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<br />r 1 <br />LJ <br />Other radio-tagged fish in the Colorado River have not displayed such dramatic <br />migratory behavior. Radio-telemetry studies conducted by the Colorado River <br />Fishery Project (Fishery Project) from 1982-1989 (Miller et al. 1982; Archer <br />et al. 1986; Osmundson and Kaeding 1989), which focused on upstream reaches of <br />the Colorado River in and around the Grand Valley, provide the best indication <br />of use of the 15-mile reach above the confluence of the Gunnison River at one <br />time or another during the field season. Movement of these fish during a <br />field season was generally limited to 25-30 miles. <br />During 1986-1988, the fishery Project radio telemetered 17 adult Colorado <br />squawfish collected from the 15-mile reach above the Gunnison River in June <br />(Osmundson and Kaeding 1989). The fish exhibited a diversity of localized <br />movement throughout the Grand Valley but spent a major part of time in the <br />15-mile reach. Two remained in the reach throughout the estimated spawning <br />period. <br />Spawning Activity <br />A suspected prespawning aggregation of adult Colorado squawfish was observed <br />by Fishery Project personnel at river mile 178.3 in the 15-mile reach above <br />the Gunnison River confluence in mid-July 1982. In the first observation, <br />three radio-tagged fish were tracked to one riverine pool area, and nine <br />adults at or near spawning condition were then captured there after limited <br />net sampling efforts. The aggregation occurred a few days after mean daily <br />water temperature had reached 20 °C and during a time when runoff flows were <br />dropping off sharply. A second aggregation was noted at river mile 175.3, <br />12 days after the initial observation. Drifting trammel nets through an area <br />occupied by two fish equipped with transmitters yielded an additional male <br />Colorado squawfish in spawning condition. During this same time period, an <br />adult female was captured near river mile 175 that weighed nearly 1 pound more <br />than when previously captured a month earlier, suggesting the development of <br />spawning (gravid) condition. <br />Larval Occurrence <br />Fishery Project studies included the routine sampling of the larval-fish <br />community both within and downstream of the ]5-mile reach. During 5 years <br />of investigation, 70 larval squawfish were collected with fine-mesh hand <br />nets from the two Colorado River reaches in the Grand Valley immediately <br />upstream and downstream of its confluence with the Gunnison River. Although <br />the sampling effort was similar in the two river reaches, 96 percent of the <br />larval captures occurred downstream of the Gunnison River confluence (river <br />miles 162-164). Only two (3 percent) of the larvae were collected from the <br />upstream reach. These observations may indicate that most fish were spawned <br />in the downstream reach or that the larvae were deposited in the upstream <br />reach and drifted downstream to the area where most of the captures were <br />recorded. <br />• <br />