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1 ] lower Green River (km 0-211) were extremely rare; their numbers were too small (13 fish captured, 1 recaptured) to allow a reliable population estimate. Gray and Desolation canyons separated the upper and lower Green River razorback sucker populations. These canyons and a low diversion dam appeared to be barriers to fish movement. The absence of the razorback sucker in Gray and lower Desolation canyons (km 211-282) suggested a lack of suitable habitat. The Green River supports the largest known population of razorback suckers among the species' native riverine habitats. However, low population density and recruitment, as well as habitat alteration, mandate increased research and management efforts to save this population (Abstract). Report 8- Spawning and Movements of Razorback Sucker, Xvrauchen texanus, in the Green River Basin of Colorado and Utah (Tyus and Karp, in review). Spawning and movements of the razorback sucker, Xvrauchen texanus, were evaluated by radiotelemetry (n=17 fish) and capture of 230 adults (105 recaptures) in the Green and Yampa rivers, 1987-1989. Ripe fish (n=194) were captured in riffles with cobble, gravel, and sand substrates from mid-April to early June. Recaptured males were ripe from 2 to 28 days and recaptured females from 2-15 days. Razorback suckers spawned during ascending and highest spring flows at water temperatures of about 14°C (range 9-17°C). Spawning migrations of 30-106 km were detected in 17 razorback suckers, but movements were more limited or undetected in other individuals. Flooded lowlands and mouths of tributary streams presumably served as resting-feeding areas for razorback suckers during the breeding season. Native flannelmouth sucker, Catostomous latipinnis, bluehead sucker, C. discobolus, and putative flannelmouth X razorback sucker hybrids in breeding condition were collected with ripe razorback suckers. The razorback sucker is in peril due to a paucity of spawning adults, hybridization with other suckers, little or no recruitment, and habitat loss (Preliminary Abstract). Report 9- Habitat Use, Spawning, and Species Associations of Humpback Chub, in the Yampa and Green Rivers, Dinosaur National Monument, Colorado and Utah (Karp and Tyus, in review). We evaluated habitat use, spawning, and species associations of a little known population of the endangered humpback chub Gila cypha in the Yampa and Green rivers, Dinosaur National Monument, from 1986 to 1989. Juvenile and adult humpback chub (N=133, 8% of all chub captures) were captured only in turbulent canyon reaches dominated by rocky runs and rapids, and were most prevalent in shoreline eddy habitats. Fish in breeding condition (N=39) were captured during declining spring runoff at river temperatures of about 20°C. Although high turbidity precluded observation of spawning behavior and spawning microhabitat, ripe males and females were captured in the same eddy habitats. Humpback chub were captured in association with 18 other fish species, including 7 native and 11 introduced forms. Of these, roundtail chub G. robusta and introduced channel catfish Ictalurus punctatus dominated the catch in habitats yielding humpback chub. Co-occurrence of ripe humpback and roundtail chubs indicated some temporal and spatial overlap in spawning, but few morphologically-intermediate fish were captured. Similarity in feeding habits and habitat use by humpback chub and channel catfish during spring runoff suggests a potential for negative interactions between these fishes. 10