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fish density was significantly higher on the Colorado River station than for the Yampa sites. Total fish density was estimated at 3,962 per km at the IS-Mile Reach station (Table 6). Total fish density on the Colorado River (3.92 per 100 m2}was 2.3 times higher than at Sevens (1. 72 fish/100 m2) and 6.4 times higher than Duffy (0.62 fish/100 m2). Native sucker density was very low at the Yampa Duffy site, where the estimate was only 25 bluehead and 20 flannel mouth per kilometer, especially when compared to the Colorado River where both native sucker estimates were over 1,500 per km{Table 6). The density of native sucker per' 100 m2 at theIS-Mile Reach was over three times higher than at Sevens and over 46 times higher that at Duffy (Table 6). Channel catfish was the only nonnative predator collected in the IS-Mile reach and its density (1.95 fish/100 m2) was comparable to that on Yampa River at the Sevens (2.01 fish/l00 m2) and at Duffy (1.SS fish/100 m2) (Table 6). Smallmouth bas~ and northern pike density was 2.2 times greater at Duffy than at the Sevens. Table 6: Population estimates with 9S% C.I. and density estimates (No.l1000m) for the 1S- Mile-Reach, Sevens and Duffy stations, fall 1999. SEVENS 15 Mile Reach. CO. R. Sevens, Yampa Duffy, Yampa No.lkm:!:95%C.1. No.l1000m2 No.lkm:!:95%C.1. No.l1000m> No.lkm:!:95%C.1.1 No.l1000m2 Total 3962~11 % 39.62 1137~16% 17.07 409~ 7% 6.14 Bluehead 1573:t20% 15.73 238~43% 3.57 25~33% 0.38 Flannelmouth 1550~17% 15.50 376~19% 5.65 20~30% 0.30 Roundtail Chub 192~83% 1.92 4 H84% 0.62 27~71% 0.41 Colo. Pikeminnow 5~NR 0.05 3~NR 0.05 8~NR 0.12 Carp 309~36% 3.09 89~196% 1.34 8~96% 0.12 Channel Catfish 195~54% 1.95 134~192% 2.01 110~108% 1.65 Small Mouth Bass - - 29~123% 0.44 83:1:60% 1.25 Northern pike - - 22~120% 0.33 3H104% 0.47 White Sucker 62:1:65% 0.62 11 0~51 % 1.65 113~11 % 1.70 White-Bluehead 50~1 03% 0.50 HNR 0.02 22~51 % 0.33 White:'.Flannel. 27~196% 0.27 85~1 04% 1.28 11 0~11 % 1.65 Brown trout 18~196% 0.18 - - ,j, On the Colorado River the same reach that was electrofished was also surveyed for habitat composition. However on the Yampa River the surveyed reach was shorter. Because 36