Polars Bears Threatened by Melting Ice

Jan. 16, 2003 -- The king of the Arctic may be going down.

Scientists who have devoted their lives to studying the polar bears that rule the far north say evidence increasingly shows the white behemoths may diminish in numbers in the coming years and possibly disappear entirely within a century.

The reason for the concern is global warming, which seems to be having its greatest impact so far on the polar regions, particularly the Arctic, the only place on the planet with polar bears. Warming trends of recent years have caused the ice pack that is so vital to the bears' survival to shrink, moving farther offshore and taking longer to form during the critical winter months when the bears load up on seals to get them through the summers.

Of course, it's a bit premature to say these clever hunters that adapted to one of the harshest environments on Earth can't make yet another adaptation to a warmer habitat, but experts are doubtful.

Leaner and Smaller

"We have grave, long-term conservation concerns for polar bears," says biologist Andrew Derocher of the University of Alberta. Derocher has spent two decades studying polar bears, including a six-year stint as the polar bear research scientist at the Norwegian Polar Institute in Tromso.

He is not alone in his concerns. Ian Stirling, an adjunct professor at the university who gained fame through his study of polar bears that have given the northern Canadian community of Churchill its identity, has documented a gradual decline in the well-being of those bears. They are leaner, smaller, and less able to find enough food to survive, according to Stirling.

That has forced many of the Churchill bears to prowl the community for scraps of food, thus threatening a tourism industry that is the town's primary source of revenue. One woman was killed by a bear there last year.

Both Derocher and Stirling blame the problem on the reduction of the polar bear's primary habitat, the ice field that blankets the circumpolar region for much of the year. As numerous scientific investigations have shown in recent years, that ice pack is thinner, smaller, and less stable than in previous years, all apparently because of record high temperatures in the Arctic.

"Polar bears are 100 percent dependent on sea ice," says Derocher. "It's the surface on which they do everything they do. They use it as a walking surface, it's a hunting surface, it's the place where they breed.

"And in particular, north of Alaska, it's also a place where very many of the bears make their maternity dens and give birth to their cubs. So basically, what you are talking about is a reduction in habitat."

Icebound Survivors

It's amazing it should come to this, considering the past survival triumphs of polar bears. They are believed to have evolved from the Siberian population of brown bears, which were isolated by glacial advances during the mid-Pleistocene era, according to the U. S. Fish and Wildlife Service.

For thousands of years they roamed the ice pack over the North Pole, turning their heavy mantle snow white. The first humans to cross into the New World encountered the bears, which became both prey and predator.

Clashes with polar bears are rare, but they do happen. Stories abound of hungry polar bears that have stalked a human, regarded as just another piece of meat in a land with not a whole lot else.

"They definitely will kill and eat humans, given the opportunity," says Derocher, but he says those encounters are rare.

"On sea ice everything is pretty much shades of white, and maybe a little bit of blue," he adds. "There's not a lot happening out there. So from a polar bear's perspective, anything that's big and dark and moving around out there could actually be something to eat."

He hasn't had much of a problem during his many trips to the ice, partly because his expeditions move primarily by helicopter, so there's lots of noise to notify bears of his presence. When they do show up, he says, it's mainly because they're curious. Once they realize it's just a bunch of scientists, he says, they seem to lose interest.

The best way to avoid them, of course, is to stay off the ice, but that's an option that isn't open to the bears themselves.

Keen Nose for Seals

Their primary food consists of ringed and bearded seals, and sea ice is essential to the hunt. The seals give birth only on the ice, so the bears have to be on the ice to capture them. The seals prefer ridges of jagged ice that look like low mountains that are formed when two sheets of ice crush together.

Derocher says during the winter the mother seal hollows out an area in a ridge, with a hole in the ice below giving her access to the water, and then covers her den with snow.

"The bears walk through these areas, searching for seals," he says. Polar bears have an amazing sense of smell — some experts say they can smell a seal 20 miles away — and that apparently guides them to the hiding place.

But Derocher says he's still amazed at how accurate they can be.

"Once they get close enough, they rear up on their hind legs and crash through the snow layer and try to pin the seal inside the lair," he says. "It's pretty fast and dramatic, and they don't always get it quite right. They may have to do a heck of a lot of digging to find the seal under the snow.

"But sometimes they get it with amazing accuracy and pop the seal right out and head off for lunch."

Stealthy Stalker

Polar bears can also stalk a seal, moving stealthily across the ice until close enough to grab it. And sometimes they just wait over a seal's breathing hole in the ice, so immobile that they look like they're asleep, and when the seal pokes its head up for a breath of fresh air, it's lunchtime for the bear.

The seals prefer the shallow waters close to shore, because that's where they find the rich nutrients they need for their own survival. But as the ice pack moves farther out to sea, that puts the bears farther away from shore, and thus farther away from the seals.

In the years ahead, the seals may learn to give birth on shore, although they've never been known to do that before, and that would put them even farther away from the bears.

So unless the bears can figure out a new lifestyle, survival is probably going to get much more difficult in the years ahead.

Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.