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27. <br />Basin, were better able to survive and successfully recruit under those • <br />natural conditions. Most species introduced to the Colorado River Basin <br />are native to areas experiencing a lesser degree of fluctuation <br />hydrologically. <br />Haynes et al. (1985a, b) reported better reproductive success of native <br />fishes relative to introduced species in the Colorado River Basin in years <br />of high peak flows. In 1983 and 1984 peak flows on the Yampa River <br />exceeded 20,000 cfs. Collection rates for Colorado squawfish larvae <br />were 800 percent higher than in years with flows less than 20,000 cfs. <br />The recurrence interval for a 20,000 cfs flow is 20 years for the lower <br />Yampa River. Haynes et al. (1985a, b) suggested that long-lived species <br />such as the Colorado squawfish and razorback sucker may have 0 <br />adapted to the extreme year-to-year fluctuation common to Upper Basin <br />rivers by relying on particular hydrologic conditions (high flow years) for <br />recruitment. The relatively shorter-lived species, which is representative <br />of introduced species in the Upper Basin, would be at a disadvantage <br />reproductively under historic conditions where annual flow variation is <br />great (Haynes et al. 1985a, b). <br />Maddux et al. (1987) reported that extreme flow changes inhibited <br />tributary spawning species. In the Grand Canyon of the Colorado River <br />most of these are exotic species. Native species which spawn in the <br />main channel, in relatively deep water would be effected to a lesser <br />0