|Listed||October 23, 1991|
|Description||Robust fish with a sharp, dorsal ridge behind the head.|
|Habitat||River channels, gravel bars.|
|Food||Algae, plankton, insects.|
|Reproduction||Spawns in the spring.|
|Threats||Lack of recruitment of young, loss of habitat.|
|Range||Arizona, California, Colorado, Nevada, Utah|
The razorback sucker is a large freshwater fish, often exceeding 6 lbs (2.7 kg) in weight and 24 in (61 cm) in length. Adults have an abrupt, sharp-edged dorsal ridge behind the head and a fleshy mouth situated on the underside the head. Younger fish, less than 6 in (15 cm) long, lack the distinctive keel. This species was originally placed in the genus Catostomus. It has also been known by the common name, humpback sucker.
In the lower Colorado River basin, razorback suckers spawn from late January through April; in the upper basin spawning takes place mostly in May and June.
After migrating considerable distances to spawning areas, females are accompanied by several males over clean gravel bars. The collection of fertilized eggs and young larvae indicates that the species is reproducing successfully. However, almost no larvae over about 0.5 in (1.3 cm) in length have been found, indicating that the species is not successfully recruiting young to the population. Adult razorback suckers feed primarily on algae, but also eat plankton, insects, and decaying organic matter
The razorback sucker shows different habitat preferences depending on the season. During the spring spawning season it is found mostly over sand, gravel, and cobble runs; flooded bottomlands; and the eddies formed at the flooded mouths of tributary streams.
In winter, the fish take up a relatively sedentary position in deeper water or the main stream channel. Studies with radio-tagged fish indicate that during the winter fish travel only about 3 mi (0.8 km) over the course of several months. Because they have not been seen by researchers, the habitat requirements of larvae and young fish are largely unknown.
First described in 1861, the razorback sucker was once an abundant species throughout the 3,500 mi (5,600 km) Colorado River basin. It is believed to have occurred in Arizona, California, Colorado, Nevada, New Mexico, Utah, Wyoming, and in the Mexican states of Baja California, Norte, and Sonoma. A significant commercial fishery for the species existed in southern Arizona during the early 1900s, and in Colorado thousands were observed during spring runoffs during the 1930s and early 1940s.
In recent decades the razorback sucker has undergone a steady decline in both range and numbers. It now occurs in about 750 mi (1,200 km) of the upper Colorado River basin and in about 200 mi (320 km) of the lower basin. The largest population of adult fish—an estimated 60,000—survives in Lake Mohave, on the Arizona-Nevada border. Small numbers of the species are also found in Lake Mead and Senator Wash Reservoir. In the upper Colorado basin an estimated 750-1,200 individuals inhabit the upper Green River and some of its tributaries in Utah and Colorado. Razorbacks are also found in the upper Green River, Utah; lower Yampa River, Colorado; and the Colorado River, near Grand Junction, Colorado. The species is present but very rare in the San Juan, Dirty Devil, and Colorado arms of Lake Powell.
Since the early 1900s, construction of dams on the Colorado River and its major tributaries have radically altered the river system, impounding nearly the entire lower basin and greatly decreasing water flows. The once abundant razorback sucker has progressively declined as the natural flow of the river has been disrupted. The changes in flow caused by dams has reduced available spawning areas and rendered other parts of the river too cold to support the species. However, of most concern to researchers is the fact that despite successful reproduction, the young are not surviving. It is believed that the present population consists almost entirely of adults. If this situation continues, the extinction of the species in the near future is a certainty.
It appears that the main causes of the death of razorback sucker larvae are predation by non-native fish species and a lack of food availability. A number of predatory species, including carp, channel catfish, flathead catfish, largemouth bass, smallmouth bass, and bluegill, feed on razorback sucker eggs and larvae. In addition, recent studies in Lake Mohave have suggested that there is not sufficient zooplankton in the lake to support the growing larvae.
Conservation and Recovery
The conservation and recovery of federally listed fish species in the Colorado River basin—the Colorado squawfish (Ptychocheilus lucius), humpback chub (Gila cypha), bonytail chub (Gila elegans), and razorback sucker—has been coordinated by the Colorado River Endangered Fishes Recovery Implementation Committee, which consists of representatives from a number of federal agencies. Protective measures for the razorback sucker will now be included in the committee's work. As part of the recovery process, a captive population of razorback suckers is held at the Dexter National Fish Hatch-ery as insurance against extinction and a population source for an ongoing restocking effort. Unfortunately, this effort does not appear to be succeeding. Over the last ten years, over 13 million razorback sucker fry have been stocked in over 50 sites in Arizona. It is believed that these juveniles were heavily preyed upon by introduced non-native fishes.
Alteration of the Colorado River system is continuing and the Fish and Wildlife Service has been in consultation with over 100 federally funded or regulated projects in the upper Colorado basin over the last decade. Among the more prominent projects are the Central Utah Project, which will divert water from the Green River, and the Two Forks Project, which will divert water from the Colorado River. These will affect listed fish species by decreasing the flow in most of the remaining riverine habitat.
U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Denver Federal Center
P.O. Box 25486
Denver, Colorado 80225
U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232
Bozek, M. A., L. J. Paulson, and J. E. Deacon. 1984."Factors Affecting Reproductive Success of Bonytail Chubs and Razorback Suckers in Lake Mohave.~ Final Report," 1416-0002-81-251. Bureau of Reclamation, Boulder City, Nevada.
Loudermilk, W. E. 1985. "Aspects of Razorback Sucker (Xyrauchen texanus, Abbott) Life History which Help Explain Their Decline." Proceedings of the Desert Fishes Council 13(1981):67-72.
Marsh, P. C., and W. L. Minckley. 1989. "Observations on Recruitment and Ecology of Razorback Sucker: Lower Colorado River, Arizona-California." Great Basin Naturalist 49(1):71-78.
Minckley, W. L., et al. 1991. "Management Toward Recovery of Razorback Sucker (Xyrauchen tex-anus)." In Battle Against Extinction, edited by W. L. Minckley and J. E. Deacon. University of Arizona Press, Tucson.
Papoulis, D. 1986. "The Effect of Food Availability on Growth and Mortality of Larval Razorback Sucker, Xyrauchen texanus." U.S. Fish and Wildlife Service, Albuquerque, New Mexico.
Rinne, John N., and W. L. Minckley. 1991. Native Fishes and Arid Lands: Dwindling Resource of the Desert Southwest. USDA Forest Service, Fort Collins, Colorado.
Tyus, H. M. 1987. "Distribution, Reproduction, and Habitat Use of the Razorback Sucker in the Green River, Utah, 1979-986." Transactions of the American Fisheries Society 116:111-116.
Tyus, H. M., and C. A. Karp. 1989. "Habitat Use and Stream-flow Needs of Rare and Endangered Fishes, Yampa River, Colorado." U.S. Fish and Wildlife Service, Biological Report 89(14).