Polar bear swam 9 days in search of sea ice, study says

From The Star (Canada): Polar bear swam 9 days in search of sea ice, study says
A mother polar bear swam for nine days straight to reach sea ice, covering nearly 700 kilometres and losing her cub in the process, according a new study on the movement of female polar bears.

The study, which links shrinking sea ice as a possible threat to polar bear cubs, also noted the bear lost 22 per cent of her body weight after swimming in the Beaufort Sea.

“It’s pretty remarkable. That’s the longest that’s ever been recorded for bear swimming non-stop,” said Anthony Pagano, the study’s lead author and a U.S. Geological Survey wildlife biologist. “Historically, there just wasn’t this extensive amount of open water that bears would be forced to swim (in).”

Initial results from the ongoing study, which used data from GPS collars on 68 bears, were presented last week at the International Bear Association Conference in Ottawa.

Scientists tracked the movements of the bears between 2004 and 2009 in the Beaufort and Chukchi Seas, and found their journeys in the water were an average of 150 kilometres long.

They also saw an increase in the number of swims over the course of the study.

“About a quarter of our . . . bears had these (greater than 50 km) swims in 2004,” Pagano said. “And in 2009, just over 60 per cent had swims.”

The long swims are likely very strenuous on the bears, said Pagano, and often fatal for their cubs.

Eleven bears had cubs when they embarked on their journeys, the study found. When researchers spotted the bears on land again, only six still had their cubs with them, meaning the cubs drowned or died shortly after reaching the ice.

Ice in the Beaufort Sea, north of the Northwest Territories and Alaska, has been declining in recent years as a result of global warming.

Arctic sea ice is at a record low this month, according to the University of Washington Polar Science Center. Sea ice volume is 47 per cent lower than it was in 1979, when researchers started collecting satellite records.

Because their ice habitat is shrinking away from land, polar bears have been forced to find food by either staying on shore or swimming vast distances to find sea ice.

To determine if the bears were swimming, rather than walking, researchers plotted the bears’ GPS locations on satellite images of sea ice, Pagano said.

“We often found there were actually gaps in the data when the bears were swimming because . . . one of the antennas can’t transmit data underwater,” he said. “We were able to use that to identify when bears were potentially swimming.”