Polar Bears Suffering as Arctic Summers Come Earlier, Study Finds
for National Geographic News
|September 21, 2006|
Inuit hunters in the Canadian Arctic have reported more polar bear
sightings near their villages in recent years. But a new study says this
doesn't mean there are more bears in the regionthere are fewer
bears, and they're hungrier.
More sightings means more bears, the reasoning goes, so regional governments have upped their hunting quotas.
In the northern Canadian province of Nunavut (see Nunavut map), wildlife officials upped hunting quotas, increasing the total allowable bear harvest by almost 29 percent 18 months ago.
But the new study suggests that at least two polar bear populations in the Canadian Arctic are in fact shrinking, and three other groups may face similar pressures.
"We have pretty good evidence that the populations are actually being overharvested, and they're both declining," said Canadian Wildlife Service polar bear biologist Ian Stirling, who co-wrote the study.
A more likely explanation for the increased bear sightings, Stirling says, is that Arctic sea ice is breaking up earlier each summer.
"The bears have less time to feed at the best time of year in order to lay on the fat they fast on through the open-water season in the summer and fall," Stirling said.
Because the breakup has arrived progressively earlier in most areas, bears are also spending more time on land instead of on ice, where they hunt. Hungry bears then push into human settlements at the end of their longer summer fasts in search of food.
Stirling and study co-author Claire L. Parkinson, a climatologist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, present their findings in the September issue of the journal Arctic.
In their study the scientists combine long-term polar bear population data with a nearly daily record of Arctic sea ice conditions gathered by two NASA satellites between 1978 and 2004.
The bear populations covered in the study were in Baffin Bay, western Hudson Bay, eastern Hudson Bay, Foxe Basin, and Davis Strait (see Canada map).
"We looked at the sea ice conditions in five Canadian Arctic polar bear regions, and in each of those we found that the sea ice breakup is occurring, overall, earlier and earlier in the year," Parkinson said.
The climatologist says the summer breakup of Arctic sea ice has crept an average of 0.75 days earlier a year, or 7 to 8 days a decade.
"I would say that the strongest likelihood for why the Arctic ice is decreasing is because the Arctic is getting warmer," Parkinson said.
"I'll leave it to other people to say whether or not the Arctic getting warmer is a global [phenomenon]."
Such changes directly impact the region's polar bears, since the Arctic predators hunt seals on the winter sea ice and must fast on land during the summer melt.
"In western Hudson Bay the ice is breaking up there now about three weeks earlier than it did only 30 years ago," Stirling, the polar bear biologist, said.
Most polar bears can handle a single season of early ice breakup, the authors write. But they add that "as the number of consecutive short ice seasons increases, the cumulative stress on the polar bears is bound to increase as well."
Ringed seals, the polar bears' main food source, also appear to have experienced either lower birth rates or lower cub-survival rates in the 1990s, perhaps as a result of poor ice conditions and other environmental changes, Stirling says.
The average weight of adult female polar bears in western Hudson Bay has dropped by nearly 150 pounds (65 kilograms) in just 25 years, from 650 pounds (295 kilograms) in 1980 to 507 pounds (230 kilograms) in 2004, the scientists say.
The UN-sponsored Intergovernmental Panel on Climate Change predicts that global warming will cause Earth's average surface temperatures to warm between 2.5 to 10.4 degrees Fahrenheit (1.4 to 5.8 degrees Celsius) within the next century.
If that forecast proves true, the five Canadian Arctic polar bear populations will experience significant declines, Stirling says.
He adds that within 20 to 30 years, adult females in western Hudson Bay may become too skinny to produce cubs.
"If that happens, then it's going to be hard on polar bears [everywhere]," he said.
"Obviously some bears will probably survive for a long time. But we won't have the kinds of numbers we have today."
In light of the study findings, the biologist has called on regional governments to use a precautionary approach to managing polar bears, reduce hunting quotas as needed, and include climate trends in developing conservation plans for the species.
He adds that countries and consumers must also reduce greenhouse gas emissions that cause global warming.
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