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<br />I <br />I' <br />I <br />I' <br />I <br />, <br />I <br />I, <br />I. <br />I <br />I' <br />I <br />I <br />I. <br />., <br />I <br />I. <br />I <br />I <br /> <br />INTRODUCTION <br /> <br />Habitat loss is one of the single greatest causes of declines in populations of native <br /> <br /> <br />fishes in North America (Williams et al. 1989). The need to preserve minimum stream flows <br /> <br /> <br />was recognized by the state of Colorado by the passage of Senate Bill 97 in 1973. Espegren <br /> <br /> <br />(1998) states that most instream flow water right filings in Colorado have been for protecting <br /> <br /> <br />minimum flow for cold water (headwater) habitats. The most common methodologies used in <br /> <br /> <br />Colorado is the R2Cross method (Nehring 1979) and Instream Flow Incremental <br /> <br /> <br />Methodology (IFIM) (Bovee 1982). IFIM estimates the amount of usable habitat for fish as a <br /> <br /> <br />function of discharge by combining habitat suitability curves with the hydraulic model. The <br /> <br /> <br />habitat component of the model has received much criticism because of assumptions implicit <br /> <br /> <br />with using suitability curves and assumptions of positive relationships between habitat <br /> <br /> <br />availability and fish abundance. Validation of these assumptions have been obstacles for <br /> <br /> <br />successfully using IFIM to model minimum flow impacts on large warm water rivers of the <br /> <br /> <br />west slope (Rose and Hahn 1989). <br />Currently there is no standardized approach to establish minimum flow needs on warm <br /> <br />water river sections, and the use of sophisticated models appear to be required in high profile <br /> <br />situations (Espegren 1998). Warm water fish assemblages appear to require a more intensive <br /> <br />approach to instream flow modeling compared to cold water fish communities. Warm water <br /> <br />river reaches tend to be lower gradient and have higher channel complexity and sediment <br /> <br />loads. Warm water fish populations tend to have higher species diversity. Nso habitat <br /> <br />suitability curves derived from microhabitat observations do not adequately describe habitat <br /> <br />use for many warm water species. A broader community-level perspective, as opposed to an <br /> <br />indicator species approach, may be required to protect all habitats of a functioning warm <br /> <br />water stream ecosystem. <br /> <br />I <br />