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introduced fish are eaten by Colorado squawfish, and may cause mortality. Conditions favorable for non-native fishes that may compete (or other adverse interactions) with Colorado squawfish should be avoided. Predacious fishes of concern include channel catfish, northern pike, and walleye Stizostedion vitreum. Migration The initiation of spawning migration is an important component of the reproductive cycle of the Colorado squawfish. Based on radiotracking data (Wick et al. 1983; Tyus and McAda 1984; Tyus 1990), fish in both Green and Yampa rivers initiated spawning migrations around the Summer Solstice; Green River fish initiated migrations about June 21 (range: May 23 to July 22) and Yampa River fish migrated about June 15 (range: May 27-July 13; Figure 4). These movements included downstream migrations in the Yampa and White rivers and upstream and downstream migrations in the Green River (Tyus et al. 1987; Tyus 1990). Flows and water temperatures were highly variable during Colorado squawfish spawning migrations and migrations were initiated earlier in low- water years (e.g., 1981) and later in higher water years, e.g., 1983. The length of time between the dates of peak spring flow and the initiation of spawning migration each year was negatively correlated with the date of the peak flow (r=-1.0, P<0.01, for the Yampa River; r=-0.8, P<0.03 for the Green River); i.e., earlier peak flows were associated with a longer interval before migration occurred (Tyus 1990). Initiation of spring migration occurred about 28 days after peak flow (range 2-42, N=4 years and 24 radiotagged fish in the Yampa River; range 4-50, N=7 years and 29 radiotagged fish in the Green River; Tyus and Karp 1989; Tyus 1990). Migration was associated with water temperatures of at least 9°C (average 14°C), but temperature-response correlations were not significant for the few years available. Homing behavior in Colorado squawfish is indicated by long-distance movement patterns and repeated recaptures of the same fish on spawning grounds in subsequent years (Wick et al. 1983; Tyus 1985, 1990). The concept of spawning fidelity in Colorado squawfish is also supported because fish use of more than one spawning area has not been detected (Tyus 1990). Different fish stocks may be separated by homing fidelity to spawning areas (reviewed by Smith 1985). Colorado squawfish spawning areas should thus be considered unique and critical to the conservation of the species. Homing of Colorado squawfish from various locations to the spawning reaches in Desolation-Gray and Yampa canyons is presumed to be an orientation to environmental conditions in the spawning reaches. Movements of fish in both up- and downstream directions is suggestive of some olfactory orientation mechanism, as proposed by Harden-Jones (1981) and others. Tributaries such as Florence Creek and Warm Springs and chemical inputs from seeps and runoff (Lake 1967; Tyus 1990) may provide gross cues for long-distance piloting to the spawning reach. More subtle cues (e.g., reproductive by-products from previously hatched young, Foster 1985) unique to specific spawning sites may 17