Metabolism study signals more trouble ahead for polar bears

Polar bears find it hard to catch enough food, even in the best hunting season

Polar bears finding it harder to catch enough seals to meet energy demands

Although polar bears have a larger range than other bears, the study also showed that because of declining sea ice the bears are having to swim and walk further than before to find seals, which increases energy expenditure.

"We've been documenting declines in polar bear survival rates, body condition, and population numbers over the past decade". "As a result, bears showed remarkable fluctuations in body mass based on their foraging success, emphasizing the feast or starvation lifestyle of these animals".

For his study, Pagano, who is also a wildlife biologist with the U.S. Geological Survey, examined adult female polar bears on sea ice in the Beaufort Sea, off the north coast of Alaska. In April 2014, 2015 and 2016, researchers outfitted nine female bears with global-positioning-system-equipped video collars and activity trackers.

On average, the bears needed almost 12,325 kilocalories per day - 1.6 times more energy than previously thought.

During the test, researchers saw about half of hunting bears lost 10 percent of their body weight in just over a week. "They need to be catching a lot of seals", he said. But later in the year, after the bears' long summer fast, those young seals are older and wiser, meaning polar bears are not able to catch as many.

In the spring, the researchers explained polar bears are mostly preying on juvenile seals. Turns out they are high-energy beasts, burning through 12,325 calories a day-despite sitting around most of the time, according to a unique metabolic analysis of wild bears published Thursday in Science. For more than a decade, San Diego Zoo Global's researchers and its USA and Canadian partners have focused on contributing to science-based conservation strategies, to preserve and understand wild populations of polar bears.

But still, "when I see pictures of big glacial blocks breaking away and the sea ice is retreating, I get anxious", Fickel admits. "They don't move a whole lot so they're basically laid out as one big buffet for the bear to go around". As sea ice continues to decline, frequent and timely monitoring of polar-bear subpopulations across Canada will be necessary to ensure co-management boards can make informed decisions. The average polar bear studied weighed about 386 pounds (175 kilograms).


Pinning down that figure is an important step in understanding what is happening to polar bears now and in the future with climate change, said polar ecologist John P Whiteman of the University of New Mexico.

Meanwhile, the most recent polar bear population estimate by USGS also indicated almost 40 percent decline over the past decade.

"We found that polar bears actually have much higher energy demands than predicted". As per the new study, to survive, during the prime hunting season, polar bears normally need more than 12,000 kilocalories per day. "Activity and movement on the sea ice strongly influenced metabolic demands", the researchers summarized in the abstract of their paper. There, Arctic warming causes sea ice to break up earlier in the summer and return later in the fall, which forces the bears to spend more time on land.

Best estimates say there are 20,000 to 30,000 polar bears in 19 different groups or populations scattered across the top of the U.S., Canada, Greenland, Norway, and Russian Federation.

"It's a really strong study", said Steven Amstrup, chief scientist for Polar Bears International, a conservation-focused organization, who was not involved with the work.

"Two-thirds of the world's polar bears could die out by 2050", cautions WWF, demanding an immediate decline in greenhouse gas emissions so the bears can stand a chance of survival.

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