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Lily Park had by far the largest sample size for fish over 15 cm, and also the largest variation between years (Table 5). Flannelmouth was the most common species found at Lily Park. Its composition was 68% in 2001 and 48% in 2000 (Table 5). The 2001 data was probably a more accurate description of species composition at Lily Park because of the extraordinary number of catfish caught in 2000 decreased the relative abundance of other species that year. Bluehead sucker, roundtail chub and Colorado Pikeminnow composition were similar between years (2001 versus 2000) at Lily park: (9% versus 7%), (0.02% versus 0.03%) and (0.1% versus 0.0%) respectively (Table 5). Within-station native fish species composition on the Yampa River was quite consistent over the four years of sampling. The differences observed were likely related to either sampling variability between years or difference inflows between years. There were large differences in species composition between stations. Flannelmouth composition was about 50% at Sevens, 5% at Duffy and 70% at Lily Park. Bluehead sucker composition was about 20% at Sevens, 4% at Duffy and 8% at Lily Park. Roundtail chub composition was at 4% at Sevens, 3% at Duffy and 0% at Lily Park. Nonnative fish comprised 85 to 90% of the fish captured at Duffy Tunnel. White sucker and hybridized white sucker averaged 71% of the catch for the first three years (Table 5). The white sucker group dropped to 50% in 2001. At Sevens, the white sucker group was consistent at 15% of the population for the four years. White sucker or hybrids were very rare at Lily Park at 0.03%. Statistics indicate that the white sucker was better suited to conditions upstream of Sevens and native suckers were better competitors at the lower two sites. There are three non-native predator species in the Yampa River that influence species composition independent of habitat availability. The northern pike was fairly commonly caught during the first two years of sampling (1998 and 1999) at Sevens and Duffy, but were uncommon in the last two years (Table 5). The trend for smallmouth bass was the reverse with the highest composition occurring in the last year, 2001 (Table 5). The most dramatic shift in smallmouth bass was at the Duffy, site, from 10% in 2000 to 33% in 2001. Channel catfish were non-native predators that had a low composition at Sevens (5%) and Duffy (4%). However at Lily Park, channel catfish composition was 40% in 2000 and 18% in 2001 (Table 5). Low flows were identified as problematic for channel catfish migration in 2000, inflating their numbers relative to normal flow years. A composition of 18% for catfish was a more likely representation for this species. In 2000, smallmouth bass comprised only 0.8% of the fish over 15 cm, but in 2001 smallmouth bass were 5 percent (Table 5). 35