Adult Polar Bears in Svalbard Are Gaining Fat Even as Arctic Sea Ice Shrinks
Polar bears now symbolize the cost of Arctic warming. As sea ice recedes, the platform they rely on to hunt prey disappears, and bears are expected to burn off their fat stores and lose weight. But in Svalbard, a Norwegian archipelago located in the Barents Sea, this trend has not continued. A new study published in Scientific reports finds that adult polar bears in the region have improved their physical condition since around 2000, even as sea ice melt has accelerated.
The result is remarkable in one of the fastest warming regions of the Arctic. Parts of the Barents Sea near Svalbard have warmed by about 35.6 degrees Fahrenheit (2 degrees Celsius) per decade since 1980, but a 2004 census estimated the polar bear population at about 2,650, with no obvious decline. Why the bears seem to be holding out remains an open question.
Measuring polar bear health over time
To better understand this question, researchers focused on body condition. For polar bears, body condition reflects the amount of fat an individual carries, which influences survival and reproduction, especially during long periods without food.
Obtaining data from oral measurements of an anesthetized polar bear.
(Image credit: Jon Aars / Norwegian Polar Institute / CC BY)
The team analyzed 1,188 capture records of 770 adult polar bears collected between 1992 and 2019 as part of a long-term monitoring program in Svalbard. During each capture, the team recorded body measurements that allowed them to estimate mass relative to body size. From this data, they calculated a body condition index, or BCI, which provides a standardized estimate of fat stores.
The researchers then compared changes in body condition over time with environmental conditions in the Barents Sea region. A central variable was the number of ice-free days each year, representing the length of time the bears could have reduced access to sea ice, their primary hunting platform.
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A different model emerges in Svalbard
Over the 27-year study period, the Barents Sea lost about 100 days of seasonal ice, adding about four ice-free days each year. In other polar bear populations, this type of rapid ice loss has been associated with a decline in health, as bears lose access to hunting grounds and burn through their fat stores.
But this model did not hold true in Svalbard. Polar bear body condition declined during the 1990s, reached its lowest level around 2000, and then began to improve in both males and females, even as sea ice continued to retreat.
When researchers analyzed changes in body condition alongside sea ice loss and climate patterns, they found no clear, direct link between warming and health decline. Instead, the data suggest that the polar bear’s condition in this region has been shaped by a changing mix of environmental factors over time, rather than ice loss alone.
What could help Svalbard’s bears
A possible explanation for the bears’ condition could be the recovery of terrestrial prey species, including reindeer and walrus, which were previously overexploited by humans. The increased availability of these animals could provide additional food sources when bears spend more time on land.
Polar bear standing on sea ice during golden hour.
(Image credit: Trine Lise Sviggum Helgerud / Norwegian Polar Institute / CC BY)
The authors also suggest that decreasing sea ice could cause prey such as seals to concentrate in smaller areas, potentially increasing hunting efficiency during periods when ice remains available.
At the same time, researchers point out that the continued loss of sea ice could ultimately have negative effects. Longer travel distances, higher energy demands, and reduced access to hunting grounds can push conditions beyond what bears can compensate for. The study concludes that findings from one region should not be generalized to all polar bear populations, highlighting the need for continued monitoring as Arctic warming continues.
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