Warming Arctic Is Taking a Toll
Saturday, April 15, 2006
The rapid melting of Arctic sea ice appears to be separating walrus young from their mothers, leaving them likely to die at sea, a team of researchers said.
During a two-month cruise off northern Alaska in 2004, a Coast Guard icebreaker came across nine lone walrus calves swimming in the deep waters -- what the scientists called a highly unusual sighting.
They report in the journal Aquatic Mammals that the pups most likely fell into the sea when a shelf of sea ice that they lived on with their mothers collapsed because of an influx of unusually warm water.
"We were on a station for 24 hours, and the calves would be swimming around us crying," said Carin Ashjian, a biologist at Woods Hole Oceanographic Institution in Massachusetts and a member of the research team. "We couldn't rescue them."
Walrus mothers and their young rarely separate during the first two years of life, which they spend mostly on sea ice that covers shallow continental shelf waters. The adult walruses feed on crabs and clams on the sea bottom and return to the ice and their cubs, who survive on mother's milk.
The team found that water flowing from the Bering Sea to the shallower continental shelf of the Chukchi Sea off northern Alaska was six degrees warmer than it had been at the same time and place two years earlier.
The breaking up of sea ice close to the shore may not only separate walruses from their young but also deny the adults a platform from which to dive for food. Sea ice remains in the waters farther offshore, researchers found, but the sea bottom is too deep for the animals to reach.
"If walruses and other ice-associated marine mammals cannot adapt to caring for their young in shallow waters without sea-ice available as a resting platform between dives to the sea floor, a significant population decline of this species could occur," the study concludes.
The recent rapid warming of the Arctic has been associated by many researchers with a global buildup of greenhouse gases produced by the burning of fossil fuels.
The researchers, who were funded by the National Science Foundation and the Office of Naval Research, said it was possible that the walrus young were separated from their mothers by a severe storm, or that the mothers were killed by hunters from nearby native communities. But they said local hunting ethics frown on killing walrus mothers with young and it was far more likely that retreating sea ice -- rather than a storm -- caused the young to become separated.
The authors said they believed their observations to be the first of their kind, although other researchers had predicted the phenomenon several years ago.