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Technical Report

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Razorback suckers (Xyrauchen texanus) and bonytail chubs (Gila elegans) were once widespread throughout the Colorado River system. The ranges and populations of these native species and others have declined in the past 50 years. Bonytail chubs appear to be extremely rare and possibly nearing extinction in the Upper Colorado River Basin. The razorback sucker is widely distributed in the upper river but is considered rare throughout most of that range and is also rare in the Grand Canyon. Razorback suckers are abundant only in a few habitats in the upper river. They congregate and spawn over a cobble bar in an eddy at the mouth of the Yampa River. Tyus (1982) collected a large number of razorback suckers in a similar habitat downstream from that location at the mouth of Ashley Creek. The Walter Walker Wildlife Refuge and Clifton Pond are also sites where razorback suckers are known to congregate for spawning. Recent specimens collected from the upper river all have been large adults.

Bonytail chubs apparently were abundant throughout the lower Colorado River early in this century. Locals believed bonytail chubs once were the most abundant fish in the river reach from Needles to Yuma. Bonytail chubs and razorback suckers were also common in Lake Mead during early impoundment and below Hoover Dam. Bonytail chubs have not been reported from Lake Mead since 1967, but razorback suckers are frequently sighted in that reservoir. Bonytail chubs are now thought to be extirpated throughout most of the lower river. Small populations of razorback suckers still occur in Lake Havasu and Senator Wash Reservoir and scattered individuals inhabit the river and irrigation canals below Parker Dam. Large populations of bonytail chubs and razorback suckers were observed spawning over gravel shelf areas of Lake Mohave during the early 1950's. Bonytail chubs are now rare in Lake Mohave, but a small population still persists in the reservoir. Razorback suckers are presently considered abundant in Lake Mohave.

Reservoir spawning activity of razorback suckers has been observed in Lake Mead, Lake Havasu, Senator Wash Reservoir, and Lake Mohave. Jonez and Sumner (1954) observed what they believed to be larval razorbacks near spawning areas south of Eldorado Canyon, and Ulmer (pers. comm.) collected larvae near Arizona Bay in 1981. One larval razorback sucker was collected below Hoover Dam in an invertebrate sampler during 1979. Several razorback eggs and larvae were collected in drift samples in the same area in 1984. Bonytail chubs also have been observed spawning in Lake Mohave, but larvae have never been collected from that reservoir. A large number of young-of-the-year razorback suckers were collected from the shores of Lake Mohave prior to filling in the early fifties. Juvenile or subadult fish of either species have not been observed or collected in recent years.

The apparent lack of young individuals in the bonytail chub and razorback sucker populations suggests that recruitment is limited. Jonez and Sumner (1954) noted that predators were numerous in the vicinity of razorback sucker and bonytail chub spawning areas. Predation on early life stages of both species is believed to be the principal factor limiting recruitment in these reservoir populations.

The U. S. Fish and Wildlife Service initiated this investigation in order to further evaluate the population status and reproductive success of razorback suckers and bonytail chubs in Lake Mohave. The principal objectives were to determine (i) the distributions and abundances of both species, (ii) whether successful spawning occurs for either species, and (iii) the primary factors affecting spawning success.


Aquatic biology; Colorado River; Freshwater fishes; Lake Mohave (Ariz.) Water temperature


Aquaculture and Fisheries | Biology | Environmental Monitoring | Environmental Sciences | Fresh Water Studies | Life Sciences | Natural Resources and Conservation | Terrestrial and Aquatic Ecology




From the Lake Mead Limnological Research Center, University of Nevada, Las Vegas.