Population Status of Colorado Pikeminnow in the Green River Basin, Utah and Colorado
DOI: 10.1577/T05-303.1
Title: Population Status of Colorado Pikeminnow in the Green River Basin, Utah and Colorado
Journal Title: Transactions of the American Fisheries Society
Volume: Volume 136
Issue: Issue 5
Publication Date: September 2007
Start Page: 1356
End Page: 1380
Published online: 9 Jan 2011
ISSN: 0002-8487
Author: Kevin R. Bestgena, John A. Hawkinsa, Gary C. Whiteb, Kevin D. Christophersonc, J. Michael Hudsond, Mark H. Fullere, D. Chris Kitcheyane, Ronald Brunsond, Paul Badamec, G. Bruce Hainese, Julie A. Jacksond, Cameron D. Walforda & Tasha A. Sorensena
a Larval Fish Laboratory, Department of Fish, Wildlife, and Conservation Biology , Colorado State University, Fort Collins, Colorado, 80523, USA
b Department of Fish, Wildlife and Conservation Biology, Colorado State University , Fort Collins, Colorado, 80523, USA
c Utah Division of Wildlife Resources , Northeast Regional Office , 152 East 100 North, Vernal, Utah, 84078, USA
d Utah Division of Wildlife Resources, Moab Field Station , 1165 South Highway 191, Suite 4, Moab, Utah, 84532, USA
e U.S. Fish and Wildlife Service , 1380 South 2350 West, Vernal, Utah, 84078, USA
Abstract: Capture-recapture sampling of 819 km of streams in the Green River subbasin, Utah and Colorado, of the Colorado River basin was conducted in 2000-2003 to estimate Population demographic parameters and recovery status for endangered Colorado pikeminnow Ptychocheilus lucius. Parameter estimates from a Huggins robust-design, multistratum model suggested a basinwide decline in the abundance of adult (total length, ≥450 mm) Colorado pikeminnow. Reductions were most severe in the middle Green River (59%) and White River (63%), the two largest Population segments. Reductions were less severe in the Yampa River (29%), Desolation-Gray Canyon (11%), and lower Green River reaches (36%). In 2001, the first year the entire subbasin was sampled, adult Colorado pikeminnow abundance was estimated at 3,304 fish (95% confidence interval, 2,900-3,707) but declined to 2,142 fish (1,686-2,598) by 2003, a 35% reduction. However, accounting for a reach not sampled in 2000 makes it likely that the reduction was 48% over the 2000-2003 period. The abundance of recruits (400-449 mm) in the study area averaged 8.9% of adult abundance. The annual survival rate for 2000-2003 was 0.65 (0.59-0.71), lower than the 0.82 rate estimated for 1991-1999; mortality exceeded recruitment. The few captures and lack of recaptures of fish of at least 800 mm suggest that apparent survival was low for large Colorado pikeminnow. The reduced abundance of adult Colorado pikeminnow was due, in part, to the weak year-classes of age-0 fish produced in the 1990s and the reduced survival of recruits and adults in 2000-2003. Based on these results, downlisting of this species is not warranted at this time. Better understanding of the factors that influence adult survival rates, abundance dynamics, and the recruitment of early life stages as well as the effects of flow recommendations and nonnative predaceous fishes would assist the conservation of Colorado pikeminnow.
Accepted: 3 Oct 2006

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