Polar Bears and Hunting: Worse Than You Think

As I've written about here at Switchboard on several occasions, far and away the biggest threat to polar bears is from climate change and its effect on the Arctic sea-ice on which they depend.  But whenever a species is threatened with extinction because of one thing (whether it's climate change, habitat destruction, or disease) carefully managing other sources of stress on that species becomes all the more important.

That's where polar bear hunting comes in.  While polar bears are protected from most hunting in the United States and Norway, both Greenland and Canada allow polar bear sport hunting--sometimes at dangerously high levels.  As for Russia, while currently hunting for polar bears is tightly controlled (at least on paper) poaching continues to be a problem. 

Now a new study predicts that hunting polices that encourage hunters to shoot male bears could lead to sudden and rapid population declines due to the "Allee effect,"  which generally refers to the phenomena where a populations overall fitness declines at lower population sizes.  The study, which was published in the Proceedings of the 'Royal Society modeled the relationship of polar bear mating behavior and breeding success in Lancaster Sound, Canada, in order to predict the effect of changes in male-to-female ratios on overall polar bear breeding success. Here are the key findings (sorry, no link available):

First, the threshold operational sex ratio, below which a component Allee effect of reduced female mating success is expected, is not constant but depends on the overall density of available breeders

In other words, the smaller the overall population density the more males you need in the population to keep mating success constant.  That's particularly important in the context of global warming, which the vast majority of experts believe will lead (and, in some areas is already leading) to lower polar bear populations.

Second, female mating success is a nonlinear function of the operational sex ratio, implying a sudden and rapid reproductive collapse if males are depleted below sustainable limits.  Owing to this nonlinearity...we recommend a precautionary harvesting approach.

This last bit is particularly interesting.  One of the studies authors is Dr. Mitchell Taylor, a biologist who works for the Canadian province of Nunavut and is one of the most prominent critics of the proposed listing of polar bears under the Endangered Species Act.  Ironically, one of the main reasons Nunavut is opposed to the listing is its fear that protecting polar bears under U.S. law will result in restrictions on the ability of U.S. hunters to import big male polar bear trophies back into the United States.