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o 01 CJ 6 :" "', N Ct) best habitat conditions for endangered fishes while maintaining the integrity of the channel geomorphology. Tyus and Karp (1989) pointed out the importance of peak flows (spring runoff) associated with reproductive activities of Colorado squawfish. They further stated that alteration of this hydrological event may affect initiation of Colorado squawfish migration and spawning. Additionally, maintenance of low stable flows in summer and fall are necessary for growth and survival of young Colorado squawfish. Miller et al. (1982) concluded from collections of larvae and young-of-year below known spawning sites that there is a downstream drift of larval Colorado squawfish following hatching. Extensive studies in the Yampa and upper Green Rivers have demonstrated downstream distribution of young Colorado squawfish from known spawning areas (Archer et al. 1986; Haynes et al. 1985). Miller et al. (1982) also found that young-of-year Colorado squawfish, from late summer through fall, preferred natural backwater areas of zero velocity and less than 1.5-foot depth over a silt substrate. Juvenile Colorado squawfish habitat preferences are similar to that of young-of-year fish, but they appear to be mobile and more tolerant of lotic conditions away from the sheltered backwater environment. Only two Colorado squawfish confirmed spawning sites, as defined in the Colorado Squawfish Recovery Plan, have been located in the Upper Basin: river mile 16.5 of the Yampa River and river mile 156.6 of the Green River. These areas have the common characteristics of coarse cobble or boulder substrates forming rapids or riffles associated with deeper pools or eddies. It is believed that a stable, clean substrate is necessary for successful spawning and incubation. Substrates are swept clean of finer sediments by high flows scouring the bed prior to the spawning period (O'Brien 1984). As a result of the 1991 Biological Opinion issued by the Service for the proposed Animas-La Plata Project, and continued through reinitiation in 1995 and a second Biological Opinion in 1996, Reclamation agreed to fund approximately 7 years of research on the San Juan River and its tributaries. While these studies are not yet complete, annual reports indicate that a small reproducing population of Colorado squawfish exists in the San Juan River. Based on radio telemetry studies and visual observations, two potential spawning areas have been located at river mile 132.0 and 131.15 (Miller 1994, Ryden and Pfeifer 1995a). Both of these sites are located in an area of the river known as the "Mixer" (RM 133.4 to RM 129.8). The highest concentration of adult Colorado squawfish in the San Juan River occurs between the Cudei Diversion (RM 142.0) and Four Corners (RM 119.2). Ryden and Pfeifer (1995a) report that a Colorado squawfish captured at river mile 74.8 (between Bluff and Mexican Hat) made a 50-60 mile migration from near Bluff, Utah, to the Mixer during the suspected spawning season in 1994. The fish then returned to within 0.4 river miles of its original capture location. Successful reproduction was documented in the San Juan River in 1987, 1988, 1992, 1993, 1994, and 1995, by the collection of young-of-year Colorado squawfish. The majority of the young-of-year squawfish were collected in the San Juan River inflow to Lake Powell (Buntjer et al. 1994, Lashmett 1994, Platania 1990, Platania, pers.comm. 1996). However, some young-of-year squawfish have also been collected from the vicinity of the Mancos River confluence in New Mexico, in the vicinity of the Montezuma Creek confluence near Bluff, Utah, and at a drift station near Mexican Hat, Utah (Buntjer et al. 1994, Platania 1990, Platania, pers. comm. 1996). In 1994, a young-of-year Colorado squawfish was collected at