Lonely polar bears resisting climate change?

They, in southeastern Greenland and almost completely isolated, the population of several hundred polar bears has apparently lived for at least two hundred years, unknown polar explorers and may provide important clues for the future of polar bears threatened by climate change. Unlike all the other nineteen polar bear populations around the North Pole, seal hunting animals are no longer dependent on crushed ice. Instead, they settle for the thin ice that froze during the late winter months and broke off at the edges of the glacier like a fishing ground. Kristin Laidre of the University of Washington in Seattle and her colleagues discovered polar bears in a remote area ten years ago and between 2015 and 2021 used radio collars to monitor more than two dozen animals.

Joachim Müller-Jung

Fejeton editor, responsible for the “Nature and Science” department.

Tissue and DNA material, as well as insights from polar bears obtained from satellite images and collected by Inuit from the area, show: Polar bears from southern Greenland not only behave and behave differently from “ordinary” relatives, but are, like publications in the current one issue of the magazine. ” Science “shows that they can also be clearly distinguished genetically. Very rarely, in recent decades and centuries, individual animals have immigrated from northern Greenland or occasionally from the Russian population and from Svalbard or Alaska, which have drifted into the southern ice fjords.

The coast of the fjords of south-eastern Greenland has been frozen for four months.

The coast of the fjords of south-eastern Greenland has been frozen for four months.

Photo: Kristin Laidre / University of Washington

What makes South Green polar bears so special is the smaller genetic distance to their relatives. Above all, it is their way to get along for many months with the ice-free habitat south of the 64th parallel and the mostly absent ice ice. Polar bears feel their favorite prey under layers of ice up to a meter thick. They usually use ice crevices for their hunting, which appear in the ice cover. The seals use cracks in the ice as air holes. Polar bears, drifting across the sea on crushed ice, will sit on the edge of these holes until the seal inhales, and then pull their prey out of the water with their powerful paws and strong claws. Many polar bears drift tens of kilometers of ice before returning to their home grounds by land.

Many animals have to fast

In south-eastern Greenland, this method of hunting is severely limited, as thick ice, which drifts in the fjords for several months, rarely forms when the Arctic warms twice as fast. While some northeastern relatives cover up to 1,500 kilometers a year, which is an average of 40 kilometers for a four-day hunt, South Greenland polar bears average only 10 kilometers. In fact, most of them stay in their home fjord all year round. The main hunting season is between February and May, when it is still very cold in the southeast. They then use the relatively thin ice that forms at the edge of the coast (“fast ice”), which breaks off and floats on the water of the fjord, to hunt seals at the edges of the ice. This border area with more fragile, short-lived ice at the edge of the glacier is called ice melange.

Image: Laidre et al./Science

However, many animals have to fast for the rest of the year, much longer than the typical fasting period of three to six months for polar bears. We owe the animals’ survival to the vast fat reserves, which are generally greater in polar bears than in all other bear species, and which can be attributed to the fact that polar bears do not actually hibernate or thrive.

It is also striking on South Greenland polar bears that significantly fewer females with young have been observed in the spring than usual – but this does not seem to affect population stability. Laidre and her team suspect that because their range is also smaller than usual, females may find fewer mating opportunities. Elizabeth Peacock of Emory University in Atlanta suspects that females give birth to fewer pups due to limited resources in the area.

Climate change could play a role. Because it has also been observed in other Arctic animals, such as seals, a rapidly changing environment can significantly reduce birth rates. However, Laidre and her colleagues do not see this as an existential threat. Given that the population in south-eastern Greenland is clearly stable so far and that ice conditions are roughly similar to those likely to prevail in the vast majority of polar bear areas around the North Pole by the end of this century, polar bear researchers even see this as a sign of hope. In their publication, Science suggests that other populations may also be able to “adapt and survive” in icy melange on ice-free Arctic coasts. However, this resilience may also have its limits, which means that if warming accelerates further, South Greenland polar bears could become the first population of their kind to become extinct. Because polar bears that survive in completely ice-free areas are not known. Icebergs that have been frozen for many months are vital for breeding in ice caves and also for animal hunting behavior.

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