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pikeminnow in the Colorado River from 1991-1994. There, survival rates for adult fish ranged <br />from 0.82 to 0.87 using two different analytical techniques (Osmundson et al. 1997; Osmundson <br />and Burnham 1998). The consistently lower recent survival estimate may be at least partially <br />responsible for declines in abundance of adult Colorado pikeminnow in the Green River Basin. <br />Comparison of the shape of the length-dependent survival rate curve from 1991-1999 <br />compared to that for the 2000 to 2003 period suggested different relationships in the two periods. <br />The 1991 to 1999 relationship showed that survival increased as a function of fish TL, eventually <br />approaching an asymptote of 1. The asymptote near 1 was an artifact of the logit relationship as <br />we do not reasonably expect 100% survival of larger fish. A key point was that a quadratic term <br />added to the relationship had a positive (albeit non-significant) slope, which indicated that <br />survival of larger and older age-classes continued to increase. <br />The survival relationship for Colorado pikeminnow for the 2000 to 2003 period was <br />different than for the 1991 to 1999 period. Addition of polynomial terms showed very high <br />survival of very small fish (we truncated the relationship at the lowest point for smaller fish at <br />350-mm TL), which was again an artifact of trajectory of the predictive model. We did this <br />because it seemed reasonable that survival of smaller-bodied Colorado pikeminnow would <br />continue to decline, similar to that for the 1991-1999 period. More importantly, the relationships <br />that described survival of larger-bodied fish for the 2000-2003 period peaked at about 580-mm <br />TL, after which survival rate declined. This was the result of the large effect for the negative <br />quadratic term for the survival rate relationships. The relationship was nearly identical when the <br />data were re-analyzed without the four largest fish (> 900-mm TL) included, which suggested <br />that the few large individuals were not the cause of the negative quadratic term. Further <br />investigation of the capture histories showed that of the 18 fish > 800-mm TL that were captured, <br />47