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The first census of polar bears living around the Chukchi Sea, between Alaska and eastern Siberia, suggests that the population has been stable and healthy over the last decade.
This contrasts with the problems faced by polar bears in other Arctic regions as their sea ice habitat shrinks. The loss of sea ice is also a problem for the Chukchi Sea, but the nearly 3,000 bears in this region do not seem to suffer as much.
"Although there is about a month of time on the preferred sea-ice habitats to hunt compared to 25 years ago, we found that the Chukchi Sea subpopulation was doing well. 2008 to 2016, "said Eric Regehr, a biologist at Polar Science at the University of Washington. Center, said today in a press release.
Regehr is the principal author of a census study published in the journal Open Access Scientific Reports. The census, conducted by researchers from the UW and federal agencies, takes stock of ten years of observations and explains why bears from the Chukchi Sea seem to be better off than their cousins from the rest of the world.
"The loss of sea ice due to climate change remains the main threat to the species, but, as this study shows, the timing and location of the effects of ice loss. sea vary, "said Regher.
Ecologists recognize 19 distinct subpopulations of polar bears, which surround the Arctic from Alaska to Russia, via Greenland and Canada. Only two of these subpopulations occupy US territory: the US-Russian Chukchi bears and the southern Beaufort Sea, which extends into Alaska and northwestern Canada.
"The southern Beaufort Sea subpopulation is well studied and there is growing evidence to suggest that it is doing poorly because of the loss of sea ice," Regehr said. Last year, a picture of a thin emaciated polar bear near Baffin Island in northern Nunavut proved to be viral and drew attention to the fate of this subpopulation.
In contrast, the Chukchi Sea is a "very rich region," said Regher.
"Most of the Chukchi Sea is shallow, with nutrient-rich waters from the Pacific. This translates into high biological productivity and, especially for polar bears, a large number of seals, "he explained.
The area is also heavily used by whales, and washed whale carcasses provide a source of food for the Chukchi Sea bears during the Arctic summer, when the ice melts.
Regehr and his colleagues collected data for their survey by studying and scoring around 60 polar bears between 2008 and 2016. GPS readings were introduced into a computer model to estimate the total size of the subpopulation. The assessment of bear health was based on data on reproduction and survival rates.
The assessment also relied on bear body fat measurements as well as reports from Alaska native hunters. "It was important to bring our science together with the observations and expertise of people who live in polar bear country all year round and understand animals in different ways," Regehr said.
In 2008, polar bears were listed as threatened within their range under the US Endangered Species Act, due to projected population declines related to sea ice loss.
Today, a joint US-Russian commission is responsible for managing the sub-populations of the Chukchi Sea. With the new assessment published, the commission has increased the subsistence catch quotas for hunters in the Chukchi Sea from 58 to 85 bears for next year. This is good news for the Alaskan tribes, who eat polar bear meat and use skins for crafts.
Regehr said scientists would continue to monitor the situation in the Chukchi Sea as the effects of global climate change are felt.
"These discoveries are good news for now, but that does not mean that the Chukchi sea bears will not be affected by the loss of ice," he said. "Polar bears need ice to hunt seals, and the ice should be degraded until the underlying problem of climate change is resolved."
Among the authors of the article in Scientific Reports, "Integrated Population Modeling provides the first empirical estimates of vital rates and abundance of polar bears in the Chukchi Sea," including Nathan Hostetter, Ryan Wilson, Karyn Rode and Michelle St. Martin and Sarah Converse.
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