Data from: Dietary habits of polar bears in Foxe Basin, Canada: possible evidence of a trophic regime shift mediated by a new top predator

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.

在多个季节性海冰覆盖区域的北极熊（Ursus maritimus）亚种群，因海冰栖息地缩减，已出现身体状况、繁殖率或种群丰度下降的现象。加拿大努纳武特地区的福克斯盆地（Foxe Basin）区域内，尽管同期海冰栖息地持续减少，该区域的北极熊亚种群规模在过去20年间基本保持稳定。本研究采用脂肪酸分析法，对福克斯盆地内北极熊的摄食习性展开分析，以期明确可能维系种群稳定的生态驱动因素。研究采集了2010至2012年间猎获的103头北极熊的脂肪组织样本。该区域内北极熊的饮食组成存在空间异质性：福克斯盆地南北部的北极熊主要以环斑海豹（Pusa hispida）为食，而哈德逊海峡（Hudson Strait）区域的北极熊则等量捕食环斑海豹与竖琴海豹（Pagophilus groenlandicus）。海象（Odobenus rosmarus）的捕食比例在福克斯盆地北部最高，这一趋势源于成年雄性北极熊具备捕获大型猎物的能力。值得注意的是，所有区域、所有年龄与性别类群的北极熊均会摄入弓头鲸（Balaena mysticetus）。由虎鲸（Orcinus orca）捕食或人类生计性捕捞遗留的弓头鲸尸体，可能在无冰期为北极熊提供重要的补充食物来源。本研究结果表明，尽管海冰栖息地持续缩减，该区域虎鲸与弓头鲸种群数量的增长，可能间接提升了北极熊的觅食成功率。然而，如果海冰持续减少最终严重限制北极熊的冰上觅食机会，顶级捕食者间的这种间接互作关系可能仅为暂时性现象。