January 26, 2011

Researchers Witness Polar Bear’s Epic Search For Ice

Scientists studying polar bears around the Beaufort Sea, north of Alaska, were amazed to witness one polar bear that swam continuously for more than nine days, covering some 426 miles, in search of sea ice.

The scientists said this endurance feat could be the result of climate change.

Polar bears are known to swim between land and sea ice floes to hunt seals. But the researchers said that increased sea ice melts push polar bears to swim much farther, risking their own health and future generations.

In their findings, published in Polar Biology, researchers from the US Geological Survey (USGS) revealed the first evidence of long distance swimming by polar bears.

"This bear swam continuously for 232 hours and 687 km and through waters that were 2-6 degrees C," said research zoologist George M. Durner. "We are in awe that an animal that spends most of its time on the surface of sea ice could swim constantly for so long in water so cold. It is truly an amazing feat."

Although bears have been observed in open water before, this is the first time one's entire journey has been followed. The bear, which was outfitted with a GPS collar, was tracked by researchers for two months as it sought out hunting grounds.

By following data transmitted by the collar and from a temperature logger implanted beneath the bear"Ëœs skin, the researchers were able to determine when the bear was in the water. The study shows that the epic adventure came at a very high cost to the bear.

"This individual lost 22% of her body fat in two months and her yearling cub," said Durner. "It was simply more energetically costly for the yearling than the adult to make this long distance swim," he explained.

The conditions in the Beaufort Sea have become more and more difficult for polar bears, and swimming for long distances between land and sea ice puts cubs at risk.

"In prior decades, before 1995, low-concentration sea ice persisted during summers over the continental shelf in the Beaufort Sea," said Durner. "This means that the distances, and costs to bears, to swim between isolated ice floes or between sea ice and land was relatively small."

"The extensive summer melt that appears to be typical now in the Beaufort Sea has likely increased the cost of swimming by polar bears," he said.

Polar bears live entirely within the Arctic Circle and subsist on a calorie-rich diet of ringed seals to survive the frozen conditions. The bears hunt their prey on frozen sea ice -- a habitat that constantly changes along with temperatures.

"This dependency on sea ice potentially makes polar bears one of the most at-risk large mammals to climate change," Said Durner.

The International Union for the Conservation of Nature (IUCN) red list identifies polar bears as a vulnerable species, citing global climate change as a "substantial threat" to their habitat.


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