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growth patterns of Colorado pikeminnow, based on analysis of capture-recapture data, has not been conducted in the Green River sub-basin. Most Colorado pikeminnow exist in rivers regulated by main stem dams. Thus, flow and water temperature management in the Green, Colorado, and San Juan River main stems have focused on restoring regimes that more closely resemble historical conditions (Poff et al. 1997; Muth et al. 2000). Release of propagated Colorado pikeminnow in the Colorado and Green River sub-basins has been limited because natural populations were thought sufficient to effect recovery (Tyus 1991). Only in the San Juan River sub-basin has use of propagated fish been extensive. Another recent emphasis of the RIP was to reduce effects of non-native fishes, in particular, large-bodied predaceous forms. Smallmouth bass Micropterus dolomieu and particularly northern pike Esox lucius, may be a formidable threat to even large-bodied Colorado pikeminnow, particularly in the Yampa River of the upper Green River sub-basin. STUDY AREA The Green River sub-basin (hereafter Green River Basin unless specified) drains high- elevation areas in southwestern Wyoming, northeastern Utah, and western Colorado (Fig. 1). The study area focused mainly on warmwater stream reaches designated as critical for recovery of Colorado pikeminnow (U. S. Fish and Wildlife Service 2002), which included the lowermost 193 RK of the Yampa River, the 555.6-RK reach of the Green River (including the lower Duchesne River) downstream of the confluence of the Yampa River to the Colorado River, and the lower 167.4 RK of the White River. River geomorphology in the study area varied; relatively low gradient, depositional reaches in valleys were interspersed with higher gradient, erosive, canyon-bound reaches. Alluvial river reaches were more braided, had mostly sand or gravel 14