This handout photo provided by the US Geological Survey, taken in 2005 shows Steve Amstrup holding triplet polar bear cubs in Prudhoe Bay, Alaska. A new U.S.-Canada study says a key polar bear population fell nearly in half in the past decade, with scientists seeing a dramatic increase in young cubs dying. Researchers chiefly blame shrinking sea ice from global warming. Scientists from the U.S. Geological Survey and Environment Canada 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. Photo: USGS / AP Photo

By SETH BORENSTEIN, AP Science Writer
17 November 2014

WASHINGTON (Associated Press) – A key polar bear population fell nearly by half in the past decade, a new U.S.-Canada study [pdf] found, with scientists seeing a dramatic increase in young cubs starving and dying.

Researchers chiefly blame shrinking sea ice from 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. […]

The study: http://www.esajournals.org/doi/abs/10.1890/14-1129.1

USGS polar bear science: http://alaska.usgs.gov/science/biology/polar_bears/

[more]

Study: Polar bears disappearing from key region


ABSTRACT: In the southern Beaufort Sea of the U.S. and Canada, prior investigations have linked declines in summer sea ice to reduced physical condition, growth, and survival of polar bears. Combined with projections of population decline due to continued climate warming and the ensuing loss of sea ice habitat, those findings contributed to the 2008 decision to list the species as threatened under the U.S. Endangered Species Act. Here, we used mark-recapture models to investigate the population dynamics of polar bears in the southern Beaufort Sea from 2001 to 2010, years during which the spatial and temporal extent of summer sea ice generally declined. Low survival from 2004 through 2006 led to a 25-50% decline in abundance. 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. For reasons that are not clear, survival of adults and cubs began to improve in 2007 and abundance was comparatively stable from 2008 to 2010 with approximately 900 bears in 2010 (90% C.I. 606-1,212). However, survival of subadult bears declined throughout the entire period. Reduced spatial and temporal availability of sea ice is expected to increasingly force population dynamics of polar bears as the climate continues to warm. However, in the short term, our findings suggest that factors other than sea ice can influence survival. A refined understanding of the ecological mechanisms underlying polar bear population dynamics is necessary to improve projections of their future status and facilitate development of management strategies.

Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline

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