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these dams have eliminated suitable habitat for native fishes, including Colorado <br />pikeminnow, from river reaches downstream for approximately 50 miles below Flaming <br />Gorge Dam and Navajo Dam. In addition to main stem dams, many dams and water <br />diversion structures occur in and upstream from critical habitat that reduce flows and <br />alter flow patterns, which adversely affect critical habitat. Diversion structures in critical <br />habitat divert fish into canals and pipes where the fish are permanently lost to the river <br />system. It is unknown how many endangered fish are lost in irrigation systems, but in <br />some years, in some river reaches, majority of the river flow is diverted into unscreened <br />canals. The high spring flows which maintain habitat diversity, flush sediments from <br />spawning habitat, increase invertebrate food production, form gravel and cobble deposits <br />important for spawning, and maintain backwater nursery habitats have been reduced by <br />flow regulation of dams and by water diversions (McAda 2003; Muth et al. 2000). <br />Predation and competition from nonnative fishes have been clearly implicated in the <br />population reductions or elimination of native fishes in the Colorado River Basin (Dill <br />1944; Osmundson and Kaeding 1989; Behnke 1980; Joseph et al. 1977; Lanigan and <br />Berry 1979; Minckley and Deacon 1968; Meffe 1985; Propst and Bestgen 1991; Rinne <br />1991). Data collected by Osmundson and Kaeding (1991) indicated that during low <br />water years nonnative minnows capable of preying on or competing with larval <br />endangered fishes greatly increased in numbers. <br />More than 50 nonnative fish species were intentionally introduced in the Colorado River <br />Basin prior to 1980 for sportfishing, forage fish, biological control and ornamental <br />purposes (Minckley 1982; Tyus et al. 1982; Carlson and Muth 1989). Nonnative fishes <br />compete with native fishes in several ways. The capacity of a particular area to support <br />aquatic life is limited by physical habitat conditions. Increasing the number of species in <br />an area usually results in a smaller population of most species. The size of each species <br />population is controlled by the ability of each life stage to compete for space and food <br />resources and to avoid predation. Some life stages of nonnative fishes appear to have a <br />greater ability to compete for space and food and to avoid predation in the existing <br />altered habitat than do some life stages of native fishes. Tyus and Saunders (1996) cites <br />numerous examples of both indirect and direct evidence of predation on razorback sucker <br />eggs and larvae by nonnative species. <br />Threats from pesticides and pollutants include accidental spills of petroleum products and <br />hazardous materials; discharge of pollutants from uranium mill tailings; and high <br />selenium concentration in the water and food chain (USFWS 2002a). Accidental spills of <br />hazardous material into critical habitat can cause immediate mortality when lethal <br />toxicity levels are exceeded. Pollutants from uranium mill tailings cause high levels of <br />ammonia that exceed water quality standards. High selenium levels may adversely affect <br />reproduction and recruitment (Hamilton and Wiedmeyer 1990; Stephens et al. 1992; <br />Hamilton and Waddell 1994; Hamilton et al. 1996; Stephens and Waddell 1998; <br />Osmundson et al. 2000). <br />10