Stable isotope and scat analyses indicate diet and habitat partitioning in northern fur seals Callorhinus ursinus across the eastern Pacific

Linking northern fur seal dive behavior to environmental variables in the eastern Bering Sea

“…Walleye pollock of year-class 0 and 1 are the most common prey in scat studies of the northern fur seal diet (Perez and Bigg 1986, Sinclair et al 1994, Sinclair et al 1996, and walleye pollock comprised 89.3% of fur seal diet as measured in scats collected within a month of our 2006 tagged females foraging trips from Reef Rookery (Zeppelin and Orr 2010). We found that, in locations with more abundant walleye pollock, northern fur seals were more likely to be actively diving, especially at night.…”

“…The dominant prey in fur seal diets is juvenile walleye pollock (Gadus chalogramma; Perez and Bigg 1986, Sinclair et al 1994, Zeppelin and Orr 2010, a species of groundfish that is commercially caught as adults. However, direct information on prey fields is difficult to collect and is not always available.…”

Combining hard-part and DNA analyses of scats with biologging and stable isotopes can reveal different diet compositions and feeding strategies within a fur seal population

“…Consequently, only the combination of these 4 methods allowed us to draw a more complete and ecologically accurate picture of the diets of lactating females within the breeding population on St. Paul Island, and to determine that estimates of diet for the population can be reflected at the individual level at different spatial and temporal scales. Zeppelin & Orr (2010). One female (Seal #6, grey crossed dot) that remained on the shelf to forage nevertheless showed isotopic values corresponding to oceanic foraging.…”

“…We collected 98 scats in August -September 2011, more than the number required to reach the maximum prey diversity (Zeppelin & Orr 2010). Fur seal colonies are made of harems with multiple females within males' territories.…”

“…Interestingly, a small breeding colony recently established on Bogoslof Island within the deep basin of the Bering Sea has been steadily increasing. The diet of these 'Bogoslof' seals seems to differ from the 'Pribilof' ones and contains more mid-water mesopelagic fish and gonatid squid and fewer walleye pollock (Zeppelin & Orr 2010). Assessing foraging strategies and diets is thus important for understanding the balance between energy input from food, and the energy spent foraging.…”