ANCHORAGE, Alaska — Pacific walrus need additional protection from the threat of climate warming but cannot be added to the threatened or endangered list because other species are a higher priority, the U.S. Fish and Wildlife Service said Tuesday.

Walrus will be added to the "warranted but precluded" list, said agency spokesman Bruce Wood, a designation under the Endangered Species Act that allows delays in listing if the agency is making progress listing other species and does not have resources to make a decision on others.

"The threats to the walrus are very real, as evidenced by this 'warranted' finding," said Geoff Haskett, the service's Alaska region director, in a statement. "But its greater population numbers and ability to adapt to land-based haulouts make its immediate situation less dire than those facing other species such as the polar bear."

He said cooperation with Alaska Native groups, the state and other partners could lessen the long-term impact of climate change for the walrus and help it avoid an endangered listing.

The decision was condemned by the Center for Biological Diversity, which in 2008 petitioned to list walrus as threatened or endangered, citing threats to walrus' sea ice habitat. Center spokeswoman Shaye Wolf said the warranted but precluded designation is a black hole for imperiled species. Some have been so designated for more than 20 years.

"This decision acknowledges the walrus is facing extinction due to climate change but the Obama administration is withholding the protections that could help the walrus survive," Wolf said.

Scientists at the National Snow and Ice Data Center have tracked a steady decline in sea ice in recent decades. Climate models have projected that summer sea ice could disappear by 2030.

Alaska's walrus population spends virtually the entire winter in the Bering Sea on the edge of sea ice that forms every year. In spring, as temperatures warm, ice melts and the edge of the sea ice moves north.

Older males spend the summer in the Bering Sea, foraging from islands or remote coastal shores. Females and pups, however, ride the ice edge through the Bering Strait and into the Chukchi and Beaufort seas, diving to the shallow continental shelf in search of clams as pups rest above them, safe from predators.

In recent years, summer sea ice in summer has receded well beyond the continental shelf over water too deep for walrus to dive to reach clams. Walrus in three of the last four years congregated by the thousands on Alaska's northwest shore. Larger numbers took refuge on the Russian side of the Chukchi Sea.

The Fish and Wildlife Service was under a court-ordered deadline to decide by Jan. 31 whether to recommend walrus for listing. Woods said the decision will be reviewed in a year. However, he noted that walrus are relatively low on the list of species on the "warranted but precluded" list.

The lower the number, the higher priority, Woods said, and walrus have been deemed a nine.

The state of Alaska has taken an aggressive approach in objecting to Arctic endangered species listings, arguing that populations have not crashed. The state sued to overturn the listing of polar bears and has given notice it will sue over designation of critical habitat.

Upward of 90 per cent of state general fund revenue comes from the petroleum industry and state officials have been looking to offshore drilling in the Beaufort and Chukchi seas, prime habitat for polar bear and walrus, to keep oil flowing in the trans-Alaska pipeline as on-shore reserves diminish.

U.S. Sen. Lisa Murkowski said walrus already are protected under the Marine Mammal Protection Act and that she was disappointed by the decision.

"Once FWS went down this road with the polar bear listing, where the agency used highly variable modeling to project 50 years into the future possible impacts of projected loss of sea ice, it was inevitable that more listings of other Arctic species would follow," she said. "I believe that the future listing of the walrus will be premature and highly speculative until we have verifiable science which shows that the projected loss of habitat does endanger a currently healthy species."

The proposed listing was endorsed by the federal Marine Mammal Commission, which oversees marine mammal conservation policies carried out by federal regulatory agencies.

"Without question, the warming of the Arctic is destroying, modifying, and curtailing walrus habitat and will continue to do so in the foreseeable future," the commission said in a letter to Rowand Gould, acting USFWS director.