Study: Polar Bear Cubs Drowning Due to Sea Ice Loss

Polar bears in peril have become an icon for the woes of a warming planet. The sea ice they rely upon to hunt seals is freezing later and breaking up earlier, while diminishing overall. Scientists believe adult polar bears have drowned when they’ve been forced to cross vast expanses of open ocean that exceed their strong swimming capacity. Now, new research shows that polar bear cubs are also drowning, confirming the dangers of ice loss to the species’ survival.

Environmental journalist Bruce Barcott reports in On Earth that “Biologists studying polar bears off the coast of Alaska have found that when cubs are forced to go on marathon swims with their mothers due to loss of sea ice, nearly half of them don’t survive the journey.” Because cubs have less body fat, they’re not as well insulated and are less buoyant, and thus more subject to hypothermia and drowning.

The study, conducted by the U.S. Geological Survey Alaska Science Center, is being announced today at the International Bear Association Conference in Ottawa.

The data were obtained by collaring 68 female bears in the Beaufort and Chukchi Sea regions and tracking their movements with GPS devices. Barcott’s article details how the data, collected from 2004-2009, revealed 50 episodes of long-distance swims of more than 30 miles. At the time of collaring, 11 of the bears that swam long distances had young cubs. Five of those mothers lost their cubs during the swim, representing a 45 percent mortality rate, the study found. Cubs that did not have to swim long distances with their mothers had an 18 percent mortality rate.

Researcher Geoff York, a study co-author who is now World Wildlife Fund’s Arctic Program polar bear expert, said, “Climate change is pulling the sea ice out from under polar bears’ feet, forcing some to swim longer distances to find food and habitat.” York said this was the first time these long swims had been quantitatively measured, filling a gap in scientists’ knowledge of how sea ice decline is impacting polar bears.

In 2008, the U.S. Fish and Wildlife Service listed polar bears as threatened under the Endangered Species Act. Each year, their future appears more tenuous as the pack ice continues to dwindle. This June, the Arctic sea ice cover was at its second-lowest extent since recordkeeping began in 1979. And because of heavy melting this month says Barcott, “The National Snow and Ice Data Center in Boulder, Colorado, reports that 2011 is now on track to drop below the record low-ice minimum set in 2007.”

Polar bear litter size is also decreasing due to sea ice decline resulting from climate change, according to a study published in Nature on February 8, 2011. If this trend continues as predicted, the polar bear population could be in serious jeopardy.

“Species everywhere are feeling the heat, but none more extreme than polar bears and other Arctic species,” says WWF’s York.

Learn more about what WWF is doing to help polar bears and address climate change, and how you can help. Start by joining WWF’s Polar Bear page on Facebook. Other valuable information resources on Facebook include Polar Bears International and The Polar Bear Blog. Take a minute to send a message via NRDC’s website to Interior Secretary Ken Salazar, urging him to support policy to protect polar bears.

You can also “Like” Natural Habitat Adventures on Facebook, to keep up with more wildlife- and conservation-related news — just click the link in the upper-right corner of this blog post. Be sure to check out our Churchill Polar Bears website, too.

It’s sometimes tough to be hopeful in the face of news such as this. But it’s all the more reason to redouble our efforts to protect our planet and its wondrous creatures, not least the Lord of the Arctic.

Yours in the commitment to conservation,

Wendy

P.S. For more of Bruce Barcott’s writing on bears, don’t miss his cover story on the rare white Spirit Bears of BC’s Great Bear Rainforest in the August 2011 National Geographic.