Laserfiche WebLink
fish were alive in 2000, and only 11 % in 2003. With only a single high recruitment year since <br />1994 (1998), it appears that recruitment events may need to be more frequent to forestall <br />population declines of Colorado pikeminnow in the Green River. <br />A reason for low abundance of recruit-sized Colorado pikeminnow in 2000 to 2003 may <br />be related to relatively low abundance of young-of-year produced in nursery areas (Fig. 20, Muth <br />et al. 2000; McAda 2002; unpublished data Utah Division of Wildlife Resources). Density of <br />age-0 Colorado pikeminnow in backwaters in autumn has declined rather dramatically since the <br />early 1990's, especially in the middle Green River. Relatively strong year-classes in the middle <br />and lower Green River were last produced in 1993. That year class would have first contributed <br />adults to the Green River Colorado pikeminnow population in year 2000, the year when estimates <br />of abundance of adult Colorado pikeminnow in the middle Green River were the highest observed <br />during this study. This recruitment scenario was based on growth rates of Colorado pikeminnow <br />presented by Osmundson et al. (1997), where an average age-0 fish in a given year-class (e.g., <br />1993) was expected grow to an average of 425 mm TL, a recruit-sized fish, six years later <br />(Osmundson et al. 1997). That same group of fish would then recruit to adult size (? 450 mm TL) <br />one year later at age 7 (e.g. year 2000). Subsequent year-classes (1994 to 1996) that would have <br />contributed adults to the Green River population of Colorado pikeminnow from 2001 to 2003 <br />were very weak in the middle Green River and only moderately strong or weak in the lower Green <br />River. <br />In the Colorado River, strong recruitment year-classes of Colorado pikeminnow were also <br />linked to strong year-classes of early life stages (Osmundson and Burnham 1998). The link <br />between early life stage year-class strength and abundance of recruit-sized Colorado pikeminnow <br />in the Green River Basin deserves further investigation. Such an analysis should include <br />55