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Five of 10 ISMP sampling localities were taken in the Yampa and White rivers, localities where <br />recruit-sized Colorado pikeminnow were either absent or rare, and the remaining three ISMP <br />localities were in the middle Green River reach. Given the relative paucity of ISMP sampling <br />sites where recruit-sized Colorado pikeminnow were abundant, the slight discrepancy between the <br />percent of recruit abundance for ISMP and abundance estimation data for the period 2000-2003 is <br />easily understood. <br />Some have argued that because Colorado pikeminnow are long-lived and recruitment may <br />be episodic, comparisons of recruitment in the periods 1991 to 1999 and 2000 to 2003 are not <br />valid. A reason offered is that we simply may not have observed a recruitment event during that <br />shorter 2000 to 2003 time period, and if one had occurred, it would balance out mortality and <br />result in a stable population. Recruitment does, however, appear to occur with reasonable <br />frequency, (e.g., Fig. 19), with moderate (N = 3) or high (N = 4) recruitment events occurring in <br />seven of nine years from 1991 to 1999. The population rate of change analysis supported that <br />assertion because in seven of nine annual intervals from 1991 to 2000, I-values were > 1. Based <br />on size-structure of Colorado pikeminnow in the Green River Basin, recruitment was low in all <br />years of this study, 2000 to 2003. The population rate of change analysis also supported that <br />assertion, because I-values were < 1, sometimes substantially so, in all years. Thus, size-structure <br />metrics and the population rate of change analysis jointly support the thesis that reduced <br />recruitment in recent years was a main factor in the apparent decline of Colorado pikeminnow <br />, abundance during the study period. <br />Some may also argue that the high recruitment years observed from 1992 to 1994 may be <br />sufficient to maintain the population for many years. However, if one assumes an annual survival <br />rate of 0.80 for fish recruited in those three high recruitment years, on average, only 21% of those <br />54