 Move over, polar bear. The Pacific walrus may be the new icon of global warming. Like polar bears, walruses are dependent on floating sea ice to rest, forage for food and nurture their young. Like polar bears, walruses are suffering because of a scarcity of summer and fall sea ice in Arctic waters that scientists attribute to climate change. And like polar bears, which were listed as threatened in 2008, protections under the Endangered Species Act may be granted to walruses, even though it is hard to get an accurate count of their population. "You don't have to know how many passengers are on the Titanic to know it's in trouble when it hits an iceberg," said Rebecca Noblin, staff attorney for The Center for Biological Diversity, which sued to obtain Endangered Species Act safeguards for the walrus. For the lumbering, long-tusked marine mammals, problems caused by scarce ice are showing up on beaches in northwestern Alaska and across the Bering Strait in northeastern Siberia. For the third time in four years, large crowds of walruses have congregated this summer on shorelines of the Chukchi Sea instead of spreading over chunks of floating ice. That ice has largely disappeared. This year, summer sea ice levels reached their third-lowest point since satellite measurements started in 1979, according to the National Snow and Ice Data Center in Boulder, Colorado. As many as 15,000 walruses began crowding the shore near Point Lay, Alaska, in August and are just starting to disperse as ice forms in chilly fall weather, federal biologists said. CROWDED BEACHES Such congregations place walruses far from the best sources of clams and other food they pluck from the icy waters and, if they are young and small, at risk of sudden and grisly death. Last year, at another Alaska shore site where a few thousand walruses had converged, biologists found the carcasses of 131 calves, apparently trampled to death in a stampede. The U.S. Fish and Wildlife Service was to announce last month its recommendation for an Endangered Species Act listing. The deadline was extended to Jan. 31 to give the agency time to evaluate two new studies. Both reports warn of a grim future. One predicts that the Chukchi Sea will be ice-free for three months a year by mid-century and up to five months by the end of the century, and that ice-free periods in the Bering Sea also will expand. The other study calculates that the ice-dependent walruses have a 40 percent chance of being extinct or in danger of extinction by century's end. A LONGER 'COMMUTE?' The latest estimate of the total Pacific walrus population is 129,000, said Joel Garlich-Miller, a Fish and Wildlife Service biologist. That figure is based on incomplete aerial surveys conducted by U.S. and Russian scientists and is probably on the low end, he said. Another key question is whether walruses stuck on shore are spending significantly more energy searching for food than they would if they could forage from floating ice. "There's this commute that's new to them, and it costs them," said Anthony Fischbach, a biologist and walrus specialist with the U.S. Geological Survey. He also suspects there may be fewer calves than there should be. "It's certainly shocking to see over 100 dead calves that were apparently healthy. But it's hard to put it in context," said Fischbach, one of the biologists who documented the carnage. "Are these the strong ones that come ashore, whereas the ones that are weaker couldn't make the 150-mile swim to shore?" To try to find answers, he and his colleagues have embarked on studies to count the adult-calf ratio within herds and use radio tracking to pin down their travels for food. Advocates of Chukchi Sea oil drilling and other development are expected to oppose any Pacific walrus listing. The state of Alaska, which supports oil drilling in walrus habitat, already has sued to overturn the listing of polar bears and formally opposed new protections considered by the government for ice-dependent Arctic seals. The state also objected to habitat protections proposed for polar bear and endangered Steller sea lions.