Polar bears at risk of starvation as Arctic summer lengthens
Polar bear (Ursus maritimus) on land in western Hudson Bay, Canada. EFE/ Washington State University/ David McGeachy EDITORIAL USE ONLY/ ONLY USE PERMITTED FOR ILLUSTRATING THE ACCOMPANYING STORY/ (CREDIT REQUIRED)

Polar bears at risk of starvation as Arctic summer lengthens


Hudson Bay, Canadá, (EFE).

Polar bears are sea-ice animals, but increasingly long Arctic summers will force them to spend more time on land, where they are unlikely to be able to adapt to living for long periods and may even risk starvation.

A study published Tuesday in Nature Communications followed 20 bears wearing camera collars and GPS for three weeks in August and September that they spent on land in Canada’s western Hudson Bay region, where a warming climate is likely to affect bears faster than in other Arctic regions.

During their time on land, when there is no sea ice, polar seals, from which they get most of their energy, are out of reach.

The study suggests that “bears do not have behavioral and energetic strategies that they can use to avoid weight loss during the summer on land, and this will get worse as they spend more time on land,” the lead author of the study, Anthony Pagano of the US Geological Survey’s Alaska Science Center, told EFE.

Feeding is not enough

Although these animals “show remarkable plasticity in their behavior, they are still at risk of starvation” due to the predicted decrease in Arctic sea ice, as the work suggests that the food they get on land does not give them enough energy to resist longer before reaching a state of starvation, Pagano said.

Previous research showed that the ice-free period in western Hudson Bay increased by three weeks between 1979 and 2015.

Bears, Pagano said, now spend an average of 130 days on land, compared with 100 to 110 days previously.

Depending on different greenhouse gas emission scenarios, it is “likely” that the time spent at sea will increase by five to 10 days per decade.

As polar bears are forced to come ashore earlier, the period during which they normally acquire most of the energy they need to survive is reduced, and it is expected that “an increase in starvation, particularly among juveniles and females with cubs,” will be seen.

In addition to measuring energy expenditure, the researchers weighed the bears before and after the three-week observation period.

From lying down to swimming

The animals displayed a variety of strategies for maintaining energy reserves, regardless of age, sex, reproductive stage (pregnant females were included), or initial body fat level.

Despite the variety of behaviors, 19 of the 20 animals lost “similar amounts of body mass,” an average of one kilogram per day.

Many adult males simply lay down to conserve energy, burning calories at a rate similar to hibernation, but 70% remained active, foraging for terrestrial foods such as berries, grasses, and bird and caribou carcasses.

Some adult females spent up to 40% of their time foraging, and although the food provided some energetic benefit, they had to expend more energy to access it.

Three swam long distances, up to 175 kilometers in open water, where two encountered marine mammal carcasses that they were unable to feed on while swimming or bring ashore.

Only one gained weight after encountering a dead marine mammal on land.

Not grizzly bears

Pagano noted that it is difficult to determine how long it would take the bears to starve because it depends on their size and body condition, although previous studies have estimated that adult males “would die of starvation if the summer fast extended to 180 days.”

Polar bears, which are “not brown bears in white coats,” are “very, very different from brown bears,” another author, Charles Robbins of Washington State University, said in a statement.

They can reach three meters and weigh more than 1,500 kilograms, compared with the two meters and 800 kilograms of their terrestrial relatives.

Maintaining that large mass, Robbins added, depends on the energy-rich blubber of seals, which they hunt best on ice.

The next goal is to use these data to predict the effects of projected sea ice loss on the reproduction and survival of specific polar bear populations in different parts of their range.EFE


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