- Rising temperatures are melting the Arctic sea ice on which polar bears hunt and limiting their access to food.
- A recent study has found a remote population of polar bears that have adapted to prey on glacial ice.
- The results could provide insight into how polar bears have survived previous warm periods over the past 500,000 years.
- But unless the rate of global warming slows, they will remain on the path to extinction, the author warns.
An isolated population of polar bears in Greenland has cleverly adapted to the retreating sea ice they rely on as a platform to hunt seals, offering a glimmer of hope for this species in at least some places in the warming Arctic.
This population of several hundred bears, which inhabits part of the south-eastern coast of Greenland along the Denmark Strait, has only survived with reduced access to ice formed from frozen seawater, feeding instead on chunks of freshwater ice that broke off the vast Greenland ice sheet, researchers said Thursday.
“They survive in fjords that are free of sea ice for more than eight months of the year because they have access to glacial freshwater ice to hunt on. This habitat, which is glacial ice, is unusual in most parts of the Arctic,” said polar scientist Kristin Laidre of the University of Washington, lead author of the study, published in the journal Science.
They have been found to be the most genetically isolated polar bears in the world, distinct from the 19 other known populations of the species. They have been almost entirely cut off from other polar bears for at least several hundred years, with no evidence of abandonment, although there is evidence of occasional arrival from elsewhere.
These bears “live on the edge of what we think is physiologically possible,” said evolutionary molecular biologist and study co-author Beth Shapiro of the University of California, Santa Cruz and the Howard Hughes Medical Institute.
“These bears are not thriving. They multiply more slowly, they are smaller. But more importantly, they survive. It’s still difficult to say whether these differences are caused by genetic adaptations or simply by a different response by polar bears to an entirely different climate and habitat,” Shapiro added.
Polar bears, about 26,000 in all, are particularly vulnerable to climate change as rising temperatures alter the Arctic landscape, robbing them of their usual sea-ice platform for hunting their main prey, ringed and bearded seals.
“The loss of Arctic sea ice is still the greatest threat to all polar bears. This study doesn’t change that,” Laidre said.
The population of Southeast Greenland is geographically confined, with rugged mountain peaks and the Greenland Ice Sheet on one side and the open ocean on the other. In the spring, bears roam sea ice and glaciers, with icebergs frozen solid in the sea ice. In the summer there is open water with floating chunks of glacial ice on the glacier fronts from which the bears hunt. This type of habitat is found only in parts of Greenland and Svalbard, an archipelago in the Arctic Ocean.
“This use of glacial ice has not been previously documented and represents a unique behavior,” said John Whiteman, senior research scientist for conservation group Polar Bears International and a biology professor at Old Dominion University in Virginia, who was not involved with the study.
“This study should also lead to a search for similar habitats throughout current polar bear range. However, glacial ice is a minor component of the Arctic sea ice cap compared to ice formed from freezing seawater,” Whiteman said.
Researchers collected genetic, movement and population data, including satellite tracking of some bears and observing them from a helicopter.
“They just look like a little yellow dot on the white ice, or you can follow their tracks in the snow to find them,” Laidre said.
Shapiro said the results could provide insight into how polar bears have survived earlier warm periods in the roughly 500,000 years since they split evolutionarily from brown bears.
“Polar bears are in trouble,” Shapiro added. “It is clear that polar bears are on the road to extinction unless we can slow the rate of global warming. The more we learn about this remarkable species, the better we can help them survive the next 50 to 100 years.”
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