Abstract 210 – Movement and survival of polar bears in relation to sea ice and harvest in Hudson Bay.

David McGeachy, Nicholas J. Lunn, Joseph M. Northrup, Vicki Trim, Evan S.
Richardson, Alyssa M. Bohart, Amélie Roberto-Charron, Guillaume Szor, Corey S. Davis, Andrew
E. Derocher

We estimated movement and survival rates between two neighbouring subpopulations of polar
bears, Western Hudson Bay (WH) and Southern Hudson Bay (SH), in relation to sea ice and
harvest using multistate live/dead recovery models to determine if recent changes in
abundance between WH and SH were due to distributional shifts or different demographic
processes. We collected skin samples from 2667 free-ranging polar bears (WH, 2017-2023,
n=1748; SH, 2021-2023, n=919) and 360 harvested 2017-2023 (WH, n=182; SH, n=178). Our
models included 3 separate geographical states where bears were sampled (A1, Nunavut
border to the Nelson River; A2, Nelson River to the SH/WH boundary; and A3, SH/WH boundary
to James Bay) and the location (western or eastern half of Hudson Bay) of remnant ice when
sea ice extent reached 10% of the winter maximum. Harvest data was used to assess harvest
vulnerability for each state. We found high interannual variability in the spatial distribution of
remnant ice within Hudson Bay which influenced polar bear distribution. In 2021, remnant ice
occurred in the east and 25% of the bears sampled in SH were identified as WH bears. In 2022,
remnant ice occurred in the west and 28% of the bears sampled in SH in 2021 were resampled
in WH. Movement continued from A3 into A2 in 2023 with movements rates higher for adult
males (0.28, 95%CI 0.18 to 0.39) than adult females (0.23, 95% CI 0.13 to 0.37). Movement
rates between the two subpopulations were similar to the increase in SH and decrease in WH
abundance derived from aerial surveys in 2021. Harvest vulnerability was not equal among the
states with A2 having a lower rate of harvest resulting in higher survival rates for bears in this
area. We conclude that the movement of bears between A2 and A3 is influenced by patterns of
remnant ice resulting in distributional shifts that likely influenced abundance estimates and
that variation in harvest vulnerability impacts survival for polar bears in Hudson Bay.