Old- Living Resources — Interior West 



325 



Fishes Recovery Team was formed. The 

 Colorado River Fishery Project was established 

 in 197S to recover threatened and endangered 

 fish in 965 km (600 mi) of the upper Colorado 

 and Green rivers. Recovery efforts intensified in 

 1987 with the Recovery Implementation 

 Program. These and other projects have funded 

 major research on the biology and habitat needs 

 of these species. 



Bonytails were historically common in the 

 mainstem Colorado, Green, Gunnison, Yampa, 

 Gila, and Salt rivers before the construction of 

 large dams. Bonytail became rare in the lower 

 river system by 1935 and suffered similar 

 declines farther upstream by the mid-1960"s. 

 The last confirmed bonytail taken from any 

 river was in 1985. Bonytail continue to be cap- 

 tured in low numbers from Lake Mohave in 

 Arizona and Nevada, a reservoir on the 

 Colorado River downstream of Hoover Dam. 



Razorback suckers were historically com- 

 mon to abundant in the Colorado mainstem and 

 portions of the Green. San Juan, Animas. 

 Duchesne, Gila, Salt, and Verde rivers. 

 Razorback suckers also had begun declining in 

 the lower river by 1935, but were commercially 

 harvested near Grand Junction. Colorado, and 

 Phoenix, Arizona, until 1950. Numbers dramat- 

 ically declined in the upper Colorado River dur- 

 ing the I970"s and I980's, and today the fish is 

 very rare. The largest river population is in the 

 Green River, Utah, and is estimated (1993) at 

 fewer than 500 adults. 



Large populations of razorback sucker 

 developed in some newly created reservoirs in 

 the lower river before fish predators became 

 abundant. For example, populations that num- 

 bered into the hundreds of thousands became 

 established in the Salton Sea, Roosevelt Lake, 

 Saguaro Lake, Lake Havasu, Lake Mead, Lake 

 Mohave, and Senator Wash Reservoir. 

 Predation by non-native fishes eventually 

 proved overwhelming, and, without recruitment 

 (addition of individuals to a population through 

 reproduction and immigration), populations dis- 

 appeared after 40 to 50 years. 



Razorback suckers are now rare except in 

 Lake Mohave, which supports the last large 

 population. Spawning is successful there, but as 

 was true at older reservoirs, young razorback 

 suckers are eaten by sunfish. bass, and other 

 fish. The reservoir population declined by 60% 

 between 1988 (59.500) and 1991 (23.300). 

 Remaining suckers are expected to die by the 

 end of the decade. 



It is unlikely that the bonytail and razorback 

 will survive in the wild. No measurable recruit- 

 ment is evident in any part of the drainage and 

 old individuals are reaching the end of their life 

 span. Bonytail are found in less than 2% of their 



former range, and razorback sucker in less than 

 25% of their fonner range (Fig. 3). 



Reasons for Decline 



The Colorado River ecosystem has been dra- 

 matically altered by water development that 

 transformed an erratic and turbulent river sys- 

 tem into a series of calm reservoirs and chan- 

 nelized river reaches. Eight dams were built 

 across the lower 563 km (350 mi) of the river by 

 1950. The historical habitat of these fish is now 

 controlled by 44 large dams and is being 

 drained by hundreds of miles of diversion 

 canals. Nursery areas, critical for early life 

 stages, have been flooded by reservoirs, and 

 upstream migration is physically blocked by 

 dams. Seasonally wami and turbid fiows of the 

 natural hydrology of the basin were replaced by 

 cold, diminished reservoir releases governed by 

 hydroelectric and downstream water demands. 



Although physical habitat changes have 

 been dramatic, subtle ecological changes may 

 have been even more damaging. Reservoirs and 

 cold tailwaters presented favorable conditions 

 to develop recreational fisheries. Although the 

 bonytail and razorback sucker were once valu- 

 able food sources, they became viewed as trash 

 fish when more desirable sportfish (e.g.. trout, 

 catfish, and bass) became established. Resource 

 agencies stocked and promoted recreational 

 fisheries, often at the expense of native fishes. 

 For example, in 1962. 723 km (450 mi) of the 

 upper Green River was poisoned to improve 

 trout production. Today, over 90% of all fish 

 found in the river system are species introduced 

 for recreational fishing. Uncounted other aquat- 

 ic plants and animals, pathogens, parasites, and 



iXvraiichen texanus). 



Fig. 3. Historical range and cur- 

 rent concentrations of bonytail 

 and razorback sucker (Minckley 

 and Deacon 1991). 



