Polar bears in part of the Arctic have grown fatter and healthier in the last three decades despite living in an area that has suffered the fastest loss of Arctic sea ice, according to a new study published in Scientific Reports.
The Norwegian Polar Institute studied 770 polar bears between 1992 and 2019, taking 1,188 body measurements and correlating the findings with the loss of sea ice in the Barents Sea, where the polar bears lived. The Barents Sea is warming through greater temperature rises than other Arctic regions, by up to around +2 °C per decade in some parts of the region. Home to one of the 20 recognised polar bear populations, the zone has lost sea ice habitat at a rate of four days/year between 1979 and 2014, more than twice as fast as any of the other polar bear habitats.
The researchers expected to see a decline in the polar bears’ body condition. But instead found that after an initial deterioration, the bears’ fatness and healthiness began to improve.
One explanation for the unexpected results put forward by the scientists is that, at the same time as sea ice has diminished, the density of ringed seals has increased, meaning the bears might have a shorter hunting season, but can hunt more efficiently. The bears are also consuming more land-based prey than previously thought available. Walruses, which have been protected since 1950, have grown in numbers, providing food, as have harbour seals, which again are more efficient to hunt, and reindeer.
Although the study seems to present good news for this population of polar bears, the authors warn that they may have been helped because the Barents Sea area is not yet at “carrying capacity,” meaning it still offers enough food to go around. With further habitat loss likely in the future, the point at which their numbers reach critical mass could be coming, making monitoring essential, the researcher said.
In addition, animal biologist John Whiteman, not involved in the study, told CNN in a statement that “body condition is only one piece of the puzzle,” arguing that fully understanding the processes at work “requires continued monitoring.”
Overall, although the Barents Sea bears showed “a high level of resistance to environmental changes induced by a warmer climate and sea ice habitat loss,” the factors leading to their improved body condition should not be extrapolated out to other polar bear populations, the researchers said, noting bears elsewhere have not demonstrated the same resilience.
