7963 - Laserfiche WebLink

Home Browse Search

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