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. Habitat use.-The timiny of spawning, and thus hatching, is critical to <br />larval survival. Spawning occurs during the period of declining flows <br />following spring peak runoff and increasing temperatures, and it occurs <br />earlier in low flow years and later in high flow years. This temporal <br />adaptation (mid-summer spawning associated with decl-fining flows) is <br />associated with the reproductive strategy of the species (Tyus 1986), <br />whereby the length of exposure of eggs and larvae to lethal cold <br />temperatures of spring and to predation is reduced, and the short growth <br />period is balanced by movement of fish into backwater nursery habitat. <br />Backwaters (shallow ephemeral shoreline embayments) were heavily utilized <br />as nursery habitats by young Colorado squawfish in the Green River, as <br />previously noted by Holden and Stalnaker (1975) and Tyus et. al. (1982). <br />These backwaters were created by gradually decreasing summer flows <br />following spring runoff (snowmelt). <br />The Colorado squawfish reproductive strategy that has evolved over <br />thousands of years may no longer be adaptive for the Green River. <br />Increased predation by introduced non-native fishes and altered flow <br />regimes from Flaming Gorge Dam have produced an environment for which the <br />Colorado squawfish is ill-suited. Reduced standing crop and growth of <br />young fish brought about by high summer flows was viewed as a significant <br />impact that could .preclude management actions (Rose and Hamill 1988). <br />However, changes in water management to flow regimes more optimal to <br />young Colorado squawfish could overcome this problem (B.D. Williams, U.S. <br />Bureau of Reclamation, personal communication). We believe the mainstream <br />Green River can be managed as a Colorado squawfish nursery area by <br />15 <br />