Global warming could doom the walrus
Rhett A. Butler, mongabay.com
April 14, 2006


Add the walrus to the list of species threatened by climate change. A new study finds unprecedented pup abandonment in the Arctic due to disappearing sea ice

A new study warns that walrus calves are being stranded by melting sea ice in the Arctic Ocean.

Researchers aboard the U.S. Coast Guard icebreaker Healy during a cruise in the Canada Basin in the summer of 2004 found lone walrus calves swimming far from shore--something never before documented. The sightings suggest that increased polar warming may be forcing mothers to abandon their pups as they follow the rapidly retreating ice northwards. If these observations portray a larger trend, a warmer Arctic may lead to decreases in the walrus population say the scientists whose research was published in the April issue of Aquatic Mammals.

The researchers found evidence of rapidly melted seasonal ice in the shallow continental shelf region where walruses feed on clams and crabs. This development is significant because walrus use sea ice as a resting platform, especially pups when their mothers dive for food.

"The young can't forage for themselves," said Carin Ashjian, a biologist at Woods Hole Oceanographic Institution and a member of the research team. "They don't know how to eat," and are dependent on their mothers' milk for up to two years.


Pacific Walrus. Image courtesy of the National Oceanic and Atmospheric Administration
"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 research team wrote.

According to a release from the Woods Hole Oceanographic Institution, the team measured an unusually warm mass of water moving onto parts of the continental shelf north of Alaska from the Bering Sea that caused seasonal sea ice to rapidly melt. Sea temperatures were more than six degrees higher than those observed at the same time and location two years earlier.

The team found that in areas where sea ice remained, the sea floor was too deep -- up to 3,000 meters (about 9,300 feet) -- for adult walrus to feed. Adult Pacific walrus (Odobenus rosmarus divergens) typically feed at depths less than 200 meters about (630 feet), using sensitive facial bristles to locate prey on the seafloor. The scientists note, "when sea ice retreats to such deep water, as it did in 2004, there are no platforms in shallow waters for mothers to rest and to leave their calves while they feed, and the pairs become separated."

The walrus warning comes as concerns mount over the impact of climate change on Arctic wildlife populations. In February, the U.S. Fish and Wildlife Service today announced that it was considering a petition to list the polar bear (Ursus maritimus) as threatened under the Endangered Species Act due to the effects of global warming, specifically receding ice and rising temperatures.

Polar bears

Drowned polar bears are being found for the first time by researchers in Alaska, who speculate that greater distances between ice sheets could be taking a toll on the bears. While bears are capable of swimming long distances — up to 60 miles (100 km) without stopping — it is conceivable that they could suffer from exhaustion during an unexpectedly arduous swim.

The loss of ice also makes it more difficult for bears to find food. Unlike grizzly bears, polar bears aren't adapted to hunting land animals like caribou, instead feeding primarily on seals. However, recent aerial surveys by the U.S. Fish and Wildlife Service show that, over the past five years, polar bears are changing their habits and spending more time on land, congregating on beaches and scavenging whale carcasses.

Extrapolating from these developments, some scientists believe that polar bears could be extinct in the wild within the next century. While the last survey in 1997 suggested that polar bears in Alaska were not endangered, next year's update might come to a different conclusion. Scientists estimate there are currently 20,000 to 25,000 polar bears world-wide.

Climate Change and Extinction

Several studies published in recent months have warned that climate change could trigger significant species extinction before the close of the 21st century. Earlier this year NASA reported that 2005 was the warmest year on record while the National Oceanic and Atmospheric Administration (NOAA) said that there was a record 2.6 parts per million (ppm) jump in levels of carbon dioxide (CO2) in the atmosphere. Atmospheric CO2 concentrations now stand at the highest level in more than 650,000 years.

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This article used press materials from the Woods Hole Oceanographic Institution









CITATION:
Rhett A. Butler, mongabay.com (April 14, 2006).

Global warming could doom the walrus finds new study.

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