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<br />.t <br />,,~-' <br /> <br />:-:-1 <br /> <br />GRAND CANYON NATIVE FISH MANAGEMENT <br /> <br />11 <br /> <br /> <br />periods, as occurs in other southwestern streams (Rinne 1975, Minckley and Rinne 1985). <br />Backwaters and sites with woody debris could have supported diverse and abundant <br />invertebrate communities (Carlson and Muth 1989). Autotrophic production may have been <br />considerabIe as suspended sediment and organic materials settled upon return to base flow <br />conditions or during droughts. <br /> <br />Adaptations of the Native Fish Fauna-Native fishes of the Grand Canyon area evoIved with <br />and adapted to the habitats and habitat-forming processes of the pre-dam CoIorado River and <br />its tributaries. The most obvious adaptations are the morphoIogical specializations common <br />to much of the fauna (reviewed by Mincldey 1991). AduIt body sizes are large (excepting <br />speckled dace, Rhinichthys oscuIus), and their shapes are fusiform and streamlined. <br />Presumed adaptations to turbuIence and high current velocities include the evolution of <br />depressed crania; large predorsaI humps or keels; elongated, thin caudal peduncIes; and large <br />falcate fins. There is a nearIy uniform presence of small eyes; smaII, deepIy embedded <br />scales; and thick, leathery skin that maximizes streamlining characteristics and minimizes <br />abrasion from. suspended sediment. <br /> <br />'-<- <br /> <br />'c',,, <br /> <br />:.:t~_ <br />~~ <br />~fi <br />:r), <br />,. <br />.::~/. <br /> <br />t;. ... <br /> <br />'-' <br /> <br />Native fishes developed wide physioIogical toIerances to temperature (approximately 0-30 <br />C; reviewed by Lechleimer 1992); tolerances of embryos (Hamman 1982, Marsh 1985) and <br />larVae (Lupher and Clarkson 1994) are more restricted.: Longevity allowed large-bodied <br />. Species to live beyond many short-term but common climatic events that rendered conditions <br />unsuitable for' successful reproduction (Mincldey 1991). The native fishes specialized <br />behaviolally to cope with probIems associated with floods, incIuding avoidance of abrasive <br />forceS and current velocities of these events (Meffe and Mincldey 1987, Mincldey and Meffe <br />1987). TIming of reproductive activity to, coincide with periods of benign environmental <br />conditions promote increased survivorship of offspring (Tyus and Karp 1989). Aberrations. <br />in~ discharge patterns during reproductive periods have been demonstrated to result in <br />pronounced increases in mortality of earIy life stages (Harvey 1987, Clarkson and Robinson <br />1993): <br /> <br /> <br />.. <br />-,. <br /> <br />,,-,' <br />"'-.' <br />.' <br />~t.~. <br /> <br />" Large-bodied native fishes utilize the larger rivers for spawning in the upper basin (Tyus <br />.1987; 1990, Tyus and Karp 1989, Kaeding et aI. 1990).. There is evidence of post-dam <br />ri1ainstem spawning by some native species in Grand Canyon, but recruitment has been <br />cOnsidered largely unsuccessful (Kaeding and Zimmermann 1983, Maddux et aI. 1987, <br />Hoffnagle 1994). Lack of successful reproduction in the CoIorado River in Grand Canyon <br />has been attributed primarily to low temperatures that retard or preclude embryonic and <br />IarviI1 development (Hamman 1982, Marsh 1985). The Colorado River in Grand Canyon <br />otherwise contains habitat characteristics similar to those successfully used for reproduction <br />by humpback chub and other native species in the upper basin (Kaeding et aI. 1990, Valdez <br />1993). '\ <br /> <br />(~);~ <br />J:i/'" <br />::'f'': <br />~4:~' <br />;1li <br />~ <br />'1~~~ <br /> <br />J<:, <br />