Actually, there shouldn’t be any polar bears in south-east Greenland – but apparently nobody told the polar bears.
Although polar bears are excellent swimmers, they are essentially land animals that feed almost exclusively on marine life. To achieve this, the giant creatures make a living as ambush predators, lying in wait next to cracks and holes in the sea ice that seals use to breathe.
But in southeastern Greenland, the sea-ice season lasts less than four months — “too short for polar bears to survive,” says Kristin Laidre, a University of Washington scientist who studies Arctic animal ecology in collaboration with the Greenland Institute of Natural Resources. Then what explains the presence of bears there?
Local hunters in Greenland have long believed that polar bears can be found year-round in the fjords to the southernmost tip of the country. When the Greenland government commissioned a study into polar bear distribution, Laidre and her team followed “invaluable” hand-drawn maps produced by their Inuit collaborators and identified previously uncharted bears living at the foot of glaciers near the abandoned southeastern settlement of Skjoldungen. Timmiarmiit.
Their research, published today in the journal Science, presents DNA evidence that about a few hundred bears in this part of Greenland are sufficiently different from their neighbors to be classified as the 20th subpopulation – a group of animals within the same species that are genetically and geographically separate – of the world’s 26,000 polar bears to be considered. Tracking data from satellite radio collars on 27 bears also confirmed that this population survived without sea ice for three months longer than scientists had thought possible. (Learn the surprising reason polar bears need sea ice to survive.)
Given that, it’s tempting to read the study as new hope that polar bears can survive with less sea ice, but the authors stress that the conclusion isn’t that polar bears are more resilient to climate change than previously thought. In places like south-east Greenland — where ice from freshwater glaciers can make up for lost sea ice — polar bears could be making their last stand.
A bear from a task
Laidre, along with Fernando Ugarte of the Greenland Institute for Natural Resources and a host of international collaborators, have combed through 36 years of movement data and DNA samples to find out what makes the bears different. The researchers were surprised to find that the site data showed a latitude boundary at about 64 degrees north. Bears living north of the line stayed there as long as the information was collected, and southeastern bears stayed south without population mixing.
While their northeastern Greenland cousins roam an average of six miles a day on sheets of sea ice, southeasterners stay closer to shore in a series of fjords — long, narrow bays carved by glaciers fed by Greenland’s ice cap. During the summer months, chunks of ice calve into the ocean, creating what scientists call freshwater-glacial mélange, a chunky slush that can be packed tight enough for polar bears to walk — and hunt — on.
Laidre found that some bears stayed in a single fjord or a few neighboring fjords for years, occupying a home range of only five or six square miles. That’s a stamp compared to the home ranges of the northeastern population, where a typical bear traveled more than 900 miles a year across the sea ice.
Stranded polar bears and an ice conveyor belt
DNA analyzes obtained by Laidre’s team in the field, from previous studies, and from samples provided by hunters show that the southeastern animals are the “most genetically isolated polar bears on the planet,” Laidre says. In other words, they are less related to their neighboring subpopulations than any of the 19 recognized subpopulations are to their neighbors.
But how did the two groups of polar bears diverge? The researchers say they see evidence of a “founder effect,” meaning the southeastern population was founded by a small number of individuals who were separated from the larger group, and their offspring interbred over generations. Genetic analyzes suggest that all southeastern bears studied share a common ancestor dating back about two hundred years.
The most likely culprit for the abandonment of founder bears in the fjords is the East Greenland Coastal Current, a huge, high-velocity southbound current along the coast of East Greenland. It essentially creates a frozen conveyor belt of sea ice off the northeast coast that breaks up into smaller floes as it sweeps south.
Every year, Ugarte says, at least a handful of bears are hurled down from the northeast and around Cape Farewell, Greenland’s southernmost point. The relatively lucky ones will be dumped in the Southwest, where they could find their way north and west to Canada. The unfortunate drown in the sea.
“What’s interesting or special about this new bear population is that they actually seem to know how to manage it,” says Ugarte. Eleven of the pursued bears were caught in the currents and covered an average of 117 miles across the ice in less than two weeks – but within a month or two all managed to return to their home fjords in the frigid waters and saunter overland.
A refuge, if only for a while
Andrew Derocher, a University of Alberta biology professor who has studied polar bears and the Arctic for over 40 years and was not involved in the study, says the research is “elegant” and has “collected some interesting results.”
He adds that seeing glacial ice supporting a population of polar bears in the absence of sea ice is not a revelation. There is the well-documented example of Svalbard, a Norwegian archipelago, where polar bears also settled in small home ranges supplemented by glacial ice.
Scientists predict that as climate change reshapes the Arctic, glaciers in fjords will remain intact longer than sea ice, potentially creating refuges — temporary retreats amid unfavorable living conditions — for species like polar bears that rely on ice for hunting.
But that doesn’t mean “saving the polar bears,” says Steven Amstrup, senior scientist at conservation organization Polar Bears International and former director for 30 years of polar bear research in Alaska at the United States Geological Survey.
Although the Arctic may be brimming with glaciers in the public imagination, much of the polar north consists of tundra, treeless plains overlying frozen ground known as permafrost. “The Arctic’s freshwater glacial ice reservoirs are mostly Greenland and Svalbard, with a small portion in far northern Canada,” says Laidre. These glacial mixes are uncommon in the Arctic and could not support large numbers of bears.
Amstrup hopes the research will “encourage scientists and managers to investigate where else in the Arctic glaciers might be helping polar bears survive longer.
“If anything, this study really is further evidence of the fundamental relationship between polar bears and ice-covered water,” he says. “Do they really care if the ice is fresh water or salt water? Probably not with sigils underneath.”
A subgroup with a different name
The authors of the study argue that Greenland’s southeastern bears should be recognized as the 20th polar bear subpopulation in the Arctic due to their genetic differences and geographic separation from those in the northeast.
Ultimately, that’s a question for polar bear experts, including Lairdre and Derocher, of the International Union for Conservation of Nature. They will consider factors including the number of bears in the population – which scientists have yet to determine exactly – and whether trying to manage them as a separate population would be beneficial.
The authors of the study see the genetic specificity of Southeastern bears as something that needs to be preserved and protected. Derocher and Amstrup do not disagree, but add a worrying note.
“My guess is that we have a small, isolated inbred population,” Derocher says, “and such populations that we know of from other studies of large carnivores are susceptible to inbreeding depression, episodes of disease, and just random demographic events.”
“From an evolutionary context, isolated populations are typically more vulnerable,” agrees Amstrup.
“This type of genetic isolation and fragmentation is something we’re likely to see much more frequently in the future as smaller and smaller groups of bears persist [more distant] areas,” says Derocher.