9588 - Laserfiche WebLink

Home Browse Search

EXECUTIVE SUMMARY Multiple-pass, capture-recapture sampling was conducted in most (819 river km) warm water reaches of the Green River Basin, Utah and Colorado, to estimate demographic parameters for recruit-sized (400 to 449 mm TL) and adult (? 450 mm TL) Colorado pikeminnow Ptychocheilus lucius. Three or four sampling passes were completed in each year for the Yampa, middle Green, and White River reaches (2000 to 2003), and the Desolation-Gray Canyon and lower Green River reaches (2001 to 2003). Parameter estimates derived from a Huggins robust-design multi-strata model suggested an apparent decline in abundance of Colorado pikeminnow throughout the Green River Basin, Colorado and Utah, over the study period. Based on the trend in annual point estimates from 2000 to 2003, reductions were most severe in the middle Green River (59 %) and the White River (63 %). Those reaches supported the highest number of Colorado pikeminnow in the Green River Basin. Apparent reductions in abundance were less severe in the Yampa River (29%), Desolation-Gray Canyon (11%), and lower Green River (36%) reaches, which supported smaller populations of Colorado pikeminnow. In 2001 when the entire basin was sampled, adult Colorado pikeminnow abundance was estimated at 3,304 (95% Cl, 2,900 to 3,707), declined to 2,772 (95% CI, 2,216 to 3,325) in 2002, and continued to decline in 2003 to 2,142 fish (95% CI, 1,686 to 2,598), a 35% reduction. Confidence limits for basin-wide estimates in 2001 and 2003 did not overlap. Assuming year 2000 population abundance in Desolation-Gray Canyon and lower Green River reaches when no sampling occurred was similar to 2001 (estimated abundance of 1,054 adults in 2001), basin- wide adult Colorado pikeminnow abundance estimates apparently declined from 4,084 in 2000 (3,030 in middle Green, Yampa, and White rivers in 2000, 95% CI, 2,467 to 3,592) to 2,142 in 2003, an apparent reduction of 48%. 3