Efficacy of Mechanically Removing Nonnative Predators from a Desert Stream

Abstract

AbstractNative fish faunas throughout the American Southwest have declined dramatically in the past century, mainly a consequence of habitat alteration and alien species introductions. We initiated this 6‐year study to evaluate the efficacy of mechanical removal of nonnative predaceous rainbow trout Oncorhynchus mykiss, brown trout Salmo trutta, yellow bullhead Ameiurus natalis and smallmouth bass Micropterus dolomieu from an open 4.6‐km reach of West Fork Gila River in southwest New Mexico, USA. Removal efforts involved intensive sampling with a 10‐ to 12‐person crew using backpack electrofishers and seines to capture fish over a 4‐ to 5‐day period each year. Additionally, two reference sites were sampled with similar methods to compare temporal changes in species mass in the absence of a removal effort. Results were mixed. Mass of yellow bullhead, rainbow trout and brown trout declined in the removal reach from 2007 through 2012, but there was no change in smallmouth bass. Concurrently, mass of Rainbow trout, yellow bullhead and smallmouth bass did not change at reference sites, but brown trout mass declined, indicating factors other than removal were driving abundance of brown trout. Occurrence of several large flathead catfish Pylodictis olivaris in the removal reach in 2012 changed what would have been a decline in overall nonnative mass to no change over the course of the study. Spikedace Meda fulgida was the only native species positively responding to predator removal. Results of this study suggest that with moderate effort and resources applied systematically, mechanical removal can benefit some native fish species, but movement of problem species from surrounding areas into removal reaches necessitates continued control efforts. Copyright © 2014 John Wiley & Sons, Ltd.