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<br /> <br />site (RK 0 to 76) and 135 km for the Jensen site (RK 348 to 483). All backwater habitats were <br />seined (70 to 100% of total backwater area) during these surveys. The Canyonlands reach was <br />not sampled after runoff in summer 1996 because only 29 fish were marked during spring and it <br />was unlikely that they would be recaptured. <br />In addition to our sampling, other fishery investigators also recorded captures of marked <br />fish. Studies that were coincident with our investigations were Interagency Standardized <br />Monitoring Program (ISMP), Colorado Squawfish Nursery Habitat Availability, and Overwinter <br />Survival of Age-O Colorado Squawfish in the Green and Colorado Rivers, and Samplingfor <br />Larval Razorback Sucker in Canyonlands National Park and Glen Canyon National Recreation <br />Area. <br /> <br />Factors that Influence Overwinter Survival <br />A variety of factors may influence overwinter survival of age-O Colorado squawfish. <br />Two factors related to operation of Flaming Gorge Dam are variability and magnitude of <br />discharge in the Green River during winter. To evaluate potential importance of these variables, <br />graphical plots were constructed that depict survival probability as a function of average daily <br />discharge and its CV during winter. Inspection of U.S. Geological Survey discharge records for <br />the Green River near Jensen, Utah, suggested that the period from 1 October to 28 February was <br />relatively stable and not influenced by spring runoff events (Figure 2); thus this interval was <br />defined as the winter period. Overwinter survival probabilities for the Canyonlands and Jensen <br />sites were plotted as functions of CV and mean discharge. Discharge data were obtained from <br />U.S. Geological Survey records (provisional) from the Green River (gage number 09315000; <br />Canyonlands site) and Jensen (gage number 09261000), Utah, gaging stations. <br />Size and energy reserves at the beginning of winter are biological factors that may <br />influence overwinter survival of age-O Colorado squawfish (Shuter and Post 1990; Thompson et <br />al. 1991). Total length was used as a measure of size and energy reserves. We attempted to <br />record TL of at least 100 young Colorado squawfish from each study site on each autumn or <br /> <br />8 <br />