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"The Colorado is probably the most utilized, controlled, and <br />fought over river in the world. It flows through lands of <br />incomparable beauty and includes nearly seven percent of the <br />nation's contiguous land mass, including parts of seven states. <br />From the time of early settlers to the present, the waters of the <br />Colorado River have been the key to development of the arid <br />region" (Crawford and Peterson, 1974:vi). <br />Waters of the Colorado River basin are not only economically <br />important, but also contain the most distinctive ichthyofauna in <br />North America, with species-level endemism approaching 75% <br />(Minckley, 1991) (93% if undescribed forms and subspecies are <br />included, as in Carlson and Muth, 1989). The parallel importance <br />of economic potential and ichthyofaunal diversity has initiated a <br />class-Lc and ongoing confrontation between development and <br />conservation (see Wydowski and Hamill, 1991). <br />From the conservation viewpoint, at risk is a unique and <br />endemic ichthyofauna of ancient origin, extending as far back as <br />the Miocene (Miller, 1959, 1961; Minckley et al., 1986). These <br />fishes possess remarkable adaptations to survive in a turbulent <br />environment. Foremost are a suite of morphological and anatomical <br />modifications which may act in concert to minimize the river's <br />impact upon the phenotype of the fish while optimizing the <br />abilities of the fish to negotiate boulder-strewn, high velocity <br />rapids. While alternative hypotheses may explain the evolution of <br />these phenotypes, morphological trends across numerous, unrelated <br />taxa speak for commonality in other than phylogeny, and the <br />selective arena of the river seems reasonable (Minckley, <br />1991:128). The majority of these fishes are endangered (or <br />candidates for such listing; see Minckley and Douglas, 1991), due <br />to numerous recent habitat modifications by modern humans. <br />The specialized morphologies of the mainstream Colorado <br />River fish fauna reach their culmination in the phenotype of <br />humpback chub (Gila cypha; Fig. 1--1), the most remarkably <br />specialized minnow in western North America and one of the most <br />bizarre in the world (Miller, 1964; Minckley, 1991; Douglas, <br />1993; and references therein). It is known only from the Colorado <br />River and its major, swift-flowing tributaries (Holden and <br />Minckley, 1980); it occurs only sporadically and is seldom <br />locally abundant, particularly when compared to other indigenous' <br />fishes. Gila cypha has been recorded from: (a) the gorge sections <br />of the Green and Yampa rivers in Utah and Colorado (Green River <br />Wilderness Area and Dinosaur National Monument, respectively); <br />(b) the Colorado River in Utah above Lake Powell (Canyonlands <br />National Park) ; and (c) the Colorado River above its junction <br />with the Green River [between confluences of the Dolores (in <br />eastern Utah) and Gunnison rivers (in western Colorado; Fig. 1-- <br />2a)]. Gila cypha was also within other canyon-bound reaches of <br />the Colorado River, as documented from archaeological remains <br />(Miller, 1955; Miller and Smith, 1984; Sigler and Miller, 1963). <br />1