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.
Highlights
Ecological flexibility can play an important role in a species’ ability to cope with environmental change
Ecology and Evolution published by John Wiley & Sons Ltd
The presence of bowhead whale in the diets of bears suggests that scavenging carcasses provided by killer whale predation may serve as an important energetic supplement, during seasons of low food availability and to younger age classes that may have difficulty catching prey
Summary
Ecological flexibility can play an important role in a species’ ability to cope with environmental change. Highly specialized species can be sensitive to climate change and habitat loss (Colles et al 2009; Kovacs et al 2011; Gilg et al 2012). Polar bears (Ursus maritimus) are top predators within their Arctic circumpolar range and may be sensitive to environmental change because of their reliance on sea ice habitat for traveling, mating, and foraging (Stirling and Derocher 1993; Laidre et al 2008). As sea ice extent and habitat quality decline because of climate warming, ice-associated prey species become less accessible.
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