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Walleye in the Green River primarily consumed fishes, including 5 non- native and 1 native species (Table 3). Of 61 stomachs examined, 24 (39.3%) were empty and 10 (16.4%) contained unidentifiable fish remains. Channel catfish, Ictalurus punctatus, and fathead minnow were the most frequently consumed non-native fishes, and flannelmouth sucker was the only native fish consumed. Vascular plant material was found in one walleye stomach. Discussion Northern pike, introduced in the Yampa River drainage in 1971, was presumed absent in Green River until first reported in 1981 (Tyus et al. 1982a). We captured the fish only in the upper Green River (km 337.8-552) from 1981 to 1986. Pike invaded the mid-section (km 192-337.7) by 1987, and it was first captured below Green River, Utah (km 192) in 1988. This invasion and downstream movement is supported by absence of the fish in the Green River in the early 1970s (Holden and Stalnaker 1975), and a first report of pike in the lower Green in 1988 (M. Moretti, personal communication). Although movements of northern pike in large rivers remain poorly documented, some studies in lakes and small streams have shown that the fish can display high mobility (Miller 1948, Ross and Winter 1981), but may only move short distances at a time (Cook and Bergersen 1988). Our recapture of two northern pike indicated that the fish can move long distances (>75 km/year) in the Yampa River. Long distance up- and downstream movement of radiotagged northern pike have also been reported by T.P. Nesler (personal communication). The majority of fishes consumed by northern pike in this study were soft- rayed forms (Table 2), as previously noted by others (Beyerle and Williams 1968; Weithman and Anderson 1977; Wolfert and Miller 1978). Channel catfish, the only spiny-rayed fish consumed, was found in two stomachs. We could not 6