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<br />I, or partially extirpated native fish faunas, and the instability of resultant <br />i <br />communities has caused management problems (Moyle et al. 1986). <br />The purpose of this study was to determine diets of northern pike and <br />walleye in the Green River, and to evaluate the degree of predation on native <br />and endangered fishes. We also document the recent invasion of northern pike <br />into the Green River basin, and the abundance and distribution of northern <br />pike and walleye in the mainstream Green River. The results of this study are <br />interpreted relative to potential interactions of these species with <br />sympatric endangered Colorado River fishes. <br />METHODS <br />Northern pike and walleye were primarily collected by electrofishing. <br />Sampling was conducted from April to November 1979-1981 and from April to June <br />1984-1988, in 517 km of the mainstream Green River. The study area included <br />the mainstream Green River from its confluence with the Yampa River in <br />Dinosaur National Monument, to a point 35 km above the confluence of the Green <br />and Colorado rivers (Fig. 1). The lower 73 km of the Yampa River was also <br />sampled 1984-1989. In 1989, spring sampling was only conducted in the Green <br />River in a 208 km reach below its confluence with the Yampa River (Fig. 1), <br />and in the lower 73 km of the Yampa River. <br />In 1979-1981, fishes were sampled with a variety of gear, including <br />electrofishing, seines, trammel nets, and wire traps, depending on gear <br />suitability, and sampling was conducted during prerunoff, runoff, and <br />postrunoff conditions. In 1984-1988, sampling included only alongshore <br />electrofishing in the prerunoff and early runoff period, and involved <br />continuous downstream coverage with a pulsed DC unit. Electrofishing <br />collections in which all shoreline habitats were sampled were considered <br />3 <br />