Quantifying the Predatory Threat of a Nonnative Fish on Native Fishes in the San Juan River

Authors: Skyler Hedden, Keith Gido, Bobby Duran, Scott Durst, Nathan Franssen, Eliza Gilbert, Crosby Hedden, Brian Hines, Mark McKinstry, Casey Pennock

Year: 2018

Abstract

Nonnative fishes, such as Channel Catfish, Ictalurus punctatus, potentially have negative impacts on native fishes, but their effects on native communities can be difficult to quantify. Specifically, predation on native fishes will likely vary spatially and temporally based upon prey availability and abiotic conditions, thus quantifying a predator’s ability to diminish native fishes needs to incorporate multiple spatial and temporal scales. To quantify the predatory threat of Channel Catfish on native fishes, stomach fullness, stomach evacuation rates, and diets were quantified throughout the San Juan River, NM, CO, and UT over both fine (24 hour) and broad (seasonally) temporal scales. Stomach fullness varied both spatially and seasonally but contrary to our expectations, no diel differences in fullness were observed. Stomach evacuation rates, measured in a laboratory setting, increased with water temperatures and fish prey items took 7-75 hours to digest to 50% of their initial wet weight. Lastly, diets were composed of both aquatic (~60%) and terrestrial (~40%) materials, of which fish remains were in a relatively low frequency (0-0.25) of stomachs and native fishes represented 52% of the total fish prey consumed by Channel Catfish. Identifying nonnative predator impacts on native species across multiple scales may help develop management strategies to minimize negative interactions between native and nonnative fishes.