Polar bears are swimming longer distances because of melting sea ice, according to a new study conducted with satellite tracking devices.
The research, presented July 19 by U.S. Geological Survey biologist Anthony Pagano at the International Bear Association Conference, identified 50 long-distance swims by adult female polar bears between 2004 and 2009 in the southern Beaufort and Chukchi seas.
“Climate change is pulling the sea ice out from under polar bears’ feet, forcing some to swim longer distances to find food and habitat,” said Geoff York, a polar bear expert at the World Wildlife Fund who co-authored the study.
There are 20,000 to 25,000 polar bears worldwide — they are listed as threatened under the U.S. Endangered Species Act — and York said they routinely swim 10 miles or more.
Researchers collected data from 68 GPS collars attached to bears over the course of six years, and combined that information with satellite imagery of sea ice. Twenty bears in the survey swam more than 30 miles at a time. The longest-distance swim was 426 miles; the longest-lasting swim was 12.7 days, with a few brief breaks on drift ice.
Eleven of the bears that swam long distances had young cubs when researchers attached the collars, and five of those mothers lost their cubs while swimming.