Scientists have identified a distinct subpopulation of polar bears in southeastern Greenland that, in an area with little sea ice, survive by hunting on the ice that comes off glaciers.
The finding suggests how a small number of bears could survive with the planet’s continued warming and the melting of the sea ice on which they normally depend.
Researchers and other experts have warned that serious risks to the polar bear population in the Arctic remain and will only be reduced by reducing greenhouse gas emissions to curb global warming.
The subpopulation, estimated at several hundred animals, was identified during a multi-year study of what was thought to be a single population of bears along the 2,880 kilometer east coast of Greenland.
Through analysis of satellite-tracked movement, tissue samples and other data, the southeastern bears were found to be isolated, physically and genetically, from others.
“It was a totally unexpected discovery,” said Kristin Laidre, a biologist at the University of Washington who has studied marine mammal ecology in Greenland for two decades. Laidre is the lead author of a paper on the bear subpopulation published Thursday in the journal Science.
Southeast Greenland is especially remote, with narrow fjords surrounded by steep mountains. At the inland end there are often glaciers that end in the water; on the other is the open sea, with a strong south current.
“These bears are very isolated geographically,” Laidre said. “They really evolved to be residents because that’s the only way to live in that area.”
The researchers estimated that this subpopulation has been isolated for at least a few centuries.
Overall, there are about 26,000 polar bears in the Arctic, in 19 officially designated subpopulations. The animals live on seasonal sea ice, hunting their primary prey, seals, as they sunbathe on the ice or climb into the water to breathe through holes in the frozen surface. But the rapid warming of the Arctic linked to human-caused greenhouse gas emissions has reduced the extent and duration of sea ice cover.
Some subpopulations, notably 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 for them and their cubs to eat.
Polar bear experts say that if the planet continues to warm, they could be extinct by the end of this century.
Southeast Greenland is relatively warm, and the fjords have less sea ice cover than many other areas with polar bears — on average, there is enough ice for them to live and hunt about 100 days a year.
“We know that’s too little for a polar bear to survive,” Laidre said. These are the types of conditions that could spread to other parts of the Arctic by the end of this century.
Laidre and his colleagues found that bears in southeastern Greenland have hunted sea ice for as long as it exists. But when it’s over, the bears have another environment to hunt: the freshwater ice that comes off the glaciers into the fjords, like icebergs and progressively smaller pieces, and that persist for most of the year.
Bears hunt on this floating mixture of ice, called “ice mélange”, in the same way they hunt on sea ice. “It gives them an extra, unusual ice shelf that bears in many other places don’t have,” Laidre said, allowing them to capture enough seals for them and their pups to survive and reproduce.
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 fjords as part of the research.
“There are limited locations in the Arctic where we see substantial and consistent production of glacial mixing,” Moon said. 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 sea ice shrinks, overall the animals will continue to be threatened by climate change.
“We expect to see major declines [das populações] of polar bears in the Arctic under current warming trajectories,” Laidre said. “And this study doesn’t change that.”
Steven Amstrup, chief scientist at conservation group Polar Bears International, who was not involved in the research, said the study was “really thorough” and “points to a very specific group of bears”.
It will be up to a group of experts, under the auspices of the International Union for Conservation of Nature, to decide whether it constitutes an official 20th subpopulation.
Translated by Luiz Roberto M. Gonçalves
