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RESULTS AND DISCUSSION YAMPA RIVER FISH SAMPLES Species Composition - Duffy and Sevens 1998 to 2000 A high degree of consistency was found in species composition of fish over 15 cm captured by electrofishing between the three year period 1998, 1999 and 2000 at the Sevens and Duffy sampling stations (Table AI). Flannelmouth suckers varied between 46% and 50% of the catch at Sevens but were only 5% at Duffy. Bluehead sucker was between 18 and 22% at Sevens, while only 4 to 6% at Duffy. Roundtail chub were fairly similar between sites with 4 to 6% of the catch at Sevens and 3 to 4% at Duffy. Colorado pikeminnow were only 0.2% of the catch at Sevens, but ranged from 0.6 to 1.5% at Duffy. Native fish were more common at Sevens and were 72% in 1998 and 68 % in 1999 and 76% in 2000. At Duffy native fish comprised only about 14% of the fish population in all three years. The most common fish at Duffy in all three years was white sucker and white sucker hybrids (white x flannel mouth and white x bluehead cross). The white sucker with crosses comprised between 69 and 73% of the catch at Duffy, compared to 13 to 17% at Sevens for the three-year period (Table AI). The next most common fish at Duffy was another non- native species, small mouth bass ranging from 6% to 10% over the three years. The consistent or stable species composition at these two sites with three years of fish data (Table AI) suggests composition is a likely a function of habitat availability of these areas. The discrepancy in species composition of small mouth bass between Duffy and Sevens strongly appears to be a function of channel morphology or habitat since both sites have similar physical conditions for flow and temperature. Nesler (1995) proposed it was reasonable to assume normal runoff flows would be adverse enough to prevent stable recruitment of small mouth base in the Yampa River. This may be correct at Sevens, but large 20 I I I I I I I I I I I I I I I I I I I