Colorado pikeminnow recruitment in the upper Colorado River basin: a new perspective for the Green River, Utah

Authors: Breen, Matthew J.*, Bestgen, Kevin R., Michaud, Christopher M.

Year: 2015 (xlvii)

Abstract

Long-term monitoring data is valuable to assess distribution and abundance of endangered fish populations and their response to environmental management and invasive species. Young-of-year (YOY) Colorado pikeminnow (Ptychocheilus lucius) sampling is ongoing since 1986 in the upper Colorado River basin as part of the Interagency Standardized Monitoring Protocol (ISMP) to monitor recruitment success of this federally endangered species. Survival of YOY pikeminnow varies greatly between years independent of spawning success as a result of numerous interacting biotic and abiotic factors including flow variation, water temperature, rearing habitat condition and availability, and competition and predation by nonnative fishes. Autumn ISMP sampling is intended to provide a large-scale (224 miles of the Green River, 111 miles of the Colorado River) snapshot of annual recruitment following spawning and summer growth periods. To accomplish this, a sub-sample of backwater habitats that meet specific criteria are seined, focusing on two nursery habitat reaches in the Green River (104 and 120 miles) downstream of known Colorado pikeminnow spawning locations. In the Green River, Utah, we observed a marked decline in autumn recruitment beginning in 1994, with the exception of high production years 2009 and 2010, and adult Colorado pikeminnow populations are declining throughout the Green River basin, the largest remaining population. In light of poor recruitment for more than two decades, preliminary data from our 2015 efforts indicate successful reproduction and late summer survival, widespread occupation of backwater habitats throughout sampling reaches, and capture of several hundred YOY pikeminnow. One potential explanation for this success may derive from summer flow regimes (i.e., base flow timing and magnitude) given that experimental water releases from the Flaming Gorge Dam have benefitted other endangered fishes (e.g., razorback sucker). Following a significant effort to analyze available data from 1979 Á¢â‚¬ ’ present, we recommend maintaining summer base flows within a specific range through manipulation of flow releases from Flaming Gorge Dam. This action is needed immediately as it offers the best opportunity to boost survival of young fish that only add to the adult population 5-8 years later. Flow management, along with invasive species control, may provide additional tools to aid recovery of Colorado pikeminnow in the upper Colorado River basin.