In a warming world, the polar bear has become the unofficial mascot of ecological collapse. We’ve all seen the photos of these majestic predators reduced to skin and bone, clinging to ever-shrinking chunks of sea ice as they try—and fail—to hunt. But on a remote Norwegian archipelago, a very different story is unfolding.
Svalbard is home to about 3,000 people, and roughly the same number of polar bears populate the Svalbard and Barents Sea region. An estimated 300 bears remain on the archipelago year-round. Across the Arctic, dwindling sea ice is depriving this species of its critical hunting ground, and Svalbard is no exception. Yet somehow, its polar bear population is thriving, with bears actually gaining weight since 2000 despite rapid loss of sea ice.
This finding, published Thursday in the journal Scientific Reports, understandably came as quite a surprise to the study’s authors. Lead author Jon Aars, a senior researcher at the Norwegian Polar Institute, told Ireland Live that when he joined NPI in 2003, he would have expected the bears to be thinner and their population to be in decline by now.
“This paper highlights how different polar bear populations can be from one another, using Svalbard as an example during more than two decades of rapid sea ice loss,” co-author Andrew Derocher, professor of biological sciences at the University of Alberta, told the advocacy group Polar Bears International.
Defying the odds
Previous research has shown that the average temperature in the Barents Sea region surrounding Svalbard has risen up to 3.6 degrees Fahrenheit (2 degrees Celsius) per decade since 1980. As a result, this area has lost sea ice habitat at a rate of four days per year between 1979 and 2014, studies show. That’s more than twice the rate of any other area home to polar bears, according to Aars and his colleagues.
Despite this, the Barents Sea polar bear population has largely remained stable since Aars conducted a census in 2004, which estimated 2,650 individuals across the region.
To investigate the drivers of this stability, Aars’s team analyzed body composition data of 770 adult polar bears measured on Svalbard between 1992 and 2019. The researchers then compared changes in the bears’ body composition index (BCI)—an indicator of fat reserves—with the number of ice-free days in the Barents Sea region over the 27-year period.
They found that the bears gained fat even as sea ice continued to disappear, with their average BCI increasing since 2000.
Complexities of a changing Arctic
The finding poses an ecological puzzle, but Aars and his colleagues have several ideas about how Svalbard’s polar bears have managed to thrive despite rapid habitat loss.
One reason may be that populations of the bears’ land-based prey, such as reindeer and walruses, are rebounding following years of overexploitation by humans, the researchers suggest. These species might be supplementing the bears’ diets as hunting marine prey—primarily ringed seals—becomes less accessible.
However, it’s also possible that sea ice loss is causing ringed seals to gather across smaller areas of sea ice, allowing the bears to hunt more efficiently. With that said, the authors predict that this benefit will subside with further reductions in sea ice, as the distances polar bears must travel across hunting grounds will increase. Researchers have already observed this phenomenon in other populations.
Piecing together the complex factors that have allowed Svalbard’s polar bears to defy the odds will require more research, according to the authors. For now, at least, this population is a testament to the fact that life often finds a way, but polar bears across the Arctic still face an existential threat.
Read the full article here
