Published: Fri, February 02, 2018
Science | By Eileen Rhodes

Melting ice puts hungry polar bears at risk

Melting ice puts hungry polar bears at risk

Shot by Paul Nicklen and Cristina Mittermeier of the nonprofit group Sea Legacy, and published on National Geographic in early December, the video ignited a firestorm of debate about what scientists know, and don't know, about the impacts of global warming on polar bears. "They need to be catching a lot of seals", Pagano said.

Polar bears rely nearly exclusively on a calorie-loaded diet of seals. Then the bear bites it on the neck and drags it onto the ice.

"The beauty of this study I think really comes from the fact that it's an all-in-one", Derocher said.

Experts estimate the total polar bear population at between 22,000 and 31,000.

The researchers hypothesize that the bears' lazy hunting style - when it works - allows them to conserve energy, helping them survive through the summer months when food is scarce.

The cameras recorded footage of bears catching seals and hauling them out of the ice, as well as of bears wrestling with large seals in frigid waters. 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. They analyzed their blood and urine. Using collars equipped with video cameras and other high-tech instruments, Pagano was able to monitor the bears over an 8- to 11-day period in the spring, when the bears hunt most actively. Underfed bears were losing 1 per cent of their body mass every day.

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This revealed that the animals were unable to catch enough prey to meet their energy needs. Measurements showed those animals lost 10 percent or more of their body mass.

The vision of a polar bear plucking a vulnerable seal off an ice floe is something familiar to wildlife documentary fanatics, BBC reports. "She might have been desperate", Pagano speculated.

Pagano's team studied the bears in a period during April over the course of three years, from 2014 to 2016, in the Beaufort Sea off Alaska.

Retreating ice sheets, a result of climate change, are forcing the bears to travel greater distances to find the food they need, which in turn causes them to expend more energy than in the past, the study said.

In the Beaufort Sea, where the study was undertaken, previous monitoring has identified a 40 per cent decline in polar bear numbers from 2001 to 2010. Five populations are thought to be stable and there's not enough known about the others to judge. "I've seen a 500-kilogram [1,100-pound] male consume 100 kilograms [200 pounds] of seal in one meal", he said. "If they were successful they did quite well". This means they need more prey, primarily seals, to meet their energy demands at a time when receding sea ice is making hunting increasingly hard for the animals. Scientists tracking bears' hunting patterns have concluded as sea ice disappears, the bears will have fewer easy kills and will spend more time swimming. She lost 22 percent of her body weight and, worse, lost the nursing cub that had started the journey with her. "Bears are going to starve to death", said photographer Paul Nicklen, a member of the crew who observed the bear.

The loss of sea ice has a domino effect on the species, which, in 2008, became the first animal listed under the Endangered Species Act due to threats from climate change.

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