Polar Bears Undertaking Marathon Swims, Populations Declining Rapidly as Sea Ice Disappears
Regional climate is warming much faster in the Arctic than it is elsewhere. Ongoing sea-ice and glacial melt is ushering in a host of ecosystems changes of broad and significant import to humankind – from opening up the Northwest Passage to maritime trade and mineral resource exploration to changes in the number and types of fish and marine species.
A new study conducted by Canadian and U.S. biologists reveals that polar bears living in Hudson Bay and Beaufort Sea are being forced to undertake marathon swims in their search for food as sea ice coverage continues to shrink. That's putting them at greater risk, particularly cubs and the infirm.
The polar bear population in the Beaufort Sea area has declined 50 percent or more in the last decade. Nearly 7 in 10 of the 100 bears the researchers monitored made one or more swims of at least 49 km (30.44 mi) in 2012. That's a 25 percent increase from 2007, according to ¨Migratory response of polar bears to sea ice loss: to swim or not to swim,¨ which was published in the April 14, 2016 edition of Ecography.
One female polar bear swam more than 400 km (248.53 mi) in nine days in 2009. Although she managed to find an ice floe of sufficient size for her to rest she lost her cub during the journey, a Melbourne Herald Sun news report highlights.
Canadian biologist and study co-author Andrew Derocher told Radio Canada International: “Some of our Alaskan colleagues had seen some very unusual swimming events in the polar bears that they were following. They had one bear that swam almost 700km, and during that swim she lost her cub and she lost over 20 per cent of her body weight.”
Derocher explained that while polar bears are extremely capable swimmers, they aren't marine mammals. “This is an animal that’s evolved to walk on sea ice, not swim in the oceans. It’s not like a seal or a walrus or some other species that’s really well designed for swimming permanently…
“The issue here is if you are a really young bear — like a young cub that’s dependent on its mother in the first couple of years — those bears are not capable of swimming long distances. They cool down, they run out of energy, they just exhaust themselves and they’re more at risk of dying. And of course at the other end of the age spectrum the older bears, the bears of poor condition, are also at risk.”
Rippling effects of Arctic climate warming
Melting sea ice has also cleared the way for orcas, aka killer whales, to enter the polar bears' hunting grounds and prey on the bears' staple source of meat: ringed and bearded seals, the scientists noted. It is also leading to a rise in the frequency and number of interactions between polar bears and humans. A northern Canadian town canceled Halloween celebration in 2014 due to the number of polar bears, the Herald Sun's Raffaella Ciccarelli noted.
Runaway human greenhouse gas emissions has been driving global mean temperatures higher towards and beyond the 2ºC (1.6ºF) tipping point determined by the world's leading climate scientists.
It's the rapid pace of climate warming that heightens the challenges polar bears and other species face, Derocher added. “The problem for the bears is the rules are changing, and they’re changing very fast,” he was quoted.
“When I started studying polar bears in 1984, sea ice in the Beaufort Sea was visible from shore year round,” Derocher told RCI. “In recent years, the ice has retreated several hundred kilometers offshore by September and it’s a much more challenging habitat for the bears to live in.”
*Image credits: A.E. Derocher, University of Alberta