A lot more than many of them are catching in prime spring hunting season, according to a new study.
Researchers followed nine polar bears over a three-year period and found that an adult polar bear requires at least one adult seal or three juveniles every 10 days to sustain itself, according to a USGS press release. This means they quickly start to lose weight that is essential for survival.
"We've been documenting declines in polar bear survival rates, body condition, and population numbers over the past decade", Pagano said in a statement. Eight to 11 days later they were all re-captured.
Polar bears have a much higher metabolism than previously thought and so are at greater risk of starvation as melting Arctic ice makes it harder for them to hunt, a study has found. The bears were fitted with Global Positioning System collars that had cameras to record point-of-view videos of each. The only way for the bears to restore that lost energy was to catch more seals.
"In the Beaufort Sea we are seeing that the ice is retreating much further to the north than it had historically", Mr Pagano said. "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.
"High-energy, high-fat lifestyle challenges an Arctic apex predator, the polar bear" was published Thursday in the February 2 issue of the journal Science.
Canada, home to two-thirds of the world's population of roughly 30,000 polar bears, has done a good job surveying subpopulations, making sure the polar bear trade is legally regulated, and incorporating traditional knowledge into polar bear management, the WWF said.
The higher metabolic rate, coupled with the fact that the bears studied now travel hundreds of kilometres further to hunt as sea ice recedes, means the bears are burning even more energy to catch fewer "energetically dense" ring seals.
The scientists estimated that an active female polar bear needed around 51 megajoules of energy a day.
In total, the bears would have to eat one adult ringed seal or 19 newborn seal pups every 10 to 12 days to avoid starvation, the researchers say.
As the Arctic heats up and more sea ice melts, polar bears must move farther than in past years. Because of the video footage, the researchers know that these bears gained weight because they caught seals.
In other areas like Hudson Bay, the sea ice is breaking up earlier in the summer and returning later in the fall, which has forced the polar bears to spend more time on land.
"That [number] tells us a lot about modelling into the future what's going to happen with the bears".
Anthony Pagano, USGS Research Wildlife Biologist, said: 'It's really quite fascinating to learn the basic behaviours of these animals and how they're using the sea-ice environment, and how dynamic the sea-ice environment is and how their behaviour might change from year to year based on the sea ice conditions that they're experiencing'.
Since then, however, the nature of threats facing polar bears has changed, and the biggest threats are now the result of human activities that are changing the climate.
Professor Whiteman said it was important to understand what happens when the bears are fasting.
However, he doesn't doubt climate change and receding ice will have an negative impact on the polar bear because of what he says should be an obvious reason. The agency's most recent population estimate suggests the bears have declined by about 40 percent over the past decade. Even today, in the middle of the bitter cold Arctic winter, satellites show there is about 770,000 square miles less sea ice than the 1981 to 2010 median (That's an area larger than Alaska and California combined).