ANCHORAGE, Alaska -- The Trump administration announced Wednesday it will not list the Pacific walrus as a threatened species based on diminished Arctic Ocean sea ice, concluding that the marine mammals have adapted to the loss.

U.S. Fish and Wildlife Service officials said they cannot determine with certainty that walruses are likely to become endangered "in the foreseeable future," which the agency defines as the year 2060.

The decision could be challenged in court by environmental groups, who say a decline in Arctic Ocean sea ice due to climate change is a threat to the walruses' future.

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The Fish and Wildlife Service said in 2011 that walruses deserve the additional protection of being declared threatened, but delayed a listing because other species were a higher priority. The agency revised the decision based on new information, said Patrick Lemons, the agency's marine mammals management chief.

"Walrus demonstrated much more ability to change their behaviors than previously thought," Lemons said. Their ability to rest on shorelines before swimming to foraging areas makes the threat of less sea ice uncertain, he added.

Shaye Wolf, climate science director for the Center for Biological Diversity, who wrote the listing petition filed in 2008, called the decision "disgraceful."

"Today's decision grossly misrepresents the science showing the walrus is threatened by climate change," she said by email. "The administration downplays the dangers of climate change, and claims without basis that the walrus will somehow adapt to the devastating loss of sea ice."

Older male walruses spend summers in the Bering Sea. Females with calves, however, ride sea ice north as it melts in spring and summer all the way through the Bering Strait into the Chukchi Sea. The ice provides a moving platform, giving walruses a place to rest and nurse, and protection from predators.

In the last decade, however, ice in the Arctic Ocean has melted far beyond the shallow continental shelf over water too deep for walruses to reach the ocean floor. Walruses instead have gathered by the thousands on beaches in northwestern Alaska and Russia, where smaller animals are vulnerable to being trampled in stampedes if the herd is spooked by a polar bear, hunter or airplane.

In the last six years, Lemons said, protections put in place in Alaska and Russia have greatly reduced trampling deaths. Walruses also have shown a willingness to swim great distances of 130 miles or more from coastal haulouts to prime foraging areas.

Arctic sea ice this summer dropped to 1.79 million square miles, about 610,000 square miles below the 30-year average.

Lemons said the Fish and Wildlife Service used climate models showing the Chukchi Sea between northwest Alaska and Russia could be ice-free in the summer by 2060. But he said information collected in the last six years makes predicting the walruses' fate uncertain beyond then, so the decision was made not to list the species.

Alaska's Republican congressional delegation hailed the decision. Sens. Lisa Murkowski and Dan Sullivan and Rep. Don Young said in a release that there hasn't been a reduction in the walrus population.

"I welcome this action by the USFWS, a decision that recognizes the health and stability of Alaska's walrus population and ignores the extreme political pressures often associated with new Endangered Species Act listings," Young said.

Wolf said last week that her group likely would sue if walruses were not listed as a threatened species.