Melting ice linked to polar bear cub mortality as moms swim farther | WWF

Melting ice linked to polar bear cub mortality as moms swim farther

Posted on
20 July 2011
Study represents the first empirical research to find a significant, increasing trend in polar bear long-distance swimming

Sea ice loss from climate change is causing polar bears to swim longer distances to find stable ice or to reach land, resulting in greater risk to their cubs, according to a new paper co-authored by a WWF expert.

“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, WWF Polar Bear Expert who is an author of the study.

“This research is the first analysis to identify a significant multi-year trend of increased long-distance swimming by polar bears. Prior research had only reported on single incidents,” said York.

U.S. Geological Survey biologist and lead author Anthony Pagano will present the study (“Long-distance swimming events by adult female polar bears in the southern Beaufort and Chukchi Seas”) on July 19 at the International Bear Association (IBA) Conference held in Ottawa, Canada.

Between 2004 and 2009 researchers collected data from 68 GPS collars deployed on adult female polar bears, in combination with satellite imagery of sea ice, to identify incidences of bears swimming more than 30 miles at a time. Researchers identified 50 long-distance swimming events during the six year period involving 20 polar bears. Swimming events ranged in distance up to 426 miles and in duration up to 12.7 days.

Eleven of the polar bears that swam long distances had young cubs at the time of collar deployment; five of those bears lost their cubs during swimming -- a 45% morality rate. In contrast, only 18% of cubs died that were not compelled to swim long distances with their mother.
A polar bear cub hitches a ride.
© WWF / Angela Plumb
Polar bear (Ursus maritimus) walking on thin ice and trying to reach the next ice block.
© WWF / Steve Morello