ESR 34:131-147 (2017)  -  DOI: https://doi.org/10.3354/esr00842

Long-term mark-recapture monitoring of a Colorado pikeminnow Ptychocheilus lucius population: assessing recovery progress using demographic trends

Douglas B. Osmundson1,3,*, Gary C. White2

1Colorado River Fishery Project, US Fish and Wildlife Service, 445 West Gunnison Ave., Suite 140, Grand Junction, CO 81505, USA
2Department of Fish, Wildlife, and Conservation Biology, Colorado State University, 1484 Campus Delivery, Fort Collins, CO 80523, USA
3Present address: 380 34 Road, Palisade, CO 81526, USA
*Corresponding author:

ABSTRACT: Colorado pikeminnow Ptychocheilus lucius, a large, endangered, piscivorous cyprinid once abundant throughout warm-water reaches of North America‚Äôs Colorado River system, has been reduced to 2 wild populations inhabiting the Colorado and Green rivers. Status and trends of these remaining populations were unknown when a recovery program was initiated in 1987. During 1991 to 2013, we used mark-recapture to monitor the smaller Colorado River population. Adult abundance was estimated and patterns of recruitment and dispersal assessed to determine if recovery actions produced a population response. In 1992, adults were rare (Ñ = 345; 95% CI = 216 to 583) in the 288 km study area, but recruitment of a strong 1986 year class began a positive trend, and adult estimates reached 674 (95% CI = 517 to 897) by 2008. A significant decline then ensued, and by 2013, an estimated 282 adults remained (95% CI = 204 to 407). Annual adult survival was relatively high and stable. Juvenile survival was variable, making catch rates of young-of-the-year unreliable predictors of later recruitment strength. An estimated average of 6.5 fish immigrated annually to the Colorado River from the larger Green River population, and movements appeared balanced in direction. Though self-sustaining over the 23 yr study, low abundance and a recent rapid decline suggest long-term population persistence is tenuous. Population increase is impeded by a high frequency of weak recruiting cohorts. Results suggest 25 yr of recovery efforts have not sufficiently addressed ongoing threats affecting recruitment, including river regulation, non-native fish invasions, and other potential threats yet to be evaluated.


KEY WORDS: Riverine fish · Endangered species · Mark-recapture · Monitoring · Recovery · River regulation · Ptychocheilus lucius · Colorado River · Colorado pikeminnow


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Cite this article as: Osmundson DB, White GC (2017) Long-term mark-recapture monitoring of a Colorado pikeminnow Ptychocheilus lucius population: assessing recovery progress using demographic trends. Endang Species Res 34:131-147. https://doi.org/10.3354/esr00842

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