Colorado pikeminnow – Noted as North America’s largest member of the minnow family (Cyprinidae), Ptychocheilus lucius is one of four members of the genus Ptychocheilus. It has inhabited the Colorado River basin since at least the mid-Pliocene Epoch (about six million years). However, between the 1930s and 1960s, a series of major dams were built on the Colorado River and its tributaries, blocking fish migrations and changing the seasonal pattern of flows and water temperature downstream. Once ranging from the Wyoming border to the Gulf of California, the Colorado pikeminnow is now restricted to the upper Colorado River basin, upstream of Glen Canyon Dam and Lake Powell (about 25 percent of its former range). Ptychocheilus lucius is a piscivore (fish-eater) and may grow to a length of two meters (six feet), though the largest found in recent years was 1.3 meters (four feet) long. Though uncommon, its distribution is widespread within warm-water habitats of the upper basin, occurring in the Colorado mainstem, Gunnison, Green, Yampa and White rivers. The continued existence of this species is threatened by habitat changes caused by altered flow regimes as well as predation and competition from non-native fish species.
Humpback chub - Also a member of the minnow family (Cyprinidae), the humpback chub Gila cypha is one of several species of the genus Gila found in warm-water reaches of the Colorado River and its tributaries. Unlike the Colorado pikeminnow, populations of humpback chub are confined to specific reaches, generally canyon-bound regions containing deep, swift water with turbulent eddies, habitat conditions the species is uniquely adapted for. One population occurs in the lower basin, within Grand Canyon National Park, and five others in the upper basin: three in the mainstem Colorado River, one in the Green River and one in the Yampa River. Only two of these populations are relatively large (thousands of individuals); the others are small and tenuous. This species is noted for the pronounced hump on its back, directly behind the head. The purpose of this hump is unclear but may be related to swimming performance in turbulent conditions. The species is omnivorous, primarily feeding on insects, crustaceans, plants and small fish. In addition to range reduction from dams, habitat change from altered flow regimes, and predation from non-native fish, humpback chub are also threatened with hybridization with other chubs, particularly the roundtail chub Gila robusta, another chub species still common in the upper basin.
Razorback sucker - The only member of the genus Xyrauchen in the sucker family (Catomstomidae), X. texanus once occurred throughout warm-water reaches of the mainstem Colorado River and its tributaries from Utah and Colorado downstream to the Gulf of California. By the 1990s the wild population in the upper Colorado River mainstem was essentially extirpated and only a few hundred individuals remained in Utah’s Green River. In the lower basin, a relatively large population persisted in Lake Mohave, downstream of Hoover Dam, up until the 1980s, but even this population has declined precipitously in the past 10-20 years. In all populations, reproductive failure or high mortality of young resulted in extremely low annual recruitment to the adult populations. Over time, natural mortality of adults without replacement by young led to gradual population declines. The prominent ridge or keel on its back, for which the razorback sucker is named, gives the species a striking appearance. The purpose of the keel is unclear but may aid in the fishes ability to swim or maintain its position in turbulent water, or may be an anti-predator device making it difficult to be swallowed, much like the spine on the back of a catfish. Razorback sucker consume zooplankton, aquatic insects, and algae. The greatest threat to the continued existence of this species appears to be predation on young by introduced, non-native fishes. In addition, alteration of river flows by dam operations have limited the flooding of river bottomlands in spring, a seasonal habitat type believed critical for first-year growth and survival of young razorback sucker. Hybridization with other species of sucker also appears to be problem.
Bonytail – This is the rarest of the three species of chub (Genus Gila) native to the upper Colorado River and the most endangered of the four big-river fishes. Historical reports indicate Gila elegans was once common in warm-water reaches throughout the upper and lower basins. The last documented individual from the upper mainstem Colorado River was captured in 1983. Some bonytail-like specimens are sometimes captured in Cataract Canyon above the Lake Powell inflow, but these may be humpback or roundtail chubs containing bonytail genes (hybrids). A handful of old adults may still occur in Lake Mohave in the lower basin but captures of these by biologists are becoming increasingly infrequent. For the most part, the species is considered extirpated in the wild. As the name implies, the caudal peduncle (narrow part of body to which the tail fin attaches) is very narrow and long, setting it apart from the other two species of chub. Old-timers referred to these fish as “broomtails.” In the 1980s, bonytails from Lake Mohave were brought to Dexter National Fish Hatchery ( New Mexico) to be used as broodstock. Progeny of these are being raised by the Colorado Division of Parks and Wildlife and have been recently released into upper Colorado River reaches. Whether these stocked bonytails will survive in the wild is not yet known. Because bonytail populations were exptirpated before biologists had a chance to study them in the wild, very little is known of their life history, their habitat requirements, or the reasons why they declined and disappeared.
Little girl and ‘catch of the day’, including eight bonytail and one Colorado pikeminnow. These fish were captured from the Colorado River near Moab, Utah around 1920. Photo courtesy of Verlyn Westwood.
Unknown chub species with some bonytail-like characteristics captured from the Colorado River in 2004. USFWS file photo.