A report shows this summer's Arctic sea ice melted to the third-lowest level since satellite monitoring began in 1979, continuing a trend of habitat loss for walrus, polar bears and other ice-dependent marine mammals.
The National Snow and Ice Data Center at the University of Colorado said sea ice coverage Friday was recorded at a summer low of 1.84 million square miles. The ice cover appeared to have reached its minimum extent for the year that day.
The average September sea ice extent from 1979 to 2000 was 2.7 million square miles. This year's coverage was 753,000 square miles fewer than that number.
The record low for summer sea ice coverage -- 1.65 million square miles -- was set in 2007.
Brendan Cummings, an attorney for the Center for Biological Diversity, said the announcement illustrated a trend for summer Arctic sea ice and means bad news for walrus.
"We're on a clear path to a seasonal ice-free Arctic," he said. "There may be year-to-year fluctuations, but the clear path is unidirectional."
The report comes days after federal biologists in Alaska confirmed that Pacific walrus have come ashore on the state's northwest coast in unprecedented numbers.
Walrus gathered near Point Lay, an Eskimo village 300 miles southwest of Barrow, numbered from 10,000 to 20,000 animals or more, according to preliminary counts.
The animals are mostly females and young walrus that ride the edge of sea ice north as it melts over the summer in the Bering Sea and into the Chukchi Sea.
Walrus historically come ashore in late summer on the Russian side of the Chukchi Sea. In 2007 and 2009, thousands came ashore on the Alaska side as sea ice receded beyond the outer continental shelf, where water is shallow enough for them to dive for clams, worms and other food.
Walrus gathered on land face threats from predators and especially stampedes. An estimated 3,500 walruses were spotted on Sept. 12, 2009, at Icy Cape, about 140 miles southwest of Barrow, but U.S. Geological Survey researchers saw a large number of carcasses just two days later. They counted 131 mostly young walruses that were likely killed when the herd was spooked. Young animals can be hurt in stampedes when a herd is startled by a polar bear, human hunters or even a low-flying airplane.
Federal biologists concluded the deaths may have been from "disturbances" that led to trampling.
The Center for Biological Diversity has petitioned to list the walrus as a threatened or endangered species because of habitat loss.
"A land-based existence will support far fewer walrus than an ice-based existence," Cummings said.
The U.S. Fish and Wildlife Service is under a court-ordered deadline to make a decision on the petition by the end of January. A study by the U.S. Geological Survey is investigating walrus foraging from shore and from ice.
Cummings' group successfully petitioned to have polar bears listed as threatened because of habitat loss due to warming.
Polar bears spend most of their lives on sea ice and use it to travel, breed and hunt, especially for their main prey, ringed seals, which are the only seals that can live in completely ice-covered waters. Ringed seals excavate snow caves on sea ice to provide shelters for pups that polar bears try to exploit.
Arctic ice usually begins melting in March and reforms in mid- to late September.
The Snow and Ice Data Center said the 2010 ice level was only the third time in satellite records that ice has fallen below the threshold of 5 millions square kilometers, or 1.93 square miles. The ice minimum for 2009 was 1.97 million square miles.
Ice loss started late this year, but May and June saw record daily average ice-loss rates.
The center said it was possible that the 2010 summer low number could be revised slightly downward because of melting or a contraction in the ice pack. The center will issue a formal announcement in October with full analysis of the possible causes behind ice conditions this year.