Can Polar Bears Keep Their Heads Above Water in a Warming World?

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Paul Souders

A new study indicates that polar bears can swim as much as 100 miles.

Polar bears are classified as marine mammals, like a seal or a walrus, which might come as a surprise given that they’re usually pictured on land. But polar bears spend a lot of their time in the waters of the Arctic, fishing or swimming among the sea ice. They may look awkward in the water, but no creature with paws is a better swimmer.

They’d better be. Arctic sea ice is declining fast, robbing the polar bear of its prime habitat and forcing them to swim longer and longer distances to reach solid ground. No other animal seems to be such a direct victim of warming, which is one reason why the polar bear has emerged as the symbol of climate change. (Another is that they look cute and cuddly—a lot more so than the Panamanian golden frog—although up close that can be a different story.) It’s a simple narrative to grasp: carbon warms the climate, Arctic sea ice melts and baby polar bears drown.

But it turns out it might not be that simple. A new study by scientists at the U.S. Geological Survey (USGS) underscores the fact that polar bears really are amazing swimmers—so good that biologists were able to document 50 swims that coverage an average length of 96 miles. The research provides clues that polar bears may be able to keep treading water even as climate change melts their habitat.

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The researchers, who published their work in the Canadian Journal of Zoology, followed 52 female polar bears in the Arctic Ocean north of Alaska from 2004 to 2009, using radio collars that could track the movements of the animals. (This is even harder than it sounds—the researchers had to use helicopters to fly over the sea ice, locate and tranquillize the subject bears.) They then compared the paths taken by the bears with maps of shifting sea ice over the same period of time, and found that the polar bears were world-class marathon swimmers. And those long, long dips in the ocean weren’t outliers—while the really long-distance swims were relatively rare, 38% of the bears surveyed took at least one such marathon swim.

It’s not clear if the long-distance swims are a new part of the polar bears’ lives, due to melting Arctic sea ice, or if they’ve always swum so much, as Karen Oakley of the USGS Alaska Science Center said:

We did not have the GPS technology on collars to document this type of swimming behavior in polar bears in prior decades. However, summer sea ice conditions in the southern Beaufort Sea have changed considerably over the last 20 to 30 years, such that there is much more open water during summer and fall. Historically, there had not been enough open water for polar bears in this region to swim the long distances we observed in these recent summers of extreme sea ice retreat.

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Of course, swimming for nearly 100 miles is exhausting, and the study can’t tell us how much energy is expended in those swims, or whether the animals can keep it up for years. Certainly a documented ability to swim those distances would seem to indicate that the polar bears could have a better chance of surviving in a warming world, but one paper can’t tell us that. Anthony Pagano, the study’s lead author, told Andrew Revkin of Dot Earth that the bear population in the study group, found in the southern Beaufort Sea, was holding steady at about 1,500 bears. And climate change is far from the only threat facing the polar bears—they’re also hunted by indigenous groups in the Arctic, and new oil and gas developments could further degrade their habitat.

It’s worth considering the new study in the light of recent research that indicates the polar bear may be considerably older as a species than scientists thought. Scientists had believe that polar bears branched off from brown bears 150,000 years ago, but Researchers in Science early this month published a DNA study arguing that the polar bear actually split off from the brown bear about 600,000 years ago. That older ancestry means that polar bears—distinct from brown bears by their white coats and webbed paws—have survived through earlier warming periods in the past. But the genetic evidence also indicates that the polar bears’ suffered when the weather was warm and their numbers dwindled. There’s no certainty they’ll survive the next warm period—one that’s fast upon us.

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