The use of acoustic deterrent devices to mitigate fishery-seal conflict at the scale of an entire coastal bay

Recovering seal populations are increasingly in conflict with aquaculture and fisheries. One potential approach to mitigate these conflicts is the use of seal deterrents, such as acoustic deterrent devices (ADDs). These devices are typically deployed near aquaculture pens or fishing gear where seal foraging is considered problematic. In the current multiyear study, we assessed the feasibility of creating a larger seal-restricted area by installing ADDs in narrow straits leading to a large (~40 km2) coastal bay. We found that fishers’ gillnets were subject to lower levels of seal-induced damage during years when ADDs were in use. However, seal-induced damage and seal sightings remained common within the bay even when the devices were operated. Catches of secondary target species seemed to respond positively to ADD deployment, whereas those of the main target species, the pikeperch (Sander lucioperca), did not significantly increase, suggesting a limited effect on the catches. Fishers’ perceptions of the use of ADDs varied but were generally positive. Overall, the results indicate that the tested approach provided only modest measurable benefits to the fishery within a large bay. One potential explanation to this finding is that the number of ADDs deployed may have been insufficient to more substantially limit seal movements into the area. The study also highlights the influence of local environmental conditions and other context-dependent factors on ADD effectiveness and the need for further research into the performance of different ADD configurations.