News of the North

Some naysayers of the affects of climate change on polar bears point to the recently completed Davis Strait population survey, which indicates an increase since the last estimate in the early 1990s, as evidence that not all populations will be negatively impacted by global warming. While there is general agreement among polar bear researchers and managers that different subpopulations of polar bears will feel the effects of environmental changes associated with global warming at different rates, it is unrealistically optimistic to assume that this species which has evolved both physiologically and behaviorally to hunt marine mammals from the platform provided by sea ice, will adapt to the loss of that habitat any better than species such as wolves and grizzly bears have adapted to habitat loss. In the words of Ian Stirling, perhaps the worlds foremost polar bear expert, “polar bears are large animals and they got that way by eating seals, not berries.”

Skeptics point to the good body condition of the bears in Davis Strait. Why, they ask, are the bears in the study not in poor condition like those in the Western Hudson Bay population? In Western Hudson Bay researchers found the condition of young and old bears to have declined significantly over the past 20 years, however prime age bears were still in good condition. This makes scene because the dominant animals and more experienced hunters would have better access to prey than younger and post-prime bears. I spent a week helping with the work in Davis Strait this summer. I don’t have hard numbers, but my impression was that while there certainly were some big healthy male bears in the sample there were also some that were not doing so well. In at least one case there was a family group where the cubs were looking a bit rough. It is quite possible that those individuals that were on the skinny side were the younger and post-prime age bears as was the case in Western Hudson Bay. It will be interesting to see if the final quantitative analysis finds differences in the body condition of different age classes of bears.

We also observed one instance of a male bear that we captured, who had killed and was eating a cub. This has been known to happen for years and is a natural occurrence among bear species. A female will not enter estrous while she is nursing cubs, so if a male bear kills a female’s cubs, she will be ready to mate sooner. Some researchers think that the incidence of infanticide and other cases of cannibalism among polar bears will increase as environmental conditions leave them more food stressed.

There is no doubt though that the numbers of bears in Davis Strait has increased since the last population estimate in the early 1990s. There are several possible reasons for why this is the case. During the earlier study the area that bears were captured in was far smaller than the recent study. This would bias the results low which could make the magnitude of the increase seem larger than it really is. Another unknown is that perhaps there were even more bears in this population a few years ago than there are now.

The crash in the price of seal skins back in the 1980s had two positive affects on the polar bear population in Davis Strait. First, fewer adult and pup seals were being harvested which resulted in an increase in their numbers. In most predator-prey systems, when the numbers of prey increase, those of the predator also increase. So less hunting = more seals and more seals = more bears. The second reason the price crash for seal skins was beneficial for bears is because there were fewer seal hunters on the ice opportunistically killing polar bears.

While the specific details of when climate change will begin to influence different polar bear populations is not known, there is agreement among most researchers that these effects will be detrimental to overall polar bear numbers. Current models predict that the Canadian Arctic Archipelago may be the last strong hold for the species in the face of climate warming. Let’s hope Nunavut and Canada can adapt its polar bear management program in ways to ensure the species persists long enough for the world to address the reasons for the loss of polar bear habitat.

–Paul Frame, Wildlife Biologist, Iqaluit, Nunavut