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abundant backwater fish species were (in descending order) red shiner (Cyprinella lutr i , <br />fathead minnow (PimWhales r elas , and Colorado squawfish. Together these three species <br />comprised 93 - 95% of all backwater fishes (Haines and Tyus 1990). All three species <br />consume chironomid larvae, and the red shiner and young Colorado squawfish also consume <br />zooplankton, and semi-aquatic insects (Catherine A. Karp, personal communication). <br />METHODS <br />Study area <br />The Green River originates in Wyoming and is part of the Colorado River drainage, <br />joining the Colorado River in southeastern Utah. 404 km above its confluence with the <br />Colorado River it enters Ouray National Wildlife Refuge (ONWR). When it reaches Jensen, <br />Utah, it has a drainage area of 47,723 km2 with an average high flow of 338 m3/sec and an <br />average low of 100 m3/sec (U.S.G.S. data). All backwaters used in this study were located on <br />ONWR and were shallow (approximately 0.75 in to 1.0 m deep) with no measurable current <br />except when the wind blew. Secchi disk visibility averaged 22 cm, and the substrate was <br />composed of soft sediments under a thin (approximately 4 cm) layer of flocculent material. <br />Experimental design <br />A randomized block design was used with three treatments per backwater and three <br />backwater replications. The treatments were: (a) a four m2 (2 x 2 m) control area, marked by <br />posts, which was open for foraging to all backwater fishes, (b) a four m2 caged area that <br />excluded all fish, and (c) a four m2 cage with 2.5 cm wide by ten cm high (spaced <br />approximately ten cm apart) perforations cut into all four sides. These perforations excluded <br />large fish such as carp QTrinus cc pio) and channel catfish Glalurus punctatusl but allowed <br />2