Polar bears are experiencing significant declines because global warming is melting their sea ice habitat, and other Arctic mammals may be in trouble, as well, according to a federal population assessment released yesterday.

There are an estimated 1,526 polar bears presently living in the southern Beaufort Sea, according to the latest estimate from the U.S. Fish and Wildlife Service -- a 33 percent decline from the service's estimate of 2,272 in 2003, the last time an assessment was conducted.

Bruce Woods, spokesman for FWS's Alaska office, said the decline may be less than what was reflected in the previous two counts because a lack of information may have inflated the 2003 numbers, but that would not change the general trend. "Polar bears are declining, as we clarified in the listing rule, because of a lack of sea ice habitat," he said.

FWS also released its assessment of the Pacific walrus, which the agency is evaluating for a potential designation as a threatened or endangered species. The agency counted about 15,000 animals, but the report said the real number is likely many times higher, because the count only included part of the mammal's habitat.

For Brendan Cummings, an attorney with the Center for Biological Diversity, the walrus numbers are clear enough. Noting that estimates of walrus populations in previous decades hovered around 200,000, he said it was "hard to imagine" how the numbers could indicate anything other than a significant decline.

"These reports publicly confirm what scientists have known for several years; polar bear and walrus populations in Alaska are in trouble," Cummings said in a statement. "And even if the population numbers are not precise, we know that without their sea-ice habitat these animals are likely doomed."

FWS was court-ordered to release its stock assessments of the two species as a result of a lawsuit filed by the Center for Biological Diversity, which successfully argued that annual reports on the species are required under the Marine Mammal Protection Act.

The service is also under a separate court order that requires it to make an initial decision on the walrus by September. Should the agency determine that the walrus merits a full review, it will have nine months to complete it. Woods said that the latest walrus estimate would not be considered in the endangered species decision because the agency was working on a more complete assessment.

Both species are at the center of an ongoing struggle between environmental groups and the Department of the Interior over the proper relationship between the Endangered Species Act and greenhouse gas regulations. Polar bears and walruses depend on sea ice for hunting, but the ice is melting because of global warming. The ice has reached record lows in recent years.

After a spate of environmental lawsuits, Interior in May 2008 designated the bear as threatened under the Endangered Species Act -- the first time a species was listed because of threats from climate change. The act requires the service to protect endangered and threatened species from all known threats, and environmental groups contend that this means protecting it from climate change by limiting greenhouse gas emissions from all federal projects.

While listing the bear, former Interior Department Secretary Dirk Kempthorne issued a special rule stating that the listing was not to result in regulation of greenhouse gases, accusing environmental groups of attempting to craft a "backdoor climate policy outside our normal system of political accountability" (E&ENews PM, May 14, 2008).

Environmental groups lobbied current Interior Secretary Ken Salazar to overturn it, but in May, he declared he would let it stand. The groups have since resumed lawsuits to overturn the rule (Greenwire, May 8).