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<br />Report 15- Abundance, growth, and diet of channel catfish, Ictalurus <br />ounctatus, in the Green and Yampa Rivers, Colorado and Utah. (Tyus <br />and Nikirk 1990) <br /> <br />Channel catfish were widely distributed in 517 km of the mainstream <br />Green and 74 km of the lower Yampa rivers in 1987 and 1988. The fish was most <br />abundant in rocky canyon habitats (average stream gradient >2 m/km), where <br />adult fish comprised 14% of electrofishing and 70% of angling catch. Pectoral <br />spine sections of 364 channel catfish of 27-756 mm total length ranged in age <br />from 0 to 22 years respectively, with an average annual growth range of 17-53 <br />mm. No difference in growth or condition factor was detected among catfish <br />collected in eight river reaches. Growth of channel catfish in the Green River <br />basin was judged slow in comparison to other areas of the United States and <br />was attributed, in part, to cold water temperatures, short growing seasons, <br />and elevated summer flow conditions. Channel catfish consumed a variety of <br />food items, but piscivory was limited to larger fish (average length 420 mm). <br />Of 575 stomachs with food (76.2%), 31% contained aquatic invertebrates,'28% <br />contained vascular plant material, 22% contained terrestrial insects, 10% <br />contained algae and detritus, and 8.5% contained fish and mice. The abundance, <br />widespread distribution, and omnivorous feeding behavior of this introduced <br />fish may affect populations of rare and endangered fishes in the Green River <br />basin. (Abstract) <br /> <br />Report 16- Migrating Mormon crickets, Anabrus simolex (Orthoptera: <br />Tettigoniidae), as food for stream fishes. (Tyus and Minck1ey 1988) <br /> <br />Migrating bands of Mormon crickets (Anabrus simolex) were observed <br />crossing the Green and Yampa rivers in Dinosaur National Monument, Colorado <br />and Utah, in 1986 and 1987. Swimming crickets were swept downstream and eaten <br />by four endemic and seven introduced fish species. Included were two <br />endangered fishes, Colorado squawfish (Ptvchocheilus lucius) and humpback chub <br />(Gila ~). Direct and indirect effects to aquatic food webs associated with <br />application of pesticides for Mormon cricket control may pose a threat to <br />these fishes and to man. (Abstract) <br /> <br />Study 5: Trophic dynamics and ecological interaction in important backwater <br />habitats. <br /> <br />Report 17- Some aspects of trophic interactions in selected backwaters and the <br />main channel of the Green River, Utah. (Grabowski and Hiebert 1989) <br /> <br />Green River backwaters and adjacent channels were sampled in the Island <br />Park, Jensen, and Ouray reaches. Average seasonal water temperature was higher <br />downstream than upstream, and warmer in the backwaters than in nearby river <br />sites. Slightly warmer water temperatures and greater nitrogen and <br />phosphorous concentrations in Ouray backwaters may stimulate production of <br />blue-green algae; a major component of the <25 um size-fraction of <br />phytoplankton (nannoplankton) in backwaters. Zooplankton densities were low in <br />both the river and backwaters, but highest in Ouray backwaters. Larger <br /> <br />14 <br />