Polar bears on thin ice
Expert believes global warming has doomed Hudson Bay population
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Hey there, time traveller!
This article was published 17/11/2011 (3974 days ago), so information in it may no longer be current.
Polar bears may survive high up in the Arctic but Manitoba’s and Ontario’s bears are all but doomed, says the world’s best-known expert on the species.
Wildlife biologist Ian Stirling, who’s been studying polar bears for 41 years, believes it is now too late to prevent the iconic Arctic species from being extirpated from the shores of Hudson Bay.
Increasingly long ice-free periods on the bay have led to less feeding on seals, lighter females, fewer births and more mortality among the southernmost subpopulations of polar bears, according to research conducted by Stirling, other biologists and climatologists over the past three decades.
Stirling believes this will lead to the disappearance of polar bears from northeastern Manitoba, northern Ontario and parts of Nunavut and Quebec within decades, barring the unlikely event the planet quickly begins to cool.
“Things definitely don’t look good for the western Hudson Bay and southern Hudson Bay populations,” Stirling said in an interview in Winnipeg on Wednesday, referring to the world’s southernmost polar-bear subpopulations.
“Long term, if we don’t stop climate warming and the continued melt of sea ice, that population will disappear, maybe in 30 or 40 years,” Stirling said. “We could keep parts of the northern ice area. We’re not going to save Hudson Bay. It’s too late for that, unless we could cool it down.”
Stirling, an adjunct professor of biology at the University of Alberta, has devoted his life to the study of marine mammals, beginning with seals and then moving on to polar bears.
He’s condensed some of his work into Polar Bears: The Natural History of a Threatened Species, which pays special attention to the well-known western Hudson Bay subpopulation, which includes all the bears in northeastern Manitoba.
As Stirling and other biologists have documented, Hudson Bay sea ice now breaks up an average of three weeks earlier at Churchill than it did three decades ago. Since polar bears consume almost all their calories on the ice, where they hunt for seals, this has led to fewer meals, declining weights, fewer births and more cannibalism among bears in the area, said Stirling, citing well-known research.
What’s less well-understood is the fact these missing weeks deprive polar bears of meals at the most crucial feeding time for the carnivores. That’s because seal pups are just the right size when sea ice breaks up.
“All seals aren’t equal, as far as polar bears are concerned,” Stirling said, noting the ideal polar-bear meal is about six weeks old.
“At that stage, they’re little balls of fat. They aren’t very smart about predators,” Stirling said. “What’s happening at breakup is the bears are losing access to the seals at the most important time.”
The average polar bear eats about 43 seals a year. Missing out on two or three of those meals is enough to cause a female polar bear to lose enough mass to give birth to underweight cubs or no cubs at all, Stirling said, noting the relationship between sea ice, feeding and fertility has profound implications for the survival of the species.
In 2010, Andrew Derocher, a former graduate student of Stirling, teamed up with a pair of mathematicians to crunch these variables in an attempt to predict the future of the western Hudson Bay subpopulation. They concluded the species will soon reach a tipping point where the population will plummet quickly.
Some conservationists fear this tipping point has arrived, as the western Hudson Bay population is declining. In 1987, biologists estimated there were 1,194 bears in the region by marking and recapturing individual bears. In 2004, the same sort of count adjusted that population down to 935.
Aerial surveys, which are considered less reliable, came up with startlingly low numbers early this year. A new reliable count is expected early in 2012, said Daryll Hedman, a Manitoba Conservation wildlife manager.
Provincial officials have been hesitant to endorse gloomy predictions by biologists. But Manitoba Conservation data bolsters the idea bears are growing hungrier.
The number of problem bears officials are forced to handle around Churchill every year is, on average, higher during years when ice breaks up earlier than usual, said Stirling. However, more sightings of bears on land can lead to the erroneous belief polar-bear populations are increasing when in fact bears are simply hungrier.
“They’re looking for an alternate food source because a large carnivore doesn’t lie down under a tree and quietly starve to death like an Arctic hare. They’re going to look for something else,” said Stirling, cautioning they won’t travel far enough to survive in the long term.
“There’s no place to move,” he said. “Up the coast is already inhabited.”