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(all species) in Utah backwaters. The fact that both Colorado pikeminnow YOY numbers and NNC were very high in 1996 suggests increased productivity and reduced competition compared to other years, and both groups benefitted. The role offlows in Colorado pikeminnow reproductive success Flows are an important factor of Colorado pikeminnow reproductive success. However, a shifting flock of variables influence the year end strength of a cohort of Colorado pikeminnow. High peak discharge is probably important for preparing spawning areas by removing fine sediments (Pitlick et al. 1998). High flows are inversely correlated with temperatures which, in combination, delay the onset of spawning. The timing of reproduction coupled with the length of growing season and the available temperatures influence growth and fall size, which in turn influence survival of pikeminnow through winter of their first year. High summer and fall flows negatively affect the amount of nursery habitat available for YOY pikeminnow. High flows and low temperatures also negatively affect the reproductive success of the sympatric and competitive non-native cyprinids. In this study, the extended high flows in 1995 resulted in poor abundance of juvenile pikeminnow in the fall, despite high larval production. The lowest flows, in 1994, resulted in both low larval production and low juvenile abundance, possibly due to the high numbers of non- native cyprinids also present. The second highest and second lowest flow years of 1993 and 1992 resulted in the second and third highest reproduction and juveniles. Whereas, the moderate flow year of 1996 resulted in the highest larval and juvenile abundance, despite high numbers of non-native cyprinids. A moderate flow scenario appears to be the most beneficial to the reproduction and recruitment of Colorado pikeminnow. A moderately high peak flow followed by a swift recession of flows to encourage high temperatures and lengthen the growing season would be ideal in some years. A cycle of flows including some high water years to reduce non-native cyprinid populations as well as moderate years to encourage Colorado pikeminnow reproduction and growth would be an effective management procedure. However, controlling the Colorado River that closely would be problematic. The Gunnison River, as regulated by the Aspinall Unit can only contribute to discharge in the Colorado River, not control it. Manipulating flows may be more difficult than predicting the outcome of flow scenarios. CONCLUSIONS • Objective 1) evaluate the effect of flows on timing and duration of Colorado pikeminnow drift and spawning o High peak discharge had the effect of delaying the onset of spawning. The onset of spawning occurred six weeks later in the highest flow year than the lowest flow year. o These data supported the suggestion that secondary flow spikes were a cue for onset of spawning, as proposed by Nesler et al. (1988). 20