Struggles of the polar bear
Climate change threatens these Arctic mammals
Earlier ice breakup hampers bears' hunt for seals
PETER CALAMAI
SCIENCE WRITER
ABOARD CCGS AMUNDSEN—Andy Derocher and Ian Stirling were hunting polar bears from a helicopter last week in the Western Arctic when they came across two of them feeding on a freshly killed seal."We thought they were a male and a female because one was considerably larger," Derocher says.Hit by a tranquilizer dart from Stirling's gun, the smaller bear keeled over almost immediately. As the two biologists watched in amazement, the bigger bear ran over to lie down beside its toppled companion. After the second bear was darted, the researchers landed and discovered these were two males travelling together."I don't like to anthropomorphize it, but polar bears are a lot more social than people give them credit for," Derocher says. And also more tender, an unexpected description to apply to a 500-kilogram animal with claws that can gouge a furrow five centimetres deep in a rival's skull.Yet, Derocher has seen mated males and females snoozing on the ice beside one another, powdery snow spread like a white duvet around their bodies.Just as we are beginning to understand what really makes polar bears tick, however, our society's dependence on fossil fuels may wind up exiling the magnificent creatures from much of the Arctic.The bears face the loss of their natural habitat from climate change triggered by rising levels of greenhouse gases in the atmosphere, the main culprit carbon dioxide from burning coal and petroleum."I think the prognosis is very grim," Derocher told an audience of Arctic researchers based aboard Canada's new science icebreaker here in Franklin Bay off the coast of the Northwest Territories this week.His forecast of how polar bears will be driven hundreds of kilometres north by thinning sea ice dovetailed naturally with the Amundsen's current mission, which is to fit together all the pieces of the complex web of Arctic life that eventually culminates in the polar bear. As well, one researcher on this leg of the year-long mission, doctoral student John Iacozza from the University of Manitoba, is collaborating with Derocher and Stirling on forecasting how climate change will affect the snow and ice conditions that polar bears need for successful hunting and reproduction.In a country that is home to more polar bears than anywhere else in the world, Derocher and Stirling represent about half of Canada's scientific research expertise into these majestic mammals. Stirling, based at the Edmonton office of the Canadian Wildlife Service, is the dean. He helped train both Iacozza and Derocher and has been studying polar bears in the Beaufort Sea and on the west side of Hudson Bay near Churchill since the 1970s.These long-term studies let the researchers spot the first impact of climate change on the bears in Hudson Bay in the late 1980s. Rising winter temperatures and earlier ice breakup along the west side of the bay meant poorer seal hunting, less well-nourished polar bears, a decline in general health and a noticeable drop in reproductive success. In 1992, that research produced the first scientific paper to warn that polar bears were especially vulnerable to climate change. Since the bears were already suffering health problems because of PCB contamination that concentrated as it rose in the food chain, they quickly became the Arctic equivalent of the caged canary used by miners to detect danger.The key to polar bears — and the reason for their severe vulnerability to climate change — is realizing that they have spent more than 200,000 years evolving from land bears to living on sea ice and adapting to the killing of seals. The bears can readily kill the seals only when both are on the ice. When there is open water for seals, the bears are largely on a starvation diet that can, in some places, last from late June until March the following year."Right now is when the bears make their bread and butter, from now until the ice breaks up," Derocher says.This is prime killing time because female ring seals are giving birth in hollows dug in the snow underneath pressure ridges that criss-cross the ice. The pressure ridges are effectively frozen rubble, the product of sheets of ice rubbing against one another, almost like the grinding of tectonic plates that produces earthquakes.Ring seals deliberately choose this rubble as a location for a haul-out hole in the ice since winds will usually mound the Arctic's meagre snowfall into hummocks along the pressure ridge. By burrowing up into that snow hummock, the females create a birth chamber and also guarantee an escape route through the hole.Except that the polar bears have got the seal's birthing behaviour down pat. Even through thick snow they can detect the seal's strong odour and, possibly, hear the mother and pups. "They rear up on their hind legs and pound down on the snow over the seal den, with their two front paws close together," Derocher explains. "They're trying to collapse the snow layer onto the pups. Then, they dig down to the bodies. I've seen a polar bear kill 10 seal pups in a stretch of a few kilometres. The pups are small right now, a little like a soft cookie. Sometime the bears just take one bite and leave the rest. The mother is the real bonus if they can also trap her."
`Polar bears are a lot more social than people give them credit for'Andy Derocher, wildlife biologist
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When the mother seal scampers, the polar bear will sometimes use its body to plug the hole that it excavated in the snow hummock. Having thus cut off the daylight, the bear waits with its snout near the hole for the mother to return and check on her offspring. When the mother seal surfaces, the lunging bear shoves its long narrow head right down the breathing hole, with fatal results for the seal.That's a variation of the "lying still hunting" technique that polar bears use out on sea ice. Now that the sun is back and the air is warming here, seals are hauling themselves out onto the ice surface. The polar bears sniff for the freshest aromas at haul-out holes and use the terrain and their stealth and camouflage to get close. Then they wait."They are consummate hunters in terms of patience. You'd swear that they were asleep, until the seal comes up," Derocher says.Seals aren't the only animal stalked by the perpetually curious polar bears. Humans are stalked as well, as Iacozza found out on a field trip."We never saw the bear but we crossed the paw prints that circled around us. You have this sense that something is watching you, and it's not very pleasant," says Iacozza, 33, who, in addition to his doctoral studies, is a geography instructor at the University of Manitoba. Iacozza, Derocher and Stirling are now stalking polar bears but with preservation in mind. The two dart-firing wildlife biologists are focusing on the health and population characteristics of bears in the Beaufort Sea area, a distinct group of a couple of thousand animals that stretches from Point Barrow in Alaska east to Victoria Island and then north to Banks Island.They'll have a more accurate count by 2006, after three years of what's called a "mark and recapture" study. That means darting about 200 bears a year, marking them with a black splotch, noting age and general condition and then getting away before the tranquilizer wears off. Then, they'll dart another couple of hundred bears the next year. Some will be ones marked the first year. Then, repeat for a third year. With the percentage of recapture in the second and third years, plus estimates of births and deaths, a formula gives a good idea of the total population.While the adult bears are tranquilized, Derocher and Stirling reach behind the curved razor-sharp canines with dental pliers to yank out a premolar tooth about the size of a cribbage peg. Decalcified in the lab, annual rings in the tooth reveal the bear's age. Males in this area live an average of 25 years, females, 29.The helicopter isn't powerful enough to hoist the bears for weighing but past records of size and fat thickness allow an indirect weight calculation. If there are cubs, they usually stay with their sedated mother long enough for the biologists to cast a rope around their torsos so they don't scamper off.While the bear population is looking healthy now, Derocher is concerned about the future, especially with the latest projections by NASA that climate change by mid-century could cause the polar sea ice to shift 400 kilometres farther north in the summer. The bears must move north with the ice to avoid being stranded on land and to begin hunting seals as soon as the pack ice extends southward again in the winter."What you're expecting a bear to do is walk anywhere from 800 kilometres to 2,000 kilometres more every summer. Where is that extra energy going to come from?" Derocher wonders. "It's probably going to have to come from energy that now goes into reproduction." With a shorter winter ice cover at the southern part of the range, the polar bears will also have less time to store up fat from the seal smorgasbord for that summer starvation period when they can expend 800 grams of body fat a day. "The seals are their fat bank account and they'll have to stretch that account for another two weeks," Derocher says.That's the biological side. Iacozza is trying to get a handle on the physical side, linking the bear's chances for survival to snow and ice characteristics that eventually will be surveyed by satellites. For starters, however, these measurements are being made from a Coast Guard helicopter that skims across the icy expanse less than five metres above the surface. A Pinocchio-like nose called an Ice Pic juts from the front of the helicopter, providing continuous readings of the thickness of the ice and snow below. Scott Holladay, a geophysicist with Geosensors Inc. of Toronto, is on board the chopper, tweaking the sensor. Meanwhile, Iacozza babysits a laser altimeter that can measure undulations in the surface of only a centimetre as well as a digital video camera constantly snapping high-resolution images of the surface.Using the digital photos and global positioning satellites, Iacozza later returns in the helicopter to within a few metres of a previous aerial track to land and measure actual snow depth at one-metre intervals along a 300 metre stretch. The final piece of information is satellite tracking of polar bears fitted with radio collars.Says Iacozza: "You can't collar bears forever. Eventually we have to be able to say where they are most likely to be, even with changing climate, so we can control visitors or establish new parks."You put a satellite image in front of me and I also have temperature and precipitation information and I should be able to say these are the areas with ice and snow conditions where we would expect to find bears. This is where they would be hunting. This is where they would be mating. This is where the females would be denning."Yet even such pioneering research may not be enough to save the polar bear across much of the Canadian Arctic if the climate modellers are anywhere near right in their projections, says a gloomy Derocher."As the sea ice goes, so goes the polar bear. If you're going to lose the sea ice, you can't expect the polar bear to instantly change colour back to black and start to eat berries and roots."
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