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1 1 have been collected above the spawning reach (RM 0-32). Juveniles: Distribution, abundance, and habitat use of juvenile Colorado squawfish in the Yampa River is poorly understood. Juvenile Colorado squawfish (60-400mm TL) are rare in the Yampa River (Miller et al. 1982, this report, Wick et al. 1983, 1955). From 1980-1987, only 1% of all Colorado squawfish greater than 60mm TL collected in the Yampa River by FWS (N=198) were juveniles. These juveniles were captured in the lower Yampa River. The downstream drift of larvae from Yampa River spawning grounds 1 .indicates the necessity for long-distance upstream movement by juveniles in order to repopulate upstream areas (Tyus 1985). Such movern~nt pro'oably occurs in late juvenile or early adult sr_a;e, a phenomenon suggested by high concentrations of juvenile Colorado squawfish (average catch rate > 0.13 fish/hour) in the lower section of the mainstream Green River and highest concentrations of adults (average catch rate > O.b fish/hour) in upstream sections (Tyus et al. 1987). Humpback chub: Adults: A total of 27 humpback chub were captured in the Yampa River (RM 7.5-47) by r^WS from 19$1-1985. An expanded effort in 1987 from RM 13-37.1 yielded an additional 32 captures, including 6 recaptures. Although taxonomic problems regarding Gila species exist in some areas (Holden and Stalnaker 1970, Valdez and Clemmer 1982), adult chubs captured in the Yampa River in 1987 were recognized as either Gila cypha (humpback chub) or G. robusta (roundtail chub) (no suspected hybrids noted following rigorous morphological inspection). A principal components analysis of 243 adult specimens (200- 26