KEY POINTS:
Global warming may not be the only threat to the polar bear. Scientists are puzzling over the discovery of the jawbone of a young polar bear in the stomach of a Greenland shark, a species that thrives in the cold waters of the far north.
The find suggests
that the polar bear may have a serious challenger to its place at the top of the Arctic food chain. Until now, only killer whales were thought to offer a threat to Ursus maritimus as the Arctic's top predator.
Kit Kovacs, a seal expert at the Norwegian Polar Institute in Tromso, stumbled across the polar bear remains while attempting to find out who or what was killing large numbers of harbour seals in the Arctic archipelago of Svalbard.
The Greenland shark, one of two species of sleeper sharks, was the obvious suspect, she said, so they performed autopsies to see what they had been eating. That's when they found the polar bear bone.
"We were so shocked, we were laughing," Kovacs said.
The prospect of a marine battle between the world's largest land predator and the Greenland shark which can grow to a length of more than six metres, is a true clash of the Titans. And it is one that is likely to have wildlife film-makers rushing for the North Pole.
Climate change has been melting polar ice cover and shrinking the natural habitat for the polar bear, now regarded as an endangered species. With polar sea ice expected to disappear altogether during the Arctic summer within a generation, there is speculation that the bears may be spending longer in the water, while hunting or moving between icebergs. This could make them a potential target for large marine predators.
Warmer waters may also be tempting more and larger sharks further north.
Shark experts were unconvinced and think it more likely that the shark would have fed on a bear's carcass, rather than killed a live bear, as even a young animal would be a fierce opponent.
Steve Campana, head of the Canadian shark research laboratory at the Department of Fisheries and Oceans, said he had not heard of sharks attacking a bear before. "It sounds like a scavenge," he told Reuters, adding that it was a "million-dollar question" for researchers as to whether Greenland sharks were preying on polar bears.
Kovacs continued, however, to stand by her theory.
"We didn't know they went to the surface to feed," she said. "We can't say whether or not the shark took a swimming young bear or ate a carcass."
LET US PREY
Weight: Adult Greenland sharks and mature polar bears weigh in at more than one tonne. The bears just have the edge.
Age: These sharks are among the oldest on the planet, some living for 200 years. Polar bears rarely live beyond 25.
Range: Polar bears can swim for up to 100km in open water. The shark can descend to depths of 2200m.
Weapons: The bears' claws are for digging in ice, its teeth are its main weapon. The shark has rows of sharp upper teeth.
- INDEPENDENT
