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Reach 4-The upper Green River reach extends from Split Mountain Campground at the lower <br />end of Dinosaur National Monument downstream 120 miles to Sand Wash, just upstream from <br />Desolation Canyon. The uppermost 10 miles are characterized by steeper gradient (mean, 4.2 ft/mi) <br />and cobble-rubble substrate. Below that point, the river enters the broad Uintah Basin floodplain and <br />is relatively slow and meandering (mean, 1.1 ft/mi) with primarily sand-silt substrate. The lowermost <br />10 miles are confined within aloes-desert canyon, also with low gradient and fine substrates. <br />Methods <br />River Flows and Water Temperatures <br />Mean-daily river flow measured at USGS gaging stations nearest to each sampling reach (Figure <br />1; Reach 1, Colorado River at Cisco, Utah; Reach 2, Colorado River at Utah-Colorado State line; <br />Reach 3, Green River at Green River, Utah; and Reach 4, Green River at Jensen, Utah) was averaged <br />for the sampling period in each reach. Various river flow parameters over the course of the year <br />were also summarized. Mean flow for the months of April through September was calculated for <br />each of the 7 years of ISMP. Mean-daily river flow for the day of highest flow during the year was <br />determined. In addition, mean flow during the period including 15 days before and 15 days after the <br />day of highest mean-daily river flow for the year was calculated (average high flow). Water <br />temperature for each reach was summarized by summing the degrees (C) by which mean-daily water <br />temperature exceeded 12, 16, and 20°C over the course of the year (accumulated temperature units). <br />Flow records were complete for all USGS gages summarized here; however, temperature records <br />were inconsistent. Gages on the Green River at Green River, Utah and Colorado River at the Utah- <br />Colorado state line used continuously recording thermographs so a true mean could be calculated. <br />However, gages on the Green River at Jensen, Utah and Colorado River at Cisco, Utah reported once <br />daily measurements (i.e. someone measured water temperature by hand once a day). Although not a <br />daily mean, these values were used in temperature calculations because they were the only data <br />available for these stations. There were also significant gaps in temperature data during some years at <br />some gages. Short gaps (i.e. 15 days or less) were filled using interpolation between temperatures <br />recorded on either end of the missing data. However, gaps longer than 15 days or gaps that occurred <br />during periods when temperatures were rapidly changing were not filled because interpolation was not <br />considered appropriate in those cases. Water temperature data were not summarized when gaps could <br />not be filled. As a result, temperature data were not summarized for Reach 2 in 1986 and 1987 and <br />for Reach 4 in 1987. <br />Colorado squawfish Sampling <br />Each reach sampled was divided into 5-mile subreaches which formed the basis for the sampling <br />design (Figure 2). A sampling crew began at the top of each reach and traveled downstream until it <br />reached a suitable backwater (surface area of at least 30 m2 and maximum depth of at least 30 cm, <br />unless the water was turbid) which it sampled with a 4.6-m-long, 3-mm-mesh seine. Two non- <br />overlapping seine hauls were taken in the backwater. Effort was recorded as area swept by the seine. <br />Colorado squawfish were measured, counted, and released alive if they were large enough to be <br />reliably identified. Fish of other species that were also large enough to reliably identify were counted <br />and released. All remaining fish in the first sample were preserved for later identification in the <br />laboratory to check for Colorado squawfish too small to be identified in the field. Non-target fishes <br />were later counted in the laboratory for this sample only. Investigators then proceeded downstream <br />4 <br />