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Length-frequency distributions for the upstream Yampa River, White River, and middle Green River reaches (Figs. 14-16) suggested presence of a larger proportion of relatively large Colorado pikeminnow, and relatively fewer fish less than 450-mm TL. In those reaches, only 7.0% of all Colorado pikeminnow captured were less than 450-mm TL. In the Yampa River, only one Colorado pikeminnow smaller than 450-mm TL was captured from 2000-2003 (2000) In contrast, the proportion of relatively small Colorado pikeminnow increased progressively downstream in the Green River (Figs. 17 and 18). For example, from 2001 to 2003, 24.7% of the Colorado pikeminnow sampled in the Deso-Gray Canyon reach of the Green River were < 450- mm TL. In the lower Green River reach, abundance of relatively small fish < 450-mm TL (including many < 100-mm TL) was even higher, at 68% of all Colorado pikeminnow captured Population-structure of recruit and adult Colorado pikeminnow in ISMP samples changed between the two periods, 1991 to 1999 and 2000 to 2003 (Fig. 19). Number of Colorado pikeminnow recruits (n = 186) in the period 1991 to 1999 averaged 24.7% (7.9 to 58.5%) of the number of adults in samples (n = 826). During the period 1991 to 1999, there were four years (three from 1992 to 1994) when proportion of recruits was high (>20%), three years when proportion of recruits was moderate (>10 to 20%), and two years when it was low (0 to 10%). In the period 2000 to 2003, number of Colorado pikeminnow recruits (n = 14) was only 3.4% (0 to 6.6%) of the number of adults present (n = 418). From 2000 to 2003, proportion of recruit-sized Colorado pikeminnow was low in all four years and zero in three of those (2001 to 2003). DISCUSSION Comparison of the point estimates derived from capture-recapture sampling and data analysis suggested that abundance of adult Colorado pikeminnow in the Green River Basin 38