Regulatory Mechanisms of Fish Community Structure and Top-Predator Production in Lake Erie

During recent decades, Lake Erie has experienced numerous anthropogenic perturbations that have altered ecosystem productivity and food-web interactions. In particular, nutrient reduction from external sources (i.e., via phosphorus abatement programs) and changing internal nutrient cycling (i.e., via dreissenid mussels) improved water clarity but reduced primary and secondary production in the lake between the late 1960s and the mid-1990s. Since then, however, Lake Erie appears to be returning to a more eutrophic condition, as evidenced by increased inputs in soluble reactive phosphorus, a return of bottom hypoxia, and a prevalence of nuisance algal blooms. Herein, we use long-term (1969-2010) assessment data on fish abundance and growth from Lake Erie’s west and central basins, in combination with historical physicochemical data, to demonstrate how fluctuating ecosystem productivity, management of Lake Erie’s top predator (walleye, Sander vitreus), and the invasions of white perch (Morone americana) and the round goby (Neogobius melanostomus) have caused the structuring mechanisms of the prey fish community to change through time from regulation by top-down processes to bottom-up processes. In turn, Lake Erie’s prey fish community shifted from a pelagic (zooplanktivorous) assemblage to a benthic-feeding assemblage, with major implications for walleye growth. We ultimately discuss the implications of these changes for ecosystem-based fisheries management in Lake Erie and elsewhere.