An appeals court has upheld a federal government plan to designate 187,000 miles of Arctic Alaska as critical habitat for polar bears.

Polar bears were listed as threatened under the Endangered Species Act in 2008, which mandated that the U.S. Fish & Wildlife Service designate critical habitat as part of a recovery plan.

The FWS plan, presented in 2010, set aside an area larger than the state of California, divided into three units: The first, Unit 1, was sea ice habitat off the coast of Alaska in the southern Beaufort and Chukchi seas; Unit 2 was the terrestrial denning area, where polar bear mothers give birth to their young; and Unit 3 was barrier island habitat just offshore. Ninety-five percent of the area was in Unit 1, because polar bears spend much of their lives traveling across and hunting on Arctic sea ice.

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In 2013, the state of Alaska, the Alaska Oil and Gas Association and a coalition of Alaskan indigenous groups challenged the ruling, contending that it resorted to “overreach” and that it failed to identify specifically where and how existing polar bears utilize the portion of the critical habitat designated as units 2 and 3. 

U.S. District Court Judge Ralph Beistline acknowledged that the FWS listing of the sea ice habitat was valid, but sided with the plaintiffs on the other two areas, and threw out the entire plan. In its appeal, FWS argued that Beistline had misconstrued EPA requirements “by holding FWS to proof that existing polar bears actually use the designated area, rather than to proof that the area is critical to the future recovery and conservation of the species.”

In other words: “sure, we can’t say that polar bear X is going to follow this specific corridor from the sea ice to these specific den sites. But we do know that polar bears travel up to 50 miles inland to make their dens in this area.” Besides, environmental groups argued that, in cases where there might be uncertainty over data, the law requires decisions that err on the side of protecting threatened species.

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The three-judge panel at the Ninth Circuit Court of Appeals agreed, and overturned the district court’s vacating of the designation.

Kassie Siegel of the Center for Biological Diversity hailed the decision as “a critical victory for polar bears at a time when there’s huge momentum on fighting climate change.” She added that, “The ruling strengthens the Endangered Species Act and affirms the commonsense idea that you can’t protect imperiled animals without protecting the places they live.”

Alaska Sen. Lisa Murkowski, in contrast, said she was “enraged” by a decision that she claimed would affect the economy of a state heavily dependent on revenues from oil exploration and production, almost all of which is along its Arctic coast and in the ocean offshore. She asserted also that polar bear numbers are “strong and healthy across Alaska’s Arctic.”

However, while a recent study found that polar bears in the Chukchi Sea appeared quite healthy, the sub-population in the southern Beaufort Sea is believed to be reduced and still declining.