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<br /> <br />re the largest predaceous fish in the Colo- <br />do River, and large size presumably was an <br />'portant attribute with apparent selective <br />advantages. Thus, a long growth period ac'" <br />&lmpanied by delayed reproduction would <br />favor large adults. Rinne et al. (1986) cited <br />~low growth (to 50.8 em total length [TL] in <br />iUne. years) and long life in hatchery-reared <br />Colorado squawfish, and speculated that a <br />I.8-m specimen might be fifty or more years <br />of age. In the Green River, Seethaler (1978) <br />iD'dicated that Colorado squawfish less than <br />42.8 cm TL were immature, and those more <br />than 50.3 cm were mature. <br /> <br />I <br />I <br />--~ <br /> <br />I <br />L_ <br /> <br />WY <br /> <br />R. <br /> <br />The Colorado Squawfish 383 <br /> <br />Work on spawning grounds from 1981 to <br />1988 found 14 ripe females (average 65.4 em <br />TL) and 194 ripe males (55.5 em TL; Tyus and <br />Karp 1989). These observations supported the <br />earlier work of Vanicek (1967), who specu- <br />lated that females grew larger and perhaps <br />older than males. However, it is probable that <br />females do not remain ripe (with expressible <br />sex products) as long as males do, and unripe <br />fish captured during the spawning season may <br />also be females. If all fish captured are divided <br />on the basis of ripeness, and secondary sex <br />characteristics such as presence of dense nup- <br />tial tubercles in males (or their absence in <br /> <br />i! <br /> <br />:1;. :1:; <br />"i Iii <br /> <br />Spawning Areas 0 <br /> <br />Nursery Areas" <br /> <br /> I N <br /> I CO t <br /> I <br /> I <br />San <br /> I 0 50 100 1~0 km <br /> I I I I <br /> <br />Fig. 19-3. Map of the Green River sub-basin, <br />showing spawning areas to which annual <br />migrations of adult Colorado squawfish have been <br />confirmed and nursery areas in which squawfish <br />larvae are common. <br />