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<br />Discharge Affects on YOY Colorado Squawfish Production <br /> <br />An analysis of flow data for the Green River suggests that elevated <br />flows during the primary nursery period (Aug-Sept) are detrimental to <br />the survival of young Colorado squawfish. This hypothesis is supported <br />by a regression of C/E values on mean August and September discharges at <br />the Jensen gauging station for all years of the study (1979-84). C/E <br />values were negatively correlated (r--o.89, p-0.05) with combined August <br />and September discharge (F;1gure 4). About 80% of the variation between <br />mean C/E was attributable to the mean daily discharge during August and <br />September, possibly because the quantity of backwater habitat available <br />to young Colorado squawfish also varies inversely with discharge. In <br />1983, CRFP measured the area of backwater habitat at three sites on the <br />Green River when flows released from Flaming Gorge Dam were 800 cf sand <br />4000 cfs (not including inflow of tributaries ). The surface elevation <br />of the river changed by 1.79 ft at RK 508 (RM 3l5), 2.12 ft. at RK 469 <br />(RM 291), and 1.94 ft at RK 403 (RM 250). Although the resultant change <br />in area of backwa ter habitat was not quantified there was a marked <br />change in available habitat between the different flows. In every case, <br />backwa ters that existed at 800 cfs were transformed into flowing habitats <br />at 4000 cfs. <br /> <br />River discharge during the nursery period may also affect the average <br />size of Colorado squawfish larvae collected in fall monitoring program <br />samples. Table 8 gives the mean total length of larvae captured in both <br />the upstream (Strata E & F) and downstream (Strata A & B) nursery areas <br />of the Green River. Although these data show no consistent differences <br />in growth rate between the two areas, in years of high discharge (1983- <br />84) the mean total length of larvae at the end of the growing season was <br />reduced by 27% from that recorded in years of more favorable flows <br />(l979-80). As in the case of C/E, mean total length was negatively <br />correlated (r-O.87, p-0.05) with mean August and Septeaaber discharge <br />(Figure 5). <br /> <br />27 <br />