Beyond encounter risk: Fleet-level heterogeneity is associated with at-vessel mortality of false killer whales in the Western and Central Pacific tuna purse seine fishery

Researchers analyzed publicly-reported interaction data submitted to the Western and Central Pacific Fisheries Commission covering 239 false killer whale (Pseudorca crassidens) interaction events from tuna purse seine vessels associated with China, Taiwan, Micronesia, Kiribati, Papua New Guinea, and Nauru during the periods 2016-2020 and 2023-2024. The study combined fishery records with environmental variables such as sea-surface temperature, salinity, dissolved oxygen, chlorophyll concentration, and water depth to identify which factors were most strongly associated with at-vessel mortality. Fleet identity was the strongest predictor of mortality, followed by year-to-year differences. Environmental conditions and geographic location explained very little of the variation in mortality rates. Operational practices, including earlier detection of trapped animals, reducing animal crowding and compression within nets, and faster and more effective release procedures may help improve mortality risk of small cetaceans in industrial tuna purse seine fisheries.