Estimating the abundance of a polar bear subpopulation at their southern global extent

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Climate warming is causing global biodiversity loss, with impacts to ecosystem function. Warming in the Arctic outpaces global averages, and projected declines in Arctic-sea ice have led to predictions of local extirpations for ice-associated species. Polar bears (Ursus maritimus Phipps, 1774) exemplify these challenges as they rely on sea ice for much of their life cycle. Further, polar bears are harvested throughout much of their range, increasing the importance of robust population monitoring in the face of climate warming. We conducted an aerial survey in summer 2021 to estimate abundance of the Southern Hudson Bay polar bear subpopulation. We estimated 1119 polar bears (95% CI = 860-1454) within the boundaries of the subpopulation, which suggested a 29% increase from the previous aerial survey in 2016. This increase was likely driven by a combination of interannual variation in the on-land distribution of bears in the Southern Hudson Bay and adjacent Western Hudson Bay polar bear subpopulations as well as reduced harvest and improved survival. Evidence from concurrent research suggests that variation in on-land distribution is the most likely driver. These results exemplify the challenges of monitoring and, particularly, managing harvest of sensitive species under the rapid environmental change caused by climate warming. Further research is needed and critical for effective harvest management of this subpopulation.