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<br />" <br /> <br />Peaking operations at Flaming Gorge are attenuated in relation to distance downstream from <br />the dam. Therefore, baseflow instability (Figures 12 and 13) progressively worsens upstream from <br />Jensen and may be severe in the Echo and Brown Park reaches. Elsewhere between Jensen and the <br />dam, the river is constrained in canyons and the problem may be somewhat aI1!~liorated by <br />geomorphology. However, peaking flows are known to interrupt insect emergences that feed the <br />trout fishery in Red Canyon immediately downstream from the dam (my observation and Larry <br />Crist, Bureau of Reclamation, Salt Lake City, UT, personal communication). Similar effects were <br />observed on the Missouri River below Holter Dam in Montana and outcry from fly fishermen <br />caused load control operations to be shifted to another dam. The effect was a translocation of <br />stream regulation effects from one river to another, thereby confounding management objectives <br />(Stanford and Hauer 1992). This illustrates the potential difficulty of changing dam operations to <br />meet the needs of endangered fishes in potamon reaches of the Upper Colorado River Basin, if <br />rhithron trout fisheries might be influenced in the process. <br /> <br />Stream Regulation Mediates Invasions of Nonnative Predators and Complicates Provision of <br />Instream Flows to Protect Endangered Fishes <br />Introduction of trout and other nonnative fish in regulated streams is an enormously <br />confounding problem in the interpretation of the ecology of regulated streams because the native <br />species virtually always seem to decline in the presence of exotics, especially if the river is <br />regulated. This pervasive ecological problem has been reviewed thoroughly (e.g., Mooney and <br />Drake 1986). Clearly, predation of natives, including endangered fishes, by exotics does occur in <br />the Upper Colorado River Basin; and red shiners (Cyprinella lutrensis), fathead minnows <br />(Pimephales promelas), walleye (Stizostedion vitreum), northern pike (Esox lucius Linnaeus), <br />channel catfish (Ictalurus punctatus), largemouth bass (Micropterus salmoides), smallmouth bass <br />and green sunfish (Lepomis cyallellus) are especially problematic invaders (cf., Karp and Tyus <br />1990, Tyus 1991b, Tyus and Haines 1991). However, Meffe (1984) and Minckley and Meffe <br />(1987) showed that intense flooding in rivers in the southwestern United States was positively <br /> <br />36 <br />