The diet and feeding ecology of gray seals (Halichoerus grypus) in United States waters, based on hard part and fatty acid analysis

Ampela, Kristen

The Graduate Center/CUNY

College of Staten Island, Biology Department, 2800 Victory Blvd 6S-143, Staten Island, NY 10314 U.S.A.

Krs10a@gmail.com

Extinct in the U.S. prior to 1958, gray seals (Halichoerus grypus) now number more than 7,000 in New England waters.  The increase is due in part to the success of the Marine Mammal Protection Act of 1972. Many fishermen suggest that seals deplete fish stocks targeted by commercial fisheries, and I wanted to examine to what extent this is true.   I analyzed hard remains from 305 seal scats and 49 seal stomachs in order to 1) determine gray seal diet composition, 2) investigate individual, regional and temporal variation in diet, and 3) identify possible seal/fishery conflicts. I used fatty acid analysis of 48 seal blubber cores to investigate variation in diet. Of 29 prey taxa recovered, 9 comprised more than 5% of the diet by weight, number and/or frequency. Of these, sand lance (Ammodytes spp.) dominated the diet by weight (54% of total) and number of prey individuals consumed (66% of total). Skates were recovered most frequently (26% of samples). Atlantic cod and Atlantic herring (Clupea harengus) comprised 6% and 4% of the diet by weight, respectively. Sand lance is not harvested commercially in the U.S., but other taxa important in the diet are, such as hake (Urophycis spp.), flounder, squid and skates. More hake (Urophycis spp.) was recovered in stomachs from southern New England and the New York Bight. Seal diet diversity is higher in spring months than in summer or winter. Male gray seals consume more silver hake (Merluccius bilinearis) than do females.  Juveniles 1-2 years old target different prey than young-of-the-year pups.