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<br />distributional attribute, but may well be used by young to locate ac- <br />ceptable habitat. Movement may be greatest in areas of marginal habi- <br />tat, such as the Colorado River in Colorado where streamflow has been <br />greatly reduced and backwater habitat is relatively scarce. <br /> <br />Reproduction and Early Life History <br /> <br />Colorado squawfish mature in 5-7 years (Vanicek and Kramer 1969, <br />Seethaler 1978). Hanman (1980) also indicated that captively spawned <br />and reared squawfish males matured in five years, females in six. <br />Spawning occurs when river temperatures are about 20 C (Holden and <br />Stalnaker 1975b), usually in July and August in the Upper Colorado <br />Basin. Spawning behavior has never been observed in the wild, but <br />Hanman (1980) observed captive fish spawn at Willow Beach National Fish <br />Hatchery. Two males would nudge a female's vent, causing her to vibrate <br />and release eggs, with the males extruding milt at the same time. The <br />adhesive eggs were broadcast with little regard for substrate and the <br />spawning act was repeated several times. Spawning took place over a <br />48-hour period in shallow depths (20-55 cm), and the eggs hatched in 96 <br />hours in 20 C water. The young fish fed on natural crustacean plankton <br />in the raceways and were 48-55 rrmin length in 110 days. <br />Observation of squawfish in the Yampa River in 1981 suggested <br />spawning occurs over riffles, adults spawn in fairly large groups of <br />males (8-10) with fewer females and they reside in adjacent pools bet- <br />ween spawning runs. The preponderance of males over females, especially <br />during spawning time, has been noted by several authors (Holden and <br /> <br />15 <br />