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... l~H THANS, AMElL FISH, SOc., 1%9, NO.2 , FIGi:IlE I.-Green River study area, showing lo_ cation of sampling stations, GR = Greendak <USGS); LH = Little Hole; BP = Bridgeport; LO = Lodore; EP = Echo Park; IP = Island Park' SM = Split Mountain; JE = Jensen (USGS); OU = Ouray, have been inundated, and operation of Flam- ing Gorge Reservoir has resulted in maj or changes in flow and temperature patterns in the river below the dam,4 The present investigation was part of a follow-up study to determine the effects of the fish control program upon fish popula- tions in Dinosaur National Monument 46 miles downstream from Flaming Gorcre Dam ~ 0 , and to assess changes on habitat and popula- tions in the Monument brought about by the closure of Flaming Gorge Dam. METHODS AND MATERIALS The study area was limited to the Green Hiver primarily in Dinosaur National Monu- ment, but collecting sites were also located 4 Vanieek, C David, Rohert II Kramer, and the late Donald Il. Fr:lllklin (MS), Di,rrihuliou of Grecn Hi,'er fishes following closure of Flaming Gorge Dam, above and below the Monument Location of sampling sites was dictated largely by ve- hicle and boat access to the river. Intensive sampling stations were established at Lodore, Echo Park, Island Park, and Split Mountain, all within Dinosaur National Monument, and supplemental statior.3 were located at Liule Hole, Bridgeport, and Ouray (Figure 1), Fish populations were sampled with nylon experimental gill nets 75. and 150-ft long with mesh sizes ranging from 3/4.inch to 3-inch stretch measure; a 30-ft, 1/4-inch mesh, nylon straight seine; a 15-ft, lI8-inch hobbinet straight seine; an electric shocker powered by a 230-volt generator and mounted on an 18-ft aluminum flat-bottomed boat fitted with stainless steel electrodes; tow nets; food strainers; and a modified scoop shovel with window.screen inserts. Fish specimens were preserved in 10-per- cent formalin in the field and later trans. ferred to 40-percent isopropyl alcohol in the laboratory. Total length (from the tip of the snout to the tip of the caudal fin when com- pressed) of all fish was measured to the nearest millimeter, and weight was recorded in grams_ Approximately 10 scales were taken from the right side of each fish just above the lateral line for age and growth determina- tions. Stomachs were taken from fish of all size groups, and contents were analyzed with the aid of a binocular microscope. Continuous recordings of water tempera- tures were made with Ryan Model D porta hIe recording thermometers, Daily temperature readings were made at all stations with a pocket thermometer when fish samples were taken, Water temperature records were also obtained from U.S, Geological Survey records for gaging stations at Greendale and Jensen, Water quality analyses were made at least once each visit to a sampling station. Two morphological variants of the Colo- rado chub were present in the area and are referred to in this study as the "round tail" Illld the "honytail." These two forms were classified as subspecies Gila robusta robusta and G. r. elegans, respectively, by Miller ( 1946), The taxollumy of these fishes is poorly ulldt~rstood alld criteria are not avail- able for distillguishing between young fish of