Agency proposes to downlist humpback chub on the Colorado River, citing recovery efforts

A key Colorado River native fish, long seen as a bellwether of ecological health in the Grand Canyon, may soon be moved off the endangered species list.

The U.S. Fish and Wildlife Service said Monday it was proposing to reclassify the humpback chub as "threatened."

The fish, a member of the minnow family that has survived and thrived in the warm, muddy waters of the Colorado for up to 5 million years, would retain some protections under the law, but not at the same level. 

The announcement was met with skepticism by at least one environmental group, which said the fish was still at great risk. Wildlife managers, by contrast, said the move was an example of a success story on the river that reduced the chub's threat of extinction. 

The humpback chub, which was placed on the endangered species list in 1973, is one of 43 endangered or threatened species in Arizona. It’s also one of two endangered fish species within the Grand Canyon, and the only chub species left within the Canyon.

Once abundant, the chub and the seven other fish species native to the Canyon were devastated by dam building, overfishing and the introduction of popular game fish such as trout and smallmouth bass, which have put the chubs and other Grand Canyon fish on their menus.

The chub also requires specific water temperatures for reproductive success. The Fish and Wildlife Service said the greatest hatching success for chub eggs is around 68 degrees. Water released through Glen Canyon Dam can cause river temperatures to plummet to an average of 46 degrees, leaving chub eggs to freeze and the unhatched fish to perish.

Three other native species — the Colorado pikeminnow, the bonytail and the roundtail chub — are no longer living in the Grand Canyon. All fell victim to human-caused changes to the Colorado’s ecosystem.

'Moving in the right direction'

The fish, with its distinctive hump that acts as a hydrological stabilizer much like a spoiler enhances a sports car's performance, once faced near-extinction, even after federal protections were enacted.

After chub numbers dropped precipitously, with one population dropping to about 2,100 individuals in the 1990s, the Upper Colorado River Endangered Fish Recovery Program, a consortium of 14 government and private entities, created a new plan to conserve and revitalize the fish.

The Fish and Wildlife Service noted that the largest humpback chub population, which lives around the confluence of the Colorado and Little Colorado rivers, has stabilized at about 12,000 adults.

“The proposed downlisting is a demonstration of success for the collaboration,” said Tom Chart, director of the upper Colorado fish recovery program.

The program’s goal is to restore the humpback chub and three other fish species in the highly regulated Colorado river system.

“We’re moving in the right direction,” said Chart. “The chub is not at danger of extinction now.”

In addition to the confluence population, biologists also have identified smaller populations living in other tributaries in the Grand Canyon.

Four other populations are in the Colorado's Upper Basin, including the Green and Yampa rivers, but they exist in far fewer numbers.

Chart said scientists are getting a better handle on how flow management and interactions with non-native fish work to conserve humpback chub populations. Also, he said, the chub are moving into the western reaches of the Canyon. Coupled with flow management and non-native fish control, as well as efforts to increase insect food stocks for fish, growth of the humpback chub’s numbers led to the decision to move the fish’s protection status down a level, Chart said.

“It’s a huge success story,” said Julie Carter, statewide native aquatics program manager for the Arizona Game and Fish Department, one of the recovery program’s partners. “This reflects a tremendous amount of work that biologists have done over the years all throughout the basin.”

Carter said the proposed action by the Fish and Wildlife Service would be the first like it for an Arizona fish since 2006 when the Gila trout was moved from the endangered species list to threatened status.

Both Carter and Chart said conservation and protection efforts would continue and the humpback chub's recovery plan would continue to be implemented. 

Fish still an indicator of river's health

Taylor McKinnon, senior public lands campaigner for the Center for Biological Diversity, was more doubtful about the feds’ request.

“This fish has been here for millions of years, but the last 100 years have been catastrophic for the Colorado River’s ecosystem,” he said. “We’ve seen many fish species pushed to the brink of extinction.”

McKinnon said the chub’s remaining Upper Colorado River Basin populations are all in decline despite the success of the Little Colorado River population. One population of humpback chub in Dinosaur National Monument recently died out, McKinnon said.

Chart said the extirpation was due to marginalized habitat in the Green River upstream of the monument after construction of Flaming Gorge Dam on the Wyoming-Utah border. He added that program managers are considering a chub re-introduction into a nearby reservoir in Colorado.

The chub community at the Little Colorado River confluence could be imperiled by a proposal to build two dams on the Little Colorado River for electric generation, McKinnon said. “That proposal is still active,” he said.

“The chub’s presence in the Colorado River is very important,” said McKinnon. “If we measure the ecological integrity of the Colorado’s system writ large, one of the primary measures of that is the extent to which its original species can still persist.

“The Colorado River without Colorado River fish is not a desirable future.”

The Fish and Wildlife Service will accept comments on its proposed downlisting through March 23.

READ MORE: How the humpback chub reflect the health of the river

Reach the reporter at debra.krol@AZCentral.com or at 602-444-8490. Follow her on Twitter at @debkrol. 

Environmental coverage on azcentral.com and in The Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow The Republic environmental reporting team at environment.azcentral.com and @azcenvironment on Facebook, Twitter and Instagram.

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