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<br />Prewitt (1977) found white sucker and their hybrids (white x tlannelmouth and <br />white x bluehead) comprised a small proportion of suckers collected (I %) at Lily Park, <br />but were 19% of the suckers at Maybell and 76% at Craig in samples taken in 1975 and <br />1976. Current white sucker composition at Sevens and Duffy appear to be similar to <br />Prewitt (1977), In this study white sucker and white hybrids were 21% at Sevens and <br />87% at Duffy of the total sucker catch. Prewitt (1977) reported white hybrids were <br />about 50% of the WSWX group at Maybell and 23% at Craig. In this study white <br />hybrids were over 50% of the sucker catch in both areas. <br /> <br />Both early and recent surveys report white sucker were rare in the Lily Park area <br />and an increasing trend for white sucker in the upstream reaches. Since there appears to <br />be a consistent longitudinal trend for white sucker, it could be that elevation or <br />temperature is a regulating factor in the increased abundance at upstream sections. <br /> <br />The highest native fish composition in the Yampa River is in the Lily Park area. <br />This is due to white sucker being very rare and tlannelmouth sucker abundant. The <br />distance between Lily Park and the Sevens is less than ten river miles and Lily Park is <br />only about 160 feet lower in elevation. A study site at Lily Park could add information <br />about white sucker distribution in upstream reaches. An effort will be made to <br />e1ectrofish this area in September 1999 and to quantify habitat availability if time <br />permits. <br /> <br />, Several differences in density and biomass were noted between the <br />representative reaches, but differences between the two surveyed sites were less <br />dramatic. Both study sites had similar total fish density and biomass estimates, but there <br />were differences between individual species. Flannelmouth sucker and catfish were <br />more common at Sevens, while white sucker and white sucker hybrids were abundant at <br />Duffy. <br /> <br />The surveyed site included a single riffle-run sequence in both Sevens and Duffy. <br />It was determined that the riffle-run sequences selected for habitat analysis did not have <br />a fish community representative of the longer reach. The Sevens representative reach <br />had five riffle-run sequences of various lengths. At Duffy there were six riffle-run <br />sequences. The 1998 fish sampling effort focused on sampling one riffle-run sequence. <br />In the 1999 field season, fish in different riffle-run sequences will be uniquely marked. <br />This will allow for a more detailed examination of the relationship between habitat and <br />fish distribution and abundance <br /> <br />INVERTEBRATES <br /> <br />The intent of the invertebrate samples was to examine for a relationship between <br />wetted riffle area and invertebrate abundance. One result was that shallow portions of <br />the riffle sampled in September 3 dried for a period ofabout 10 days and then <br />reinundated about 20 days prior to sampling on October 8. This indicates that <br />recolonization of reinundated portions of these riffles would require more time than <br />observed. However since mean density was similar at Duffy for September and <br />October a reduction in flows during that' period did not appear to impact total density. <br /> <br />20 <br />