Humpback Chub- EP

CRE AT-RISK SPECIES VIGNETTES – Larry Stevens

• Humpback Chub
• The humpback chub (HBC; Gila cypha Miler 1946) was listed as an endangered species in 1967.
• It is an odd-shaped fish and is endemic to the Colorado River basin.
• HBC’s pronounced dorsal hump has been hypothesized to stabilize its swimming in turbulent water, but experimental studies fail to support that proposition, and suggest the hump reduces the likelihood of predation by Colorado pikeminnow (Ptychocheilus lucius Girard 1856; Portz and Tyus 2004).
• HBC was formerly widespread throughout the lowland portions of the Colorado River, and was caught in abundance at Lees Ferry immediately after closure of Glen Canyon Dam. However, it has entirely disappeared from that reach. *It is now restricted to several populations in the Upper Basin and several concentrations in Grand Canyon, the largest and only reproducing population of which occurs in and around the confluence of the Little Colorado River at Mile 61L.
• HBC in the mainstream Colorado River undertake a springtime spawning run from April-June into the lower Little Colorado River.
• HBC are opportunistic predators, feeding on aquatic and terrestrial invertebrates, and on smaller fish, including their own young.
• HBC may live nearly 20 yr or more.
• Reasons for HBC endangerment include dam-related colder water temperatures and the introduction of non-native picscivorous fish and fish parasites.
• Young HBC drifting from the Little Colorado River in summer enter the cold mainstream, which shocks them physiologically, retards their growth, and harbors an array of predatory, non-native fish, particularly catfish and brown trout.
• Although rainbow trout have been implicated as predators responsible for HBC decline, recent population trends suggest little relationship between the two species.
• HBC are regarded as an umbrella species, whose protection ensures protection of the Colorado River ecosystem.
• However, its solitary, narrowly-ranging, aquatic life history may not well protect wide-ranging fish like suckers or Colorado pikeminnow, nor wetland or riparian species, like Kanab ambersnail or southwestern willow flycatcher.
• Nonetheless, a tremendous amount of time and money have been spent studying and protecting HBC, and it is one of the better known fish species.
• At the time of writing, a total of about 9,000 adult HBC exist, well above the number that would trigger U.S. Fish and Wildlife Service conservation actions to conserve this species.
• In addition to the improving health of the wild, mainstream population, HBC have been introduced into the Little Colorado River upstream from Chute Falls, into Shinumo and Havasu Creeks, and a captive population has been established at the Dexter National Fish Hatchery in Dexter, New Mexico.