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38 <br />development, especially in upper distributional ranges. In low-flow <br />years, main-channel temperatures may be sufficient to trigger gonadal <br />development even in extreme upstream areas. The effect of cooler water <br />temperatures in 1982 was also evident in that spawning time was almost a <br />month later than in 1981. <br />The effect of colder river temperatures on native fish reproduction <br />in general was dramatically evident on the Green River below Flaming <br />Gorge Dam. Holden and Crist (1978) reported that reproduction of two <br />native suckers, the flannelmouth sucker (Catostomus latipinnis) and the <br />bluehead sucker (Catostomus discobolus), was curtailed in the tailwaters <br />of Flaming Gorge Dam downstream to the confluence with the Yampa River. <br />These fish reproduce earlier in the year and at cooler temperatures than <br />do Colorado squawfish. After inlet modifications to Flaming Gorge Dam, <br />reproduction resumed for these species in lower sections of the Green <br />River up to Ladore and Alcove Brook (upstream from the Yampa River <br />confluence). <br />Seethaler (1978) reported large numbers of adult-size Colorado <br />squawfish congregating below Flaming Gorge Dam just after closure in <br />1962. However, as tailwaters cooled, adult Colorado squawfish abundance <br />declined dramatically in the Green River reach between Flaming Gorge Dam <br />and the Yampa River confluence and no reproduction was evident. After <br />the dam inlet modification in June 1978, adult squawfish responded to <br />the warmer temperatures by returning to the lower segments of this river <br />reach (Holden and Crist, 1978). Radiotagged squawfish were tracked into <br />this segment of the Green in 1982 by the USFWS (Miller et al., 1983). <br />The inconsistent migration patterns noted in USFWS Colorado squawfish <br />radiotelemetry studies on the Upper Green River 1979-1982 may be caused