Reproduction, abundance, and recruitment dynamics of young Colorado Pikeminnow, Ptychocheilus lucius, in the Green River Basin, Utah and Colorado, 1979-2012

Authors: Kevin R.* Bestgen, Angela A. Hill

Year: 2015 (xlvii)

Abstract

We assessed long-term patterns of Colorado pikeminnow Ptychocheilus Lucius reproduction and age-0 recruitment in the Green and Yampa rivers of the upper Colorado River basin to better understand reasons for declining abundance of adults. Timing of reproduction in summer was positively related to date of peak spring runoff flow as well as water temperatures. Abundance of larvae produced from spawning areas was positively correlated with both spring peak and summer base flows (mean July-August flow) in the lower Yampa River and the lower Green River. In low flow years, few larvae were produced from spawning areas and transported to nursery habitat reaches in summer (e.g., 1994, 2002, 2007) so few age-0 pikeminnow were evident, especially in middle Green River backwaters in autumn. In most other years, production of larvae was thought sufficient to produce more age-0 fish but other factors controlled their survival and recruitment to autumn. Densities of age-0 Colorado pikeminnow in middle and lower Green River backwaters declined over the study period. Exact mechanisms controlling abundance of age-0 Colorado pikeminnow were not known, but moderate base flow levels were consistent with higher abundance in most years and lower abundance was noted in lower and higher base flow years. Growth of age-0 Colorado pikeminnow was positively related to length of the summer growing season and summer water temperature. Higher base flow levels were also associated with reduced autumn abundance of red shiner Cyprinella lutrensis, a potential competitor and predator on early life stages of native fishes. Although data patterns were messy, a result of high variability in pikeminnow abundance and environmental factors, a clear signal was that Green River base flows in summer and autumn need to be increased to favor survival of larger numbers of age-0 Colorado pikeminnow and bolster populations of adult life stages.