In the vulnerable polar bear population of the Southern Beaufort Sea, a pattern is emerging — step-like periods of decline followed by longer periods of stability.
So concludes a new study of polar bear survival and abundance from 2001 to 2016 in the Alaska portion of the Beaufort. The study, by scientists at the U.S. Geological Survey and published in the journal Ecology and Evolution, found low survival rates from 2003 to 2006, with improvements from 2006 to 2008, followed by stability that was punctuated by a sharp decline in 2012.
“It looks like it’s kind of stair-stepping down,” said Jeffrey Bromaghin, a USGS research statistician and lead author of the study.
The study calculated an estimated average polar bear population for the Alaska portion of the Southern Beaufort Sea: 565 animals.
Since the Alaska portion is roughly two-thirds of the whole Southern Beaufort Sea population, the study’s estimate is consistent with the 900-bear total estimated for the entire population that was reported in a 2015 study also led by Bromaghin.
To get the numbers, the USGS scientists fed data from fieldwork during each of those years that temporarily captured bears. In all, there were 1,224 observations of 868 individual bears, made in spring field seasons when biologists capture and tag the animals. The probability of survival was calculated using models that factored in sex, age classes and other characteristics.
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There are a few possible explanations for the survival and abundance pattern, according to the study. Since carrying capacity is dwindling, the loss of some bears could be giving a temporary boost to the surviving bears by eliminating some competition. Another possible explanation: Surviving bears are more adapted to changing habitat, able to get scraps of butchered bowhead whales lefts on the beach by hunters and other food from land, for example.
Whatever the direct mechanism, the step pattern is going in a single direction: down.
Although there are fluctuations, “we haven’t seen any strong, good growth,” Bromaghin said.
That downward direction is likely to continue as habitat continues to get compressed, he said. “The climate projects are for continued warming and continued ice loss,” he said.
In all, the study said, the Southern Beaufort Sea population is lower than at any time since the passage of the Marine Mammal Protection Act, the 1972 law that included a prohibition to sport hunting of polar bears in Alaska. The 900-bear estimate made in 2015 reflected a 40 percent loss in a decade, according to the USGS.
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The new study comes as the U.S. Fish and Wildlife Service is embarking on its periodic review of polar bears and whether the current status as threatened remains appropriate. Under the Endangered Species Act, the status of listed species gets reviews every five years, “based on the best scientific and commercial data available at the time of the review,” according to the service’s Oct. 5 Federal Register notice. The notice requests submission of such scientific and commercial info new since the last polar bear status review, which was released in 2017.
That 2017 status review found that no change was warranted to the threatened listing made in 2008.
“New data indicate that the global threat of habitat loss identified in the 2008 listing decision remains. . .Hence, climate change effects on sea ice and polar bears and their prey will very likely continue for several decades or longer unless greenhouse gases in the atmosphere can be held at suitable levels, primarily by reducing greenhouse gas emissions,” said that status review.
The new study about survival rates and abundance is the type of information that is helpful in the review, said Andrea Medeiros, a spokeswoman for the Fish and Wildlife Service. The service is not seeking expert information rather than public comment at this point in the process, she said. If a change in listing status is recommended, there would be a rulemaking process that would be a time for public comment, she said.
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Of the 19 polar bear populations in the Arctic, most face possible collapse by the century’s end unless there is sweeping action to curb global climate change, according to a study published last year.
In the shorter term, some polar bear populations are in significantly better shape than others. While the Southern Beaufort Sea population is considered among the most vulnerable to climate change, the other Alaska population — in the Chukchi Sea between Alaska and Russia — is in much better shape.
A pair of recent studies by scientists from the USGS and other institutions examines the Chukchi bears’ current resilience to loss of ice caused by climate change.
One study ties the Chukchi bears’ condition to the condition of Chukchi seals, which are also dependent on sea ice.
Another study said the Chukchi population, in its current abundance, could sustain an annual hunt of 85 bears if two-thirds of the harvested animals are males. That study, by scientists from the University of Washington, the USGS, Fish and Wildlife Service and North Slope Borough, holds a caveat: It is unknown how much longer the Chukchi population will withstand the loss of sea ice in its habitat.
Additional USGS polar bear studies are in the works, Bromaghin said, including one led by USGS polar bear research leader Todd Atwood that evaluates bears’ body conditions. There is also a joint project planned with Canadian scientists to examine polar bear biopsies.
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While climate change is considered the main threat to polar bears, several environmental groups are also citing oil industry operations as additional threats.
A lawsuit filed on Sept. 16 challenges the Biden administration’s renewal of a permit allowing North Slop oil operators to disturb polar bears, including non-lethal hazing methods chase or move them away from certain locations.
The incidental-take authorization, a five-year permit, includes some updates reflecting new research and research needs. It also covers a smaller geographic area than did the previous permit.
The lawsuit argues that the Fish and Wildlife Service, in reauthorizing the permit, overlooked near-certain impacts to cubs, including death, rejected reasonable suggestions for mitigation, such as a potential 1-mile buffer around known dens, and made other mistakes. The oil operations, as authorized by the permit, “will exacerbate the threat of climate change” to Southern Beaufort Sea polar bears, said the lawsuit, filed in U.S. District Court in Anchorage.