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I I I I I ~ I ;1 I I I I I I I I t I I INTRODUCTION The Little Snake River is a small, unregulated tributary in the Upper Colorado River Basin in Wyoming and Colorado. As an unregulated river, it contributes important components of flow and sediment to the Yampa and Green rivers (Andrews 1978; O'Brien 1987). Most tributaries, like the Little Snake River, have received little research attention and therefore the role of tributaries as habitat for endangered and native fishes is poorly understood. Previous sampling in the Little Snake River focused on the area near the confluence with the Yampa River (Miller et a1.1982; Wick et al. 1991), although Hawkins et al. (1997) sampled sites 100-km upstream of the confluence. Endangered Colorado pikeminnow (Ptychocheilus lucius) and humpback chub (Gila cypha) move into the Little Snake River from the adjacent Yampa River (Miller et a1.1982; Karp and Tyus 1990; Tyus 1990; Marsh et al. 1991; Wick et al. 1989 and 1991, Hawkins et al. 1997). But the intent and duration of their use of the Little Snake River was uncertain due to limited sampling. Primary questions were whether humpback chub are year-round residents in the Little Snake River or migrants from another location and, if migrants, then from where do they originate? The goals of this study were to better understand the longitudinal and seasonal composition of the fish community of the Little Snake River with an emphasis on locations and movements of humpback chub. Our objectives were to: 1. Describe longitudinal composition of the Little Snake River fish community. 2. Describe seasonal changes in composition of the Little Snake River fish community during spring, summer, and autumn. 3. Determine resident fishes in the Little Snake River. 4. Characterize location and movements of humpback chub in the Little Snake River using PIT tag recaptures and radio telemetry. 5. Determine which species reproduce in the Little Snake River using larval collections.