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20-25°C, but the July-August backwater temperatures at fish capture <br />averaged 25-28°C. Thus, backwater temperatures were higher than the 21- <br />26°C temperature range in which the hatchery fish were raised and we <br />expected Green River fish to grow faster in backwaters. Otoliths from fish <br />collected in 1987 (x=42.4 mm, range 29-65 mm TL, N=28) indicated a great <br />degree of variability between the ages calculated from TL and those <br />obtained by reading daily growth rings in the otoliths (R. Muth, Colorado <br />State University, personal communication). However, the wild fish averaged <br />about 13 d younger than that calculated from TL. We presumed that the <br />Green River fish grew faster than the hatchery-raised fish, and that <br />hatching dates of these fish were not predicted accurately by the equation <br />we used. -Such equations need more validation by aging wild fish of <br />different sizes before they should be applied to fish management. <br />Colorado squawfish spawning times have been estimated by others. Our <br />back-calculated hatching dates, after adjustment to spawning date by <br />subtracting five days, were similar to results of Nesler et al. (1988) <br />for the Yampa River spawning area for 1983-1986. However, they collected <br />smaller fish (93% < 22 mm TL), than we did (39% < 22 mm, 61% 22-45 mm) and <br />presumably obtained a better estimation of spawning date. Tyus and Karp <br />(1989) did not rely only on larval catches to estimate spawning of <br />Colorado squawfish, and based their "optimum spawning period" on the <br />average dates of appearance of radio-tagged adults on the spawning <br />grounds, collections of ripe fish, and back-calculated spawning dates for <br />the years 1981-1987 in the Yampa River. All of these studies were in <br />general agreement with respect to average annual spawning dates. <br />14 <br />