August 22, 2008
Polar Bears Spotted Making Long Open Ocean Swims
Observers flying over Alaska's northwest coast spotted nine polar bears in one day swimming in the open ocean.
Scientists say this is an increase from previous surveys that may indicate warming conditions are forcing bears to make riskier, long-distance swims to stable sea ice or land.
The survey flight was scouting land for the Minerals Management Service in advance of future offshore oil development. The MMS in February leased 2.76 million acres within an offshore area slightly smaller than Pennsylvania.
Project director Janet Clark said observers Saturday were looking for whales but also recorded walrus and polar bears. She said many were swimming north and ranged from 15 to 65 miles off shore.
Polar bears were declared a threatened species in May because of an alarming loss of summer sea ice and forecasts that the trend would continue, according to Department of Interior Secretary Dirk Kempthorne.
Polar bears spend most of their lives on sea ice, which they use as a platform to hunt their primary prey, ringed seals. Shallow water over the continental shelf is the most biologically productive for seals, but pack ice in recent years has receded far beyond the shelf.
One consequence of less ice will be more energy-sapping, long-distance swims by polar bears trying to reach feeding, mating or denning areas, conservation groups say.
The bears could have been on a patch of ice that broke up northwest of Alaska's coast, according to Steven Amstrup, senior polar bear scientist for the U.S. Geological Survey in Anchorage.
"The bears that had been on that last bit of ice that remained over shallow shelf waters, are now swimming either toward land or toward the rest of the sea ice, which is a considerable distance north," he said in an e-mail response to questions."
Amstrup said it probably is not a big deal for a polar bear in good condition to swim 10 or 15 miles, but swims of 50 to 100 miles could be exhausting.
He said they have some observations of bears swimming into shore when the sea ice was not visible on the horizon. "In some of these cases, the bears arrive so spent energetically, that they literally don't move for a couple days after hitting shore."
He said only further research would tell the effect of greater swimming distances on polar bear populations.
"Polar bears can swim quite well, but they are not aquatic animals," he said. "Their home is on the surface of the ice."
Mark Serreze of the National Snow and Ice Data Center said satellite data Saturday showed the main body of pack ice about 400 miles offshore with one ribbon about 100 miles off Alaska's coast.
The animals' origin and destination could not be known without radio collar monitoring, Clark said.
"To go out there and say they were going from this point to this point would be complete speculation," Clark said.
So far, observers have no indication of the fate of the nine polar bears observed Saturday.