Why Polar Bears Are Doing Better Than You Think
Last year Greenpeace campaigners in the UK paraded a giant polar bear puppet the size of a double-decker bus through the streets of Westminster to protest against planned drilling in the Arctic. This year the polar bears made it into the Houses of Parliament, as a Canadian professor told a meeting there Wednesday night that the animals are not as endangered as many think.
Dr Susan Crockford, an evolutionary biologist at the University of Victoria, British Columbia, Canada, told a meeting of the Global Warming Policy Foundation think tank that there were “good reasons not to worry about polar bears.”
Crockford, who writes a blog on polar bear science, argues that polar bears are “a conservation success story” and that “we can say for sure that there are more polar bears now than there were 40 years ago,” following a rebound in the population since a 1973 agreement protecting them from commercial and unregulated sport hunting.
Crockford says the current polar bear population is “almost certainly” at a level “well above” the official estimate of 20,000-25,000, and could be as high as 27,000-32,000. She told the meeting that even those producing the official figures had admitted to her in an email that the numbers were “simply a qualified guess given to satisfy public demand.”
While hunting was a major threat to polar bear populations in the past, current popular concern focuses on the impact of shrinking sea ice on their habitat. But Crockford argued the animals can cope better with change than many think.
She says they have survived through over a hundred thousand years or more of “highly variable” sea ice coverage, including past interglacial periods warmer than today, with conditions in which computer models suggest they should have been near extinct.
“Adaptation is what they’re all about, and their primary adaptation is getting fat,” she told the meeting, explaining that the bears’ ability to fast for several months at a time enables them to survive through lengthy periods when their icy hunting grounds are in retreat.
The animals need spring and early summer ice, during March through June, to gorge on young, fat seals and build up their reserves. But many bears fast for two to four months every summer, and it is only in September that sea ice tends to be at its lowest extent, outside their critical feeding period.
Crockford highlighted their “efficient fat storage” with the example of one animal that was measured rising from 218 to 910 pounds in just eight months, and added that unlike black and brown bears, the polar bear can go into a “walking hibernator” state to reduce its metabolism while still on the move.
Crockford said that newly formed ice each year can reach thicknesses of up to two meters, and that the bears need only 30 centimeters of ice to support their weight, and around 1.4 meters to hold a winter den.
Sometimes the ice can be too thick, she said, preventing the ring seals on which they prey from drilling holes in the ice. Polar bear numbers in the Beaufort Sea have suffered large declines for this reason in periods including 1974, 1984, and 1992 at times of exceptionally thick sea ice, although their numbers have bounced back a few years later.
Crockford called for further studies and the release of currently unpublished work to provide more information on population trends.