Bonytail (Gila elegans)

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. Bonytail are thought to spawn at 2 to 3 years of age during late June and early July. Bonytail eat insects, plankton, and plant matter.

Status and distribution:

  • Listed as endangered and given full protection under the Endangered Species Act in 1980.
  • Endangered under Colorado law since 1976.
  • Protected under Utah law since 1974.

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. (Also see: Historical perspective.)

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 no young, 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.

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.

Working to recover the species

Actions being taken to recover the bonytail include:

  • Managing water to provide adequate instream flows to create beneficial water flow
  • Constructing fish passages and screens at major diversion dams to provide endangered fish with access to hundreds of miles of critical habitat
  • Restoring floodplain habitat
  • Monitoring fish population numbers
  • Managing nonnative fishes

In addition, the Recovery Program works to reestablish naturally self-sustaining populations of bonytail through propagation and stocking. The Recovery Program maximizes the genetic diversity of broodstock used to produce fish in hatcheries to increase the likelihood that stocked fish will survive and reproduce in the wild.

To support stocking efforts in the Upper Colorado River Basin, bonytail are raised at two hatchery facilities: the state of Colorado’s J.W. Mumma Native Aquatic Species Restoration Facility in Alamosa, Colorado and the state of Utah’s Wahweap Fish Hatchery in Big Water, Utah. All bonytail come from the U.S. Fish and Wildlife Service’s Dexter National Fish Hatchery and Technology Center in Dexter, New Mexico, which maintains the bonytail broodstock.

Bonytail raised at these facilities are stocked in the Green and upper Colorado rivers in Colorado and Utah. Stocked fish have been recaptured in several locations and habitats within these river systems. Researchers monitor these fish closely for evidence of reproduction. Stocking efforts in the Upper Colorado River Basin have expanded into floodplain wetlands to enhance bonytail growth and survival.

Recovery goals

Bonytail will be considered eligible for downlisting from “endangered” to “threatened” and for removal from Endangered Species Act protection (delisting) when all of the following conditions are met:

  • Self-sustaining fish populations reach the required numbers in areas of the Green and Upper Colorado River sub-basins and the Lower Colorado River Basin, and a genetic refuge is established in the Lower Basin as identified in the chart below.
  • Essential habitats, including required stream flows, are legally protected.
  • Other identifiable threats that could significantly affect the population are removed.

Over a 5-year monitoring period:
  • Maintain reestablished populations in Green River and upper Colorado River subbasins, each > 4,400 adults
  • Maintain established genetic refuge* of adults in lower basin
  • Maintain two reestablished populations in lower basin, each > 4,400 adults
For 3 years beyond downlisting:
  • Maintain populations in Green River and upper Colorado River subbasins, each > 4,400 adults
  • Maintain genetic refuge* of adults in lower basin
  • Maintain two populations in lower basin, each > 4,400 adults
*A “genetic refuge” is a group of fish that, as a whole, represent a substantial portion of the genetic variability of the species.