Diet of Beluga Whales, Delphinapterus leucas, in Alaska from Stomach Contents, March-November

摘要

At least five stocks of beluga whales, Delphinapterus leucas, are found in Alaska waters: Beaufort Sea, eastern Chukchi Sea, eastern Bering Sea, Bristol Bay, and Cook Inlet. The two northernmost stocks (Beaufort Sea and eastern Chukchi Sea) are highlymigratory: the two southernmost stocks (Bristol Bay and Cook Inlet) are nonmigratory. Little is known about the seasonal movements and distribution of the eastern Bering Sea stock. Beluga populations in Alaska are thought to be stable or increasing, except for the Cook Inlet stock which is listed as endangered under the Endangered Species Act.We analyzed stomach contents from beluga whales collected between the months of March and November taken in subsistence harvests, from belugas found dead, andfrom belugas collected for research. We describe prey species and their percent frequency of occurrence (% FO) as well as potential biases from the seasonality of prey relative to the timing of sampling, and differentialfeeding and digestion. Diet was highly variable among stocks. The predominantfish species of the Beaufort Sea stock was Arctic cod, Bo-reogadus saida (21% FO), although shrimp(60% FO) and smoothskin octopus, Ben-thoctopus leioderma (42Vo FO) were found morefrequently. Although the eastern Chukchi Sea stock ate more saffron cod, Eleginus gracilis (7% FO) than Arctic cod (3% FO), shrimp (73% FO) and echiurids (27% FO) were moreprevalent than fish. The eastern Bering Sea stock had the most diverse diet, and dominant fish species included saffron cod (95% FO), rainbow smelt, Osmerus mordax (62% FO), several species of scul-pin (Family Cottidae) and flatfish (Family Pleuronectidae), both at 48% FO, and Arctic cod at 43%. Dominant invertebrates included shrimp (86% FO), with polychaetes, isopods, bivalves, amphipods, and echiurids ranging from 29 to 38% FO. Pacific salmon, Onchorhyncus spp., predominated over cod in Bristol Bay(81% FO) and Cook Inlet (67% FO) beluga stocks, and invertebrates appeared to be less prevalent prey. In Bristol Bay, smelt were also eaten more often (43% FO) than cod (3% FO), while in Cook Inlet cod were eaten more often (39% FO) than smelt (11% FO).Invertebrates were common in the diet of all Alaska beluga stocks and shrimp (mostly from the family Crangoni-dae) were the most prevalent.