Q. I'm confused about polar bear numbers. Some news reports state that polar bears should not be listed as a threatened species—and, in fact, their numbers are actually increasing. If this is true, then why are scientists worried about population declines?
A. It's important to note that scientists lack historical data on polar bear numbers—they have only rough estimates. But we do know that polar bear populations dropped sharply due to over-harvesting in the 1960s. When restrictions on polar bear harvests were imposed in the early 1970s, polar bear populations rebounded. But polar bears now face an entirely different problem—the loss of their sea-ice habitat—and to say that their total numbers are increasing is simply not true.
What are the facts? At the 2009 meeting of the IUCN Polar Bear Specialist Group, scientists reported that of the 19 subpopulations* of polar bears:
* 8 are declining
* 3 are stable
* 1 is increasing
By comparison, in 2005:
* 5 were declining
* 5 were stable
* 2 were increasing
*Insufficient data to determine the fate of the other 7 populations
Scientists have linked these population declines to loss of the sea ice habitat essential to the polar bear's survival.
Polar bears rely on the sea ice to hunt seals, their primary prey. But climate warming in the Arctic has led to dramatic sea ice losses. In 2009, the summer melt-off in the Arctic was equal to the size of Alaska, Texas, and the state of Washington combined.
These sea ice losses have greatly shortened the polar bears’ seal-hunting season, which has led to a scientifically documented decline of 22% since 1987 in the best-studied population, Western Hudson Bay, and a drop in condition in the second best-studied population, the Southern Beaufort Sea. The Southern Beaufort Sea bears are showing the same signs of stress—such as smaller adults and fewer yearling bears—that the Western Hudson Bay bears did before that population crashed.
Scientists predict that if present warming trends continue, we'll lose two-thirds of the world's polar bears by 2050 and all of them by the end of the century. And this time, the problem is not from over-harvesting, which is now carefully regulated and doesn't impact the species as a whole, but from sea ice losses caused by a build-up of greenhouse gases resulting from human activity. This is a harder problem to solve, but scientists emphasize that it's not too late to save polar bears and their habitat if we act soon to greatly reduce carbon emissions.
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