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o The above results indicate that the drift stations were not sampling the same cohort of <br />larvae, although there could be overlap. The cohorts could be affected by one or more <br />of the following: <br />a) Larval mortality exceeds reproduction between Loma and Westwater. <br />b) Some larvae drift past more than one site, contributing to downstream abundance. <br />c) Some larvae are no longer behaviorally available to passive drift sampling <br />techniques, due to asize-related shift from drift to backwater use at 10-12 mm. <br />d) Spawning occurs between all sites. <br />RECONIMENDATIONS <br />Flows <br />• Peak discharge: We recommend a cycle of moderate and high flow years (peak discharge <br />> 1024 m3/s [36,155 cfs]), while avoiding low flows which favor non-native cyprinids <br />over Colorado pikeminnow. <br />o Moderate to high peak flows resulted in the highest transport abundance of Colorado <br />pikeminnow larvae during this five year study. However, no peak discharges > 1455 <br />m3/s (51400 cfs) occurred, so effects of extremely high discharge events are not <br />known. <br />o The moderate discharge of 813 m3/s (28,700 cfs) resulted in the highest juvenile <br />abundance. <br />o High peak discharges and high runoff flows were most detrimental to non-native <br />cyprinids. <br />• Base flow: After run-off, flows should decline quickly and stabilize, to allow <br />temperatures to rise early, in order to maximize growth and thereby overwinter survival. <br />o Mean length of Colorado pikeminnow in the fall was negatively correlated with the <br />magnitude and duration of peak runoff flows. In 1995, high peak discharge and runoff <br />flows contributed to delayed spawning and decreased degree accumulation, resulting <br />in a shorter, less than optimum growing season. <br />o The greater mean length of Colorado pikeminnow in the fall in low water years was <br />positively correlated with increased overwinter survival. <br />23 <br />