Bonytail Chub
**This fish must be returned to the water unharmed as quickly as possible.** Bonytail Chub have gray or olive-colored backs. Silver sides. White bellies, with slight bump behind their head. An extremely thin caudal peduncle (area ahead of tail). The bonytail is the rarest of the endangered, native fish of the Colorado River and is thought to have evolved around 3-5 million years ago. It has large fins and a streamlined body that is pencil-thin near its tail. Its name describes the fish as an elegant swimmer and member of the “chub” group of minnows. The bonytail has a gray or olive-colored back, silver sides, and a white belly. Bonytail can grow to 22 inches or more and have been known to live up to 50 years.
About This Species
Bonytail were once common in portions of the upper and lower Colorado River basins. In the early 1900s, Chuck Mack of Craig, Colorado, called them “broomtails” because “…you could get a firm grip on their bony tail.” Chuck and other old-timers used to catch these fish in the Upper Colorado River Basin along with Colorado pikeminnow and razorback sucker.
Today, the bonytail is among North America’s most endangered fish species. Its distribution and numbers are so low that it is threatened with extinction. No reproducing populations are known in the wild.
Recognizing that fewer bonytail were being seen in the Colorado River, and those that were observed were all older fish, biologists captured 34 adults from Lake Mohave from 1976 to 1988, and 16 from 1988 to 1989. These fish were held in fish hatcheries. The young of these Lake Mojave fish, and the few remaining adults in hatcheries and in the wild, make up the entire known population of bonytail in the world.
More Information:
Commonly Found
Bonytails are restricted to warm-water reaches of main-stem streams, but they have been found in reservoirs and backwaters of the Colorado and Green Rivers. They are also captive-reared in ponds.
Range
Bonytails formerly ranged throughout the Colorado River Basin but are currently restricted to Mesa and Moffat Counties, which includes the Yampa, Green, Colorado and Gunnison rivers. They also occur in parts of Arizona, California, Nevada, and Utah. They are extirpated from their historic range in New Mexico and Wyoming.
Habitat
All fish must have connectivity among habitats, suitable for all life cycles, including spawning, rearing, feeding, and refuge. Dams and other barriers to fish movement can have both positive and negative effects for fishes of conservation concern. Barriers can block contact with non-native predatory fish or non-native fish that alter the gene pool of native fish, but they can also prevent desirable gene flow among populations. Additionally, barriers can prevent migration and repatriation by fish that drifted downstream as larvae and young fish. Due to the difficulty of generalizing effects of barriers, they are not included in the scorecard. Relatively little is known about bonytail habitat because major surveys had not been conducted prior to extirpation from most of their historic range. The following is based on the little information available.
Because there were so few bonytail in existence when recovery efforts began, their preferred habitat is still unknown. Their large fins and streamlined body enable bonytail to swim in swift river flows. Through research and monitoring of stocked fish, researchers continue to gain information to help determine this species' life-history needs and ways to improve their survival.
Diet
Bonytails are omnivorous, consuming insects, other aquatic invertebrates, plant material (e.g., leaves, stems, debris, and wood fragments), and small vertebrates, such as fish and amphibians. They feed mostly at night.
Reproduction
Historically, the species spawned in the spring and summer over gravel substrate. Many bonytail are now produced in fish hatcheries, with the offspring released into the wild when they are large enough to survive in the altered Colorado River system environment. Females produce between 1,000 and 17,000 eggs. Hatching occurs about nine hours after fertilization and swim-up begins generally 48 to 120 hours later. Survival rate of young fish is about 17 to 38 percent. Bonytail are thought to spawn at 2 to 3 years of age during late June and early July.
Threats to Species
Conservation Status Federal: Listed as Endangered in 1980. Colorado: Listed as Endangered and designated Tier 1 Species of Greatest Conservation Need.
Once widespread, bonytail populations declined sharply after construction of dams that resulted in temperature and flow changes and with introduction of non-native fish that compete with and/or prey upon bonytail. USFWS determined that at least 4,400 individuals are needed for a minimum viable population (MVP). If and when a MVP becomes self-sustaining, a five-year monitoring effort must confirm continued existence of the MVP. Three additional years of monitoring and sustainability of the MVP will be required for delisting.