2026/07/01 by Tiffany Goh, Enrico Pirotta, Oriol Giralt Paradell +2
paper · doi:10.1002/aqc.70415
ABSTRACT When empirical bycatch data are limited, risk‐based assessments offer a valuable tool for identifying areas where marine mammals and fisheries are most likely to interact. The harbour porpoise ( Phocoena phocoena ) is among the most vulnerable to incidental capture in gillnet fisheries. Although protected under European legislation, monitoring and mitigation efforts in Ireland remain insufficient to fully assess and address bycatch. Recent harbour porpoise abundance estimates indicate a declining trend in Irish waters, with bycatch considered a potential contributing factor. Here, we assessed seasonal spatial patterns of harbour porpoise–gillnet interaction risk by combining predicted porpoise distribution with gillnet fishing effort data for summer and winter between 2015 and 2022. Allowable bycatch thresholds, representing the maximum number of individuals that can be removed without causing population decline, were calculated using 2022 abundance estimates and a range of recovery factors and intrinsic growth rates for porpoises within the Irish Exclusive Economic Zone. Areas of elevated bycatch risk were consistently identified in the Celtic Sea and along the continental shelf off Ireland's west coast, indicating persistent zones of potential exposure. Calculated bycatch thresholds were low across all parameterisations, suggesting limited tolerance for additional mortality in a declining population. Although empirical bycatch data are required to determine the bycatch rate, these findings highlight priority areas for monitoring and mitigation. Overall, this study provides a spatially explicit framework to inform precautionary management of harbour porpoise–gillnet interactions in Irish waters.