Baby Walruses Stranded by Melting Arctic Ice, Experts Say

Adrianne Appel
for National Geographic News

March 27, 2006

Melting Arctic ice may be putting walrus pups in peril, researchers say.

A team of scientists working in the Arctic Ocean in 2004 says it encountered nine Pacific walrus pups struggling alone in the water far from shore.

Typically walrus pups live on ice close to shore and are inseparable from their mothers.

"I'm not a walrus expert, but we thought it was unusual,'' said Lee Cooper, a marine ecologist at the University of Tennessee in Knoxville, who led the team.

"The baby walruses would swim up to the boat. It was heartbreaking,'' he said.

Melting Arctic sea ice is the most likely explanation for the stranded pups, Cooper said. His team was in the region to study the intrusion of warm Bering Sea water into the Arctic Ocean.

"The sea ice has retreated, so it is only [now found] over the open ocean, where [the water] is about 12,000 feet [3,650 meters] deep. This is too deep for [a] walrus,'' Cooper said.

Walruses prefer shallow water, because they dive for food and can only reach depths of about 300 feet (90 meters).

Cooper believes the lone pups they saw had either followed their mothers far out into the ocean in search of solid ice or had floated out to sea on broken ice chunks that then melted.

Chadwick Jay, a walrus expert with the United States Geological Survey in Anchorage, Alaska, agreed that melting ice was the likely reason for the lone pups.

Pups are sometimes separated from their mothers by storms or hunting, he said, but neither of those appeared to be the case with the pups Cooper's team observed.

"Given the fact that these were so far offshore, [those causes] may be not as likely,'' Jay said.

Jay says there's little help for pups once they're separated from their mothers, even if the young are reunited with another walrus group.

"There have been reports of females adopting an orphan [pup], but more times than not they'll perish,'' he said.

"Ice Has Disappeared"

Pacific walruses are about 10 feet (3 meters) long, weigh 1,900 to 2,700 pounds (862 to 1,225 kilograms), and sport 3-foot-long (1-meter-long) tusks.

In winter, female walruses stay in the Bering Sea, which lies south of the Bering Strait between Alaska and Russia (map).

In summer the females follow the ice north through the strait to the Chukchi Sea. There they congregate by the thousands on ice close to the Alaskan shore.

Pups are dependent on their mothers for the first two years, Jay said. They ride on their mothers' backs and rest on the ice while the mothers dive for clams and other food.

"They're quite dependent on [their mothers] and may suckle until they are a year old,'' Jay said.

Cooper's team believes warmer water flowing north from the Bering Sea is largely responsible for melting the Arctic ice on which the walruses live. The team's study appears in the latest issue of the journal Aquatic Mammals.

In July and August 2004 the highest surface temperature in the Chukchi Sea was 7ºC (44.6ºF), they report. This compares to a much cooler 1ºC (33.8ºF) for the same period in 2002.

Moreover, in the area known as the continental shelf—the shallow seas that border the coastline—there was extensive ice cover in 2002, researchers say. In 2004 the ice was gone by mid-July.

"The ice has disappeared off the continental shelf,'' Cooper said.

New Survey

On March 20 a team of biologists, including Jay and experts from the U.S. Fish and Wildlife Service (FWS), began a survey in the northern Bering Sea to estimate the size of the Pacific walrus population.

The survey has been planned for some time, but it is more pressing now given the reports of melting ice, FWS officials say.

"As the world is changing around [the walruses] we need to be on it, to track what's coming up,'' said Rosa Meehan, program chief of the FWS marine mammals management unit.

"We are very interested in what the changes in snow and ice are doing to all ice-dependent species,'' she added.

Last week Meehan's office announced it would conduct a review of the polar bear population to see if the bears should be listed as endangered species. (Read "Polar Bears Being Considered for U.S. Endangered List.")

The last walrus survey was conducted in 1990 and found an estimated 201,000 walruses in the region, Meehan says.

She calls those numbers "stale'' and in need of updating.

"The bottom line is we don't know what the bottom line is for walrus,'' Meehan said.

In the new survey, researchers will use surveillance planes to count walruses on the ice using thermal imaging. Meanwhile, another group will track 93 adult walruses from the ground using satellite tags.

"We're really trying to get out there and get the information we need so we can track this [trend],'' Meehan said.

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