Gray and Harbor Seal Bycatch and Depredation in New England Sink-Gillnet Fisheries

Gray seals (Halichoerus grypus) and harbor seals (Phoca vitulina) are often taken as bycatch in sink-gillnet fisheries in New England and are believed to consume and damage fish in gillnets.  As seal populations increase, interactions with fisheries are likely to increase, affecting both seal stocks and the New England fishing industry.  The extent of these interactions will be assessed through field observations of depredation and bycatch on commercial gillnet fishing vessels in New England waters May – July 2014.  Seals taken incidentally during these trips will be assessed for species, age, sex, and general health (determined by blubber thickness, weight, level of hydration, and size of lymph nodes); trends will be identified.  Seal damaged catch will be quantified and monetary losses will be calculated. There is some controversy among fishermen and scientists concerning the identification of seal depredation compared to other sources of depredation (e.g. spiny dogfish (Squalus acanthias)).  Characteristic depredation will be identified by offering large fish to captive seals and other predators. Damaged fish will be analyzed for the unique bite marks of predatory species that can be used in the field for accurate identification.  This study is crucial to understanding the complexities of seal-fishery interactions.