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on0373 remain with regard to habitat and flow needs, reproductive success and reestablishment of viable populations. An overview of the occurrence and habitat types of each of the endangered species is provided below. For a more detailed description of habitat requirements, behavior and the occurrence of the endangered fish, readers are referred to the Phase II Flow Recommendations - Yampa River (U.S. Fish and Wildlife Service, 1989) and the Final Biological Opinion for the Operation of Flaming Gorge Dam (U.S. Fish and Wildlife Service, 1992). Colorado Squawfish IPtychocheilus luciusl The Colorado squawfish was listed as endangered in 1967 by the U.S. Fish and Wildlife Service. The Colorado squawfish evolved as the main predator fish in the CoIorado River system. In the Upper Colorado River Basin, the species historically occurred in the CoIorado, Green, White, Yampa, Dolores, Gunnison, San Juan, Uncompahgre and Animas rivers and in many small tributaries. Today, most of these areas contain only remnant populations and few reproducing populations exist. CoIorado squawfish require a wide distribution of habitat types to satisfy various life history requirements and in response to seasonal changes in river stage. During the falI and winter months, adult squawfish occupy a variety of velocity distributions including slow runs, slack waters, eddies and backwaters (VaIdez and Masslich, 1989). Squawfish will often select certain river reaches in the upper Yampa River and remain active in these areas throughout the winter, During the spring and early sunimer months, adult squawfish are most often found in seasonally inundated shoreline habitats (Tyus, 1990). As flow levels drop during the mid- summer, adult squawfish generally move back into the main river channel habitats. During the mid- to late-summer, adults occupy a variety of habitats including eddies, pools, runs and shoreline backwaters (Tyus et aI., 1984 and 1987), Young-of-the-year squawfish usualIy are found in shalIow backwater areas over silt or sand substrates (Valdez et. al. 1982). Juveniles use similar habitat to that of young-of-the-year, although they utilize a wider range of flows, depths and veIocities (Miller et aI., 1982). Migration of squawfish generally occurs during early summer, although migration appears to be a function of hydrologic conditions with earlier migrations observed during low water years (Tyus, 1990). Migration is generally related to the reproductive cycle. The period of migration appears to be a function of the timing of peak river flow, with migration generally initiated some 28 days following the peak. Migration has also been associated with warmer water temperatures, which begin to rise after the peak flow period. The annual spawning period for squawfish generally lasts 4 to 5 weeks. Spawning areas include the white water canyons of the Yampa and Green Rivers (U.S. Fish and Wildlife Service, 1993). Spawning has also been related to hydrologic conditions, generally occurring earlier in Iow water years (U.S. Fish and Wildlife Service, 1992), and temperature, generally occurring in a range between 22 to 25 degrees centigrade (Tyus, 1990). Spawning generally occurs during July and August during declining flows. After spawning, adult squawfish are commonly found in a variety of habitats including eddies, backwaters and shorelines. Based on larval fish studies in the Green River, CoIorado squawfish emerged from the substrates and entered the stream drift as young fry (Haynes et. ai, 1984). Larval fish then drifted downstream for approximately 6 days, 9