Yellowstone Lake Ecosystem Restoration: A Case Study for Invasive Fish Management

Todd M Koel,Nathan A Thomas,Lusha M Tronstad,Robert E Gresswell,Christopher S Guy,Brian D Ertel,David P Sweet,Colleen R Detjens,Alexander V Zale,Patricia E Bigelow,Todd J Stuth,Jeffery D Davis,Michael E Ruhl,Drew J Macdonald,Philip D Doepke,Travis O Brenden,Hayley C Glassic,Jeffery L Arnold,John M Syslo,P J White

doi:10.3390/fishes5020018

Abstract

Invasive predatory lake trout Salvelinus namaycush were discovered in Yellowstone Lake in 1994 and caused a precipitous decrease in abundance of native Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri. Suppression efforts (primarily gillnetting) initiated in 1995 did not curtail lake trout population growth or lakewide expansion. An adaptive management strategy was developed in 2010 that specified desired conditions indicative of ecosystem recovery. Population modeling was used to estimate effects of suppression efforts on the lake trout and establish effort benchmarks to achieve negative population growth (λ < 1). Partnerships enhanced funding support, and a scientific review panel provided guidance to increase suppression gillnetting effort to >46,800 100-m net nights; this effort level was achieved in 2012 and led to a reduction in lake trout biomass. Total lake trout biomass declined from 432,017 kg in 2012 to 196,675 kg in 2019, primarily because of a 79% reduction in adults. Total abundance declined from 925,208 in 2012 to 673,983 in 2019 but was highly variable because of recruitment of age-2 fish. Overall, 3.35 million lake trout were killed by suppression efforts from 1995 to 2019. Cutthroat trout abundance remained below target levels, but relative condition increased, large individuals (> 400 mm) became more abundant, and individual weights doubled, probably because of reduced density. Continued actions to suppress lake trout will facilitate further recovery of the cutthroat trout population and integrity of the Yellowstone Lake ecosystem.

Highlights

Apex predatory fishes introduced to freshwaters of the United States Intermountain West are invasive because they can spread within lakes or through interconnected river networks and pose a high risk to native species [1,2]
Because lake trout population growth rates are most sensitive to changes in age-0 survival [18,137,138], we developed and experimentally assessed methods to reduce it, with the intent of implementing an integrated pest management (IPM) approach on Yellowstone Lake
This ecosystem restoration program illustrates that predatory fish invasions can be managed and controlled over large areas, even if total eradication may not be feasible

Summary

Introduction

Apex predatory fishes introduced to freshwaters of the United States Intermountain West are invasive because they can spread within lakes or through interconnected river networks and pose a high risk to native species [1,2]. Introduction of a novel apex predator to a freshwater ecosystem may result in cascading changes whereby inverse patterns in abundance, productivity, or biomass of populations or communities emerge across links in the aquatic food web [1,11]. Given that invasive predatory fishes have been introduced to all large lakes and rivers in the Western United States [12,13,14], mitigating negative effects from these introductions is a widespread problem faced by resource managers

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Discussion

Conclusion