title: Dietary habits of polar bears in Foxe Basin, Canada: possible evidence of a trophic regime shift mediated by a new top predator.
abstract: Polar bear (Ursus maritimus) subpopulations in several areas with seasonal sea ice regimes have shown declines in body condition, reproductive rates, or abundance as a result of declining sea ice habitat. In the Foxe Basin region of Nunavut, Canada, the size of the polar bear subpopulation has remained largely stable over the past 20 years, despite concurrent declines in sea ice habitat. We used fatty acid analysis to examine polar bear feeding habits in Foxe Basin and thus potentially identify ecological factors contributing to population stability. Adipose tissue samples were collected from 103 polar bears harvested during 2010-2012. Polar bear diet composition varied spatially within the region with ringed seal (Pusa hispida) comprising the primary prey in northern and southern Foxe Basin, whereas polar bears in Hudson Strait consumed equal proportions of ringed seal and harp seal (Pagophilus groenlandicus). Walrus (Odobenus rosmarus) consumption was highest in northern Foxe Basin, a trend driven by the ability of adult male bears to capture large-bodied prey. Importantly, bowhead whale (Balaena mysticetus) contributed to polar bear diets in all areas and all age and sex classes. Bowhead carcasses resulting from killer whale (Orcinus orca) predation and subsistence harvest potentially provide an important supplementary food source for polar bears during the ice-free period. Our results suggest that the increasing abundance of killer whales and bowhead whales in the region could be indirectly contributing to improved polar bear foraging success despite declining sea ice habitat. However, this indirect interaction between top predators may be temporary if continued sea ice declines eventually severely limit on-ice feeding opportunities for polar bears.
authors.affiliation: Department of Biology York University Toronto Ontario M3J 1P3 Canada.
authors.forename: Melissa P
authors.initials: MP
authors.lastname: Galicia
authors.affiliation: Faculty of Environmental Studies York University Toronto Ontario M3J 1P3 Canada.
authors.forename: Gregory W
authors.initials: GW
authors.lastname: Thiemann
authors.affiliation: Wildlife Research Section Department of Environment Government of Nunavut P.O. Box 209 Igloolik Nunavut X0A 0L0 Canada.
authors.forename: Markus G
authors.initials: MG
authors.lastname: Dyck
authors.affiliation: Fisheries and Oceans Canada 501 University Crescent Winnipeg Manitoba R3T 2N6 Canada.
authors.forename: Steven H
authors.initials: SH
authors.lastname: Ferguson
authors.affiliation: Higdon Wildlife Consulting 912 Ashburn Street Winnipeg Manitoba R3G 3C9 Canada.
authors.forename: Jeff W
authors.initials: JW
authors.lastname: Higdon
keywords: Bowhead whales (Balaena mysticetus); Canadian Arctic; climate change; feeding ecology; killer whales (Orcinus orca); marine food web; marine mammals; polar bear (Ursus maritimus); quantitative fatty acid signature analysis