Polar bear swims for 9 days in search of sea ice

One of Alaska's own polar bear experts is making headlines this week with a new revelation about the toll climate change is taking on polar bears as a result of melting sea ice. In one of the most dramatic signs ever documented of how shrinking Arctic sea ice impacts polar bears, researchers at the U.S. Geological Survey in Alaska have tracked a female bear that swam nine days across the deep, frigid Beaufort Sea before reaching an ice floe 426 miles offshore.

The marathon swim came at a cost: With little food likely available once she arrived, the bear lost 22% of her body weight and her year-old female cub, who set off on the journey but did not survive, the researchers said.

"Our activity data suggests that she swam constantly for nine days, without any rest. Which is pretty incredible," said George M. Durner, a USGS zoologist and a lead author of the study, published last month in the journal Polar Biology.

"We have observed other long-distance swimming events. I don't believe any of them have been as long in time and distance as what we observed with her," he said. "How often does this happen? We're trying to get a handle on that."

Polar bears spend much of their waking lives on the shifting Arctic sea ice floes. They survive mainly on the ringed seals that are also dependent on sea ice and swim in abundance in the relatively shallow coastal waters of the continental shelf.

Polar bears spend much of their waking lives on the shifting Arctic sea ice floes. They survive mainly on the ringed seals that are also dependent on sea ice and swim in abundance in the relatively shallow coastal waters of the continental shelf.

But sea ice has been melting dramatically in recent years, forcing polar bears during the fall open-water periods to either forage from shore or swim longer distances in search of sea ice.

Bears that retreat to land usually find little or no food there, and "typically … spend the duration fasting while they await the re-formation of ice needed to access and hunt seals," according to a 2008 government study.

"We are in awe that an animal that spends most of its time on the surface of sea ice could swim constantly for so long in water so cold," George M. Durner told BBC News of the "marathon" bear, which reported the findings Tuesday. Durner is a research zoologist with the U.S. Geological Survey in Anchorage at the Alaska Science Center.

With data collected over a two-month period in 2008 using data from a GPS-equipped radio collar, along with body temperature monitoring equipment and motion sensors previously attached to the bear., Durner and his colleagues chronicled the bear's eastward journey along the Alaska coast, during which she made that incredible nine-day, 426-mile swim from land to floating pack ice over the sea's deep waters. Along the way, she lost her yearling cub and 22 percent of her body weight: more than 100 pounds.

"Our observation confirms that yes, indeed, polar bears are capable of, they have the ability to undergo these extraordinary behaviors such as long distance swimming. No one else has been able to provide data like this before," Durner said in an interview from his Anchorage office Tuesday, January 25, 2011.

The comprehensive data comes from a unique mix of hi-tech gadgets that were affixed to the bear in August 2008, each equipped with computer chips that recorded and preserved the data that scientists were able to download two months later, when the bear was again captured.

Through satellite tracking, motion detectors and thermometers they kept tabs on her every hour of every day. They not only knew where she was but also whether she was walking or swimming, resting or active, and how warm or cold it was outside or in the water and, with a sensor buried in the fat beneath her skin, they recorded her own body temperature -- a blend of gadgets designed to assist not only the ongoing studies, but also a USGS University of Wyoming study looking specifically at the physiology of polar bear on land and sea ice during summer in the Beaufort Sea. For scientists, having all of the technology on a single animal was a rare expedition that, as best as it could, let them travel alongside the mother bear via data diary.

"What makes her particularly unique is the wealth of data that we have available from this animal to be able to tell a story about what she experienced," Durner said.

What was her life like in the two months scientists eavesdropped on her? She started as a healthy, 500-pound bear that was lactating and caring for a yearling cub. At some point she left Alaska's coast and went for a swim in search of sea ice, the floating surface bears use to travel over hunting grounds.

Along the way, during the swimming journey that went on far longer than scientists have to-date recorded, she lost her cub. Durner suspects it died from exhaustion during the long, 426-mile swim from land to pack ice, but there's no way to know for sure. The floating ice pack was farther off shore than usual -- a trend attributed to melting sea ice and climate change. And it was over deep waters which aren't as food-rich as the shallower continental shelf, over which summer pack ice in years past has been found.

By the time scientists caught up with the polar bear again in October 2008, she had traveled hundreds of miles eastward toward Canada. Her cub was gone, she had stopped lactating and she had lost a lot a weight.

In the past, polar bears haven't had to swim as far to reach the ice, Durner said, adding that the mother bear probably had no idea what she was getting herself into.

"The bear probably went swimming back in 2008 and probably didn't say to itself, 'I've got 687 kilometers to swim.' It probably just said, 'I'll go swimming and pretty soon I'll come to the sea ice habitat where I want to be," he said.

The bear's journey shows that while, yes, polar bears can adapt to changing environments, it comes at great cost, Durner said. Cubs may not be able to survive the hardships and females may not be able to maintain enough body weight to give birth or successfully care for their young.

Norway's 'Spy on the ice'

High Tech Cams get High Tech videos of Polar Bears

Durner and his colleagues aren't the only people employing technology to help satisfy their curiosity about what polar bears are up to at any given moment. On the other side of the Arctic Ocean, the British Broadcasting Corp. recently had its own surveillance operation underway. In Svalbard, an island cluster in Norway's northernmost region, the "Spy on the Ice" crews deployed specially designed video cameras to surreptitiously gather hard-to get images.

Polar Bears Play Football with Spy Cams

While "Blizzard cam," "snowball cam," "drift cam" (left) and "iceberg cam" look like they belong in "Star Wars V: The Empire Strikes Back," they are actually a collection of covert, cold-weather camera housings created to operate unmanned and withstand the arctic climate. Some, equipped with skis, can quietly travel up to 40 mph and remain operational for up to a week. Motion and heat sensors allow the cameras to lay in wait until the bears show up, coming to life just in time to record the action.

Polar Bear Flirtation

In one clip, a snowball cam (left) chronicled a cub's first emergence out of the birthing den. And although a blizzard left a blanket of snow clouding the lens, a paw swipe from the curious mother cleared the view, which the camera also caught. The program's narrator sums up the remarkable results: "The cub's first steps outside the den, filmed by his mother."

Cub Emerges for first time from winter den

In another clip, iceberg cam records images above and below the water and manages to capture a polar bear's stealthy hunt for a seal. Iceberg Cam (left) was designed to blend seamlessly amongst the ice flows. It’s powerful thrusters produced enough speed to keep up with swimming bears. Iceberg Cam was decked out with two cameras for above and below water filming. It's an impressive display of clever planning and predator prowess, and in one shot the bear is caught eerily popping up behind the seal undetected, just before slinking back into the water to make its move.

Knowing that polar bears are curious and may even be prone to vandalism, the camera's designers equipped blizzard cam (the gadget which slides, self-propelled on skis, along the ice and snow shown at right) with a getaway plan. In the event of an attack, it's able to deploy snowball cam as a decoy -- a distraction meant to keep the bears occupied long enough for the larger module to flee to safety.

Turns out, it works. But the bears did get the better of the cams. One consolation? Snowball cam filmed to the very end of its paw-smashing, teeth-tugging demise.

Polar Bears Smash SpyCams on Ice

The result is a stunning collection of footage chronicling the life of the polar bear, from which the BBC recently aired a 60-minute program, "Polar Bear: Spy on the Ice."

Source:
Alaska Dispatch, "Polar bear swims for 9 days in search of sea ice", by Jill Burke, accessed January 28, 2011
Los Angeles Times, "Polar bear's long swim illustrates ice melt", accessed January 31, 2011