A Clever Population of Polar Bears Survives on Glacial Ice in Greenland

The genetically distinct group of predators uses calved ice to hunt seals when the sea ice has melted

Polar bear
A polar bear on glacial ice in southeast Greenland.  Thomas Johansen / NASA

Polar bears in the Arctic Circle rely on sea ice to help them hunt for seals, their main source of food. But with warming temperatures brought on by human-caused climate change, that sea ice is melting sooner in the spring and freezing later in the fall, forcing the bears to go hungry for longer periods of time than they normally do.

Now, researchers have discovered a unique group of polar bears who’ve found an innovative way to survive in the absence of sea ice: By hunting from the ice that breaks off glaciers. The bears live in southeast Greenland and are a genetically distinct subpopulation, which suggests they’ve been isolated from other polar bears for around 200 years, according to a paper published this week in Science.

The findings offer a glimmer of hope for a species that, without intervention to halt climate change, will be trending towards extinction by the end of the decade. The researchers urged caution against extrapolating their findings to other populations of polar bears, who live in areas without glacial ice and are still increasingly threatened by the planet’s warming. The Arctic Ocean, research has found, is warming four times faster than the rest of the world.

The dots on the left map show the locations where samples from Greenland polar bears were collected. The new Southeast Greenland population, shown as red dots, is located between 60 and 64 degrees north. The map at the right shows the 19 current polar bear subpopulations, with colored dots showing the location of other samples used in the analysis. Laidre et al. / Science

“[The findings] show us how some polar bears might persist under climate change, but I don’t think glacier habitat is going to support huge numbers of polar bears,” Kristin Laidre, a polar research scientist at the University of Washington, tells CNN’s Ashley Strickland. “There’s just not enough of it. We still expect to see large declines in polar bears across the Arctic under climate change.”

When temporary ice sheets form on the ocean during each fall’s freeze, the bears walk across it in search of food, often by sitting next to gaps in the ice and waiting for seals to come up for air. When the ice melts in the spring thaw, polar bears typically survive between 100 and 180 days without food until the ice forms again, reports Live Science’s Harry Baker. As temperatures rise, however, that fasting period is becoming longer, which is harming the bears and pushing them toward starvation.

The bears living in southeast Greenland go even longer without sea ice—around 250 days. But they’ve been able to continue hunting during that period by using glacial mélange, or chunks of ice that break off from glaciers into the water.

Polar bear and cubs
An adult female polar bear (left) and two 1-year-old cubs walk over snow-covered freshwater glacier ice in Southeast Greenland in March 2015. Kristin Laidre / University of Washington

Researchers had long known about the southeast Greenland bears because of indigenous knowledge and historical records. But until now they hadn’t studied these bears’ genetics and behavior. Scientists studied 36 years of GPS collar tracking data, tissue samples, helicopter observations and other data to get a fuller picture of the polar bears. Though exact numbers were hard to estimate, they suspect there are around 300 individuals in this group, per Live Science.

Whether this population of bears will receive any future protection or be subjected to management practices is up to the government of Greenland, per a statement from the researchers. The International Union for Conservation of Nature, meanwhile, will determine whether the bears should be an internationally recognized subpopulation of polar bears.

There are roughly 26,000 polar bears remaining across the globe and their status ranges from “vulnerable” to “special concern” to “threatened,” depending on which country is making the designation.

And though the southeast Greenland bears have adapted to survive in their surroundings, rising temperatures may ultimately cause their glacial ice to shrink, too. As Steve Armstrup, a scientist with Polar Bears International who was not involved in the study, tells the New York Times’ Henry Fountain, the study “is not some kind of salvation for polar bears.” While the southeast Greenland bears are able to hunt via glacial ice today, he says, “going into the future, that will change unless we arrest the rise of global greenhouse gases.”

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