2010-11-22_REVISION - M2009023 (7)

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report that a Colorado pikeminnow captured at river mile (RM) 74.8 (between Bluff and Mexican Hat) made a 50-60 mile migration to the Mixer during the suspected spawning season in 1994. Two locations in the San Juan River have been identified as potential spawning areas based on radio telemetry and visual observations (Miller 1994; Ryden and Pfeifer 1995a; Miller and Ptacek 2000). Both locations occur within the "Mixer" (RM 133 to 129.8), a geomorphically ,distinct reach of the San Juan River. The upper spawning location is located at RM 132. The lower spawning location is located at RM 131.15. Both locations. consist of complex habitat associated with cobble bar and island complexes. Habitat at these locations was similar to spawning habitats described for the Yampa River and is composed of side channels, chutes, riffles, slow runs, backwaters and slackwater areas near bars and islands. Substrate in the riffle areas is clean cobbles, primarily 3 to 4 inches in diameter (Miller and Ptacek 2000). Spawning habitat at the lower spawning area, based on radio telemetry and visual observations, is composed of a fast narrow chute with a small adjacent eddy. During 1993 radio tagged Colorado pikeminnow were observed moving to suspected spawning locations in the "Mixer" beginning around July 1. Fish were on suspected spawning areas between approximately July 12 to July 25. During this period flows in the San Juan River were on the descending limb of the spring runoff. Temperatures increased from approximately 20 ° to 25 dC (68 ° to 77 °F) during the same time period. Observations in other years show a similar pattern. However, specific spawning times and duration of the spawning period appear to vary from year to year. Information on radio-tagged adult Colorado pikeminnow during fall suggests that fish seek out deep water areas in the Colorado River (Miller et al. 1982, Osmundson and Kaeding 1989), as do many other riverine species. River pools, runs, and other deep water areas, especially in upstream reaches, are important winter habitats for Colorado pikeminnow (Osmundson et al. 1995). Very little information is available on the influence of turbidity on the endangered Colorado River fishes. Osmuadson and Kaeding (1989) found that turbidity allows use of relatively shallow habitats ostensibly by providing adults with needed cover; this allows foraging and resting in areas otherwise exposed to avian or land predators. Tyus and Haines (1991) found that young Colorado pikeminnow in the Green River preferred backwaters that were turbid. Clear conditions in these shallow waters might expose young fish to predation from wading birds or introduced, sight-feeding, pisaivorous fish. It is unknown whether the river was as turbid historically as it is today. For now, it is assumed that these endemic fishes evolved under natural conditions of high turbidity; therefore the retention of these highly turbid conditions is probably an important factor in maintaining the ability of these fish to compete with nonnatives that may not have evolved under similar conditions. 8