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<br />11/14/01 draft report, Schmidt and Box <br /> <br />Abstract <br />Field sampling and a simulation model demonstrate that fall populations of Colorado <br />pikeminnow (Ptychocheilus lucius) larvae in backwaters of the middle Green River are a very small <br />proportion of the number of larvae that drift downstream a few months earlier. In some years, <br />larvae are more densely congregated in restricted meandering areas of the middle Green River, but <br />the population is more evenly distributed in other years. A simulation model predicts that fewer <br />larvae populate backwaters of the middle Green River if drift occurs at times when discharge is <br />high, such as caused by delayed release of high discharges from Raming Gorge Dam. Channel <br />simplification has the potential to decrease the role of restricted meandering reaches as larval <br />habitat. The simulation model does not do a good job of predicting variation in mean catch per unit <br />effort oflarval fish, indicating that parameterization of the model and the field sampling program on <br />which catch per unit effort is calculated should be evaluated. Many of the critical parameters that <br />control abiotic factors of larval drift are not known at this time. <br />Keywords: Colorado pikeminnow, fluvial geomorphology, Green RiVer, simulation model, dams <br /> <br />2 <br />