Using simulation modeling to inform management of invasive species: A case study of eastern brook trout suppression and eradication

Ecosystem impacts due to invasive species continue to attract significant conservation effort worldwide. In aquatic ecosystems, physical interventions such as suppression and eradication of non-native species are typically expensive, long-term commitments, with few examples of lasting success in the absence of significant ongoing effort. Control of non-native species is a major conservation and restoration challenge, as a species' demographic resilience and connectivity within networks can limit the ability of suppression or eradication efforts to influence populations. Simulation tools can provide valuable insights for the management of these systems - from evaluation of tradeoffs between time and effort to prediction of relative success rates of alternative strategies in changing environments. In the Pacific Northwest region of the U.S., the eastern brook trout (EBT; Salvelinus fontinalis) is a non-native invasive species that competes with native fish species across a wide spatial scale due to extensive human-mediated introduction starting in the early 20th century. The goal of this study was to simulate the individual movement and demographics of EBT before, during, and following implementation of control efforts in tributaries within the Pend Oreille River watershed. The ultimate purpose of the model was to inform mitigation decisions through the investigation of alternative management actions in an adaptive management framework. Our results indicate that eradication of EBT is improbable in large systems via electrofishing, but suppression is a viable alternative given sustained management efforts. Changes to scheduling, effort, and length of electrofishing suppression treatments had minimal effects on EBT population recovery times. We reproduced the effects of compensatory responses to control treatments, including increases in juvenile survival and emigration rates, and demonstrated that these mechanisms are likely drivers of recovery following treatment. Our study highlights the many benefits of incorporating spatially explicit, individual-based models into management plans for the control of invasive species.