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were collected between 7 and 25 August at 10 sites between km 0.5 to <br />19.6 (stratum 1) in low-velocity habitats, i.e., backwaters (3), embayment <br />(1), pool (2), concavity (1), and 13 in isolated pools. <br />Age at time of capture (using methods described in Haynes and Muth <br />(1982) and Haynes et al., (in press)) was 5-15 days post-spawning for <br />drift collections (27 Jul) and 9-45 days for seine collections in the <br />Colorado River study area. Estimated spawning dates in the Colorado River <br />are 13-23 July for drift-caught animals and 10 July - 15 August for seine <br />specimens. In the Yampa River, spawning is estimated to have occurred <br />from 6 to 28 July 1982. <br />Analysis of YOY squawfish, 1979-82 <br />Since 1979, 102 YOY squawfish have been collected in the Colorado River <br />study area (Table 4), of which 89 were collected in Stratum H and 13 <br />in Stratum K. In the Yampa, only Stratum 3 (Deerlodge Park area) was <br />sampled in 1979 while Cross Mountain Canyon (Stratum 5), Lily Park (Stratum <br />4), and the downstream Dinosaur National Monument reach (Strata 1 and 2) <br />were added in 1980. A total of 89 YOY squawfish has been collected in <br />the Yampa during 1980-82 (Table 4), all of which were collected in the <br />lowermost 30 km of Dinosaur National Monument (Stratum 1). <br />In the Colorado River, estimated spawning dates during 1979-82 based upon <br />maximum and minimum size per collection and estimated growth rate ranged <br />from 18 June (1981) to as late as 26 August (1980) (Fig. 1). In the <br />Yampa, spawning is estimated to have occurred as early as 16 June (1980) <br />and as late as 3 August (1981) (Fig. 2). In 1981, we estimated that <br />spawning occurred in the lower Yampa as early as 25 June, which correlates <br />closely with the dates and locations of ripe radio-marked adults observed <br />over apparent spawning gravels in the same area by Tyus et al. (1981), i.e., <br />26 June - 10 July km 19.6 - 0.2. Comparative data for 1982 are not <br />available. Fish growth-rate is temperature-dependent (De Vlaming 1972), <br />and lower late-August water temperatures can be expected to reduce rate <br />of squawfish growth. Therefore estimated late-summer spawning dates should <br />probably be adjusted forward. Since growth rate-temperature data for <br />young squawfish are lacking, it is not possible, however, to determine to <br />what extent late-season spawning periods should be corrected. <br />Our estimated spawning periods indicate that squawfish spawning occurred <br />as water levels were decreasing and water temperatures were rising <br />(Fig. 1, 2). The possible interrelationships between spawning, flows, <br />and water temperature have been the subject of intense discussion and <br />speculation and has been summarized by Haynes et al. (in press}, <br />At this time, the influence of temperature upon spawning is apparently <br />based upon observations of adult ripeness by Vanicek and Kramer (1969), <br />hatchery observations by Toney (1974) and Hamman (1981), and this report. <br />>_,~ <br />