1/16/2012 9:01:07 PM
A Look at Polar Bear Numbers
By Dr. Steven C. Amstrup, Chief Scientist
One of the most frequent myths we hear about polar bears is that their numbers are increasing and have, in fact, more than doubled over the past 30 years.
Tales about how many polar bears there used to be (with claims as low as 5,000 in the 1960s) are undocumented, but cited over and over again. Yet no one I know can come up with a legitimate source for these numbers.* One Russian extrapolation presented in 1956 suggested a number of 5,000 to 8,000, but that figure was never accepted by scientists. The fact is that in the 1960s we had no idea how many polar bears there were. Even now, about half of our polar bear population estimates are only educated guesses. Back then, the best we had over most of the polar bear's range were uneducated guesses. Polar bear science has come a long way since then.
We do know (and I have published papers on this) that some polar bear populations grew after quotas were imposed in Canada, aerial hunting ceased in Alaska, and trapping and hunting were banned in Svalbard. All of these events occurred in the late 60s or early 70s, and we know some populations responded—as you would expect. Some populations were not being hunted back then (or were hunted very little) and those were probably unaffected by these three actions.
Back then, the sea ice was solid and not noticeably in retreat. With stable habitat, polar bears were a renewable resource that could be harvested on a sustainable basis.
But the most important point is that whatever happened in the past is really irrelevant. Polar bear habitat is disappearing due to global warming. Even the most careful on-the-ground management doesn't matter if polar bears don't have the required habitat.
Polar bears depend on the sea ice surface for catching their prey. A shorter duration of ice cover over their productive hunting areas means less opportunity to hunt. A reduction in sea ice has been statistically linked to reduced stature and weight in polar bears and to lower survival rates of cubs. So, it doesn't really matter that hunting is now largely under control or that we know a lot about other impacts people might have on bears. Without habitat, polar bears will disappear no matter what else we do. If a farmer has 100 cows out in a pasture, and every year he goes out and paves over some of his pasture, pretty soon he won't have enough habitat to support 100 cows. And, each time he paves over a little more land, his remaining land will hold fewer cattle. There may be some short-term enhancements of the remaining habitat that will forestall the inevitable. But, when his whole pasture is paved there will be no cows! Declining habitat now and the assurance it will decline in the future is why polar bears were listed as a threatened species. Discussions about how many bears may have lived in the past before and after hunting quotas have no bearing on this new situation.
Planetary physics require the world to warm as greenhouse gas concentrations rise, so without greenhouse gas mitigation, the ice will continue to melt. For an animal dependent on sea ice to survive, the prospects are not good. As the ice decline continues, the plight of the polar bear only can worsen.
* For an fascinating look at where this widely repeated myth comes from, read "Magic Number: A sketchy 'fact' about polar bears keeps going ... and going .. and going" by Peter Dykstra, published in the Society of Environmental Journalists' SEJournal.