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apparent annual mortality rate (1 - S = mortality* 100) estimated for adult Colorado pikeminnow <br />in the Green River Basin. <br />Comparison of recruit abundance in ISMP samples in two periods, 1991 to 1999 and 2000 <br />to 2003, provided even more compelling evidence that poor recruitment played a major role in the <br />decline of abundance of adult Colorado pikeminnow in the Green River Basin during this study. <br />During the 1991 to 1999 period, Colorado pikeminnow recruit abundance was 24.7% of adult <br />abundance. Given that apparent average annual mortality rate of the average-sized fish in the <br />Green River Basin from 1991 to 1999 was about 20% (1 - 0.80 = 0.20* 100), that level of recruit <br />abundance should equal or exceed losses to mortality. Recruitment rates higher than mortality <br />would explain an apparently expanding population of Colorado pikeminnow in the Green River <br />Basin in the period 1991 to 1999, based on ISMP catch/effort data. Similarly, lower abundance of <br />recruits (3.4% of adult abundance) in 2000 to 2003 (including three years at zero), coupled with <br />higher apparent mortality rates, appears to explain, in part, the apparently declining population of <br />Colorado pikeminnow in the Green River Basin in the period 2000 to 2003. <br />An implicit assumption of this recruitment scenario is that ISMP samples accurately <br />portrayed the population structure of Colorado pikeminnow in the Green River Basin. Similarity <br />of the percent of recruits from ISMP samples (3.4%) for 2000 to 2003 (a subset of abundance <br />estimate data) and the proportion of recruits to adults in abundance estimates for the same period <br />(8.9%) mostly validates that assumption. The slightly lower proportion of recruits in ISMP <br />samples compared to abundance estimates is likely explained by the under-weighting of ISMP <br />samples in areas that contained relatively large numbers of recruit-sized Colorado pikeminnow. <br />Only two of 10 ISMP sampling localities (both in the lower Green River reach) were located in <br />areas where 400-449-mm TL Colorado pikeminnow were abundant (McAda 2002; this study). <br />53