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Figure 1. Distribution of adult Colorado pikeminnow (>500 mm long) in the Colorado <br />River. Catch rates (fish per mile) were averaged across sampling (electrofishing and <br />trammel netting) passes in each year and these values from five years (1991-1994 and <br />1998) were averaged. See Osmundson and Burnham (1998) for sampling methodology <br />and Osmundson (1996) for strata locations. <br />T <br />a <br />E <br />i._ <br />0.8 <br />0.6 <br />0.4 <br />0.2 <br />0 <br />Adult distribution <br />(> 500 mm long) <br />2 3 4 5 6 7 8 9 <br />Study strata I 5-mile reach <br />Radio-telemetry studies show upstream and downstream movement of adult Colorado <br />pikeminnow in the main stem Colorado River (McAda and Kaeding 1991). The most <br />dramatic movement was exhibited by a fish implanted with a radio transmitter at Gypsum <br />Canyon in upper Lake Powell on April 5, 1982. The fish was contacted next in the lower <br />Cataract Canyon area on July 9, 1982. The next contact was made above the Black <br />Rocks area of Ruby Canyon, some 160 miles upstream. The movement was <br />accomplished in 41 days and is believed to be related to spawning. At the end of <br />September 1982, this fish was located in the 15-mile reach (river mile 178), nearly 200 <br />river miles from it's furthest documented downstream location. <br />Other radio-tagged fish in the Colorado River have not displayed such dramatic <br />migratory behavior. Radio-telemetry studies conducted during 1982-1989, which <br />focused on upstream reaches of the Colorado River in and around the Grand Valley, <br />provide the best indication of use of the 15-mile reach above the confluence of the <br />Gunnison River. Movement of these fish during a field season was generally limited to <br />25-30 miles (Osmundson and Kaeding 1989, McAda and Kaeding 1991). <br />The river downstream of the Grand Valley supports adult Colorado pikeminnow, in fact., <br />the entire river, from the confluence with the Green River upstream to Palisade, <br />Colorado, provides important habitat for sub- and young adults. The primary importance <br />of reaches downstream of the Grand Valley is in providing nursery areas for larvae and <br />rearing areas for juveniles. Concentrations of larvae and young-of-year occur in <br />backwaters in the 65-mile, low-gradient reach between Moab, Utah and the confluence <br />with the Green River (McAda et al. 1994). These backwaters are especially important <br />during the Colorado pikeminnow's critical first year of life. Juveniles dwell in these <br />downstream reaches until they are five or more years old. Then many begin extensive <br />upstream migrations seeking habitats more suited to needs of subadults and adults <br />(Osmundson et al. 1998). <br />15