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Table 2 <br />Colorado squawfish captures in the Colorado and Green Rivers, <br />Standardized sampling, 1979-1981 <br />Strata_? <br />Size Class A B C D E F G H I J <br />Colorado River <br />Young-of-the <br />year 11 285 17 15 3 2 3 <br />Juvenile 3 36 14 6 3 1 2 <br />Adult 9 3 6 5 1 16 3 <br />Green River <br />Young-of- <br />the-year 276 106 32 23 160 320 <br />Juvenile 82 28 28 4 95 43 <br />Adult 9 13 3 4 17 22 <br />1/ See Figure 1 for strata location. Each strata represents <br />a homogenous river section systematically sampled. Strata range from <br />A, the lowest sections of the rivers, to F on the Green River and J on <br />the Colorado, the highest sections. <br />Juvenile squawfish were scarce in most collections, probably due to <br />gear selectivity. General trends in juvenile distribution showed the <br />squawfish more prevalent in the lower 100 miles of the main Colorado <br />River above Lake Powell (Figure 2). Juveniles were more prevalent in the <br />Green River between the White River's confluence and Desolation Canyon, <br />and in Labyrinth Canyon (Figure 3). <br />Collections of larvae in the lower 20 miles of the Yampa River in <br />1981 documented the first spawning grounds for Colorado squawfish. <br />Collections of large numbers of larvae in the Green River below Split <br />Mountain and Gray Canyons indicated that these areas too may have spawn- <br />ing grounds (Figure 3). Work in the Yampa and Green Rivers indicated a <br />downstream drift of Colorado squawfish larvae. Larval squawfish appa- <br />rently drifted downstream away from the swifter, more harsh environments <br />that provide suitable spawning habitat into the more moderate river <br />reaches with a greater prevalence of the needed backwaters and other <br />quiet water niches. <br />In the Colorado River the picture is not as clear for YOY distribu- <br />tion (Figure 2). Collections of a few larvae below Loma (RM 154) and the <br />presence of apparently good spawning habitat suggests that spawning <br />occurred between Loma and Black Rocks. Most YOY squawfish in the Colo- <br />rado River were collected between Potash (RM 47) and the head of Cataract <br />Canyon (RM 3). This distribution suggests: (1) poor or no survival from <br />the upstream spawning activity; (2) drift of larvae may have been more <br />extensive, over 100 miles, than anticipated, perhaps because of the <br />absence of good nursery habitat for a considerable distance downstream of <br />~ Loma; (3) the YOY fish may have come from the Green River, since the <br />Green River empties into this section and may be the source of many of <br />these small Colorado squawfish although YOY would have to swim upstream <br />from the confluence; and (4) spawning may have occurred in the Professor <br />Valley area (RM 78) from which these YOY could have emigrated. <br />8