Functional traits and stable isotopes reveal trophic interactions in a highly invaded reservoir: implications for fisheries

Aquatic ecosystems worldwide face significant threats, with human activities and biological invasions reshaping their dynamics and structure. Invasive species are among the biggest threats in freshwater ecosystems and cost to the global economy billions every year. Dams, even if human created, serve as species reservoirs and provide multiple ecosystem services. This study investigates the functional diversity and trophic ecology of the fish assemblage in the Zimapan dam in Mexico, a highly disturbed ecosystem that receives wastewater from one of the world's megacities along with industrial discharges. We focused on species coexistence, ecological niches, and the impact on local fisheries of tilapia. We identified eight species and two subspecies inhabiting this dam, only one of which is native, and observed functional complementarity among them. However, we observed trophic niche overlap, particularly between tilapia and other species, suggesting potential competition for resources. Our findings suggest that black bass predation, introduced for recreational fishing, is contributing to the decline of tilapia fisheries, a crucial economic activity for local communities. We provide recommendations for managing this complex ecosystem, emphasising the importance of continuous monitoring and regulation to sustain both biodiversity and human livelihoods.