Svalbard Polar Bears Gain Weight Despite Arctic Sea Ice Loss

Polar bears can reveal a great deal about conditions in the Arctic. When food becomes difficult to obtain, their physical condition quickly reflects it. When hunting improves, they regain weight. Declining sea ice has generally resulted in slimmer polar bears and smaller populations.

This is why the situation around Svalbard – located between Norway’s northern coastline and the North Pole – is so surprising. Although sea ice is still disappearing, adult polar bears in the area have not become less healthy.

In fact, many now weigh more than they did in previous years. For a polar bear, additional fat is far from insignificant: it can determine whether an individual survives the year.

Fast warming, unexpected results

The Barents Sea surrounding Svalbard has warmed for several decades. Since 1980, temperatures across the region have increased by up to 2°C per decade.

For wildlife dependent on sea ice, such shifts would normally mean fewer opportunities to hunt and more challenging periods of the year.

Yet these polar bears did not appear to decline as many people anticipated. A 2004 survey put the population at roughly 2,650 bears, and that figure remained broadly stable for years.

This stability persisted while sea ice continued to retreat, leaving scientists uncertain about how the bears were managing in such a rapidly warming environment.

Measuring polar bear health over decades

To investigate, researchers from the Norwegian Polar Institute examined the bears’ bodies in detail. Jon Aars and his colleagues led the research.

They assessed 1,188 body-measurement records from 770 adult polar bears on Svalbard, gathered between 1992 and 2019.

The researchers concentrated on the body composition index, or BCI, which indicates fat stores and general physical condition.

Fat is crucial because polar bears depend on these reserves during extended intervals with limited food, particularly when sea ice restricts hunting. The team compared shifts in BCI against changes in sea ice.

Across the 27-year study period, ice-free days in the Barents Sea region rose by approximately 100, increasing at about four days annually. Reduced ice would typically mean poorer access to seals, the bears’ principal prey.

However, the findings showed something else. The average BCI among sampled adult polar bears increased after 2000. Put simply, the bears carried more fat despite falling sea ice levels.

Less ice does not mean leaner bears

One potential reason may be found on land rather than on the ice. The researchers suggest that the better body condition of Svalbard polar bears may be linked to recovering populations of terrestrial prey formerly over-exploited by people, including reindeer and walrus.

Hunting limits and conservation measures enabled these animals to recover, providing bears with alternative sources of food as hunting from sea ice became more difficult.

Prey behaviour as the ice contracts could be another influence. The authors also suggest that sea ice loss may cause prey species, including ringed seals, to gather in smaller areas of remaining sea ice.

If seals become concentrated in more confined locations, polar bears may be able to hunt them more efficiently, even where the overall ice cover is reduced.

A fragile success

This more positive picture carries an important warning. The researchers are not claiming that polar bears are protected from continuing warming.

They speculate that additional sea ice losses could harm Svalbard populations by extending the distances polar bears must cover to reach hunting areas.

Longer swims and walks use more energy and increase the likelihood of injury or death – difficulties already recorded in other polar bear populations.

Energy balance is vital for a polar bear. A modest improvement in hunting success may help temporarily, but the calculation changes once the ice retreats too far. Fat accumulated in one season might not be sufficient for longer and more demanding trips in the following one.

Lessons for a warming Arctic

The results underline how adaptable polar bears may be, at least in certain locations and over limited periods. They also demonstrate that Arctic regions do not all react to warming in the same manner.

The availability of local prey, human activity in the past and geography each affect how animals respond to change.

The authors conclude that further research is required to establish how separate polar bear populations may adapt to a warming Arctic in future.

Svalbard’s bears may be gaining time rather than avoiding the threat. Their present condition provides understanding, not reassurance, of just how complicated and uneven climate-change impacts can be.

The complete study appeared in the journal Scientific Reports.