These Greenland polar bears can survive with less sea ice

Scientists have identified a distinct subpopulation of polar bears in southeast Greenland which, in an area with little sea ice, survives by hunting ice that breaks off glaciers.

The discovery suggests a means by which a small number of bears could survive as warming continues and more of the sea ice they normally rely on disappears. But researchers and other polar experts have warned that serious risks to the overall population of polar bears in the Arctic remain and will only be mitigated by reducing greenhouse gas emissions to curb global warming.

The subpopulation, believed to number several hundred animals, was identified during a multi-year survey of what was thought to be a single population of bears along the entire 1-mile-long east coast of Greenland. 800 miles. Through analysis of satellite-tracked movements, tissue samples, and other data, bears in the southeast have been shown to be isolated, both physically and genetically, from others.

“It was a completely unexpected finding,” said Kristin Laidre, a biologist at the University of Washington who has studied the ecology of marine mammals in Greenland for two decades. Dr. Laidre is the lead author of an article on the subpopulation published Thursday in the journal Science.

Southeast Greenland is particularly isolated, with narrow fjords hemmed in by steep mountains. At the inland end, there are often glaciers that end in water; at the other end is the open ocean, with a strong current flowing south. “These bears are very geographically isolated,” Dr Laidre said. “They’ve really evolved into residents because that’s the only way to live there.” Researchers have estimated that this subpopulation has been isolated for at least several hundred years.

Overall, there are around 26,000 polar bears around the Arctic, in 19 officially designated subpopulations. The animals live on seasonal sea ice, hunting their main prey, seals, as seals bask on the ice or seek air through breathing holes. But rapid Arctic warming linked to human-made greenhouse gas emissions has reduced the extent and duration of sea ice cover.

Some subpopulations, including one in the southern Beaufort Sea off Alaska and Canada, are already in decline because the ice doesn’t persist long enough for bears to hunt enough food for themselves. and their offspring. Polar bear experts say that if the world continues to warm, polar bears could all but disappear by the end of the century.

Southeast Greenland is relatively warm and the fjords there have less sea ice than many other areas where polar bears live – on average, about 100 days a year with enough ice for them to live and hunt . “We know that’s just too little for a polar bear to survive,” Dr Laidre said. These are the kinds of conditions that could become widespread elsewhere in the Arctic at the end of this century.

Dr. Laidre and his colleagues found that bears in southeast Greenland hunt on sea ice when it is present. But when it’s gone, the bears have another ice to hunt: the freshwater ice that breaks off the glaciers in the fjords, in the form of icebergs and smaller and smaller pieces, and which persists most of the year.

Bears hunt from this floating mix of ice, called glacial mix, the same way they hunt from pack ice. “It gives them an extra, unusual ice shelf that bears don’t have in many other places,” Dr Laidre said, allowing them to catch enough seals for them and their offspring to survive and thrive. .

But habitats like this are rare, said Twila Moon, a scientist at the National Snow and Ice Data Center in Boulder, Colorado, who analyzed sea ice and glacial ice cover in the fjords as part of the research. .

“There are limited places in the Arctic where we see substantial and consistent production of glacial mixing,” Dr Moon said. In addition to parts of Greenland, the Norwegian archipelago of Svalbard has glaciers that end in water.

So while these particular conditions may allow some bears to survive as sea ice continues to shrink, overall the animals will continue to be threatened by climate change.

“We expect to see large declines in polar bears in the Arctic under current warming trajectories,” Dr Laidre said. “And this study doesn’t change that.”

Steven Amstrup, chief scientist of conservation group Polar Bears International, who was not involved in the research, said the study was “really thorough” and “points to a very low-key group of bears”.

Whether this is an official 20th subpopulation is up to a panel of experts to decide, under the auspices of the International Union for Conservation of Nature. “I don’t know if this will benefit this group of bears in terms of safety or general welfare in the future,” Dr Amstrup said.

He said he agreed with the researchers that, as he put it, “this is no kind of salvation for polar bears.” On the one hand, he said, warming is causing all kinds of ice to retreat and disappear, including glaciers. Thus, the glaciers of the Greenland fjords will not continue to end in water and produce glacial mixing indefinitely. The study, he said, “shows a transient benefit for these bears.”

“They can survive now, even if the ice-free days in terms of sea ice are too great,” added Dr Amstrup. “But in the future, that will change unless we stop the rise in global greenhouse gases.”

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