Population Growth Could Move Humpback Chub From Endangered To Threatened Under ESA

Growth in the population of the humpback chub, an endangered fish in the Colorado River system, has the U.S. Fish and Wildlife Service proposing that the species be upgraded to "threatened" under the Endangered Species Act.

The Service recently completed a species status assessment and a 5-year status review that concluded the current risk of extinction is low, such that the species is not in danger of extinction throughout all of its range. The SSA explained that the largest population of humpback chub, which is found in the Colorado and Little Colorado rivers in Grand Canyon National Park is a stable population of about 12,000 adults.  

The assessment also explained that four smaller populations in the Green and Colorado rivers of the upper Colorado River basin have persisted and do not appear to be in immediate danger of extinction.  All five populations are wild, persisting without the need for hatchery stocking, the Service said in a release. These population-monitoring results, when coupled with ongoing flow management and nonnative predatory fish control, mean that the humpback chub will be considered for reclassification from endangered to threatened in the next year. 

Although this unique fish is making a big step toward recovery it still needs help, the Service said.  Conservation work by a diverse group of stakeholders has been one of the key contributions in recovering this native fish. State, tribal, federal, and private stakeholders collaborate via the Upper Colorado River Endangered Fish Recovery Program (established in 1988) and the Glen Canyon Dam Adaptive Management Program (established in 1997) to continue the monitoring programs and to reduce threats to this species’ recovery. 

“Endangered species recovery in altered and heavily managed ecosystems like the Colorado River is a complicated endeavor,” said Service Mountain-Prairie Regional Director Noreen Walsh.  “Our best chance for continued success rests in the power of these collaborative partnerships.”

The humpback chub, which was first described as a unique species from collections in the Grand Canyon in the 1940s, was not discovered in the upper Colorado River basin until the 1970s.  It was placed on the original list of endangered species in 1967.

Humpback chub prefer canyon-bound reaches of river where they complete their life cycle in swift, turbulent currents. The species gets its name from the fleshy hump behind its head that acts a bit as a rudder.  That adaptation coupled with large, curved fins, allows the species to maintain position in the turbulent flows. Habitat alterations (from changes in river flows and inundation of canyon reaches), and competition and predation from invasive species are the greatest threats to the humpback chub. 

In the 5-year review, the Service also recommends that the species recovery plan be revised to incorporate the best available scientific information on the species needs and actions that will be necessary to eventually delist humpback chub.  Efforts to propose reclassification and to revise the recovery plan will be ongoing in the coming year.  The proposed reclassification rule and the revised recovery plan will be made available for public comment in the future.