Acoustic seal deterrents in mitigation of human–wildlife conflicts in the whitefish fishery of the River Iijoki in the northern Baltic Sea area

Recovery of many seal populations has intensified seal-fishery conflicts. Acoustic deterrent devices (ADDs), designed to deter seals while minimising collateral harm, provide a potential solution. We investigated feasibility of ADDs to protect a European whitefish (Coregonus lavaretus) fishery in the River Iijoki, Finland, which enters the Baltic Sea. A sound barrier produced by a line of ADDs across the river efficiently prevented grey (Halichoerus grypus) and ringed (Pusa hispida) seals from passing the barrier line, thereby increasing catches, decreasing damage to fishing gear and catch and resulting in fewer seal sightings in the area safeguarded by ADDs. Hence, blocking access of seals to a river or its section by ADDs during a critical fishing period is a promising method for reducing seal-induced catch losses. However, long-term assessments of impacts of ADDs are still needed to verify the overall effectiveness.