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10 Spawning Activity A suspected prespawning aggregation of adult Colorado squawfish was observed by Fishery Project personnel at river mile 178.3 in the 15-mile reach above the Gunnison River confluence in mid-July 1982. In the first observation. three radio-tagged fish were tracked to one riverine pool area, and nine adults at or near spawning condition were then captured there after limited net sampling efforts. The aggregation occurred a few days after mean daily water temperature had reached 20' C and during a time when runoff flows were dropping off sharply. A second aggregation was noted at river mile 175.3, 12 days after the initial observation. Drifting trammel nets through an area occupied by two fish equipped with transmitters yielded an additional male Colorado squawfish in spawning condition. During this same time period, an adult female was captured near river mile 175 that weighed nearly 1 pound more than when previously captured a month earlier. suggesting the development of spawning (gravid) condition. Larval Occurrence Fishery Project studies included the routine sampling of the larval-fish community both within and downstream of the 15-mile reach. During 5 years of investigation, 70 larval squawfish were collected with fine-mesh hand nets from the two Colorado River reaches in the Grand Valley immediately upstream and downstream of its confluence with the Gunnison River. Although the sampling effort was similar in the two river reaches, 96 percent of the larval captures occurred downstream of the Gunnison River confluence (river miles 162-164). Only two (3 percent) of the larvae were collected from the upstream reach. These observations may indicate that most fish were spawned in the downstream reach or that the larvae were deposited in the upstream reach and drifted downstream to the area where most of the captures were recorded. In August of 1995 several larval Colorado squawfish were captured in the 15-mile reach (Doug Osmundson, pers. comm.). Postlarval Young-of-Year Occurrence No postlarval young-of-year Colorado squawfish greater than 25 mm total length were collected from above the Gunnison River confluence in a total of 57 samples collected in the fall of 1982-1986. However. a total of 62 Colorado squawfish were collected in an 18-mile reach of the Colorado River below the confluence of the Gunnison River (54 samples). The 1982-1984 catch rate of young-of-year Colorado squawfish in the 10-mile reach immediately downstream of the confluence of the Gunnison River (river miles 160-170)