In Epic Nine-Day Swim, Polar Bear Loses Her Yearling Cub

Faced with rapidly disappearing summer sea ice in the Beaufort Sea, north of Alaska, a female polar bear was forced to make a nine-day, 426-mile swim in search of ice floes, a trip that caused her to lose 22 percent of her body fat and killed her yearling cub, according to U.S. researchers. Scientists from the U.S. Geological Survey placed a GPS collar on the female bear to track its movement for two months as it sought out ice floes from which to hunt its favored prey, ringed seals. The resulting data showed that the female made the longest swim ever recorded by a polar bear, as it continuously paddled through waters that were 2 to 6 degrees C (3.6 to 11 F) for nine days. (A data logger under the bear’s skin recorded sea temperatures.) “We were in awe that an animal that spends most of its time on the surface of the sea could swim constantly for so long in water so cold,” said zoologist George M. Durner. “It is truly an amazing feat.” The energy expended in the swim caused the bear to lose 22 percent of her body fat in two months and also killed her year-old cub. Such stress on polar bears is leading to declines in more southerly populations as rapidly rising Arctic temperatures melt summer sea ice.