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+ ovaries; in May at a water temperature of 13°C. Walleye in other locations <br />usually spawn at cooler water temperatures (3.3-7.2°C, Sigler and Miller 1963; <br />5.6° to 11.1°C, Scott and Grossman 1973). No small walleye (<395 mm TL) were <br />captured in this study. <br />Young of the endangered humpback chub, Gila cypha; bonytail chub, G. <br />elegans; razorback sucker, Xyrauchen texanus; and Colorado squawfish, <br />Ptychocheilus Lucius may be potential prey for northern pike and walleye. None <br />of these fishes were identified in stomachs of northern pike or walleye, but <br />our ability to detect such predation was constrained by a small sample size of <br />stomachs that contained food, rarity of endangered fishes, and inability to <br />identify all of the fishes eaten. <br />Sympatry of adults of northern pike, walleye, and endangered fishes is a <br />cause for concern, particularly if such resource sharing occurs during periods <br />of limited availability. We collected northern pike, walleye, and Colorado <br />squawfish in similar shoreline habitats in the mainstream Green River, and <br />radiotagged northern pike and Colorado squawfish were syntopic in the Green <br />and Yampa rivers (Valdez and Masslich 1989, Wick and Hawkins 1989). Northern <br />pike were captured in shallow, flooded habitats also utilized by razorback <br />sucker. <br />Stocking programs for northern pike and walleye have been discontinued by <br />state agencies in Colorado and Utah (G.M. Davis, P.J. Martinez; personal <br />communication), and the relative absence of small fish of both species <br />suggests that reproduction in the mainstream Green River is low or non- <br />existent during most years. However, the continuing invasion of northern pike <br />and walleye into the Green River from established, reproducing stocks should <br />be monitored, and their interactions with endangered fishes further evaluated <br />8 <br />