Declining fall weights of female polar bears, western Hudson Bay, 1980 to 2007

LifeLinkedtoIce Declining fall weights of female polar bear


Box 10. Declines in polar bear body condition
In areas where sea ice melts completely in the summer polar bears may be forced onto land. Earlier sea ice break-up in these areas reduces the amount of time bears have for hunting seals on the ice. In some areas where this is occurring, bears are becoming thinner, resulting in decreases in survival and reproduction.


Changes in sea ice over the past two decades have led to significant declines in physical condition of bears in the western Hudson Bay [277, 299], southern Hudson Bay [300], and Baffin Bay populations [279]. Regehr et al. 2007 [278] showed that survival decreased in association with earlier sea ice break-up and that this contributed to a 22% decline in the size of the western Hudson Bay polar bear population between 1987 and 2004. Reduced survivorship in relation to sea ice conditions has also been demonstrated in the southern Beaufort Sea polar bear population [301].


For the western Hudson Bay population, the body condition of bears measured during the ice-free period declined from 1980 to 2007, as did the average weight of female polar bears in the fall (Figure 30). The female bears weighed were suspected to be pregnant.


For the Baffin Bay population, the decline in body condition since the early 1990s is associated with deteriorating ice conditions [279]. Polar bears were in significantly worse condition in years with less summer sea ice cover, starting in the 1990s when ice in these regions began its sharp decline (Table 2).


Figure 30. Declining fall weights of female polar bears, western Hudson Bay, 1980 to 2007

Body weights were estimated for females on their own, and thus likely to be pregnant.

Source: Stirling and Derocher 2012 [269]



Conservation of Arctic Flora and Fauna (CAFF) 

The data can be downloaded freely. Users are requested to reference the source.

Eamer, J., Donaldson, G.M., Gaston, A.J., Kosobokova, K.N., Lárusson, K.F., Melnikov, I.A., Reist, J.D., Richardson, E., Staples, L., von Quillfeldt, C.H. 2013. Life Linked to Ice: A guide to sea-ice-associated biodiversity in this time of rapid change. CAFF Assessment Series No. 10. Conservation of Arctic Flora and Fauna, Iceland. ISBN: 978-9935-431-25-7.



269. Stirling, I., and Derocher, A.E. 2012. Effects of climate warming on polar bears: A review of the evidence. Global Change Biology 18(9): 2694-2706. doi:10.1111/j.1365-2486.2012.02753.x.
277. Stirling, I., Lunn, N.J., and Iacozza, J. 1999. Long-term trends in the population ecology of polar bears in western Hudson Bay in relation to climatic change. Arctic 52(3): 294-306.
278. Regehr, E.V., Lunn, N.J., Amstrup, S.C., and Stirling, L. 2007. Effects of earlier sea ice breakup on survival and population size of polar bears in western Hudson bay. Journal of Wildlife Management 71(8): 2673-2683. doi:10.2193/2006-180.
279. Rode, K.D., Peacock, E., Taylor, M., Stirling, I., Born, E.W., Laidre, K.L., and Wiig, O. 2012. A tale of two polar bear populations: Ice habitat, harvest, and body condition. Popul. Ecol. 54(1): 3-18. doi:10.1007/s10144-011-0299-9.
299. Stirling, I., and Parkinson, C.L. 2006. Possible effects of climate warming on selected populations of polar bears (Ursus maritimus) in the Canadian Arctic. Arctic 59(3): 261-275.
300. Obbard, M.E., Cattet, M.R.L., Moody, T., Walton, L.R., Potter, D., Inglis, J., and Chenier, C. 2006. Temporal trends in the body condition of southern Hudson Bay polar bears. Climate Change Research Information Note No. 3. Applied Research and Development Branch, Ministry of Natural Resources, Government of Ontario, Ontario.
301. Regehr, E.V., Hunter, C.M., Caswell, H., Amstrup, S.C., and Stirling, I. 2010. Survival and breeding of polar bears in the southern Beaufort Sea in relation to sea ice. Journal of Animal Ecology 79(1): 117-127. doi:10.1111/j.1365-2656.2009.01603.x.


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