A case study on attempts to remove invasive Largemouth Bass from two small lakes in Québec

Abstract Objective The intentional and accidental introduction of nonnative fishes has damaged freshwater ecosystems around the world. The Largemouth Bass Micropterus nigricans (LMB) is regarded as one of the most commonly introduced nonnative species globally. In 2021, LMB were detected for the first time (as an introduced species) in Lac Kingsmere (13 ha) and Lac Mulvihill (1 ha) within Gatineau Park, Québec, Canada. It is unknown how, when, or why LMB were introduced. Working with community partners, we used mechanical removal methods over 3 years in an attempt to reduce this invasive LMB population in Lac Kingsmere and Lac Mulvihill. Here, we present a case of LMB removal in small temperate lakes. Methods We used snorkel surveys and angling to identify adults and nesting males and destroy their nests. Further, shoreline seining and pot traps were used to remove young-of-the-year and subadult bass. Community members also contributed to removals via organized angling and reporting. Results Between 2023 and 2026, the number of active LMB nests in Lac Kingsmere decreased from 25 to 0. From 2024 to 2025, the total abundance and biomass of LMB captured via seining and angling decreased substantially, with over 90% decreases in abundance and 45% and 75% reductions in biomass for Lac Kingsmere and Lac Mulvihill, respectively. No nests were observed and no adults were captured in Lac Mulvihill, although a small quantity of young-of-the-year and age-1 bass were captured. Conclusions The results of this study show that high-intensity mechanical removal conducted across several years can greatly suppress invasive LMB populations in small, closed lake systems. To achieve eradication, additional monitoring that is focused on the removal of nesting males and fertilized eggs will be necessary for several more years. Community participation proved essential for early detection, sustained effort, and local stewardship. This case confirms that active population reduction of an established invasive species is feasible at small spatial scales and offers a practical model for similar freshwater systems.