The Alliance for the Wild Rockies and Friends of the Wild Swan filed a lawsuit in U.S. District Court Tuesday, challenging the U.S. Fish and Wildlife Service’s recovery plan for bull trout, which was finalized last September.

Listed under the Endangered Species Act in 1999, bull trout in the continental U.S. have struggled throughout the past century under pressure from invasive species, habitat degradation and warmer waters.

Conservation groups were quick to criticize the plan last year, in particular singling out a provision allowing up to 25 percent of the remaining populations to ultimately disappear within four of the six geographically defined recovery units.

Officials with the federal wildlife agency have defended that language as realistic, given the anticipated effects of climate change. As the average water temperatures of streams, rivers and lakes increase, they expect some water bodies currently home to bull trout populations to become uninhabitable for the cold water-dependent species.

“Bull trout lost an estimated 60 percent of their historical habitat range before they were even listed as ‘threatened’ on the Endangered Species List,” Mike Garrity, the alliance’s executive director, said in a Wednesday press release. “The U.S. Fish and Wildlife Service has dragged its feet on bull trout for over 20 years now and the sad truth is that the only actions the agency has taken to keep these iconic native fish from going extinct are those the court has mandated due to lawsuits by conservationists over the decades.”

In developing the plan, the service focused on identifying and minimizing specific threats, rather than the traditional reliance population numbers and critical habitat designation.

In an interview with the Daily Inter Lake last September, Steve Duke, a senior biologist with the service, said the approach will provide more flexibility to regional and state management agencies to tailor their conservation approaches.

Measures of success, he added, can be defined by those agencies depending on what works best for them — including redd counts, which Fish, Wildlife and Parks has used for decades to track bull trout populations in Montana.

The lawsuit alleges nine violations of the Endangered Species Act in the recovery plan, including the allowable extirpation of some bull trout populations, omitting recovery objectives and failing to incorporate agency guidelines to develop recovery plans, not using specific demographic information to define successful recovery, not including habitat standards and failing to address the effects of climate change.

Along with the Fish and Wildlife Service, the suit also names the service’s Pacific Region director, Robyn Thorson, the U.S. Department of the Interior and department Secretary Sally Jewell as defendants.

A spokesman for the Fish and Wildlife Service said Wednesday the agency doesn’t comment on pending litigation.

Reporter Sam Wilson can be reached at 758-4407 or by email at swilson@dailyinterlake.com.