygiel, W., Svecovs, F., Grelowski, A., Strods, G. and Cervoncevs, V. 2006. Research report from the Latvian-Polish acoustic survey in the central-eastern Baltic (October 2005). 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Shvetsov, F., Grygiel, W., Fetter, M., Chervontsev, V., and Rudneva, A. 1992. Distribution and size of herring and sprat stocks in the Baltic Proper, determined by the acoustic method (October, 1991). ICES C.M. 1992/J:8. ICES | WGBIFS 2019 249 Svecovs, F., Grygiel, W., Grelowski A., Slembarski, J., Strods, G., Putnis, I., Cervoncevs, V., Kazmers, I. 2012. Cruise report of the joint Latvian-Polish Baltic international acoustic survey – BIAS 2012 on the r/v “Baltica” in the ices subdivisions 26N and 28 of the Baltic sea (10-19.10.2012), BIOR-Riga/SFI-Gdynia document (February 2013), 48 pp. (mimeo). Shvetsov, F., Feldman, V., Severin, V., Zezera, A., Strods, G. 2002. Application of Hydroacoustic Survey Results in Studies of Eastern Baltic Sprat Distribution and Migration Pattern. Proceedings of the 6th European Conference on Underwater Acoustics. Gdansk p. 457-461. Svecovs, F., Strods, G., Berzins, V., Makarcuks, A., Cervoncevs, V., Spegys, M. 2010. Cruise report of the joint Latvian- Lithuanian Baltic acoustic spring survey – BASS 2010 on the r/v “Darius” in the ices subdivisions 26N and 28 of the Baltic sea (12-19.05.2010), BIOR-Riga/FRL-Klaipeda document (September 2010), 30 pp. (mimeo). Svecovs, F., Strods, G., Berzins, V., Makarcuks, A., Putnis, I., Spegys, M. 2011. Cruise report of the joint Latvian- Lithuanian Baltic acoustic spring survey – BASS 2011 on the r/v “Darius” in the ices subdivisions 26N and 28 of the Baltic sea (10-22.05.2011), BIOR-Riga/FRL-Klaipeda document (February 2012), 33 pp. (mimeo). Svecovs, F., Strods, G., Berzins, V., Makarcuks, A., Putnis, I., Kruze, E. 2012. Cruise report of the joint Latvian- Lithuanian Baltic acoustic spring survey – BASS 2012 on the r/v “Darius” in the ices subdivisions 26N and 28 of the Baltic sea (31.05-08.06.2012), BIOR-Riga/FRL-Klaipeda document (February 2013), 24 pp. (mimeo). Svecovs, F., Strods, G., Berzins, V., Makarcuks, A., Putnis, I., Cervoncevs, V., Rubene, G. 2013. Cruise report of the Latvian Baltic acoustic spring survey – BASS 2013 on the r/v “Ulrika” in the ices subdivisions 26N and 28 of the Baltic sea (21-29.05.2013), BIOR-Riga document (March 2013), 32 pp. (mimeo). Svecovs, F., Strods, G., Makarcuks, A., Sepp, E., Arula, T., Berzins, V., Putnis, I., Rubene, G. 2014. Cruise report of the joint Latvian-Estonian Baltic acoustic spring survey – BASS 2014 on the r/v “Ulrika” in the ices subdivisions 26N, 28, 29 and 32W of the Baltic sea (14-26.05.2014), BIOR-Riga/EMI-Tallinn document (March 2015), 37 pp. (mimeo). Svecovs, F., Strods, G., Makarcuks, A., Sepp, E., Arula, T., Putnis, I. 2015. Cruise report of the joint Latvian-Estonian Baltic acoustic spring survey – BASS 2015 on the r/v “Ulrika” in the ices subdivisions 26N, 28, 29 and 32W of the Baltic sea (12-24.05.2015), BIOR-Riga/EMI-Tallinn document (March 2016), 28 pp. (mimeo). Svecovs, F., Wyszynski, M., Slembarski, J., Witalis, B., Strods, G., Cervoncevs, V., Putnis, I. 2011. Cruise report of the joint Latvian-Polish Baltic international acoustic survey – BIAS 2011 on the r/v “Baltica” in the ices subdivisions 26N and 28 of the Baltic sea (11-21.10.2011), BIOR-Riga/SFI-Gdynia document (February 2012), 33 pp. (mimeo). Svecovs, F., Wyszynski, M., Slembarski, J., Wodzinowski, T., Strods, G., Cervoncevs, V., Putnis, I., Kruze E., Bajinskis J. 2013. Cruise report of the joint Latvian-Polish Baltic international acoustic survey – BIAS 2013 on the r/v “Baltica” in the ices subdivisions 26N and 28 of the Baltic sea (09-18.10.2013), BIOR-Riga/SFI-Gdynia document (March 2014), 50 pp. (mimeo). Svecovs, F., Wyszynski, M., Witalis, Slembarski, J., B., Strods, G., Makarcuks, A., Vingovatova, A., Rubene, G., Cervoncevs, V., Putnis, I. 2016. Cruise report of the joint Latvian-Polish Baltic acoustic spring survey – BASS 2016 on the r/v “Baltica” in the ICES subdivisions 26N and 28.2 of the Baltic sea (12-21.10.2016), BIOR-Riga/SFI-Gdynia document (March 2016), 33 pp. (mimeo). 250 ICES | WGBIFS 2019 ANNEX. TABLES AND FIGURES Table 1. Fish control-catch statistics in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018 Haul number Date ICES rectangle ICES SD Mean bottom depth [m] Headrope depth [m] Vertical opening [m] Trawling speed [knt] Trawling direction [°] Geographical position Time Start Haul duration [min] Total catch [kg] Start End Latitude 00°00.0'N Longitude 00°00.0'E Latitude 00°00.0'N Longitude 00°00.0'E 1 2018-05-19 41G9 26 58 36 16 3.3 150 56°04.2' 19°47.4' 56°02.8' 19°48.7' 07:50 30 334.879 2 2018-05-19 41H0 26 59 40 18 3.4 190 56°21.8' 20°10.5' 56°20.3' 20°09.7' 16:10 30 531.270 3 2018-05-19 41G9 26 87 55 18 3.0 220 56°22.0' 19°49.4' 56°21.3' 19°48.5' 19:05 15 783.505 4 2018-05-20 42G9 28.2 127 60 18 3.0 50 56°34.0' 19°14.1' 56°34.6' 19°15.5' 09:50 20 719.680 5 2018-05-20 42H0 28.2 127 60 18 3.0 100 56°38.4' 20°10.9' 56°38.2' 20°13.8' 15:45 30 575.887 6 2018-05-20 42H0 28.2 72 45 18 2.9 90 56°36.8' 20°28.0' 56°36.8' 20°30.6' 18:05 30 155.420 7 2018-05-21 42H0 28.2 62 38 18 3.0 270 56°53.0' 20°24.5' 56°53.0' 20°21.6' 10:25 30 201.910 8 2018-05-21 42H0 28.2 158 60 18 3.1 270 56°53.1' 20°04.7' 56°53.2' 20°03.4' 13:00 15 124.323 9 2018-05-21 42G9 28.2 162 55 18 3.1 280 56°53.1' 19°25.5' 56°53.3' 19°23.0' 16:50 30 785.184 10 2018-05-22 43G9 28.2 177 60 18 3.1 90 57°06.9' 19°40.0' 57°06.8' 19°41.9' 08:25 20 89.315 11 2018-05-22 43H0 28.2 100 60 18 3.0 90 57°07.2' 20°27.5' 57°07.2' 20°29.1' 12:50 15 446.753 12 2018-05-22 43H1 28.2 60 15 18 3.0 305 57°20.2' 21°13.4' 57°21.0' 21°11.4' 18:10 30 24.703 13 2018-05-23 43H0 28.2 127 60 18 3.1 280 57°23.2' 20°33.9' 57°23.4' 20°30.9' 09:15 30 448.073 14 2018-05-23 43H0 28.2 239 60 18 3.1 285 57°18.2' 20°04.7' 57°18.7' 20°01.9' 12:40 30 561.220 15 2018-05-23 43G9 28.2 105 60 17 2.8 20 57°28.8' 19°29.6' 57°29.8' 19°30.3' 17:20 20 1719.607 16 2018-05-24 44G9 28.2 115 60 18 3.1 180 57°37.2' 19°41.5' 57°36.4' 19°41.4' 07:40 15 110.549 17 2018-05-24 44H0 28.2 153 60 18 3.0 185 57°36.3' 20°26.4' 57°34.7' 20°26.0' 12:10 30 846.980 18 2018-05-24 44H0 28.2 103 60 16 2.9 180 57°51.0' 20°44.1' 57°49.8' 20°43.7' 16:25 20 102.344 19 2018-05-24 44H1 28.2 79 55 18 3.1 175 57°52.0' 21°04.3' 57°51.0' 21°04.5' 19:10 20 378.390 SD26 1649.654 SD28.2 7290.338 SD26+28.2 8939.992 ICES | WGBIFS 2019 251 Table 2. Number of measured and aged fish individuals in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018 SD 26 Sprat Herring Cod Flounder Fourbeard rockling Three spined stickleback Smelt Total Samples taken Measurements 3 3 1 2 9 analyses 3 1 4 Fish measured 615 194 56 7 872 Fish analysed 280 117 397 SD 28.2 Sprat Herring Cod Flounder Fourbeard rockling Three spined stickleback Smelt Total Samples taken Measurements 16 16 10 11 10 4 1 68 analyses 16 14 30 Fish measured 3278 2662 478 216 17 4 1 6656 Fish analysed 1432 1461 2893 SUM Sprat Herring Cod Flounder Fourbeard rockling Three spined stickleback Smelt Total Samples taken Measurements 19 19 11 13 10 4 1 77 analyses 19 15 34 Fish measured 3893 2856 534 223 17 4 1 7528 Fish analysed 1712 1578 3290 252 ICES | WGBIFS 2019 Table 3. The values of meteorological and hydrological parameters registered at the trawling position and depth in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018 Haul number Date of catch Meteorological parameters Trawling depth Hydrological parameters wind wind force sea state air temper. atmospheric Headrope Footrope temperature salinity oxygen direction [°B] [Degrees] [°C] pressure [hP] [m] [m] [°C] [PSU] [ml/l] 1 2018-05-19 N 5 3-4 9 1016 36 52 3.62 7.47 7.89 2 2018-05-19 N 4-5 3 10 1022 40 58 3.42 7.48 8.40 3 2018-05-19 N 4 3 10 1023 55 73 4.23 8.68 6.46 4 2018-05-20 N 3 1-2 10 1028 60 78 4.83 9.10 1.91 5 2018-05-20 N 3 1-2 13 1029 60 78 4.08 8.43 5.21 6 2018-05-20 W 3 2 11 1028 45 63 3.42 7.50 8.11 7 2018-05-21 changeable 2 1 12 1029 38 56 3.01 7.43 8.67 8 2018-05-21 changeable 2 1 15 1028 60 78 5.17 9.43 1.84 9 2018-05-21 changeable 2 1 15 1026 55 73 5.57 9.94 0.50 10 2018-05-22 E 3 2 12 1021 60 78 4.69 8.77 3.24 11 2018-05-22 E 2 1-2 13 1020 60 78 5.11 9.35 1.60 12 2018-05-22 NE 2 1 12 1020 15 33 3.51 7.39 8.23 13 2018-05-23 changeable 2 1 12 1020 60 78 4.28 8.91 2.87 14 2018-05-23 changeable 2 1 13 1023 60 78 5.17 9.42 1.48 15 2018-05-23 W 3 1-2 14 1024 60 77 5.35 9.79 1.25 16 2018-05-24 N 3-4 2 12 1028 60 78 4.73 9.22 2.21 17 2018-05-24 NE 4 2 11 1029 60 78 5.51 9.79 1.85 18 2018-05-24 N 4-5 3 13 1029 60 76 5.02 9.39 2.08 19 2018-05-24 N 4-5 3 12 1029 55 73 4.76 9.25 2.49 Mean 53 70 4.50 8.78 4.02 ICES | WGBIFS 2019 253 Table 4. Fish control-catch results by species in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018 Haul number Date ICES rectangle ICES SD Total Cactch [kg] Catch per species [kg] sprat herring cod flounder threespine stickleback Fourbeard rockling smelt 161789 161722 164712 172894 166365 126450 126736 1 2018-05-19 41G9 26 334.879 332.000 2.740 0.139 2 2018-05-19 41H0 26 531.270 520.064 11.206 3 2018-05-19 41G9 26 783.505 589.056 177.944 15.643 0.862 4 2018-05-20 42G9 28.2 719.680 652.384 60.702 5.146 1.223 0.214 0.011 5 2018-05-20 42H0 28.2 575.887 466.650 89.095 13.161 6.926 0.055 6 2018-05-20 42H0 28.2 155.420 142.729 12.411 0.280 7 2018-05-21 42H0 28.2 201.910 201.668 0.222 0.020 8 2018-05-21 42H0 28.2 124.323 103.040 4.890 14.236 2.103 0.010 0.044 9 2018-05-21 42G9 28.2 785.184 634.627 140.253 8.800 1.504 10 2018-05-22 43G9 28.2 89.315 69.479 12.868 5.133 1.802 0.033 11 2018-05-22 43H0 28.2 446.753 344.800 87.280 10.141 4.450 0.082 12 2018-05-22 43H1 28.2 24.703 11.780 12.920 0.003 13 2018-05-23 43H0 28.2 448.073 220.707 215.043 7.778 4.484 0.061 14 2018-05-23 43H0 28.2 561.220 473.461 74.019 10.179 3.561 15 2018-05-23 43G9 28.2 1719.607 1300.986 411.342 6.479 0.628 0.172 16 2018-05-24 44G9 28.2 110.549 51.501 51.998 6.692 0.337 0.021 17 2018-05-24 44H0 28.2 846.980 647.940 198.956 0.084 18 2018-05-24 44H0 28.2 102.344 58.327 43.973 0.010 0.034 19 2018-05-24 44H1 28.2 378.390 242.548 135.842 SD26 1649.654 1441.120 191.890 15.643 1.001 SD28.2 7290.338 5622.627 1551.814 87.745 27.298 0.622 0.198 0.034 SD26+28.2 8939.992 7063.747 1743.704 103.388 28.299 0.622 0.198 0.034 254 ICES | WGBIFS 2019 Table 5. BASS statistics of pelagic fish species from the Latvian-Polish BASS in the Baltic Sea ICES SD 26N and 28.2 conducted by r/v "Baltica" in the period of 18-25.05.2018 Table 5A ICES ICES Trawl Herring Sprat NASCPEL σ × 104 TS calc. SD Rect. No L, cm w, g n, % L, cm w, g n, % m2/nm2 m2 dB 26 41G9 1,3,4 18.24 36.30 3.60 11.13 7.56 96.36 945.50 -49.95 1.27 41H0 1,2 13.18 14.18 1.05 11.86 9.13 98.95 357.16 -49.68 1.35 28 42G9 4,5,8,9 17.66 35.90 3.18 11.10 7.47 96.75 471.28 -50.02 1.25 42H0 5,6,7,8 16.30 27.58 2.46 10.51 6.52 97.44 341.77 -50.51 1.12 43G9 10,14,15 16.66 27.54 6.72 10.76 7.06 93.25 628.12 -50.10 1.23 43H0 11,12,13,14 16.67 27.35 8.77 11.23 7.80 91.15 552.65 -49.70 1.35 43H1 12 11.22 10.18 31.83 9.12 4.34 68.17 162.56 -51.15 0.96 44G9 15,16 16.61 27.06 8.14 10.64 6.87 91.84 489.77 -50.10 1.23 44H0 17,18,19 16.53 25.54 9.42 10.33 6.30 90.53 288.45 -50.23 1.19 44H1 12,19 15.89 24.03 10.90 9.59 5.09 89.08 232.00 -50.66 1.08 Table 5B ICES ICES Area ρ Abundance, n × 106 n, % Biomass, kg × 103 SD Rect. nm2 n × 106/nm2 N NHERRING NSPRAT herring sprat W WHERRING WSPRAT 26 41G9 1000.0 7.44 7486.37 269.73 7216.64 3.60 96.36 64384.54 9791.40 54593.14 41H0 953.3 2.64 2516.70 26.41 2490.29 1.05 98.95 23118.32 374.36 22743.97 28 42G9 986.9 3.77 3764.72 119.67 3645.05 3.18 96.75 31534.69 4296.70 27238.00 42H0 968.5 3.06 3017.01 74.44 2942.57 2.46 97.44 21227.54 2053.39 19174.15 43G9 973.7 5.11 4998.66 336.05 4662.60 6.72 93.25 42191.82 9256.06 32935.76 43H0 973.7 4.10 4040.30 354.70 3685.60 8.77 91.15 38444.71 9702.39 28742.32 43H1 412.7 1.69 695.66 221.45 474.20 31.83 68.17 4312.69 2253.95 2058.74 44G9 876.6 3.99 3510.60 285.66 3224.94 8.14 91.84 29896.24 7730.35 22165.88 44H0 960.5 2.42 2344.35 220.86 2123.49 9.42 90.53 19012.31 5641.04 13371.27 44H1 824.6 2.15 1777.89 193.82 1584.07 10.90 89.08 12727.23 4657.77 8069.46 ICES | WGBIFS 2019 255 Table 6. Sprat stock characteristics in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018 Table 6A CANUM Age group ∑ ICES SD ICES Rect. 1 2 3 4 5 6 7 8+ 26 41G9 107112 105631 86145 296897 12943 8963 3613 12674 633978 41H0 17349 14948 31174 99255 7573 7417 2263 4652 184631 28 42G9 97923 86870 75207 279633 19706 13614 7004 11950 591908 42H0 114534 26700 30718 111677 9584 6639 2992 1337 304181 43G9 176665 113403 65575 270927 9208 11697 6938 13325 667738 43H0 39362 42592 57714 152914 16786 6423 5286 5141 326218 43H1 3122 54 108 325 72 18 3699 44G9 169516 95336 44697 207695 4434 9193 6638 11524 549032 44H0 117954 49704 23771 107723 5313 3903 1525 6176 316071 44H1 81507 7541 13697 23212 724 2038 1385 1259 131363 Table 6B n × 106 Age group ∑ ICES SD ICES Rect. 1 2 3 4 5 6 7 8+ 26 41G9 1219.27 1202.41 980.60 3379.61 147.33 102.03 41.13 144.26 7216.64 41H0 234.00 201.61 420.47 1338.75 102.14 100.04 30.52 62.75 2490.29 28 42G9 603.02 534.96 463.14 1722.01 121.35 83.84 43.13 73.59 3645.05 42H0 1107.97 258.29 297.16 1080.33 92.71 64.22 28.94 12.94 2942.57 43G9 1233.60 791.86 457.89 1891.80 64.29 81.67 48.45 93.04 4662.60 43H0 444.71 481.20 652.05 1727.62 189.65 72.57 59.72 58.09 3685.60 43H1 400.18 6.94 13.88 41.64 9.25 2.31 0.00 0.00 474.20 44G9 995.71 559.99 262.54 1219.97 26.04 54.00 38.99 67.69 3224.94 44H0 792.46 333.93 159.71 723.73 35.70 26.23 10.25 41.49 2123.49 44H1 982.88 90.93 165.16 279.91 8.73 24.58 16.70 15.18 1584.07 Table 6C n, % Age group ∑ ICES SD ICES Rect. 1 2 3 4 5 6 7 8+ 26 41G9 16.90 16.66 13.59 46.83 2.04 1.41 0.57 2.00 100.00 41H0 9.40 8.10 16.88 53.76 4.10 4.02 1.23 2.52 100.00 28 42G9 16.54 14.68 12.71 47.24 3.33 2.30 1.18 2.02 100.00 42H0 37.65 8.78 10.10 36.71 3.15 2.18 0.98 0.44 100.00 43G9 26.46 16.98 9.82 40.57 1.38 1.75 1.04 2.00 100.00 43H0 12.07 13.06 17.69 46.87 5.15 1.97 1.62 1.58 100.00 43H1 84.39 1.46 2.93 8.78 1.95 0.49 100.00 44G9 30.88 17.36 8.14 37.83 0.81 1.67 1.21 2.10 100.00 44H0 37.32 15.73 7.52 34.08 1.68 1.23 0.48 1.95 100.00 44H1 62.05 5.74 10.43 17.67 0.55 1.55 1.05 0.96 100.00 Table 6D W, kg × 103 Age group ∑ ICES SD ICES Rect. 1 2 3 4 5 6 7 8+ 26 41G9 3850.09 9041.83 8603.66 28606.99 1477.98 1070.36 410.01 1532.22 54593.14 41H0 871.02 1727.83 3965.07 12817.81 1071.41 1193.37 337.92 759.55 22743.97 28 42G9 1905.04 4049.13 3877.13 14125.50 1156.63 890.39 446.02 788.14 27238.00 42H0 3767.73 1911.26 2440.33 9046.86 906.86 661.19 292.28 147.64 19174.15 43G9 4267.06 5939.10 3784.40 15963.73 650.95 850.12 507.89 972.52 32935.76 43H0 1413.20 3470.22 5324.84 14702.15 1868.50 714.77 642.63 606.00 28742.32 43H1 1366.63 62.18 130.44 383.17 91.23 25.07 0.00 0.00 2058.74 44G9 3451.06 4228.71 2220.79 10327.04 258.18 561.25 404.88 713.96 22165.88 44H0 2388.03 2506.36 1320.77 5984.39 361.55 268.36 111.81 430.00 13371.27 44H1 2775.48 748.67 1407.02 2434.83 100.79 246.18 181.80 174.69 8069.46 256 ICES | WGBIFS 2019 Table 6E W, % Age group ∑ ICES SD ICES Rect. 1 2 3 4 5 6 7 8+ 26 41G9 7.05 16.56 15.76 52.40 2.71 1.96 0.75 2.81 100.00 41H0 3.83 7.60 17.43 56.36 4.71 5.25 1.49 3.34 100.00 28 42G9 6.99 14.87 14.23 51.86 4.25 3.27 1.64 2.89 100.00 42H0 19.65 9.97 12.73 47.18 4.73 3.45 1.52 0.77 100.00 43G9 12.96 18.03 11.49 48.47 1.98 2.58 1.54 2.95 100.00 43H0 4.92 12.07 18.53 51.15 6.50 2.49 2.24 2.11 100.00 43H1 66.38 3.02 6.34 18.61 4.43 1.22 100.00 44G9 15.57 19.08 10.02 46.59 1.16 2.53 1.83 3.22 100.00 44H0 17.86 18.74 9.88 44.76 2.70 2.01 0.84 3.22 100.00 44H1 34.39 9.28 17.44 30.17 1.25 3.05 2.25 2.16 100.00 Table 6F w, g Age group ∑ ICES SD ICES Rect. 1 2 3 4 5 6 7 8+ 26 41G9 3.16 7.52 8.77 8.46 10.03 10.49 9.97 10.62 7.56 41H0 3.72 8.57 9.43 9.57 10.49 11.93 11.07 12.10 9.13 28 42G9 3.16 7.57 8.37 8.20 9.53 10.62 10.34 10.71 7.47 42H0 3.40 7.40 8.21 8.37 9.78 10.30 10.10 11.41 6.52 43G9 3.46 7.50 8.26 8.44 10.12 10.41 10.48 10.45 7.06 43H0 3.18 7.21 8.17 8.51 9.85 9.85 10.76 10.43 7.80 43H1 3.42 8.96 9.40 9.20 9.86 10.84 4.34 44G9 3.47 7.55 8.46 8.46 9.91 10.39 10.38 10.55 6.87 44H0 3.01 7.51 8.27 8.27 10.13 10.23 10.91 10.36 6.30 44H1 2.82 8.23 8.52 8.70 11.55 10.02 10.89 11.51 5.09 Table 6G L, g Age group ∑ ICES SD ICES Rect. 1 2 3 4 5 6 7 8+ 26 41G9 8.54 11.19 11.79 11.66 12.46 12.77 12.53 12.97 11.13 41H0 8.96 11.60 12.03 12.09 12.51 13.32 12.87 13.45 11.86 28 42G9 8.52 11.21 11.63 11.56 12.21 12.76 12.70 12.93 11.10 42H0 8.63 11.13 11.58 11.64 12.33 12.50 12.65 13.28 10.51 43G9 8.64 11.07 11.48 11.57 12.30 12.55 12.70 12.70 10.76 43H0 8.44 11.01 11.49 11.64 12.28 12.37 12.77 12.82 11.23 43H1 8.58 11.92 12.08 11.97 12.25 12.75 9.12 44G9 8.64 11.08 11.53 11.57 12.24 12.53 12.66 12.70 10.64 44H0 8.34 11.10 11.55 11.51 12.39 12.63 13.13 12.64 10.33 44H1 8.19 11.56 11.71 11.81 13.12 12.56 13.16 13.50 9.59 ICES | WGBIFS 2019 257 Table 7. Herring stock characteristics in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018 Table 7A CANUM Age group ∑ ICES SD ICES Rect. 1 2 3 4 5 6 7 8+ 26 41G9 61 559 935 9806 528 4317 3337 4153 23696 41H0 1242 461 31 152 2 21 2 45 1958 28 42G9 99 799 1182 8476 502 3276 2194 2905 19433 42H0 2221 294 405 1866 179 932 722 1075 7695 43G9 1934 2755 10684 16364 1706 5937 4227 4520 48127 43H0 1724 696 7301 7679 1760 5637 3838 2760 31395 43H1 1304 59 93 34 110 85 42 1728 44G9 1804 2647 11185 16201 1135 5514 5641 4505 48633 44H0 1011 9317 7120 1680 6235 4032 3478 32873 44H1 1697 339 2339 3209 714 3591 2180 2004 16073 Table 7B n × 106 Age group ∑ ICES SD ICES Rect. 1 2 3 4 5 6 7 8+ 26 41G9 0.69 6.37 10.64 111.62 6.01 49.14 37.99 47.27 269.73 41H0 16.76 6.21 0.42 2.05 0.03 0.29 0.03 0.60 26.41 28 42G9 0.61 4.92 7.28 52.20 3.09 20.18 13.51 17.89 119.67 42H0 21.49 2.85 3.92 18.05 1.73 9.02 6.98 10.40 74.44 43G9 13.51 19.24 74.60 114.27 11.91 41.45 29.51 31.56 336.05 43H0 19.47 7.86 82.49 86.76 19.88 63.69 43.37 31.18 354.70 43H1 167.18 0.00 7.60 11.94 4.34 14.11 10.86 5.43 221.45 44G9 10.60 15.55 65.70 95.16 6.67 32.39 33.13 26.46 285.66 44H0 0.00 6.79 62.60 47.83 11.29 41.89 27.09 23.37 220.86 44H1 20.46 4.09 28.20 38.69 8.61 43.31 26.28 24.17 193.82 Table 7C n, % Age group ∑ ICES SD ICES Rect. 1 2 3 4 5 6 7 8+ 26 41G9 0.26 2.36 3.94 41.38 2.23 18.22 14.08 17.53 100.00 41H0 63.46 23.53 1.61 7.78 0.13 1.10 0.13 2.27 100.00 28 42G9 0.51 4.11 6.08 43.62 2.58 16.86 11.29 14.95 100.00 42H0 28.87 3.83 5.27 24.25 2.33 12.11 9.38 13.97 100.00 43G9 4.02 5.73 22.20 34.00 3.55 12.34 8.78 9.39 100.00 43H0 5.49 2.22 23.26 24.46 5.61 17.96 12.23 8.79 100.00 43H1 75.49 3.43 5.39 1.96 6.37 4.90 2.45 100.00 44G9 3.71 5.44 23.00 33.31 2.33 11.34 11.60 9.26 100.00 44H0 3.08 28.34 21.66 5.11 18.97 12.27 10.58 100.00 44H1 10.56 2.11 14.55 19.96 4.44 22.34 13.56 12.47 100.00 Table 7D W, kg × 103 Age group ∑ ICES SD ICES Rect. 1 2 3 4 5 6 7 8+ 26 41G9 8.72 164.76 327.95 3505.50 222.03 1801.34 1598.05 2163.05 9791.40 41H0 168.23 96.84 10.29 50.72 1.29 9.60 1.01 36.38 374.36 28 42G9 8.32 124.21 196.88 1674.65 98.02 772.65 565.50 856.47 4296.70 42H0 193.98 45.20 108.42 542.75 51.44 337.98 293.73 479.90 2053.39 43G9 95.46 299.09 1716.88 2920.16 361.55 1441.84 1055.76 1365.32 9256.06 43H0 100.57 152.53 1981.25 2352.02 544.68 1915.40 1412.31 1243.64 9702.39 43H1 863.35 0.00 158.06 270.96 109.21 357.15 291.80 203.43 2253.95 44G9 72.07 242.68 1415.51 2434.01 211.27 1145.56 1117.09 1092.16 7730.35 44H0 0.00 126.02 1297.49 1180.36 260.91 1137.24 812.82 826.20 5641.04 44H1 105.67 67.50 576.61 907.63 201.19 1168.37 784.27 846.53 4657.77 258 ICES | WGBIFS 2019 Table 7E W, % Age group ∑ ICES SD ICES Rect. 1 2 3 4 5 6 7 8+ 26 41G9 0.09 1.68 3.35 35.80 2.27 18.40 16.32 22.09 100.00 41H0 44.94 25.87 2.75 13.55 0.34 2.56 0.27 9.72 100.00 28 42G9 0.19 2.89 4.58 38.98 2.28 17.98 13.16 19.93 100.00 42H0 9.45 2.20 5.28 26.43 2.51 16.46 14.30 23.37 100.00 43G9 1.03 3.23 18.55 31.55 3.91 15.58 11.41 14.75 100.00 43H0 1.04 1.57 20.42 24.24 5.61 19.74 14.56 12.82 100.00 43H1 38.30 0.00 7.01 12.02 4.85 15.85 12.95 9.03 100.00 44G9 0.93 3.14 18.31 31.49 2.73 14.82 14.45 14.13 100.00 44H0 0.00 2.23 23.00 20.92 4.63 20.16 14.41 14.65 100.00 44H1 2.27 1.45 12.38 19.49 4.32 25.08 16.84 18.17 100.00 Table 7F w, g Age group ∑ ICES SD ICES Rect. 1 2 3 4 5 6 7 8+ 26 41G9 12.60 25.87 30.83 31.40 36.93 36.66 42.07 45.76 36.30 41H0 10.04 15.58 24.22 24.70 38.60 33.18 30.40 60.57 14.18 28 42G9 13.61 25.24 27.06 32.08 31.69 38.30 41.86 47.88 35.90 42H0 9.03 15.87 27.66 30.06 29.70 37.49 42.06 46.16 27.58 43G9 7.07 15.55 23.01 25.56 30.34 34.78 35.77 43.26 27.54 43H0 5.16 19.41 24.02 27.11 27.39 30.07 32.57 39.88 27.35 43H1 5.16 20.80 22.69 25.15 25.31 26.88 37.48 10.18 44G9 6.80 15.61 21.55 25.58 31.68 35.37 33.72 41.27 27.06 44H0 18.55 20.73 24.68 23.11 27.15 30.01 35.36 25.54 44H1 5.16 16.51 20.44 23.46 23.36 26.98 29.84 35.03 24.03 Table 7G L, g Age group ∑ ICES SD ICES Rect. 1 2 3 4 5 6 7 8+ 26 41G9 13.00 15.92 17.19 17.01 18.11 18.19 19.10 19.75 18.24 41H0 11.71 13.83 15.68 15.66 18.00 17.54 18.00 23.33 13.18 28 42G9 13.19 15.85 16.16 16.55 17.03 17.89 18.46 19.75 17.66 42H0 11.26 13.79 16.47 16.81 16.97 18.29 19.06 20.01 16.30 43G9 11.00 14.08 15.75 16.04 17.25 18.05 18.49 19.37 16.66 43H0 9.25 14.86 16.02 16.32 16.66 17.22 17.73 18.99 16.67 43H1 9.25 16.36 16.45 16.88 17.31 17.70 19.80 11.22 44G9 10.20 13.89 15.46 16.03 17.75 18.24 18.15 19.25 16.61 44H0 14.59 15.23 16.04 15.71 16.69 17.31 18.45 16.53 44H1 9.25 14.17 15.18 15.70 15.47 16.58 17.15 18.48 15.89 Table 8. BASS statistics related to cod from the Latvian-Polish BASS in the Baltic Sea ICES SD 26N and 28.2 conducted by r/v "Baltica" in the period of 18-25.05.2018 Table 5A ICES ICES NASCPEL σ × 104 TS calc. ρ Abundance Biomass SD Rect. L, cm w, g m2/nm2 m2 dB n × 106/nm2 n × 106 kg × 103 26 41G9 29.87 263.51 6.74 -37.79 20.91 0.0032 3.22 849.45 41H0 28 42G9 28.92 233.54 5.90 -38.01 19.86 0.0030 2.93 684.34 42H0 29.49 255.42 6.47 -37.82 20.75 0.0031 3.02 770.26 43G9 27.51 229.02 2.94 -38.37 18.30 0.0016 1.56 357.71 43H0 28.55 240.50 6.47 -38.10 19.46 0.0033 3.24 778.45 43H1 44G9 27.75 275.03 1.97 -38.18 19.10 0.0010 0.90 248.26 44H0 28.83 234.46 2.77 -38.04 19.73 0.0014 1.35 316.38 44H1 31.95 305.45 1.01 -37.26 23.64 0.0004 0.35 107.81 ICES | WGBIFS 2019 259 Table 9. Number of sprat eggs and larvae per 1 m2 or per 10 minutes of sampling on water surface in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018 Aquatory Northern part Central part Southern part Depth strata >70m <70m >70m <70m >70m <70m Eggs (per 1m2) 70.70 – 104.00 92.90 511.00 11.40 Larvae (per 1m2) 1.43 – 5.19 - 21.40 - Eggs (per 10 min. of haul on the water surface) 1.80 – 22.40 1.25 2.00 6.50 Larvae (per 10 min. of haul on the water surface) 0.25 – 1.09 2.25 3.00 0.50 Northern part of the Gotland Basin – to the north from 57°30’N Central part of the Gotland Basin – between 56°30’N and 57°30’N Southern part of the Gotland Basin – to the south from 56°30’N. Table 10. The average number and average biomass of zooplankton organisms in 0-100m water column per volume unit in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018 Species Biomass (mg/m3) Biomass (%) Acartia spp. 27.373 14.10 Eurytemora affinis 0.425 0.22 Temora longicornis 31.361 16.15 Centropages hamatus 13.134 6.76 Pseudocalanus sp. 11.135 5.73 Harpacticoida 0.003 0.00 Oithona sp. 0.064 0.03 Bosmina 0.019 0.01 Evadne 6.927 3.57 Podon 0.425 0.22 Synchaeta spp. 72.674 37.42 Polychaeta larvae 2.996 1.54 Bivalvia larvae 0.105 0.05 Fritillaria borealis 27.558 14.19 Copepoda 83.495 42.99 Cladocera 7.371 3.80 Rotatoria 72.674 37.42 Varia 30.659 15.79 Total 194.199 100.00 260 ICES | WGBIFS 2019 Figure 1: Cruise track design and trawling positions of the Latvian-Polish BASS on the r/v "Baltica" in the period of 18- 25.05.2018. ICES | WGBIFS 2019 261 Figure 2: Locations of the hydrological, ichthyoplankton and zooplankton stations performed during the Latvian-Polish BASS on the r/v "Baltica" in the period of 18-25.05.2018. 262 ICES | WGBIFS 2019 Figure 3: CPUE [kg/h] ranges distribution of dominant fish in the catch hauls in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018. ICES | WGBIFS 2019 263 Figure 4: CPUE [kg/h] of dominant pelagic fish in the catch hauls in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018. 0 500 1000 1500 2000 2500 3000 3500 4000 4500 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 C PU E [k g/ h] Haul No sprat herring SD 28.2SD 26 264 ICES | WGBIFS 2019 Figure 5: Acoustic parameter NASC distribution in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018. ICES | WGBIFS 2019 265 Figure 6: Sprat distribution in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018. 266 ICES | WGBIFS 2019 Figure 7: Herring distribution in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018. ICES | WGBIFS 2019 267 Figure 8: Sprat length distributions in control catches in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018. Figure 9: Herring length distributions in control catches in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018. 0 4 8 12 16 20 24 28 6. 5 7. 0 7. 5 8. 0 8. 5 9. 0 9. 5 10 .0 10 .5 11 .0 11 .5 12 .0 12 .5 13 .0 13 .5 14 .0 L,cm SD 26, n = 615 SD 28.2, n = 3278 0 2 4 6 8 10 12 14 16 Fr eq ue nc y, % L, cm SD 28.2, n = 2662 SD 26, n = 194 268 ICES | WGBIFS 2019 Figure 10: Cod length distributions in control catches in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018. Figure 11: Flounder length distributions in control catches in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018. 0 2 4 6 8 10 12 14 16 Fr eq ue nc y, % L, cm SD 26, n = 56 SD 28.2, n = 478 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 Fr eq ue nc y, % L, cm SD 28.2, n = 216 ICES | WGBIFS 2019 269 Figure 12: Changes of the main meteorological parameters (wind force, direction and the daily air temperature) during the Latvian-Polish BASS in the Baltic Sea ICES SD 26N and 28.2 conducted by r/v "Baltica" in the period of 18-25.05.2018. 270 ICES | WGBIFS 2019 31 Figure 13: Horizontal distribution of the main hydrological parameters (temperature, salinity, oxygen content) measured in the surface water layer of the Gotland Deep in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018. ICES | WGBIFS 2019 271 32 Figure 14: Horizontal distribution of the main hydrological parameters (temperature, salinity, oxygen content) measured in the haul depth layer of the Gotland Deep in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018. 272 ICES | WGBIFS 2019 33 Figure 15: Horizontal distribution of the main hydrological parameters (temperature, salinity, oxygen content) measured in the bottom water layer of the Gotland Deep in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018. ICES | WGBIFS 2019 273 34 Figure 16: Vertical distribution of the seawater temperature, salinity and oxygen content at the deepest part (Station 37) of the Gotland Basin in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS conducted by r/v "Baltica" in the period of 18-25.05.2018. 9,20 9,12 8,57 7,96 5,07 1,480,29 0,33 0,50 0,54 0,19 0,00 0,00 0 25 50 75 100 125 150 175 200 225 0 2 4 6 8 10 12 14 temperature [°C] salinity PSU oxygen content [ml/l] 274 ICES | WGBIFS 2019 35 Figure 17: Vertical distribution of the seawater temperature, salinity and oxygen content along the hydrological profile in the Baltic Sea ICES SD 26N and 28.2 from the Latvian-Polish BASS survey conducted by r/v "Baltica" in the period of 18- 25.05.2018. ICES | WGBIFS 2019 275 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania Federal Research Institute for Rural Areas, Forestry and Fisheries Thünen Institute of Sea Fisheries (TI-SF)1 Thünen Institute of Baltic Sea Fisheries (TI-OF)2 Survey Report FRV Solea German Acoustic Autumn Survey (GERAS) 01 – 19 October 2018 Matthias Schaber1 & Tomas Gröhsler2 1 INTRODUCTION .................................................................................................................................. 2 1.1 Background ................................................................................................................................. 2 1.2 Objectives ................................................................................................................................... 2 1.3 Survey summary ......................................................................................................................... 2 2 SURVEY DESCRIPTION & METHODS APPLIED ..................................................................................... 2 2.1 Cruise narrative .......................................................................................................................... 2 2.2 Survey design .............................................................................................................................. 3 2.3 Acoustic data collection ............................................................................................................. 3 2.4 Calibration .................................................................................................................................. 3 2.5 Biological data – trawl hauls ....................................................................................................... 4 2.6 Hydrographic data ...................................................................................................................... 4 2.7 Data analysis ............................................................................................................................... 4 3 RESULTS .............................................................................................................................................. 6 3.1 Hydroacoustic data (M. Schaber) ............................................................................................... 6 3.2 Biological data (T. Gröhsler) ....................................................................................................... 7 3.3 Biomass and abundance estimates ............................................................................................ 7 3.4 Hydrography ............................................................................................................................... 9 4 DISCUSSION ...................................................................................................................................... 10 5 SURVEY PARTICIPANTS ..................................................................................................................... 11 6 REFERENCES ..................................................................................................................................... 11 7 FIGURES ............................................................................................................................................ 13 8 TABLES .............................................................................................................................................. 20 276 ICES | WGBIFS 2019 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 2 1 INTRODUCTION 1.1 Background The cruise was part of an international hydroacoustic survey providing information on stock parameters of small pelagics in the Baltic Sea, coordinated by the ICES Working Group of International Pelagic Surveys (WGIPS) and the ICES Baltic International Fish Survey Working Group (WGBIFS). Further WGBIFS contributors to the Baltic survey are national fisheries research institutes of Sweden, Poland, Finland, Latvia, Estonia and Lithuania. FRV Solea participated for the 31st time. The survey area covered the western Baltic Sea including Kattegat, Belt Sea, Sound and Arkona Sea (ICES Subdivisions (SD) 21, 22, 23 and 24). Altogether, 1211 nmi (plus 107 nmi night and daytime transects for comparison) of hydroacoustic transects were covered. The survey effort was comparable to previous years. 1.2 Objectives The survey has the main objective to annually assess the clupeoid resources of herring and sprat in the Baltic Sea in autumn. The reported acoustic survey is conducted every year to supply the ICES Herring Assessment Working Group for the Area South of 62°N (HAWG) and Baltic Fisheries Assessment Working Group (WGBFAS) with an index value for the stock size of herring and sprat in the Western Baltic area (Kattegat/Subdivisions 21 and Subdivisions 22, 23 and 24). The following objectives were planned:  Hydroacoustic measurements for the assessment of small pelagics in the Kattegat and western Baltic Sea including Belt Sea, Sound and Arkona Sea (ICES Subdivisions 21, 22, 23 and 24)  (Pelagic) trawling according to hydroacoustic registrations  Hydrographic measurements on hydroacoustic transects and after each fishery haul  Identification and recording of species- and length-composition of trawl catches  Collection of biological samples of herring, sprat and additionally European anchovy and cod for further analyses 1.3 Survey summary In the majority of sampled rectangles, mean NASC values per nautical mile were distinctly higher than the values measured in 2017 and in SD 22 and SD 21 (in 2 and 3 cases, respectively) higher than the long-time mean values. Despite this increase from 2017, the majority of rectangles sampled in 2018 still showed mean NASC values below the long time mean. While NASC values measured were higher in ICES Subdivisions 21, 22 and 23 (in comparison with 2017), levels in SD 24 were in all but two rectangles distinctly lower than the already low NASC values measured in the previous year. While in SD 23, as in 2017, unusually low NASC values (albeit higher than in the previous year) were measured, indicating absence of the dense aggregations of herring usually observed in that area at this time of the year. On a repetition of the transect in SD 23 during daytime for comparison, NASC values measured were distinctly higher than those recorded during nighttime, indicating higher presence of clupeids in the area. For species allocation and identification, altogether 62 fishery hauls were conducted (including 58 valid hauls during the survey and 3 valid hauls on comparison transects). Vertical hydrography profiles were measured on 106 stations. 2 SURVEY DESCRIPTION & METHODS APPLIED 2.1 Cruise narrative The 754th cruise of FRV Solea represents the 31st subsequent GERAS survey. Embarkation of scientific crew as well as equipment of FRV Solea with all hydroacoustic equipment and biological sampling gear took place on the morning of October 1st in Kiel harbor. On the same afternoon, Solea left port for the calibration of scientific echosounders. The calibration site off Strande that had been chosen for ICES | WGBIFS 2019 277 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 3 calibration in the previous year was again approached based on the prevailing weather conditions that were considered acceptable (4-5 Bft, westerly winds). After calibration the vessel returned to Kiel harbor in the late evening to allow switching of survey operations to night time. Leaving of port and start of survey was scheduled for October 2nd in the afternoon. The hydroacoustic survey operations commenced October 2nd at 06:00 PM in SD 22 in Kiel Bight. Generally, survey operations were conducted during nighttime to account for the more pelagic distribution of clupeids during that time. Adverse weather conditions at the beginning of the survey required to start survey operations in the westerly survey area of the comparatively sheltered western Baltic SD 22. In the first night of survey operations, weather conditions deteriorated (10 Bft westerly winds) but allowed continuation of the survey in the narrow Belt Sea. After finishing SD 22, survey operations commenced in SD 24 and SD 23 which both were covered as planned due to favorable weather conditions, as was SD 21 afterwards. Regular survey operations were accomplished on October 16th. After a switch of survey operations back to daytime, a comparative sampling (hydroacoustics and fishery) of SD 23 (Sound) was conducted to validate weak registrations recorded during the regular, initial passage. The scientific program was finished on October 18th, 04:45 PM. The ship arrived at Marienehe port on October 19th, 07:00 AM. Altogether, the following survey schedule was accomplished: Belt Sea (SD 22) 02. - 06.10. Arkona Sea (SD 24) 07. - 11.10. Sound (SD 23) 12.10. Kattegat (SD 21) 13. - 16.10. Sound (day) (SD 23) 18.10. Total survey time 15 nights (+ 1 day comparison in SD 23) Fishery hauls 62 (58 valid, 2 invalid, 3 daytime comparison) CTD-casts 106 Hydroacoustic transects 1211 nmi (+ 107 nmi transects for comparison) Overall regular hydroacoustic transect length was 1211 nmi (2016: 1167 nmi). 2.2 Survey design ICES statistical rectangles were used as strata for all Subdivisions (ICES, 2014). The area was limited by the 10 m depth line. The survey area in the Western Baltic Sea is characterized by a number of islands and sounds. Consequently, parallel transects would lead to an unsuitable coverage of the survey area. Therefore a zig-zag track was adopted to cover all depth strata regularly and sufficiently. Overall regular cruise track length was 1211 nmi covering a survey area of 12 400 nmi2 (Figure 1). 2.3 Acoustic data collection All acoustic investigations were performed during night time to account for the more pelagic distribution of clupeids during that time. The main pelagic species of interest were herring and sprat. Hydroacoustic data were recorded with a Simrad EK80 scientific echosounder with hull-mounted 38, 70, 120 and 200 kHz transducers at a standard ship speed of 10 kn. Post-processing and analysis were conducted with Echoview 9 software (Echoview Software Pty Ltd, 2018). Mean volume back scattering values (Sv) were integrated over 1 nmi intervals from 10 m below the surface to ca. 0.5 m over the seafloor. Interferences from surface turbulence, bottom structures and scattering layers were removed from the echogram. The transducer settings applied were in accordance with the specifications provided in ICES (2015, 2017). 2.4 Calibration All transducers (38, 70, 120 and 200 kHz) were calibrated prior to the beginning of the survey in acceptable weather conditions from an anchored vessel in Strande Bay/Kiel Bight (54°25.35 N, 10°12.29 E). Overall calibration results were considered good based on calculated RMS values. 278 ICES | WGBIFS 2019 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 4 Resulting transducer parameters were applied for consecutive data-collection and post-processing of hydroacoustic survey data. Calibration results for the 38 kHz transducer are given in Table 1. 2.5 Biological data – trawl hauls Trawl hauls were conducted with a pelagic gear “PSN388” in midwater layers as well as near the seafloor. Mesh size in the codend was 10 mm. It was planned to carry out at least two hauls per ICES statistical rectangle. Both trawling depth and net opening were continuously controlled by a netsonde during fishing operations. Trawl depth was chosen in accordance with echo distributions on the echogram. Normally, a vertical net opening of about 7-9 m was achieved. The trawling time usually lasted 30 minutes but was shortened when echograms and netsounder indicated large catches. To validate and allocate echorecordings, altogether 62 fishery hauls were conducted (Figure 1), out of which 57 valid (night time) hauls were utilized for further processing. From each haul sub-samples were taken to determine length and weight of fish. Samples of herring and sprat were frozen for additional investigations (e.g. determining sex, maturity, age). 2.6 Hydrographic data Hydrographic conditions were measured after each trawl haul and in regular distances on the survey transect. On each corresponding station, vertical profiles of temperature, salinity and oxygen concentration were measured using a “Seabird SBE 19 plus” CTD. Water samples for calibration purposes (salinity) were taken on every station. Altogether, 106 CTD-profiles were measured (Figure 6). 2.7 Data analysis All data analyses were conducted using GERIBAS II software (arivis, 2014) and Microsoft Office. The pelagic target species sprat and herring are often distributed in mixed layers together with other species. Thus, echorecordings cannot be allocated to a single species. Therefore the species composition allocated to echorecordings was based on corresponding trawl catch results. For each rectangle species composition and length distributions were determined as the unweighted mean of all trawl results in this rectangle. From these distributions the mean acoustic cross section  was calculated according to the following target strength-length (TS) relation: TS References Clupeoids = 20 log L (cm) - 71.2 ICES (1983) Gadoids = 20 log L (cm) - 67.5 Foote et al. (1986) Scomber scombrus = 20 log L (cm) - 84.9 ICES (2017) The total number of fish (total N) in one rectangle was estimated as the product of the mean area scattering cross section (SA) and the rectangle area, divided by the corresponding mean cross section. The total number was separated into the categories mentioned above and further into herring and sprat according to the mean catch composition. In accordance with the guidelines in the “SISP Manual of International Baltic Acoustic Surveys (IBAS)” (ICES, 2017) further calculations were performed as follows: Fish species considered: Herring (Clupea harengus) Transparent goby (Aphia minuta) European Anchovy (Engraulis encrasicolus) Cod (Gadus morhua) Three-spined stickleback (Gasterosteus aculeatus) Whiting (Merlangius merlangus) Saithe (Pollachius pollachius) Mackerel (Scomber scombrus) ICES | WGBIFS 2019 279 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 5 Fish species considered (contd.): Sprat (Sprattus sprattus) Horse mackerel (Trachurus trachurus) Norway pout (Trisopterus esmarckii) Poor cod (Trisopterus minutus) Exclusion of trawl hauls with very low catches: Haul No. Rectangle Subdivision (SD) 6 40G0 22 12 38G0 23 29 38G2 24 45, 49 41G2 21 53 43G1 21 57 42G2 21 Exclusion of trawl hauls due to net damage: Haul No. Rectangle Subdivision (SD) 31 39G2 24 52 41G1 21 Exclusion of day time trawl hauls: Haul No. Rectangle Subdivision (SD) 60-61 40G2 23 62 41G2 23 Inclusion of hauls with low catches: Despite low catches of both herring and sprat the following hauls were not excluded from the analysis as they were the only trawl hauls conducted in the corresponding rectangles and thus provided the only available information on species composition in the following rectangles: Haul No. Rectangle Subdivision (SD) 2, 3 40G0 22 4 41G0 22 5 40G1 22 9 39G1 22 29 38G2 24 47 41G0 21 Usage of neighboring trawl information for rectangles which contain only acoustic investigations: Rectangle/SD to be filled with Haul No. of Rectangle/SD 43G2/21 58 and 54-56 42G2 and 43G1/21 39F9/22 7 and 8 40F9 and 39G0/22 40F9/22 2, 3 40G0/22 39G2/23 32 and 33 39G2 and 39G3/24 37G4/24 23, 26, 27 38G4/24 280 ICES | WGBIFS 2019 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 6 Application of the separation function (SF): In the western Baltic, the distribution areas of two stocks, the Western Baltic Spring Spawning herring (WBSSH) and the Central Baltic herring (CBH) overlap. Survey results from recent years indicated that in SD 24, which is part of the WBSSH management area, a considerable fraction of CBH is present and correspondingly erroneously allocated to WBSSH stock indices (ICES, 2013). Accordingly, a stock separation function (SF) based on growth parameters derived from 2005 to 2010 has been developed to quantify the proportion of CBH and WBSSH in the area (Gröhsler et al., 2013; Gröhsler et al., 2016). The estimates of the growth parameters based on baseline samples of WBSSH and CBH in 2011-2017 and in 2018 support the applicability of the SF (Oeberst et al., 2013, WD Oeberst et al., 2014; WD Oeberst et al., 2015; WD Oeberst et al., 2016; WD Oeberst et al., 2017; WD Gröhsler and Schaber, 2018, WD Gröhsler and Schaber, 2019). In SD 24, the SF was finally also applied to ICES rectangle 39G2 (SD 23 area) since biological samples of 39G2 (SD 24 area) were used to raise the corresponding recorded SA values. In 2018, the age-length distribution of herring in SD 22 and SD 23 indicated a low contribution of fish of CBH origin. Thus, the SF was not applied in subdivisions 22 and 23 in 2018. Accordingly, the applicability of the SF continued in 2018 despite the occurrence of some CBH in the GERAS baseline samples of WBSSH in SD 21 and 23. The ICES Herring Assessment Working Group for the area south of 62° N (HAWG)) is yearly supplied with an index for this survey (GERAS), which now excludes CBH in 2005-2017 and in general covers the total standard survey area, excluding ICES rectangles 43G1 and 43G2 in SD 21 and 37G3 and 37G4 in SD 24, which were not covered in 1994-2004. 3 RESULTS 3.1 Hydroacoustic data (M. Schaber) Figure 2 depicts the spatial distribution of mean NASC values (5 nmi intervals) measured on the hydroacoustic transects covered in 2018. The majority of these NASC measurements can be allocated to clupeids. In many rectangles surveyed, mean NASC values were significantly higher than those recorded in 2017, in some rectangles also above the long-time survey average. However, despite this increase from the previous year, mean NASC per rectangle was in the majority of rectangles still well below the long-term average. On ICES subdivision scale, mean NASC values were higher than in the previous year in subdivisions 21, 22 and 23, but significantly lower in SD 24. In SD 21, overall NASC values measured were distinctly higher than those measured in the previous year. Only in one rectangle (42G1), mean NASC per 1 nmi EDSU was lower. SD 21 had the largest fraction of rectangles with NASC values exceeding not only the 2017 measurements (in 6 out of 7 rectangles) but also the long-term survey mean (in 3 out of 7 rectangles). Aggregations were mostly patchy along the cruisetrack, with the exception of the northern part of the Kattegat area surveyed, where increased NASC levels were measured more continuously. In SD 22, mean NASC values recorded were also higher than the previous year in 6 out of 11 rectangles surveyed (similar values recorded in 2 out of 11 rectangles). In some rectangles, the increase in NASC measured was almost tenfold, but originated from only short transect sections in the area that usually is characterized by very low NASC levels. In comparison to the long-term survey mean, all but 2 rectangles in SD 22 showed decreased NASC values. No clear aggregation or area of increased NASC measurements was evident. As in the previous year, the large aggregations of big herring that usually can be observed in SD 23 in the Sound were not present in autumn 2018. Although NASC values were distinctly higher than the levels measured in 2017, they still were well below the long-term survey mean. A replicate measurement of parts of the transect in SD 23 during night time and a full daytime replicate a few days later corroborated these findings, although daytime measurements showed somewhat increased NASC values in the area. ICES | WGBIFS 2019 281 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 7 In SD 24, mean NASC values were significantly lower than the values measured in 2017 in 6 out of 9 rectangles surveyed. The only exception -with a fourfold increase from the previous year- was rectangle 37G2 (west of Fischland-Darß-Zingst Peninsula), an area with usually very low NASC measurements. As in the years before, higher aggregations were detected north-east and east of Rügen Island, but also –to a lesser degree- in the central and northern parts of the Arkona Basin. 3.2 Biological data (T. Gröhsler) Fishery hauls according to ICES Subdivision: SD Hauls (n) 21 15 (incl. 1 invalid haul) 22 18 23 8 (incl. 3 daytime hauls) 24 21 (incl. 1 invalid haul) Altogether, 1 623 individual herring, 917 sprat, 295 European anchovies and 166 sardines were frozen for further investigations (e.g. determining sex, maturity, age). Results of catch compositions by Subdivision are presented in Tables 2-5. Altogether, 41 different species were recorded. Herring were caught in 58, sprat in 56 hauls (of 58 day- and nighttime hauls). SD 23, which is typically characterized by the highest mean catch rates per station (kg 0.5 h-1), showed the lowest values ever recorded (during nighttime hauls). In contrast to 2017, when sardines (Sardina pilchardus) only appeared in catches from SD 21, this species in 2018 was also caught in SD 22 and SD 23. As in previous years, anchovy (Engraulis encrasicolus) were present in the whole survey area, albeit in a higher frequency of occurrence compared to 2017 (7 of 57 hauls in 2017; 26 of 58 day- and nighttime hauls in 2018). Altogether, the following fish species were sampled and processed: Species Length measurements (n) Prevalence (n of hauls) Aphia minuta 761 37 Belone belone 22 13 Clupea harengus 12 915 58 Ctenolabrus rupestris 49 8 Cyclopterus lumpus 8 5 Engraulis encrasicolus 523 26 Eutrigla gurnadus 14 7 Gadus morhua 248 24 Gasterosteus aculeatus 1 214 39 Gobius niger 14 7 Limanda limanda 222 19 Merlangius merlangus 887 44 Merluccius merluccius 12 3 Mullus surmuletus 3 3 Neogobius melanostomus 8 3 Platichthys flesus 51 13 Pleuronectes platessa 28 10 Pomatoschistus minutus 208 32 Sardina pilchardus 245 17 Scomber scombrus 195 16 Sprattus sprattus 10 515 56 282 ICES | WGBIFS 2019 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 8 Species Length measurements (n) Prevalence (n of hauls) Trachinus draco 177 17 Trachurus trachurus 617 46 Trisopterus esmarkii 30 4 Others 183 - Figures 3 and 4 show relative length-frequency distributions of herring and sprat in ICES subdivisions 21, 22, 23 and 24 for the years 2017 and 2018. Compared to results from the previous survey in 2017, the following conclusions for herring can be drawn (Figure 3):  Catches in SD 21 showed a multimodal distribution with modes at 11.75 cm, 15.25-15.75 cm and 21.2.5-21.75 cm. This is in contrast to 2017, when a bimodal distribution showed modes at 14.75 and 17.75 cm,  The catches in SD 22 were dominated by the incoming year class (ca. ≤15 cm) with a mode at 13.25 cm. This is in contrast to a multimodal distribution with two modes at 11.25 cm and 15.26 cm and one mode of 18.75 cm in 2017.  As in the two years before, larger herring (>20 cm) were more or less absent from night time catches conducted in SD 23. The catches in 2018 as in 2017 were dominated by the contribution of the incoming year class (ca. ≤15 cm), showing a mode at 13.25 cm in 2017 and at 12.25 in 2018 cm.  In SD 24, the herring length-frequency distribution was characterized by a similar contribution of the incoming year class (ca. ≤15 cm) and older herring (>15 cm) in both years. However, the bimodal distribution in 2018 showed a higher contribution of younger herring (ca. ≤15 cm) (≤15 cm: mode 2017/11.75 cm and mode 2018/13.75 cm; >15 cm: mode 2017/18.25 cm and mode 2018/17.75 cm). Relative length-frequency distributions of sprat in the years 2017 and 2018 (Figure 4) can be characterized as follows:  In SD 21 catches of the incoming year class (ca. ≤10 cm) were virtually absent in both years. The catches were dominated by the contribution of larger sprat.  In SDs 22 and 24, the sprat length-frequency distribution was characterized by a similar contribution of the incoming year class (ca. ≤10 cm) and older sprat in both years. However, the bimodal distribution in 2018 showed slightly more of the incoming year class (<10 cm), at the same time less of older sprat.  In SD 23, the catches were dominated by the incoming year class (ca. ≤10 cm) in 2018, whereas the catches in 2017 showed a bimodal distribution with equivalent contributions of the incoming year class (ca. ≤10 cm) and older sprat.  Altogether, the present contribution of the incoming year class (ca. ≤10 cm) seemed to be rather low. 3.3 Biomass and abundance estimates The total abundance of herring and sprat is presented in Table 6. Estimated numbers of herring and sprat by age group and SD/rectangle are given in Table 7 and Table 10. Corresponding mean weights by age group and SD/rectangle are shown in Table 8 and Table 11. Estimates of herring and sprat biomass by age group and SD/rectangle are summarized in Table 9 and Table 12. ICES | WGBIFS 2019 283 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 9 3.3.1 Herring incl. Central Baltic Herring (CBH) The herring stock in Subdivisions 21-24 was estimated to be 4.3 x 109 fish (Table 7) or 90.0 x 103 tonnes (Table 9). For the included area of Subdivisions 22-24 the number of herring was calculated to be 2.9 x 109 fish or 59.8 x 103 tonnes. 3.3.2 Herring excl. Central Baltic Herring (CBH) Estimated numbers of herring excluding CBH in SDs 21-24 by age group and SD/rectangle for 2017 are given in Table 13. Corresponding herring mean weights by age group and SD/rectangle are shown in Table 14. Estimates of herring biomass excluding CBH by age group and SD/rectangle are summarized in Table 15. Removal of the CBH fraction in SD 24 (and in rectangle 39G2 of SD 23) from the herring HAWG-GERAS index (standard index area: excl. results of rectangles 43G1 and 43G2 of SD 21 as well as 37G3 and 37G4 of SD 24) resulted in biomass reductions of 19.8 % with corresponding reductions in numbers of 10.9 % (-15.8 % and -12.7 %, respectively in 2017; Figure 5). 3.3.3 Sprat The estimated sprat stock in Subdivisions 21-24 was 4.7 x 109 fish (Table 10) or 57.2 x 103 tonnes (Table 12). For the included area of Subdivisions 22-24 the number of sprat was calculated to be 3.8 x 109 fish or 43.1 x 103 tonnes. The overall abundance estimate in 2018 was dominated by on year old sprat (year class 2017, Figure 4 and Table 10). 3.4 Hydrography Vertical profiles of temperature and salinity were measured with a SeaBird SBE CTD-probe on a station grid covering the whole survey area. Hydrography measurements were either conducted directly after a trawl haul or, in case of no fishing activity, in regular intervals along the cruise track. Altogether, 106 CTD casts were conducted during this survey. Surface temperatures ranged from ca. 14°C in the Kiel Bight (SD 22) and ca. 13 °C in the Kattegat area to (SD 21) around 10-11°C in the northern Arkona Basin (SD 24)(Figure 6). Bottom temperatures were similar in most parts of Subdivisions 21, 22 and 23, but due to strong thermohaline layering in most parts of the Arkona Basin and the area of the Bornholm Basin covered were significantly different in SD 24. While bottom temperatures in the central Arkona Sea exceeded surface temperatures (maximum temperatures around 13 °C), bottom temperatures in the Bornholm Basin area were comparatively low at around 8 °C. As usual due to the hydrographic nature of the western Baltic Sea, Surface salinities showed a large gradient (from ca. 7.5 PSU in the eastern Arkona Sea to > 25 PSU in the Kattegat). Compared to the previous year, surface salinity in the western parts of the survey area (SD 22) was comparatively high at levels of ca. 20 PSU. Salinity near the seafloor ranged from 8 PSU in the Arkona Sea to ca. 34 PSU in the Kattegat. Especially in the Sound (SD 23), a very strong stratification with steep salinity gradients was observed. Surface waters were well oxygenated throughout the survey area. Near the seafloor, local anoxic conditions were measured in the inner Mecklenburg Bight/Bay of Lübeck as well as in the southwestern part of the Little Belt (SD 22). Anoxic conditions above the seafloor were observed in the southern part of the Little Belt and the inner Mecklenburg Bight. Reduced oxygen levels were also measured in the deeper parts of the Bornholm Basin area covered. 284 ICES | WGBIFS 2019 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 10 4 DISCUSSION Compared to 2017, the present estimates of herring (total survey area incl. CBH) show a further significant decrease in stock biomass, whereas abundance values increased: Herring (incl. CBH) Difference compared to 2017 Area Numbers (%) Biomass (%) Subdivisions 22-24 +18 -41 Subdivisions 21-24 +56 -19 Herring (excl. CBH) Difference compared to 2017 Area Numbers (%) Biomass (%) Subdivisions 22-24 +19 -49 Subdivisions 21-24 +63 -22 Compared to 2017, the present significant increase in numbers together with the continuing decrease in biomass was mainly driven by a higher contribution of 0-group herring (2018/2017: +177 %) that are characterized by lower mean weights, and also by a lower number of older and thus heavier herring of ages 2-7 (-39 %). The present herring biomass estimates (total survey area incl. CBH & excl. CBH) represent the second lowest recorded values in the whole time series since 1993. The usually recorded dominant high number of large herring fish in SD 23 (the Sound), which is seen as an important transition and aggregation area for the WBSSH stock during its spawning migration (Nielsen, 1996), was in 2018 as in 2016-2017 for the third time since many years almost absent. This complete absence could, as in the previous year, be explained by delayed immigration of WBSSH from the feeding areas in the Skagerrak in 2018. The exceptionally low numbers in 2016 and even further decreased numbers in 2017 and 2018 of large and older herring could also be explained by the very low recruitment, which was recorded by the N20 during the last years. The sustained downward trend in recruitment could explain the further disappearance of older herring in time. The strong correlation of N20 with the 1-age group (Polte et al., 2018) of GERAS index supports this assumption. Methodological biases leading to the low numbers observed can again not be ruled out, but at least in terms of overall acoustic detections of clupeids seem unlikely. While differences in catchability might contribute to varying fractions of (old) herring in daytime vs. nighttime catches, as indicated by a higher fraction of big WBBSH in the daytime hauls, the small-scale NASC distribution recorded during the regular night-transect in SD 23 and another comparison sampling during daytime a few days later did not differ notably between the two transect runs (Figure 7). Possible shifts in distribution of the large herring aggregations towards shallower areas that cannot be surveyed with the current survey design and setup may also have occurred. During daytime passes of the survey area (transition) as well as during the comparison survey in SD 23 during daytime, aggregations of angling boats in shallow areas (but partly also areas covered in the survey) were observed with occupants catching big herring with rod and line. Additionally, during a diversion of the vessel into Copenhagen port for disembarking of a crew member after the survey had been accomplished, enormous and continuous aggregations of clupeids were detected on the echosounder in shallow water (depth < 15 m). A comparison with echorecordings from this section, if available from previous years, is intended to address these possible shifts and to investigate whether a corresponding fraction of herring had been distributed in these areas in years with high registrations along the regular transects as well. Migrations of herring out of the sound can be triggered by hydrographic conditions in a way that barotropic inflow events in late summer and early autumn prevent deoxygenation in the Sound. This leads to prolonged aggregations of herring in the Sound (Miethe et al., 2014). In 2018, no such ICES | WGBIFS 2019 285 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 11 migration can be assumed since no older and bigger herring were detected in corresponding areas of the adjacent SD 24, nor was there an indication of according hydrographic conditions driving herring out of the Sound. 5 SURVEY PARTICIPANTS Name Function Institute Dr. M. Schaber Hydroacoustics, Cruise leader TI-SF B. Lüdke Hydroacoustics, Hydrography TI-SF B. Stefanowitsch Hydroacoustics, Fishery biology TI-SF M. Koth Fishery biology TI-OF S.-E. Levinsky Fishery biology DTU Aqua (DK) S. Winning Fishery biology TI-OF/TI-SF 6 REFERENCES Arivis (2014) GERIBAS II software, version 2.1.0. Echoview Software Pty Ltd (2018) Echoview software, version 9. Echoview Software Pty Ltd, Hobart, Australia. Foote, K.G., Aglen, A. and Nakken, O. (1986) Measurement of fish target strength with a split-beam echosounder. Journal of the Acoustical Society of America, 80(2): 612-621. Gröhsler, T., Oeberst, R., Schaber, M., Larson, N. and Kornilovs, G. (2013) Discrimination of western Baltic spring-spawning and central Baltic herring (Clupea harengus L.) based on growth vs. natural tag information. ICES Journal of Marine Science, 70 (6): 1108-1117. doi:19.1093/icesjms/fst064. Gröhsler, T., Schaber, M., Larson, N. and Oeberst, R. (2016) Separating two herring stocks from growth data: long-term changes in survey indices for Western Baltic Spring Spawning Herring (Clupea harengus) after application of a stock separation function. Journal of Applied Ichthyology 32: 40-45; doi: 10.1111/jai.12924 Gröhsler, T. and Schaber, M. (2019 in prep.). Applicability of the Separation Function (SF) in 2018. WD for WGBIFS 2019. Gröhsler, T. and Schaber, M. (2018). Applicability of the Separation Function (SF) in 2017. WD for WGBIFS 2018. ICES (2017) SISP Manual of International Baltic Acoustic Surveys (IBAS). Series of ICES Survey Protocols SISP 8 – IBAS. 47pp. ICES (2015) Report of the Workshop on scrutinisation procedures for pelagic ecosystem surveys (WKSCRUT). ICES CM 2015 / SSGIEOM: 18 ICES (2013) Report of the Benchmark Workshop on Pelagic Stocks (WKPELA 2013). ICES Document CM 2013/ACOM: 46 ICES (1983) Report of the Planning Group on ICES coordinated herring and sprat acoustic surveys. ICES Document CM 1983/H:12. Miethe, T., Gröhsler, T., Böttcher, U. and von Dorrien, C. (2014) The effects of periodic marine inflow into the Baltic Sea on the migration patterns of Western Baltic spring-spawning herring. ICES Journal of Marine Science, 71(3): 519-527. Nielsen, J. R. (1996) Acoustic monitoring of herring related to the establishment of a fixed link across the Sound between Copenhagen and Malmö. DFU-rapport Nr. 11-96, ISSN 1395-8216, 93pp. Oeberst, R., Gröhsler, T., Schaber, M. and Larsen, N. (2013) Applicability of the Separation Function (SF) in 2011 and 2012. WD 01 for HAWG. ICES Document CM 2013/ACOM06: Sec 14: 819-825 & WD for WGBIFS. ICES Document CM 2013/SSGESST:08: Annex 9: 399-405. Oeberst, R., Gröhsler, T. and Schaber, M. (2014) Applicability of the Separation Function (SF) in 2013. WD for WGIPS 2014. 286 ICES | WGBIFS 2019 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 12 Oeberst, R., Gröhsler, T. and Schaber, M. (2015) Applicability of the Separation Function (SF) in 2014. WD for WGIPS 2015. Oeberst, R., Gröhsler, T. and Schaber, M. (2016) Applicability of the Separation Function (SF) in 2015. WD for WGBIFS 2016. Oeberst, R., Gröhsler, T. and Schaber, M. (2017) Applicability of the Separation Function (SF) in 2016. WD for WGIPS 2017. Gröhsler, T. and Schaber, M. (2018) Applicability of the Separation Function (SF) in 2017. WD for WGBIFS 2018. Polte, P. and Groehsler, T. (2018) 2017 Western Baltic spring spawning herring recruitment monitored by the Rügen Herring Larvae Survey. WD for HAWG. ICES Document CM 2018/ACOM07: Annex 6: 868-871 ICES | WGBIFS 2019 287 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 13 7 FIGURES Figure 1: FRV Solea cruise 754/2018. Cruise track (dark green lines) and fishery hauls (red diamonds). ICES statistical rectangles are indicated in the top and right axis. Thick black lines separate ICES subdivisions (SD). 288 ICES | WGBIFS 2019 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 14 Figure 2: FRV Solea cruise 754/2018. Cruise track (thin grey lines) and mean NASC (5 nmi intervals, dots). ICES statistical rectangles are indicated in the top and right axis. Thick black lines separate ICES subdivisions (SD). ICES | WGBIFS 2019 289 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 15 Figure 3: FRV Solea cruise 754/2018. Herring (Clupea harengus) length-frequency distribution (bars) compared to previous year (cruise 740/2017, lines). Daytime comparison hauls conducted in SD 23 are included. 0 5 10 15 20 25 30 4.75 5.75 6.75 7.75 8.75 9.75 10.75 11.75 12.75 13.75 14.75 15.75 16.75 17.75 18.75 19.75 20.75 21.75 22.75 23.75 24.75 25.75 26.75 27.75 28.75 29.75 30.75 31.75 32.75 33.75 34.75 35.75 % N Total Length (cm) Subdivision 21 N2018= 22,145 (N-Unterprobe = 2,293) N2017= 6,540 (N-Unterprobe = 1,232) 0 5 10 15 20 25 30 4.75 5.75 6.75 7.75 8.75 9.75 10.75 11.75 12.75 13.75 14.75 15.75 16.75 17.75 18.75 19.75 20.75 21.75 22.75 23.75 24.75 25.75 26.75 27.75 28.75 29.75 30.75 31.75 32.75 33.75 34.75 35.75 % N Total Length (cm) Subdivision 22 2017 2018 N2018= 12,846 (N-measured = 3,008) N2017= 1,502 (N-measured = 1,457) 0 5 10 15 20 25 30 4.75 5.75 6.75 7.75 8.75 9.75 10.75 11.75 12.75 13.75 14.75 15.75 16.75 17.75 18.75 19.75 20.75 21.75 22.75 23.75 24.75 25.75 26.75 27.75 28.75 29.75 30.75 31.75 32.75 33.75 34.75 35.75 % N Total Length (cm) Subdivision 24 N2018= 7,356 (N-measured = 4,342) N2017= 12,197 (N-measured = 6,238) 0 5 10 15 20 25 30 4.75 5.75 6.75 7.75 8.75 9.75 10.75 11.75 12.75 13.75 14.75 15.75 16.75 17.75 18.75 19.75 20.75 21.75 22.75 23.75 24.75 25.75 26.75 27.75 28.75 29.75 30.75 31.75 32.75 33.75 34.75 35.75 % N Total Length (cm) Subdivision 23 daytime hauls nighttime hauls N2018= 8,566 (N-measured = 3,272) N2017= 1,170 (N-measured = 548) 290 ICES | WGBIFS 2019 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 16 Figure 4: FRV Solea cruise 754/2018. Sprat (Sprattus sprattus) length-frequency distribution (bars) compared to previous year (cruise 740/2017, lines). Daytime comparison hauls conducted in SD 23 are included. 0 5 10 15 20 25 30 35 40 45 50 3.25 3.75 4. 25 4.75 5.25 5.75 6.25 6.75 7.25 7.75 8.25 8.75 9.25 9.75 10.25 10.75 11.25 11.75 12.25 12.75 13.25 13.75 14.25 14.75 15.25 15.75 16.25 16.75 17.25 17.75 18.25 18.75 % N Total Length (cm) Subdivision 21 N2018= 16,875 (N-Unterprobe = 2,046) N2017= 11,645 (N-Unterprobe = 1,439) 0 5 10 15 20 25 30 35 40 45 50 3.25 3.75 4.25 4.75 5.25 5.75 6.25 6.75 7.25 7.75 8.25 8.75 9.25 9.75 10.25 10.75 11.25 11.75 12.25 12.75 13.25 13.75 14.25 14.75 15.25 15.75 16.25 16.75 17.25 17.75 18.25 18.75 % N Total Length (cm) Subdivision 22 2018 2017 N2018= 15,034 (N-measured = 2,328) N2017= 35,807 (N-measured = 1,850) 0 5 10 15 20 25 30 35 40 45 50 3.25 3.75 4.25 4.75 5.25 5.75 6.25 6.75 7.25 7.75 8.25 8.75 9.25 9.75 10.25 10.75 11.25 11.75 12.25 12.75 13.25 13.75 14.25 14.75 15.25 15.75 16.25 16.75 17.25 17.75 18.25 18.75 % N Total length (cm) Subdivision 23 daytime hauls nighttime hauls N2018= 3,764 (N-measured = 1,725) N2017= 535 (N-measured = 531) 0 5 10 15 20 25 30 35 40 45 50 3.25 3.75 4.25 4.75 5.25 5.75 6.25 6.75 7.25 7.75 8.25 8.75 9.25 9.75 10.25 10.75 11.25 11.75 12.25 12.75 13.25 13.75 14.25 14.75 15.25 15.75 16.25 16.75 17.25 17.75 18.25 18.75 % N Total Length (cm) Subdivision 24 N2018= 24,474 (N-measured = 4,416) N2017= 56,479 (N-measured = 4,320) ICES | WGBIFS 2019 291 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 17 Figure 5: Relative changes in abundance and biomass of Western Baltic Spring Spawning herring in ICES Subdivisions 21-24 (2005-2018) after application of the stock separation function (SF, Gröhsler et al., 2013) to the abundance and biomass index generated from German acoustic survey data (GERAS). *2015 excl. of CBH in SD 22 and SD 24 and mature herring (stages ≥6) in SD 23; **2016 excl. of CBH in SD 22 and SD 24 -40.0% -35.0% -30.0% -25.0% -20.0% -15.0% -10.0% -5.0% 0.0% Numbers (millions) Biomass (t) 292 ICES | WGBIFS 2019 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 18 Figure 6: FRV Solea cruise 754/2018: Hydrography. CTD stations are depicted as blue dots in the area map (lower panel). Temperature (°C, top panels), salinity (PSU, middle panels and oxygen concentration (ml/l, lower panels) near the surface (left) and near the seafloor (right). ICES | WGBIFS 2019 293 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 19 Figure 7: FRV Solea cruise 754/2018. Comparison of NASC-values/clupeid distribution during night (left) and daytime (right) sampling in the Sound (ICES Subdivision 23). Cruise track (thin grey lines) and mean NASC (1 nmi intervals, dots). 294 ICES | WGBIFS 2019 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 20 8 TABLES Table 1: FRV Solea cruise 754/2018: Simrad EK80 calibration report (38 kHz Transducer). Date: 01.10.2018 Calibration Site: Strande Bay/Kiel Bight (54°25.35 N, 10°12.29 E) Transceiver Type: WBT Software Version: EK80 1.12.2 Reference Target: Tungsten (WC-Co) 38.1 mm Transducer: ES38-7 Serial No. 147 Frequency: 38000 Hz Beamtype: Split/Narrow Gain: 26.62 dB Equivalent Beam Angle: -20.7 dB Beamwidth Athw.: 6.35 deg Beamwidth Along.: 6.27 deg Offset Athw.: 0.33 deg Offset Along.: -0.26 deg Depth: 4.20 m Pulse Duration: 1.024 ms Power: 2000 W TS Detection: Min. Value: -50.0 dB Min. Spacing: 0.0 Max. Gain Comp.: 3.0 dB Min. Echolength: 0.8 Max. Echolength: 1.8 Environment: Absorption Coeff.: 0.005297 Sound Velocity: 1487.32 m/s Temperature: 14.7 °C Salinity: 19 PSU Calibration results: Transducer Gain: 26.81 dB SaCorrection: -0.08 dB Beamwidth Athw.: 6.32 deg Beamwidth Along.: 6.19 deg Offset Athw.: -0.25 deg Offset Along.: 0.08 deg RMS-Error: 0.10 ICES | WGBIFS 2019 295 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 21 Table 2: FRV Solea cruise 754/2018: Catch composition (kg 0.5 h-1) by haul in SD 21. Haul No. 45 46 47 48 49 50 51 53 54 55 56 57 58 Species/ICES Rectangle 41G2 41G1 41G0 41G1 41G2 42G2 42G1 43G1 43G1 43G1 43G1 42G2 42G2 APHIA MINUTA 0.02 0.01 + + + 0.01 0.01 + 0.01 BELONE BELONE 0.09 0.04 0.09 0.04 CARCINUS 0.01 + + CLUPEA HARENGUS 0.86 773.09 0.10 40.81 0.51 12.76 1.48 0.54 30.40 9.53 31.81 0.62 5.32 ENGRAULIS ENCRASICOLUS 0.14 0.54 0.02 2.08 0.02 0.77 1.38 0.04 0.01 EUTRIGLA GURNARDUS 0.12 + + GASTEROSTEUS ACULEATUS 0.01 + + + 0.01 LIMANDA LIMANDA 0.24 LOLIGO 0.03 0.01 0.04 0.01 0.02 0.03 0.02 LOLIGO FORBESI 0.01 + 0.05 0.01 + 0.22 0.01 0.01 MERLANGIUS MERLANGUS 0.15 0.15 0.12 0.30 0.18 0.46 0.01 0.52 MERLUCCIUS MERLUCCIUS 0.01 0.01 MULLUS SURMULETUS 0.01 POLLACHIUS VIRENS 1.04 POMATOSCHISTUS MINUTUS + + + + + + SARDINA PILCHARDUS 0.07 0.07 0.02 0.03 1.26 0.20 0.30 SCOMBER SCOMBRUS 3.51 0.23 1.18 0.59 1.98 11.99 0.28 0.22 0.17 3.19 2.83 SEPIOLA + 0.05 0.01 + SPRATTUS SPRATTUS 114.26 0.05 92.57 0.08 0.10 2.32 0.01 0.21 4.33 14.41 0.56 32.28 SQUALUS ACANTHIAS 12.28 1.70 TRACHINUS DRACO 0.03 1.52 4.82 0.39 2.53 0.11 0.18 0.08 0.04 0.28 0.37 TRACHURUS TRACHURUS 0.02 + 0.10 0.39 + + 0.03 0.04 0.28 0.08 0.12 0.06 TRISOPTERUS ESMARKI 0.01 0.10 TRISOPTERUS MINUTUS 0.08 Total 0.92 892.63 0.40 141.26 2.16 13.51 10.78 12.72 32.21 30.36 48.44 4.86 41.72 Medusae 0.47 0.00 7.07 1.06 0.31 0.41 0.23 0.15 3.28 1.05 1.33 0.18 2.27 Haul 52 Haul No. 59 Total not valid Species/ICES Rectangle 41G2 APHIA MINUTA 0.01 0.07 BELONE BELONE 0.26 CARCINUS 0.01 CLUPEA HARENGUS 6.59 914.42 ENGRAULIS ENCRASICOLUS 5.00 EUTRIGLA GURNARDUS 0.12 GASTEROSTEUS ACULEATUS + 0.02 LIMANDA LIMANDA 0.05 0.29 LOLIGO + 0.16 LOLIGO FORBESI 0.31 MERLANGIUS MERLANGUS 0.12 2.01 MERLUCCIUS MERLUCCIUS 0.00 0.02 MULLUS SURMULETUS 0.01 POLLACHIUS VIRENS 1.04 POMATOSCHISTUS MINUTUS + SARDINA PILCHARDUS 0.02 1.97 SCOMBER SCOMBRUS 26.17 SEPIOLA 0.06 SPRATTUS SPRATTUS 4.13 265.31 SQUALUS ACANTHIAS 13.98 TRACHINUS DRACO 0.29 10.64 TRACHURUS TRACHURUS 0.44 1.56 TRISOPTERUS ESMARKI 0.11 TRISOPTERUS MINUTUS 0.08 Total 11.65 1243.62 Medusae 3.81 21.61 + = < 0.01 kg 296 ICES | WGBIFS 2019 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 22 Table 3: FRV Solea cruise 754/2018: Catch composition (kg 0.5 h-1) by haul in SD 22. Haul No. 1 2 3 4 5 6 7 8 9 10 11 12 13 Species/ICES Rectangle 38G0 40G0 40G0 41G0 40G1 40G0 39G0 39G0 39G1 38G0 38G0 38G0 37G0 APHIA MINUTA + + 0.01 + 0.01 0.04 0.01 + + + BELONE BELONE 0.03 0.05 0.09 0.05 0.13 0.05 0.18 CLUPEA HARENGUS 0.86 0.44 0.79 0.91 0.81 2.08 103.78 6.58 4.62 0.42 10.25 CRANGON CRANGON + + 0.01 + CTENOLABRUS RUPESTRIS 0.02 0.01 0.05 0.23 0.02 CYCLOPTERUS LUMPUS 0.07 0.71 ENGRAULIS ENCRASICOLUS + 0.15 0.60 0.12 0.06 0.19 0.02 0.03 EUTRIGLA GURNARDUS 0.03 GADUS MORHUA 0.04 0.30 GASTEROSTEUS ACULEATUS 0.15 0.08 + + 5.50 0.01 1.00 0.17 + GOBIUS NIGER 0.01 + + + 0.02 LIMANDA LIMANDA 0.37 0.01 0.01 0.02 0.13 0.03 0.22 0.13 LOLIGO + LOLIGO FORBESI + + 0.01 + MERLANGIUS MERLANGUS 0.02 0.01 0.12 0.08 0.02 0.36 0.02 0.02 0.01 MULLUS SURMULETUS 0.01 0.01 NEOGOBIUS MELANOSTOMUS 0.01 0.01 PLATICHTHYS FLESUS PLEURONECTES PLATESSA 0.44 POLLACHIUS VIRENS 3.94 POMATOSCHISTUS MINUTUS + 0.01 + 0.01 + PUNGITIUS PUNGITIUS + SARDINA PILCHARDUS 0.16 0.01 SCOMBER SCOMBRUS 1.90 0.04 SOLEA VULGARIS 0.71 0.26 SPRATTUS SPRATTUS 0.29 0.75 0.06 0.03 0.04 0.25 134.79 8.30 13.81 22.97 SYMPHODUS MELOPS 0.01 SYNGNATHUS TYPHLE + TRACHINUS DRACO 0.12 0.19 TRACHURUS TRACHURUS 0.01 0.01 0.08 0.02 0.01 0.06 0.28 0.06 0.01 + 0.09 TRISOPTERUS ESMARKI + TRISOPTERUS MINUTUS + Total 1.42 1.28 1.43 1.90 1.35 0.11 2.63 242.20 5.99 20.98 19.69 0.61 33.55 Medusae 14.44 43.12 4.86 3.67 1.93 2.81 2.31 3.01 2.62 3.20 7.63 12.26 16.77 Haul No. 14 15 16 17 18 Total Species/ICES Rectangle 38G1 37G1 37G1 37G1 37G1 APHIA MINUTA + + + 0.07 BELONE BELONE 0.09 0.67 CLUPEA HARENGUS 14.03 4.25 2.39 8.23 7.04 167.48 CRANGON CRANGON + 0.01 CTENOLABRUS RUPESTRIS + 0.01 0.34 CYCLOPTERUS LUMPUS 0.78 ENGRAULIS ENCRASICOLUS 0.03 1.20 EUTRIGLA GURNARDUS 0.01 0.04 GADUS MORHUA 0.38 2.13 2.85 GASTEROSTEUS ACULEATUS 0.05 0.04 0.58 0.17 7.75 GOBIUS NIGER 0.03 LIMANDA LIMANDA 0.67 19.80 0.08 0.92 22.39 LOLIGO + LOLIGO FORBESI 0.01 MERLANGIUS MERLANGUS 0.04 2.54 0.08 0.40 3.72 MULLUS SURMULETUS 0.02 NEOGOBIUS MELANOSTOMUS 0.02 PLATICHTHYS FLESUS 0.48 0.47 0.33 1.28 PLEURONECTES PLATESSA 0.45 1.15 0.18 2.22 POLLACHIUS VIRENS 3.94 POMATOSCHISTUS MINUTUS + + 0.02 PUNGITIUS PUNGITIUS + SARDINA PILCHARDUS 0.02 0.19 SCOMBER SCOMBRUS 0.04 0.10 2.08 SOLEA VULGARIS 0.97 SPRATTUS SPRATTUS 4.41 13.03 0.34 0.10 2.58 201.75 SYMPHODUS MELOPS 0.01 SYNGNATHUS TYPHLE + TRACHINUS DRACO 0.31 TRACHURUS TRACHURUS 0.01 0.02 0.06 1.36 2.08 TRISOPTERUS ESMARKI + TRISOPTERUS MINUTUS + Total 19.70 41.75 5.48 9.32 12.84 422.23 Medusae 7.02 5.09 2.80 8.85 10.89 153.29 + = < 0.01 kg ICES | WGBIFS 2019 297 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 23 Table 4: FRV Solea cruise 754/2018: Catch composition (kg 0.5 h-1) by haul in SD 23. Table 5: FRV Solea cruise 754/2018: Catch composition (kg 0.5 h-1) by haul in SD 24. Haul No. 40 41 42 43 44 *60 *61 *62 Total Species/ICES Rectangle 40G2 40G2 41G2 41G2 40G2 40G2 40G2 41G2 APHIA MINUTA 0.14 0.08 0.03 0.03 0.01 + + 0.29 CLUPEA HARENGUS 4.31 9.52 14.98 38.02 12.60 0.51 95.03 2.48 177.45 CRANGON CRANGON + + + CTENOLABRUS RUPESTRIS + + ENGRAULIS ENCRASICOLUS 0.01 0.01 + 0.03 0.05 EUTRIGLA GURNARDUS + 0.24 0.24 GADUS MORHUA 4.77 29.29 9.29 3.70 47.05 GASTEROSTEUS ACULEATUS + 0.06 0.03 + 0.01 0.02 0.12 LEANDER + + + LIMANDA LIMANDA 0.72 1.77 2.49 LOLIGO + + 0.38 0.38 MERLANGIUS MERLANGUS 0.11 0.04 0.09 1.31 11.57 0.06 13.18 PLATICHTHYS FLESUS 0.43 0.43 PLEURONECTES PLATESSA 0.40 0.40 POMATOSCHISTUS MINUTUS + + + + + PSETTA MAXIMA 0.54 0.54 SARDINA PILCHARDUS 0.01 0.01 0.14 + 0.03 + 0.19 SEPIOLA 0.02 0.02 SPRATTUS SPRATTUS 9.82 0.32 1.62 3.08 3.93 2.26 1.60 0.35 22.98 TRACHINUS DRACO 0.05 0.37 0.07 0.49 TRACHURUS TRACHURUS + 0.03 0.02 0.64 0.02 0.23 0.01 0.95 TRISOPTERUS ESMARKI + + Total 19.60 39.35 17.55 46.02 38.04 2.83 100.64 3.22 267.25 Medusae 0.23 0.83 0.75 0.13 0.51 4.31 0.15 0.58 7.49 + = < 0.01 kg Haul No. 19 20 21 22 23 24 25 26 27 28 29 30 32 Species/ICES Rectangle 37G2 38G2 38G3 38G3 38G4 38G3 37G3 38G4 38G4 38G3 38G2 38G2 39G2 APHIA MINUTA + + + + BELONE BELONE 0.19 CLUPEA HARENGUS 2.51 0.80 1.45 1.07 1.33 4.78 8.12 33.12 4.51 8.95 0.95 1.24 2.02 CRANGON CRANGON + + + + + + CYCLOPTERUS LUMPUS 0.13 0.47 ENGRAULIS ENCRASICOLUS + 0.03 GADUS MORHUA 0.20 0.11 2.02 1.91 5.43 28.19 8.98 7.20 0.42 0.74 0.01 GASTEROSTEUS ACULEATUS 0.47 0.19 0.02 + 0.12 0.03 2.22 1.13 1.00 GOBIUS NIGER + + LIMANDA LIMANDA 1.42 0.08 0.31 MERLANGIUS MERLANGUS 0.09 1.11 0.70 10.44 110.99 15.61 0.46 3.46 0.02 + MYOXOCEPHALUS SCORPIUS + NEOGOBIUS MELANOSTOMUS + PLATICHTHYS FLESUS 0.16 0.64 1.27 4.45 2.34 0.21 0.46 PLEURONECTES PLATESSA 1.61 1.25 0.28 0.22 0.55 POMATOSCHISTUS MINUTUS + 0.02 + + 0.01 + 0.01 + + 0.02 PUNGITIUS PUNGITIUS + SCOMBER SCOMBRUS 0.55 SCOPHTHALMUS RHOMBUS 0.55 SPRATTUS SPRATTUS 5.57 0.39 11.78 77.20 56.20 4.62 4.37 13.78 4.53 20.99 0.01 0.71 0.16 STIZOSTEDION LUCIOPERCA 0.71 1.27 TRACHURUS TRACHURUS 0.09 0.21 0.11 0.11 0.15 0.02 0.04 0.01 + Total 10.43 4.94 18.16 92.33 63.15 154.72 40.72 54.57 10.04 35.20 3.31 3.57 3.24 Medusae 1.64 16.14 4.95 1.97 64.22 2.13 2.18 2.64 18.35 4.51 10.93 16.19 3.62 Haul 31 Haul No. 33 34 35 36 37 38 39 Total not valid Species/ICES Rectangle 39G3 39G3 39G4 39G4 39G3 39G3 39G2 APHIA MINUTA + + + + BELONE BELONE 0.19 CLUPEA HARENGUS 5.27 13.03 7.49 17.44 15.63 12.40 50.41 192.52 CRANGON CRANGON + + + CYCLOPTERUS LUMPUS 0.79 1.39 ENGRAULIS ENCRASICOLUS 0.04 0.02 0.09 GADUS MORHUA 3.81 1.36 1.00 10.07 5.30 76.75 GASTEROSTEUS ACULEATUS 0.13 0.12 0.02 0.09 0.01 5.55 GOBIUS NIGER + LIMANDA LIMANDA 1.81 MERLANGIUS MERLANGUS 0.01 1.66 1.08 0.24 0.12 0.29 146.28 MYOXOCEPHALUS SCORPIUS + NEOGOBIUS MELANOSTOMUS + PLATICHTHYS FLESUS 0.26 + 9.79 PLEURONECTES PLATESSA 3.91 POMATOSCHISTUS MINUTUS 0.01 + + + 0.01 0.08 PUNGITIUS PUNGITIUS + SCOMBER SCOMBRUS 0.55 SCOPHTHALMUS RHOMBUS 0.55 SPRATTUS SPRATTUS 0.32 25.63 2.47 21.42 3.41 11.66 28.12 293.34 STIZOSTEDION LUCIOPERCA 1.98 TRACHURUS TRACHURUS 0.01 + 0.75 Total 9.60 42.85 12.06 39.19 29.25 29.66 78.54 735.53 Medusae 1.30 0.54 2.79 0.63 4.55 3.94 1.60 164.80 + = < 0.01 kg 298 ICES | WGBIFS 2019 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 24 Table 6: FRV Solea, cruise 754/2018. Survey statistics by area. Sub- ICES Area Sa Sigma N total Herring Sprat NHerring NSprat division Rectangle (nm²) (m²/NM²) (cm²) (million) (%) (%) (million) (million) 21 41G0 108.1 40.2 0.261 166.50 4.08 3.06 6.80 5.10 21 41G1 946.8 121.9 2.394 482.10 44.19 55.38 213.04 266.97 21 41G2 432.3 77.3 1.316 253.93 48.59 39.64 123.39 100.65 21 42G1 884.2 49.5 1.550 282.37 24.10 40.54 68.05 114.47 21 42G2 606.8 219.9 2.227 599.17 54.31 42.97 325.42 257.49 21 43G1 699.0 129.3 1.393 648.82 72.44 18.77 470.00 121.80 21 43G2 107.0 357.2 1.399 273.20 57.40 35.06 156.80 95.79 21 Total 3,784.2 2706.09 1363.50 962.27 22 37G0 209.9 99.1 1.543 134.81 32.78 65.17 44.20 87.85 22 37G1 723.3 94.7 1.383 495.27 51.43 28.09 254.69 139.15 22 38G0 735.3 92.6 1.120 607.94 37.57 40.90 228.43 248.67 22 38G1 173.2 121.8 1.082 194.97 61.77 35.60 120.42 69.41 22 39F9 159.3 40.7 1.227 52.84 37.76 30.09 19.95 15.90 22 39G0 201.7 36.0 1.227 59.18 37.76 30.09 22.34 17.81 22 39G1 250.0 65.2 0.262 622.14 0.00 0.00 0.00 0.00 22 40F9 51.3 150.7 1.231 62.80 45.80 28.71 28.77 18.03 22 40G0 538.1 71.8 1.231 313.86 45.80 28.71 143.76 90.11 22 40G1 174.5 279.2 1.497 325.45 43.06 2.78 140.12 9.04 22 41G0 173.1 46.9 1.368 59.34 26.81 1.45 15.91 0.86 22 Total 3,389.7 2928.60 1018.59 696.83 23 39G2 130.9 132.8 1.050 165.56 46.43 3.32 76.88 5.49 23 40G2 164.0 485.3 1.633 487.38 44.60 28.63 217.36 139.55 23 41G2 72.3 501.0 1.289 281.01 75.75 16.12 212.88 45.29 23 Total 367.2 933.95 507.12 190.33 24 37G2 192.4 132.9 1.623 157.55 26.97 70.02 42.49 110.31 24 37G3 167.7 192.4 3.105 103.91 16.49 74.83 17.13 77.75 24 37G4 875.1 21.7 1.898 100.05 20.48 74.26 20.49 74.30 24 38G2 832.9 131.8 0.670 1638.45 11.85 10.57 194.18 173.23 24 38G3 865.7 254.5 3.112 707.97 8.26 76.26 58.49 539.87 24 38G4 1034.8 229.5 1.898 1251.25 20.48 74.26 256.22 929.15 24 39G2 406.1 181.7 1.094 674.48 37.67 22.26 254.11 150.15 24 39G3 765.0 262.0 2.355 851.08 46.04 46.68 391.83 397.30 24 39G4 524.8 278.8 2.341 625.01 27.39 68.69 171.18 429.30 24 Total 5,664.5 6,109.75 1406.12 2881.36 22-24 Total 9,421.4 9,972.30 2931.83 3768.52 21-24 Total 13,205.6 12,678.39 4295.33 4730.79 ICES | WGBIFS 2019 299 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 25 Table 7: FRV Solea, cruise 754/2018. Numbers (millions) of herring incl. CBH by age/W-rings and area. Table 8: FRV Solea, cruise 754/2018. Mean weight (g) of herring incl. CBH by age/W-rings and area. Sub- Rectangle/ division W-rings 0 1 2 3 4 5 6 7 8+ Total 21 41G0 5.10 1.70 6.80 21 41G1 91.20 90.35 24.18 4.74 1.62 0.95 213.04 21 41G2 122.39 0.83 0.06 0.11 123.39 21 42G1 64.74 3.05 0.25 68.04 21 42G2 162.53 144.11 15.72 1.78 0.67 0.62 325.43 21 43G1 468.92 1.08 470.00 21 43G2 156.48 0.32 156.80 21 Total 1,071.36 241.44 40.21 6.63 2.29 1.57 0.00 0.00 0.00 1,363.50 22 37G0 41.12 2.66 0.13 0.07 0.15 0.07 44.20 22 37G1 229.70 21.86 0.56 1.07 1.39 0.10 254.68 22 38G0 223.66 4.09 0.36 0.09 0.22 228.42 22 38G1 120.11 0.06 0.19 0.06 120.42 22 39F9 19.07 0.70 0.13 0.03 0.03 19.96 22 39G0 21.35 0.78 0.14 0.03 0.03 22.33 22 39G1 0.00 22 40F9 28.77 28.77 22 40G0 143.76 143.76 22 40G1 113.75 14.93 10.25 0.90 0.28 140.11 22 41G0 12.25 2.69 0.72 0.03 0.23 15.92 22 Total 953.54 47.77 12.48 2.28 2.33 0.17 0.00 0.00 0.00 1,018.57 23 39G2 74.71 0.71 0.19 0.32 0.64 0.15 0.11 0.04 76.87 23 40G2 204.19 8.11 1.29 0.66 2.24 0.75 0.13 217.37 23 41G2 209.84 1.55 0.71 0.19 0.37 0.18 0.03 212.87 23 Total 488.74 10.37 2.19 1.17 3.25 1.08 0.27 0.00 0.04 507.11 24 37G2 36.63 2.00 0.64 0.97 1.79 0.30 0.12 0.02 0.02 42.49 24 37G3 3.30 0.94 2.28 3.06 3.20 2.16 0.95 0.36 0.89 17.14 24 37G4 7.41 2.49 1.18 2.37 3.96 1.87 0.57 0.28 0.36 20.49 24 38G2 177.60 5.74 0.51 2.05 6.23 1.23 0.60 0.11 0.11 194.18 24 38G3 27.44 4.67 3.41 5.77 9.12 4.50 1.63 0.64 1.32 58.50 24 38G4 92.61 31.09 14.71 29.63 49.56 23.43 7.16 3.51 4.53 256.23 24 39G2 234.24 6.64 1.13 2.66 6.76 1.58 0.76 0.17 0.17 254.11 24 39G3 169.98 55.86 14.87 36.25 73.55 26.79 8.03 3.21 3.29 391.83 24 39G4 9.09 25.49 11.82 28.75 46.53 30.02 10.15 4.29 5.05 171.19 24 Total 758.30 134.92 50.55 111.51 200.70 91.88 29.97 12.59 15.74 1,406.16 22-24 Total 2,200.58 193.06 65.22 114.96 206.28 93.13 30.24 12.59 15.78 2,931.84 21-24 Total 3,271.94 434.50 105.43 121.59 208.57 94.70 30.24 12.59 15.78 4,295.34 Sub- Rectangle/ division W-rings 0 1 2 3 4 5 6 7 8+ Total 21 41G0 19.64 42.50 25.36 21 41G1 22.89 51.20 73.06 81.30 85.88 99.58 42.71 21 41G2 13.23 48.82 54.24 32.00 13.51 21 42G1 12.45 43.94 69.92 14.07 21 42G2 13.98 50.86 68.58 94.20 81.07 117.66 33.72 21 43G1 11.49 40.90 11.56 21 43G2 12.12 38.54 12.17 21 Total 13.23 50.77 71.26 83.95 84.47 106.72 22.16 22 37G0 10.90 34.81 68.00 31.00 33.56 52.00 12.68 22 37G1 10.06 34.69 63.16 46.61 34.77 52.00 12.60 22 38G0 9.07 36.19 78.50 31.06 34.43 9.70 22 38G1 9.33 63.80 63.80 63.80 9.47 22 39F9 14.16 35.77 66.43 48.78 34.32 15.34 22 39G0 14.16 35.77 66.43 48.78 34.32 15.32 22 39G1 0.00 22 40F9 11.77 11.77 22 40G0 11.77 11.77 22 40G1 18.89 42.80 65.12 63.80 35.94 25.14 22 41G0 18.07 38.02 71.90 32.41 37.50 24.18 22 Total 11.41 37.62 65.85 52.63 35.06 52.00 0.00 0.00 0.00 13.46 23 39G2 12.01 31.71 41.62 39.74 31.93 48.43 44.98 59.32 12.69 23 40G2 10.58 39.94 44.60 36.57 37.64 32.67 43.40 12.33 23 41G2 10.94 50.05 69.35 65.30 46.99 29.17 43.40 11.55 23 Total 10.95 40.89 52.37 42.10 37.58 34.28 44.04 59.32 12.06 24 37G2 12.92 29.79 27.81 36.72 32.09 35.43 41.92 67.38 67.38 15.58 24 37G3 9.04 38.06 59.92 59.90 55.09 56.46 62.23 65.36 62.02 47.94 24 37G4 10.12 34.25 53.15 50.08 42.32 51.20 54.82 54.15 60.90 32.86 24 38G2 10.08 33.15 36.89 36.25 34.34 38.23 36.73 47.05 51.17 12.19 24 38G3 10.49 34.57 56.06 56.09 47.02 57.99 57.79 65.73 62.27 32.01 24 38G4 10.12 34.25 53.15 50.08 42.32 51.20 54.82 54.15 60.90 32.87 24 39G2 12.69 32.48 35.51 37.85 33.77 41.66 39.73 45.23 56.11 14.44 24 39G3 13.53 33.45 43.73 41.97 37.16 43.47 51.71 47.85 58.31 28.07 24 39G4 14.19 33.96 53.72 68.89 54.06 86.92 90.18 91.30 89.49 61.30 24 Total 11.86 33.70 50.13 52.21 42.94 60.68 65.56 65.95 69.60 28.43 22-24 Total 11.46 35.06 53.22 52.12 42.77 60.36 65.37 65.95 69.57 20.40 21-24 Total 12.04 43.79 60.10 53.85 43.23 61.13 65.37 65.95 69.57 20.96 300 ICES | WGBIFS 2019 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 26 Table 9: FRV Solea, cruise 754/2018. Total biomass (t) of herring incl. CBH by age/W-rings and area. Table 10: FRV Solea, cruise 754/2018. Numbers (millions) of sprat by age and area. Sub- Rectangle/ division W-rings 0 1 2 3 4 5 6 7 8+ Total 21 41G0 100.2 72.3 172.4 21 41G1 2,087.6 4,625.9 1,766.6 385.4 139.1 94.6 9,099.2 21 41G2 1,619.2 40.5 3.3 3.5 1,666.5 21 42G1 806.0 134.0 17.5 957.5 21 42G2 2,272.2 7,329.4 1,078.1 167.7 54.3 73.0 10,974.6 21 43G1 5,387.9 44.2 5,432.1 21 43G2 1,896.5 12.3 1,908.9 21 Total 14,169.6 12,258.6 2,865.4 556.6 193.5 167.6 0.0 0.0 0.0 30,211.2 22 37G0 448.2 92.6 8.8 2.2 5.0 3.6 560.5 22 37G1 2,310.8 758.3 35.4 49.9 48.3 5.2 3,207.9 22 38G0 2,028.6 148.0 28.3 2.8 7.6 2,215.3 22 38G1 1,120.6 3.8 12.1 3.8 1,140.4 22 39F9 270.0 25.0 8.6 1.5 1.0 306.2 22 39G0 302.3 27.9 9.3 1.5 1.0 342.0 22 39G1 0.0 22 40F9 338.6 338.6 22 40G0 1,692.1 1,692.1 22 40G1 2,148.7 639.0 667.5 57.4 10.1 3,522.7 22 41G0 221.4 102.3 51.8 1.0 8.6 385.0 22 Total 10,881.4 1,797.0 821.8 119.98 81.7 8.8 0.00 0.00 0.0 13,710.6 23 39G2 897.3 22.5 7.9 12.7 20.4 7.3 5.0 2.4 975.4 23 40G2 2,160.3 323.9 57.5 24.1 84.3 24.5 5.6 2,680.4 23 41G2 2,295.7 77.6 49.2 12.4 17.4 5.3 1.3 2,458.8 23 Total 5,353.3 424.0 114.7 49.3 122.1 37.0 11.9 0.0 2.4 6,114.6 24 37G2 473.3 59.6 17.8 35.6 57.4 10.6 5.0 1.4 1.4 662.1 24 37G3 29.8 35.8 136.6 183.3 176.3 122.0 59.1 23.5 55.2 821.6 24 37G4 75.0 85.3 62.7 118.7 167.6 95.7 31.3 15.2 21.9 673.3 24 38G2 1,790.2 190.3 18.8 74.3 213.9 47.0 22.0 5.2 5.6 2,367.4 24 38G3 287.9 161.4 191.2 323.6 428.8 261.0 94.2 42.1 82.2 1,872.3 24 38G4 937.2 1,064.8 781.8 1,483.9 2,097.4 1,199.6 392.5 190.1 275.9 8,423.2 24 39G2 2,972.5 215.7 40.1 100.7 228.3 65.8 30.2 7.7 9.5 3,670.5 24 39G3 2,299.8 1,868.5 650.3 1,521.4 2,733.1 1,164.6 415.2 153.6 191.8 10,998.4 24 39G4 129.0 865.6 635.0 1,980.6 2,515.4 2,609.3 915.3 391.7 451.9 10,493.9 24 Total 8,994.7 4,547.0 2,534.3 5,822.1 8,618.3 5,575.6 1,964.9 830.3 1,095.5 39,982.8 22-24 Total 25,229.3 6,768.0 3,470.8 5,991.4 8,822.1 5,621.5 1,976.8 830.3 1,097.9 59,808.0 21-24 Total 39,398.8 19,026.6 6,336.2 6,547.9 9,015.6 5,789.0 1,976.8 830.3 1,097.9 90,019.1 Sub- Rectangle/ division Age group 0 1 2 3 4 5 6 7 8+ Total 21 41G0 2.13 1.27 1.36 0.23 0.11 5.10 21 41G1 107.64 44.24 63.62 40.74 9.80 0.93 266.97 21 41G2 2.76 95.15 2.15 0.48 0.07 0.05 100.66 21 42G1 104.95 6.08 2.18 0.80 0.30 0.16 114.47 21 42G2 1.29 152.89 23.71 45.14 27.57 6.89 257.49 21 43G1 0.33 114.65 5.68 0.70 0.36 0.09 121.81 21 43G2 0.44 90.48 4.09 0.51 0.23 0.06 95.81 21 Total 4.82 667.89 87.22 113.99 70.00 17.30 0.00 1.09 0.00 962.31 22 37G0 10.27 16.12 38.92 9.98 11.65 0.73 0.16 87.83 22 37G1 54.51 35.43 23.55 6.59 10.20 6.22 2.65 139.15 22 38G0 113.11 30.40 65.46 17.48 20.42 1.42 0.38 248.67 22 38G1 69.22 0.19 69.41 22 39F9 0.96 4.49 6.65 1.65 1.99 0.15 15.89 22 39G0 1.08 5.03 7.45 1.85 2.23 0.17 17.81 22 39G1 0.00 22 40F9 10.98 0.50 3.57 1.36 1.41 0.20 18.02 22 40G0 54.89 2.52 17.83 6.82 7.04 1.02 90.12 22 40G1 5.11 1.97 1.97 9.05 22 41G0 0.33 0.34 0.09 0.09 0.85 22 Total 315.02 95.01 168.88 47.79 57.00 9.91 0.00 3.19 0.00 696.80 23 39G2 0.62 2.10 1.67 0.58 0.45 0.07 0.01 5.50 23 40G2 121.04 12.10 2.49 0.53 3.08 0.16 0.16 139.56 23 41G2 43.45 1.66 0.14 0.01 0.03 45.29 23 Total 165.11 15.86 4.30 1.12 3.56 0.23 0.17 0.00 0.00 190.35 24 37G2 6.77 48.04 32.96 11.35 9.36 1.23 0.51 0.04 0.04 110.30 24 37G3 55.46 18.62 2.35 0.66 0.56 0.07 0.03 77.75 24 37G4 13.82 18.71 20.54 10.18 8.71 1.48 0.74 0.06 0.06 74.30 24 38G2 83.98 47.88 25.98 8.21 6.65 0.13 0.39 173.22 24 38G3 134.72 208.91 117.87 39.73 32.26 4.41 1.69 0.14 0.14 539.87 24 38G4 172.82 233.97 256.83 127.34 108.95 18.48 9.21 0.78 0.78 929.16 24 39G2 16.43 48.30 46.34 19.52 15.70 2.77 0.91 0.09 0.09 150.15 24 39G3 46.02 136.02 124.09 45.14 37.11 6.27 2.21 0.23 0.23 397.32 24 39G4 70.30 117.64 120.44 58.06 49.78 7.97 4.64 0.23 0.23 429.29 24 Total 600.32 878.09 747.40 320.19 269.08 42.81 20.33 1.57 1.57 2,881.36 22-24 Total 1,080.45 988.96 920.58 369.10 329.64 52.95 20.50 4.76 1.57 3,768.51 21-24 Total 1,085.27 1,656.85 1,007.80 483.09 399.64 70.25 20.50 5.85 1.57 4,730.82 ICES | WGBIFS 2019 301 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 27 Table 11: FRV Solea, cruise 754/2018. Mean weight (g) of sprat by age and area. Table 12: FRV Solea, cruise 754/2018. Total biomass (t) of sprat by age and area. Sub- Rectangle/ division Age group 0 1 2 3 4 5 6 7 8+ Total 21 41G0 16.32 17.41 18.44 18.11 19.08 17.30 21 41G1 14.69 18.28 19.39 20.76 20.68 23.63 17.58 21 41G2 3.43 10.52 15.50 18.81 18.60 19.08 10.48 21 42G1 12.55 15.85 19.16 21.03 20.76 23.63 12.95 21 42G2 2.86 12.73 18.12 19.55 20.17 19.71 15.36 21 43G1 3.00 12.62 15.15 19.13 19.92 19.66 12.78 21 43G2 2.92 12.46 15.17 18.91 19.73 19.61 12.59 21 Total 3.20 12.66 17.64 19.43 20.51 20.27 23.63 14.59 22 37G0 6.00 13.58 15.41 16.24 16.07 18.15 20.50 14.19 22 37G1 5.54 12.15 14.67 17.28 17.63 22.90 20.50 11.27 22 38G0 5.03 13.46 15.41 16.38 16.25 18.23 20.50 10.61 22 38G1 5.19 10.11 5.20 22 39F9 5.49 13.26 15.24 16.41 16.21 17.74 14.36 22 39G0 5.49 13.26 15.24 16.41 16.21 17.74 14.36 22 39G1 0.00 22 40F9 7.10 11.60 16.17 16.76 16.71 17.74 10.62 22 40G0 7.10 11.60 16.17 16.76 16.71 17.74 10.62 22 40G1 16.40 16.40 16.40 16.40 22 41G0 13.01 15.43 16.40 16.40 14.70 22 Total 5.62 12.90 15.42 16.54 16.53 21.08 20.50 10.92 23 39G2 6.14 11.76 13.99 14.75 15.01 16.78 18.23 12.46 23 40G2 5.75 11.41 17.24 17.84 19.76 25.00 25.00 6.84 23 41G2 4.87 10.87 15.72 15.00 15.68 5.13 23 Total 5.52 11.40 15.93 16.21 19.13 22.50 24.60 6.60 24 37G2 5.29 11.77 14.16 15.35 15.54 16.78 17.61 19.77 19.77 12.86 24 37G3 4.03 9.18 13.10 15.35 15.65 16.84 17.28 5.73 24 37G4 5.33 11.58 14.59 16.21 16.31 17.64 17.92 19.77 19.77 12.64 24 38G2 4.38 10.32 13.90 15.08 15.37 15.51 16.83 8.42 24 38G3 4.23 11.33 14.01 15.31 15.51 16.96 17.73 19.77 19.77 10.76 24 38G4 5.33 11.58 14.59 16.21 16.31 17.64 17.92 19.77 19.77 12.64 24 39G2 4.80 12.23 14.17 15.55 15.76 17.42 18.13 19.77 19.77 12.96 24 39G3 5.29 11.83 14.35 15.45 15.58 17.21 18.25 19.77 19.77 12.75 24 39G4 4.89 11.69 14.51 16.05 16.21 17.32 18.56 19.77 19.77 12.67 24 Total 4.76 11.50 14.37 15.86 16.01 17.40 18.07 19.77 19.77 11.89 22-24 Total 5.13 11.63 14.57 15.95 16.13 18.11 18.12 20.26 19.78 11.44 21-24 Total 5.12 12.05 14.84 16.77 16.90 18.64 18.12 20.89 19.78 12.08 Sub- Rectangle/ division Age group 0 1 2 3 4 5 6 7 8+ Total 21 41G0 34.8 22.1 25.1 4.2 2.1 88.2 21 41G1 1,581.2 808.7 1,233.6 845.8 202.7 22.0 4,693.9 21 41G2 9.5 1,001.0 33.3 9.0 1.3 1.0 1,055.1 21 42G1 1,317.1 96.4 41.8 16.8 6.2 3.8 1,482.1 21 42G2 3.7 1,946.3 429.6 882.5 556.1 135.8 3,954.0 21 43G1 1.0 1,446.9 86.1 13.4 7.2 1.8 1,556.3 21 43G2 1.3 1,127.4 62.1 9.6 4.5 1.2 1,206.1 21 Total 15.4 8,454.6 1,538.2 2,215.0 1,435.9 350.7 0.0 25.8 0.0 14,035.6 22 37G0 61.6 218.9 599.8 162.1 187.2 13.3 3.3 1,246.1 22 37G1 302.0 430.5 345.5 113.9 179.8 142.4 54.3 1,568.4 22 38G0 568.9 409.2 1,008.7 286.3 331.8 25.9 7.8 2,638.7 22 38G1 359.3 1.9 361.2 22 39F9 5.3 59.5 101.4 27.1 32.3 2.7 228.2 22 39G0 5.9 66.7 113.5 30.4 36.2 3.0 255.7 22 39G1 0.0 22 40F9 78.0 5.8 57.7 22.8 23.6 3.6 191.4 22 40G0 389.7 29.2 288.3 114.3 117.6 18.1 957.3 22 40G1 83.8 32.3 32.3 148.4 22 41G0 4.3 5.3 1.5 1.5 12.5 22 Total 1,770.7 1,226.0 2,604.0 790.6 942.3 208.9 0.0 65.4 0.0 7,607.9 23 39G2 3.8 24.7 23.4 8.6 6.8 1.2 0.2 68.5 23 40G2 696.0 138.1 42.9 9.5 60.9 4.0 4.0 955.3 23 41G2 211.6 18.0 2.2 0.2 0.5 232.5 23 Total 911.4 180.8 68.5 18.2 68.1 5.2 4.2 0.0 0.0 1,256.3 24 37G2 35.8 565.4 466.7 174.2 145.5 20.6 9.0 0.8 0.8 1,418.8 24 37G3 223.5 170.9 30.8 10.1 8.8 1.2 0.5 445.8 24 37G4 73.7 216.7 299.7 165.0 142.1 26.1 13.3 1.2 1.2 938.8 24 38G2 367.8 494.1 361.1 123.8 102.2 2.0 6.6 1,457.7 24 38G3 569.9 2,367.0 1,651.4 608.3 500.4 74.8 30.0 2.8 2.8 5,807.1 24 38G4 921.1 2,709.4 3,747.2 2,064.2 1,777.0 326.0 165.0 15.4 15.4 11,740.7 24 39G2 78.9 590.7 656.6 303.5 247.4 48.3 16.5 1.8 1.8 1,945.5 24 39G3 243.5 1,609.1 1,780.7 697.4 578.2 107.9 40.3 4.6 4.6 5,066.2 24 39G4 343.8 1,375.2 1,747.6 931.9 806.9 138.0 86.1 4.6 4.6 5,438.6 24 Total 2,857.9 10,098.5 10,741.7 5,078.4 4,308.3 744.9 367.3 31.1 31.1 34,259.2 22-24 Total 5,540.0 11,505.3 13,414.2 5,887.2 5,318.7 959.0 371.5 96.5 31.1 43,123.3 21-24 Total 5,555.4 19,960.0 14,952.4 8,102.2 6,754.5 1,309.7 371.5 122.2 31.1 57,158.9 302 ICES | WGBIFS 2019 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 28 Table 13: FRV Solea, cruise 754/2018. Numbers (m) of herring excl. CBH in SDs 24 (23) by age/W-rings & area. Table 14: FRV Solea, cruise 754/2018. Mean weight (g) of herring excl. CBH in SDs 24 (23) by age/W-rings & area. Sub- Rectangle/ division W-rings 0 1 2 3 4 5 6 7 8+ Total 21 41G0 5.10 1.70 6.80 21 41G1 91.20 90.35 24.18 4.74 1.62 0.95 213.04 21 41G2 122.39 0.83 0.06 0.11 123.39 21 42G1 64.74 3.05 0.25 68.04 21 42G2 162.53 144.11 15.72 1.78 0.67 0.62 325.43 21 43G1 468.92 1.08 470.00 21 43G2 156.48 0.32 156.80 21 Total 1,071.36 241.44 40.21 6.63 2.29 1.57 0.00 0.00 0.00 1,363.50 22 37G0 41.12 2.66 0.13 0.07 0.15 0.07 44.20 22 37G1 229.70 21.86 0.56 1.07 1.39 0.10 254.68 22 38G0 223.66 4.09 0.36 0.09 0.22 228.42 22 38G1 120.11 0.06 0.19 0.06 120.42 22 39F9 19.07 0.70 0.13 0.03 0.03 19.96 22 39G0 21.35 0.78 0.14 0.03 0.03 22.33 22 39G1 0.00 22 40F9 28.77 28.77 22 40G0 143.76 143.76 22 40G1 113.75 14.93 10.25 0.90 0.28 140.11 22 41G0 12.25 2.69 0.72 0.03 0.23 15.92 22 Total 953.54 47.77 12.48 2.28 2.33 0.17 0.00 0.00 0.00 1,018.57 23 39G2 74.71 0.69 0.09 0.07 75.56 23 40G2 204.19 8.11 1.29 0.66 2.24 0.75 0.13 217.37 23 41G2 209.84 1.55 0.71 0.19 0.37 0.18 0.03 212.87 23 Total 488.74 10.35 2.09 0.92 2.61 0.93 0.16 0.00 0.00 505.80 24 37G2 36.63 1.75 0.05 0.07 38.50 24 37G3 3.30 0.94 2.21 2.02 0.46 0.12 0.06 0.01 0.01 9.13 24 37G4 7.41 2.49 0.97 0.73 0.24 0.12 0.04 0.00 0.00 12.00 24 38G2 177.60 5.74 0.17 183.51 24 38G3 27.44 4.56 3.05 2.87 0.73 0.38 0.14 0.07 0.03 39.27 excl. CBH 24 38G4 92.61 31.09 12.12 9.14 2.96 1.47 0.44 0.05 0.05 149.93 24 39G2 234.24 6.46 0.37 0.15 241.22 24 39G3 169.98 55.28 8.86 4.65 0.55 0.33 0.35 0.04 0.04 240.08 24 39G4 9.09 25.49 9.88 14.45 8.77 12.72 3.85 0.90 0.98 86.13 24 Total 758.30 133.80 37.68 34.08 13.71 15.14 4.88 1.07 1.11 999.77 22-24 Total 2,200.58 191.92 52.25 37.28 18.65 16.24 5.04 1.07 1.11 2,524.14 21-24 Total 3,271.94 433.36 92.46 43.91 20.94 17.81 5.04 1.07 1.11 3,887.64 Sub- Rectangle/ division W-rings 0 1 2 3 4 5 6 7 8+ Total 21 41G0 19.64 42.50 25.36 21 41G1 22.89 51.20 73.06 81.30 85.88 99.58 42.71 21 41G2 13.23 48.82 54.24 32.00 13.51 21 42G1 12.45 43.94 69.92 14.07 21 42G2 13.98 50.86 68.58 94.20 81.07 117.66 33.72 21 43G1 11.49 40.90 11.56 21 43G2 12.12 38.54 12.17 21 Total 13.23 50.77 71.26 83.95 84.47 106.72 22.16 22 37G0 10.90 34.81 68.00 31.00 33.56 52.00 12.68 22 37G1 10.06 34.69 63.16 46.61 34.77 52.00 12.60 22 38G0 9.07 36.19 78.50 31.06 34.43 9.70 22 38G1 9.33 63.80 63.80 63.80 9.47 22 39F9 14.16 35.77 66.43 48.78 34.32 15.34 22 39G0 14.16 35.77 66.43 48.78 34.32 15.32 22 39G1 0.00 22 40F9 11.77 11.77 22 40G0 11.77 11.77 22 40G1 18.89 42.80 65.12 63.80 35.94 25.14 22 41G0 18.07 38.02 71.90 32.41 37.50 24.18 22 Total 11.41 37.62 65.85 52.63 35.06 52.00 13.46 23 39G2 12.01 31.98 59.32 59.32 12.29 23 40G2 10.58 39.94 44.60 36.57 37.64 32.67 43.40 12.33 23 41G2 10.94 50.05 69.35 65.30 46.99 29.17 43.40 11.55 23 Total 10.95 40.92 53.64 44.23 38.97 31.99 43.40 12.00 24 37G2 12.92 31.04 67.38 67.38 13.91 24 37G3 9.04 38.06 60.86 67.60 78.39 89.40 95.35 100.69 100.69 42.85 24 37G4 10.12 34.25 58.64 73.04 84.22 122.79 114.97 100.69 100.69 25.83 24 38G2 10.08 33.15 51.17 10.84 24 38G3 10.49 34.90 59.63 71.32 95.56 140.93 106.93 148.80 100.69 25.09 excl. CBH 24 38G4 10.12 34.25 58.64 73.04 84.22 122.79 114.97 100.69 100.69 25.82 24 39G2 12.69 32.82 54.77 59.32 13.32 24 39G3 13.53 33.58 55.41 67.54 81.46 97.27 189.17 100.69 100.69 21.29 24 39G4 14.19 33.96 58.92 97.27 119.05 138.88 150.81 180.98 194.47 78.10 24 Total 11.86 33.81 58.10 82.02 106.80 135.94 148.10 171.37 183.49 23.14 22-24 Total 11.46 35.14 59.78 79.29 88.34 129.11 144.77 171.37 183.49 17.00 21-24 Total 12.04 43.85 64.77 80.00 87.92 127.14 144.77 171.37 183.49 18.81 ICES | WGBIFS 2019 303 Working document Baltic International Fish Survey Working Group (WGBIFS) 25 - 29 March 2019, Klaipeda/Lithuania 29 Table 15: FRV Solea, cruise 754/2018. Total biomass (t) of herring excl. CBH in SDs 24 (23) by age/W-rings & area. Sub- Rectangle/ division W-rings 0 1 2 3 4 5 6 7 8+ Total 21 41G0 100.2 72.3 172.4 21 41G1 2,087.6 4,625.9 1,766.6 385.4 139.1 94.6 9,099.2 21 41G2 1,619.2 40.5 3.3 3.5 1,666.5 21 42G1 806.0 134.0 17.5 957.5 21 42G2 2,272.2 7,329.4 1,078.1 167.7 54.3 73.0 10,974.6 21 43G1 5,387.9 44.2 5,432.1 21 43G2 1,896.5 12.3 1,908.9 21 Total 14,169.6 12,258.6 2,865.4 556.6 193.5 167.6 0.0 0.0 0.0 30,211.2 22 37G0 448.2 92.6 8.8 2.2 5.0 3.6 560.5 22 37G1 2,310.8 758.3 35.4 49.9 48.3 5.2 3,207.9 22 38G0 2,028.6 148.0 28.3 2.8 7.6 2,215.3 22 38G1 1,120.6 3.8 12.1 3.8 1,140.4 22 39F9 270.0 25.0 8.6 1.5 1.0 306.2 22 39G0 302.3 27.9 9.3 1.5 1.0 342.0 22 39G1 0.0 22 40F9 338.6 338.6 22 40G0 1,692.1 1,692.1 22 40G1 2,148.7 639.0 667.5 57.4 10.1 3,522.7 22 41G0 221.4 102.3 51.8 1.0 8.6 385.0 22 Total 10,881.4 1,797.0 821.8 119.98 81.7 8.8 0.00 0.00 0.0 13,710.6 23 39G2 897.3 22.1 5.3 4.2 928.8 23 40G2 2,160.3 323.9 57.5 24.1 84.3 24.5 5.6 2,680.4 23 41G2 2,295.7 77.6 49.2 12.4 17.4 5.3 1.3 2,458.8 23 Total 5,353.3 423.6 112.1 40.7 101.7 29.8 6.9 0.0 0.0 6,068.0 24 37G2 473.3 54.3 3.4 4.7 0.0 0.0 0.0 0.0 0.0 535.7 24 37G3 29.8 35.8 134.5 136.6 36.1 10.7 5.7 1.0 1.0 391.2 24 37G4 75.0 85.3 56.9 53.3 20.2 14.7 4.6 0.0 0.0 310.0 24 38G2 1,790.2 190.3 8.7 0.0 0.0 0.0 0.0 0.0 0.0 1,989.2 24 38G3 287.9 159.1 181.9 204.7 69.8 53.6 15.0 10.4 3.0 985.3 excl. CBH 24 38G4 937.2 1,064.8 710.7 667.6 249.3 180.5 50.6 5.0 5.0 3,870.8 24 39G2 2,972.5 212.0 20.3 8.9 0.0 0.0 0.0 0.0 0.0 3,213.7 24 39G3 2,299.8 1,856.3 490.9 314.1 44.8 32.1 66.2 4.0 4.0 5,112.3 24 39G4 129.0 865.6 582.1 1,405.6 1,044.1 1,766.6 580.6 162.9 190.6 6,727.0 24 Total 8,994.7 4,523.6 2,189.4 2,795.4 1,464.2 2,058.2 722.7 183.4 203.7 23,135.1 22-24 Total 25,229.3 6,744.1 3,123.3 2,956.1 1,647.6 2,096.8 729.7 183.4 203.7 42,913.7 21-24 Total 39,398.8 19,002.8 5,988.7 3,512.6 1,841.0 2,264.3 729.7 183.4 203.7 73,124.9 304 ICES | WGBIFS 2019 Survey Summary Table WGBIFS 2019 Name of the survey (abbreviation): GERAS / BIAS (GER) (FRV Solea SB754) Target Species: Herring (Clupea harengus, Western Baltic Spring Spawning Herring WBSSH; Central Baltic Herring CBH), Sprat (Sprattus sprattus), Anchovy (Engraulis encrasicolus), European Pilchard (Sardina pilchardus) Survey dates: 01-19 Oct 2018 Summary: The objectives of the survey were carried out successfully and as planned in all of the covered ICES Subdivisions. Adverse weather conditions occurred during the first night of the survey in the southwestern part of SD 22 (Kiel Bight) but did not require interruption of survey operations and are not considered to affect acoustic estimates (see below). Altogether, 62 trawl hauls were carried out during the survey providing biological data for age stratified abundance estimation of target species herring and sprat (58 valid hauls utilized for estimates). Measured NASC values per 1 nmi EDSU allocated to clupeids were higher in most parts of the survey area in comparison to the previous year (exception SD 24), but below the long-term survey mean. A further decrease in abundance of Western Spring Spawning Herring (-22% and -49% in SD 21-24 and 22-24 respectively) was recorded to the second lowest levels of the time series since 1993. Abundance increased (+56% and +19% respectively) due to a high contribution of 0-group herring. In sprat, abundance and biomass in the survey area declined by 37 % and 43% respectively. As in the previous years, dense aggregations of large, mature herring seemed to be absent from their overwintering area in SD23. contributi Description Survey design Stratified systematic (parallel where applicable) design. Start point not randomized. Index Calculation method GERIBAS II Software. Index based on mean NASC per ICES statistical rectangle. Random/systematic error issues Survey design and transects restricted by area topography. No fully systematic coverage of survey area possible. Indications of large herring aggregations outside the surveyed transects/time period were registered. Specific survey error issues (acoustic) There are some bias considerations that apply to acoustic-trawl surveys only, and the respective SISP should outline how these are evaluated: Bubble sweep down Bubble sweep down due to adverse weather conditions occurred in some areas but did not affect significant parts of the depth layers utilized for integration or occurred in an area with known low fish densities (southwestern part of SD 22). Extinction (shadowing) No particular issues as targets are scattered in loose aggregations in most of the surveyed areas during the survey operation. Blind zone Night-time distribution of clupeids in surface layers (i.e. within blind zone and near-field) is assumed to occur but is not quantified. (Integration start depth 10 m). Dead zone No particular issue as clupeids are mostly distributed pelagic and away from seafloor during night-time survey operations. ICES | WGBIFS 2019 305 Allocation of backscatter to species Directed trawling. Mixed species category applied throughout survey. Species allocations based on combined trawl haul composition (per ICES statistical rectangle). Target strength As listed in SISP Survey manual (ICES, 2017). Calibration All survey frequencies calibrated and results within recommended tolerances (Demer et al., 2015). Specific survey error issues (biological) There are some bias considerations that apply to acoustic-trawl surveys only, and the respective SISP should outline how these are evaluated: Stock containment Time series: It is assumed that WBSSH (primary target species) is contained within the survey area. An unquantified but assumedly low degree of mixing of WBSSH and CBH (Central Baltic Herring) can occur outside of the survey area (east of SD 24). Due to transects often determined by topography/bathymetry, aggregations of WBSSH in shallower areas not sampled by the survey may have been missed. 2018 survey: Survey area covered as planned. Stock containment considered achieved. Stock ID and mixing issues Time series: WBSSH and CBH mix at varying degrees in different parts of the survey area (especially in SD 24). Separation of stocks is achieved through application of an age-growth based stock separation function (SF) (Gröhsler et al. 2013). 2018 survey: The present results support the continued applicability of the SF despite occurrence of some CBH in the GERAS baseline samples of WBSSH in SDs 21 and 23. Measures of uncertainty (CV) none Biological sampling Time series: Based on survey design restrictions, comprehensive sampling is not feasible in all statistical rectangles surveyed. Biological information from neighboring rectangles is used for generating estimates in these cases. This mostly applies to rectangles with low abundance. 2018 survey: Biological information for some rectangles used/amended from neighbouring rectangles. Were any concerns raised during the meeting regarding the fitness of the survey for use in the assessment either for the whole times series or for individual years? (please specify) Did the Survey Summary Table contain adequate information to allow for evaluation of the quality of the survey for use in assessment? Please identify shortfalls 306 ICES | WGBIFS 2019 1 Working paper on the WGBIFS meeting in Klaipeda (Lithuania) 25-29.03.2019 Research report from the Polish part of the Baltic International Acoustic Survey on board of the r.v. “Baltica” (28.09 - 13.10.2018) Beata Schmidt and Włodzimierz Grygiel National Marine Fisheries Research Institute, Gdynia (Poland) INTRODUCTION The autumn acoustic-biotic surveys has been carried out in the Baltic Proper since 1978, however on the very beginning as the Swedish-German (GDR) cruise, not fully coordinated by the ICES (Håkansson et al. 1979, Hagström et al. 1989). The initial Polish acoustic survey in the southern Baltic was conducted in July 1981, on board of the r.v. “Profesor Siedlecki” (Orłowski 1982, 1991). In October 1982, the National Marine Fisheries Research Institute (NMFRI) began simultaneous the acoustic, biological and fisheries investigations focused on herring and sprat stocks size estimation and their spatial distribution, mostly in the southern Baltic (Grzebielec et al. 1995). The above-mentioned survey can be accepted as the beginning of somewhat regular autumn acoustic surveys in the Polish EEZ. In the 1980s, the NMFRI contribution to those surveys was limited to chartering of commercial stern cutter the m/t “HEL-100”, which was designated for fish control-hauls realization. Moreover, the NMFRI delegates participated in several autumn acoustic surveys on board of the Swedish r.v. “Argos” (Hagström et al. 1989). Sporadically, also the Polish r.v. “Profesor Siedlecki” participated in the Baltic acoustic surveys, e.g. in May 1985, October 1989 and 1990. In the 1980s and at the beginning of 1990s, the ICES Planning Group for Hydroacoustic Surveys in the Baltic with close cooperation of the ICES Working Group on Assessment of Pelagic Stocks in the Baltic were responsible for logistically coordination of international acoustic surveys (Anon. 1991a). The mentioned ICES working and planning groups were also answerable on implementation of collected international data to the final assessment of Baltic sprat and herring stocks biomass and abundance (Anon. 1991b). Since 1994, the permanent participation of the Polish r.v. "Baltica", managed by the NMFRI in Gdynia, has took place in the framework of the ICES Baltic International Acoustic Surveys (BIAS) long-term programme. The ICES Baltic International Fish Survey Working Group (WGBIFS) coordinates methods of investigations, timing of surveys, spatial allocation of surveying vessels and general pattern of pelagic control-hauls distribution in the Baltic regarding the BIAS acoustic surveys. The above-mentioned working group is also responsible for the compilation of international results needed for seasonal assessment of clupeids stocks size in the Baltic. The set of international input data and recommendations are next transferred to the ICES Baltic Fisheries Assessment Working Group [WGBFAS] for final evaluation of fish stocks size and a prediction of annual TAC of given species. The reported Polish BIAS/2018 survey was conducted on board of the r.v. “Baltica” inside the Polish EEZ, in the period of 28.09.-13.10.2018. The survey was focused on monitoring of clupeids and cod spatial-seasonal distribution in pelagic zone of the southern Baltic (parts of the ICES Subdivisions 24, 25 and 26). The EK60 SIMRAD acoustic system with the new determined calibration parameters were applied to completing the BIAS survey tasks. The Polish Fisheries Data Collection Programme for 2018 and the European Union (the Commission Regulations Nos. 1639/2001, 1581/2005, 665/2008, 1078/2008, 2008/949/EC, 2010/93/EU) financially and logistically supported the Polish BIAS survey marked with internal No. 18/2018/MIR-PIB. The WGBFAS will use recently collected BIAS data for tuning clupeids stock biomass assessment and spatial distribution based on data from commercial catches in 2018. Acoustic estimates are, until present time, the commercial fishery independent unique source of input data available to the WGBFAS. The main goal of current paper is a brief description of results of analysis focused on sprat, herring and cod stocks size (biomass, abundance) changes and their spatial distribution as well as ICES | WGBIFS 2019 307 2 the CPUE variation within the Polish part of the southern Baltic at autumn 2018. Moreover, the paper contains description of sprat, herring and cod selected biological parameters variation. The principal hydrological parameters fluctuation in the water column of the southern Baltic are also described. MATERIAL AND METHODS Research team personnel The main research tasks of the Polish BIAS/2018 survey on board of the r.v. "Baltica" were realized by the NMFRI (Gdynia) nine members of the scientific team, with Szymon Smolinski as a cruise leader. The group of researchers was composed of: Beata Schmidt – hydroacoustician, Zuzanna Celmer – hydroacoustician, Julia Gutkowska – intern, sprat analyses, Grzegorz Modrzejewski – technician, sprat analyses, Wojciech Deluga – technician, herring analyses, Ireneusz Wybierala - technician, herring analyses, Krzysztof Radtke - ichthyologist, cod and other fish species analyses, Anetta Ameryk – hydrologist. The course of the cruise The r.v. “Baltica” left the Gdynia port on 28th of September 2018 at 07:00 a.m. and was navigated in the east direction, where, to the south of the Hel Peninsula, the acoustic integration and biological sampling started towards the north. During the first two days, the research tasks were carried out along the transects located at the Gdansk Bay and the Gdansk Deep. On the third day of the cruise (30 of September 2018), at the mouth of the Vistula River a successful calibration of the acoustic system SIMRAD EK60, installed on the vessel, was carried out. In the following days, the survey operations were conducted in the ICES subdivision 26 in easterly direction. Deterioration of weather conditions (storm) made it impossible to carry out research tasks on the 3rd of October. The survey operations were resumed the following day. The acoustic integration was completed on the 12th of October 2018. The r/v “Baltica” returned to the Gdynia port on 13th of October 2018 around 7:15 a.m. Survey design and realization – sampling description The ICES statistical rectangles, designated by the ICES-WGBIFS as mandatory to Poland, were fully covered with the standard acoustic-biotic researches during BIAS 2018 cruise (Fig. 2). The SIMRAD EK60 version 2.2.0, a split beam scientific echosounder, linked with the GPT transceivers, operating at 38 and 120 kHz frequencies, as in the previous years, was used in the recent Polish BIAS 2018 survey. Calibration of the vessel’s acoustic system was performed on 30th of September 2018 at following location: λ = 019°22.95' E and φ = 54°26.24'N over seabed depth of 50 m (Fig. 2). The echosounder calibration was performed as described in Simrad (2012) using the copper spheres of diameters 60 mm and 23 mm for 38 kHz and 120 kHz frequencies respectively as reference targets. Calibration results obtained in September 2018 were considered as good for 38 kHz (RMS=0.12) and 120 kHz (RMS=0.18). Resulting transducer parameters were applied for consecutive data-collection and post-processing of hydroacoustic survey data. Calibration results for the 38 kHz transducer are given in Figure 1. The acoustic sampling was performed along the pre-selected acoustic transects on the distance of 829 NM. The echo-integration data were collected in a daytime at the ship speed of 7 kn. To maintain comparability with historical data, pre-selected echo-integration transects were planned in a similar pattern as were in recent years, i.e. since autumn 2013 BIAS survey, when transects were reshaped comparing with period of 2009-2012. 308 ICES | WGBIFS 2019 3 The settings of the hydroacoustic equipment were as described in the IBAS Manual (ICES, 2017). The post processing of the stored raw data was done using the Echoview software (www.echoview.com). Only 38 kHz transmitter’s data were taken into further processing because that frequency is recommended for fish trace recording. The acoustic analysis were carried out taking into account the new calibration constants determined during the calibration (for the first two days of acoustic recording, the calibrations constants were corrected in Echoview software). As the first step of acoustic data checking, all visible interferences from the sea surface, turbulences and bottom structures visible on echogram were excluded from further analysis. The minimum threshold on mean volume backscattering strength Sv was set to -60 dB. Calculation of parameter SA [m 2NM-2] (hereinafter called NASC) for 1 nautical mile elementary standard distance units (ESDUs) was carried out by integrating Sv values (in linear domain) from 10 m below the sea surface to about 0.5 m over the seafloor and then averaged it within 1 NM interval. Than the mean NASC (Nautical Area Scattering Coefficient) per ICES rectangles were calculated. Also, weighted mean NASC per ICES SDs were calculated with use of size of investigated areas as weight. Overall 38 catch-stations (1 in the ICES SD 24, 20 in the ICES SD 25 and 17 in the ICES SD 26) were conducted by the r.v. “Baltica” in the period of 28.09 - 12.10.2018 (Fig. 2, Table 3), using the herring small-meshed pelagic trawl type WP53/64x4, with 6 mm mesh bar length in the codend (Table 3). All control-catches were accepted as representative from technical point of view. The trawling depth was chosen in accordance with echo distribution, visible on the screen of echosound. Because of a relatively high vertical opening (up to 20 m) of applied a pelagic trawl and the technical-acoustics disturbances from a set vessel-trawl, the areas shallower than 30-m were not controlled by the trawls. The trawling time for many hauls was 30 minutes, however it was shortened when echogram and net-sounder indicated large concentration of fishes in the operation area of a fishing gear. In the cases of two-layer fish concentrations appearing, the net was used for 15 minutes in each layer. The mean speed of surveying vessel during trawling ranged from 3.1 to 3.5 knots. Fish catches were localized on the depth ranged from 19 to 61 m from the sea surface (position of the headrope of trawl). At trawling positions, depth to the bottom varied from 28 to 108 m. Fish caught in each control-haul was separated by species and weighted. The results of catch per unit effort (CPUE) of dominated fish species and their average share in the r/v “Baltica” pelagic catches are presented in Table 3 and Figs. 5-7. The samples for sprat, herring and cod were taken for length, age and mass measurements. Fish total length distribution (Fig. 8) and the mean mass were determined in the 0.5-cm classes - in the case of clupeids and 1-cm classes in the case of cod. The numerical share of juvenile, undersized (below minimum landing/protective size) sprat, herring and cod in samples was determined (Table 4) based on fish length distribution results. For sprat the minimum commercial size (the separate length) is equal to 10.0 cm, for herring is equal to 16.0 cm and for cod is 35.0 cm. Detailed ichthyological analyses were made according to standard procedures (Anon., 2012), directly on board of surveying vessel. Overall, 37, 35 and 3 representative samples were taken for the length and mass determination of sprat, herring and cod, respectively. The length and mass were measured for 6820 sprat, 7725 herring and 407 cod individuals. Respectively, 533, 715 and 125 individuals of the above-mentioned species were biologically analysed (sex, maturity, stomach fullness and age). Before each haul and at the standard hydrological stations located within the Polish EEZ, the seawater temperature, salinity and oxygen content were measured continuously from the sea surface to the seabed. Totally, 50 hydrological stations were inspected using the CTD SeaBird 911+ probe combined with the rosette sampler. Oxygen content was determined by the standard Winkler’s method. The hydrological raw data, aggregated to the 1-m depth stratums, were the source of information about the abiotic factors potentially influencing fish’s spatial distribution. The basic meteorological parameters i.e. air temperature, air pressure, wind direction and force, and sea state were registered at the each catch-station with the automatic station MILOS 500. ICES | WGBIFS 2019 309 4 Data analysis Due to herring and sprat normally cannot be distinguished from other species by visual inspection of the echogram, species composition and fish length distributions from trawl catch results are used to aid acoustic species identification. Such data analysis is sectioned according to the ICES statistical rectangles. For each ICES rectangle, based on trawl results performed within, the share of all fish species numbers and its length distribution, as the unweighted mean, were calculated. Our intention was to carry out at least two control-hauls per ICES rectangle, according to the guidelines in the “SISP Manual of International Baltic Acoustic Surveys (IBAS)” (ICES, 2017). However, during BIAS cruise in 2018, in rectangles 38G4, 38G7 and 37G8 only one haul per rectangle was performed, and no one haul was completed in rectangle 39G9. In such cases, the haul made in an adjacent rectangular with similar hydrology condition and resulted with similar species share and length distribution were included into analysis in given rectangle. In this way, haul No. 20 and haul No. 1 were included into analysis in ICES rectangles 38G4 and 37G8 respectively. In rectangle 39G9 species composition and length distribution was based on results from hauls No. 8 and No. 12. However analysis in ICES rectangle 38G7 were based on only one haul carried out within (the nearest haul in 38G5 rectangle were performed in different hydrological condition, and was assumed as unrepresentative for shallow 37G5 ICES rectangle). In case when the mean numerical share of sprat herring and cod in ICES rectangle exceeded 99%, other species were excluded from further calculations. Based on species distributions the mean acoustic cross section  was calculated according to the following target strength-length (TS) relation: TS References Clupeoids = 20 log L (cm) - 71.2 ICES 1983 Gadoids = 20 log L (cm) - 67.5 Foote et al. 1986 The total number of fish in each the ICES rectangle was estimated as a product of the mean NASCs from scrutinized acoustic data and a rectangle area, divided by the corresponding mean acoustic cross-section . Clupeids abundance was separated as sprat or herring according to their mean share in control-catches of given the ICES rectangle. RESULTS Acoustic results The spatial distribution of mean NASC values (5 NM intervals), predominantly derived from clupeids, measured on hydroacoustic transects during BIAS 2018 survey is presented on Figure 3. Considerable differences in the mean NASC values on ICES subdivisions and ICES rectangles as well as annual scales existed (Tables 1, 2). In 2018, the mean NASC values in the ICES SD 24 and 25 was 52 and 64%, respectively smaller than in the ICES SD 26 (558.3 m2NM- 2). Overall NASC values recorded in the Polish EEZ during BIAS 2018 survey were higher as recorded during BIAS 2017 and clearly higher than at autumn 2016. Comparing to the previous years, the mean NASC values recorded in 2018 survey remained at a similar level as recorded in 2016 and 2017 in SD25, and as much as two-fold increase in SD26 was observed. In SD 24 it remained at similar level as in the previous year and increased three times comparing to 2016. Similar to autumn 2017, during BIAS 2018 survey, the highest NASC values were recorded in the south-eastern Polish part of the Gulf of Gdansk - in ICES rectangles 37G8, 37G9 and 38G9 mean NASC values exceeded 1000 m2Nm2 and were almost twice as high as in 2017 (Table 2). The highest NASC value per 1 NM equal to 13440 m2NM-2 was recorded for 103rd mile of the integration, located in the ICES rectangle 37G9, where the bottom depth was 70 m (Fig. 4). 310 ICES | WGBIFS 2019 5 Fish catches, biological parameters and stocks size In September-October 2018, overall, 17 fish species were recorded in 38 scrutinized pelagic control-hauls taking place in the Polish parts of the ICES Subdivisions 24, 25 and 26 (Table 3, Fig. 2). Totally, 8516.8 kg of fish in 38 hauls were caught, and the mean share of sprat, herring, cod and all other species was adequately, 58.3; 39.7; 1.6 and 0.5%. Zero fish catches in single hauls were not achieved. Any sea-mammals and any sea-birds wasn’t detected in the control- catches. Sprat dominated by mass in control-hauls and herring was placed on the second position with the mean CPUE in the entire study area amounted 473.8 and 201.2 kg h-1, respectively. Sprat and herring occurred in each pelagic control-haul. Cod can be considered as a significant bycatch in accomplished the pelagic trawl catches (Table 3, Figs. 5-7). The mean CPUE and the mean share of cod in all inspected parts of the Polish marine waters was 7.8 kg h-1 and 1.6%, respectively. Values of share of cod in mass of the pelagic control-catches decreased from west to east of scrutinized areas and in the ICES Subdivisions 24, 25 and 26 amounted adequately: 7.4; 2.0 and 0.6% on average. The appearance of cod was noticed in 63% of hauls number. From the remaining fish species only salmon and flounder with total catch of 27.8 and 4.6 kg in the entire study area was remarkable as component of bycatch. In the ICES Subdivision 26, sprat clearly prevailed by the mean CPUE (890.7 kg h-1) and the mean share (85%) in 17 hauls realised inside the Polish part of the mentioned subdivision. The fish catches composition in the middle and western parts of the Polish EEZ (the ICES Subdivisions 24 and 25) was dominated by herring, but sprat played the second role regarding CPUE and mean share in total weight of caught fishes (Figs. 5-7). The mean share of herring and sprat e.g. in the ICES SD 25 (overall 20 hauls was realised there) was 62 and 35%, respectively, and the mean CPUE of above-mentioned fish species was 247.5 and 138.9 kg h-1. The highest CPUE of sprat (varied from 737.4 to 5281.4 kg h-1) was obtained in a limited number of research catches conducted in the vicinity of the Peninsula of Hel and in the south-eastern part of the Gulf of Gdańsk (ICES SD 26; Figs. 2, 5). Somewhat high CPUE (911.3 kg h-1) of sprat was achieved also in a haul made on a border between the Slupsk Furrow and the Gdansk Deep. The highest CPUE of herring (changed from 419.5 to 727.6 kg h-1) was obtained in several control-catches accomplished along almost completely the northern part of the Polish EEZ. The highest CPUE of cod, amounted 73.7 and 79.1 kg h-1 was achieved in two hauls accomplished in the Gdansk Deep and western part of the Slupsk Furrow. The results of sprat, herring and cod some biological features investigations in September- October 2018 are presented in Figure 8 and Tables 4, 8, 11, 14. The total length of species dominated in control-hauls conducted in the all investigated areas ranged as follows:  sprat – 7.0 ÷ 15.5 cm (avg. l.t. = 11.5 cm, avg. W = 10.0 g),  herring – 8.0 ÷ 27.5 cm (avg. l.t. = 18.3 cm, avg. W = 37.7 g),  cod – 19.0 ÷ 54.0 cm (avg. l.t. = 34.8 cm, avg. W = 328.7 g). The bimodal shape of length distribution curves for sprat in September-October 2018 was differ from one-peak curves characteristic for September-October 2017 samples (Fig. 8). However, in both years the main frequency apex, according to given ICES subdivision was distinguish in the same length class (Fig. 8). In samples from the ICES Subdivision 26 dominated specimens from class 11.5 cm, in the ICES Subdivision 25 - from class 12.5 cm and in the ICES Subdivision 24 - from class 13.5 cm, representing adults, commercially sized sprat. In samples from September-October 2018 the second, minor frequency apex, representing young, undersized specimens is visible for sprat from the length classes of 8.0; 9.0 and 9.5 cm, in the case of the ICES Subdivisions 26, 25 and 24, respectively. In the recent BIAS survey, the mean numerical share of undersized sprat (in Poland determined as <10.0 cm total length) in given ICES subdivision was significantly higher than during the same type of survey in 2017 (Table 4). For example, in the ICES Subdivision 25 values of mentioned parameter were 0.2 and 18.6% adequately, in autumn 2017 and 2018. The mean bycatch of undersized sprat in the entire study area was 1.2 and 21.3%, respectively in 2017 and 2018. ICES | WGBIFS 2019 311 6 For herring collected in September-October 2018, the unimodal shape of length distribution curve was characteristic for samples originated from the ICES Subdivisions 25 and 26, but for the ICES Subdivision 24 it was multimodal shape (Fig. 8). In samples from the ICES Subdivisions 25 and 26 dominated specimens from the same length class 17.0 cm however, in the ICES Subdivision 24 - from classes 18.5 and 20.5 cm, representing adults, commercially sized herring. In the distinction from above mentioned, the bimodal shape of length distribution curves was characteristic for herring samples from September-October 2017 (Fig. 8). For herring collected in the ICES Subdivisions 24 and 25, the maximum of numerical share was visible in the length class 17.5 cm, but in a case of samples from the ICES Subdivision 26 – in the length class 12.0 cm, representing young, undersized specimens. For herring samples from September-October 2017, the second, smaller than above frequency apex was noticed in the length classes 12.5 cm, 12.0 cm and 17.5 cm adequately, in the ICES Subdivisions 24, 25 and 26. In the recent BIAS survey, the mean numerical share of undersized herring (in Poland determined as <16.0 cm total length) in given ICES subdivision was significantly lower than during the same type of survey in 2017 (Table 4). For example, in the ICES Subdivision 26 values of mentioned parameter were 80.9 and 14.9% adequately, in autumn 2017 and 2018. The mean bycatch of undersized herring in the entire study area was 23.7 and 11.0%, respectively in 2017 and 2018. The length distribution curves for cod sampled in the ICES Subdivisions 24, 25 and 26 in September-October 2017 and 2018 were multimodal, without one specific length class dominated by frequency (Fig. 8). However, should be underlined that numbers of cod sampled in the ICES Subdivision 24 was much smaller than in two other ICES subdivisions. In recently collected samples, cod with the length class 33 cm prevailed by numbers in the ICES Subdivision 25, and with the length classes 30-35 cm - in the ICES Subdivision 26. The BIAS/2018 data for cod from the ICES Subdivision 24 can be considered as not representative. The mean numerical share of undersized cod (determined as <35.0 cm total length) not differed much between ICES subdivisions as well as between the BIAS/2017 and BIAS/2018 surveys. The mean bycatch of undersized cod in the entire study area was 46.6 and 54.5%, respectively in 2017 and 2018 (Table 4). Data reflects changes of the mean weight of sprat, herring and cod per age groups according to ICES rectangles inspected during the BIAS/2018 survey are presented in Tables 8, 11 and 14. The basic data evaluated in September-October 2018, including data on Baltic sprat, herring and cod stocks total abundance and biomass per age groups and the ICES rectangles, adequately to echosounding under frequency of 38 kHz are given in Tables 6, 7, 9, 10, 12 and 13. The above-mentioned materials are strongly linked with data on BIAS/2018 cruise statistics and average NASC values for acoustically covered ICES rectangles, within the Polish EEZ (Table 5). The mean biomass surface density of sprat, herring and cod, per ICES subdivisions and ICES rectangles, located within the Polish marine waters is reflected in Figures 9, 11, 12. The abundance of above-mentioned species per age groups, according to inspected in autumn 2017 and 2018 the Polish parts of the ICES Subdivisions 24, 25 and 26 is demonstrated in Figure 10. In September/October 2018, the highest mean biomass surface density of sprat stock was estimated for the ICES rectangles: 37G9 and 37G8 (both located in the southern part of Gdansk Bay), where amounted: 149.4 and 67.9 t NM-2, respectively (Fig. 11). The minimum value of this parameter was noticed in the western parts of investigated Polish marine waters, in ICES rectangle 38G5 and amounted 1.6 t NM-2. Comparing to 2017, the much higher mean biomass surface density per rectangle in SD26 was observed. In 2018 the mean biomass density of sprat in the ICES SD 24 was much lower than in 2017 (6.3 and 20.8 t NM-2 in 2018 and 2017 respectively), whereas it remained on the same level in the ICES SD 25 (5.3 and 5.2 t NM-2 in 2018 and 2017 respectively) and it was much higher in the ICES SD 26 in 2018 (21.2 t NM-2) than in 2017 (2.9 t NM-2) (Fig. 9). In September/October 2018, the highest mean biomass surface density of herring stock was estimated for the ICES rectangle 38G9 (80.8 t NM-2) – located in the eastern part of Gdansk Deep (Fig. 11). The recent pattern of herring surface biomass density distribution per ICES rectangles can be considered as almost a mirror picture from autumn 2017 (Fig. 11). In 2018 the mean 312 ICES | WGBIFS 2019 7 biomass density of herring in the ICES SD 24 was much higher than in 2017 (1.7 and 23.4 t NM- 2 in 2018 and 2017 respectively), whereas in others ICES SDs it remained on the similar level: around 15 t NM-2 for both years in ICES SD25 and 26.4 and 29 t NM-2 for 2017 and 2018 respectively in ICES SD26 (Fig. 9). During the BIAS 2018 cruise the highest mean biomass surface density of cod was estimated for the ICES rectangles: 38G8 (7.9 t NM-2) – located in the Gulf of Gdansk Deep (Fig. 12). In other rectangles the mean biomass surface density of cod was fluctuated from 0.03 to 3.0 t NM-2. However, in four ICES rectangles, namely: 37G5, 37G8, 37G9 and 38G7 – located in the southern part of the Polish EEZ (in the vicinity of seacoast), appearance of cod was not detected (Tables 3, 13, Fig 12). In 2018 the biomass density of Baltic cod was on similar level in all three ICES SDs and amounted 1.1, 0.9 and 1.2 t NM-2 in SD24, SD25 and SD26 respectively (Fig. 9). Comparing to 2017 data, in 2018 mean biomass surface density of cod was lower in ICES SD26 (1.9 t NM-2 in 2017 and 1.2 t NM-2 in 2018 ) and on the same level in SD25 (0.9 t·NM-2). In September/October 2018, the total biomass (B1), the mean surface biomass density (B2) and abundance (A) of dominants significantly differed between fish species and the ICES subdivisions: ICES SD parameter sprat herring cod 24 B1 (tons) 6485.7 24201.0 1106.2 B2 (t NM-2) 6.3 23.4 1.1 A (·106 indiv.) 523.5 494.2 3.0 25 B1 (tons) 38095.5 105480.0 6285.8 B2 (t NM-2) 5.3 14.8 0.9 A (·106 indiv.) 3550.8 2694.7 20.5 26 B1 (tons) 102490.3 140512.4 5940.5 B2 (t NM-2) 21.2 29.0 1.2 A (·106 indiv.) 12045.9 4115.0 18.6 The above listed data indicate that the centre of fish resources temporal distribution in the Polish EEZ, during reported the BASS/2018 survey was located in ICES SD26 in the southern and central parts of Gdansk Basin (Figs. 11, 12). Meteorological and hydrological characteristics of the southern Baltic Changes of the main meteorological parameters – wind velocity and direction, and air temperature in consecutive days of the Polish BIAS survey carried out in 2018 are illustrated in Figure 13. The air temperature during reported survey varied from 8.5 to 16.8°C (avg. was 12.6°C). The wind force changed from 1 to 6°B, and winds from the south-west direction were prevailed. During fishing operations prevail the moderate wind (5°B) mostly from south-west directions (Table 15). The strongest wind directions, occurred during fishing operations, were from north. The main hydrological parameters at the depths of fish pelagic catches (Table 15), i.e. in the range of 19-90 m (with 18 m vertical net opening on average) changed in the relatively broad ranges. The seawater temperature fluctuated from 3.6 to 16.4°C (the mean was 8.4°C), salinity from 7.3 to 16.3 PSU (the mean was 9.1 PSU) and oxygen content from 0.09 at haul No. 23 (the Bornholm Basin, depth 90m) to 7.6 ml l-1 (the mean was 4.9). Horizontal distribution of the seawater temperature, salinity and oxygen content in the near bottom zone of the southern Baltic (within the Polish waters) is illustrated in Fig. 14. The temperature in near bottom layer was changing horizontally within the range of 4.1-16.1°C and the mean was 7.9°C. The lowest seawater temperature was recorded at the hydrological station ICES | WGBIFS 2019 313 8 No. 71 (westward from the Gdansk Deep) and the highest at the calibration station, i.e. southern part of the Gdansk Bay (Fig. 2). Salinity in the bottom waters varied from 7.3 PSU – noticed at the catch-stations No. 6 and 7 (southern part of in the Gdansk Gulf), to the maximum of 16.6 PSU - appeared at the hydrographical station No. IBY5 (the Bornholm Basin). Oxygen content near bottom of deep waters varied from 0.00 ml l-1 – measured at the catch-station No. 3 and hydrological station G2 (in the Gdansk Deep at depth 103 and 106 m respectively) to the maximum of 7.2 ml l-1 – calculated at the catch-station No. 30 in ICES rectangle 38G7 (the mean was 3.1 ml l- 1). The vertical distribution of the seawater temperature, salinity and oxygen content, along the hydrological research profile determined in the southern Baltic during BIAS 2018 survey is presented on Fig. 15. In both deep basins, the Bornholm Basin and the Gdansk Deep, unfavourable conditions for effective reproduction of the Eastern Baltic cod existed. Especially in the Gdank Deep water with oxygen condition for effective spawning didn’t occure – the water saline enough for effective spawning (above 11PSU) is located in hypoxic water layer (with oxygen content below 2 ml l-1). CONCLUSION The ICES Baltic International Fish Survey Working Group and the Baltic Fisheries Assessment Working Group for the Baltic clupeids and cod stocks size analysis and their spatial distribution characteristics can apply the Polish BIAS-2018 survey data obtained by the r.v. “Baltica” scientific team for stock assessment purposes. Results presented in this paper can be considered as representative for the Polish part of the southern Baltic, namely for the ICES Sub- divisions 24, 25 and 26. The base acoustic, fisheries, biological and hydrological data collected during reported survey will be stored in the ICES Data-Center international databases, managed by the ICES Secretariat and designated experts from WGBIFS. 314 ICES | WGBIFS 2019 9 References: Anon. 1991a. Report of the Planning Group for Hydroacoustic Surveys in the Baltic. ICES CM 1991/J:28. Anon. 1991b. Report of the Working Group on Assessment of Pelagic Stocks in the Baltic. ICES CM 1991/Assess:18. Anon., 2012. Manual for International Baltic Acoustic Surveys (IBAS). Version 1.01, 30-03-2012 Helsinki, Finland; ICES Addendum 2: WGBIFS Manual for Baltic Acoustic Surveys, Version 1.01; 24 pp. Elwertowski, J., Orłowski A., 1984. Composition, distribution and biomass of juvenile sprat in May 1983 in the Southern Baltic. Bulletin of the Sea Fish. Inst., Gdynia, 3-6 (83/86); 5-13. Elwertowski, J., Orłowski A., Richert S., 1984. Badania oceanograficzno-rybackie południowego Bałtyku prowadzone w maju 1983 r. na r.v. Profesor Siedlecki. Bulletin of the Sea Fish. Inst., Gdynia, 1-2; 3- 15. Foote, K.G., Aglen, A. and Nakken, O. (1986) Measurement of fish target strength with a split-beam echosounder. Journal of the Acoustical Society of America, 80(2): 612-621. Grzebielec, R., Paciorkowski A., Wyszyński M., Grygiel W., 1995. Polish hydroacoustic assessment survey of herring, sprat and cod stocks in ICES Subdivisions 25 and 26 of the Baltic conducted in October 1994. ICES C.M. 1995/J:18, B.F.C.; 24 pp. Hagström, O., L-E. Palmén, N. Håkansson, D. Kästner, H. Bremer-Rothbart, W. Grygiel, M. Wyszyński 1989. Acoustic estimates of the herring and the sprat stocks in the Baltic Proper, October 1988. ICES C.M. 1989/J:26, B.F.C.; 9 pp. Håkansson, N., Kollberg, S., Falk, U., Goetze, E., Rechlin, O. 1979. A hydroacoustic and trawl survey of herring and sprat of the Baltic proper in October 1978. Fischerei-Forschung, 17(2); 7-23. ICES. 1983. Report of the Planning Group on ICES coordinated herring and sprat acoustic surveys. ICES Document CM 1983/H:12. ICES. 2017, SISP Manual of International Baltic Acoustic Surveys (IBAS). Series of ICES Survey Protocols SISP 8 – IBAS. 47pp. ICES. 2018, Report of the Baltic International Fish Survey Working Group (WGBIFS) 24-28 March 2018 Lyngby, Copenhagen, Denmark; ICES CM 2018/EOSG:6. Kruk, G., Smolinski Sz., Schmidt B., Wodzinowski T., 2018. Research report from the Polish part of the Baltic International Acoustic Survey on board of the r.v. “Baltica” (13-30.09.2017). Working paper, WGBIFS meeting in Copenhagen (Denmark), 24-28.03.2018; 28 pp. Orłowski, A. 1982. Zasoby ryb polskiej strefy Bałtyku oszacowane metodą hydroakustyczna podczas rejsu r.v. „Profesor siedlecki” w roku 1981. Biuletyn Mor. Inst. Ryb., Gdynia, 1-6 (69-74); 23-28. Orłowski, A. 1991. Hydroacoustic surveys of fish distribution in relation to environment. Acta Ichthyol. Pisc., Szczecin, XXI; 181-192. Shvetsov, F., Baturin V., Goetze E., Oeberst R., Kästner D., 1986. Preliminary results of a joint hydroacoustic sprat survey by the USSR and GDR in Baltic in May 1986. ICES C.M. 1986/J:15, B.F.C. Shvetsov, F., Grygiel W., Fetter M., Chervontsev V., Rudneva A., 1992. Distribution and size of herring and sprat stocks in the Baltic Proper, determined by the acoustic method (October, 1991). ICES C.M. 1992/J:8, B.F.C.; 10 pp. Simrad. 2012. Simrad EK60, Reference Manual, release 2.4.X. Kongsberg Maritime AS; 256 pp. Smoliński Sz., Schmidt B., Wodzinowski T., Sprawozdanie z bałtyckiego międzynarodowego rejsu akustycznego (BIAS) przeprowadzonego w polskiej EEZ na statku r.v. Baltica w dniach 28.09- 13.10.2018 roku., MIR-PIB, Gdynia; 22pp., (mimeo). ICES | WGBIFS 2019 315 10 Table 1. Weighted mean NASC values (m2 NM-2) for the Polish parts of the ICES SDs 24, 25 and 26, calculated with use of areas of ICES rectangles as weight, for BIAS 2016, 2017 and 2018 cruises. Table 2. Average NASC values (m2 NM-2) for the acoustically covered ICES rectangles, within the Polish EEZ, in 2016, 2017 and 2018 BIAS cruises. 24 89.2 253.5 268.1 25 172.3 195.7 201.4 26 248.4 261.6 558.3 < NASC > BIAS 2016 < NASC > BIAS 2017 < NASC > BIAS 2018 ICES SDs 24 38G4 1034.8 89.2 253.5 268.1 25 37G5 642.2 100.7 178.6 208.3 25 38G5 1035.7 209.5 191.1 175.4 25 38G6 940.2 151.8 55.5 133.6 25 38G7 471.7 41.2 9.8 85.6 25 39G5 979 220.2 334.5 176.7 25 39G6 1026 241.1 176.7 222.1 25 39G7 1026 189.6 125.9 298.5 25 40G7 1013 125.9 383.8 244.7 26 37G8 86 767.5 549.2 1021.7 26 37G9 151.6 2739.7 1333.1 2121.4 26 38G8 624.6 336 248.9 927 26 38G9 918.2 170.9 381.9 1024.8 26 39G8 1026 118.7 249.1 367.4 26 39G9 1026 57.6 99.1 159.9 26 40G8 1013 172.4 152.9 231.8 < NASC > BIAS 2018 < NASC > BIAS 2016 ICES SDs ICES rectangles Area [NM2] < NASC > BIAS 2017 316 ICES | WGBIFS 2019 11 Table 3. Fish control-catches data from the Polish BIAS survey conducted on board of the r.v. “Baltica” in September/October 2018. Table 4. The mean numerical share of young, undersized fishes per ICES SDs (the Polish BIAS/2018 and BIAS/2017). Geographical position start end latitude longitude latitude longitude N E N E 1 28-09-2018 38G8 26 54°32.3' 18°53.1' 54°31.9' 18°54.7' 66 29 16 3.4 110 09:45 20 5107.51 5093.64 13.83 0.040 2 28-09-2018 38G8 26 54°48.0' 18°55.0' 54°47.2' 18°58.2' 98 40 17 3.1 115 14:20 30 996.34 837.16 158.88 0.265 0.040 3 29-09-2018 38G9 26 54°49.9' 19°11.4' 54°49.9' 19°18.9' 106 32 15 3.2 105 09:40 30 202.10 2.94 199.16 4 29-09-2018 38G9 26 54°35.6' 19°09.5' 54°35.1' 19°11.8' 81 47 18 3.1 105 14:00 30 833.82 737.42 94.49 1.380 0.540 5 29-09-2018 37G9 26 54°29.6' 19°20.5' 54°29.5' 19°20.9' 69 35 18 3.1 10 16:45 5 5290.73 5281.42 8.83 0.480 6 30-09-2018 37G9 26 54°25.4' 19°18.4' 54°25.8' 19°18.9' 51 29 18 3.2 30 10:40 10 1452.31 1440.31 11.67 0.325 7 30-09-2018 37G8 26 54°28.3' 18°55.0' 54°29.7' 18°55.9' 63 35 18 3.1 20 13:40 30 109.34 103.10 5.27 0.770 0.200 0.001 8 01-10-2018 39G8 26 55°24.6' 18°59.9' 55°25.4' 18°58.1' 89 36 19 3.0 310 07:35 30 116.64 67.12 48.84 0.434 0.244 9 01-10-2018 40G8 26 55°43.8' 18°55.8' 55°43.6' 18°54.9' 86 55 18 2.9 245 11:35 15 738.29 6.80 727.56 3.932 10 01-10-2018 40G8 26 55°51.2' 18°40.0' 55°49.8' 18°40.0' 108 40 16 3.1 180 14:50 30 97.85 47.70 28.46 0.262 21.420 0.004 11 01-10-2018 40G8 26 55°35.6' 18°40.3' 55°34.3' 18°40.4' 85 35 20 3.0 180 18:25 30 111.51 1.34 108.16 2.010 12 02-10-2018 39G8 26 55°08.9' 18°41.3' 55°08.8' 18°42.8' 92 39 20 3.0 100 08:00 20 248.31 75.42 168.96 3.375 0.558 13 02-10-2018 38G8 26 54°54.2' 18°41.5' 54°54.5' 18°43.0' 86 55 20 3.0 75 11:25 20 651.03 51.87 522.03 73.716 3.120 0.291 14 04-10-2018 39G8 26 55°14.6' 18°21.1' 55°14.4' 18°22.6' 81 45 16 3.0 100 10:15 20 406.20 317.13 83.01 6.060 15 04-10-2018 40G8 26 55°35.7' 18°27.1' 55°35.4' 18°29.3' 94 51 18 3.0 100 14:55 30 326.29 48.62 264.16 13.510 16 05-10-2018 39G5 25 55°12.4' 15°57.2' 55°13.2' 15°59.3' 89 57 18 3.0 60 09:55 30 257.20 106.64 143.88 6.680 17 05-10-2018 38G6 25 54°53.4' 16°01.4' 54°54.0' 16°03.5' 63 44 16 3.0 50 13:55 30 311.26 164.64 126.84 3.360 14.240 1.706 0.470 18 05-10-2018 37G5 25 54°29.8' 15°58.9' 54°29.6' 15°56.3' 43 22 18 3.2 255 18:20 30 83.49 12.64 70.48 0.370 19 06-10-2018 38G4 24 54°41.7' 14°49.7' 54°42.8' 14°51.3' 55 36 16 3.2 30 08:00 30 312.91 83.78 200.30 23.110 0.306 5.410 20 06-10-2018 38G5 25 54°39.4' 15°00.7' 54°40.7' 15°01.8' 57 36 18 3.0 25 09:40 30 829.55 121.36 699.30 8.450 0.440 21 06-10-2018 37G5 25 54°29.9' 15°20.6' 54°29.6' 15°22.1' 47 28 16 3.0 110 17:00 20 101.10 31.56 69.18 0.360 22 06-10-2018 38G5 25 54°35.7' 15°20.0' 54°37.2' 15°20.2' 56 38 17 3.1 5 18:30 30 127.17 0.16 97.76 28.760 0.496 23 07-10-2018 39G5 25 55°08.2' 15°39.8' 55°06.9' 15°39.7' 90 50 17 3.0 185 13:10 30 310.27 164.04 138.34 7.820 0.070 24 07-10-2018 38G5 25 54°57.1' 15°39.4' 54°55.8' 15°38.9' 80 60 17 3.0 180 16:15 30 98.30 14.18 83.88 0.240 25 08-10-2018 39G6 25 55°06.2' 16°19.0' 55°05.2' 16°17.2' 73 53 16 3.0 220 08:00 30 644.54 46.50 578.64 15.716 3.160 0.180 0.340 26 08-10-2018 38G6 25 54°41.9' 16°18.6' 54°43.3' 16°19.9' 40 20 16 3.0 25 13:00 30 35.43 27.12 8.28 0.026 27 09-10-2018 39G6 25 55°09.2' 16°38.4' 55°09.9' 16°40.4' 67 42 16 3.0 55 07:20 30 176.52 74.80 101.36 0.356 28 09-10-2018 39G6 25 55°21.5' 16°40.6' 55°22.6' 16°42.3' 63 38 16 3.2 45 10:10 30 692.54 483.06 207.62 1.844 0.019 0.002 29 09-10-2018 39G7 25 55°14.5' 17°01.4' 55°15.1' 17°02.7' 85 50 16 3.0 55 15:40 20 741.11 91.29 648.42 1.395 30 10-10-2018 38G7 25 54°59.0' 17°21.0' 54°59.0' 17°22.0' 28 13 13 3.2 90 09:00 15 1053.24 1032.60 20.64 31 10-10-2018 39G7 25 55°10.0' 17°20.1' 55°09.9' 17°23.3' 60 37 17 3.0 90 11:30 30 171.91 105.14 45.82 0.440 19.860 0.652 32 10-10-2018 39G7 25 55°18.2' 17°21.3' 55°18.5' 17°23.7' 82 61 18 3.0 75 14:30 30 358.83 18.84 260.90 79.090 33 10-10-2018 40G7 25 55°32.2' 17°33.0' 55°32.4' 17°35.7' 43 23 16 3.1 80 18:30 30 502.20 5.56 492.52 3.410 0.710 34 11-10-2018 39G7 25 55°26.5' 17°41.1' 55°25.9' 17°43.3' 78 44 18 3.2 125 07:40 30 563.58 142.34 419.48 0.954 0.804 35 11-10-2018 39G7 25 55°19.1' 17°38.9' 55°19.9' 17°36.6' 79 52 18 3.0 305 10:10 30 541.30 80.04 455.00 5.850 0.150 0.260 36 11-10-2018 39G8 26 55°10.2' 18°00.6' 55°09.9' 18°02.3' 45 20 18 3.0 115 16:55 20 913.05 911.31 1.74 37 12-10-2018 39G8 26 55°19.7' 18°00.7' 55°18.9' 18°02.8' 74 43 20 3.1 130 08:00 30 177.97 118.38 51.96 7.630 38 12-10-2018 40G7 25 55°44.2' 17°59.0' 55°44.1' 17°56.3' 63 40 18 3.0 260 12:30 30 337.51 55.78 280.74 0.990 three spined stickleback The ship's course during fishing [°] Trawling duration [min.] CPUE [kg·h-1] Local time of shutting net sprat Headrope depth from the sea surface [m] Vertical net oppening [m] Trawling speed [w] Haul no Date ICES rectangles ICES SDs Mean bottom depth [m] nine spined stickleback plaice turbot CPUE of particular fish species four- bearded rockling smelt whiting shorthorn sculpin straightn ose pipefish herring cod flounder salmon lumpfish river lamprey great sand eel SD24 SD25 SD26 Mean SD24 SD25 SD26 Mean sprat < 10 cm 0 0.2 2.9 1.2 16.2 18.6 25.1 21.3 herring < 16 cm 25.3 22.5 80.9 23.7 3.8 8.5 14.9 11.0 cod < 35 cm 60.6 41.2 ­ 46.6 25.0 58.0 53.1 54.5 Species Fish threshold length BIAS 2017 Mean share in % numbers BIAS 2018 Mean share in % numbers ICES | WGBIFS 2019 317 12 Table 5. Cruise statistics of the Polish BIAS survey on board of the r.v. “Baltica”, 28.09-13.10.2018. sprat herring cod total sprat herring cod 24 38G4 31 2.72 268.1 1034.8 51.3 48.4 0.3 1020.7 523.5 494.2 3.0 Sum SD24 31 1020.7 523.5 494.2 3.0 25 37G5 44 2.01 208.3 642.2 59.5 40.5 0.0 667.1 396.9 270.2 0.0 25 38G5 76 3.53 175.4 1035.7 24.3 73.8 1.9 515.2 125.2 380.1 10.0 25 38G6 68 1.32 133.6 940.2 89.4 10.6 0.0 952.1 851.3 100.6 0.3 25 38G7 22 1.31 85.6 471.7 99.3 0.7 0.0 309.2 306.9 2.3 0.0 25 39G5 31 2.12 176.7 979 71.3 28.5 0.2 817.3 583.1 232.9 1.4 25 39G6 79 2.22 222.1 1026 54.9 45.0 0.1 1024.5 562.1 461.5 0.9 25 39G7 97 2.62 298.5 1026 47.5 51.9 0.7 1170.8 555.8 607.3 7.6 25 40G7 17 3.06 244.7 1013 20.9 79.0 0.0 809.8 169.6 639.9 0.3 Sum SD25 434 7133.8 6266.0 3550.8 2694.7 20.5 26 37G8 9 1.00 1021.7 86 98.3 1.7 0.0 876.4 861.7 14.7 0.0 26 37G9 29 1.06 2121.4 151.6 99.8 0.2 0.0 3039.9 3032.9 7.0 0.0 26 38G8 46 1.66 927.0 624.6 77.5 22.1 0.4 3496.6 2710.4 771.1 15.1 26 38G9 56 2.21 1024.8 918.2 50.8 49.2 0.0 4248.9 2158.2 2090.7 0.1 26 39G8 98 1.38 367.4 1026 86.1 13.9 0.1 2729.9 2350.1 378.3 1.4 26 39G9 26 1.87 159.9 1026 71.6 28.4 0.0 878.2 628.8 249.0 0.4 26 40G8 100 2.58 231.8 1013 33.4 66.4 0.2 909.5 303.9 604.2 1.5 Sum SD26 364 4845.4 16179.5 12045.9 4115.0 18.6 < NASC> [m2·NM-2] Area [NM2] Abundance · 106 ICES SDs ICES rectangles EDSU [NM] <σ> [m2·10-4] species composition [%] 318 ICES | WGBIFS 2019 13 Table 6. Abundance of sprat (in millions of individuals) per age groups, ICES rectangles and ICES SDs, estimated using acoustic method, based on data collected during the Polish BIAS survey on board of the r.v. “Baltica”, 28.09-13.10.2018. Table 7. Biomass of sprat (in tons) per age groups, ICES rectangles and ICES SDs, estimated using acoustic method, based on data collected during the Polish BIAS survey on board of the r.v. “Baltica”, 28.09-13.10.2018. 24 38G4 81.59 26.42 104.05 139.15 124.61 44.51 1.60 0.00 1.60 523.53 Sum SD24 81.59 26.42 104.05 139.15 124.61 44.51 1.60 0.00 1.60 523.53 25 37G5 253.90 25.32 29.50 44.21 34.22 6.98 2.70 0.00 0.07 396.91 25 38G5 5.39 4.87 22.54 42.42 35.96 11.01 2.86 0.07 0.07 125.19 25 38G6 491.71 31.73 83.70 125.24 96.75 14.81 6.79 0.40 0.16 851.30 25 38G7 86.89 39.37 51.50 65.64 53.72 7.05 2.69 0.00 0.00 306.86 25 39G5 0.00 20.69 116.08 213.83 178.30 38.53 14.72 0.00 0.91 583.06 25 39G6 10.40 18.30 116.88 201.60 166.49 33.63 13.54 0.77 0.46 562.08 25 39G7 57.11 89.95 124.81 152.65 110.59 13.11 7.44 0.10 0.07 555.81 25 40G7 3.55 32.92 40.41 47.58 37.03 5.64 2.47 0.00 0.03 169.62 Sum SD25 908.96 263.15 585.43 893.17 713.06 130.75 53.21 1.34 1.77 3550.84 26 37G8 242.23 389.36 119.33 84.98 25.61 0.20 0.00 0.00 0.00 861.71 26 37G9 583.06 1337.51 534.61 412.61 158.76 4.95 0.00 1.42 0.00 3032.91 26 38G8 352.99 853.09 588.18 623.65 271.99 15.43 2.35 2.67 0.00 2710.35 26 38G9 270.10 317.05 356.45 700.72 443.55 53.70 3.00 13.60 0.00 2158.15 26 39G8 752.56 272.61 421.27 581.55 292.89 23.53 0.42 5.30 0.00 2350.13 26 39G9 33.77 72.38 159.57 231.18 118.69 10.73 0.28 2.17 0.00 628.77 26 40G8 45.34 19.13 51.63 107.73 68.24 9.15 0.66 2.00 0.00 303.87 Sum SD26 2280.05 3261.13 2231.04 2742.41 1379.73 117.68 6.72 27.15 0.00 12045.90 ICES SDs ICES rectangles Age 0 Age 1 Age 2 Age 3 Age 4 Age 5 Age 6 Age 7 Age 8+ Total sprat abundance [mln indiv.] 24 38G4 452.57 265.82 1320.27 1908.45 1789.63 691.56 28.71 0.00 28.71 6485.72 Sum SD24 452.57 265.82 1320.27 1908.45 1789.63 691.56 28.71 0.00 28.71 6485.72 25 37G5 1293.38 229.27 354.47 583.28 461.01 106.48 38.08 0.00 1.26 3067.23 25 38G5 29.85 48.46 283.02 581.08 502.02 168.83 41.55 1.44 1.26 1657.53 25 38G6 2356.30 307.57 1015.57 1616.71 1288.54 222.68 91.45 7.86 2.78 6909.45 25 38G7 436.93 369.02 610.78 838.84 704.22 99.76 35.60 0.00 0.00 3095.15 25 39G5 0.00 209.71 1457.95 2870.02 2441.12 581.13 211.04 0.00 15.79 7786.77 25 39G6 44.73 192.48 1452.72 2674.88 2274.29 509.03 190.53 15.11 8.01 7361.77 25 39G7 262.31 842.41 1464.80 1919.62 1429.43 192.66 95.51 1.92 1.17 6209.83 25 40G7 17.26 313.23 470.95 606.05 485.02 82.18 32.63 0.00 0.47 2007.79 Sum SD25 4440.76 2512.16 7110.27 11690.48 9585.65 1962.74 736.38 26.33 30.75 38095.51 26 37G8 808.65 2859.65 1081.04 827.08 261.10 2.46 0.00 0.00 0.00 5839.97 26 37G9 2146.89 9773.83 4861.33 4107.11 1673.81 66.00 0.00 19.32 0.00 22648.29 26 38G8 1322.32 6439.33 5650.42 6587.03 3044.24 210.21 36.11 36.24 0.00 23325.89 26 38G9 930.36 2441.81 3598.68 8202.74 5494.20 749.41 45.98 184.79 0.00 21647.96 26 39G8 2729.36 2196.07 4170.96 6433.43 3421.03 320.57 6.48 71.97 0.00 19349.87 26 39G9 138.12 617.42 1594.93 2582.88 1397.57 147.45 4.34 29.51 0.00 6512.21 26 40G8 180.53 166.21 536.63 1266.25 843.51 134.94 10.96 27.12 0.00 3166.15 Sum SD26 8256.22 24494.33 21493.98 30006.52 16135.45 1631.02 103.86 368.94 0.00 102490.34 Age 7 Age 8+ Total sprat biomass [t] Age 2 Age 3 Age 4 Age 5 Age 6ICES SDs ICES rectangles Age 0 Age 1 ICES | WGBIFS 2019 319 14 Table 8. Mean weight of sprat (in grams) per age groups, ICES rectangles and ICES SDs, based on data collected during the Polish BIAS survey on board of the r.v. “Baltica”, 28.09-13.10.2018. Table 9. Abundance of herring (in millions of individuals) per age groups, ICES rectangles and ICES SDs, estimated using acoustic method, based on data collected during the Polish BIAS survey on board of the r.v. “Baltica”, 28.09-13.10.2018. 24 38G4 5.55 10.06 12.69 13.72 14.36 15.54 17.96 ­ 17.96 12.39 MW SD24 5.55 10.06 12.69 13.72 14.36 15.54 17.96 17.96 12.39 25 37G5 5.09 9.05 12.02 13.19 13.47 15.25 14.11 ­ 17.33 7.73 25 38G5 5.54 9.96 12.56 13.70 13.96 15.33 14.51 19.60 17.33 13.24 25 38G6 4.79 9.69 12.13 12.91 13.32 15.03 13.46 19.60 17.33 8.12 25 38G7 5.03 9.37 11.86 12.78 13.11 14.16 13.22 ­ ­ 10.09 25 39G5 ­ 10.13 12.56 13.42 13.69 15.08 14.34 ­ 17.33 13.36 25 39G6 4.30 10.52 12.43 13.27 13.66 15.14 14.07 19.60 17.33 13.10 25 39G7 4.59 9.37 11.74 12.58 12.93 14.70 12.84 19.60 17.33 11.17 25 40G7 4.86 9.51 11.65 12.74 13.10 14.58 13.23 ­ 17.33 11.84 MW SD25 4.89 9.55 12.15 13.09 13.44 15.01 13.84 19.60 17.33 10.73 26 37G8 3.34 7.34 9.06 9.73 10.19 12.37 ­ ­ ­ 6.78 26 37G9 3.68 7.31 9.09 9.95 10.54 13.34 ­ 13.59 ­ 7.47 26 38G8 3.75 7.55 9.61 10.56 11.19 13.62 15.35 13.59 ­ 8.61 26 38G9 3.44 7.70 10.10 11.71 12.39 13.96 15.35 13.59 ­ 10.03 26 39G8 3.63 8.06 9.90 11.06 11.68 13.62 15.35 13.59 ­ 8.23 26 39G9 4.09 8.53 9.99 11.17 11.77 13.75 15.35 13.59 ­ 10.36 26 40G8 3.98 8.69 10.39 11.75 12.36 14.75 16.52 13.59 ­ 10.42 MW SD26 3.62 7.51 9.63 10.94 11.69 13.86 15.47 13.59 8.51 Age 6 Age 7 Age 8+ Mean W sprat [g] Age 1 Age 2 Age 3 Age 4 Age 5ICES SDs ICES rectangles Age 0 24 38G4 16.10 16.92 0.00 51.06 215.67 105.02 49.95 27.46 12.04 494.23 Sum SD24 16.10 16.92 0.00 51.06 215.67 105.02 49.95 27.46 12.04 494.23 25 37G5 8.79 38.15 12.62 36.06 95.35 30.26 26.95 12.13 9.85 270.17 25 38G5 5.13 40.44 15.76 54.72 124.94 45.14 45.46 27.17 21.32 380.09 25 38G6 23.23 11.47 4.69 9.44 26.66 8.17 8.00 4.90 4.01 100.57 25 38G7 0.69 0.39 0.17 0.15 0.56 0.15 0.13 0.02 0.03 2.30 25 39G5 6.77 47.02 15.96 29.41 79.89 21.74 17.92 7.59 6.58 232.88 25 39G6 12.71 125.12 46.33 48.54 159.06 31.76 23.37 7.83 6.81 461.52 25 39G7 4.21 98.11 33.19 83.52 220.74 64.16 56.96 24.69 21.74 607.31 25 40G7 0.00 91.94 27.34 97.47 227.40 76.34 67.21 25.93 26.26 639.89 Sum SD25 61.52 452.64 156.05 359.30 934.60 277.71 246.01 110.26 96.61 2694.72 26 37G8 4.18 5.71 0.91 0.97 1.48 0.74 0.41 0.12 0.20 14.71 26 37G9 4.31 1.44 0.24 0.38 0.37 0.20 0.06 0.00 0.00 7.01 26 38G8 168.22 118.98 54.26 49.63 149.30 75.42 54.27 35.92 65.10 771.10 26 38G9 77.06 373.53 195.44 197.36 532.01 274.67 177.88 84.55 178.20 2090.69 26 39G8 64.54 48.00 30.43 31.98 90.38 49.09 28.72 12.32 22.87 378.33 26 39G9 1.91 35.25 25.20 26.57 71.90 39.33 22.41 9.17 17.24 248.99 26 40G8 0.22 73.23 66.87 71.46 188.59 99.04 51.57 19.38 33.80 604.16 Sum SD26 320.44 656.15 373.34 378.35 1034.03 538.50 335.32 161.45 317.41 4115.00 Age 6 Age 7 Age 8+ Total herring abundance [mln indiv.] Age 1 Age 2 Age 3 Age 4 Age 5ICES SDs ICES rectangles Age 0 320 ICES | WGBIFS 2019 15 Table 10. Biomass of herring (in tons) per age groups, ICES rectangles and ICES SDs, estimated using acoustic method, based on data collected during the Polish BIAS survey on board of the r.v. “Baltica”, 28.09-13.10.2018. Table 11. Mean weight of herring (in grams) per age groups, ICES rectangles and ICES SDs, based on data collected during the Polish BIAS survey on board of the r.v. “Baltica”, 28.09-13.10.2018. 24 38G4 201.66 422.53 0.00 2867.15 10070.05 5751.00 2275.66 1675.86 937.13 24201.02 Sum SD24 201.66 422.53 0.00 2867.15 10070.05 5751.00 2275.66 1675.86 937.13 24201.02 25 37G5 96.01 1152.67 417.37 1533.76 3680.32 1329.04 1293.37 695.93 558.67 10757.13 25 38G5 66.24 1224.17 548.06 2550.71 5374.51 2244.00 2382.68 1622.75 1294.94 17308.06 25 38G6 216.67 328.92 144.44 424.38 1107.20 376.81 412.89 292.42 240.81 3544.55 25 38G7 7.84 10.62 4.44 5.71 19.17 5.91 5.52 1.12 1.28 61.61 25 39G5 89.59 1329.67 462.77 1166.15 2883.05 969.65 856.05 430.26 388.29 8575.48 25 39G6 178.30 3352.13 1240.01 1696.18 5236.46 1306.30 1024.32 420.58 377.93 14832.21 25 39G7 57.91 2885.36 1039.84 3487.66 8292.83 2804.31 2725.47 1433.30 1254.08 23980.77 25 40G7 0.00 2836.63 934.29 4288.39 8760.62 3376.46 3246.46 1465.66 1511.65 26420.16 Sum SD25 712.56 13120.17 4791.23 15152.95 35354.15 12412.48 11946.75 6362.02 5627.66 105479.97 26 37G8 29.31 110.15 23.42 25.68 48.60 25.29 16.89 6.57 11.81 297.71 26 37G9 33.87 29.97 6.05 9.40 10.25 5.93 2.08 0.00 0.00 97.56 26 38G8 1313.79 2562.48 1613.56 1594.21 5610.73 2973.54 2618.32 2154.17 3989.81 24430.61 26 38G9 728.17 8334.37 5916.52 6148.76 19035.47 10528.45 8217.63 4895.52 10395.38 74200.27 26 39G8 535.90 1079.71 959.12 1010.09 3123.49 1746.39 1258.33 682.97 1237.49 11633.48 26 39G9 19.82 861.10 786.39 828.59 2438.06 1395.90 970.52 494.05 905.95 8700.38 26 40G8 2.88 1914.40 2057.98 2191.17 6364.33 3404.83 2206.54 1098.74 1911.47 21152.34 Sum SD26 2663.72 14892.18 11363.04 11807.90 36630.93 20080.33 15290.32 9332.03 18451.92 140512.36 Age 5 Age 6 Age 7 Age 8+ Total herring biomass [t] Age 0 Age 1 Age 2 Age 3 Age 4ICES SDs ICES rectangles 24 38G4 12.52 24.97 ­ 56.15 46.69 54.76 45.56 61.03 77.83 48.97 MW SD24 12.52 24.97 56.15 46.69 54.76 45.56 61.03 77.83 48.97 25 37G5 10.93 30.21 33.08 42.53 38.60 43.92 47.98 57.36 56.69 39.82 25 38G5 12.91 30.27 34.77 46.61 43.02 49.71 52.41 59.73 60.73 45.54 25 38G6 9.33 28.68 30.78 44.97 41.53 46.10 51.62 59.73 60.01 35.25 25 38G7 11.31 26.95 26.14 38.94 33.99 40.53 42.24 45.41 43.01 26.81 25 39G5 13.24 28.28 28.99 39.65 36.09 44.61 47.77 56.68 59.04 36.82 25 39G6 14.03 26.79 26.77 34.94 32.92 41.13 43.83 53.71 55.48 32.14 25 39G7 13.77 29.41 31.33 41.76 37.57 43.71 47.85 58.05 57.69 39.49 25 40G7 ­ 30.85 34.18 44.00 38.53 44.23 48.30 56.52 57.56 41.29 MW SD25 28.99 30.70 42.17 37.83 44.70 48.56 57.70 58.25 38.88 26 37G8 7.02 19.29 25.65 26.43 32.78 34.19 41.65 56.17 59.62 20.23 26 37G9 7.86 20.89 25.29 24.51 27.35 29.79 33.05 ­ ­ 13.93 26 38G8 7.81 21.54 29.74 32.12 37.58 39.43 48.25 59.97 61.29 31.68 26 38G9 9.45 22.31 30.27 31.16 35.78 38.33 46.20 57.90 58.33 35.49 26 39G8 8.30 22.49 31.52 31.59 34.56 35.57 43.81 55.46 54.10 30.75 26 39G9 10.36 24.43 31.21 31.18 33.91 35.49 43.30 53.85 52.56 34.94 26 40G8 13.26 26.14 30.77 30.66 33.75 34.38 42.79 56.71 56.55 35.01 MW SD26 8.31 22.70 30.44 31.21 35.43 37.29 45.60 57.80 58.13 34.15 Mean W herring [g] Age 4 Age 5 Age 6 Age 7 Age 8+ ICES rectangles Age 0 Age 1 Age 2 Age 3ICES SDs ICES | WGBIFS 2019 321 16 Table 12. Abundance of cod (in millions of individuals) per age groups, ICES rectangles and ICES SDs, estimated using acoustic method, based on data collected during the Polish BIAS survey on board of the r.v. “Baltica”, 28.09-13.10.2018. Table 13. Biomass of cod (in tons) per age groups, ICES rectangles and ICES SDs, estimated using acoustic method, based on data collected during the Polish BIAS survey on board of the r.v. “Baltica”, 28.09-13.10.2018. 24 38G4 0.00 0.00 1.66 0.98 0.26 0.06 0.00 0.00 0.00 2.96 Sum SD24 0.00 0.00 1.66 0.98 0.26 0.06 0.00 0.00 0.00 2.96 25 37G5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 25 38G5 0.00 0.00 8.73 1.15 0.08 0.00 0.00 0.00 0.00 9.95 25 38G6 0.00 0.00 0.19 0.09 0.00 0.00 0.00 0.00 0.00 0.28 25 38G7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 25 39G5 0.00 0.05 0.97 0.37 0.01 0.00 0.00 0.00 0.00 1.40 25 39G6 0.00 0.00 0.69 0.14 0.05 0.00 0.04 0.00 0.00 0.91 25 39G7 0.00 0.00 4.19 3.36 0.08 0.00 0.00 0.00 0.00 7.63 25 40G7 0.00 0.00 0.14 0.15 0.00 0.00 0.00 0.00 0.00 0.29 Sum SD25 0.00 0.05 14.90 5.26 0.21 0.00 0.04 0.00 0.00 20.47 26 37G8 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 26 37G9 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 26 38G8 0.00 0.20 8.29 5.65 0.97 0.00 0.00 0.00 0.00 15.12 26 38G9 0.00 0.00 0.04 0.04 0.01 0.00 0.00 0.00 0.00 0.09 26 39G8 0.00 0.00 0.87 0.51 0.06 0.00 0.00 0.00 0.00 1.44 26 39G9 0.00 0.00 0.27 0.13 0.02 0.00 0.00 0.00 0.00 0.43 26 40G8 0.00 0.00 0.83 0.51 0.12 0.00 0.00 0.00 0.00 1.47 Sum SD26 0.00 0.20 10.31 6.85 1.19 0.00 0.00 0.00 0.00 18.55 ICES rectangles Age 0 Age 1 Age 2 Age 3ICES SDs Total cod abundance [mln indiv.] Age 4 Age 5 Age 6 Age 7 Age 8+ 24 38G4 0.00 0.00 467.11 424.23 147.94 66.93 0.00 0.00 0.00 1106.20 Sum SD24 0.00 0.00 467.11 424.23 147.94 66.93 0.00 0.00 0.00 1106.20 25 37G5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 25 38G5 0.00 0.00 1785.27 411.30 50.91 0.00 0.00 0.00 0.00 2247.48 25 38G6 0.00 0.00 58.83 34.02 0.00 0.00 0.00 0.00 0.00 92.85 25 38G7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 25 39G5 0.00 2.97 266.96 144.43 5.26 0.00 0.00 0.00 0.00 419.62 25 39G6 0.00 0.00 177.81 48.88 38.64 0.00 40.94 0.00 0.00 306.26 25 39G7 0.00 0.00 1181.85 1845.76 45.95 0.00 0.00 0.00 0.00 3073.56 25 40G7 0.00 0.00 51.72 94.31 0.00 0.00 0.00 0.00 0.00 146.03 Sum SD25 0.00 2.97 3522.44 2578.70 140.76 0.00 40.94 0.00 0.00 6285.80 26 37G8 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 26 37G9 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 26 38G8 0.00 13.28 1860.66 2504.89 521.43 0.00 0.00 0.00 0.00 4900.27 26 38G9 0.00 0.00 12.19 14.99 4.16 0.00 0.00 0.00 0.00 31.34 26 39G8 0.00 0.00 196.91 236.42 24.51 0.00 0.00 0.00 0.00 457.84 26 39G9 0.00 0.00 61.59 61.96 5.93 0.00 0.00 0.00 0.00 129.47 26 40G8 0.00 0.00 185.58 180.84 55.10 0.00 0.00 0.00 0.00 421.52 Sum SD26 0.00 13.28 2316.93 2999.11 611.13 0.00 0.00 0.00 0.00 5940.45 Age 8+ Total cod biomass [t] Age 3 Age 4 Age 5 Age 6 Age 7ICES SDs ICES rectangles Age 0 Age 1 Age 2 322 ICES | WGBIFS 2019 17 Table 14. Mean weight of cod (in grams) per age groups, ICES rectangles and ICES SDs, based on data collected during the Polish BIAS survey on board of the r.v. “Baltica”, 28.09-13.10.2018. 24 38G4 ­ ­ 281.16 432.54 575.60 1085.00 ­ ­ ­ 373.61 MW SD24 25 37G5 ­ ­ ­ ­ ­ ­ ­ ­ ­ 25 38G5 ­ ­ 204.58 358.21 641.35 ­ ­ ­ ­ 225.78 25 38G6 ­ ­ 311.96 362.68 ­ ­ ­ ­ ­ 25 38G7 ­ ­ ­ ­ ­ ­ ­ ­ ­ 25 39G5 ­ 55.00 275.79 390.83 423.95 ­ ­ ­ ­ 25 39G6 ­ ­ 258.69 352.60 841.99 ­ 1080.00 ­ ­ 336.64 25 39G7 ­ ­ 281.87 548.67 596.25 ­ ­ ­ ­ 402.61 25 40G7 ­ ­ 368.88 646.80 ­ ­ ­ ­ ­ MW SD25 236.35 490.24 655.48 1080.00 306.92 26 37G8 ­ ­ ­ ­ ­ ­ ­ ­ ­ 26 37G9 ­ ­ ­ ­ ­ ­ ­ ­ ­ 26 38G8 ­ 65.00 224.36 443.14 537.23 ­ ­ ­ ­ 324.08 26 38G9 ­ ­ 319.15 353.93 333.93 ­ ­ ­ ­ 336.96 26 39G8 ­ ­ 225.82 465.28 381.21 ­ ­ ­ ­ 316.97 26 39G9 ­ ­ 225.22 465.25 291.43 ­ ­ ­ ­ 303.24 26 40G8 ­ ­ 222.81 351.44 460.73 ­ ­ ­ ­ 287.32 MW SD26 65.00 224.73 437.77 514.74 320.20 Age 7 Age 8+ Mean W cod [g] Age 2 Age 3 Age 4 Age 5 Age 6ICES SDs ICES rectangles Age 0 Age 1 ICES | WGBIFS 2019 323 18 Table 15. Values of the basic meteorological and hydrological parameters recorded in September/October 2018 at the positions of the r.v. "Baltica" fish control catches (Smoliński et al., 2018). 1 28-09-2018 09:45 13.5 WNW 6 3 16.18 7.35 6.1 37 2 28-09-2018 14:20 12.3 NW 6 4 15.76 7.31 6.21 48 3 29-09-2018 09:40 11.7 NW 4 2 4.4 7.45 7.43 41 4 29-09-2018 14:00 12.2 WNW 4 2 9.92 7.39 5.57 56 5 29-09-2018 16:45 13.7 WSW 3 2 16.36 7.3 5.95 44 6 30-09-2018 10:40 10.8 S 5 2 15.88 7.31 6.18 38 7 30-09-2018 13:40 14.4 S 5 3 15.89 7.34 6.1 44 8 01-10-2018 07:35 13.6 W 3 2 4.5 7.45 6.79 46 9 01-10-2018 11:35 13.6 WSW 3 2 4.17 8.6 4.02 64 10 01-10-2018 14:50 12.9 NW 3 2 3.74 7.46 7.55 48 11 01-10-2018 18:25 12.7 NW 3 2 4.54 7.46 7.1 45 12 02-10-2018 08:00 11.7 W 5 3 4.27 7.44 7.41 49 13 02-10-2018 11:25 11 WSW 6 3 5.91 10.6 0.63 65 14 04-10-2018 10:15 11.7 W 5 3 3.61 7.57 7.15 53 15 04-10-2018 14:55 10.4 W 5 3 5.14 8.89 4.98 60 16 05-10-2018 09:55 13.7 SW 5 3 9.1 11.37 3.58 64 17 05-10-2018 13:55 14.4 SW 6 4 8.9 12.3 3.56 52 18 05-10-2018 18:20 16.3 SW 5 3 14.9 7.53 6.29 31 19 06-10-2018 08:00 13.2 S 5 3 6.95 11.75 2.1 43 20 06-10-2018 09:40 13.6 SW 4 2 7.32 12.13 1.98 45 21 06-10-2018 17:00 15.3 SW 4 2 6.17 10.34 5.67 37 22 06-10-2018 18:30 15 SW 4 2 7.64 12.14 2.25 46 23 07-10-2018 13:10 9.4 N 7 5 7.41 16.28 0.09 90 24 07-10-2018 16:15 10.5 N 6 3 10.41 12.81 3.35 60 25 08-10-2018 08:00 11.7 SW 4 3 9.89 14.7 0.95 61 26 08-10-2018 13:00 11.2 SW 5 3 14.71 7.52 6.25 28 27 09-10-2018 07:20 13.1 SW 5 3 4.88 8.05 6.29 50 28 09-10-2018 10:10 12 SW 5 3 5.96 9.28 3.95 46 29 09-10-2018 15:40 13.5 SW 5 3 4.92 9.14 4.69 58 30 10-10-2018 09:00 13.4 SW 4 2 12.46 7.42 6.79 19 31 10-10-2018 11:30 13 SW 3 2 9.34 7.51 6.87 45 32 10-10-2018 14:30 13.8 SW 3 2 6.1 10.22 0.39 70 33 10-10-2018 18:30 12.4 SW 3 2 10.35 7.58 6.88 31 34 11-10-2018 07:40 14.1 SE 4 2 4.72 7.59 6.92 53 35 11-10-2018 10:10 14.5 SE 5 2 5.25 9.83 1.66 61 36 11-10-2018 16:55 15.7 E 5 3 14.15 7.39 6.31 28 37 12-10-2018 08:00 14.3 SE 5 3 3.76 7.55 6.67 53 38 12-10-2018 12:30 14.3 SE 5 3 4 8.21 5.41 49 Salinity [PSU] Oxygen [ml l-1] Depth of measurement [m] * date of the mean depth of the control-caches (in the middle of trawl vertical opening) Haul no Date of catch Haul start time Meteorological parameters Air temperature [°C] Wind direction Wind force [B] Sea state Hydrological parameters* Temperature [°C] 324 ICES | WGBIFS 2019 19 Fig. 1. R.v. “Baltica” cruise BIAS 2018: Simrad EK60 calibration report (38 kHz transducer). ICES | WGBIFS 2019 325 20 Fig. 2. Location of realized investigations during the Polish BIAS survey on board of the r.v. “Baltica”, 28.09–13.10.2018. Fig. 3. Cruise track (thin dashed line) and the mean NASC (5 NM intervals, bubbles) recorded during BIAS 2018 cruise. 326 ICES | WGBIFS 2019 21 Fig. 4. An example of an echogram analysis for 103rd mile of the integration, NASC = 13440 m2 NM-2 (ICES rectangle 37G9, bottom depth 70 m; 29.09.2018). Fig. 5. CPUE [kg h-1] of fish species per single pelagic hauls conducted in the Polish EEZ (BIAS/2018 survey). 5666.97 13440.68 13440.68 5666.97 8507.23 ICES | WGBIFS 2019 327 22 Fig. 6. Mean CPUE [kg h-1] per fish species and the ICES SDs (the Polish BIAS/2018 survey). Fig. 7. Share (%) of sprat, herring, cod and other fishes in the mass of total catches per the ICES SDs (the Polish BIAS/2018). total sprat herring cod others 0 500 1000 1500 C P U E [ k g h - 1 ] SD 24 SD 25 SD 26 mean 328 ICES | WGBIFS 2019 23 Fig. 8. Length distribution of sprat, herring and cod in samples taken from the control-catches conducted during the Polish BIAS/2017 and BIAS2018 surveys. ICES | WGBIFS 2019 329 24 Fig. 9. Mean biomass surface density [t NM-2] of sprat, herring and cod in the ICES Subdivisions 24, 25 and 26 in the Polish BIAS 2017 and 2018 surveys. 0 10 20 30 40 b io m a s s d e n s it y [ t N M -2 ] sprat herring cod 20.76 6.27 1.71 23.39 1.07 ICES SD 24 2017 2018 0 10 20 30 40 sprat herring cod b io m a s s d e n s it y [ t N M -2 ] 5.19 5.34 15.71 14.79 0.86 0.88 ICES SD 25 0 10 20 30 40 sprat herring cod b io m a s s d e n s it y [ t N M -2 ] 2.89 21.15 26.38 29.00 1.85 1.23 ICES SD 26 330 ICES | WGBIFS 2019 25 Fig. 10. Abundance (in mln indiv.) of sprat, herring and cod stocks per age groups, according to the ICES Subdivisions 24, 25 and 26, based on data from the Polish BIAS surveys in 2017 and 2018. ICES | WGBIFS 2019 331 26 Fig. 11. Biomass surface density of sprat and herring [t NM-2] per ICES rectangles, estimated using acoustic method, and based on data collected during the Polish BIAS 2017 and 2018 surveys. 332 ICES | WGBIFS 2019 27 Fig. 12. Biomass surface density of cod [t NM-2] per ICES rectangles, estimated using acoustic method, and based on data collected during the Polish BIAS 2017 and 2018 surveys. ICES | WGBIFS 2019 333 28 Fig. 13. Changes of meteorological parameters during consecutive days of the Polish BIAS survey in September/October 2018 (fig. Wodzinowski after Smoliński et al., 2018). 334 ICES | WGBIFS 2019 29 Fig. 14. Horizontal distribution of the seawater temperature, salinity and oxygen content in the near seabed layer of the southern Baltic in September/October 2018 (fig. Wodzinowski after Smoliński et al., 2018). ICES | WGBIFS 2019 335 30 Fig. 15. Vertical distribution of the seawater temperature, salinity and oxygen content, along the hydrological research profile determined in the southern Baltic (September/October 2018); X- and Y- axes reflects distance (in kilometres) and depth (in meters) from the sea surface to the seabed, respectively (fig. Wodzinowski after Smoliński et al., 2018). 336 ICES | WGBIFS 2019 MARINE RESEARCH INSTITUTE, KLAIPEDA UNIVERSITY RESEARCH REPORT FROM THE BALTIC INTERNATIONAL ACOUSTIC SURVEY (BIAS) IN THE ICES SUBDIVISION 26 (LITHUANIAN EXCLUSIVE ECONOMIC ZONE) OF THE BALTIC SEA (Vessel “169” and Vessel N55 ; 18.10. - 19.10.2018) Working paper on the WGBIFS meeting in Klaipeda, Lithuania, 25.03-29.03.2019 Klaipeda, October, 2018 Lithuania ICES | WGBIFS 2019 337 1. INTRODUCTION The main objective is to assess clupeid resources in the Baltic Sea. The international acoustic survey in October is traditionally coordinated within the frame of the Baltic International Acoustic Survey (BIAS). The reported acoustic survey is conducted every year to supply the ICES: Baltic Fisheries Assessment Working Group (WGBFAS) and Fisheries Service under the Ministry of Agriculture of The Republic of Lithuania (FS) with an index value for the stock size of herring, sprat and other species in the Subdivision 26 of the Baltic area. Lithuanian BIAS surveys organized and realized by the Marine Research Institute delegates on board of the vessel “169”. Annual verification of herring, sprat and cod stocks size and their spatial distribution in the pelagic zone of the Lithuanian Exclusive Economic Zone (LEEZ) waters with applied an acoustic method, along preselected:  determination of herring, sprat and cod (usually dominants in catches) proportion by numbers and by mass in pelagic control-catches and an evaluation of their fishing efficiency, i.e. catch per unit effort (CPUE) in the investigated area,  characteristics of dominants age-length-mass structure, sex, sexual maturation, feeding intensity,  a preliminary evaluation of herring and sprat new recruiting year-class strength,  analysis of the vertical and horizontal changes of the basic hydrological parameters (seawater temperature, salinity, oxygen content) in areas inspected by the vessel “Darius”. 2. MATERIALS AND METHODS 2.1. Personnel The main research tasks of the BIAS survey on board of the vessel "169" for fish sampling and vessel NZ55 for acoustic records were realized by the Marine Research Institute two members of the scientific team. The group of researchers was composed of: M. Špėgys, MRI KU, Klaipeda - cruise leader and acoustics; J.Fedotova MRI KU, Klaipeda – scientific staff and fish sampling. 2.2. Narrative The cruise of BIAS survey took place from 18-th to 19-th of October 2018. The cruise was intended to cover parts of ICES subdivisions (SD) 26, constituting the Lithuanian Exclusive Economic zone in 40H0 and 40G9 rectangles. 2.3. Survey design The statistical rectangles were used as strata (ICES 2016). The area is limited by the 20 m depth line. The scheme of transects is defined as the regular. The average speed of a vessel for the period of acoustic survey was 8 knots. The average speed of the vessel with a trawl was 2.8 knots. Duration of trawling was 30 minutes. The survey was conducted in the daytime from 08.00 up to 20.00. The survey area was 1520 nm2 and the distance used for acoustic estimates was 111 nm. The entire cruise track with positions of the trawling is shown in Fig. 1. 2.4. Calibration The SIMRAD EK60 echo sounder with split beam transducer ES38 - 12 was calibrated (17 of October 2018) at the site of 30 m depth, located 3.5 nm northwest of Klaipeda harbour according to the BIAS manual (ICES 2016). Sv correction after calibration was set to -0.79 dB. 338 ICES | WGBIFS 2019 THE RESULTS OF CALIBRATION PROCEDURE FOR EK60 SCIENTIFIC ECHOSOUNDER Date: 17.10.2018 Place : near Klaipeda port Type of transducer Split – beam for 38 kHz Gain (38 kHz) 21.94 dB Athw. Angle Sens 12.5 Along. Angle Sens 12.5 Athw. Beam Angle 12.5 Along. Beam Angle 12.96 Athw. Offset Angle 0.62 Along. Offset Angle 0.29 SA Correction (38 kHz) -0.79 dB 2.5. Acoustic data collection The acoustic sampling was performed around the clock. The main pelagic species of interest were herring and sprat. The SIMRAD EK60 echo sounder with hull mounted 38 kHz transducer ES38- 12 was used during the cruise. The specific settings of the hydro acoustic equipment were used as described in the BIAS manual (ICES 2016). The post-processing of the stored echo signals was made using the Sonar4 (Balk & Lindem, 2005). The mean volume back scattering values Sv, were integrated over 1 nm intervals, from 10 m below the surface 1 m to the bottom. Contributions from air bubbles, bottom structures and noise scattering layers were removed from the echogram using Sonar4. 2.6. Biological data – fishing stations All trawling was done with the pelagic gear in the midwater as well as near the bottom. The mesh size in the cod end was 10 mm. The intention was to carry out at least two hauls per ICES statistical rectangle. The trawling depth was chosen by the echogram, in accordance to the characteristic of echo records from the fish. Normally, the trawl had vertical opening of about 12 m. The trawling time lasted 30 minutes. Caught fishes, before the length measurements, were separated by species and weighed, and the species catches proportion as well as the CPUE was determined for given species from each haul. The sample of fish from each catch-station was taken for the length-mass structure analyses. Fish sampling of the total length distribution and the mean mass at the 0.5-cm classes - in the case of clupeids and 1-cm classes in the case of cod were determined. From each haul sub-samples were taken to determine length and weight composition of fish. Samples of herring and sprat were analyzed for further investigations on the board of vessel (i.e. sex, maturity, age). 2.7. Data analysis The pelagic target species sprat and herring are usually distributed in mixed layers in combination with other species, so that it is impossible to allocate the integrator readings to a single species. Therefore, the species composition was based on the trawl catch results. For each rectangle the species composition and length distribution were determined as the mean - weighted of all trawl results in this rectangle. From these distributions the mean acoustic cross section was calculated according to the following target strength-length (TS) relationships: Clupeoids TS = 20 log L (cm) - 71.2 (ICES 1983/H:12) Gadoids TS = 20 log L (cm) - 67.5 (Foote et al. 1986) The total number of fish (total N) in one rectangle was estimated as the product of the mean area scattering cross section (Sa) and the rectangle area, divided by the corresponding mean cross section (). The total numbers were separated into herring and sprat according to the mean catch composition. ICES | WGBIFS 2019 339 3. RESULTS 3.1. Biological data 1670 herrings, 1195 sprats and 1 lumpfish, 1 three-spined stickleback, 137 cods, 1 flounder and 1 river lamprey were measured in 6 hauls. Totally 367 individuals of sprat, 755 of herring and 137 cods were biologically analyzed (age, sex, maturity, stomach fullness). The results of the catch composition are presented in Table 1. Ichthyologic analyses were performed directly on board of surveying vessel, according to the ICES WGBIFS standard procedures. The numerical share of juvenile, undersized (below minimum landing/protective size) sprat and herring in the samples was determined based on fish length distribution results. For sprat, the minimum commercial size (the separate length) is equal to 10.0 cm, for herring is equal to 16.0 cm. The length distributions of herring and sprat in BIAS survey show in Fig. 2 and 3. Herring represented both rectangles practically. Sprat dominated only in first trawl catch - 99.3% (coastal rectangle 40H0). Most of herring were fish 3-6 years and 16.5-19.5 length classes in the both rectangles. In the rectangle 40H0 more than 81% of sprat was represented by fish 1-2 years and 10.5-11.0 cm. In the western part of LEEZ (40G9 rectangle ICES) 82.6% of sprat was adult fish 11.4-12.3 cm length and 2-4 ages. Young fish of last year generation was about 9% in the 40H0 rectangle and only 3.4% in the 40G9 rectangle. 3.2. Acoustic data The survey statistics concerning the survey area, the mean Sa, the mean scattering cross-section , the estimated total number of fishes, the percentages of herring, sprat per rectangle are shown in Table 2-12. 3.3. Abundance estimates BIAS survey statistics (aggregated data for herring and sprat) of total abundance herrings and sprats are presented in Tables 2-4. The estimated age composition of sprat and herring are given in Tables 5, 10. The estimated number sprat and herring by age group and rectangle are given in Table 6, 11. The estimates of sprat and herring biomass by age group and rectangle are summarised in Table 7, 12. The corresponding mean weights and mean length by age group and rectangle for each species are shown in Table 8-9 and 13-14. The herring stock was estimated to be 4420.4*106 fish or about 167577.1 tones. Only in 40H0 rectangle 0.1% of herring stock was 0+ age and 12.5 cm length class. In the far rectangle they were not at all (Fig. 2 and Table 8). The sprat stock was estimated 15379.8*106 fish or about 137770.6 tones. (Fig. 3 and Table 5). Comparison of the acoustic results from last years (2010-2018) indicated that investigated herring stock abundance have increasing tendency in the LEEZ. In 2018 was recorded the highest average parameters of the herring stock densities in the rectangle 40H0 (Fig.4). Compared with last year, the abundance of sprat stock decreased by more than 3 times, and biomass - more than 2.5 times. As in 2017, the high-density sprat concentrations indicated in the northern part of the ICES rectangle 40H0. 3.4. Hydrologic data The basic hydrological parameters (seawater temperature, salinity and oxygen contents) were measured from the surface to the bottom after every haul if weather conditions were favorable. 340 ICES | WGBIFS 2019 Totally, 6 hydrological stations were making. The hydrological and hydro biological research profiles location is presented in Table.15. Water temperature in hauls was from 9.4 to 14,3 ºC. Differences between the first haul and others caused by wind direction. Wind direction was south in the first half day of cruise. Later wind direction changed to east, south-east. There was no thermocline in 2018 of October. Salinity was about 7.2 ‰ in all hauls and depts. The oxygen-condition was excellent in all hauls and depts. 4. REFERENCES Balk, H. & Lindem, T. 2005. Sonar4, Sonar5 and Sonar6 post processing systems, operator manual version 5.9.6. Norway: Balk and Lindem. pp. 1-381 ICES 1983. Report of the Planning Group on ICES co-ordinated herring and sprat acoustic surveys. ICES CM 1983/H:12. ICES 2016. Manual for the international acoustic survey (BIFS). CM2003/G:05 Ref.: D, H; Appendix 9, Annex 3 Foote, K.G., Aglen, A. & Nakken, O. 1986. Measurement of fish target strength with a split-beam echosounder. J.Acoust.Soc.Am. 80(2):612-621. ICES | WGBIFS 2019 341 Figure 1. The survey grid and trawl hauls position of F/V “DARIUS” (18-19 October 2018) Table 1 Catch composition (kg/1hour) per haul (F/V "169", 18.10- 19.10.2018) ICES subdivision 26 Haul No 1 2 3 4 5 6 Date 18.10.201 8 18.10.201 7 18.10.201 8 19.10.201 8 19.10.201 8 19.10.201 8 Validity Valid Valid Valid Valid Valid Species/ICES rectangle 40H0 40G9 40G9 40G9 40H0 40H0 Clupea harengus 59.06 90.0 366.71 547.08 120.0 Sprattus sprattus 40.0 30.94 27.58 31.50 280.0 Cyclopterus lumpus 0.57 Gasterosteus aculeatus 0.004 0.01 Baltic cod 5.16 261.42 Platichthys flesus 0.284 0.26 Lampetra fluviatilis 0.29 Total 40.284 90.57 90.0 400.0 840.0 400.0 342 ICES | WGBIFS 2019 Figure 2 Length distribution of herring (%) (BIAS, 18.10- 19.10.2018 Figure 3 Length distribution of sprat (%) (BIAS, 18.10- 19.10.2018) 0 5 10 15 20 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 % Ilgis, cm 40H0 Mean length: 17,8 cm 0 5 10 15 20 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 % Length, cm 40G9 Mean length: 17,7 cm 0 5 10 15 20 25 30 6 7 8 9 10 11 12 13 14 % Length, cm 40H0 Mean length: 10,85 cm 0 5 10 15 20 25 30 6 7 8 9 10 11 12 13 14 % Length, cm 40G9 Mean length: 11,96 cm ICES | WGBIFS 2019 343 Table 2 BIAS survey statistics (abundance of herring and sprat), 18.10- 19.10.2018 ICES SD 26 ICES Area ρ Abundance, mln Biomass, tonn Rect. nm^2 mln/nm2 N sum N her N spr W sum W her W spr 40H0 1012,1 19,35 19587,3 4265,0 15322,3 300023 161896,9 138126,1 40G9 1013,0 0,21 212,8 155,4 57,4 6325 5680,1 644,5 Table 3 BIAS survey statistics (aggregated data of herring and sprat), 18.10- 19.10.2018 ICES SD 26 ICES No Herring Sprat SA TS calc. Rect. trawl L, cm w, g Numb.,% L, cm w, g Numb.,% m2/nm2 dB 40H0 1,5,6 17,80 37,96 21,77 10,85 9,01 78,23 12,2 -73,0 40G9 2,3,4 17,77 36,56 73,01 11,96 11,22 26,99 54,5 -46,8 Table 4 BIAS survey statistics (herring and sprat), 18.10- 19.10.2018 ICES SD 26 ICES Rect. Area nm2 SA m2/nm2 σ *10^4 nm2 Abundance mln. Species composition (%) herring sprat 40H0 1012 12,2 0,00628 19587,3 21,77 78,23 40G9 1013 54,5 2,59587 212,8 73,01 26,99 Table 5 BIAS survey estimated age composition (%) of sprat, 18.10- 19.10.2018 SD 26 Rect. Age Total 0 1 2 3 4 5 6 7 8 40H0 100,0 8,6 45,3 36,3 7,3 2,5 0,03 40G9 100,0 3,4 6,8 35,1 28,4 19,1 3,1 2,9 0,7 0,5 Table 6 BIAS survey estimated number (millions) of sprat, 18.10- 19.10.2018 SD 26 Rect. Age Total 0 1 2 3 4 5 6 7 8 40H0 15322,3 1313,5 6946,9 5560,4 1120,6 376,1 4,8 40G9 57,4 2,0 3,9 20,2 16,3 10,9 1,8 1,6 0,4 0,3 Table 7 BIAS survey estimated biomass (in tons) of sprat, 18.10- 19.10.2018 SD 26 Rect. Age Total 0 1 2 3 4 5 6 7 8 40H0 138126 6769 57093 56694 12954 4551 65 40G9 644 7 35 214 195 136 23 23 6 4 Table 8 BIAS estimated mean weights (g) of sprat, 18.10- 19.10.2018 SD 26 Rect. Age Mean 0 1 2 3 4 5 6 7 8 40H0 9,01 5,2 8,2 10,2 11,6 12,1 13,6 40G9 11,22 3,7 9,0 10,6 12,0 12,5 13,0 13,9 13,9 14,5 344 ICES | WGBIFS 2019 Table 9 BIAS estimated mean length (cm) of sprat, 18.10- 19.10.2018 SD 26 Rect. Age Total 0 1 2 3 4 5 6 7 8 40H0 10,85 8,5 10,2 11,3 12,0 12,2 13,0 40G9 11,96 8,0 10,5 11,4 12,1 12,3 12,7 13,2 13,5 13,8 Table 10 BIAS estimated age composition (%) of herring, 18.10- 19.10.2018 SD 26 Rect. Age Total 0 1 2 3 4 5 6 7 8 40H0 100,0 0,1 13,0 7,8 17,6 23,3 15,0 13,7 4,7 4,7 40G9 100,0 6,3 6,2 14,7 35,2 19,2 13,2 2,9 2,3 Table 11 BIAS survey estimated number (millions) of herring, 18.10- 19.10.2018 SD 26 Rect. Age Total 0 1 2 3 4 5 6 7 8 40H0 4265,0 5,0 554,7 333,7 751,9 995,2 639,4 584,2 200,6 200,4 40G9 155,4 0,0 9,8 9,7 22,9 54,6 29,8 20,5 4,5 3,6 Table 12 BIAS survey estimated biomass (in tons) of herring, 18.10- 19.10.2018 SD 26 Rect. Age Total 0 1 2 3 4 5 6 7 8 40H0 161897 71 12399 8582 24358 36410 28430 28700 10844 12102 40G9 5680 0 196 258 714 1865 1203 987 258 199 Table 13 BIAS survey estimated mean weights (g) of herring, 18.10- 19.10.2018 SD 26 Rect. Age Total 0 1 2 3 4 5 6 7 8 40H0 37,96 14,3 22,4 25,7 32,4 36,6 44,5 49,1 54,1 60,4 40G9 36,56 20,1 26,7 31,1 34,2 40,3 48,2 57,5 55,0 Table 14 BIAS survey estimated mean length (cm) of herring, 18.10- 19.10.2018 SD 26 Rect. Age Total 0 1 2 3 4 5 6 7 8 40H0 17,80 12,5 14,4 15,6 16,8 17,4 18,8 19,4 20,3 21,2 40G9 17,77 14,4 15,8 16,6 17,2 18,2 19,5 21,0 20,5 ICES | WGBIFS 2019 345 Figure 4 Biomass and abundance of herring by acoustic survey results from October of 2010 – 2018 in ICES rectangles 40H0 and 40G9 Figure 5. Biomass and abundance of sprat by acoustic survey results from October of 2010 – 2018 in ICES rectangles 40H0 and 40G9 Table 15. The values of hydrological parameters registered at the catching depth in the Baltic Sea ICES SD from the Lithuanian BIASS survey conducted by f/v "169" in the period of 18.10- 19.10.2018. Haul number Date of catch Trawling depth, m Hydrological parameters Temperature, °C Salinity, ‰ Oxygen, ml/l 1 2018.10.18 34 14.3 7.2 6.8 2 2018.10.18 51 11.8 7.2 7.2 3 2018.10.18 56 9.9 7.2 7.6 4 2018.10.19 75 9.4 7.2 7.7 5 2018.10.19 63 10.3 7.2 7.5 6 2018.10.19 45 11.0 7.3 7.4 Average 0 30000 60000 90000 120000 150000 180000 0 1000 2000 3000 4000 5000 2010 2011 2012 2013 2014 2015 2016 2017 2018 tmln. vnt. 40H0 Biomass Abundance 0 30000 60000 90000 120000 150000 180000 0 1000 2000 3000 4000 5000 2010 2011 2012 2013 2014 2015 2016 2017 2018 tmln. vnt. 40G9 Biomass Abundance 0 50000 100000 150000 200000 250000 0 5000 10000 15000 20000 25000 30000 35000 40000 45000 2010 2012 2014 2016 2018 mln. t40H0 Biomass Abundance 0 50000 100000 150000 200000 250000 0 5000 10000 15000 20000 25000 30000 35000 40000 45000 2010 2011 2012 2013 2014 2015 2016 2017 2018 mln. t40G9 Biomass Abundance 346 ICES | WGBIFS 2019 1 REPORT FROM THE JOINT ESTONIAN-POLISH BIAS 2018 CONDUCTED BY THE R.V. “BALTICA” IN THE NORTH-EASTERN BALTIC SEA (21-31 October 2018) by Miroslaw Wyszynski*, Elor Sepp**, Tiit Raid** and Tycjan Wodzinowski* * National Marine Fisheries Research Institute, Gdynia (Poland) ** University of Tartu, Estonian Marine Institute, Tallinn (Estonia) Introduction The recent joint Estonian-Polish Baltic International Acoustic Survey (BIAS), marked with the number 5/2018/NMFRI/TUEMI was based on the procurement contract No 6- 20/HR/68-13 between the University of Tartu/Estonian Marine Institute in Tallinn and the National Marine Fisheries Research Institute in Gdynia. The survey was conducted in the Estonian EEZ (the ICES Sub-divisions 28.2, 29 and 32). The Estonian Data Collection Program for 2018 and the European Union (the Commission regulations Nos. 665/2008, 199/2008 and 2010/93/EU) financially supported the EST-POL BIAS 2018. Timing, surveying area in the North-eastern Baltic Sea and the principal methods of investigations concerns the above mentioned survey were designed and coordinated by the ICES WGBIFS (ICES 2018¹). The main aims of the reported cruise were:  to provide the echo-integration and to collect the acoustic data along the planned transects in the north-eastern Baltic Sea,  to conduct the fish pelagic control-catches at the fish concentration locations,  to collect ichthyological samples specially for herring and sprat,  to provide hydrological monitoring (water temperature, salinity and oxygen content) at the catch locations. Personnel The EST-POL BIAS 2017 scientific staff was composed of 8 persons: Miroslaw Wyszynski (NMFRI, Gdynia – Poland) – survey leader Bartlomiej Nurek (NMFRI, Gdynia – Poland) – acoustician Tycjan Wodzinowski (NMFRI, Gdynia – Poland) – hydrologist Tiit Raid (TUEMI, Tallinn – Estonia) – Estonian scientific staff leader Ain Lankov (TUEMI, Tallinn - Estonia) – ichthyologist Andrus Hallang (TUEMI, Tallinn - Estonia) – ichthyologist Viktor Kajalainen (TUEMI, Tallinn - Estonia) – ichthyologist Elor Sepp (TEMI, Tallinn - Estonia) – acoustician ¹ICES 2018. Report of the Baltic International Fish Survey Working Group (WGBIFS). ICES CM 2018/EOSG: 06, Ref. ACOM and SCICPOM; 380 pp. ICES | WGBIFS 2019 347 2 Narrative The reported survey took place during the period of 21-31 October 2018 (according to the survey research plan). The at sea researches (echo-integration, fish control catches and hydrological stations) were conducted aboard r.v. “Baltica” within Estonian EEZ (the ICES Sub-divisions 28.2, 29 and 32), moreover inside the territorial waters of this country not shallower than 20 m depth. The survey started from the Gdynia port (Poland) on 20.10.2018 early morning and was navigated in the North-eastern direction to the Ventspils port (Latvia) for the Estonian scientific team embarkation on board the vessel and next to the entering point of planed acoustic transect crossing Estnioan EEZ boundary at the geographical position 5752’2N 02114’7E on October 21 (Fig. 1). The at sea researches were ended on 28.10.2018 at 22:30 o’clock. Due to heavy stormy weather (sea state 4-5) the vessel reached the port Ventspils for disembarkation Estonian scientific team on October 31. Then the r.v. “Baltica” started its journey to the home-port in Gdynia (Poland), reaching it on 01.11.2018 afternoon. Survey design and realization The r.v. “Baltica” realized 841.7 Nm echo-integration transect and 19 fish control- catches (Fig. 1, Tab. 1). All planed ICES rectangles were covered with acoustic transect and control catches except rectangle 46H0 in SD 29. Bulk of control catches were performed in the daylight except three of them performed at nightfall between 06:00 and 07:30 p.m.). The pelagic trawl type WP 53/64x4 (with 6 mm mesh bar length in the codend) was used for catches. Trawling duration was from 5 to 20 minutes, due to high fish density observed on the net-sounder monitor. The mean speed of vessel while providing echo-integration was 8.0 knots, in case of trawling it was 3.0 knots. Overall, 4 hauls were conducted in SD 28.2, 5 hauls in SD 29 and 10 hauls in SD 32. The length measurements (in 0.5 cm classes) were realized for 3805 sprat and 3354 herring individuals. Totally, 337 sprat and 515 herring individuals were taken for biological analysis (Tab. 2). Acoustic data were collected with the EK-60 echo-sounder equipped with “Echo-view V4.10” software for the data analysis. The acoustic equipment was calibrated before the survey (in September 2018) according to the methodology described in the “SISP Manual of International Baltic Acoustic Surveys (IBAS)”, Version 2.0 (ICES, 2017). The basic acoustic and biological data collected during recently carried out survey will be stored in the BIAS_DB.mdb and the new acoustic data base WKBIFS-ACOU in the accepted CSV or XML formats, managed by ICES. Data analysis The MYRIAX “EchoView v.4.10” software was used for the analysis of the acoustic data. The total number of fish in each the ICES rectangle was estimated as a product of the mean NASCs from scrutinized acoustic data and a rectangle area, divided by corresponding mean acoustic cross-section (σ) which is based on the trawl catch results. The abundance of clupeids was separated into sprat and herring according to the mean catch composition. Mean target strength (TS) – one of the principal acoustic parameter – of clupeids was calculated according to following formula: 348 ICES | WGBIFS 2019 3 TS = 20 log L – 71.2 Due to fortunate weather conditions, all transects and planned trawls were conducted according to the plan. Catch results and fish measurements Overall, 12 fish species were recognized in hauls performed at the North-eastern Baltic Sea in October 2018. Sprat was prevailing species by mass in the total catch with the mean share amounted 71.9 % (especially high in SD 28.2 – 86.4%, but lowest in SD 32 – 53.1%). The second one was herring with mean share by mass 27,6% (maximum in SD 32 – 45.9%). The rest 10 species (cod, flounder, three and nine spine sticklebacks, shorthorn sculpin, smelt, lumpfish, vendace, straightnose pipefish and lamprey) represented only about 0.5% of the total mass in average. The detailed catch and CPUE results are presented in the Table 1 and Fig. 2. The biological sampling is shown in Table 2. Mean CPUE for all species in the investigated area in October 2018 amounted 1188.6 kg/h (comparing to 1085.4 kg/h in the same period in 2017, 729.5 kg/h in 2016 and 845.5 kg/h in 2015). The most valuable CPUEs for sprat were noted in SDs 28.2 and 29, but for herring – in SDs 29 and 32. The mean CPUEs of sprat were as follow: 1488.1 kg/h in ICES SD 28.2, 1260.0 kg/h in SD 29 and 398.5 kg/h in SD 32. The mean CPUEs in case of herring were: 228.4, 374.4 and 344.5 kg/h in SDs 28.2, 29 and 32 respectively. The length distributions of sprat and herring according to the ICES Sub-divisions 28.2, 29 and 32 are shown on Fig. 3 and 4 respectively. The sprat length distribution curves represent similar character in three investigated SDs. First frequency pick representing sprat generation born in 2018 take place on 7-8.5 cm length classes and shows low quantity in all investigated Sub-divisions 28.2, 29 and 32. The second one representing adult sprat placed on 10.5-11.5 cm length classes. The length distribution curves by Sub-divisions in case of herring show generally the same picture – modal frequency picks fell to 14.5-15.5 cm length classes. Moreover the curves shows very low abundance of herring generation born in 2018 in all SDs. Three and nine spine sticklebacks as well as smelt were the most frequently species in bycatch, particularly in SD 32. Their length distributions are presented at Fig. 5-7. Acoustic results The survey statistics concerning the survey area, the mean NASC, the mean sigma, the estimated total number of fish, the percentages of herring and sprat per ICES statistical rectangles are presented in Table 3. Fish concentrations were found generally lower than in previous years. Abundance and biomass estimates The estimated abundances of herring and sprat by age group and Sub-division/ICES statistical rectangle are given in Table 4. The estimated biomass by age group and Sub- division/ICES statistical rectangle is shown in Table 5. Corresponding mean weights by age group and Sub-division/ICES statistical rectangle are summarized in Table 6. The spatial distribution of sprat biomass was similar to previous survey, abundance being highest in Gulf of Finland and west of islands Hiiumaa and Saaremaa. The abundance ICES | WGBIFS 2019 349 4 and biomass of herring was highest in the western part of Gulf of Finland and lowest in the Baltic Proper. The average weight of herring was similar to the previous survey, abundance of herring was slightly higher and abundance of sprat about two times lower compared to the previous survey. Meteorological and hydrological characteristics. The 19 hydrological stations at the start control catches positions were inspected with the SeaBird 911 CTD-probe combined with the rosette sampler. Oxygen content was determined by SBE43 sensor. The calibration was performed with the Winkler method. The row data aggregated to the 1-m depth stratum. The wind velocity varied from 0.5 to 20.1 m/s and average was 9.1 m/s. The most often wind direction was not tantamount to describe. The air temperature ranged from 2.2 °C to 13.4 °C, and average temperature was 7.2 °C (Fig. 8). The seawater temperature in the surface layers varied from 9,92 to 12.00 °C (the mean was 11.46 °C).The lowest surface temperatures were recorded at the haul 19. The highest ones were noticed at the hauls 3 and 4. The minimum value of salinity in Practical Salinity Unit (PSU) was 4.93 at the haul 3 in the surface layer. The maximum was 6.92 PSU at the haul 19. The mean value of salinity was 6.25 PSU. The oxygen content in the surface layers of investigated the research area varied in the range of 6.79 ml/l (haul 4) up to 7.22 ml/l (haul 19). The mean value of surface water oxygen content was 7.03 ml/l. The temperature of near bottom layer was changing in the range of 4.56 (haul 15) to 12.05 °C (haul 3), the mean was 6.19 °C. Salinity in the bottom waters varied from 4.94 to 11.60 PSU, and the mean was 9.20 PSU. The low values of salinity was at the haul 3. The highest values of salinity were noticed at the haul 18. Oxygen content varied from 0.00 ml/l to 7.06 ml/l at the haul 3. The mean was 1.62 ml/l. The zero values of this parameter were noticed at the hauls: 1, 8, 9, 10, 11, 13, 14, 17, 18, 19 (Fig. 9 and 10). The vertical distribution of the seawater temperature, salinity and oxygen content along the hydrological profile connected with haul No 18 located at deepest station in SD 28.2 is shown at Fig. 11. Generally the hydrological investigations showed the vast none oxygenated area below 70 m depth from southern part of Estonian EEZ to the mouth of Finland Bay. The temperature at the hauls layer was changing in the range from 4.03 (haul 19) to 12.01 °C (hauls 3 and 4), the mean was 7.57 °C. Salinity haul waters varied from 4.92 (haul 3) up to 10.13 PSU (haul 17), and the mean was 7.20 PSU. Oxygen content varied from 1.87 ml/l (haul 14) to 7.20 ml/l (haul 19), the mean was 4.93 ml/l (Tab. 7). The final report from the EST-POL BIAS 2018 will be presented at the meeting of the ICES Baltic International Fish Survey Working Group (WGBIFS) at March 25-29, 2019 in Klaipeda (Lithuania). 350 ICES | WGBIFS 2019 5 Fig. 1. Acoustic transects and pelagic fish control catches (trawling start positions) with connected hydrological stations realized during the joint EST-POL BIAS (October, 2018). ICES | WGBIFS 2019 351 6 Table 1. Catch [kg] and CPUE [kg/h] results during the joint Estonian-Polish BIAS conducted by r.v. “Baltica” in Estonian EEZ in October 2018. Geographical position Time Haul no Date ICES ICES start end Haul Total catch rectangle Sub-division latitude longitude latitude longitude start end duration [kg] sprat herring cod flounder straightnose lamprey shorthorn nine-spined three-spined smelt lumpfish vendace (SD) 00°00.0'N00°00.0'E00°00.0'N 00°00.0'E [min] pipefish sculpin stickleback stickleback 1 2018-10-22 48H4 32 59°36.8' 24°16.7' 59°36.0' 24°17.8' 12:45 12:55 10 157,540 19,425 136,760 0,012 0,063 1,280 2 2018-10-22 48H4 32 59°44.2' 24°54.2' 59°44.2' 24°55.6' 16:05 16:20 15 300,640 272,951 26,576 0,031 0,872 0,210 3 2018-10-23 48H7 32 59°32.5' 27°23.3' 59°32.4' 27°21.6' 07:40 08:00 20 47,618 16,377 30,887 0,078 0,009 0,143 0,124 4 2018-10-23 48H6 32 59°34.9' 26°58.7' 59°35.1' 26°57.2' 10:00 10:15 15 99,880 77,786 21,664 0,090 0,270 0,070 5 2018-10-23 48H6 32 59°45.2' 26°17.8' 59°45.3' 26°15.9' 13:55 14:15 20 315,147 128,616 178,020 0,067 0,283 8,161 6 2018-10-23 48H5 32 59°45.1' 25°56.4' 59°45.3' 25°54.6' 16:00 16:15 15 80,700 4,834 73,824 0,097 1,945 7 2018-10-23 48H5 32 59°44.9' 25°27.7' 59°45.1' 25°25.8' 18:10 18:30 20 29,970 5,586 22,885 0,018 0,378 1,103 8 2018-10-25 47H4 32 59°28.5' 24°05.0' 59°28.4' 24°03.9' 07:55 08:05 10 229,820 207,435 21,902 0,023 0,253 0,207 9 2018-10-25 47H3 32 59°28.5' 23°45.8' 59°28.1' 23°44.1' 09:45 10:05 20 418,560 112,802 302,158 0,168 3,432 10 2018-10-25 47H3 32 59°20.0' 23°10.8' 59°19.4' 23°09.0' 13:00 13:20 20 272,850 137,162 134,152 0,226 1,310 11 2018-10-25 47H2 29 59°20.5' 22°45.7' 59°20.8' 22°44.0' 15:20 15:40 20 491,982 103,494 386,761 0,232 0,020 0,393 1,082 12 2018-10-25 47H2 29 59°12.2' 22°28.0' 59°11.6' 22°27.2' 18:00 18:15 15 123,931 9,791 112,330 0,301 0,014 0,049 1,446 13 2018-10-26 47H1 29 59°15.8' 21°38.6' 59°15.6' 21°39.6' 09:10 09:20 10 318,006 315,996 1,430 0,166 0,033 0,381 14 2018-10-26 47H1 29 59°07.2' 21°15.5' 59°06.0' 21°16.1' 12:10 12:30 20 180,220 94,922 84,631 0,307 0,360 15 2018-10-26 46H1 29 58°52.3' 21°32.8' 58°51.9' 21°33.7' 15:40 15:55 15 943,018 942,440 0,0002 0,578 16 2018-10-28 45H1 28.2 58°04.3' 21°33.7' 58°04.1' 21°33.5' 07:20 07:25 5 388,287 387,920 0,063 0,025 0,279 17 2018-10-28 45H0 28.2 58°04.2' 20°45.3' 58°03.5' 20°44.5' 11:00 11:20 20 116,055 5,542 105,724 4,555 0,234 18 2018-10-28 45H0 28.2 58°22.2' 20°26.2' 58°21.6' 20°25.9' 15:45 15:55 10 227,534 161,846 65,480 0,114 0,094 19 2018-10-28 45H1 28.2 58°22.2' 21°02.7' 58°22.0' 21°02.3' 19:25 19:30 5 43,040 25,807 16,889 0,034 0,284 0,026 Total 28.2 774,916 581,115 188,156 4,555 0,025 0,034 0,632 0,026 0,373 catch 29 2057,157 1466,643 585,152 0,232 0,166 0,301 0,034 0,782 3,269 0,578 32 1952,725 982,974 948,828 0,145 0,183 2,753 17,718 0,124 [kg] Sum 4784,798 3030,732 1722,136 4,787 0,166 0,0002 0,145 0,326 0,251 4,167 21,013 0,951 0,124 Haul no Date ICES ICES Haul Total rectangle Sub-division duration CPUE sprat herring cod flounder straightnose lamprey shorthorn nine-spined three-spined smelt lumpfish vendace (SD) [min] [kg/h] pipefish sculpin stickleback stickleback 1 2018-10-22 48H4 32 10 945,240 116,550 820,560 0,072 0,378 7,680 2 2018-10-22 48H4 32 15 1202,560 1091,804 106,304 0,124 3,488 0,840 3 2018-10-23 48H7 32 20 142,854 49,131 92,661 0,234 0,027 0,429 0,372 4 2018-10-23 48H6 32 15 399,520 311,144 86,656 0,360 1,080 0,280 5 2018-10-23 48H6 32 20 945,441 385,848 534,060 0,201 0,849 24,483 6 2018-10-23 48H5 32 15 322,800 19,336 295,296 0,388 7,780 7 2018-10-23 48H5 32 20 89,910 16,758 68,655 0,054 1,134 3,309 8 2018-10-25 47H4 32 10 1378,920 1244,610 131,412 0,138 1,518 1,242 9 2018-10-25 47H3 32 20 1255,680 338,406 906,474 0,504 10,296 10 2018-10-25 47H3 32 20 818,550 411,486 402,456 0,678 3,930 11 2018-10-25 47H2 29 20 1475,946 310,482 1160,283 0,696 0,060 1,179 3,246 12 2018-10-25 47H2 29 15 495,724 39,164 449,320 1,204 0,056 0,196 5,784 13 2018-10-26 47H1 29 10 1908,036 1895,976 8,580 0,996 0,198 2,286 14 2018-10-26 47H1 29 20 540,660 284,766 253,893 0,921 1,080 15 2018-10-26 46H1 29 15 3772,073 3769,760 0,000 0,001 2,312 16 2018-10-28 45H1 28 5 4659,446 4655,040 0,754 0,305 3,348 17 2018-10-28 45H0 28 20 348,165 16,626 317,172 13,665 0,702 18 2018-10-28 45H0 28 10 1365,204 971,076 392,880 0,684 0,564 19 2018-10-28 45H1 28 5 516,480 309,684 202,668 0,408 3,408 0,312 28.2 1722,324 1488,107 228,368 3,416 0,076 0,102 1,199 0,078 0,978 29 1638,488 1260,030 374,415 0,139 0,199 0,0002 0,241 0,023 0,499 2,479 0,462 32 750,148 398,507 344,453 0,044 0,078 1,045 5,984 0,037 Total 1188,590 854,613 327,899 0,756 0,052 0,00004 0,023 0,079 0,068 0,933 3,818 0,328 0,020 Mean CPUE by SDs [kg/h] Catch per species [kg] CPUE per species [kg/h] 352 ICES | WGBIFS 2019 7 Table. 2. Biological sampling in the r.v.”Baltica” joint EST-POL BIAS in October 2018. SD 28.2 sprat herring cod flounder straightnose lamprey shorthorn nine-spined three-spined smelt lumpfish vendace SUM pipefish sculpin stickleback stickleback Samples measurements 4 4 1 1 1 3 1 2 1 18 taken analyses 4 3 7 Fish measured 762 752 22 1 14 111 1 2 3 1668 Fish analysed 114 152 266 SD 29 sprat herring cod flounder straightnose lamprey shorthorn nine-spined three-spined smelt lumpfish vendace SUM pipefish sculpin stickleback stickleback Samples measurements 5 4 1 1 1 3 2 4 4 1 26 taken analyses 5 4 9 Fish measured 977 741 1 1 1 3 4 49 30 3 1810 Fish analysed 128 156 284 SD 32 sprat herring cod flounder straightnose lamprey shorthorn nine-spined three-spined smelt lumpfish vendace SUM pipefish sculpin stickleback stickleback Samples measurements 10 10 2 6 10 9 47 taken analyses 10 10 20 Fish measured 2066 1861 2 57 299 252 4537 Fish analysed 131 207 338 TOTAL sprat herring cod flounder straightnose lamprey shorthorn nine-spined three-spined smelt lumpfish vendace SUM pipefish sculpin stickleback stickleback Samples measurements 19 18 2 1 1 2 4 9 17 14 3 1 91 taken analyses 19 17 36 Fish measured 3805 3354 23 1 1 2 4 75 459 283 5 3 8015 Fish analysed 373 515 888 ICES | WGBIFS 2019 353 8 Table 3. The BIAS survey basic biological and acoustic data concerning the clupeid stocks inhabiting the north- eastern Baltic Sea in October 2018. Area [NM2] Share [%-indiv.] Total abundance [x106] Abundance density [106/NM2] NASC [m2/NM2] σ [cm²] ICES Sub-div. ICES rectangle herring sprat 28 45H0 947.2 49.5 49.0 6077.71 6.417 1230.9 1.92 28 45H1 827.1 11.4 85.6 10072.83 12.178 1559.4 1.28 29 46H1 921.5 10.5 86.6 4176.16 4.532 594.2 1.31 29 46H2 258.0 10.5 86.6 749.20 2.904 380.8 1.31 29 47H1 920.3 11.4 87.9 3337.90 3.627 460.8 1.27 29 47H2 793.9 71.3 26.7 4290.86 5.404 1020.8 1.89 32 47H3 536.2 40.1 58.7 2724.64 5.081 792.0 1.56 32 48H4 835.1 39.3 57.9 17615.05 21.093 3106.9 1.47 32 48H5 767.2 63.0 18.7 4156.42 5.418 888.2 1.64 32 48H6 776.1 23.6 71.6 5122.51 6.600 853.9 1.29 32 48H7 851,4 54.5 42.9 2681.14 3.149 430.2 1.37 Average 35.0 61.1 6.946 1028.9 1.48 Total 8434 61004.43 354 ICES | WGBIFS 2019 9 Table 4. Abundance (in 106 indiv.) of herring and sprat per age groups according to the ICES rectangles and Sub-divisions of the north-eastern Baltic in October 2018. ICES ICES rectangle HERRING – age groups Sub- div. 0 1 2 3 4 5 6 7 8+ total 28 45H0 10.59 109.69 471.83 316.35 1550.20 65.69 317.55 97.83 65.96 3005.70 28 45H1 46.76 150.01 213.52 99.35 431.49 14.81 74.33 18.31 103.53 1152.10 total 57.35 259.69 685.34 415.71 1981.69 80.50 391.88 116.14 169.49 4157.80 29 46H1 19.38 50.70 59.41 58.94 167.62 20.10 26.51 21.58 15.13 439.38 29 46H2 3.48 9.10 10.66 10.57 30.07 3.61 4.76 3.87 2.71 78.83 29 47H1 4.28 35.71 52.16 59.60 159.33 19.71 22.83 16.97 9.06 379.66 29 47H2 38.51 437.98 548.38 472.13 1139.88 147.97 151.21 96.52 28.13 3060.72 total 65.65 533.49 670.62 601.25 1496.90 191.39 205.29 138.94 55.04 3958.58 32 47H3 4.28 70.42 210.87 289.27 277.18 140.85 84.06 15.16 1092.10 32 48H4 145.04 791.16 2025.81 1687.34 1359.87 558.62 309.46 48.26 6925.56 32 48H5 26.95 258.92 668.66 712.25 604.29 208.48 114.37 26.21 2620.13 32 48H6 31.78 248.95 268.71 292.84 228.74 89.34 42.95 5.14 1208.45 32 48H7 77.81 966.38 182.50 101.66 78.50 29.22 19.75 4.20 1460.02 total 285.86 2335.83 3356.56 3083.36 2548.57 1026.51 570.59 98.97 13306.25 Grand total 408.86 3129.02 4712.52 4100.31 6027.17 1298.40 1167.76 354.05 224.53 21422.63 ICES | WGBIFS 2019 355 10 Table 4. Continued ICES ICES rectangle SPRAT – age groups Sub- div. 0 1 2 3 4 5 6 7 8+ Total 28 45H0 83.73 212.44 726.46 168.92 623.28 828.64 197.09 52.29 84.54 2977.40 28 45H1 1035.61 1386.42 2231.52 513.56 1550.56 1415.80 278.40 82.06 132.24 8626.16 total 1119.34 1598.86 2957.99 682.47 2173.84 2244.43 475.49 134.35 216.78 11603.55 29 46H1 9.87 711.21 481.23 274.96 1098.38 779.15 197.32 33.12 29.39 3614.63 29 46H2 1.77 127.59 86.33 49.33 197.05 139.78 35.40 5.94 5.27 648.47 29 47H1 305.36 772.39 423.30 165.56 650.22 487.04 102.35 14.00 12.17 2932.40 29 47H2 75.75 212.69 130.99 81.77 291.25 238.38 72.40 21.05 21.31 1145.59 total 392.76 1823.89 1121.86 571.61 2236.90 1644.34 407.46 74.11 68.14 8341.08 32 47H3 45.60 587.64 261.54 67.95 471.59 122.71 7.65 10.06 23.64 1598.38 32 48H4 219.46 4246.86 1434.48 446.16 2849.52 787.28 28.19 59.43 127.08 10198.46 32 48H5 20.14 252.20 96.86 39.26 245.92 80.40 7.46 8.42 25.45 776.11 32 48H6 55.07 1880.60 495.60 117.20 817.62 223.47 10.92 22.43 43.27 3666.17 32 48H7 13.27 379.54 118.52 51.39 361.77 141.33 14.94 19.75 47.48 1147.99 total 353.54 7346.82 2407.00 721.97 4746.42 1355.20 69.15 120.09 266.92 17387.11 Grand total 1865.64 10769.57 6486.85 1976.05 9157.16 5243.97 952.10 328.55 551.84 37331.74 356 ICES | WGBIFS 2019 11 Table 5. Biomass (in tons) of herring and sprat per age groups according to the ICES rectangles and Sub-divisions of the north-eastern Baltic in October 2018. ICES ICES rectangle HERRING – age groups Sub-div. 0 1 2 3 4 5 6 7 8+ total 28 45H0 48.72 1708.61 9420.03 7360.92 38774.53 2004.15 8359.90 3395.16 2432.69 73504.71 28 45H1 179.23 2000.89 3930.29 2199.06 10192.56 432.10 1957.41 604.16 379.90 21875.59 total 228 3709 13350 9560 48967 2436 10317 3999 2813 95380 29 46H1 74.31 652.04 1034.93 1243.27 3832.73 470.06 693.80 587.37 478.61 9067.13 29 46H2 13.33 116.98 185.67 223.04 687.59 84.33 124.47 105.37 85.86 1626.65 29 47H1 16.98 470.33 991.45 1292.03 3673.16 457.18 568.71 433.23 270.00 8173.05 29 47H2 131.06 5660.44 9697.29 9692.74 24159.04 3293.00 3625.44 2358.83 773.92 59391.76 total 236 6900 11909 12451 32353 4305 5012 3485 1608 78259 32 47H3 19.13 841.75 3488.54 5620.63 5646.68 3132.19 2035.86 444.74 0.00 21229.53 32 48H4 524.96 8697.86 33350.14 32117.82 27270.13 12421.67 7702.45 1342.98 0.00 123428.02 32 48H5 90.29 2789.78 10972.88 13528.87 12116.24 4502.21 2768.76 683.06 0.00 47452.09 32 48H6 122.46 2676.86 4490.45 5725.65 4883.36 2059.01 1028.46 128.39 0.00 21114.65 32 48H7 341.66 10103.39 2904.07 1918.36 1546.84 645.46 473.51 104.26 0.00 18037.56 total 1098 25110 55206 58911 51463 22761 14009 2703 0 231262 Grand total 1562 35719 80466 80922 132783 29501 29339 10188 4421 404901 ICES | WGBIFS 2019 357 12 Table 5. Continued ICES ICES rectangle SPRAT – age groups Sub- div. 0 1 2 3 4 5 6 7 8+ total 28 45H0 293.73 1694.27 6653.45 1550.15 6104.39 8746.57 2183.30 596.40 1029.87 28852.12 28 45H1 2695.84 10154.92 19036.55 4389.54 13768.39 13916.41 2911.68 935.44 1532.75 69341.52 total 2990 11849 25690 5940 19873 22663 5095 1532 2563 98194 29 46H1 30.99 5351.73 3824.67 2494.87 9674.14 7433.00 1999.82 368.98 327.03 31505.23 29 46H2 5.56 960.10 686.15 447.58 1735.55 1333.48 358.77 66.20 58.67 5652.05 29 47H1 1174.08 5571.94 3291.22 1536.93 5711.93 4717.72 1021.62 163.43 141.37 23330.25 29 47H2 271.60 1528.13 1013.25 756.83 2578.47 2297.37 747.74 242.35 250.38 9686.11 total 1482 13412 8815 5236 19700 15782 4128 841 777 70174 32 47H3 165.52 4186.83 2078.59 592.50 4096.94 1144.54 84.28 103.43 253.37 12705.99 32 48H4 942.68 28536.61 10807.01 3823.46 24290.15 7101.35 319.84 592.54 1384.42 77798.06 32 48H5 85.11 1716.27 758.81 347.98 2177.63 757.85 84.82 87.06 286.39 6301.92 32 48H6 279.70 13110.33 3811.16 1017.50 7076.20 2069.08 125.07 228.79 467.60 28185.43 32 48H7 68.42 2629.71 925.26 464.90 3308.10 1365.57 157.59 199.80 492.63 9611.99 total 1541 50180 18381 6246 40949 12438 772 1212 2884 134603 Grand total 6013 75441 52886 17422 80522 50883 9995 3584 6224 302971 358 ICES | WGBIFS 2019 13 Table 6. Mean weight (in grams) of herring and sprat per age groups, according to the ICES rectangles of the north-eastern Baltic in October 2018. ICES ICES rectangle HERRING – age groups Sub-div. 0 1 2 3 4 5 6 7 8+ avg. 28 45H0 4.60 15.58 19.97 23.27 25.01 30.51 26.33 34.70 36.88 24.46 28 45H1 3.83 13.34 18.41 22.13 23.62 29.18 26.33 32.99 3.67 18.99 29 46H1 3.83 12.86 17.42 21.09 22.87 23.38 26.17 27.22 31.63 20.64 29 46H2 3.83 12.86 17.42 21.09 22.87 23.38 26.17 27.22 31.63 20.64 29 47H1 3.97 13.17 19.01 21.68 23.05 23.19 24.92 25.53 29.79 21.53 29 47H2 3.40 12.92 17.68 20.53 21.19 22.25 23.98 24.44 27.51 19.40 32 47H3 4.47 11.95 16.54 19.43 20.37 22.24 24.22 29.33 19.44 32 48H4 3.62 10.99 16.46 19.03 20.05 22.24 24.89 27.83 17.82 32 48H5 3.35 10.77 16.41 18.99 20.05 21.60 24.21 26.06 18.11 32 48H6 3.85 10.75 16.71 19.55 21.35 23.05 23.95 25.00 17.47 32 48H7 4.39 10.45 15.91 18.87 19.70 22.09 23.97 24.85 12.35 ICES | WGBIFS 2019 359 14 Table 6. Continue ICES ICES rectangle SPRAT – age groups Sub- div. 0 1 2 3 4 5 6 7 8+ avg. 28 45H0 3.51 7.98 9.16 9.18 9.79 10.56 11.08 11.41 12.18 9.69 28 45H1 2.60 7.32 8.53 8.55 8.88 9.83 10.46 11.40 11.59 8.04 29 46H1 3.14 7.52 7.95 9.07 8.81 9.54 10.14 11.14 11.13 8.72 29 46H2 3.14 7.52 7.95 9.07 8.81 9.54 10.14 11.14 11.13 8.72 29 47H1 3.84 7.21 7.78 9.28 8.78 9.69 9.98 11.67 11.61 7.96 29 47H2 3.59 7.18 7.74 9.26 8.85 9.64 10.33 11.51 11.75 8.46 32 47H3 3.63 7.12 7.95 8.72 8.69 9.33 11.01 10.28 10.72 7.95 32 48H4 4.30 6.72 7.53 8.57 8.52 9.02 11.35 9.97 10.89 7.63 32 48H5 4.23 6.81 7.83 8.86 8.86 9.43 11.38 10.33 11.25 8.12 32 48H6 5.08 6.97 7.69 8.68 8.65 9.26 11.46 10.20 10.81 7.69 360 ICES | WGBIFS 2019 15 Fig. 2. Distribution of CPUE values (kg/h) for herring, sprat and other species in the pelagic fish control catches during the joint EST-POL BIAS in the North-eastern Baltic Sea, October 2018. ICES | WGBIFS 2019 361 16 0 4 8 12 16 20 24 28 6, 5 7, 0 7, 5 8, 0 8, 5 9, 0 9, 5 10 ,0 10 ,5 11 ,0 11 ,5 12 ,0 12 ,5 13 ,0 13 ,5 14 ,0 14 ,5 15 ,0 L,cm SD 28.2 SD 29 SD 32 Fig. 3. Sprat length distributions from the control catches conducted by the r.v. “Baltica” during the joint EST-POL BIAS in the SDs 28.2, 29 and 32 (October, 2018). 0 4 8 12 16 20 Fr eq ue nc y, % L, cm SD 28.2 SD 29 SD 32 Fig. 4. Herring length distributions from the control catches conducted by the r.v. “Baltica” during the joint EST-POL BIAS in the SDs 28.2, 29 and 32 (October, 2018). 362 ICES | WGBIFS 2019 17 0 4 8 12 16 20 Fr eq ue nc y, % L, cm SD 32 Fig. 5. Smelt length distribution from the control catches conducted by the r.v. “Baltica” during the joint EST-POL BIAS in the SD 32 (October, 2018). 0 4 8 12 16 20 24 28 32 36 40 Fr eq ue nc y, % L, cm SD 28.2 SD 29 SD 32 Fig. 6. Three-spined stickleback length distributions from the control catches conducted by the r.v. “Baltica” during the joint EST-POL BIAS in the SDs 28.2, 29 and 32 (October, 2018). ICES | WGBIFS 2019 363 18 0 4 8 12 16 20 24 28 32 36 40 Fr eq ue nc y, % L, cm SD 32 Fig. 7. Nine-spined stickleback length distribution from the control catches conducted by the r.v. “Baltica” during the joint EST-POL BIAS in the SD 32 (October, 2018). 364 ICES | WGBIFS 2019 19 Fig.8. Changes of the main meteorological parameters during joint EST-POL BIAS conducted in October 2018 (A and B – wind direction and velocity, C – air temperature). ICES | WGBIFS 2019 365 20 Figure 9. Distribution of the seawater temperature, salinity and oxygen content in the near bottom waters (EST-POL BIAS, October 2018). 366 ICES | WGBIFS 2019 21 Fig. 10. Vertical distribution of the seawater temperaturę, salinity and oxygen content along the hydrological horizontal profile (EST-POL BIAS, October 2018). ICES | WGBIFS 2019 367 22 Haul 18 – hydrological profile Figure 11. Vertical distribution of the seawater temperature, salinity and oxygen content along the hydrological profile connected with haul No 18 located at deepest station in SD 28.2 (October 2018). 368 ICES | WGBIFS 2019 23 Table 7. Values of the basic meteorological and hydrological parameters recorded in October 2018 at the positions of the r.v. “Baltica” fish control catches during EST-POL BIAS. Haul Date Mean number of catch headrope depth wind wind force sea state air temper. atmospheric temperature salinity oxygen [m] direction [°B] [°C] pressure [hP] [°C] [PSU] [ml/l] 1 2018-10-22 55 WNW 5 3 5 1009 5.53 7.16 3.77 2 2018-10-22 40 W 5 3 10 1007 9.93 6.17 5.87 3 2018-10-23 15 SW 5 3 6 1000 12.01 4.92 7.11 4 2018-10-23 22 SW 5 3 6 996 12.01 5.13 7.04 5 2018-10-23 45 S 5 3 8 989 8.43 6.32 4.89 6 2018-10-23 40 S 5 3 7 987 10.43 6.07 5.91 7 2018-10-23 46/10 S 5 3 7 984 9.61 6.19 5.58 8 2018-10-25 50 SSE 4 2 5 994 8.28 6.60 5.28 9 2018-10-25 58/45 SSE 5 2-3 5 994 5.35 8.22 2.91 10 2018-10-25 40/52 ESE 5 2 5 994 5.68 7.90 3.81 11 2018-10-25 57 NE 3 2 7 994 6.72 7.61 4.82 12 2018-10-25 40 NW 5 2-3 8 994 6.42 7.46 4.40 13 2018-10-26 45 NW 6 3-4 7 998 6.55 7.07 5.93 14 2018-10-26 40/60 NW 5 3-4 6 1000 4.76 9.05 1.87 15 2018-10-26 35 NW 5 3 7 1001 6.20 7.25 5.85 16 2018-10-28 20 NNE 6 3-4 4 1014 11.51 6.91 6.99 17 2018-10-28 60 NE 6 3-4 5 1020 5.58 10.13 1.94 18 2018-10-28 50 NE 6 3-4 5 1022 4.85 9.21 2.44 19 2018-10-28 30 NE 6 3-4 5 1025 4.03 7.46 7.20 * data at the mean depth of the fish control catch Meteorological parameters Hydrological parameters* ICES | WGBIFS 2019 369 Natural Resources Institute Finland Latokartanonkaari 9 FI-00790 HELSINKI, FINLAND Tel. +358 29 532 6000 kirjaamo@luke.fi Baltic International Acoustic Survey Report for R/V Aranda Cruise 3/2018 ICES_BIAS2018 29th September – 11th October 2018 Juha Lilja and Jukka Pönni ICES | WGBIFS 2019 371 INTRODUCTION International hydroacoustic surveys have been conducted in the Baltic Sea since 1978 (Håkansson et al. 1979). The initial Finnish-Estonian (FIN-EST) research survey on the R/V Baltica was realised in October 2006 (Grygiel et al. 2007), in the framework of the long-term ICES Baltic International Acoustic Surveys (BIAS) programme. The FIN-EST BIAS surveys on the R/V Baltica were continued until 2012. Since 2007, Finland and Sweden joined together to additionally cover Bothnian Sea (ICES Subdivision 30). In 2012 Sweden could not support the funding of the survey in the Bothnian Sea due to economic difficulties within the DCF program and therefore the coverage of the SD30 had to be based on Finnish funding which resulted in half the normal effort (ICES 2013). In 2013, Finland installed fishing equipment and a Simrad EK60 echo sounder into the R/V Aranda and used the vessel in order to cover ICES SDs 29N, 30, and 32N. In 2017, the R/V Aranda was in dry dock for major renovation and therefore Danish R/V Dana was hired for Finnish BIAS2017 survey. The Baltic International Acoustic Survey (BIAS), is mandatory for the countries that have exclusive economic zone (EEZ) in the Baltic Sea, and is a part of the Data Collection Framework. The BIAS survey in September/October are co-ordinated and managed by the ICES working group WGBIFS. The main objective of BIAS is to assess clupeoid resources in the Baltic Sea. The survey will provide data to the ICES Baltic Fisheries Assessment Working Group (WGBFAS). The aim of the cruise was to carry out Baltic International Acoustic Survey on herring and sprat covering SDs 29N, 30, and 32N during the autumn 2018, within the remit of the Natural Resources Institute Finland (Luke). MATERIALS AND METHODS NARRATIVE The cruise was completed in two legs covering most of the Bothnian Sea (BS), the Northern Baltic Sea and the Gulf of Finland (GoF). Altogether 31 stations of 49 planned were completed during the survey. The research area, cruise track and trawl stations are shown in Figure 1. At every station also a CTD (Conductivity Temperature Depth) cast was made. The R/V Aranda departed from the harbour of Helsinki (Finland) on Sat 29.09.2018 at 23:00 (UTC 20:00) and the direct at sea researches begun. Investigations were continued in the northern direction to SD 30. All at sea researches were finalised in the morning 11.10.2018 and the vessel was navigated back to the port of Helsinki. The Finnish BIAS 2018 survey had interruptions when the fishing could not be performed due to stormy weather and breakdown of the fishing gear. Therefore, only two fishing stations could be realized in ICES SD 29 and none in SD 32. SURVEY DESIGN AND HYDROGRAPHICAL DATA During the cruise, echo-integration was performed along the survey track from ICES Sub-Divisions 29N, 30, and 32N. A dual system SeaBird CTD instrument was used with state-of-the-art sensors for salinity, temperature, oxygen, connectivity and distance to seabed. 372 ICES | WGBIFS 2019 CALIBRATION The SIMRAD EK60 echo sounder with all transducers was calibrated on 29.9.2018, according to the IBAS manual (ICES 2017). Values from the calibration were within required accuracy. ACOUSTIC DATA COLLECTION The acoustic sampling was performed around the clock. SIMRAD EK60 echo sounder with the 38 kHz hull mounted transducer (ES38B) was used for the acoustic data collection. The settings of the hydroacoustic equipment were as described in the IBAS manual (ICES 2017). The post processing of the stored raw data was done using the Echoview software (www.echoview.com). The mean volume back scattering values (Sv) were integrated over 1 nautical mile elementary distance sampling units (ESDUs) from 10 m below the surface to the bottom at 10 m intervals. DATA ANALYSIS The pelagic target species sprat and herring are usually distributed in mixed layers in combination with other species so that it is impossible to allocate the integrator readings to a single species. Therefore the species composition was based on the trawl catch results. For each rectangle the species composition and length distribution were determined as the unweighted mean of all trawl results in this rectangle. In the case of lack of sample hauls within an individual ICES rectangle (due to gear problems, bad weather conditions or other limitations) a mean from hauls from neighboring rectangles was used. From these distributions the mean acoustic cross-section was calculated according to the target strength-length (TS) relationships found below. Clupeoids: TS = 20 log L (cm) - 71.2 (ICES 1983/H:12) Gadoids: TS = 20 log L (cm) - 67.5 (Foote et al. 1986) Salmonids and 3-spined stickleback were assumed to have the same acoustic properties as herring. The total number of fish (total N) in one rectangle was estimated as the product of the mean area scattering cross section sA and the rectangle area, divided by the corresponding mean cross section δ (sigma). The total number was separated into different fish species according to the mean catch composition in the rectangle. ICES | WGBIFS 2019 373 PERSONNEL Cruise leader during the survey was Juha Lilja from Natural Resources Institute Finland (Luke). The acoustic measurements were performed by Natural Resources Institute Finland (Luke) and fish sampling together by Luke and Swedish University of Agricultural Sciences (SLU). The participating scientific crew can be seen in the list below. Juha Lilja Luke Cruise Leader, Acoustics Panu Hänninen SYKE CTD Jukka Pönni Luke Fish sampling Arto Koskinen Luke Fish sampling Hannu Harjunpää Luke Fish sampling Meri Helisevä Luke Fish sampling Velimatti Leinonen Luke Fish sampling Mikko Leminen Luke Fish sampling Timo Myllylä Luke Fish sampling Mikko Olin Luke Fish sampling Jari Raitaniemi Luke Fish sampling Per Andersson SLU Fish sampling Rickard Yngwe SLU Fish sampling Sami Vesala Luke Fish sampling, Trawling Pasi Ala-opas Luke Trawling Markku Gavrilov Luke Trawling Pentti Kananen Luke Trawling Otto Kiukkonen Private specialist Trawling, equipment maintenance Kimmo Kirstua Private specialist Trawling, equipment maintenance Peter Koskinen Private specialist Trawling, equipment maintenance Konsta Isometsä Luke Acoustics Erkki Jaala Luke Acoustics Perttu Rantanen Luke Database maintenance Petri Sarvamaa Luke Database maintenance Luke: Luonnonvarakeskus / Natural Resources Institute Finland SLU: Sveriges lantbruksuniversitet / Swedish University of Agricultural Sciences SYKE: Suomen ympäristökeskus / Finnish Environment Institute 374 ICES | WGBIFS 2019 RESULTS FISH CATCHES, BIOLOGICAL AND HYDRO-METEOROLOGICAL DATA The number of planned trawling stations was 49. From these, 31 trawling stations were accomplished, and from those 30 were counted as “valid” (technically sound hauls and sufficient catch for a sample) (Table 1). The total number of trawling stations in Bothnian Sea (ICES SD 30) was 27 and 3 in northern Baltic proper (SD 29) .The northern Gulf of Finland (SD 32) remained without trawl samples due to storm in the beginning of the journey and gear damage on the way back. Several trawling stations in SD 29 were also skipped due to same reasons. The 5395 kg combined catches (Table 1) consisted of 16 fish species (5309 kg) and mostly unidentified organic matter categorized as “waste” (86 kg), but also including large number of mysids and small amounts of the isopod Saduria entomon. The most common and abundant species were herring (Clupea harengus) (4008 kg), three-spined stickleback (Gasterosteus aculeatus) (1142 kg) and sprat (Sprattus sprattus) (144 kg). All observed species are presented in Table 2. From the sub-samples of the 30 fish catches a total of 13493 measurements for species- specific length distributions (0,5 cm interval for herring and sprat, and 1 cm interval for other species) were performed according to Table 3. Ten individual samples per statistical rectangle for age determination and maturity definitions by length-class were collected from herring and sprat, 3346 and 849 samples respectively (Table 4). The mean weights for each length-class were also derived from these individual fish samples. In addition from SD 30, 8 samples of 15 herring individuals to Finnish National Institute for health and Welfare (THL) for investigation of environmental toxins, 3 samples of 150 herring individuals for analysis of environmental toxins to Naturhistoriska Riksmuséet (NRM) of Sweden, 14 DNA- samples of 50 herring to check the spawning period of Bothnian Sea herring in comparison to other Baltic herring stocks for SLU and University of Uppsala and 1 sample of 20 kg herring for Swedish National Food Agency (NFA) to analyse the dioxin contents were collected and frozen. Hydrographical data: temperature (°C), oxygen concentration (ml/l), salinity (psu), sound speed (m/s), oxygen concentration (% saturation), conductivity (mS/cm) and sound speed (m/s) were measured and results are shown in Figures 5 and 6. Total of 32 CTD casts were done during the entire cruise. Here only a part of the CTD casts is presented. ABUNDANCE ESTIMATES The total area covered by the Finnish BIAS survey was 16519 square nautical miles (nmi2), 22 rectangles, and after the scrutinizing, the distance used for acoustic estimates was 1654 nautical miles (nmi). The cruise track and positions of trawl hauls are shown in Figure 1. In Figure 2, the abundance of herring and sprat per age groups are shown according to the ICES Sub-divisions during Finnish BIAS surveys 2017 and 2018. Length distributions for herring and sprat by ICES subdivision in 2018 are shown in Figure 3 and herring length distributions in SD 30 in years 2014- 2018 in Figure 4. The total abundance of herring and sprat is presented in Table 6. Estimated numbers of herring and sprat by age group and Subdivision/rectangle are given in Table 7 and Table 10, respectively. Corresponding mean weights by age group and Subdivision/rectangle are shown in Table 8 and Table 11, respectively. Estimates of herring and sprat biomass by age group and Subdivision/rectangle are summarized in Table 9 and Table 12, respectively. ICES | WGBIFS 2019 375 REFERENCES Foote, K.G., Aglen, A. and Nakken, O. 1986. Measurement of fish target strength with a split-beam echosounder. J. Acoust. Soc. Am. 80(2):612-621. Grygiel, W., O. Kaljuste, A. Grelowski and J. Pönni 2007. Research report from the Estonian- Finnish-Polish BIAS type survey in the north-eastern Baltic (October 2006). Working paper on the WGBIFS meeting in Rostock, 26-30.03.2007; 23 pp., [in:] ICES CM 2007/LRC:06, Ref. ACFM. Håkansson, N., Kollberg, S., Falk, U., Götze, E. and Rechlin, O. 1979. A hydroacoustic and trawl survey of herring and sprat stocks of the Baltic proper in October 1978. Fischerei-Forschung, Wissenschaftliche Schriftenreihe 17(2):7-2. ICES 1983. Report of the Planning Group on ICES coordinated herring and sprat acoustic surveys. ICES C.M. 1983/H:12. ICES 2017. Manual for the International Baltic Acoustic Surveys (IBAS), Version 2.0. Series of ICES Survey Protocols, SISP 8 – IBAS. 376 ICES | WGBIFS 2019 TABLES, MAP, AND FIGURES Table 1. Trawl catches (kg) by species/category during the Finnish BIAS-survey in 2018. H au l n u m . H au l n am e IC ES S D A m m o d yt e s to b ia n u s C lu p e a h ar e n gu s C o re go n u s la va re tu s C yc lo p te ru s lu m p u s G as te ro st e u s ac u le at u s H yp e ro p lu s la n ce o la tu s La m p e tr a fl u vi at ili s Li p ar is li p ar is N e ro p h is o p h id io n O sm e ru s e p e rl an u s P o m at o sc h is tu s m ic ro p s P u n gi ti u s p u n gi ti u s Sa d u ri a e n to m o n Sa lm o s al ar Sp ra tt u s sp ra tt u s Ta u ru lu s b u b al is "W as te " Fi sh c at ch ( kg ) C at ch t o ta l ( kg ) 1 49G9-1 29 137.96 10.21 0.04 0.01 0.01 9.95 6.82 158.17 165.00 2 50G8-1 30 28.97 28.72 0.003 0.01 0.00 2.61 7.38 60.32 67.70 3 50G7-1 30 100.34 21.41 0.03 0.001 4.22 126.00 126.00 4 51G7-1 30 109.24 29.41 0.01 0.00 0.34 3.00 139.00 142.00 5 51G8-1 30 85.64 111.54 0.004 1.65 1.17 198.84 200.00 6 51G9-1 30 4.62 150.81 0.27 3.15 158.86 158.86 7 52G7-1 30 178.44 32.24 0.32 210.68 211.00 8 52G8-1 30 0.018 266.66 14.79 0.70 1.84 282.17 284.00 9 52G9-1 30 268.20 13.54 0.001 10.22 3.04 291.97 295.00 10 53G9-1 30 0.003 48.02 5.57 0.01 0.01 0.00 5.21 1.18 58.82 60.00 11 53G8-1 30 172.81 49.67 0.04 0.02 7.47 222.54 230.00 12 53G8-2 30 83.71 11.80 0.18 0.00 0.32 95.68 96.00 13 53G9-2 30 162.79 9.01 0.02 0.001 0.00 2.29 0.89 174.10 175.00 14 54G8-1 30 182.89 1.37 0.001 9.74 184.26 194.00 15 55G9-1 30 262.84 6.90 0.01 0.26 0.98 270.02 271.00 17 55H0-2 30 97.21 0.08 1.62 0.02 0.002 8.67 0.12 11.60 0.003 0.69 119.19 120.00 18 54G9-1 30 256.40 0.71 0.04 0.06 5.80 257.14 263.00 19 54H0-1 30 115.86 6.29 4.35 0.00 8.63 0.86 135.14 136.00 20 53H0-1 30 68.26 3.25 0.04 0.00 5.67 3.78 77.22 81.00 21 53H0-2 30 250.94 4.85 0.01 0.001 0.01 8.09 1.10 263.89 265.00 22 52G9-2 30 234.47 46.78 0.10 0.00 3.74 7.91 285.08 293.00 23 52H0-1 30 30.89 20.82 0.02 0.34 51.73 52.07 24 52H0-2 30 0.029 167.67 9.42 0.01 0.00 0.79 0.09 177.91 178.00 25 51G9-2 30 0.022 217.16 6.02 0.12 0.001 0.00 0.23 8.44 223.56 232.00 26 51H0-1 30 192.84 38.06 0.00 0.37 8.73 231.27 240.00 27 51H0-2 30 101.10 133.25 0.07 0.00 20.27 2.31 254.68 257.00 28 50H0-1 30 0.001 79.61 259.77 0.02 0.00 12.10 1.49 351.51 353.00 29 50G9-1 30 0.049 35.08 69.97 0.05 0.00 0.26 0.59 105.41 106.00 30 48G9-1 29 0.013 67.52 0.17 44.61 0.001 0.03 0.002 0.02 0.18 31.45 143.98 144.00 0.135 4008.12 0.08 0.17 1142.41 0.06 0.10 0.57 0.016 13.18 0.002 0.02 0.24 0.46 143.79 0.003 86.27 5309.12 5395.62Total (kg) ICES | WGBIFS 2019 377 Table 2. English, scientific, and Finnish names of observed species in Finnish 2018 BIAS-survey. Fishnames English Scientific Finnish Striped Seasnail Liparis liparis Imukala Greater Sandeel Hyperoplus lanceolatus Isotuulenkala Saduria entomon Saduria entomon Kilkki Sprat Sprattus sprattus Kilohaili Three-spined Stickleback Gasterosteus aculeatus Kolmipiikki Smelt Osmerus eperlanus Kuore Nine-spined Stickleback Pungitius pungitius Kymmenpiikki Common Goby Pomatoschistus microps Liejutokko Atlantic Salmon Salmo salar Lohi Lamprey Lampetra fluviatilis Nahkiainen Longspined Bullhead Taurulus bubalis Piikkisimppu Small Sandeel Ammodytes tobianus Pikkutuulenkala Lumpsucker Cyclopterus lumpus Rasvakala Whitefish Coregonus lavaretus Siika Baltic Herring Clupea harengus membras Silakka Straightnose Pipefish Nerophis ophidion Siloneula Table 3. Number of length measurements /species and Sub-Division in Finnish 2018 BIAS-survey. Species ICES SD Total 29 30 Liparis liparis 24 24 Hyperoplus lanceolatus 5 5 Sprattus sprattus 366 1640 2006 Gasterosteus aculeatus 187 1745 1932 Osmerus eperlanus 3 138 141 Pungitius pungitius 2 4 6 Pomatoschistus microps 2 2 Salmo salar 1 1 2 Lampetra fluviatilis 3 3 Ammodytes tobianus 1 10 11 Cyclopterus lumpus 2 2 Coregonus lavaretus 2 2 Clupea harengus membras 673 8668 9341 Nerophis ophidion 3 13 16 Total 1240 12253 13493 378 ICES | WGBIFS 2019 Table 4. Individual samples of herring and sprat (for age determination) per SD. L-class Sprat Herring 29 30 Sprat Total 29 30 Herring Total 40 1 1 50 1 1 55 1 1 60 2 2 65 6 6 70 4 1 5 6 10 16 75 7 2 9 6 20 26 80 6 6 6 35 41 85 4 1 5 6 39 45 90 1 1 2 5 44 49 95 3 2 5 3 38 41 100 14 12 26 2 29 31 105 20 36 56 2 30 32 110 20 72 92 2 43 45 115 20 84 104 2 67 69 120 20 109 129 7 80 87 125 20 118 138 20 113 133 130 15 112 127 20 137 157 135 2 90 92 20 142 162 140 51 51 20 159 179 145 18 18 20 167 187 150 5 5 20 183 203 155 20 187 207 160 20 185 205 165 20 190 210 170 19 190 209 175 13 180 193 180 4 173 177 185 4 143 147 190 2 111 113 195 3 100 103 200 83 83 205 1 52 53 210 39 39 215 27 27 220 10 10 225 8 8 230 2 2 235 1 1 240 1 1 245 2 2 250 1 1 255 1 1 265 1 1 Total 156 714 870 273 3034 3307 ICES | WGBIFS 2019 379 Table 5. Numbers and locations of fishing stations (WGS-84) during Finnish BIAS-survey in 2018. H au l n ro H au l n am e D at e IC ES S D St ar t la ti tu d e St ar t lo n gi tu d e En d la ti tu d e En d lo n gi tu d e H au l d u ar at io n ( m in ) H au l s p ee d ( kn o t) H au l d is ta n ce ( n m i) C at ch ( kg ) Sa m p le w ei gh t (k g) H ea d ro p e d ep th ( m ) B o tt o m d ep th ( m ) D o o rs s p re ad ( m ) Tr aw l h ei gh t (m ) 1 49G9-1 30.09.2018 29 600173N 193090E 595775N 193038E 118 3 5.9 165 34.06 50 150 104 18 2 50G8-1 01.10.2018 30 603967N 185562E 603705N 185498E 51 3 2.55 67.7 22.07 15 85 80.4 18 3 50G7-1 01.10.2018 30 604887N 174843E 604685N 175845E 57 2.5 2.38 126 17.36 23 50 56 18 4 51G7-1 02.10.2018 30 610603N 175190E 610608N 175629E 44 3 2.2 142 33.66 10 65 65 18 5 51G8-1 02.10.2018 30 610620N 184740E 610697N 185070E 35 2.8 1.63 200 49.9 7 68 64.5 20 6 51G9-1 02.10.2018 30 610720N 190826E 611126N 190876E 84 3 4.2 159 159 15 65 65 18 7 52G7-1 02.10.2018 30 613826N 174954E 613823N 175551E 60 2.8 2.8 211 46.5 8 65 66 20 8 52G8-1 03.10.2018 30 613737N 182069E 613460N 182083E 60 3 3 284 52.9 7 50 64.3 20 9 52G9-1 03.10.2018 30 614117N 190609E 614392N 190669E 60 3 3 295 54 11 68 64.1 23 10 53G9-1 03.10.2018 30 620105N 191641E 615640N 190890E 123 2.5 5.13 60 43 18 70 69.4 20 11 53G8-1 03.10.2018 30 620366N 180808E 620500N 181141E 45 2.9 2.18 230 47.64 11 80 63.7 20 12 53G8-2 04.10.2018 30 620978N 183356E 621266N 183461E 60 3 3 96 24.5 10 93 69 20 13 53G9-2 04.10.2018 30 622017N 191305E 622361N 191584E 80 3.2 4.27 175 50.7 15 107 64 20 14 54G8-1 04.10.2018 30 623525N 184953E 623525N 185694E 67 2.6 2.9 194 36.08 75 180 100 15 15 55G9-1 04.10.2018 30 630326N 190327E 630524N 191505E 60 3.3 3.3 271 50.94 10 160 64 20 16 55H0-1(INV) 05.10.2018 30 631423N 201729E 631215N 201462E 52 3 2.6 0 18 75 98 ? 17 55H0-2 05.10.2018 30 631160N 201169E 631311N 200624E 64 2.8 2.99 120 50.16 10 77 68 20 18 54G9-1 05.10.2018 30 623836N 193285E 623942N 192774E 66 2.8 3.08 263 39.1 75 130 104 15 19 54H0-1 05.10.2018 30 623608N 201619E 623474N 201373E 44 2.5 1.83 136 39.66 18 80 64 18 20 53H0-1 06.10.2018 30 622667N 201188E 622554N 200687E 60 2.7 2.7 81 29.16 20 100 70 20 21 53H0-2 06.10.2018 30 620699N 201855E 620469N 200988E 105 3 5.25 265 51 10 125 61.2 22 22 52G9-2 06.10.2018 30 615854N 194924E 615651N 194132E 47 2.7 2.11 293 46.48 8 85 65.8 20 23 52H0-1 07.10.2018 30 614862N 200311E 614467N 200483E 74 3.2 3.95 54 54 15 118 77 20 24 52H0-2 07.10.2018 30 615090N 202546E 615489N 202098E 90 3 4.5 178 51.5 15 105 68 20 25 51G9-2 07.10.2018 30 612204N 195393E 612429N 194929E 76 2.5 3.17 232 41.48 80 110 96.3 20 26 51H0-1 07.10.2018 30 612014N 201217E 611978N 201726E 60 2.5 2.5 240 45.98 10 125 66.5 22 27 51H0-2 08.10.2018 30 611518N 204410E 611297N 204357E 55 2.5 2.29 257 54.12 10 80 63 20 28 50H0-1 08.10.2018 30 605726N 201232E 605578N 200920E 52 2.6 2.25 353 60.74 10 90 63 20 29 50G9-1 08.10.2018 30 604648N 193650E 604483N 193647E 44 2.8 2.05 106 45.16 9 79 66.3 20 30 48G9-1 09.10.2018 29 595855N 191427E 595721N 191133E 44 2.8 2.05 144 50.03 10 121 65 20 31 48H2-1(INV) 10.10.2018 29 593388N 225820E 593360N 225613E 20 2.8 0.93 37 30 70 ? 380 ICES | WGBIFS 2019 Table 6. Survey statistics by area r/v Aranda in 2018. ICES ICES N Area Sa  N total Herring Sprat Cod 3-spinn. SD Rect. NM (million/nm²) (nm²) (m²/nm²) (cm²) (million) (%) (%) (%) (%) 48G9 29 66 11.0702 772.8 488.936 0.4416706 8555 8.74 6.50 0.00 84.74 49G9 29 75 3.11671 564.2 411.528 1.320391 1758 53.04 7.76 0.00 39.17 50G7 30 28 6.47108 403.1 497.363 0.7685943 2608 38.37 0.33 0.00 61.29 50G8 30 63 10.1289 833.4 503.912 0.4974978 8441 31.87 1.26 0.00 66.84 50G9 30 70 10.2243 879.5 412.434 0.4033852 8992 3.41 0.04 0.00 96.54 50H0 30 53 15.4379 795.1 659.793 0.4273842 12275 3.30 0.66 0.00 96.04 51G7 30 28 7.50025 614.5 659.606 0.8794451 4609 21.04 0.25 0.00 78.71 51G8 30 57 13.6208 863.7 708.411 0.5200938 11764 12.74 0.17 0.00 87.09 51G9 30 78 2.38904 865.8 295.364 1.2363284 2068 11.09 0.33 0.00 88.57 51H0 30 57 3.88623 865.7 304.675 0.7839878 3364 14.38 2.23 0.00 83.39 52G7 30 23 3.42927 482.6 398.875 1.1631477 1655 30.77 0.00 0.00 69.23 52G8 30 62 3.32223 852 580.548 1.7474654 2831 58.19 0.43 0.00 41.38 52G9 30 73 2.92436 852 353.065 1.2073215 2492 31.13 1.63 0.00 67.24 52H0 30 75 3.82982 852 350.095 0.9141296 3263 36.70 0.28 0.00 63.00 53G8 30 61 3.53901 838.1 354.268 1.0010347 2966 21.13 0.00 0.00 78.84 53G9 30 64 2.86282 838.1 375.526 1.3117371 2399 62.71 2.98 0.00 34.28 53H0 30 87 1.79535 838.1 310.989 1.7321865 1505 71.42 5.42 0.00 23.14 54G8 30 29 1.07239 642.2 273.097 2.5466156 689 91.71 0.00 0.00 8.28 54G9 30 72 1.11124 824.2 281.441 2.5326702 916 97.27 0.00 0.00 2.72 54H0 30 35 3.68667 727.9 409.955 1.1119923 2684 59.71 4.43 0.00 33.86 55G9 30 31 1.44731 625.6 279.85 1.9335861 905 74.57 0.16 0.00 25.26 55H0 30 27 2.25631 688.6 326.239 1.4458975 1554 57.07 13.11 0.00 16.31 ICES | WGBIFS 2019 381 Table 7. Numbers (millions) of herring by age and area (r/v Aranda 2018). SD Rect 0 1 2 3 4 5 6 7 8+ Total 29 48G9 172.18 225.06 130.36 57.20 86.86 17.81 22.86 11.27 24.14 747.73 29 49G9 98.58 186.92 234.44 113.00 158.33 38.69 40.57 20.39 41.79 932.71 30 50G7 477.64 251.02 124.56 46.76 47.41 13.00 10.12 5.49 25.00 1000.99 30 50G8 2634.81 27.78 14.81 6.02 4.12 0.79 0.98 0.28 0.33 2689.93 30 50G9 4.31 58.87 97.29 42.53 47.89 14.57 12.24 6.74 22.36 306.80 30 50H0 98.51 113.36 92.54 33.33 33.99 8.98 7.58 4.19 12.75 405.25 30 51G7 31.78 78.01 253.95 144.67 172.75 53.84 48.97 35.20 150.61 969.78 30 51G8 73.64 54.15 388.55 272.51 360.74 112.73 90.62 42.04 103.23 1498.20 30 51G9 4.40 26.70 60.48 34.94 49.86 15.44 12.59 6.27 18.79 229.46 30 51H0 96.09 91.41 100.19 45.29 61.57 19.99 16.43 10.64 42.13 483.75 30 52G7 3.99 6.92 101.83 91.99 145.98 47.95 37.39 19.01 54.24 509.30 30 52G8 36.55 57.53 443.11 313.40 399.50 118.56 89.39 41.95 147.23 1647.22 30 52G9 56.92 72.18 164.34 111.63 163.16 53.37 43.12 24.93 86.01 775.68 30 52H0 195.61 476.58 257.01 92.89 95.13 25.85 21.08 9.73 23.80 1197.68 30 53G8 1.58 13.98 126.16 95.67 149.68 49.83 40.95 28.19 120.83 626.86 30 53G9 458.28 298.96 265.64 137.15 175.02 53.28 42.72 20.19 53.47 1504.72 30 53H0 121.53 273.49 219.40 112.36 145.28 46.86 40.75 23.25 91.70 1074.62 30 54G8 0.52 26.51 163.79 115.57 159.87 50.52 38.96 18.79 57.04 631.57 30 54G9 3.30 93.47 272.67 153.83 190.04 56.23 43.67 20.69 56.94 890.84 30 54H0 727.06 488.75 144.17 48.75 70.95 24.28 19.60 14.38 64.46 1602.41 30 55G9 61.73 60.24 190.87 104.22 117.66 34.57 29.91 16.41 59.59 675.20 30 55H0 294.36 200.62 161.84 71.98 72.54 19.56 18.47 10.73 36.64 886.73 382 ICES | WGBIFS 2019 Table 8. Mean weight (g) of herring by age and area (r/v Aranda 2018). SD Rect. 0 1 2 3 4 5 6 7 8+ 29 48G9 3.84 13.92 18.71 22.12 22.05 23.31 27.05 26.89 29.89 29 49G9 3.58 14.26 19.25 21.88 21.93 23.84 25.78 24.20 32.94 30 50G7 5.77 13.41 21.09 25.14 27.49 29.51 30.46 36.74 50.82 30 50G8 4.61 12.40 20.24 24.79 25.63 26.28 26.39 26.58 26.61 30 50G9 7.31 16.33 22.32 25.52 28.34 30.46 31.60 36.32 43.05 30 50H0 5.60 15.39 21.37 24.87 27.75 29.49 30.68 35.53 43.39 30 51G7 7.71 14.89 23.62 26.06 28.75 31.52 32.91 39.62 46.51 30 51G8 4.86 17.65 24.34 26.76 29.05 30.29 30.78 33.45 36.92 30 51G9 6.04 16.28 23.37 26.47 29.52 30.99 31.70 34.46 39.91 30 51H0 5.03 15.64 22.12 25.94 29.32 31.50 33.14 38.48 45.05 30 52G7 4.94 18.29 25.38 27.56 29.87 30.84 31.40 34.79 40.22 30 52G8 6.77 16.27 24.52 26.65 28.66 29.99 30.21 34.56 46.29 30 52G9 5.65 15.70 23.98 26.88 29.58 31.20 32.46 37.06 42.43 30 52H0 6.70 14.55 21.35 25.12 27.62 29.20 29.91 32.72 38.21 30 53G8 8.19 17.12 24.68 27.12 29.88 31.66 33.28 39.26 47.51 30 53G9 5.03 14.93 22.62 26.17 28.93 30.55 31.09 34.06 37.43 30 53H0 6.42 14.51 22.57 26.15 29.08 31.25 32.60 37.63 45.27 30 54G8 14.17 17.02 24.40 26.82 29.16 30.51 31.11 34.56 41.49 30 54G9 12.54 16.38 23.46 26.14 28.62 30.09 30.57 34.03 43.16 30 54H0 5.22 14.16 20.11 26.03 29.52 31.22 33.64 38.89 50.91 30 55G9 5.29 16.13 23.38 25.86 28.32 30.45 31.60 37.08 44.18 30 55H0 5.18 14.25 22.17 25.35 27.80 30.00 31.13 37.02 42.87 ICES | WGBIFS 2019 383 Table 9. Total biomass (ton) of herring by age and area (r/v Aranda 2018). SD Rect. 0 1 2 3 4 5 6 7 8+ Total 29 48G9 660.4 3133.3 2439.2 1265.5 1915.3 415.0 618.5 303.0 721.8 11471.9 29 49G9 352.8 2664.6 4511.9 2472.0 3472.9 922.3 1045.9 493.5 1376.4 17312.4 30 50G7 2755.1 3366.2 2626.7 1175.6 1303.1 383.6 308.2 201.7 1270.7 13390.9 30 50G8 12142.1 344.6 299.9 149.2 105.6 20.9 25.9 7.4 8.7 13104.2 30 50G9 31.5 961.6 2171.7 1085.4 1357.3 443.8 386.9 244.7 962.5 7645.4 30 50H0 551.6 1744.4 1977.2 829.1 943.2 264.9 232.5 149.0 553.2 7245.2 30 51G7 244.9 1161.8 5999.0 3770.0 4966.5 1697.0 1611.7 1394.6 7004.5 27850.1 30 51G8 357.6 955.7 9457.3 7292.1 10478.5 3414.6 2789.4 1406.2 3811.2 39962.6 30 51G9 26.5 434.8 1413.5 924.8 1471.5 478.3 399.2 215.9 749.7 6114.3 30 51H0 482.9 1429.7 2216.2 1175.1 1805.5 629.6 544.3 409.5 1898.2 10591.0 30 52G7 19.7 126.6 2584.0 2535.7 4359.9 1478.9 1174.1 661.2 2181.4 15121.5 30 52G8 247.5 935.8 10864.1 8351.4 11449.4 3555.9 2700.9 1449.8 6814.7 46369.5 30 52G9 321.4 1133.5 3941.6 3000.2 4826.9 1665.3 1399.8 924.1 3649.0 20861.9 30 52H0 1311.2 6932.7 5487.5 2333.7 2627.4 754.9 630.3 318.4 909.5 21305.5 30 53G8 12.9 239.3 3114.0 2594.7 4472.3 1577.4 1362.9 1106.7 5740.5 20220.6 30 53G9 2306.6 4462.4 6009.6 3588.7 5063.3 1628.1 1327.9 687.8 2001.2 27075.6 30 53H0 779.7 3967.6 4952.8 2937.6 4224.7 1464.6 1328.5 874.8 4151.7 24682.0 30 54G8 7.4 451.2 3996.1 3100.0 4662.0 1541.7 1212.2 649.2 2366.5 17986.2 30 54G9 41.4 1530.6 6396.3 4021.3 5439.2 1692.1 1335.0 704.3 2457.3 23617.4 30 54H0 3791.9 6919.4 2899.6 1269.1 2094.7 758.1 659.3 559.1 3281.9 22233.1 30 55G9 326.4 971.5 4463.0 2694.8 3331.8 1052.8 944.9 608.5 2632.3 17026.1 30 55H0 1525.8 2859.6 3587.9 1824.7 2016.5 586.7 575.0 397.4 1570.9 14944.5 384 ICES | WGBIFS 2019 Table 10. Numbers (millions) of sprat by age and area (r/v Aranda 2018). SD Rect 0 1 2 3 4 5 6 7 8+ Total 29 48G9 54.53 166.73 41.27 25.86 142.43 108.35 7.51 8.35 1.21 556.26 29 49G9 18.58 35.28 9.15 5.54 33.73 27.48 2.46 3.15 1.07 136.43 30 50G7 0.00 1.55 0.91 0.45 1.25 3.52 0.19 0.20 0.58 8.65 30 50G8 6.74 27.00 9.62 4.32 12.83 37.75 1.88 2.21 4.08 106.44 30 50G9 0.00 0.01 0.19 0.16 0.64 1.97 0.12 0.24 0.46 3.78 30 50H0 0.00 6.54 6.05 3.83 12.64 37.81 2.56 3.85 7.41 80.69 30 51G7 0.00 1.81 1.02 0.64 1.88 5.45 0.08 0.15 0.36 11.40 30 51G8 0.65 0.97 1.55 0.89 2.93 9.18 0.73 1.10 2.23 20.22 30 51G9 0.00 0.63 0.60 0.36 1.09 3.19 0.19 0.26 0.50 6.81 30 51H0 0.00 3.61 4.93 3.46 12.30 36.63 2.28 3.76 7.98 74.95 30 52G7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 30 52G8 0.00 0.94 0.53 0.42 1.41 4.92 0.57 0.95 2.37 12.11 30 52G9 0.00 1.02 1.47 1.38 5.73 19.35 1.95 3.40 6.24 40.54 30 52H0 0.00 0.36 0.75 0.54 1.58 4.84 0.23 0.34 0.57 9.21 30 53G8 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 30 53G9 0.00 3.71 4.57 3.20 10.75 33.42 2.70 4.34 8.82 71.51 30 53H0 0.00 4.62 5.65 3.89 12.70 38.94 2.76 4.34 8.65 81.56 30 54G8 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 30 54G9 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 30 54H0 0.00 7.13 6.09 4.76 17.78 56.24 4.24 7.27 15.25 118.75 30 55G9 0.00 0.00 0.05 0.05 0.28 0.83 0.05 0.09 0.13 1.47 30 55H0 0.00 43.51 21.61 10.88 28.48 82.64 3.82 3.86 8.91 203.71 ICES | WGBIFS 2019 385 Table 11. Mean weight (g) of sprat by age and area (r/v Aranda 2018). C Rect. 0 1 2 3 4 5 6 7 8+ 29 48G9 3.47 8.54 9.83 9.88 10.30 10.62 12.13 11.45 12.60 29 49G9 3.02 8.41 9.98 9.99 10.59 10.86 12.14 11.97 13.32 30 50G7 9.26 11.52 12.34 12.41 12.64 13.27 14.69 15.98 30 50G8 3.10 9.61 10.84 12.15 12.40 12.50 13.18 14.35 14.13 30 50G9 12.15 12.71 12.88 13.36 13.50 14.87 14.98 15.19 30 50H0 10.32 11.89 12.66 12.89 13.17 14.07 14.79 14.92 30 51G7 10.28 11.79 12.28 12.51 12.46 11.53 13.05 12.97 30 51G8 5.00 8.88 10.89 12.85 13.29 13.44 14.19 14.64 15.22 30 51G9 9.92 11.88 12.52 12.78 12.98 13.80 14.65 14.79 30 51H0 10.06 12.10 12.81 13.06 13.29 14.20 14.70 15.18 30 52G7 30 52G8 10.37 11.73 13.38 13.56 13.92 14.62 15.14 15.82 30 52G9 10.02 12.56 13.34 13.70 13.93 14.86 15.04 15.29 30 52H0 10.28 12.31 12.61 13.01 13.04 13.89 14.19 14.12 30 53G8 30 53G9 10.26 11.99 12.92 13.10 13.46 14.39 14.96 15.24 30 53H0 9.71 12.06 12.80 13.05 13.32 14.28 14.83 15.14 30 54G8 30 54G9 30 54H0 9.96 12.12 13.05 13.32 13.53 14.48 14.77 15.30 30 55G9 13.37 13.33 13.55 13.56 14.15 13.90 13.77 30 55H0 9.75 11.50 12.17 12.31 12.42 13.06 14.56 15.06 386 ICES | WGBIFS 2019 Table 12. Total biomass (ton) of sprat by age and area (r/v Aranda 2018). SD Rect. 0 1 2 3 4 5 6 7 8+ Total 29 48G9 189.24 1423.09 405.72 255.38 1466.35 1151.12 91.11 95.61 15.27 5092.89 29 49G9 56.14 296.77 91.32 55.34 357.16 298.51 29.82 37.71 14.22 1236.98 30 50G7 0.00 14.35 10.47 5.56 15.56 44.43 2.48 2.96 9.25 105.07 30 50G8 20.88 259.54 104.30 52.55 159.18 471.81 24.76 31.76 57.69 1182.47 30 50G9 0.00 0.06 2.36 2.06 8.59 26.56 1.81 3.56 7.05 52.05 30 50H0 0.00 67.46 71.92 48.56 163.00 498.08 36.07 56.97 110.51 1052.57 30 51G7 0.00 18.60 12.01 7.88 23.55 67.92 0.98 1.96 4.72 137.64 30 51G8 3.26 8.61 16.90 11.39 38.97 123.34 10.33 16.03 33.90 262.74 30 51G9 0.00 6.28 7.10 4.50 13.86 41.44 2.61 3.80 7.36 86.94 30 51H0 0.00 36.28 59.70 44.37 160.62 486.79 32.33 55.28 121.13 996.51 30 52G7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 30 52G8 0.00 9.74 6.18 5.56 19.14 68.51 8.31 14.40 37.49 169.34 30 52G9 0.00 10.26 18.44 18.38 78.53 269.58 29.01 51.22 95.40 570.82 30 52H0 0.00 3.70 9.23 6.86 20.57 63.14 3.15 4.84 8.02 119.49 30 53G8 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 30 53G9 0.00 38.12 54.87 41.34 140.82 449.97 38.88 64.89 134.42 963.31 30 53H0 0.00 44.81 68.17 49.81 165.79 518.93 39.39 64.42 130.97 1082.29 30 54G8 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 30 54G9 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 30 54H0 0.00 70.98 73.78 62.15 236.76 760.62 61.40 107.37 233.35 1606.41 30 55G9 0.00 0.00 0.61 0.69 3.80 11.24 0.66 1.19 1.81 19.99 30 55H0 0.00 424.32 248.49 132.44 350.63 1026.23 49.89 56.21 134.23 2422.45 ICES | WGBIFS 2019 387 Figure 1. Cruise track and trawl stations of r/v Dana during the Finnish BIAS-survey in 2018. Figure 2. Abundance of herring and sprat per age groups according to the ICES Sub-divisions in Finnish BIAS surveys 2017 and 2018. 388 ICES | WGBIFS 2019 Figure 3. Proportional length distributions of measured herring and sprat in Sub-Divisions 29 and 30. 0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 4 0 6 0 7 5 9 0 1 0 5 1 2 0 1 3 5 1 5 0 1 6 5 1 8 0 1 9 5 2 1 0 2 2 5 2 4 0 2 5 5 P ro p o rt io n Length (mm) Herring 2018 SD 29 SD 30 0 0,05 0,1 0,15 0,2 0,25 0,3 4 0 5 0 5 5 6 0 6 5 7 0 7 5 8 0 8 5 9 0 9 5 1 0 0 1 0 5 1 1 0 1 1 5 1 2 0 1 2 5 P ro p o rt io n Length (mm) Sprat 2018 SD 29 SD 30 ICES | WGBIFS 2019 389 Figure 4. Length distributions of herring from acoustic surveys in Sub-Division 30 in years 2014- 2018 390 ICES | WGBIFS 2019 Figire 5. Map of the CTD stations (blue dots) during the Finnish BIAS-survey in 2018. ICES | WGBIFS 2019 391 Figure 6. Vertical distribution of the sound velocity, conductivity, water temperature, salinity, and oxygen concentration in three stations (in purple and red in SD30, and green in SD29). 392 ICES | WGBIFS 2019 Baltic International Acoustic Survey Report for R/V Dana Survey 2018-10-02 - 2018-10-14 Niklas Larson SLU - Institute of Marine Research, Lysekil, Sweden 1 ICES | WGBIFS 2019 393 Contents 1 Introduction 3 2 Methods 4 2.1 Narrative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2 Survey design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.3 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.4 Acoustic data collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.5 Data analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.6 Hydrographic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.7 Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 Results 5 3.1 Biological data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2 Acoustic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.3 Abundance estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4 Discussion 6 5 References 7 6 Tables, map and figures 8 2 394 ICES | WGBIFS 2019 1 Introduction International hydroacoustic surveys have been conducted in the Baltic Sea since 1978. The starting point was the cooperation between Institute of Marine Research (IMR) in Lysekil, Sweden and the Institute fu¨r Hochseefisherei und Fishverarbeitung in Rostock, German Democratic Republic in October 1978, which produced the first acoustic estimates of total biomass of herring and sprat in the Baltic Main basin (H˚akansson et al., 1979). Since then there has been at least one annual hydroacoustic survey for herring and sprat stocks and results have been reported to ICES. The Baltic International Acoustic Survey (BIAS), is mandatory for the countries that have exclusive economic zone (EEZ) in the Baltic Sea, and is a part of the Data Collection Framework as stipulated by the European Council and the Commission (Council Regulation (EC) No 199/2008 and the Commission DCF web page1). IMR in Lysekil is part of the Department of Aquatic Resources within Swedish University of Agricultural Sciences and is responsible for the Swedish part of the EU Data Collection Framework and surveys in the marine environment. The Institute assesses the status of the marine ecosystems, develops and provides biological advices for managers for the sustainable use of aquatic resources. The BIAS survey are co-ordinated and managed by the ICES working group WGBIFS. The main objective of BIAS is to assess herring and sprat resources in the Baltic Sea. The survey will provide data to the ICES Baltic Fisheries Assessment Working Group (WGBFAS). 1https://datacollection.jrc.ec.europa.eu/dcf-legislation 3 ICES | WGBIFS 2019 395 2 Methods 2.1 Narrative Since R/V Argos was taken out of service in 2011, Sweden has chartered R/V Dana for the BIAS survey. The scientific staff was Swedish and the ship crew was Danish. This year’s calibration of the SIMRAD EK60 sounder was made at Gullmarsfjorden on the Swedish west coast, the location change occurred 2011 because the normal calibration site at Ho¨go¨n is inaccessible for Dana due to deeper draft. The first part of the cruise started 2018-10-02 inbetween Sweden and Bornholm at the border between ICES subdivision (SD) 24 and SD 25, and ended 2018-10-14 close to where it started. The total cruise covered SD 27 and parts of 25, 26, 28 and 29. 2.2 Survey design The stratification is based on ICES statistical rectangles with a range of 0.5 degrees in latitude and 1 degree in longitude (figure 1). The areas of all strata are limited by the 10 m depth line2. The aim is to use parallel transects spaced on regular rectangle basis normally at a maximum distance of 15 nautical miles and with a transect density of about 60 nautical miles per 1000 square nautical miles. The irregular shape of the survey area assigned to Sweden and the weather conditions makes it difficult to fulfill this. The total area covered was 20832 square nautical miles and the distance used for acoustic estimates was 1247 nautical miles. The cruise track and positions of trawl hauls are shown in figure 2. 2.3 Calibration The SIMRAD EK60 echo sounder with the transducer ES38B was calibrated at Borno¨ in Gullmarssfjorden 2018-10-02 and 2018-10-03 according to the BIAS manual.3 Values from the calibration were within required accuracy. The change of calibration site was decided after correspondance with Simrad. Due to the distance between the calibration site and the survey area the gain was recalculated using the equation: G = G0 + 10 ∗ log10(c20/c2) (Bodholt 2002) 2.4 Acoustic data collection The acoustic sampling was performed around the clock. SIMRAD EK604 echo sounder with the 38 kHz transducer (ES38b) mounted on a towed body is used for the acoustic transect data collection, additionally a hull mounted 38 kHz transducer (ES38B) was used during the fishing stations (the towed body is taken aboard when fishing). The settings of the hydroacoustic equipment were as described in the BIAS manual5. The post processing of the stored raw data was made using the software LSSS6. The mean volume back scattering values (Sv) were integrated over 1 nautical mile elementary sampling distance units (ESDUs) from 10 m below the surface to the bottom. Contributions from air bubbles, bottom structures and scattering layers were removed from the echogram using LSSS. 2.5 Data analysis The pelagic target species sprat and herring are usually distributed in mixed layers in combination with other species so that it is impossible to allocate the integrator readings to a single species. Therefore 2ICES CM 2011/SSGESST:05 Addendum 2 3See footnote 5 4http://www.simrad.com/ek60 5See footnote 5 6www.marec.no/english/products.htm 4 396 ICES | WGBIFS 2019 the species composition was based on the trawl catch results. For each rectangle the species composition and length distribution were determined as the unweighted mean of all trawl results in this rectangle. In the case of lack of sample hauls within an individual ICES rectangle (due to gear problems, bad weather conditions or other limitations) a mean from hauls from neighboring rectangles was used. From these distributions the mean acoustic cross-section was calculated according to the target strength-length (TS) relationships found in table 1. Clupeoids TS = 20 log L (cm) - 71.2 (ICES 1983/H:12) Gadoids TS = 20 log L (cm) - 67.5 (Foote et al. 1986) Trachurus trachurus TS = 20 log L (cm) - 73.0 (Misund, 1997 in Pen˜a, 2007) Fish without swim bladder TS = 20 log L (cm) - 84.9 ICES CM2011/SSGESST:02,Addendum 2 Salmonids and 3-spined stickleback were assumed to have the same acoustic properties as herring. Table 1: Target strength-length (TS) relationships The total number of fish (total N) in one rectangle was estimated as the product of the mean area scattering cross section sA and the rectangle area, divided by the corresponding mean cross section σ. The total number was separated into different fish species according to the mean catch composition in the rectangle. 2.6 Hydrographic data CTD casts were made with a ”Seabird 9+” CTD when calibrating the acoustic instruments and whenever a haul was conducted, additional hydrographic data was collected on a selection of these stations. 2.7 Personnel The participating scientific crew can be seen in table 2 Svensson, Matilda IMR, Lysekil, Sweden Fish sampling Jernberg, Carina IMR, Lysekil, Sweden Fish sampling Johannesson, Per IMR, Lysekil, Sweden Technician calibration Larson, Niklas IMR, Lysekil, Sweden Scientific & Expedition leader, Acoustics Lo¨vgren, Olof IMR, Lysekil, Sweden Acoustics Johansson, Marianne IMR, Lysekil, Sweden Fish sampling Palmen-Bratt, Anne-Marie IMR, Lysekil, Sweden Fish sampling Sjo¨berg, Rajlie IMR, Lysekil, Sweden Fish sampling Svenson, Anders IMR, Lysekil, Sweden Expedition leader, Acoustics Tell, Anna-Kerstin SMHI, Gothenburg Oceanography Table 2: Participating scientific crew 3 Results 3.1 Biological data In total 46 trawl hauls were carried out, 15 in SD 25, 2 in SD 26, 14 in SD 27, 9 in SD 28 and 6 hauls in SD 29. 2010 herrings and 1473 sprats were aged. Catch compositions by trawl haul is presented in Table 8. Length distributions for herring and sprat by ICES subdivision are shown in figures 3 to 12. 5 ICES | WGBIFS 2019 397 3.2 Acoustic data The survey statistics concerning the survey area, the mean backscatter [sA], the mean scattering cross section [σ], the estimated total number of fish, the percentages of herring, sprat and cod per Sub- division/rectangle are shown in Table 3. 3.3 Abundance estimates The total abundances of herring and sprat by age group per rectangle are presented in Table 4 and 6. The corresponding mean weights by age group per rectangle are shown in Tables 5 and 7. 4 Discussion The data collected during the survey should be considered as representative for the abundance of the pelagic species during the BIAS in 2015 for SD25 to 29 and thus can be used in the assessment work done by WGBFAS. 6 398 ICES | WGBIFS 2019 5 References Bodholt, H. The effect of water temperature and salinity on echo sounder measurments. ICES Sympo- sium on Acoustics in Fisheries, Montpellier June 2002, paper no 123. Foote, K.G., Aglen, A. and Nakken, O. 1986. Measurement of fish target strength with a split-beam echosounder. J.Acoust.Soc.Am. 80(2):612-621. H˚akansson, N.; Kollberg, S.; Falk, U.; Go¨tze, E., Rechlin, O. 1979. A hydroacoustic and trawl survey of herring and sprat stocks of the Baltic proper in October 1978. Fischerei-Forschung, Wissenschaftliche Schriftenreihe 17(2):7-2 ICES. 2012. Report of the Baltic International Fish Survey Working Group (WGBIFS) March 2012, Helsinki, Finland. ICES CM 2012/SSGESST:02. 531 pp. ICES. 2012. Report of the Baltic Fisheries Assessment Working Group 2012 (WGBFAS), 12 - 19 April 2012, ICES Headquarters, Copenhagen. ICES CM 2012/ACOM:10. 859 pp. Misund, O. A., Beltestad, A. K., Castillo, J., Knudsen, H. P., and Skagen, D. 1997. Distribution and acoustic abundance estimation of horse mackerel, and mackerel in the northern North Sea, October 1996. ICES WG on the assessment of anchovy, horse mackerel, mackerel and sardine, Copenhagen, 9/9-18/9, 1997. Pen˜a, H. 2008. In situ target-strength measurements of Chilean jack mackerel (Trachurus symmetricus murphyi) collected with a scientific echosounder installed on a fishing vessel. - ICES Journal of Marine Science 65: 594-604. Council Regulation (EC) No 199/2008: http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2008:060:0001:0012:EN:PDF Commission DCF web page: http://datacollection.jrc.ec.europa.eu/dcf-legislation 7 ICES | WGBIFS 2019 399 6 Tables, map and figures SD RECT AREA SA SIGMA NTOT HHer HSpr HCod 25 39G4 287.3 791.8 2.740 830.17 39.80 47.48 0.627 25 39G5 979.0 355.2 1.798 1934.04 15.67 84.18 0.121 25 40G4 677.2 938.6 2.503 2539.82 42.08 55.40 0.419 25 40G5 1012.9 457.8 1.765 2627.68 14.19 83.97 0.046 25 40G6 1013.0 645.3 2.029 3221.14 43.46 45.19 0.007 25 40G7 1013.0 301.1 2.083 1464.29 46.01 53.97 0.000 25 41G6 764.4 779.6 2.440 2442.44 67.85 30.32 0.010 25 41G7 1000.0 718.0 1.407 5101.19 15.95 65.16 0.011 26 41G8 1000.0 728.5 1.820 4002.81 38.33 55.27 0.029 27 42G6 266.0 593.5 0.347 4549.02 0.22 0.76 0.000 27 42G7 986.9 390.5 0.844 4567.30 4.31 45.40 0.000 27 43G7 913.8 922.9 1.301 6479.86 41.47 7.46 0.000 27 44G7 960.5 351.3 1.284 2627.19 27.80 38.20 0.006 27 44G8 456.6 575.2 0.879 2988.47 23.01 2.59 0.000 27 45G7 908.7 374.7 0.483 7056.85 4.48 5.95 0.000 27 45G8 947.2 547.1 0.477 10865.99 2.87 7.03 0.000 27 46G8 884.8 652.8 0.412 14009.62 2.69 0.92 0.001 28 42G8 945.4 306.9 1.243 2335.00 25.44 36.60 0.000 28 43G8 296.2 1057.7 0.535 5853.36 1.95 16.44 0.000 28 43G9 973.7 3211.8 0.802 38983.71 16.70 5.99 0.000 28 44G9 876.6 294.3 1.227 2102.21 22.76 49.64 0.003 28 45G9 924.5 1500.3 1.461 9491.81 35.22 45.28 0.007 29 46G9 933.8 526.1 0.625 7861.60 9.78 11.84 0.001 29 46H0 933.8 744.2 1.034 6722.13 0.49 84.22 0.000 29 47G9 876.2 685.8 0.638 9418.19 3.50 29.63 0.000 Table 3: Survey statistics 8 400 ICES | WGBIFS 2019 SD RECT NSprTOT NSpr0 NSpr1 NSpr2 NSpr3 NSpr4 NSpr5 NSpr6 NSpr7 NSpr8 25 39G4 394.20 2.15 6.46 58.59 15.51 235.66 50.41 0.00 25.42 0.00 25 39G5 1628.09 157.92 118.54 76.97 258.07 645.60 158.47 89.22 8.48 114.81 25 40G4 1407.15 73.83 60.88 33.53 254.06 699.50 93.74 163.38 0.00 28.23 25 40G5 2206.37 12.11 137.77 266.61 839.70 372.26 11.99 334.27 185.86 45.79 25 40G6 1455.62 98.33 22.78 113.02 141.60 767.02 103.48 127.40 82.00 0.00 25 40G7 790.32 157.49 62.55 43.40 71.70 366.84 32.35 48.15 7.85 0.00 25 41G6 740.64 140.45 24.27 22.58 129.76 352.69 51.08 6.60 13.21 0.00 25 41G7 3324.11 360.86 175.86 197.67 773.13 1353.05 336.34 68.43 29.38 29.38 26 41G8 2212.21 665.50 200.51 149.76 136.03 935.44 43.60 48.22 22.70 10.45 27 42G6 34.46 5.74 2.15 0.00 10.41 10.62 2.44 0.86 1.54 0.68 27 42G7 2073.53 499.27 154.33 158.75 277.11 906.60 45.56 0.00 9.76 22.18 28 42G8 854.58 245.47 241.60 0.00 50.09 277.19 32.34 6.20 0.00 1.68 27 43G7 483.24 115.97 8.00 23.89 92.38 197.61 5.42 32.46 0.00 7.51 28 43G8 962.49 84.51 136.16 32.87 146.49 511.76 29.11 0.00 0.00 21.60 28 43G9 2335.88 374.45 314.64 0.00 195.96 1123.09 199.73 22.88 40.38 64.76 27 44G7 1003.65 128.66 154.76 183.00 43.59 484.09 9.55 0.00 0.00 0.00 27 44G8 77.26 24.88 6.55 0.00 1.57 20.69 8.38 0.00 9.17 6.02 28 44G9 1043.51 600.07 47.70 99.51 58.68 225.36 6.21 2.74 2.74 0.51 27 45G7 419.61 209.16 58.55 13.54 6.98 125.99 1.51 1.98 0.95 0.95 27 45G8 763.66 116.21 145.68 73.57 67.25 258.33 44.24 37.91 18.92 1.56 28 45G9 4297.98 430.66 376.25 73.74 802.83 2069.23 391.06 81.62 50.39 22.21 27 46G8 128.33 56.17 14.22 1.85 7.25 28.90 9.88 4.09 2.31 3.66 29 46G9 930.62 441.14 122.39 77.70 134.20 125.95 13.58 3.28 10.30 2.07 29 46H0 5661.10 1390.75 1705.63 187.53 693.19 1449.91 86.94 60.22 20.07 66.86 29 47G9 2790.66 941.20 233.44 70.36 375.59 738.99 333.07 8.46 0.00 89.55 Table 4: Estimated number (millions) of sprat SD RECT WSpr0 WSpr1 WSpr2 WSpr3 WSpr4 WSpr5 WSpr6 WSpr7 WSpr8 25 39G4 4.00 10.67 12.33 14.33 15.42 17.00 13.50 25 39G5 4.80 9.67 10.00 12.43 13.77 14.80 15.25 18.00 16.50 25 40G4 3.31 9.50 10.50 13.60 13.86 17.00 17.00 16.00 25 40G5 3.50 10.00 13.00 13.00 13.50 16.00 15.67 15.33 16.50 25 40G6 3.52 7.50 11.00 11.00 12.95 15.25 15.20 15.00 25 40G7 3.85 8.42 10.67 12.67 12.45 12.00 14.25 17.33 25 41G6 3.33 8.43 13.00 11.83 12.16 12.50 15.00 16.00 25 41G7 3.57 7.62 9.67 11.29 11.58 13.00 14.00 14.00 15.00 26 41G8 3.76 8.12 9.67 10.67 11.07 14.33 13.75 12.00 13.00 27 42G6 3.32 7.80 10.75 11.42 12.00 12.00 12.67 14.33 27 42G7 3.71 8.10 9.67 10.80 11.29 12.50 15.00 13.33 28 42G8 4.00 7.47 9.00 11.11 12.25 14.00 12.00 27 43G7 3.21 6.75 10.00 10.33 11.41 13.50 12.40 13.67 28 43G8 3.92 7.56 8.00 10.60 10.88 12.00 12.33 28 43G9 3.88 7.55 9.50 10.76 12.25 12.00 13.50 12.50 27 44G7 3.73 8.86 10.60 10.50 10.94 12.00 27 44G8 3.79 8.80 10.00 10.70 10.67 12.43 11.33 28 44G9 4.17 6.71 8.62 11.00 10.08 11.00 10.00 12.00 12.00 27 45G7 3.59 7.62 9.00 9.00 10.56 13.00 12.50 13.00 13.50 27 45G8 3.96 7.86 9.67 11.67 11.60 12.60 12.83 12.00 13.00 28 45G9 3.87 7.80 7.00 8.60 9.85 12.33 13.67 14.00 12.00 27 46G8 4.09 8.71 12.00 10.33 10.00 11.50 13.00 14.00 11.00 29 46G9 3.96 8.50 8.20 9.57 11.11 12.00 13.00 12.00 13.50 29 46H0 3.95 8.08 8.50 10.40 9.88 11.50 12.00 12.00 12.00 29 47G9 3.84 7.88 10.00 9.83 10.09 10.33 13.00 12.67 Table 5: Estimated mean weights (g) of sprat 9 ICES | WGBIFS 2019 401 SD RECT NHerTOT NHer0 NHer1 NHer2 NHer3 NHer4 NHer5 NHer6 NHer7 NHer8 25 39G4 330.40 11.20 24.19 51.97 19.49 135.07 51.52 23.07 10.98 2.91 25 39G5 303.09 20.43 33.71 34.59 41.91 149.32 11.00 6.02 4.23 1.89 25 40G4 1068.84 37.87 88.93 155.12 124.34 469.88 94.92 93.65 4.11 0.00 25 40G5 372.91 37.17 58.78 63.25 30.54 152.93 10.65 12.50 3.83 3.27 25 40G6 1399.93 6.66 99.84 159.31 118.80 821.80 96.35 89.86 7.33 0.00 25 40G7 673.74 0.00 10.06 28.96 116.41 355.80 136.08 23.14 0.00 3.29 25 41G6 1657.10 1.68 22.78 65.31 151.91 1115.52 224.72 36.35 35.43 3.41 25 41G7 813.43 16.79 28.76 92.59 129.23 412.40 112.45 11.09 2.95 7.16 26 41G8 1534.44 0.00 7.38 57.08 249.66 747.15 283.13 132.84 53.48 3.72 27 42G6 9.92 7.06 2.86 0.00 0.00 0.00 0.00 0.00 0.00 0.00 27 42G7 197.04 0.71 10.06 14.02 29.78 107.26 29.91 4.48 0.82 0.00 28 42G8 594.00 2.74 23.84 111.88 91.64 340.65 8.08 9.52 4.32 1.33 27 43G7 2687.49 32.73 169.04 431.62 519.23 1327.42 173.60 13.59 20.26 0.00 28 43G8 113.88 5.13 32.01 18.26 13.95 39.60 3.90 1.03 0.00 0.00 28 43G9 6508.81 197.91 53.08 843.39 566.41 3360.02 532.22 644.46 311.31 0.00 27 44G7 730.39 36.97 32.14 191.12 145.00 267.15 51.91 4.06 2.03 0.00 27 44G8 687.67 2.63 34.37 220.86 65.07 351.91 10.54 0.00 2.29 0.00 28 44G9 478.40 2.86 1.63 42.03 40.08 198.08 151.33 16.42 8.47 17.48 27 45G7 315.98 57.62 24.83 72.03 68.26 63.73 26.68 0.00 2.83 0.00 27 45G8 311.61 63.52 25.68 50.47 40.69 120.15 8.95 1.08 1.08 0.00 28 45G9 3343.48 223.84 365.13 662.42 283.60 1498.54 282.59 0.00 27.35 0.00 27 46G8 377.34 6.58 21.77 32.80 40.05 212.62 52.93 7.71 2.89 0.00 29 46G9 768.95 24.69 113.85 167.20 25.81 336.93 94.77 2.85 0.00 2.85 29 46H0 32.89 16.46 8.05 4.79 0.00 3.59 0.00 0.00 0.00 0.00 29 47G9 329.92 156.28 47.91 69.51 12.47 42.82 0.92 0.00 0.00 0.00 Table 6: Estimated number (millions) of herring SD RECT WHer0 WHer1 WHer2 WHer3 WHer4 WHer5 WHer6 WHer7 WHer8 25 39G4 13.30 37.80 46.00 62.71 46.24 73.88 61.56 74.80 48.00 25 39G5 11.21 19.86 32.70 44.00 35.53 54.44 61.40 47.00 63.00 25 40G4 11.84 21.80 44.33 70.82 45.05 77.85 55.14 86.50 25 40G5 12.37 26.36 22.69 38.75 36.46 50.00 45.67 51.00 51.00 25 40G6 6.80 19.08 23.57 40.14 35.83 52.00 47.88 56.00 25 40G7 18.50 22.00 35.78 32.54 42.77 44.67 40.00 25 41G6 5.50 17.17 20.71 29.40 33.74 43.69 52.43 56.80 74.00 25 41G7 5.27 18.67 22.43 28.00 33.29 41.50 51.20 58.00 47.00 26 41G8 15.00 23.20 28.30 30.76 33.88 45.50 44.33 47.00 27 42G6 4.42 6.30 27 42G7 4.00 15.72 19.83 24.50 30.75 34.11 38.33 38.00 28 42G8 4.17 14.53 20.92 26.14 29.50 41.25 40.00 50.33 47.00 27 43G7 4.35 14.75 19.44 25.00 26.75 32.88 34.50 40.00 28 43G8 5.40 14.82 20.00 26.83 25.12 28.50 44.00 28 43G9 3.79 13.00 19.67 26.00 27.33 33.17 33.33 34.67 27 44G7 4.64 14.06 21.00 26.60 26.91 34.57 37.50 46.00 27 44G8 4.50 14.82 20.17 26.33 26.96 34.75 34.00 28 44G9 4.64 15.33 19.82 26.00 26.75 33.40 36.25 39.67 35.00 27 45G7 4.71 14.00 19.55 23.56 24.42 27.20 36.50 27 45G8 4.06 13.93 19.09 23.83 26.22 29.75 39.00 35.00 28 45G9 4.47 14.71 20.14 22.50 25.50 28.83 25.00 27 46G8 3.70 14.73 20.75 23.40 25.83 30.89 35.33 33.50 29 46G9 4.07 14.69 19.45 25.33 26.50 32.11 34.00 38.00 29 46H0 3.38 12.43 17.75 20.00 29 47G9 4.12 13.27 18.00 22.00 23.36 28.00 Table 7: Estimated mean weights (g) of herring 10 402 ICES | WGBIFS 2019 Species 2 4 6 8 10 12 14 16 1 Ammodytidae 2 Clupea harengus 39.37 52.58 19.03 260.96 825.02 55.48 354.43 0.75 3 Cyclopterus lumpus 0.16 0.38 0.52 0.25 4 Gadus morhua 6.29 0.63 2.52 0.55 0.51 5 Gasterosteus aculeatus 0.00 0.04 0.13 4.90 0.60 3.33 32.09 108.00 6 Hyperoplus lanceolatus 0.01 7 Lampetra fluviatilis 8 Liparis liparis 0.00 9 Merlangius merlangus 3.22 10 Myoxocephalus scorpius 0.78 0.52 11 Nerophis ophidion 0.00 12 Pholis gunnellus 0.01 13 Platichthys flesus 1.07 0.09 0.10 14 Pleuronectes platessa 0.15 15 Pomatoschistus 0.12 0.01 0.11 16 Pungitius pungitius 0.02 0.04 0.02 0.17 0.64 17 Salmo salar 18 Scophthalmus maximus 19 Sprattus sprattus 14.21 24.16 79.28 256.28 21.42 42.60 450.99 4.92 20 Trachurus trachurus Table 8: Catch composition per haul. Species 18 20 22 24 26 28 30 32 1 Ammodytidae 2 Clupea harengus 56.17 397.29 112.50 515.03 7.26 177.42 74.39 16.91 3 Cyclopterus lumpus 0.09 0.08 0.24 2.53 0.17 4 Gadus morhua 0.51 5 Gasterosteus aculeatus 28.41 26.16 17.60 42.68 23.67 49.05 120.93 14.41 6 Hyperoplus lanceolatus 7 Lampetra fluviatilis 8 Liparis liparis 9 Merlangius merlangus 10 Myoxocephalus scorpius 0.08 11 Nerophis ophidion 12 Pholis gunnellus 13 Platichthys flesus 0.25 14 Pleuronectes platessa 15 Pomatoschistus 16 Pungitius pungitius 0.10 0.04 0.04 0.06 0.01 0.17 0.06 0.01 17 Salmo salar 18 Scophthalmus maximus 19 Sprattus sprattus 43.32 18.26 12.92 4.94 387.35 7.58 69.42 7.56 20 Trachurus trachurus Table 8 (continued): Catch composition per haul 11 ICES | WGBIFS 2019 403 Species 34 36 38 40 42 44 47 49 1 Ammodytidae 2 Clupea harengus 0.57 3.73 42.19 47.03 138.58 18.85 7.12 3.83 3 Cyclopterus lumpus 0.09 0.36 0.27 0.13 0.61 0.33 4 Gadus morhua 0.09 0.55 5 Gasterosteus aculeatus 27.97 85.75 120.06 121.83 57.35 66.67 43.80 7.11 6 Hyperoplus lanceolatus 0.12 0.05 7 Lampetra fluviatilis 0.06 8 Liparis liparis 9 Merlangius merlangus 10 Myoxocephalus scorpius 11 Nerophis ophidion 0.00 0.00 0.01 0.00 0.01 0.00 0.03 12 Pholis gunnellus 13 Platichthys flesus 14 Pleuronectes platessa 15 Pomatoschistus 16 Pungitius pungitius 0.02 0.06 0.01 0.01 0.02 0.08 0.19 17 Salmo salar 0.27 18 Scophthalmus maximus 0.27 0.02 19 Sprattus sprattus 1.07 18.62 7.91 2.07 11.49 97.22 555.42 1671.03 20 Trachurus trachurus Table 8 (continued): Catch composition per haul Species 51 53 55 57 59 61 63 65 1 Ammodytidae 0.00 2 Clupea harengus 12.90 40.68 224.29 3.96 39.24 76.82 162.34 87.06 3 Cyclopterus lumpus 0.08 0.63 0.30 0.83 0.13 4 Gadus morhua 0.24 0.72 5 Gasterosteus aculeatus 35.26 73.62 4.91 8.97 2.15 6.94 42.37 48.43 6 Hyperoplus lanceolatus 0.01 7 Lampetra fluviatilis 8 Liparis liparis 9 Merlangius merlangus 10 Myoxocephalus scorpius 11 Nerophis ophidion 0.00 0.03 12 Pholis gunnellus 13 Platichthys flesus 0.05 0.10 14 Pleuronectes platessa 15 Pomatoschistus 16 Pungitius pungitius 0.04 0.03 0.02 0.00 17 Salmo salar 18 Scophthalmus maximus 19 Sprattus sprattus 88.59 85.67 18.55 191.20 383.23 2.02 23.50 9.75 20 Trachurus trachurus Table 8 (continued): Catch composition per haul 12 404 ICES | WGBIFS 2019 Species 67 69 71 73 75 77 79 81 1 Ammodytidae 2 Clupea harengus 2.47 337.68 236.32 495.27 100.38 57.99 281.66 145.70 3 Cyclopterus lumpus 0.56 1.64 0.27 0.36 0.96 4 Gadus morhua 5.55 5 Gasterosteus aculeatus 8.04 26.22 48.14 3.31 1.09 1.47 6 Hyperoplus lanceolatus 7 Lampetra fluviatilis 0.13 8 Liparis liparis 9 Merlangius merlangus 10 Myoxocephalus scorpius 11 Nerophis ophidion 0.00 12 Pholis gunnellus 13 Platichthys flesus 1.01 14 Pleuronectes platessa 15 Pomatoschistus 0.02 16 Pungitius pungitius 0.01 17 Salmo salar 18 Scophthalmus maximus 0.31 19 Sprattus sprattus 9.18 81.16 227.93 222.56 35.35 153.29 52.49 136.94 20 Trachurus trachurus Table 8 (continued): Catch composition per haul Species 83 85 87 89 91 1 Ammodytidae 2 Clupea harengus 243.35 1247.80 46.54 35.39 63.65 3 Cyclopterus lumpus 0.58 0.73 0.55 0.73 4 Gadus morhua 0.74 0.95 3.67 1.86 5 Gasterosteus aculeatus 0.52 12.85 0.30 6 Hyperoplus lanceolatus 7 Lampetra fluviatilis 8 Liparis liparis 9 Merlangius merlangus 10 Myoxocephalus scorpius 11 Nerophis ophidion 12 Pholis gunnellus 13 Platichthys flesus 0.14 0.56 0.18 0.15 14 Pleuronectes platessa 15 Pomatoschistus 16 Pungitius pungitius 0.04 0.12 0.05 17 Salmo salar 18 Scophthalmus maximus 19 Sprattus sprattus 94.77 245.99 93.99 55.80 191.72 20 Trachurus trachurus Table 8 (continued): Catch composition per haul 13 ICES | WGBIFS 2019 405 Figure 1: Map over which ICES square are allocated to each country (On axes: longitude, latitude and ICES name of square eg:41G8) 14 406 ICES | WGBIFS 2019 Figure 2: cruise track(red), positions of trawl hauls (blue) and survey grid (ICES squares)(grey) 15 ICES | WGBIFS 2019 407 05 10 15 20 4 5 6 7 8 9 10 11 12 13 14 15 16 Lengthclass (cm) % o f N um be r Sprat SD25 Figure 3: Length distribution of sprat from subdivision 25 0 5 10 15 20 25 4 5 6 7 8 9 10 11 12 13 14 15 16 Lengthclass (cm) % o f N um be r Sprat SD26 Figure 4: Length distribution of sprat from subdivision 26 16 408 ICES | WGBIFS 2019 05 10 15 20 25 4 5 6 7 8 9 10 11 12 13 14 15 16 Lengthclass (cm) % o f N um be r Sprat SD27 Figure 5: Length distribution of sprat from subdivision 27 0 5 10 15 20 4 5 6 7 8 9 10 11 12 13 14 15 16 Lengthclass (cm) % o f N um be r Sprat SD28 Figure 6: Length distribution of sprat from subdivision 28 17 ICES | WGBIFS 2019 409 05 10 15 20 25 30 35 40 4 5 6 7 8 9 10 11 12 13 14 15 Lengthclass (cm) % o f N um be r Sprat SD29 Figure 7: Length distribution of sprat from subdivision 29 0 5 10 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Lengthclass (cm) % o f N um be r Herring SD25 Figure 8: Length distribution of herring from subdivision 25 18 410 ICES | WGBIFS 2019 05 10 15 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Lengthclass (cm) % o f N um be r Herring SD26 Figure 9: Length distribution of herring from subdivision 26 0 5 10 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Lengthclass (cm) % o f N um be r Herring SD27 Figure 10: Length distribution of herring from subdivision 27 19 ICES | WGBIFS 2019 411 05 10 15 20 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Lengthclass (cm) % o f N um be r Herring SD28 Figure 11: Length distribution of herring from subdivision 28 0 5 10 15 20 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Lengthclass (cm) % o f N um be r Herring SD29 Figure 12: Length distribution of herring from subdivision 29 20 412 ICES | WGBIFS 2019 INSTITUTE OF FOOD SAFETY, ANIMAL HEALTH AND ENVIRONMENT – BIOR, RIGA (LATVIA) THE CRUISE REPORT FROM THE LATVIAN BALTIC INTERNATIONAL ACOUSTIC SURVEY – BIAS 2018 ON THE F/V “ULRIKA” IN THE ICES SUBDIVISIONS 26N AND 28 OF THE BALTIC SEA (17-26 October 2018) GUNTARS STRODS•JANIS GRUDULS•FAUSTS SVECOVS•VIESTURS BERZINS• •ALLA VINGOVATOVA•IVARS PUTNIS•VADIMS CERVONCEVS• Riga, March 2019 ICES | WGBIFS 2019 413 INTRODUCTION More less regular acoustic estimations of pelagic fish stocks in the Baltic Sea initiated by BaltNIIRH (now BIOR) and Institute für Hochseefischerei in Rostock (GDR) was performed since 1983, but the first scattered surveys was made since 1977 [Shvetsov 1983, Hoziosky et al. 1987, Shvetsov et al. 1988]. Several years in May (2005-2008) BIOR as assignee of BaltNIIRH, LatFRI and LatFRA cooperated with Polish SFI in Gdynia, but before – in 2003-2004 with AtlantNIRO in Kaliningrad, Russia. In 2009 due to collapse of Latvian economy the survey was not performed. In 2010 we resumed our international cooperation in the fisheries research, but this time on the Lithuanian r/v “Darius” board. The collaboration lasted for three years till the 2012. The Latvian Baltic International Acoustic Survey (BIAS) in the ICES Sub-divisions 26N and 28 in October 2018 was conducted on Latvian commercial fishing vessel “Ulrika” with which crew and the owners cooperation in research for pelagic fish distribution and feeding conditions in the recent decade has developed a very close and productive. The reported cruise was organized on the basis of the agreement between the Institute of Food Safety, Animal Health and Environment (BIOR) from Riga and the fishing company “Vergi” Ltd from Jurmala. The vessel was operated within the Latvian and Swedish EEZs (ICES Sub-divisions 26N and 28). The “Latvian National Fisheries Data Collection Programme, 2018” in accordance with the EU Commission Regulations No.1639/2001 and No.1581/2004 was partly subsidized this cruise. It was coordinated by the ICES Baltic International Fish Survey Working Group (WGBIFS). Pelagic research catches carried out during an acoustic survey are the information source, independent from topical preferences in fishery, about quantitative changes in a process of clupeids geographical and bathymetrical distribution in the Baltic. Hydrological parameters measurements are the information source about abiotic factors (seawater temperature, salinity, oxygen content) influencing sprat and herring spatial distribution. Echo-integration results along the pre-selected tracks are the basic materials for fish stock biomass calculation. The ICES Baltic Fisheries Assessment Working Group (WGBFAS) can apply the present BASS data for clupeids (especially for sprat) stock biomass assessment and spatial distribution updating. The basic acoustic and biological data collected during recently carried out survey are stored in the BAD1 and acoustic.db international databases, managed by the ICES Secretariat. The main aims of cruise were: • to collect the echo-integration data for the estimation of the clupeids stocks biomass and abundance in the central-eastern Baltic; • to collect materials from the fish control catches for investigations of the Baltic sprat, and in lesser degree herring, spawning stocks spatial distribution in the offshore waters of Latvia and Sweden, moreover for analyses of the age-length structure and recruiting year-class strength of these fishes populations; • to collect sprat and herring stomachs samples for feeding condition and food components analyses; • to analyse the vertical and horizontal changes of the basic hydrological parameters (temperature, salinity and oxygen content) at the trawling positions and at the standard HELCOM hydrological stations; • to collect the zooplankton and ichthyoplankton samples at the referring area. 414 ICES | WGBIFS 2019 MATERIALS AND METHODS Personnel The scientific staff was composed of three persons: G. Strods – scientific staff and cruise leader, acoustics, fish sampling Janis Gruduls – fish sampling, hydrobiology and hydrology V. Cervoncevs – herring sampling. Survey description The reported BIAS survey of the f/v “Ulrika” took place during the period of 17-26 October 2018. The vessel left the port of Ventspils on 21.05.2013 at 00:05 o’clock GMT+02:00. The sea researches were conducted in the period of 17-21.10.2018 and 24-26.10 within Latvian and Swedish EEZs (ICES Sub-divisions 26N and 28). The research activity had been stopped at 20:00 o’clock GMT+02:00 on 26th of October and the vessel returned back to the port of Ventspils for the scientific team disembarkation there. The almost full eight working days were utilized for fulfilling the survey purposes and two days for scientific team transfer and equipment installation and stripping. Survey performance The survey echo-integration tracks were planned in a similar pattern as in the previous years, due to historical comparability of the data. Overall 513 nautical miles long survey tracks was observed and recorded with hydroacoustic equipment. The final pattern of transects was covered with a relatively good density. The area covered in October 2018 was 7080.2 nm2, in the northern part of the ICES Sub-division 26 – 1953.3 nm2 and in Sub-division 28 – 5126.9 nm2 (Fig. 1). The pre-selection of the pelagic fish catches based on the ICES statistical rectangle area (with range of 0.5 degree in latitude and 1 degree in longitude) and the vertical distribution of clupeids actual density pattern along the transect. The intention was to carry out at least two control hauls per the ICES statistical rectangle. The water depth range- layer with sufficient for fish oxygen content (minimum 1.5-2.0 ml/l) were taken into account in the process of the hauls distribution. Totally 16 control haul in the pelagic offshore zone were conducted with the pelagic trawl with max. 76 m horizontal opening, max. 24 m vertical opening and 10 mm mesh bar length in the codend. The trawling depth and the net opening were controlled by the sonar type IGEK. The trawl headrope positions in particular hauls were localized on the depth range from 7 to 80 m from the sea surface (Tab. 1). Mean headrope depth location in all investigated areas was 39 m. The trawl mouth vertical opening ranged from 20 to 24 m (mean – 20 m) and horizontal opening ranged from 72 to 76 m (mean – 76 m). The mean bottom depth at trawling positions varied from 32 to 246 m (mean for all investigated area – 106 m). Totally, 5 hauls were localized in the ICES Sub-division 26 and 11 hauls in the ICES Sub-division 28. On the whole, 13 catch samples were taken in the Latvian EEZ and 3 samples were taken from the hauls made along Latvian and Sweden EEZs border. The catches were made at the daylight between 07:39 a.m. and 16:30 p.m. GMT+02:00. The mean speed of the vessel during trawling was 3.2 knots. The trawling time of the single valid haul lasted for 30 minutes, with an exception of 2 hauls with 20 minutes duration and 2 hauls with 15 duration. All hauls can be accepted as representative (valid from technical point of view). The samples of sprat, herring and cod were taken from each catch station to determine the species proportion, length-mass relationship, sex, maturity and age-length relationship. Measured and analyzed fish amount shown in Table 2. Detailed ichthyological analyses were made according to standard procedures, directly on board of surveying vessel. Species composition and fish length distributions were based on trawl catch results. Mean target strength of clupeid fishes was calculated according to the following formula [ICES 1983, 2012]: for clupeids: TS = 20logL-71.2; for gadoids: TS = 20logL-67.5; cross section σ = 4π10a/10×Lb/10. The total number of fish in each ICES rectangle was estimated as a product of the mean area scattering cross-section – NASC (SA) and the rectangle area, divided by corresponding mean acoustic cross-section. Fish abundance was separated into different species according to the mean catch composition in the given rectangle. ICES | WGBIFS 2019 415 The basic hydrological parameters (seawater temperature, salinity and oxygen contents) were measured from the surface to the bottom after every haul if weather conditions was favorable. Totally, 19 hydrological stations were inspected during survey on f/v “Ulrika”. The location of hydrological and hydrobiological research profiles is presented in Fig. 2. The Seabird SBE 19plus was used for above-mentioned measurements. The row data were aggregated to the 10 m depth stratums. Zooplankton samples were collected at the positions of the hydrological stations or after trawling. Totally 13 zooplankton stations were realized and 22 zooplankton samples were taken. Zooplankton has been collected with Judday net (mouth opening 0.1 m2, mesh size 160 μm). This net was towed vertically from the depths 50 and 100, or from the bottom in case of lesser depth, to the water surface. Samples from 100 m deep were conserved in 2.5% unbuffered formaldehyde solution with sea water, but samples from 50 m depth were fixed by spirit solution with sea water and both processed during the year. RESULTS Biological data Catch statistics Catch per SD and species of the survey are given in Tab. 3-6. The total length of dominant pelagic fish species ranged as follows: • sprat – 7.5÷14.5 cm (average TL = 11.8 cm), 2.6÷16.6 g (average W = 9.9 g); • herring – 8.5÷21.5 cm (average TL = 16.8 cm), 4.0÷60.0 (average W = 29.2 g); Acoustical and biological estimates The basic acoustic and biological data (surveyed area statistics, mean NASC, the mean scattering cross-section, calculated target strength, the total number of fish, percentages of herring and sprat) per ICES rectangles, collected in October 2018, as well as the estimated abundance and biomass of sprat and herring per above mentioned rectangles are given in Tab. 4. The age structured data of sprat and herring are aggregated in Tab. 5-6. The geographical distribution of NASC, sprat and herring stock densities in the central-eastern Baltic in October 2018 are shown in Fig. 4-6. 416 ICES | WGBIFS 2019 Figure 1. Cruise track design and hauls of the Latvian Baltic International Acoustic Survey on the f/v "Ulrika", 17-26.10.2018. ICES | WGBIFS 2019 417 Figure 2. Locations of the hydrological and hydrobiological stations performed during the Latvian Baltic International Acoustic Survey on the f/v "Ulrika", 17-26.10.2018. (red dots - HELCOM stations; black rings - hydrological stations; Green triangles - zooplankton stations). 418 ICES | WGBIFS 2019 Table 1. Fish control-catch results in the Baltic Sea ICES SD 26N and 28 from the Latvian Baltic International Acoustic Survey on the f/v "Ulrika", 17-26.10.2018. Haul number Date ICES rectangle ICES SD Mean bottom depth [m] Headrope depth [m] Horizontal opening [m] Vertical opening [m] Trawling speed [knt] Trawling direction [°] Geographical position Time Start Haul duration [min] Total catch [kg] Start End Latitude 00°00.0'N Longitude 00°00.0'E Latitude 00°00.0'N Longitude 00°00.0'E 1 17.10.2018 41H0 26 32 7 72 24 3.2 270 56°06'10'' 20°31'11'' 56°06'10'' 20°28'21'' 09:30 30 3.368 2 17.10.2018 41G9 26 65 45 76 20 3.0 260 56°06'10'' 19°32'54'' 56°06'00'' 19°30'57'' 14:45 20 753.720 3 18.10.2018 41G9 26 134 60 76 20 3.3 85 56°22'59'' 19°19'20'' 56°23'02'' 19°22'25'' 08:38 30 416.620 4 18.10.2018 41G9 26 100 60 76 20 3.2 90 56°23'09'' 19°46'47'' 56°23'15'' 19°48'41'' 12:05 20 420.267 5 18.10.2018 41H0 26 62 35 76 20 2.8 40 56°23'57'' 20°15'24'' 56°25'12'' 20°17'19'' 15:19 30 170.108 6 19.10.2018 42H0 28 78 30/50 76 20 3.1 270 56°38'33'' 20°26'22'' 56°38'20'' 20°23'38'' 07:53 30 206.640 7 19.10.2018 42G9 28 134 40 76 20 3.2 260 56°38'57'' 19°29'26'' 56°38'31'' 19°26'37'' 13:52 30 577.780 8 20.10.2018 42G9 28 121 30 76 20 3.4 90 56°51'16'' 19°37'07'' 56°51'14'' 19°39'57'' 08:02 30 72.160 9 20.10.2018 42H0 28 126 40 76 20 3.1 90 56°50'35'' 20°15'25'' 56°50'44'' 20°19'05'' 11:36 30 18.543 10 20.10.2018 43H0 28 74 50 76 20 3.3 0 57°00'36'' 20°47'56'' 57°01'22'' 20°48'01'' 16:04 15 281.540 11 21.10.2018 43H0 28 152 20 76 20 3.4 270 57°06'35'' 20°16'35'' 57°06'18'' 20°13'34'' 07:39 30 330.000 12 21.10.2018 43H0 28 246 50 76 20 3.2 40 57°19'03'' 20°07'24'' 57°19'59'' 20°09'22'' 13:17 30 2.385 13 21.10.2018 43H0 28 67 45 76 20 3.0 60 57°22'10'' 20°40'54'' 57°23'01'' 20°43'18'' 16:30 30 421.545 14 25.10.2018 44H0 28 128 30 76 20 3.2 270 57°36'14'' 20°39'37'' 57°36'12'' 20°38'12'' 15:04 15 620.226 15 26.10.2018 44H0 28 105 40 76 20 3.1 120 57°52'12'' 20°24'54'' 57°51'43'' 20°27'38'' 09:14 30 560.850 16 26.10.2018 44H1 28 70 33 74 22 3.1 100 57°51'30'' 21°22'13'' 57°51'18'' 21°24'51'' 14:17 30 1600.570 SD26 2013.05.21-22 41G9-41H0 26 1764.083 SD28 2013.05.23-29 42H0-44H1 28 4692.239 SD26+28 2013.05.21-29 41G9-44H1 26-28 6456.322 ICES | WGBIFS 2019 419 Table 2. Number of measured and aged fish individuals in the Baltic Sea ICES SD 26N and 28.2 from the Latvian Baltic International Acoustic Survey on the f/v "Ulrika", 17-26.10.2018. SD 26 Sprat Herring Others Total Samples taken measurements 5 5 9 19 analyses 5 5 10 Fish measured 921 880 64 1865 Fish analysed 265 450 715 SD 28.2 Sprat Herring Cod Total Samples taken measurements 10 10 24 44 analyses 8 7 15 Fish measured 1727 1660 429 3816 Fish analysed 939 646 1585 SUM Sprat Herring Cod Total Samples taken measurements 15 15 33 63 analyses 13 12 25 Fish measured 2648 2540 493 5681 Fish analysed 1204 1096 2300 Table 3. Fish control-catch results by species in the Baltic Sea ICES SD 26N and 28 from the Latvian Baltic International Acoustic Survey on the f/v "Ulrika", 17-26.10.2018. Fish Species SD 26 SD 28.2 Total SD Sprat 1021.055 3325.720 4346.775 Herring 728.950 1273.716 2002.667 Cod 11.877 40.645 52.522 Flounder 0.110 0.441 0.551 Turbot 0.086 0.086 Stickleback 1.800 49.392 51.192 Smelt 0.022 0.022 Fourbeard rockling 0.040 0.200 0.240 Shorthorn sculpin 0.120 0.590 0.710 Lumpfish 0.108 1.366 1.474 Snakeblenny 0.083 0.083 Total Fish 1764.083 4692.239 6456.322 420 ICES | WGBIFS 2019 Figure 3. CPUE [kg/h] ranges distribution of sprat and herring in the catch hauls in the Baltic Sea ICES SD 26N and 28 from the Latvian Baltic International Acoustic Survey on the f/v "Ulrika", 17-26.10.2018. ICES | WGBIFS 2019 421 Table 4. Survey statistics of pelagic fish species from the Latvian BIAS in the Baltic Sea ICES SD 26N and 28.2 conducted by f/v "Ulrika" in the period of 17-26.10.2018. Table 4A ICES ICES Trawl Herring Sprat NASCPEL σ × 104 TS calc. SD Rect. No L, cm w, g n, % L, cm w, g n, % m2/nm2 m2 dB 44H1 14, 16 16.3 31.2 <0.1 10.9 8.9 >99.9 233 1.1743 -50.3 28 44H0 14, 15 15.7 23.7 1.3 10.8 8.8 98.7 291 1.1689 -50.3 43H1 10, 16 17.6 33.0 8.8 11.1 9.1 91.2 163 1.3784 -49.6 43H0 10, 11, 12, 13 17.1 30.4 86.8 11.3 9.3 13.2 557 2.6047 -46.8 42H0 6, 9, 10 17.5 32.7 67.0 11.4 9.5 33.0 346 2.4287 -47.1 42G9 7, 8 16.2 27.5 10.5 11.9 10.0 89.5 469 1.5175 -49.2 26 41H0 1, 5 16.9 30.4 7.1 11.3 9.7 92.9 357 1.4110 -49.5 41G9 2, 3, 4 17.1 29.9 70.2 11.8 10.6 29.8 951 2.4667 -47.1 Table 4B ICES ICES Area ρ Abundance, n × 106 n, % Biomass, kg × 103 SD Rect. nm2 n × 106/nm2 N NHERRING NSPRAT herring sprat W WHERRING WSPRAT 44H1 824.6 1.98 1636.3 0.1 1636.2 <0.1 >99.9 14204 2 14499 28 44H0 960.5 2.49 2392.9 30.0 2362.9 1.3 98.7 20990 712 20891 43H1 412.7 1.18 486.6 42.9 443.7 8.8 91.2 5461 1417 4045 43H0 973.7 2.14 2082.6 1807.6 274.9 86.8 13.2 57596 54890 2567 42H0 968.5 1.42 1379.3 924.6 454.8 67.0 33.0 34964 30262 4301 42G9 986.9 3.09 3053.1 319.2 2733.9 10.5 89.5 37566 8773 27467 26 41H0 953.3 2.53 2413.1 172.0 2241.1 7.1 92.9 27373 5226 21691 41G9 1000.0 3.86 3856.6 2707.0 1149.6 70.2 29.8 92587 80929 12134 422 ICES | WGBIFS 2019 Table 5. Sprat stock characteristics from the Latvian BIAS in the Baltic Sea ICES SD 26N and 28.2 conducted by f/v "Ulrika" in the period of 17-26.10.2018. Table 5A n × 106 Age group ∑ ICES SD ICES Rect. 0 1 2 3 4 5 6 7 8+ 44H1 240 490 198 145 510 8 8 18 18 1636 28 44H0 543 576 201 234 576 116 47 24 47 2363 43H1 158 58 48 169 5 5 444 43H0 8 93 24 22 79 11 22 11 5 275 42H0 44 86 59 37 162 20 27 7 12 455 42G9 87 482 289 231 973 128 243 115 185 2734 26 41H0 178 575 288 340 658 70 60 36 36 2241 41G9 73 239 131 103 414 115 39 13 22 1150 Table 5B n, % Age group ∑ ICES SD ICES Rect. 0 1 2 3 4 5 6 7 8+ 44H1 14.6 30.0 12.1 8.9 31.2 0.5 0.5 1.1 1.1 100.0 28 44H0 23.0 24.4 8.5 9.9 24.4 4.9 2.0 1.0 2.0 100.0 43H1 35.7 13.1 10.7 38.1 1.2 1.2 100.0 43H0 3.0 33.7 8.9 7.9 28.7 4.0 7.9 4.0 2.0 100.0 42H0 9.7 19.0 13.0 8.1 35.7 4.3 5.9 1.6 2.7 100.0 42G9 3.2 17.6 10.6 8.5 35.6 4.7 8.9 4.2 6.8 100.0 26 41H0 7.9 25.7 12.9 15.2 29.4 3.1 2.7 1.6 1.6 100.0 41G9 6.3 20.8 11.4 9.0 36.1 10.0 3.4 1.2 1.9 100.0 Table 5C W, kg × 103 Age group ∑ ICES SD ICES Rect. 0 1 2 3 4 5 6 7 8+ 44H1 1126.2 4064.2 1913.1 1506.5 5267.1 90.1 98.3 218.7 215.1 14499.4 28 44H0 2539.3 4971.7 2026.3 2441.5 6215.6 1307.2 553.8 289.2 546.0 20890.5 43H1 1215.7 531.5 498.9 1668.7 62.3 67.6 4044.7 43H0 39.7 712.8 230.3 225.9 805.9 113.0 242.5 130.1 67.0 2567.2 42H0 186.5 682.0 560.5 389.2 1703.0 222.5 308.8 89.6 158.4 4300.5 42G9 428.9 4122.8 2698.2 2622.8 10491.2 1431.8 3051.0 1435.3 2424.6 28706.6 26 41H0 733.5 4711.6 2843.8 3854.1 7079.7 761.8 743.4 480.4 482.5 21690.9 41G9 319.8 2140.7 1386.2 1196.7 4820.2 1335.8 489.7 155.1 289.4 12133.7 Table 5D w, g Age group ∑ ICES SD ICES Rect. 0 1 2 3 4 5 6 7 8+ 44H1 4.7 8.3 9.7 10.4 10.3 10.9 11.9 12.2 12.0 8.9 28 44H0 4.7 8.6 10.1 10.4 10.8 11.3 11.9 12.3 11.7 8.8 43H1 7.7 9.1 10.5 9.9 11.8 12.8 9.1 43H0 4.9 7.7 9.4 10.4 10.2 10.4 11.1 12.0 12.3 9.3 42H0 4.2 7.9 9.5 10.5 10.5 11.3 11.5 12.2 12.9 9.5 42G9 4.9 8.5 9.3 11.3 10.8 11.2 12.5 12.5 13.1 10.5 26 41H0 4.1 8.2 9.9 11.3 10.8 10.9 12.3 13.5 13.3 9.7 41G9 4.4 8.9 10.6 11.6 11.6 11.6 12.5 11.7 13.3 10.6 Table 5E L, g Age group ∑ ICES SD ICES Rect. 0 1 2 3 4 5 6 7 8+ 44H1 8.8 10.4 11.3 11.7 11.7 12.0 12.5 13.0 13.3 10.9 28 44H0 8.7 10.6 11.4 11.6 11.8 12.1 12.6 13.0 12.8 10.8 43H1 10.2 11.1 11.9 11.5 12.5 13.5 11.1 43H0 8.8 10.3 11.3 11.8 11.8 11.9 12.3 12.8 13.0 11.3 42H0 8.5 10.6 11.4 12.1 12.0 12.5 12.7 13.0 12.8 11.4 42G9 9.1 10.8 11.3 12.3 12.0 12.3 13.0 13.0 13.3 11.9 26 41H0 8.4 10.6 11.5 12.2 11.9 12.1 12.8 13.3 12.5 11.3 41G9 8.7 10.9 11.8 12.3 12.3 12.4 12.7 13.1 13.8 11.8 ICES | WGBIFS 2019 423 Table 6. Herring stock characteristics from the Latvian BIAS in the Baltic Sea ICES SD 26N and 28.2 conducted by f/v "Ulrika" in the period of 17-26.10.2018. Table 6A n × 106 Age group ∑ ICES SD ICES Rect. 0 1 2 3 4 5 6 7 8+ 44H1 28 44H0 4 5 4 11 1 4 1 1 30 43H1 2 6 14 3 9 5 5 43 43H0 53 118 230 592 158 296 191 171 1808 42H0 6 50 123 297 85 202 85 76 925 42G9 25 36 49 144 17 32 8 9 319 26 41H0 2 45 12 22 27 24 15 12 11 172 41G9 253 270 331 1066 289 422 52 25 2707 Table 6B n, % Age group ∑ ICES SD ICES Rect. 0 1 2 3 4 5 6 7 8+ 44H1 28 44H0 12.0 18.1 12.0 36.1 4.8 12.0 2.4 2.4 100.0 43H1 4.0 13.9 31.7 6.9 20.8 10.9 11.9 100.0 43H0 2.9 6.5 12.7 32.7 8.7 16.4 10.5 9.5 100.0 42H0 0.7 5.5 13.3 32.1 9.2 21.8 9.2 8.2 100.0 42G9 7.7 11.2 15.4 45.0 5.3 10.1 2.4 3.0 100.0 26 41H0 1.2 26.3 7.1 13.0 15.8 14.1 8.9 7.1 6.5 100.0 41G9 9.3 10.0 12.2 39.4 10.7 15.6 1.9 0.9 100.0 Table 6C W, kg × 103 Age group ∑ ICES SD ICES Rect. 0 1 2 3 4 5 6 7 8+ 44H1 28 44H0 73.2 105.5 98.8 277.2 27.6 130.8 31.5 31.5 747 43H1 52.4 176.4 424.2 103.8 313.2 196 233 1466.3 43H0 1118.3 2737.6 6394 17286.4 5166.6 9886.4 7181.6 7746.3 57313.6 42H0 125.4 1230 3259.5 8969.4 3000.5 7090.2 3272.5 3245.2 30247.5 42G9 512.5 849.6 1313.2 4089.6 508.3 1068.8 299.2 317.7 8932 26 41H0 32 940.5 282 587.4 839.7 777.6 577.5 460.8 532.4 5314.8 41G9 5540.7 6318 9400.4 32619.6 10693 15867.2 2074.8 1205 80127.2 Table 6D w, g Age group ∑ ICES SD ICES Rect. 0 1 2 3 4 5 6 7 8+ 44H1 28 44H0 18.3 21.1 24.7 25.2 27.6 32.7 31.5 31.5 24.9 43H1 26.2 29.4 30.3 34.6 34.8 39.2 46.6 34.1 43H0 21.1 23.2 27.8 29.2 32.7 33.4 37.6 45.3 31.7 42H0 20.9 24.6 26.5 30.2 35.3 35.1 38.5 42.7 32.7 42G9 20.5 23.6 26.8 28.4 29.9 33.4 37.4 35.3 28.0 26 41H0 16.0 20.9 23.5 26.7 31.1 32.4 38.5 38.4 48.4 30.9 41G9 21.9 23.4 28.4 30.6 37.0 37.6 39.9 48.2 29.6 424 ICES | WGBIFS 2019 Figure 4. Acoustic parameter NASC distribution from the Latvian BIAS in the Baltic Sea ICES SD 26N and 28.2 conducted by f/v "Ulrika" in the period of 17-26.10.2018. ICES | WGBIFS 2019 425 Figure 5. Sprat distribution (n×106) from the Latvian BIAS in the Baltic Sea ICES SD 26N and 28.2 conducted by f/v "Ulrika" in the period of 17-26.10.2018. 426 ICES | WGBIFS 2019 Figure 6. Herring distribution (n×106) from the Latvian BIAS in the Baltic Sea ICES SD 26N and 28.2 conducted by f/v "Ulrika" in the period of 17-26.10.2018. ICES | WGBIFS 2019 427 Annex 8: List of presentations made at the WGBIFS 2019 meeting 1. BASS presentation of Estonia, made by Elor Sepp (Estonia); 2. BASS presentation of Latvia, made by Guntars Strods (Latvia); 3. BASS presentation of Lithuania, made by Marijus Spegys (Lithuania); 4. BASS presentation of Poland, made by Beata Schmidt (Poland); 5. BASS presentation of Germany, made by Paco Rodriguez-Tress (Germany); 6. BIAS presentation of Finland, made by Juha Lilja (Finland); 7. BIAS presentation of Estonia, made by Elor Sepp (Estonia); 8. BIAS presentation of Latvia, made by Guntars Strods (Latvia); 9. BIAS presentation of Lithuania, made by Marijus Spegys (Lithuania); 10. BIAS presentation of Poland, made by Beata Schmidt (Poland); 11. BIAS presentation of Germany, made by Paco Rodriguez-Tress (Germany); 12. BIAS presentation of Sweden, made by Niklas Larson (Sweden); 13. BITS presentation of Estonia, made by Elor Sepp (Estonia); 14. BITS presentation of Latvia, made by Ivo Sics (Latvia); 15. BITS presentation of Lithuania, made by Marijus Spegys (Lithuania); 16. BITS presentation of Poland, made by Krzysztof Radtke (Poland); 17. BITS presentation of Germany, made by Andrés Velasco (Germany); 18. BITS presentation of Denmark, made by Henrik Degel (Denmark); 19. Presentation of summary actions on WGCHAIRS, made by Olavi Kaljuste (Sweden); 20. Presentation about the WKSABI outcomes relevant for WGBIFS, made by Vaishav Soni (ICES secretariat); 21. Presentation about the data availability and quality of BITS data in DATRAS for the swept area effort index calculations, made by Henrik Degel (Denmark). All these presentations are available in the folder “Presentations” in the WGBIFS 2019 SharePoint site. 428 ICES | WGBIFS 2019