Polar bears that can survive without pack ice

A polar bear family crosses glacial ice in south-east Greenland. ©NASA OMG

More adaptable than expected: Researchers report that there is a possibly climate change-resistant polar bear population in south-east Greenland. The animals of this largely isolated group are not dependent on the disappearing sea ice, but hunt seals from floating fragments of the glacier. This allows these polar bears to exist under conditions that are predicted to prevail in much of the high Arctic in the late 21st century. At least coastal regions characterized by glaciers could serve as refuges for the species, say the scientists.

They are the rulers of a remote region, but that hasn’t saved polar bears from problems in the age of man: populations of the white giants have declined sharply in many places in recent decades. Researchers attribute this to an effect of climate change: as a result of warming, the habitat of polar bears – the pack ice – is shrinking. As a result, their often extensive migratory movements are impaired and, above all, the predators lose their hunting grounds. Because polar bears usually lie in wait for seals at holes and edges of the sea ice. If climate change and ice retreat continue according to forecasts, the drastic environmental changes in the far north could mean the end of polar bears, so it is feared.

But the study by researchers led by Kristin Laidre from the University of Washington in Seattle now gives at least some hope. They set their sights on polar bears that live in a special distribution area: in south-eastern Greenland, which is characterized by glaciers and fjords. “At first it was only basic knowledge that there were some bears there. But nobody would have guessed how special they are – that they are a previously unknown subpopulation of the species,” says Laidre. The scientists’ results are based on genetic information, movement data, habitat analyzes and behavioral observations, taking into account the traditional knowledge of the local population.

Southeast Greenland bears are special

As the team reports, the investigations of the animals’ genetic make-up revealed that they form a polar bear population that differs particularly significantly from other groups. “It’s the most genetically isolated polar bear population on the planet,” says co-author Beth Shapiro of the University of California, Santa Cruz. Further research data supported this finding: “We know that this population has lived separately from other polar bears for at least several hundred years and that their population has remained small during this time,” says Shapiro. According to the team’s estimates, the polar bear community in Southeast Greenland is only a few hundred bears.

Tracking via satellite shows polar bears in northeast Greenland (blue lines) migrate across the sea ice to hunt. The polar bears in south-east Greenland (red lines), on the other hand, move within their home fjords and the immediate vicinity. © Laidre et al./Science

The formation of a group with special genetic traits has to do with the isolated location of the habitat, the researchers explain: it is bordered by mountains and the sea, which is characterized by a fast-flowing coastal current. Satellite tracking of adult females also showed that, compared to most other polar bears that travel far across sea ice to hunt, South East Greenland bears are more likely to be local: migrating on the ice within sheltered fjords or climbing mountains to explore neighboring glacial valleys across the sea to reach the Greenland ice sheet. The researchers report that some of the bears that were examined drifted an average of 190 kilometers on small ice floes that were caught by the south-bound east Greenland coastal current. At the end of the journey, the animals jumped off and then migrated back north to their home fjords by land.

Glacier break instead of pack ice as a hunting platform

Probably the most important finding from the study, however, is that the animals can cope with the hunting conditions in their habitat. The bears in south-east Greenland only have access to the sea ice for four months, which polar bears normally use as a platform for seal hunting. In the other two-thirds of the year, however, they use an alternative there, the scientists report: they hunt seals from pieces of ice that break off from the Greenland ice sheet. “In a way, these animals provide a clue as to how polar bears in Greenland might live under future climate scenarios. This is because today’s sea ice conditions in south-east Greenland are similar to those predicted for north-east Greenland towards the end of this century,” says Laidre.

In other words, if polar bears survive in the conditions of south-east Greenland, similar glacial coastal regions could serve as refuges for them. Thus, there seems to be a chance of survival if the pack ice continues to recede as a result of climate change. “Against the backdrop of conservation concerns, our results give hope — I think they show us how at least some polar bears might survive under climate change,” Laidre said. “However, we have to be careful when extrapolating our findings because the glacial ice that allows bears to survive in southeast Greenland is absent in most parts of the Arctic. Habitats shaped by glaciers will therefore probably not be able to accommodate large numbers of polar bears. We therefore still expect a sharp decline in polar bears in the Arctic due to climate change,” the scientist concludes.

Source: University of Washington, professional article: Science, doi: 10.1126/science.abk2793

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