Three decades of observer records reveal ongoing risks of marine mammal depredation and entanglement in Canada’s Atlantic fisheries

Abstract Marine mammals adapt foraging strategies in response to human activities and environmental change, often resulting in conflicts with fisheries. Whale-fishery interactions, including depredation and entanglement, pose significant challenges for both marine conservation and fisheries management. This study presents the first comprehensive, multi-fishery analysis of marine mammal behaviour and gear-associated incidents using at-sea observer (ASO) records collected between 1990 and 2023 across Canada’s North Atlantic. The final dataset comprised 5184 marine mammal sightings reported by ASOs across multiple fisheries. The aims were to: (1) assess the severity of incident records, ranging from close approaches, depredation, injury, entanglement, and death; (2) calculate the minimum frequency of sightings and incidents by gear type and target species; and (3) identify trends in depredation incidents across species and fisheries. Results reveal widespread depredation behaviour by deep-diving northern bottlenose (Hyperoodon ampullatus) and sperm whales (Physeter macrocephalus), particularly in Greenland halibut (Reinhardtius hippoglossoides) fisheries. Gillnets and bottom trawls were responsible for most entanglement incidents, with small odontocetes like harbour porpoises (Phocoena phocoena) experiencing relatively higher rates of severe entanglement. Entanglement rates for endangered northern bottlenose whales exceeded limits considered sustainable under current recovery objectives. Minimum annual incident rates exceeded 3 observed events per year for long-finned pilot whales (Globicephala melas) and 1.8 for harbour porpoises, across all reported sightings. Risks varied across regions, gear types, and species. These findings highlight the need for fishery-specific mitigation, spatial management, and expanded observer coverage to reduce harmful interactions and promote long-term coexistence between marine mammals and fishing operations.