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Razorback suckers exhibited both local and long-distance spring and summer movements (Tyus 1987; Tyus and Karp, in review). Two spawning migrations include movement between lower Yampa and upper Green (below boundary DNM) rivers, and movement between upper Green River and Ouray area (Old Charley Wash and lower Duchesne River, Tyus and Karp, in review). Blockage of stream passage would interrupt spawning movements of razorback sucker in the Green River basin. There is some indication that some razorback suckers exhibit a spawning fidelity to a specific riffle (Tyus and Karp, in review) and the importance of this phenomenon needs further evaluation, particularly in reintroduction efforts. The capture and artificial spawning of ripe razorback suckers in the lower Yampa and upper Green rivers (FWS unpublished data) and the tentative identification of larvae in upper Green River seine collections (R. T. Muth and D. Snyder, personal communication) indicates that razorback suckers reproduce successfully in the upper Green River basin. However, there is little indication of recruitment to the juvenile stage throughout the Colorado River basin (Holden 1978; McAda and Wydowski 1980; Minckley 1983; Tyus 1987; Marsh and Minckley 1989; Tyus and Karp, in review). Standing crops of razorback suckers in the Green River are presumably old fish (Minckley et al., in prep) and no documented recruitment has occurred since the 1960s. The apparent lack of widespread recruitment has been attributed to habitat alteration, such as lower water temperatures (Marsh 1985) and predation by introduced common carp Cyprinus car io, green sunfish, channel catfish, flathead catfish Pylodictus olivaris, and other non-native fishes (Minckley 1983; Brooks et al. 1985; Tyus 1987; Marsh and Langhorst 1988; Marsh and Minckley 1989). Predation by non-native fishes is believed a serious threat to the survival and recovery efforts of razorback sucker. The absence of young fish in the Green River basin population may also be linked with the reduced availability of inundated shorelines due to curtailment of spring flooding following closure of Flaming Gorge Dam. Naturally inundated lowlands such as Old Charley Wash and Stewart Lake Drain should be made accessible to razorback suckers in the spring. The introduction of young fish (reared at Ouray National Wildlife Refuge from sex products taken from wild fish captured on nearby Green River spawning grounds) may ultimately result in natural recruitment if the number of spawning adults, and consequently the number of young fish, is increased. Habitat requirements of this species in riverine environments are not well known because of the scarcity of extant populations (Minckley 1983; Lanigan and Tyus 1989) and the absence of younger life history stages (McCarthy and Minckley 1987; Tyus 1987). Adult razorback suckers in the Green River basin are old individuals (Tyus 1987, Minckley et al., in prep.) and the low number of reproducing razorback suckers is considered limiting (Lanigan and Tyus 1989; Tyus and Karp, in review). High spring flows, warming river temperatures, and inundated shorelines and bottomlands are considered essential to successful reproduction in this species. PART III. SUMMARY AND RECOMMENDATIONS Summary General The Green River basin is an important riverine system for the maintenance and recovery of the endangered Colorado River fishes. Flows of the tributary Yampa River are singularly important for maintaining a spring peak on the 24