Laserfiche WebLink
<br />populations in the Colorado River near Grand Junction after three consecutive <br />years of low spring runoff. McAda and Kaeding (1989) and Valdez (1990) <br />observed the same phenomenon for the Colorado River in Utah for the same <br />species over the same period. High spring runoff may be important in reducing <br />the numbers of these introduced fishes. Numerous investigators have <br />hypothesized that introduced species have negatively affected Colorado <br />squawfish through predation or competition (e.g. Karp and Tyus 1990 and <br />references therein). Therefore, reducing the population size of introduced <br />species through high spring flows is desirable. Minckley and Meffe (1987) <br />reported that some introduced species were eliminated from some Arizona <br />streams after high runoff events. Introduced species will never be eliminated <br />from the Colorado River by high runoff, but regular high-runoff events may <br />play a role in limiting the numbers of undesirable species. <br />Razorback sucker <br />High spring runoff may also be important to successful reproduction of <br />razorback sucker. Although spawning is being attempted, recruitment to the <br />adult population is very low or nonexistent in the Upper Colorado River Basin <br />(McAda and Wydoski 1980; Tyus 1987). Razorback suckers spawn in spring (McAda <br />and Wydoski 1980; Tyus 1987; Osmundson and Kaeding 1990), during the period <br />when streamflow is at or near the annual maximum. Water temperature during <br />spring runoff is relatively low in the main channel (often less than 15 °C, <br />USGS records), yet Marsh (1985) reported the highest hatching success for <br />razorback sucker eggs at 20 °C. Hamman (1985) and Inslee (1982) also believed <br />the optimum temperature for reproduction was at or near 20 °C, a temperature <br />not reached in the main channel of the Colorado River for a month or more <br />27 <br />