In the southeastern corner of Greenland, scientists have discovered an unexpected population of polar bears. This population has developed several habits for survival in its strange – as far as polar bears are concerned – habitat, and the bears’ genome is quite different from that of many of their relatives. In addition to the novelty these animals represent, they could also help educate scientists about how more traditional bears will fare in a warming Arctic.
Several things distinguish this group of bears. For much of the year they survive by hunting for ice that falls into the ocean after the break-up of a Greenland glacier; the ice floats in the fjords these bears call home. This is in contrast to most other populations of polar bears, which require sea ice to hunt. According to the World Wildlife Fund, there are between 22,000 and 31,000 polar bears in the world.
The research team used seven years of data collected in the region, along with 30 years of historical data. For the new data, the team contacted local hunters and used tissue samples taken from the hunters’ kills to sequence the bears’ genomes. They also used fieldwork, satellite data — which also allowed them to study the region’s geographic and sea ice conditions — and tracking collars to get a sense of the bears’ movements.
“There’s a really big set of data here,” Twila Moon, co-author of the paper and deputy chief scientist at the National Snow and Ice Data Center, told Ars. “It took a lot of time in the field. This is a very remote area that requires difficult, time-consuming and challenging conditions for fieldwork.”
alienated
Southeastern Greenland is quite poorly studied. This is due to the rugged, mountainous terrain and unforgiving weather, including heavy snowfall. These difficulties probably also explain why the bears are isolated. The region is surrounded by mountains, by the Greenland ice sheet and by the Danish Straight.
Most polar bears use sea ice to hunt, but this is a limited option for the southeastern Greenland bears. The region only sees sea ice between February and May. However, movement data suggests that the bears behave differently from their relatives. They probably walk on glacial ice flowing into the fjords and travel up the mountains to reach other fjords in search of food, often seals.
“We found that sea ice rarely existed for more than four months a year — in some fjords, in some years, much less than that,” Moon said.
According to the collected and sequenced samples, the bears are genetically quite different from others in the same species. There are 19 other polar bear populations observed, and their genomes are relatively similar to each other; this isolated subpopulation stands out. According to the research, they are the most genetically isolated population of polar bears on Earth, and they may have been in this part of Greenland for hundreds of years.
A bear of a problem
As climate change continues to lower sea ice levels, bears in other regions may adapt to live like the population in southeastern Greenland. However, Moon suggested not to get too excited about this possibility. “There may be a tendency to want to feel that this is a… [feeling of] “The polar bears have been saved,” she said. “Unfortunately there are very [few] locations that provide a lot of glacial ice in this way… For many Arctic polar bears, that kind of ice is not available.”
This means that many populations of polar bears will not have the opportunity to adapt to life on glacial ice, as the population in Southeast Greenland has. The numbers of these Greenland bears are also quite small – only a few hundred individuals – possibly because of the difficulties the terrain presents when the bears try to find a mate. As such, regions such as southeastern Greenland may not be able to sustain large herds of bears. Another problem: The Greenland ice sheet, which provides the glacial ice the bears use to hunt, is also melting. This is true for other glaciers around the Arctic, Moon said.
However, the bears in southeastern Greenland have an edge in their difficult habitat. Because the Greenland ice sheet is losing ice, it is not retreating equally everywhere along the coast. Southeast Greenland gets a lot of snow in the winter, which helps to feed the glaciers. The researchers also note that the region could act as a small-scale climate refuge, a place where the species could survive for a while if the sea ice continues to shrink. The paper also notes that a few similar habitats exist in other parts of the Arctic, such as Svalbard — a Norwegian area — and other parts of Greenland.
“We don’t expect that coastal ice to retreat from its current location as quickly as parts of the ice sheet, say, on the west or southwest coast,” Moon said. “It’s a nuanced environment.”
Science, 2022. DOI: 10.1126/science.abk2793 (About DOIs)
