Their icy hunting grounds are rapidly shrinking, but polar bears in Norway’s remote Svalbard archipelago have defied the odds by bulking up instead of wasting away, a study has found.
The Barents Sea has lost sea ice faster than other areas that have polar bears as temperatures have risen there more than in other Arctic regions, according to the research published in the journal Scientific Reports.
But instead of growing leaner like polar bears in other parts of the Arctic where the sea ice they use for hunting grounds is retreating, those in Svalbard have gained body fat.
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Jon Aars, the study’s lead author and a scientist at the Norwegian Polar Institute, said polar bears in Svalbard had become plumper by feasting on land-based prey such as reindeer and walruses, species that had recovered after being over-exploited by humans, the study said.
“The increase in body condition during a period of significant loss of sea ice was a surprise,” he said.
Warmer temperatures have also made it easier for them to hunt ringed seals that crowded in smaller sea ice areas.
Polar bears in Svalbard have become plumper, Norwegian scientists have found. (Norwegian Polar Institute: Trine Lise Sviggum Helgerud)
Bears’ fat measured
The scientists analysed the body condition index (BCI) of 770 adult bears between 1995 and 2019 to determine how much — or how little — fat they carried.
They found that their BCI fell until 2000 but increased in subsequent years despite a period of rapid loss of sea ice.
The total polar bear population of the Barents Sea was estimated at between 1,900 and 3,600 in 2004 and may have increased since then, the study said.
The increase in air temperature has been two to four times higher in the Arctic than the global average over recent decades.
When polar bears are too skinny, reproduction levels go down, so bears in good condition is good news for the population. (Norwegian Polar Institute: Jon Aars)
The Barents Sea has experienced even greater increases in temperature than other regions in the Arctic over the past four decades, rising by up to 2 degrees Celsius per decade in some areas, the study said.
The area has also lost sea ice habitat at a rate of four days per year between 1979 and 2014, more than twice as fast as other regions hosting polar bears, it said.
Sarah Cubaynes, a researcher at French environmental research centre CEFE who was not involved in the study, said the Svalbard findings “may seem surprising because they contradict the results of studies conducted in other polar bear populations”.
The physical condition of polar bears in Hudson Bay, northeastern Canada, for example, “has greatly declined due to warming”, Ms Cubaynes said.
Scientists were surprised by results of a study that found polar bears in Svalbard have gained condition, despite sea ice reduction. (Norwegian Polar Institute: Jon Aars)
Unexpected results
Had he been asked to predict when he started working at NPI in 2003 what would happen to the bears, Mr Aars said he would have declared at the time that they “would likely be skinnier”.
“And we see the opposite, bears are now in better condition, even though they are forced to be on land much more of the time, without the ability to hunt ringed seals,” he said.
A deterioration in body condition is usually a sign of future demographic problems for the Arctic animals.
The Barents Sea has experienced even greater increases in temperature than other regions in the Arctic. (Norwegian Polar Institute: Jon Aars)
“When conditions get worse, with less access to food, we anticipate to first see that bears get skinnier, that they do not accumulate so much fat reserves,” Mr Aars said.
“This we expect to see before things get even worse, and survival and reproduction decreases significantly.”
The unexpected results in Svalbard underscore the importance of not extrapolating findings from one region to another, the study said.
One of the mainstays of a polar bear’s diet is ringed seals. (Norwegian Polar Institute: Geir Wing Gabrielsen)
The situation in Svalbard “indicates a complex relationship between habitat, ecosystem structure, energy intake, and energy expenditure”, the authors wrote.
While Mr Aars said the good body condition of Svalbard’s polar bears was “good news”, the study warned that they were “likely to be negatively affected in the near future” by a warming planet and shrinking sea ice.
The bears may still be able to prey on walruses and reindeer, but “we think they still depend on hunting seals on the ice”, he said.
AFP