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<br />introduced fish are eaten by Colorado squawfish, and may cause mortality. <br />Conditions favorable for non-native fishes that may compete (or other adverse <br />interactions) with Colorado squawfish should be avoided. Predacious fishes of <br />concern include channel catfish, northern pike, and walleye Stizostedion <br />vitreum. <br /> <br />Migration <br /> <br />The initiation of spawning migration is an important component of the <br />reproductive cycle of the Colorado squawfish. Based on radiotracking data <br />(Wick et a1. 1983; Tyus and McAda 1984; Tyus 1990), fish in both Green and <br />Yampa rivers initiated spawning migrations around the Summer Solstice; Green <br />River fish initiated migrations about June 21 (range: May 23 to July 22) and <br />Yampa River fish migrated about June 15 (range: May 27-July 13; Figure 4). <br />These movements included downstream migrations in the Yampa and White rivers <br />and upstream and downstream migrations in the Green River (Tyus et al. 1987; <br />Tyus 1990). <br /> <br />Flows and water temperatures were highly variable during Colorado <br />squawfish spawning migrations and migrations were initiated earlier in low- <br />water years (e.g., 1981) and later in higher water years, e.g., 1983. The <br />length of time between the dates of peak spring flow and the initiation of <br />spawning migration each year was negatively correlated with the date of the <br />peak flow (r=-1.0, P<O.OI, for the Yampa River; r=-0.8, P<0.03 for the Green <br />River); i.e., earlier peak flows were associated with a longer interval before <br />migration occurred (Tyus 1990). Initiation of spring migration occurred about <br />28 days after peak flow (range 2-42, N=4 years and 24 radiotagged fish in the <br />Yampa River; range 4-50, N=7 years and 29 radiotagged fish in the Green <br />River; Tyus and Karp 1989; Tyus 1990). Migration was associated with water <br />temperatures of at least 90C (average 140C), but temperature-response <br />correlations were not significant for the few years available. <br /> <br />Homing behavior in Colorado squawfish is indicated by long-distance <br />movement patterns and repeated recaptures of the same fish on spawning grounds <br />in subsequent years (Wick et al. 1983; Tyus 19B5, 1990). The concept of <br />spawning fidelity in Colorado squawfish is also supported because fish use of <br />more than one spawning area has not been detected (Tyus 1990). Different fish <br />stocks may be separated by homing fidelity to spawning areas (reviewed by <br />Smith 1985). Colorado squawfish spawning areas should thus be considered <br />unique and critical to the conservation of the species. <br /> <br />Homing of Colorado squawfish from various locations to the spawning <br />reaches in Desolation-Gray and Yampa canyons is presumed to be an orientation <br />to environmental conditions in the spawning reaches. Movements of fish in both <br />up- and downstream directions is suggestive of some olfactory orientation <br />mechanism, as proposed by Harden-Jones (19Bl) and others. Tributaries such as <br />Florence Creek and Warm Springs and chemical inputs from seeps and runoff <br />(lake 1967; Tyus 1990) may provide gross cues for long-distance piloting to <br />the spawning reach. More subtle cues (e.g., reproductive by-products from <br />previously hatched young, Foster 1985) unique to specific spawning sites may <br /> <br />17 <br />