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(R. A. Valdez, pers. comm.). Kaeding and Zimmerman (1983:585) <br />similarly noted that individuals larger than 145 mm TL were never <br />taken in the mainstream above the confluence, even though mature <br />fish were present there. Third, hydrologic and thermal profiles <br />of the LCR are consistent with the pre-dam Colorado River, but <br />differ markedly from the post-dam river. <br />If G. cypha has altered its life history to accommodate dam- <br />induced changes in the mainstem Colorado River, then its long- <br />term persistence within the Grand Canyon is tied more intimately <br />to the LCR than previously believed. The evolutionary effects of <br />such a life-history alteration can only be speculated upon. <br />one potential saving factor (Committee, 1991:4) is that <br />ecosystem components are linked to one another and to flow <br />regimes imposed by the dam. Flows can therefore be manipulated to <br />manage the river and protect the environment in GCNP. This offers <br />the possibility that temperature, sediment load, and volume of <br />discharge from the dam may eventually mimic a natural hydrograph, <br />at least during parts of the year. This could, in turn, enhance <br />long-term survival of G. cypha (but may conversely allow upriver <br />movement of introduced fishes from Lake Mead; Minckley, <br />1991:146). In spite of such optimism, political and economic <br />forces drive the system, even at the expense of cost efficiency <br />(Leopold, 1991). These forces likewise impact indigenous fishes, <br />and transform their conservation from the realm of science to <br />that of politics. <br />12