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I I I I I I I I I I I I I I I I I I I Species Composition and Relative Abundance Native species dominated the drift except in 1994 (Table 1). On the Colorado River, either speckled dace (Rhinichtyhs osculus; [SD]) or roundtail chub (Gila robusta; [CH]) were the most common native taxa collected. Since humpback chub (Gila cypha) have not been collected upstream of Black Rocks, it was assumed that all chub collected upstream ofthere were roundtail chub. On the Gunnison River roundtail chub typically was the most common species sampled (Table 2). Bluehead sucker (Catostomus discobolus [BH]) was fairly common in the drift for both rivers, except in 1994. Flannelmouth sucker (Catostomus latipinnis; [FM]) was present but uncommon at most stations during the study period. Colorado pikeminnow (CPM) comprised between 1.5 and 3.6% of the drift at the Loma station, and from zero to 1.5% at other stations. The most common non-native species was fathead minnow (Pimephales promelas; [FH]). Carp (Cyprinus carpio; [CP]), green sunfish (Lepomis cyanellus; [GS], red shiner (Cyprinella lutrensis; [RS], sand shiner (Notropis stramineous; [SS]) and white sucker (Catostomus commersoni; [WS] were also collected. The two lowest runoff years (1992 and 1994) were the years with the lowest percentage of native species in the drift at the Loma station (Table 1) and the lowest number of native larvae taken on the Colorado River stations (Appendix 2, Figures 1 and 5). This was mainly due to very poor chub numbers collected in 1994 compared to other years. Both chub and speckled dace numbers were highest during the highest water year 1995 (Appendix 2, Figure 7). The pattern for trends in composition for native fish was the same as for Colorado pikeminnow at the Loma station i. e. the proportion of pikeminnow was lowest in 1994 and highest in 1995. 9