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<br />. <br /> <br />. <br /> <br />Provision of sufficient water quantity and timing of flows delivered to certain <br />river locations are considered of utmost importance for recovery of endangered <br />fishes in the Yampa River. Delineation of critical river reaches are presented <br />in Table 1. The following briefly reviews the needs of the endangered fishes <br />(for further detail see Tyus and Karp 1989) by season (Julian dates represent <br />the onset and end of each season). Because life history and flow requirements <br />do not change precisely with Julian defined seasons, actual interim flow <br />recommendations are made on a monthly basis (Table 2). Mean monthly flows hide <br />the variability inherent in the natural river system and are used only to <br />identify water volumes, The 50% exceedence flows (equalled or exceeded 50% of <br />the time - see example Flow Duration Curve in Figure 2), which correlate <br />closely with average monthly flows for the period of record, are presented in <br />Table 2 and Figure 2. Flow events considered important toward recovery of the <br />rare Colorado River fishes in the Yampa and Green rivers are presented. In <br />making its recommendation, the Service recognized that protection of a single <br />species or life history stage does not adequately protect all species, because <br />each has different requirements for survival. <br /> <br />I. Spring (March 21-June 21) <br /> <br />Colorado sauawfish <br /> <br />The reproductive cycle in Colorado squawfish presumably begins soon after <br />spawning, but gonadal activity increases in spring in response to endogenous <br />and exogenous factors. In early spring, adults move into flooded or <br />protected areas where they feed and ostensibly prepare for spawning. Annual <br />spawning migrations are associated with high spring flows, and on the <br />average, radiotagged adults in the Yampa River initiated migrations with <br />flows ranging from about 4,200 cfs to 8500 cfs (Tyus and Karp 1989). Spring <br />migrations were also associated with increasing water temperatures that <br />exceeded about 14C (range 9.2-19.4C), and a long period of daylight (summer <br />solstice, June 19). These relationships are similar in the Green River as <br />well, and chemical imputs from flooded lands, and other cues may act in <br />concert or in sequence with flows, temperatures, and photoperiod to <br />influence timing of the spawning migrations. Spawning of Colorado squawfish <br />in the Yampa River, 1981-1988 occurred about 26 days (range 17-33 d) after <br />the start of spawning migrations, with minimum water temperatures of 19C and <br />maximum temperatures of 24C. Spawning generally occurred earlier in low <br />water years and later in high water years--presumably in response to changes <br />in the annual distribution hydrograph. Although all of the environmental <br />conditions required in the spawning reaches remain unknown, some <br />requirements include cleaning and preparation of cobble beds, and formation <br />of eddy habitats used by staging fish. In addition, high spring flows <br />mobilize and deliver sediment downstream, creating and maintaining nursery <br />habitats in the Green River. <br /> <br />Razorback sucker <br /> <br />Reproduction of the razorback sucker is not well understood with respect to <br />riverine conditions needed for migration cues, vitellogenesis, final <br />maturation, egg deposition, and larval survival. However, spawning in the <br />lower Yampa and upper Green rivers (1975, 1981, 1988 and 1989) occurred with <br />increasing flows and temperatures associated with highest spring runoff <br />(average 14C, range 9-17C). Curtailment of hi9h spring flows in the Green <br /> <br />3 <br />