Laserfiche WebLink
probabilities of capture may be needed in river reaches with relatively small populations of <br />Colorado pikeminnow if more precise estimates are desired. <br />• Capture-recapture sampling conducted in sections of the Green River Basin from 2000 <br />to 2003 suggested a decline in abundance of Colorado pikeminnow in the Green River Basin, <br />Colorado and Utah, over the study period. Based on the trend in annual point estimates, <br />reductions were most severe in the middle Green River and the White River. Those reaches <br />supported the highest number of Colorado pikeminnow in the Green River Basin. Reductions in <br />abundance were less severe in the Yampa, Desolation-Gray Canyon, and lower Green River <br />reaches. Significance of trends in point estimates were based on comparison of confidence limits <br />for pairs of years, regression analysis to investigate the strength of trends of point estimates over <br />time, the relative precision of point estimates, and our perception of the biological importance of <br />the trends observed. <br />• Survival rates for adult Colorado pikeminnow from 2000 to 2003 were lower than <br />survival rates estimated from ISUT data collected from 1991 to 1999. This suggested that <br />apparent declines in abundance of adult Colorado pikeminnow in 2000 to 2003 were caused, in <br />part, by lower survival rates. <br />• There was no support for the hypothesis that reduced survival of adult Colorado <br />pikeminnow was due to sampling mortality. <br />• Abundance of recruit-sized fish during 2000 to 2003 sampling in the Green River Basin <br />was lower than from ISMP sampling from 1991 to 1999. Recruitment rates may be less than <br />mortality rates of adults during the study period. This suggested that apparent declines in <br />abundance of adult Colorado pikeminnow in the Green River Basin in 2000 to 2003 were caused, <br />in part, by lower recruitment rates. <br />59