Scienceline » Are Polar Bears Victims of the New Cold War?

Are Polar Bears Victims of the New Cold War?

Climate change may be affecting the bears' habitat.

By Emily V. Driscoll, posted February 5th, 2007.

A male polar bear is stalking his prey. Suddenly, he makes a beeline for his target. Punching a massive paw through the victims' snowy den, he gives his prey, a mother and two offspring, little chance. The bear bites down on her neck. The ensuing struggle collapses the den, suffocating the cubs.

But the victims are not ringed or bearded seals, typical polar bear food. They are also polar bears, victims of a perplexing act of cannibalism that researchers fear may become increasingly common as global warming puts more pressure on the Arctic's largest predator.

This 2004 incident, reported by Steven Amstrup of the U.S. Geological Survey's Alaska Science Center, was the first report of polar bear cannibalism in two decades of study in the Beaufort Sea area of northern Alaska, and in 30 years of studies in northwestern Canada. Since then, Amstrup has documented two additional cases.

"We can't say the observations we made are definitely related, but they are consistent with changes seen in the Arctic," said Amstrup. Other experts agree that cannibalism could be a harbinger of a decline in the polar bear population.

"We've never seen evidence of a male footprint in a female's den," said environmentalist Deborah Williams, who explained that females usually build dens in secluded areas away from male polar bears. Williams is president of Alaska Conservation Solutions, an environmental organization devoted to fighting global warming.

Polar bear populations are decreasing in the southern Beaufort Sea region of Alaska and the western and southern Hudson Bay in Canada. As a result, the U.S. Fish and Wildlife Service accepted a proposal last December to designate polar bears as a threatened species under the Endangered Species Act. Over the next year the organization will evaluate scientific data about polar bears before making a decision.

Some prominent researchers suspect that changes in the climate are a leading threat to polar bear survival. Polar bears are especially vulnerable to rising Arctic temperatures because they hunt, mate and usually make their dens on sea ice. "There is no evidence they can survive on land without sea ice," Williams said.

Polar bears move inland and live off stored body fat during summer months when sea ice levels are lowest. In the fall, when the ice returns, they venture off land to resume hunting for seals.

With warmer temperatures, the bears must wait longer for the ice to return. Researchers think that's a key reason why they're seeing more evidence of polar bear starvation and cannibalism, and why fewer cubs are surviving their first year than in the past.

Arctic sea ice has declined eight percent per decade since 1978, with a record low in 2005, according to satellite data collected by the federally funded National Snow and Ice Data Center. "Ultimately as the sea ice goes, so go polar bears," Amstrup said.

There is a "greater cumulative body of evidence that polar bears are being affected," said Amstrup, adding when "one year the polar bears are in prime condition and the next thing you see them dead on sea ice - it gets your attention."

Autopsies show the bears are starving. The two bears Amstrup found in his 2006 Beaufort Sea study had no fat in their bone marrow, "a clear indication of death due to starvation," said Williams. He said it was "the very first time scientists observed and documented polar bear starvation."

Amstrup's research also documented that polar bears are having smaller litters. He found that from 1990 to 2006 fewer cubs were reaching six months, compared to cubs born between 1976 and 1989.

The July issue of the journal Polar Biology reported four dead polar bears floating in the open waters of the Beaufort Sea in 2004 and attributed the deaths to drowning. But, not everyone is convinced by the data coming in.

"I'm going to write a letter to the World Wildlife Fund to ask who did an autopsy that found polar bears drowned," said Fred Goldberg, an authority on polar history and exploration at the Royal Institute of Technology in Stockholm, Sweden.

Aerial surveys of the area between 1987 and 2003 found no evidence of polar bears drowning. Goldberg also stated that since the bears were protected from hunting in 1973, "there have never been so many polar bears."

Mitchell Taylor, a polar bear researcher for the Canadian province of Nunavut, where many natives hunt polar bears legally, agrees and submitted a petition to the U.S. Fish and Wildlife Service opposing listing polar bears as threatened. He stated that only two populations of bears are decreasing because of climate change and "it's not clear how polar bears…will be impacted." Along the Davis Strait in Nunavit, Taylor said he found fat bears "pigging out on blueberries" and "catching seals in open water."

In fact, the decline in polar bears has not been uniform across the arctic; the overall population has increased since the 1970's, when most hunting was banned by treaty. More recent trends, however, have been troubling. Of the 19 separate polar populations, five are declining, two are increasing, five are stable, and there is insufficient data for seven more, according to the Polar Bear Specialist Group, a team of scientists dedicated to preserving the bears.

Andrew Derocher, a polar bear researcher and biology professor at the University of Alberta, led a study that found no evidence that polar bears can make the transition to become a land predator. They try to hunt in open water, but do not appear successful. "It is prudent to act sooner rather than later," since large carnivores are not easy to conserve, he said.

Some, however, see the general rise in polar bear population and scoff at the possibility of regulation. "The law doesn't say to look at any possible future threat. It says look at the data…if it's not endangered then it's not endangered," said H. Sterling Burnett, a senior fellow from the National Center for Policy Analysis, a non-profit organization that promotes private alternatives to government regulation, who has written about the polar bear issue.

What counts, he said, is the number of polar bears that exist right now, not some possible decrease in the future. He noted the overall polar bear population has rebounded from about 10,000 to 20,000 and asserted that warm temperatures in the 1930s were similar to current conditions, yet polar bears survived then.

As for the reports of cannibalism, he said, "We can't say we know it is a new phenomenon" because researchers do not have good data from earlier decades.

Burnett's statement "contains a grain of truth to deceive the population" said Kassie Siegel of the Center of Biological Diversity who is the lead author of the petition to designate polar bears as threatened. As for the warm spell in the 1930s, Amstrup said that temperatures weren't as warm or as uniform across the Arctic, adding that there's no evidence that there were large decreases in sea ice, as there is now.

In the overall picture, said Williams, the Alaska activist, "polar bears are just one reason of literally thousands of reasons we must reduce greenhouse gas emissions. They are the tip of the iceberg."