Diet of beluga whales, Delphinapterus leucas, in Alaska from stomach contents, March-November

At least fi ve 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 highly migratory; 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, and from 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 differential feeding and digestion. Diet was highly variable among stocks. The predominant fi sh species of the Beaufort Sea stock was Arctic cod, Boreogadus saida (21% FO), although shrimp (60% FO) and smoothskin octopus, Benthoctopus leioderma (42% FO) were found more frequently. 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 more prevalent than fi sh. The eastern Bering Sea stock had the most diverse diet, and dominant fi sh species included saffron cod (95% FO), rainbow smelt, Osmerus mordax (62% FO), several species of sculpin (Family Cottidae) and fl atfi sh (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. Pacifi c 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 Crangonidae) were the most prevalent. Introduction At least fi ve stocks of beluga whales, Delphinapterus leucas, occur in the waters of Alaska (Fig. 1). These stocks were tentatively identifi ed by their summer distributions (Frost and Lowry, 1990; Richard et al., 2001), and were later confi rmed genetically (O’Corry-Crowe et al., 1997, 2002, 2010). The distribution of beluga whales in Alaska is discontinuous from Yakutat Bay1, 2 to Cook Inlet to Bristol Bay. The entire area from Bristol Bay northward and eastward to Canada is used by belugas; the Bering and Chukchi seas are used year-round and the Beaufort Sea is used in summer (Frost and Lowry, 1990). 1There is a small group of <20 belugas that appear to be resident in Yakutat Bay, a deepwater fi ord (Laidre et al., 2000; Allen and Angliss, 2011) 2O’Corry-Crowe, G. , W. Lucey, C. Bonin, E. Henniger, and R. Hobbs. 2006. The ecology, status and stock identify of beluga whales, Delphinapterus leucas, in Yakutat Bay, Alaska. Rep. to U.S. Mar. Mamm. Comm., NMFS-YSB-YTT, 22 p. Beluga whales in Alaska appear to follow one of two life history strategies: migratory and nonmigratory. Migratory stocks use shallow nearshore and deepwater offshore habitats (Hazard, 1988; Frost and Lowry, 1990), and include the eastern Chukchi Sea stock (population size ~4,000 (Allen and Angliss, 2011)) and the Beaufort Sea or Mackenzie stock (population size ~39,000 (Harwood et al., 1996; Allen and Angliss, 2011)). Nonmigratory stocks use shallow, estuarine habitats year-round and include the Bristol Bay and Cook Inlet stocks. The Bristol Bay population is increasing (Lowry et al., 2008) and is estimated to be ~3,000 (Allen and Angliss, 2011). Local sightings and satellite telemetry confi rm that belugas occur in Bristol Bay in all months of the year (Harrison and Hall, 1978; Frost and Lowry, 1990; Lensink3; Quakenbush and Citta4; Quaken bush5). The population in Cook Inlet is estimated to be 312 whales and appears to be decreasing at 1.6% per year (Hobbs et al., 2015). The population declined dramatically between 1994 and 1998 (Hobbs et al., 2000) and the stock was determined to be depleted under the Marine Mammal Protection Act in 2000 (NOAA, 2000); the original cause of the decline is believed to be overharvest. Between 1999 and 2006 the harvest was restricted to fi ve 3Lensink, C. J. 1961. Status report: beluga studies. Alaska Dep. Fish Game, Juneau. Unpubl. rep., 38 p. 4Quakenbush, L. , and J. Citta. 2006. Fall movements of beluga whales captured in the Nushagak River in September 2006. Unpubl. rep. to Alaska Beluga Whale Committee, P.O. Box 69, Barrow Alaska 99723, 9 p. 5Quakenbush, L. , Alaska Dep. Fish Game, 1300 College Road, Fairbanks. Unpubl. data.