9436

• UCREFRP Catalog Number: 9436
• Author: McAda, C. W.
• Title: Subadult and Adult Colorado Pikeminnow Monitoring; Summary of Results, 1986-2000.
• USFW Year: 2002.
• USFW - Doc Type: Recovery Program Project Number 22,
• Copyright Material: NO

EXECUTIVE SUMMARY.
Colorado pikeminnow (Ptychocheilus lucius) is a large piscivorus cyprinid endemic to
the Colorado River basin that is currently listed as endangered under the Endangered Species
Act of 1973 (as amended). A cooperative recovery program was developed to provide
funding for research and management actions that would ultimately lead to recovery of the
species. As part of that recovery program, the Interagency Standardized Monitoring Program
(ISMP) was begun to measure trends in relative abundance of adult Colorado pikeminnow in
large segments of its range in the upper Colorado River basin.
ISMP sampled 186 miles of four rivers in the upper basin -the Green (five reaches, 77
mi), Colorado (three reaches, 54 mi), White (two reaches, 30 mi), and Yampa (three reaches,
25 mi) rivers. Sampling was done by electrofishing both shorelines of the sampling reaches
using hard-bottom electrofishing boats. Relative abundance of Colorado pikeminnow was
estimated by mean catch per effort (CPE; fish captured per hour of electrofishing) by river and
by year.
Sampling began in 1986 and terminated in 2000. Significant differences in mean CPE
among years and significant positive relationships over time indicated that the Colorado
pikeminnow population increased during the 15-year study period. The most dramatic
increases occurred in the Green and White rivers, with a lesser increase in the Colorado and
Yampa rivers. Relative abundance, as estimated by electrofishing CPE, dropped off in the
Colorado River in the last two years of sampling; however, it continued to climb in the Green
and White rivers. Relative abundance in the Yampa and Colorado rivers exhibited two or
more plateaus rather than steady increases as occurred in the White and Green rivers.
ISMP detected an increasing trend in the adult Colorado pikeminnow population.
However, the sampling design did not allow robust estimation of actual population size.
ISMP was terminated after an expanded study was initiated that was specifically designed to
develop mark-recapture population estimates for all areas in the upper basin occupied by
Colorado pikeminnaw. This report provides a final summary of ISMP data for adult Colorado
pikeminnow.
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