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However, various problems required plan modification. In the fall of 1999, catch data from the Interagency Standardized Monitoring Program (ISMP) and preliminary sampling effort by our office showed low numbers of young-of-year Colorado pikeminnow in the middle Green River, suggesting catch rates would be too low to calculate a meaningful population estimate. As a result, sampling was confined to the Ouray Backwater Complex for fall 1999 and spring 2000, giving us the best opportunity to obtain recaptures. Population estimates were made for two backwaters in this reach. The entire 40- mile study reach was sampled in fall and spring, 2000, 2001, and 2002, although three passes were completed only once, and two passes on all other occasions. A sampling pass consisted of seining all backwaters > 30 m2 in area within this reach. Backwaters were defined as shallow ephemeral embayments adjacent to the main river channel with no measurable water velocity. All Colorado pikeminnow <100 mm total length (TL) were marked with syringe-injected elastomer (Northwest Marine Technology, Shaw Island, Washington) and released into their backwater of origin. Fish recaptured in an intermediate pass were marked again before release. Overwinter survival probability was calculated by dividing each spring estimate by the estimate from the previous autumn. Overwinter size selective growth and mortality were evaluated using quantile-quantile (q-q) plots of young-of-year Colorado pikeminnow length-frequency distributions from fall and spring (Post and Evans 1989; Converse et al. 1997; Post et al. 1998; McAda and Rye11999). Movement Young-of-year Colorado pikeminnow marked on each sampling pass were used to study movement patterns. The 40-mile reach was divided into eight 5-mile sections. Different colors (e.g., red, orange, yellow, green) and mark locations (i.e., base of the anal fin, left or right side of dorsal fin, posterior or anterior of the dorsal fin) were used to distinguish fish among sampling passes and 5-mile sections. Fish sampling began at Bonanza Bridge at river mile (RM) 289.4 and extended downstream to vii