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l' , lJ ~ 1114# Ho..,vJ KII~s 0- JJe S' Jer l'i'l l ~ 0'704-2. " Reprinted from THE SOUTHWESTERN NATURALIST Vol. 30, No.2, :rune 1991 Made in United States of America OCCURRENCE OF TWO ENDANGERED FISHES IN THE LITTLE SNAKE RIVER, COLORADO ~ EDMUND J. WICK, JOHN A. HAWKINS, AND THOMAS P. NESLER ~ Department oj Fishery and Wildlife Biology, Colorado State University, Fort Collins, CO 80523 (EJW, JAH) Colorado Division oj Wildlife, 317 West Prospect, Fort Collins, CO 80526 (TPN) The Little Snake River (Fig. 1) delivers sig- nificant amounts of water and sediments to the Yampa River yet has been generally disregarded as potential habitat for endangered fishes. Wild, self-sustaining populations of endangered Colo- rado squawfish, Ptychocheilus lucius, and hump- back chub, Gila cYPha, occur in the Yampa River, but past surveys have not documented their oc- currence in the Little Snake River (Holden, 1973). However, unconfirmed reports by local ranchers (Seethaler, 1978) and anglers suggested that Col- orado squawfish and humpback chub use the riv- er periodically. We report the first documented occurrence of Colorado squawfish and suspected humpback chub in the Little Snake River, Moffat Co., Colorado, during spring 1988. Information on Colorado squawfish use of the Little Snake River was gathered ancillary to investigations on winter habitat and spring migration of adult Col- orado squawfish in the Yampa River. Observa- tions of potentially suitable habitat for humpback chub and Colorado squawfish in the canyon sec- tion of the lower Little Snake River led to ini- tiation of fish sampling. Collection of humpback- like chubs of the Gila complex led to funding of studies to determine extent of use of the lower Little Snake River by endangered and other na- tive fishes. Relative abundance of fishes collected during this investigation is reported. Taxonomic uncertainty remains a problem with the Gila complex of the Colorado River Basin and is the focus of ongo~udies by the Recovery Implementation Program for endangered fish species in the Upper Colorado River Basin. Re- sults of these studies should clarify the taxonomic status of the chub from the Little Snake River. Photographs of suspected humpback chub from the Little Snake River were examined by re- searchers currently working on projects related to the taxonomy and distribution of humpback chub. They concluded that one or more of the suspected humpback chub from the Little Snake River could be within the range of variability observed in populations of humpback chub from Little Colorado River, Lower Green River, and Yampa Canyon (R. Valdez, H. Tyus, and R. Muth, pers. comm.). Another opinion expressed by researchers familiar with the Gila complex problem is that the humpback-like fish from the Little Snake River may be hybrids between fishes within the Gila complex. The study area extended from the Little Snake River-Yampa River confluence (river kilometer 0.0) upstream to river km (RK) 56.0. From RK 56.0 'downstream to RK 14.0 (Moffat County Road no. 10 bridge), the Little Snake River me- andered through pasture and crop lands. River substrate in this reach was predominantly sand. At RK 12.9, the river entered a steep-walled, sandstone canyon 3.2 km long. In the upper 1.6 km, the canyon was constricted, stream gradient was steep, and river substrate consisted mainly of boulder, rubble, and cobble. Deep, turbulent eddies were formed along canyon walls and be- hind large boulders during spring runoff. During baseflow, these eddies became pools that provided deep-water habitat for large concentrations of fishes. These pools were deeper and more cOm- mon than those outside the canyon. At baseflow in July through October, the deepest pool had a maximum depth of 3 m, an area of 5 by 20 m of water 2 m deep, and an area of 5 by 40 m of water 1 m deep. The lower 1.6 km of the canyon was less constricted with some braided sections. Substrate was mostly cobble and gravel. Below the canyon, from RK 9.7 to RK 0.0, the river flowed over sand substrate through irrigated crop lands and cottonwood bottomlands. During base- flow, the wide, low-gradient reaches above and below the canyon provided few habitats suitable for fishes since pools were few, scattered, and usually shallow. Flows in the Little Snake River ranged from 127 m3/s on 20 May to 0.03 m3 Is in September (Ugland et al., 1989). Flows declined rapidly in June from a high of 71 m3/s on 7 June to 11