Scientists have identified a distinct subpopulation of polar bears in southeastern Greenland that, in an area with little sea ice, can survive by hunting on ice that breaks down glaciers.
The discovery suggests a way a small number of bears could survive if global warming continues and more of the sea ice they normally depend on disappears. But the researchers and other polar experts warned that serious risks to the overall polar bear population 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 study of what was believed to be a single population of bears along the entire 1,800-mile eastern coast of Greenland. Analysis of satellite-tracked movements, tissue samples and other data revealed that the bears in the Southeast were both physically and genetically isolated from the others.
“This was an entirely unexpected finding,” said Kristin Laidre, a biologist at the University of Washington who has spent two decades studying the ecology of marine mammals in Greenland. dr. Laidre is the lead author of a paper on the subpopulation published Thursday in the journal Science.
Southeast Greenland is particularly remote, with narrow fjords hemmed in by steep mountains. On the landward side, there are often glaciers that end in the water; on the other side is open ocean, with a strong southward flowing current. “These bears are very geographically isolated,” said Dr. laidre. “They’ve really evolved into residents because that’s the only way to live down there.” The researchers estimate that this subpopulation had been isolated for at least several hundred years.
In all, there are an estimated 26,000 polar bears around the Arctic, in 19 officially designated subpopulations. The animals live on the seasonal sea ice, hunting their primary prey, seals, while the seals bask on the ice or come to air through breathing holes. But the rapid warming of the Arctic associated with human-caused greenhouse gas emissions has reduced the extent and duration of sea ice cover.
Some subpopulations, most notably one in the southern Beaufort Sea off Alaska and Canada, are already declining because the ice doesn’t last long enough for the bears to hunt enough food for themselves and their offspring. Polar bear experts say that if the world continues to warm, polar bears could be nearly extinct by the end of the century.
Southeast Greenland is relatively warm and the fjords there have less sea ice than many other polar bear areas – about 100 days a year on average with enough ice to live on and hunt. “We know that’s just not enough for a polar bear to survive,” said Dr. laidre. Those are the conditions that could become widespread elsewhere in the Arctic later this century.
dr. Laidre and her colleagues found that bears in Southeast Greenland hunt on sea ice while it’s nearby. But once it’s gone, the bears have other ice to hunt: the freshwater ice that flakes off the glaciers in the fjords as icebergs and smaller chunks, and that lasts most of the year.
The bears hunt this floating mix of ice, called glacial melange, in the same way they hunt the sea ice. “It gives them an extra and unusual ice platform that bears in a lot of other places don’t have,” said Dr. Laidre, allowing them to capture enough seals to survive and thrive.
But habitats like these 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 in the fjords as part of the study.
“There are limited locations in the Arctic where we see substantial and consistent production of glacial blend,” said Dr. moon. In addition to some areas in Greenland, the Norwegian archipelago of Svalbard has glaciers that end in the water.
So while these special conditions may allow some bears to survive as the sea ice continues to shrink, in general the animals will be threatened by climate change.
“We expect a large decline in polar bears across the Arctic under current warming trajectories,” said Dr. laidre. “And this research doesn’t change that.”
Steven Amstrup, chief scientist with conservation group Polar Bears International, who was not involved in the study, said the study was “really thorough” and “indicates a very discrete group of bears.”
Whether it’s a 20th official subpopulation is for a group of experts to decide, under the auspices of the International Union for Conservation of Nature. “It’s not clear to me whether this will benefit this group of bears in terms of their safety or their overall wellbeing going forward,” said Dr. Amstrup.
He said he agreed with the researchers that, as he put it, “this is not some sort of rescue for polar bears.” For starters, he said, warming is causing all types of ice to retreat and disappear, including glaciers. So the glaciers in the Greenlandic fjords will not continue to end up in the water and produce glacial blends forever. The study, he said, “shows a temporary benefit to these bears.”
“They can now survive, even though the ice-free days are too great in terms of sea ice,” added Dr. Amstrup to it. “But as we go into the future, that will change unless we stop the increase in global greenhouse gases.”