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¦ In the Green River, Colorado and Utah, 1987, biologically <br />important diet overlap (index values > 0.60) occurred <br />between age-0 Colorado squawfish and red shiner and was <br />primarily attributed to the high relative importance of <br />immature midges in diets of both species. Larval red shiner <br />were identified in guts of some age-0 Colorado squawfish <br />[Muth and Snyder 19951. <br />¦ Observations on behavioral interactions under laboratory <br />conditions suggested that in shared habitats, red shiner may <br />adversely affect growth and survival of age-0 Colorado <br />squawfish [Karp and Tyus 1990a] . <br />¦ Under laboratory conditions, adult red shiner ate larvae <br />of Colorado squawfish and razorback sucker. Predation rate <br />and efficiency decreased as larvae developed, during <br />darkness, in the presence of alternative invertebrate prey, <br />and in turbid water [R. Muth and D. Beyers, unpublished data] . <br />¦ About 5% of 433 adult red shiner collected from the <br />Colorado and Green rivers, Canyonlands National Park, Utah, <br />in spring and early summer 1994 had larval fish in their <br />guts. Larvae were identified as cypriniform and most were <br />catostomids (species undetermined because larvae were too <br />digested for accurate identification) [R. Muth, unpublished <br />data]. <br />Options for Control in the Upper Colorado River Basin: <br />Controlling or limiting red shiner will be difficult because <br />of its extremely high abundance, ubiquitous distribution, <br />high adaptability, high reproductive potential, and ability <br />to rapidly re-colonize. <br />Mechanical Removal.-Partial, temporary removal might be <br />achieved by periodic seining of selected low-velocity <br />habitats. Blocking access of adult red shiner to portions <br />of low-velocity habitats in the lower Green River, <br />Canyonlands National Park, was successfully tried using net <br />exclosures [R. Muth, -personal observation] . <br />Chemical Treatment. Traditional chemical treatments (e.g., <br />rotenone) kill indiscriminantly and are not a viable control <br />option. Red shiner has been targeted in two chemical- <br />eradication projects in the Virgin River, Utah. Populations <br />were substantially reduced after treatment but rapidly <br />rebounded [L. Lentsch, personal observation] . <br />41