Nine polar bears were observed in one day swimming in open ocean off Alaska's northwest coast, 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 bears were spotted in the Chukchi Sea on a flight by a federal marine contractor, Science Applications International Corp.

It was hired 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.

Observers Saturday were looking for whales but also recorded walrus and polar bears, said project director Janet Clark. Many were swimming north and ranged from 15 to 65 miles off shore, she said.

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Department of Interior Secretary Dirk Kempthorne in May declared polar bears a threatened species because of an alarming loss of summer sea ice and forecasts the trend will continue.

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.

Conservation groups fear that one consequence of less ice will be more energy-sapping, long-distance swims by polar bears trying to reach feeding, mating or denning areas.

Steven Amstrup, senior polar bear scientist for the U.S. Geological Survey in Anchorage, said the bears could have been on a patch of ice that broke up northwest of Alaska's coast.

"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.

It probably is not a big deal for a polar bear in good condition to swim 10 or 15 miles, Amstrup said, but swims of 50 to 100 miles could be exhausting.

"We have some observations of bears swimming into shore when the sea ice was not visible on the horizon," he said. "In some of these cases, the bears arrive so spent energetically, that they literally don't move for a couple days after hitting shore."

Only further research can tell the effect of greater swimming distances on polar bear populations, he said.

"Polar bears can swim quite well, but they are not aquatic animals," he said. "Their home is on the surface of the ice."

Satellite data Saturday showed the main body of pack ice about 400 miles offshore with one ribbon about 100 miles off Alaska's coast, said Mark Serreze of the National Snow and Ice Data Center.

Clark said the animals' origin and destination could not be known without radio collar monitoring.

"To go out there and say they were going from this point to this point would be complete speculation," Clark said.

Observers have no indication of the fate of the nine polar bears observed Saturday.