Evolving nonnative fish control efforts in the middle Green River

Authors: Richard Staffeldt, Robert Schelly, Matthew Breen

Year: 2016 (xlviii)

Abstract

A growing complement of nonnative fish species in the upper Colorado River basin (UCRB) presents one of the most serious threats to imperiled native fishes. Out of more than 50 species of nonnative fishes, three predatory species are of major concern and have been the focus of intensive mechanical removal efforts: Smallmouth Bass (Micropterus dolomieu), Walleye (Sander vitreus), and Northern Pike (Esox lucius). Over the last 15 years, these efforts have been increased in scope and honed for efficiency throughout the UCRB. Here we consider the effectiveness of nonnative fish control by the Utah Division of Wildlife Resources in the middle Green River for each of these piscivorous species. Smallmouth Bass captures have decreased markedly since 2013, presumably due to multiple years of environmental conditions unfavorable to Smallmouth Bass recruitment (high spring peak flows, cooler spring/summer temperatures), combined with our targeting of ‘hotspots’ and disruption of known spawning grounds. Walleye are an emerging threat in the system, and have become the focus of dedicated removal efforts since 2014; annual captures have remained steady in recent years. Currently riverine recruitment is limited, despite identification of a spawning area in 2015 located in Dinosaur National Monument. Steps are being taken to eliminate local reservoir sources of Walleye (rotenone treatments, screening). Adult Northern Pike have been effectively targeted with early spring fyke-netting while attempting to spawn in backwaters, tributaries, and off-channel wetlands, with the exception of a successful cohort following extended spring peak flows in 2011. This talk will evaluate the effectiveness of our nonnative mechanical removal methods based on trends in capture rates in recent years.