The Southern Hudson Bay (SH) population of polar bears (Ursus maritimus) resides in a seasonal sea ice environment and is the most southerly population in the species’ range. Therefore, SH polar bears may be among the first to show negative effects associated with climate warming and consequent loss of sea ice. Polar bears in the neighboring Western Hudson Bay (WH) population have declined significantly in body condition since the mid-1980s, and a recent study indicated that the size of the WH population declined by about 22% between 1987 and 2004. Similarly, SH bears have shown a significant decline in body condition since the mid-1980s, and an assessment of the current status of the SH population was therefore needed. We applied open population capture-recapture models to data collected from 1984-86 and 1999- 2005 to estimate population size and survival. The size of the SH population appears to be unchanged from the mid-1980s (1984-1986: 641, 95% CI = 401, 881) vs. 2003-2005: 681 (95% CI = 401, 961). Point estimates of survival for subadults and adult females were 94% (95% CI = 68%, 100%) in 1984-1985 to 89% (95% CI = 79%, 99%) in 2003-2005, but imprecision exhibited by overlap of the confidence intervals prevented us from unequivocally concluding that this 5% decline in survival was not a chance occurrence. Similarly, a decline of 7% in survival was estimated for subadult and adult males over the same time period (male survival estimates = 88% (95% CI = 77%, 100%) in 1984-1985; 81% (95% CI = 66%, 96%), but again we could not unequivocally conclude that this decline was not chance. There was weak evidence of lower survival of cubs, yearlings, and senescent adults in the recent time period. This, combined with the evidence of significant declines in body condition for all age and sex classes, which were greatest for pregnant females and subadults, suggests this population may be under increased stress at this time. However, we did not find any clear association between survival and cub-ofthe-year body condition, average body condition for the age class, or extent of ice cover in our data. This lack of association could be real or attributable to the coarse scale of our average body condition measure, or to limited sample size and few years of intensive sampling. That the WH population appears to be in decline, but the SH population does not, might be explained by changes to sea ice patterns which to date have been greater in the western half of Hudson Bay (breakup 10 days earlier per decade) than in the eastern and southern portions of Hudson Bay (breakup 5-8 days earlier per decade). However, if the trend in sea ice patterns (i.e., earlier melt and later freeze-up) continues in eastern and southern Hudson Bay, the SH population will likely respond similarly to the WH population and begin to decline.
Click on title to download individual files attached to this item.
Potential Metadata Source