Genetically isolated population of polar bears discovered in Greenland don't need sea ice to survive

The image of a bear perched on a solitary piece of ice in the middle of a melting sea has been, for decades, the symbol of the impacts of climate change on animal life. Now, they have just discovered a population of polar bears that has been living for centuries in the conditions that the Arctic will have at the end of the century, when some models predict that these bears will appear on the precipice of extinction. They are genetically distinct, have different hunting patterns and rarely stray from their fjord base. Does this guarantee their survival? Perhaps not, but they will live when their congeners have become extinct.

About 25,000 polar bears remain in the Arctic region. They are grouped into 19 subpopulations that occupy spaces as distant as Alaska, Greenland or the island of Svalbard. But they all depend on sea ice. It is here that their two main sources of protein, the ringed or bearded seals, make their breathing holes, rest and have their pups. These are the moments that the bears take advantage of to hunt them. But for four decades, there has been less ice in the Arctic: its extent is getting smaller in the cold months and it retreats more and more in the summer months. That forces polar bears to risky swims following the ice line or seek their fortune on land. The situation is so extreme that it has led many specimens to exchange seals for eggs. They have now discovered the 20th subpopulation and it is the first that does not depend on sea ice for survival.

In 2014, researchers from various countries launched an investigation in southeastern Greenland. They knew, from sightings and testimonies of local hunters, that there were polar bears, but they did not know how many they were, their movements or their hunting patterns. Since then they have sighted about three hundred and have placed tracking devices on about thirty of them. In parallel, with the help of locals, who may hunt them for subsistence, they collected tissues from almost 400 specimens obtained since 1983 for analysis. The results of the follow-up and the genetic study have been quite a surprise.

“They are the southernmost bears and are geographically isolated from the others, so they don’t interact very often or interbreed with other subpopulations.”

Kristin Laidre, polar scientist at the University of Washington

The conclusions of the work, published in Scienceshow that these bears are genetically different from other populations, which is why their authors defend that the International Union for Conservation of Nature classifies them as subpopulation number 20. The main author of the study, Kristin Laidre, a polar scientist at the University of Washington, says that genetic differentiation is due to isolation: “They are the southernmost bears in the polar bear range and are geographically isolated from one another, so they don’t interact very often or interbreed with other bears.” other subpopulations.

The geography of the area is key to the isolation. Occupying an area of ​​about 700,000 square kilometers and a coastline of 3,200 kilometers, it is an area of ​​fjords that go up to 1,000 meters into the land where hundreds of glaciers surrounded by mountains end. With an average height of the ice covering the island at 2,135 meters, the bears cannot go inland. To the west is the sea, one in which three strong marine currents coincide that participate in the transfer of water from the Arctic to the Atlantic and vice versa and that make its journey very dangerous. To the north, an imposing mountain range cuts them off. They could reach the west side of the island by going south, but that’s where the few humans living in Greenland are concentrated. And the bears have learned that it is not a good idea to approach these beings and their weapons.

The maps show the territories of the polar bear.  The one on the left, the animals tracked in Greenland.  The one on the right indicates the limits of the 19 subpopulations.  In red, the newly discovered.
The maps show the territories of the polar bear. The one on the left, the animals tracked in Greenland. The one on the right indicates the limits of the 19 subpopulations. In red, the newly discovered.LAIDRE ET AL./SCIENCE

Telemetry from tracking devices confirms this isolation and lack of relationships with northern bears. It also shows that they are practically sedentary. While their congeners in northern Greenland move an average of 40 kilometers every four days and travel up to 1,500 kilometers a year, this new population does not move more than 10 km in four days. In fact, many animals do not leave their fjord for years. The researchers found that half of the ringed bears had been carried by the current up to 120 nautical miles from their base and all ended up returning to their territory.

What surprised scientists is that this area of ​​Greenland seems the least suitable for polar bears to live. There is no sea ice for most of the year, about 250 days. That’s as much as doubling the 100 to 180 days bears survive seasonal fasting. How do they live then? Direct observation confirmed to scientists that there are ringed seals in the area. What they also saw is that they are hunted when they rest on the thin sheets of freshwater ice that break off from glaciers. They are unstable, very cracked, but that is what they are most of the year and the ursids have adapted their way of hunting to this fragile setting.

“Ice conditions in southeastern Greenland today look similar to what has been predicted for the northeast by the end of the century,” says Laidre. By then, on this huge island and in almost the entire Arctic region, a very marked retreat of the ice is expected, which would only remain around the North Pole in the summer months. “In a sense, these bears give an idea of ​​how Greenland bears may fare in future climate scenarios,” the researcher concludes in a note from her university.

For the authors of the study, this area could function as a climate refuge. But will it be enough to save the species? Experts outside this investigation doubt it. This is the case of Anthony Pagano, a biologist at the United States Geological Survey, a scientific agency of the US government. Pagano works on the ground in Alaska, studying local populations of polar bears. In 2018, he published research showing that, with the ongoing melting, these animals are living on borrowed time, beyond the possibilities offered by increasingly rare prey. No, it’s not that the seals are going extinct, it’s that there is no ice.

“Ice-associated seals can remain in open water when no sea ice is present. Polar bears are capable of swimming, but they are not adapted to stay exclusively in open water.

Anthony Pagano, biologist at the United States Geological Survey

“Ice-associated seals, such as ringed and bearded seals, can remain in open water when sea ice is not present,” Pagano explains in an email. “Polar bears are capable of swimming, but they are not adapted to stay exclusively in open water. Its morphology is similar to that of other land mammals. Additionally, there have been few observations of polar bears catching seals in open water. So without the sea ice, they can’t hunt or eat their main prey,” he adds.

As for whether the population now discovered could serve as an adaptive model for other populations, Pagano is very doubtful. “As the research mentions, this type of glacier habitat is rare in the Arctic, with the exception of some areas of Greenland and Svalbard. So, these areas can serve as possible refuge, but such habitats would not be available for the majority of polar bears distributed throughout the Arctic, “says Pagano.

The same opinion is held by Steven C. Amstrup, scientific director of the conservation organization Polar Bears International. “This new article that appears in Science documents a small group of polar bears that have been able to survive in an area where sea ice decline has already been great enough to prevent them from persisting in the region. This apparent exception is possible due to the extensive network of fjords and glaciers that host a melange glacial (freshwater that melts from tidewater glaciers and forms an ice cap on the sea surface),” says Amstrup. Fresh water freezes at a higher temperature than salt water, so “even when conditions there don’t allow sea ice to persist, they can maintain an ice sheet that serves polar bears to continue hunting seals that live under that ice”, adds the American scientist.

“If we allow the ice to disappear, the polar bears will disappear with it”

Steven C. Amstrup, Chief Scientist of the conservation organization Polar Bears International

But Amstrup is quick to point out: “This is therefore not a new behavior or adaptation of the bears, they continue to hunt sea seals from an ice surface. It just so happens that the only ice left in this area is largely fresh water. There may be some other areas like this in other parts of the Arctic, but in the general scheme of things, such habitats are rare and could only support a few bears.”

There is one last detail that both Laidre, on the part of the authors of the discovery, and the two outside experts highlight: the ice of the glaciers is also retreating inland. As Amstrup states, “ultimately, this habitat will melt and disappear just like sea ice.” And with the melting, the newly discovered bears will also be doomed if the emissions that warm the Arctic are not reduced. Amstrup remembers saying it in an interview years ago: “As the sea ice goes, so does the polar bear.” That fact, he now adds, “has not changed, and if we allow the ice to disappear, the polar bears will disappear with it.”

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