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, i)ulG9b . . Colorado Squawfish IPtychocheilus luciusl The Colorado squawfish was listed as endangered in 1967 by the U.S. Fish an<l Wildlife Service. The Colorado squawfish evolved as the main predator fish in the Colorado River system. In the Upper Colorado River Basin, the species historically occurred in the Colorado, 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. Colorado squawfish require a wide distribution of habitat types to saUsfy various life history requirements and in response to seasonal changes in river stage. During the fall and winter months, adult squawfish occupy a variety of velocity distributions including slow runs; slack waters, eddies and backwaters (Valdez and Masslich, 1989). Squawfish select certain river reaches in the upper Yampa River and generally remain active in these areas throughout the winter. Some local movements appears to be related to avoidance of floating ice jams. over what would be the case without the project. Flow fluctuations during the winter may affect squawfish use of some habitat areas. Valdez and Masslich (1989) believed that a rapid change in river stage altered locations of squawfish preferred microhabitats and resulted in increased movement. During the spring and early summer months, adult squawfish are most often 'found in seasonally inundated shoreline habitats (Tyus, 1990). As flow levels drop during the mid- summer, adult squawfish general1y 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 a!., 1984 and 1987). Adult fish rely on cover provided by boulders and flooded vegetation. 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 general1y 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 riffle and pool habitats in Yampa Canyon on the lower Yampa River (Tyus and Karp, 1989). Spawning has also been related to hydrologic conditions, generany occurring earlier in low 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. There are no reports of squawfish occurring within the Elkhead Reservoir area or the 6- mile section of Elkhead Creek downstream of the reservoir. . Adult Colorado squawfish have been captured in the lower 124 miles of the Yampa River, and.larvae have been found in the low~r 19 miles of the Yampa River in Dinosaur National Monument (Miller et. ai, 1982; Wick et. a!. 1986; Tyus and Haines 1991). Young, juvenile, and adult squawfish have been conected in the Green River from the mouth of the Yampa River to its confluence with the Colorado River (Maddux et. al. 1993a).. Critical habitat has been proposed for the Colorado squawfish in areas downstream of Elkhead Reservoir, including the Yampa River from RM 137.7 to its confluence with the Green River, the Green River between its confluences with the Yampa and Colorado Rivers, and the Colorado River from the Green River confluence to Lake Powell (Maddux et. a!. 1993b). 9 i4L;,';Ji.