Abstract 309 – Sea ice dynamics influence movement patterns of adult female polar bears of the Southern Hudson Bay subpopulation

Martyn Obbard and Kevin R. Middel

To access seals, polar bears (Ursus maritimus) move large distances over the sea ice in winter.
Already documented declines in ice duration for Hudson Bay are predicted to continue, likely
affecting polar bear movement patterns. Using data from GPS collars, 2007-2011, we describe
movement patterns of adult female polar bears of the Southern Hudson Bay (SH)
subpopulation. We tested effects of season and reproductive class on movement rates,
distance travelled, displacement distance and direction, and home range size. Except for
denning females, reproductive class had no effect on movement rates, which were greatest
during freeze-up and least during summer. Across all reproductive classes and seasons, mean
hourly movement rate was 0.63 km/h. Mean annual distance moved by non-denning females
was 4771 km. During freeze-up, bears moved north-easterly from the Ontario coast towards
the Belcher Islands and Québec following the forming ice edge. During breakup, bears moved
southerly towards the Ontario coast and away from the residual ice that occurs north of the
Ontario coast. In fall, denning females moved southerly and inland to den. Mean annual
minimum convex polygon (MCP) home range size was 153, 866 km2, with no effect of
reproductive class nor change over time. Home range estimates from kernel density estimators
and Brownian bridge movement models (BBMM) varied by reproductive class and were smaller
than MCP ones. BBMM estimates likely yield more realistic patterns of space use by polar
bears. Using data from satellite collars, 1997-2003, we compared travel distance and home
range size between periods (1997-2003; 2007-2011). We found weak evidence of a difference
in distance moved between periods, perhaps due to a period of ice stability in the 2000s. Our
results identified patterns of use of extensive areas of Hudson Bay by SH bears in winter..