Laserfiche WebLink
was positive, total length was increased using a weight-length regression equation. If fish growth was <br />negative, total length was held constant at the value for the previous day. <br />RESULTS AND DISCUSSION <br />Overwinter Survival and Movement of Young-of-Year Colorado Pikeminnow <br />Population and Overwinter Survival Estimates <br />Over a three year period of this study, a total of 732 young Colorado pikeminnow ( 30-100 mm <br />TL) were captured, 404 were marked and released (fish captured on the last pass during spring sampling <br />were not marked), and 38 fish were recaptured. In the first year of the study (fall 1999, spring 2000), we <br />concentrated our sampling in the Ouray Backwater Complex and made population estimates for two <br />backwaters (BA) for the fall and spring. In BA#1 the estimate was 218 fish in the fall and 153 fish in the <br />spring; in BA#2 the estimate was 87 fish in the fall and 115 fish in the spring. All these estimates were <br />imprecise, with the coefficient of variation (CV) ranging from 0.22 to 0.83, the result of small numbers of <br />captures and recaptures. The probability of capture for individual fish was highly variable, ranging from <br />0.01 to 0.32. <br />The second kind of abundance estimate was for the 40-mile reach. For the autumn of 2000, we <br />estimated 735 age-0 fish in the reach, and for the spring 2001, we estimated 260 age-1 fish. For autumn <br />of 2001, the estimate was 670 age-0; for spring 2002, the estimate was 1,320 age-1 fish. These estimates <br />were also highly variable, with CV ranging between 0.25 and 0.59. The probabilities of capture ranged <br />from 0.03 to 0.16. In general, the probabilities of capture were smaller for the 40-mile reach than for the <br />individual backwaters, because far fewer seine hauls per backwater were made. <br />Oveiwinter survival estimates for the 40-mile reach could not be calculated because population <br />estimates were too imprecise. Two of four spring estimates were greater than the corresponding fall <br />estimates. We looked at fall and spring length-frequency distributions for evidence of size-selective <br />x