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<br />. <br /> <br />. <br /> <br />7 <br /> <br />Colorado Squawfish <br />Biological Requirements <br /> <br />The life-history phases that appear to be critical to the Colorado squawfish <br />include spawning, egg fertilization, and development of larvae through the <br />first year of life. These phases of Colorado squawfish development are also <br />tied closely to specific habitat requirements. Natural spawning of Colorado <br />squawfish is initiated at approximately 20 degrees Celsius (C). Spawning, <br />both in the hatchery and in the field, generally occurs in a I-month timeframe <br />between June 15 and August 15, although high-flow water years may suppress <br />river temperatures and delay spawning in the natural system until September. <br /> <br />Temperature also has an effect on egg development and hatching. In laboratory <br />studies, egg mortality was lUO percent in a control test at 13 degrees C. At <br />16 to 18 degrees C, egg development was slightly retarded, but hatching <br />success and survival of larvae was higher. At 20 to 26 degrees C, development <br />and survival through the larval stage was up to 59 percent. <br /> <br />Juvenile temperatures preference tests showed that preferred temperatures <br />ranged from 21.9 to 27.6 degrees C. The most preferred temperature for <br />juveniles and adults was estimated to be 24.6 degrees C (Miller, <br />et al., 1982). Temperatures near 24 degrees C are also needed for optimal <br />development and 9rowth of young (Miller, et al., 1982). <br /> <br />Recent field studies have further defined the preferred spawning habitat for <br />Colorado squawfish. 8ased on field observations, primarily from the lower <br />Yampa River in Colorado and main stem Green River in Utah, Colorado squawfish <br />prefer to spawn in low gradient, braided reaches with riffles and cobble bars <br />that are in close proximity to deep pools used for adult staging and resting. <br />Although exact location of spawning areas in the Colorado River have not been <br />identified, the presence of larvae near the confluence of the Gunnison River, <br />in the Lorna to Blackrocks reach, and near the confluence of the Dolores River, <br />suggest that spawning occurs nearby. <br /> <br />Related to spawning of Colorado squawfish is the migration of these fish to a <br />spawning area. Miller, et ale (1982) have demonstrated the occurrence of <br />spawning migrations in the Green and Yampa Rivers and similar movement has <br />been noted in the main stem Colorado River. In the Green River subbasin, such <br />migrations are typified by upstream and downstream movement of adult squawfish <br />in the spring and early summer months, often over long distances, to a <br />specific reach where spawning takes place (Tyus, 1983; Archer, et al., 1984). <br /> <br />Miller, et al. (1982) concluded from collections of larvae and young-of-year <br />(yay) below suspected spawning sites that there is a downstream drift of <br />larvae and yay Colorado squawfish following hatching. Larval drift is thought <br />to range from a few miles (1-10 miles) to many miles (up to 100 miles). <br /> <br />Miller et al. (1982) also indicated that yay Colorado squawfish, frorn late <br />summer through fall, preferred natural backwater areas of zero velocity and <br />