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Bioloov <br />The life-histon• phases that appear to be most critical for the Colorado pikeminnow include <br />spawning, egg fertilization, and development of larvae through the first year of life. These <br />phases of Colorado pikeminno~v development aze tied closely to specific habitat requirements. <br />Natural spawning of Colorado pikeminnow is initiated on Lhe descending limb of the annual <br />hydrosraph as water temperatures approach 20° C. Spawning, both in the hatchery and in the <br />field, generally occurs in a 2-month timeframe between July 1 and September 1, although high <br />flow water yeazs may suppress river temperatures and extend spawning in the natural system into <br />September. Conversely, during low flow yeazs when the water warms eazlier, spawning may <br />occur in late June. <br />Temperature also has an effect on egg development and hatching. In the laboratory, egg <br />mortality was 100 percent in a controlled test at 13° C. At 16° C to 18° C, development of the egg <br />is slightly retarded, but hatching success and survival of larvae was higher. At 20° C to 26° C, <br />development and survival through the larval stage was up to 59 percent (Hamman 1981). <br />Juvenile temperature preference tests showed that preferred temperatures ranged from 21.9° C to <br />27.6° C. The most preferred temperature for juveniles and adults was estimated to be 24.6° C. <br />• Temperatures neaz 24° C aze also needed for optimal development and growth of young (Miller et <br />al. 1982). <br />Most information on Colorado pikeminnow reproduction was gathered from spawning sites on <br />the lower 20 miles of the Yampa River and in Gray Canyon on the Green River (Tyus et al. 1982; <br />Tyus and McAda 1984; Tyus 1985; Wick et al 1985; Tyus 1990). Colorado pikeminnow spawn <br />after the peak runoff season from June to mid-August. Spawning begins when water <br />temperatures reaches 18° to 2S° C, and peak spawning activity occurs between 22° to 2S° C <br />(Haynes et al. 1984; Archer et al. 1985; Tyus 1990). During the decline in water level following <br />peak runoff, spawning adult fish move into run-riffle aeeas and occupyrun, eddy, and pool <br />habitats (Tyus 1990). Afrer spawning, adult Colorado pikenunnow utilized a variety of riverine <br />habitats including eddies, backwaters, shorelines, and others (Tyus 1990). <br />Specific spawning sites of Colorado pikeminnow have not been identified outside of the Green <br />River Basin. However, spawning has been confirmed by the presence of larval pikeminnow in <br />two reaches of the Colorado River; Black Rocks to Loma, and Grand Junction to Clifton (McAda <br />and Kaeding 1991). The presence of larval pikeminnow aggregations and suitable spawning <br />habitat in the Colorado River neaz Cataract Canyon, Professor Valley, and upstream from the <br />Dolores River confluence indicate spawning is occurring in or neaz these areas as well (Archer et <br />al. 1985; Valdez 1990). <br />Data indicates that clean cobble substrates aze necessary for spawning and incubation (Tyus and <br />Karp 1989). Several studies on the cobble cleaning process have been conducted at a knowtt <br />spawning location in Yampa Canyon. O'Brien (1984) studied the hyd:-aulic and sediment <br />transport dynamics of the cobble baz within the Yampa River spawning site and duplicated some <br />