Abstract 127 – Comparison in the ecology of two polar bear populations experiencing sea ice loss

Karyn Rode, Todd Atwood, Ryan Wilson, Jeff Bromaghin, Anthony Pagano, Dave
Douglas

Polar bears are recognized in 19 populations across the circumpolar Arctic. Across their range
they occupy habitats that vary in annual sea ice dynamics, ecology, and rates and degrees of
sea ice loss. Over the past decade, a wide range of studies have been conducted that shed light
on polar bear ecology and their limits to adapting to environmental change. The two adjacent
populations with ranges in Alaska have provided informative case studies. Both populations
occupy habitats in which sea ice is available year-round but retreats northward in the summer.
As sea ice loss has occurred, both populations have increasingly summered on land. In the
southern Beaufort Sea (SBS), bears come onshore in northern Alaska where most bears feed on
the remains of subsistence-harvested bowhead whales. In the Chukchi Sea (CS), the majority of
bears that summer on land come to Wrangel and Herald islands as sea ice retreats, the
northernmost land masses. In contrast to SBS bears, CS bears largely rest along the immediate
coastline. However, despite access to a consistent and predictable food resource on shore in
the SBS, the population declined in recent years whereas the CS population has appeared
stable. Studies of bear behavior and ecology on the sea ice suggest that SBS bears had a series
of years with poor access to prey over the narrow continental shelf leading to low cub survival
and subsequent population decline. In contrast, polar bears in the CS occupy habitat over a
vast, shallow continental shelf that appears to support higher densities, abundance, and wider
distribution of bearded and ringed seals. As summer and spring sea ice loss have occurred in
the CS, bears appear to have maintained access to their prey. This presentation will synthesize
multiple studies conducted in the two populations that suggest that differences in regional
ecology and geography play important roles in determining polar bear sensitivity to sea ice loss.