The Center for Biological Diversity, which filed the petition, said the receding sea ice is causing walruses to abandon the ice and congregate on shorelines, where the habitat and food supply cannot support so many walruses.
The petition to list the walruses as threatened under the Endangered Species Act was filed as the U.S. Fish and Wildlife Service is deciding whether to list polar bears as threatened because sea ice has diminished.
"The Arctic is in crisis from global warming," said Shaye Wolf, a Center biologist and lead author of the group's petition.
"Arctic sea-ice is disappearing at a stunning rate that vastly exceeds the predictions of the best climate models."
The first step for the Fish and Wildlife Service would be to determine whether the petition contains "substantial information" within 90 days if practicable, said Bruce Woods, an agency spokesman in Anchorage. If the petition passes that first hurdle, the agency would have nine months to perform a status review on walruses.
Oil and gas development, shipping, and greenhouse gas emissions affecting the Arctic would be subject to greater regulation if the walrus is listed as threatened.
Summer sea ice last summer receded to the lowest level since satellite measurements began in 1979, according to the National Snow and Ice Data Center at the University of Colorado. The scientists say they do not expect summer sea ice to bounce back without changes in current warming trends.
Sea ice in the Chukchi Sea, the part of the Arctic Ocean between Alaska's northwest coast and the Russian Far East, receded well beyond the shallow outer continental shelf over water too deep for walruses to dive to reach clams and other benthic creatures they eat.
As many as 6,000 walruses in late summer and fall abandoned ice over deep water and congregated on Alaska's northwest shore. Herds were larger on the Russian side, one group reached up to 40,000 animals. Russian observers estimated 3,000 to 4,000 mostly young walruses died in stampedes when herds rushed into the water at the sight of a polar bear, hunter or low-flying aircraft.
Biologists also worry that if walruses congregate on coastlines every summer, they will put tremendous pressure on nearby foraging areas rather than rich offshore feeding areas they historically have reached by living on the edge of the ice pack.
"The Pacific walrus is an early victim of our failure to address global warming," Wolf said. "As the sea ice recedes, so does the future of the Pacific walrus."
Wolf also said walruses are likely to be affected by petroleum development. The U.S. Minerals Management Service on Wednesday accepted high bids on 2.76 million acres of Chukchi Sea ocean bottom. Five other lease sales in the Pacific walrus's habitat in the Chukchi, Beaufort and Bering seas off Alaska's shore are planned by 2012.
Increased oil and gas development and a proliferation of shipping routes pose threats to the Pacific walrus from the heightened risk of oil spills and rising levels of noise pollution and human disturbance, according to the group.
