Polar bears could face extinction faster than thought, study says

Georgia Reed
February 4, 2018

Polar bears can readily hunt seals on sea ice, but it's much more hard to catch the prey when the ice is gone and bears end up expending energy by traveling over greater distances. They also measured the bears' metabolic rates using blood and urine samples.

"This study identifies the mechanisms that are driving those declines by looking at the actual energy needs of polar bears and how often they're able to catch seals", he continued. That could explain the 40% decline in polar bear population in the southern Beaufort Sea between 2001 and 2010 as noted by an earlier study.

"To us, it really stressed the feast-or-famine lifestyle that these bears have", Pagano said.

Using the Global Positioning System and video collars and the metabolic information, the researchers determined that the more a bear had to search for food the more energy it used.

Polar bears live in a remote and inhospitable environment far from most human settlements. But he added, "I think it confirms all the reasons to be concerned about polar bears from a conservation perspective are intact".

But the scientists found the bear's metabolic rate was 1.6 times greater than previously thought - akin to that of other carnivores. In contrast, the four bears that actually caught and ate ringed seals gained nearly 10 percent of their body mass. Five of the bears lost weight and four of them lost 2.9 to 5.5 pounds a day.

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"We've documented declines in the population, declines in the abundance, declines in the survival rates, declines in the body condition in the population", said lead author Anthony Pagano, a research wildlife biologist with the U.S. Geological Survey's Anchorage office.

Back in 1973, when the five Arctic states first agreed to manage polar bears, the largest threat to polar bears was over-hunting, so their first agreement was mainly directed towards harvesting-management programs and protected areas. One female bear Griffen studied swam 426 miles over nine days. By the fall, the young seals are older and wiser, and polar bears are not able to catch as many. That's why the melting of the Arctic sea ice threatens polar bear survival.

But understanding the exact relationship between the loss of ice and the plight of the polar bear has been a little murky because it's hard to track the movements of these enormous apex predators in remote regions.

"We now have the technology to learn how they are moving on the ice, their activity patterns, and their energy needs, so we can better understand the implications of these changes we are seeing in the sea ice", Pagano said. A few of the bears travelled more than 155 miles (250 kilometers) in about 10 days off the northern coast of Alaska in the Beaufort Sea, Pagano said. During that time the bear crossed into Canada, having walked almost 270 miles (430 kilometers) since her collar had been applied.

The study suggests that polar bears need more energy to survive than previously thought-and they might not be catching enough prey to meet those demands. Four of the bears lost nearly 10 percent of their body mass - about 40 pounds (18 kilograms). "This study identifies the mechanisms that are driving those declines by looking at the actual energy needs of polar bears and how often they're able to catch seals", Anthony Pagano of U.S. Geological Survey, now a Ph.D. candidate at University of California, Santa Cruz and first author of the paper, said in a statement Thursday. As per the new study, to survive, during the prime hunting season, polar bears normally need more than 12,000 kilocalories per day.

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