A key polar bear population fell nearly by half in the past decade, a new U.S.-Canada study found, with scientists seeing a dramatic increase in young cubs starving and dying.
Researchers chiefly blame shrinking sea ice on global warming.
Scientists from the U.S. Geological Survey and Environment Canada captured, tagged and released polar bears in the southern Beaufort Sea from 2001 to 2010. The bear population shrank to about 900 in 2010, down from about 1,600 in 2004. That area is one of two main U.S. polar bear regions.
"These estimates suggest to me that the habitat is getting less stable for polar bears," said study lead author Jeff Bromaghin, a USGS statistician.
Wildlife biologist Steve Amstrup, who started the study for the USGS and left to become chief scientist at the conservation group Polar Bear International, said his early research in the 1980s found about 1,800 polar bears in the region.
"The habitat was profoundly different by the late 1990s, early 2000s," said Amstrup, a co-author of the study in the journal Ecological Applications.
Bromaghin said only two of 80 polar bear cubs the team tracked between 2004 and 2007 survived. Normally about half of cubs live.
"We suspect that they are dying of starvation," Bromaghin said.
In this part of the Arctic, there used to be more sea ice in the summer; that's where seals lived, and seals are what bears eat. With limited access to seals, cubs probably starved, he said.
Arctic summer sea ice had been declining since the late 1970s but "we've seen over the past decade, decade and a half, the rate of decline has really accelerated," said Mark Serreze, director of the National Snow and Ice Data Center in Colorado. And 2007 was "a wake-up call" for scientists because sea ice shrank to a low scientists had not expected or seen before. Sea ice levels dropped even lower in 2012 and have recovered a tad since.