Polar bears not only mammals affected by warming in Arctic

Changes may shift habits of predators' favorite meal - ringed seal

Posted: Sunday, February 25, 2007

ANCHORAGE - Polar bears get fat eating ringed seals, and to avoid that fate, Alaska's smallest pinniped digs out snow caves on the sea ice, where they surface to breathe and give birth. Global warming is making that more difficult.

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Snow is melting sooner on Arctic sea ice, moving up the time when snow lairs dug by ringed seals collapse.

For nursing mothers, that means their helpless pups can be left vulnerable to polar bears and foxes, their usual enemies. A collapsed lair leaves pups susceptible to freezing. It even makes them vulnerable to avian predators such as ravens and gulls, which kill by pecking out the pups' eyes and brains.

"We're seeing snow melts happening when many of the pups are still dependent on those caves," said Brendan Kelly, a seal and walrus researcher for more than 30 years.

While polar bears have become the "canaries in the mine shaft," warning of the effects of warming in the Arctic, climate change also is having effects on other marine mammals.

Polar bears eat as many as 43 ringed seals per year. Both depend on sea ice, which has been shrinking at an alarming rate. The seals also are pursued by both Inupiat and Yupik Eskimo hunters, who rely on them for their subsistence diets.

"We focus on polar bears because they're charismatic megafauna, and that's fine," Kelly said. "I don't think people really comprehend how dramatic a negative impact this is going to be on Eskimo cultures. This loss of sea ice, we're not just taking away the bison here. We're rolling up the plains behind the bison."

Kelly is vice provost for research at the University of Alaska Southeast. For the next two years, he will be on loan to the National Science Foundation, where he will manage the Arctic National Sciences program.

He has conducted long-term studies of ringed seal behavior with help from trained Labrador retrievers, which sniff out their lairs. Using an underwater net, Kelly has captured seals and outfitted them with satellite transmitters to track their movement.

But while some climate models envision the Arctic to be largely ice-free during the summer within 50 years, and the federal government is considering listing polar bears as "threatened" under the Endangered Species Act because of their dependence on sea ice, no such effort is under way for the ringed seal. With the enormous expense and obstacles trying to count a species that lives in such a remote region, spends much of its time in the water and births pups out of sight under snow, scientists have no accurate count of ringed seals.

That means there's no way to tell if collapsed lairs are affecting their numbers, Kelly said.

"Most of what we're talking about is speculation," said Tim Ragen, executive director of the U.S. Marine Mammals Commission.

And he said for the ecological effects of climate change, there's nothing people can do about it other than prevention.

"You can't say, OK, we're going to compensate for a loss of ice, Ragen said. "We make snow machines so we can keep our ski runs going. We're not going to do that in the Arctic. We're not going to be able to create lots of ice habitat."

Ringed seals, the most numerous of the seals that thrive off Alaska's coasts, are the only seals that can survive in completely ice-covered waters. They do so by digging out breathing holes in the ice.

An adaptation on their front flippers, unusually stout claws, allow them to excavate ice.

"They do that as soon as freeze-up starts and then throughout the winter," Kelly said. "They'll maintain a hole throughout the winter by repeatedly coming to it and scratching at the ice. There may be two meters or more of ice by the end of the winter season."

Canadian scientists have documented unusual weather events, including rain, that led to collapsed lairs followed by a hard freeze that killed pups on bare ice. A thaw and a collapsed lair followed by a hard freeze can kill pups.

"There's this sort of counterintuitive circumstance where animals are freezing to death as a result of climate warming," Kelly said.

"The big question is, can they make a transition from reproducing in snow lairs, on the ice, to reproducing on land, if the ice isn't there in the reproductive season," he said. "I don't know but that seems like a big question for them.

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