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<br />fishes using PHABSIM have been judged <br />inappropriate because certain habitats used <br />by the fish were not easily simulated, mi- <br />crohabitat parameters used were not ac- <br />cepted as the only factors required by the <br />fish, and conflicting flows have been ob- <br />tained for different species and life stages <br />in the same location (Valdez et al. 1990; <br />unpublished FWS reports on file in Grand <br />Junction, Colorado). Because microhabitat <br />availability is not the only factor limiting <br />fish populations (Orth 1987), the IFIM or <br />any other method cannot be accepted as <br />valid for determining flow needs of en- <br />dangered fishes unless the ecosystem is <br />wen understood and the relationship be- <br />tween flows and standing crops of target <br />organisms is established. <br />Many western states now acknowledge <br />fisheries resources as a beneficial use of <br />water (Reiser et al. 1989) and set standards <br />to protect these resources based on mini- <br />mum flows (McKinney and Taylor 1988). <br />Because minimum flows are usually de- <br />fined as those needed to protect the envi- <br />ronment to a reasonable degree (e.g., Col. <br />Rev. Stat. ~ 37-92-102[3]), state water boards <br />and other water development interests are <br />hesitant to endorse use of empirical fish <br />habitat data for instream flows without the <br />use of some model that allows them to <br />choose minimum flows. For this reason, <br />agencies have spent much time and money <br />developing minimum flow methods that <br />are acceptable for water appropriation. <br />Stalnaker (1990) argued that "minimum <br />flow is a myth," when minimum flows have <br />been the basis for reserving water for <br />stream fisheries. He points out that as wa- <br />ter is appropriated, the minimum flow be- <br />comes the management target. This prac- <br />tice means that the minimum becomes the <br />average flow, and resultant low flows are <br />undesirable for stream communities. Only <br />instream flow regimes that provide wet, <br />average, and dry years will meet life re- <br />quirements of most fishes (Stalnaker 1981) <br />and this includes endangered Colorado <br />River fishes. <br />Thus,. recovery of Colorado River fishes <br />is problematic given the survival flow phi- <br />losophy because: (1) habitats are presumed <br />marginal, (2) there is insufficient infor- <br />mation on the life history of the fishes, and <br />(3) water managers tend to consider only <br />minimum flows. <br /> <br />I H. M. Tyus <br /> <br />Recovery Flows <br /> <br />Recovery of endangered Colorado River <br />fishes to a nonendangered status requires <br />a guiding philosophy that is different from <br />the philosophy that prevails in commercial <br />and sport fisheries management. Instead, <br />a conservation ethic (Soule and Wilcox <br />1980; Frankel 1983) must be developed to <br />perpetuate natural systems. Management <br />practices must be developed to achieve ad- <br />equate distribution, abundance, and rela- <br />tive numbers of species, not mere "status <br />quo." Thus, effective recovery of the en- <br />dangered fishes will require new research <br />and management methods to protect and <br />restore stream resources as the highest goals <br />(Beecher 1990) for instream standards. <br />In identifying such standards, it is nec- <br />essary to determine the ecological require- <br />ments and specific habitat needs of the <br />fishes. These requirements and needs <br />would be best evaluated in least-altered <br />systems in which the fish are most abun- <br />dant. The need to evaluate endangered <br />species in least-altered systems is based on <br />the assumption that conditions in which <br />a species evolves are also those in which <br />it is most likely to maintain an adaptive <br />advantage over other forms. However, <br />habitats used by endangered fishes in the <br />upper Colorado River basin continue to <br />change, and an evaluation of optimum hab- <br />itat requirements is problematic. <br />Habitat changes that have resulted in the <br />endangerment of Colorado River fishes are <br />unknown, but they are due in part to hu- <br />man-induced change. As an example, early <br />operation of Flaming Gorge and Fonte- <br />neUe dams on the upper Green River in <br />the 1960's eliminated most of the native <br />fishes in 128 km of river above Dinosaur <br />National Monument (Baxter and Simon <br />1970; Vanicek et al. 1970) and recent op- <br />erations have not provided acceptable flow <br />and temperature conditions for native fish <br />populations for many kilometers down- <br />stream (Vanicek et al. 1970). Standing crops <br />of endangered fishes in the Green River <br />below its confluence with the Yampa River <br />are presumably being maintained by the <br />more natural flow and temperature regi- <br />mens of the latter system (Holden and Wick <br />1982; Tyus and Karp 1989). Successful re- <br />production of Colorado squawfish in the <br />lower Green River continues because of <br /> <br />31 II~ <br />