A second of four endangered fish that are the subject of local and regional recovery efforts has been proposed for a downgrade to threatened status, suggesting those efforts are bearing fruit.

The U.S. Fish and Wildlife Service on Thursday said it is proposing the reclassification of the razorback sucker, following its proposal earlier this year to do the same for the humpback chub.

Those fish, along with the bonytail and the Colorado pikeminnow, have been the focus of recovery projects including working with partners to provide optimal river flows in a 15-mile stretch of the Colorado River just upstream of the confluence of the Gunnison River in Mesa County.

The U.S. Fish and Wildlife Service said its proposal for the razorback sucker is based on a recently completed species status assessment and five-year status review for the fish. The agency has determined the current risk of extinction is low, with the fish no longer in danger of extinction throughout its range. Large populations of adults have been re-established in the Colorado, Green and San Juan rivers, and the fish also is present in Lake Powell, Lake Mead, Lake Mohave and Lake Havasu.

"Our partners along the Colorado River have restored flow, created habitat, removed nonnative predators, and re-established populations across these species range," Tom Chart, director of the Upper Colorado River Endangered Fish Recovery Program, said in a news release. "These partnerships have improved conditions, proving long-term commitments are a key component to recovery."

The razorback sucker once occupied an area from Wyoming to Mexico, often traveling hundreds of miles a year, the Fish and Wildlife Service says. Its name refers to a bony keel behind its head that helps it stay in place when flows increase.

Recovery efforts have involved state, tribal, federal, and private stakeholders participating in the Upper Colorado River Endangered Fish Recovery Program, the San Juan River Recovery Implementation Program and the Lower Colorado River Multi-Species Conservation Partnership.

This week, the Senate Energy and Natural Resources Committee approved a bill to extend endangered fish recovery programs in the  Upper Colorado and San Juan rivers through the 2023 fiscal year.

The Fish and Wildlife Service will be pursuing the reclassification of the razorback sucker and revision of its recovery plan in the coming year, and the public will have a chance to comment during the proposal stage.

The Colorado pikeminnow also has been showing promising signs of recovery, although its prospects have been jeopardized somewhat by walleye that prey on young pikeminnow.

Predation of young razorback suckers also has proven a challenge to its recovery.

The fish is part of the lake sucker family, prefers low-velocity habitats in backwaters, floodplains and reservoirs, and evolved in a habitat with one large-bodied predator, the Colorado pikeminnow, the Fish and Wildlife Service says.

As a result, young razorback suckers have few defense mechanisms and are especially vulnerable to being eaten, especially by toothed, nonnative predators.

The Fish and Wildlife Service credits intensive management efforts centered on stocking programs for bringing about a remarkable recovery for the fish, especially in the Green and Colorado rivers.

The population in the Green River rebounded to more than 30,000 adults today, whereas in the mid-1990s officials were able to capture a few fish each year.

Still, it says juvenile razorback suckers are routinely reaching adulthood only in the Lake Mead population, with the other populations being maintained through stocking because the young are eaten by nonnative fish.

"Scientists are hard at work to determine the best ways to encourage survival of juveniles to naturally sustain the population," the agency said in its news release.

It said a wetland managed on the Green River for the fish "has produced over 2,000 young-of-year individuals in the past five years, the first substantial number of juveniles seen in over 30 years" in the Upper Colorado River Basin.

Officials have been pursuing strategies to target nonnative predators by removing northern pike, walleye and smallmouth bass from waterways and installing nets to control their escape from area reservoirs.

Taylor McKinnon with the Center for Biological Diversity said the criteria set forth in the recovery plan for the fish require that, to move it from endangered to threatened, survival of wild-born young fish must exceed mortality of adult fish, which isn't occurring in the Upper Basin.

"While there are lots of hatchery fish, and while some of those fish are spawning, none of their young are surviving to adolescence or reproduction. Until that happens, we're still a long way from self-sustaining populations that the recovery plan envisions and the law requires," he said.

"With literally zero wild-spawned fish surviving in the Colorado and Green rivers, it's difficult to see how (the Fish and Wildlife Service) can justify downlisting," he said. "The fish is still endangered in the Upper Basin, and each dollar spent on downlisting is a dollar starved from actual recovery."

He said climate change and increased aridification of the region also threaten river flows relied on by the fish, including flooding flows in the spring and necessary minimum flows the rest of year.

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