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Valdez et al (1992) reported no significant changes in species composition between the 1990 and <br />1991 samplings to a similar surveys done in 1981 and concluded the ichthyofaunal communty <br />remained relatively stable over that ten year period. <br />The Colorado Division of Wildlife has sampling locations established in the Dolores River. <br />Mike Japhet (biologist in Durango, Colorado) has sampled a 1,000 ft reach below the Dove <br />Creek pump station beginning in1986 and has accumulated 16 years of data over the last 19 year <br />period. Dove Creek site is located in Reach 6 defined by Valdez et al. (1992). The Dove Creek <br />site was sampled by wade electrofishing using a stationary shore shocker. At least one pass were <br />made, but in most years there were two passes at the site. <br />The three most common species collected at the Dove Creek site over the 18 year period were <br />roundtail chub, speclded dace and mottled sculpin. Mottled sculpin was the most common <br />species and 1986, 1987 and 1989 (about 50%), but ranked fourth in 2002 and 2003 and was fifth <br />in 2004 at only 8%. Flannelmouth sucker were rare at Dove Creek (1.3% for the period). Green <br />sunfish were rare from 1986 to 2002 (0 to 1%), but ranked second in 2004 with 21% of the catch <br />(CDOW data obtained from Mike Japhet). <br />The three most common species collected in 1991 in Reach 6 by Valdez were roundtail chub <br />(27%), speclded dace (24%) and flannelmouth sucker (22%). Mottled sculpin were the least <br />common species (<1%) found by Valdez in 1991 in Reach 6. <br />Fish community composition was fairly stable at the Dove Creek site from 1986 to 2000 (Japhet, <br />CDOW). During that time period the nonnative fish with the greatest influence were brown and <br />rainbow trout. When trout were excluded, native species comprised between 95 to 100% of the <br />remaining catch at Dove Creek site from 1986 to 2000. In 2002, 2003 and 2004 native <br />composition dropped to 79, 76 and 67%, respectively (trout excluded). The large increase in <br />fathead nunnow and green sunfish after 2002 appear to be a result of habitat or temperature <br />alternations due to reduced flow conditions in recent years. <br />Another Colorado Division of Wildlife st<idy area was established by Rick Anderson (Researcher <br />in the Grand Junction Office) in Big Gypsum Valley which is about 15 miles downstream of the <br />confluence of Disappointment Creek in Reach 5. Anderson (2002) sampled the fish community <br />at Big Gypsum in 2000 and 2001 as part of a habitat suitability/instream flow study. The Big <br />Gypsum site was again sampled in 2004 as part of a drought evaluation study on various rivers <br />(Anderson 2005). <br />Anderson (2002) did mark and recapture sampling that produced density and biomass estimates <br />for fish larger than 150 mm. In 2000 the two most common species for larger fish (<150 mm) <br />were roundtail chub (55%) and flannelmouth sucker (16%) and these were also the most <br />common fish in 2001 (Table 1). k1 2004 roundtail chub were 29% and flannelmouth sucker <br />were rare at only 2%. The density estimates for roundtail chub and flannelmouth sucker were <br />very low on the Dolores River compared to the other study rivers and Anderson (2005) <br />suggested a high degree of fine sedimentation had impacted productivity. <br />15 <br />