Polar bears forced to swim longer distances because of diminished sea ice off Alaska's coast may be paying a price in lost cubs or precious calories, according to a study by the US Geological Survey. The study reviewed data from female polar bears in the Chukchi and southern Beaufort seas that wore GPS collars and took swims of roughly 31 miles between 2004 and 2009. Eleven were mothers with cubs. In six cases, dependent cubs survived the swim when they were spotted again two months to a year later. But in five cases, cubs could not be located after the long-distance swim.
Cub survival rate was higher for bears that were not recorded taking long-distance swims. Researchers cannot say for sure that the missing cubs drowned, but the evidence suggests long-distance swimming may be risky, a USGS zoologist said yesterday. According to the National Snow and Ice Data Center, polar bears' sea ice habitat has shrunk from 2.7 million square miles to a a record low 1.65 million square miles in 2007. (Read more polar bear stories.)