(Bloomberg) -- The Biden administration is standing by a Trump-era decision to strip the gray wolf of endangered species protections, arguing the move was backed by sound science, even though it is being fought by conservationists in court.

The U.S. Fish and Wildlife Service defended the delisting call in a letter to Earthjustice, one of the environmental groups challenging the move.

“We made our delisting determination using the best scientific and commercial data available,” Gary Frazer, the assistant director for ecological services, said in the letter. “Our delisting action recognizes the successful recovery of one of the most iconic species to our nation’s natural heritage, which currently numbers more than 6,000 wolves, greatly exceeding our recovery goals for the Northern Rocky Mountains and Western Great Lakes populations.”

When the Trump administration announced the decision last October, it called the move an Endangered Species Act success story. After more than 45 years of protection under the statute, gray wolf populations had recovered enough to warrant the shift, the Fish and Wildlife Service said at the time.

However, in January, six environmental groups filed a lawsuit in a California-based federal district court challenging the decision, saying the Fish and Wildlife Service had only evaluated the health of wolf populations in the Midwest, overlooking the species’ status in California, Washington, Maine and other states.

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