Study: Polar Bear Populations Have Plummeted 40 Percent in Alaska and Canada

Scientists attribute the steep decline to melting sea ice as the Arctic warms.

(Photo: P. Graas/Getty Images)

Nov 17, 2014· 1 MIN READ
David Kirby has been a professional journalist for 25 years. His third book, Death at Seaworld, was published in 2012.

A study published Monday found that polar bear populations along the southern Beaufort Sea in northeast Alaska and Canada plunged 40 percent over a decade.

The likely culprit, according to scientists, is melting sea ice triggered by climate change.

The study, published online in the journal Ecological Applications, concluded that the number of polar bears in the area fell from 1,500 to 900 between 2001 and 2010.

“There have been some signs of decline in past studies, including a 2010 paper that hypothesized that the population was probably declining, but this now confirms that hypothesis,” Jeffrey Bromaghin, a research statistician at the U.S. Geological Survey and the study’s lead author, said in a phone interview.

Previous studies linked declines in summer sea ice due to warming temperatures to “reduced physical condition, growth, and survival of polar bears,” the report said.

Polar bears depend on sea ice to let them travel across the frozen water to hunt for seals—their preferred diet—that emerge through cracks in the ice to breathe.

The study found that low survival rates from 2004 through 2006 led to a 25 to 50 percent decline in the number of bears in the region.

“We hypothesize that low survival during this period resulted from 1) unfavorable ice conditions that limited access to prey during multiple seasons; and possibly 2) low prey abundance,” the authors wrote.

“We’ve seen the same sort of trend in the Hudson Bay population, which has been studied quite a bit,” Bromaghin said. “We see low survival for a couple of years where the population takes a downward step, then levels off for a while.”

During the years of steepest decline, between 2003 and 2007, polar bear cubs fared the worst. Just two out of 80 cubs documented in Alaska during those years are known to have survived.

Though adult and cub populations began to improve in 2007, the number of subadult bears—those between the ages of two and four—has continued to fall.

“Our estimates would suggest that whatever change there was in the ecosystem in 2007, it allowed adults and cubs to be doing a little bit better, but subadults are still struggling some,” Bromaghin said.

The reason for that stabilization, ironically, might be climate change itself.

Warming temperatures in the Arctic region have led to a change in crack patterns that appear in the ice, perhaps providing greater hunting opportunities for the bears.

“We don’t know what the changes were, but ancillary evidence points in that direction,” Bromaghin said.

He noted that a Canadian study found that the distribution of seals killed by polar bears began changing in 2007. “We started noticing more kill sites, so either the seals are more abundant or somehow more available to the bears,” he said.

“Here are concrete numbers to show us that the impacts of climate change are happening now,” Margaret Williams, managing director for World Wildlife Fund’s Arctic Program in Alaska, said in an email.

“We know human activities have caused global wildlife populations to drop by over half in the last 40 years,” she said. “We need to change course if we want to stop further habitat loss and ensure resilient wildlife populations, both in the Arctic and around the world.”