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percent 50 miles upstream near Duffy Tunnel (Anderson, in press). Flannelmouth suckers in the Yampa River are known to hybridize with bluehead sucker and white sucker (Carlson et al. 1979). Determining age by scale analysis indicated that flannelmouth sucker can reach at least 10 years of age in the Yampa River (Carlson et al. 1979). Flannelmouth suckers utilize several different habitats and feeding strategies during various life stages. Young flannel mouth suckers are often associated with backwaters, slow runs or pools (Holden and Stalnaker 1975; Joseph et al. 1977). Adults occupy pools and eddies in larger streams, but will often move into shallow riffles to feed between rocks (Joseph et al. 1977). Carlson et al. (1979) found flannelmouth suckers using a wide range of habitat and substrate types on the Yampa River; however, these fish seemed to prefer relatively shallow water with sand or small cobble substrates. Joseph et al. (1977) suggested that larvae of flannelmouth suckers feed primarily on crustaceans and other small aquatic invertebrates. As these fish get older their diet consists primarily of bottom materials including organic debris, algae, and invertebrates (Joseph et al. 1977; Arizona Game and Fish 1996). Gut samples from tlannelmouth suckers collected from the Yampa River during August and September 1975 contained mostly periphytoll (algae) and a few invertebrates (Carlson et al. 1979). The bluehead sucker is native to streams in the Upper Colorado River basin (Joseph et al. 1977). Vanicek et al. (1970) reported that the bluehead sucker was common within the canyon section of the Green River in Dinosaur National Monument. Holden and Stalnaker (1975) found the bluehead sucker "common" to "abundant" at sample locations at the Yam pa, Gunnison, and middle to upper Green and Colorado Rivers. Between July 1975 and October 1977 bluehead suckers composed 7.8% to 28.0% of the fish collections in the Yampa River between Dinosaur National Monument and the town of Hayden, Colorado (Carlson et al. 1979). The bluehead sucker also hybridized with white and tlannelmouth suckers in the Yampa River. Adult bluehead suckers exhibit a strong use of specific habitat types (Holden and Stalnaker 1975). This species typically occurs in runs or riffles with rock or gravel substrates (Vanicek 1967; Holden and Stalnaker 1975; Carlson et al. 1979). Juvenile bluehead suckers occur in slower water than adults, and juveniles have been collected from shallow riffles, backwaters, and eddies with silt or gravel substrates (Vanicek 1967). The percent composition of bluehead sucker, for all fish over 15 dm, was estimated to be 27% downstream of Sunbeam (RM 60-64) and 5 percent 50 miles upstream near Duffy Tunnel (Anderson, in press). 33