Can Supplemental Forage Enhance the Performance of Predators in Trophically Limited Reservoirs: Results from a Large-Scale Experiment

Artificial impoundments provide essential anthropogenic services and can support popular recreational sport fisheries.  However, the novel food webs created can affect the performance of desired sport fishes.  We implemented a large-scale field experiment across three small reservoirs to determine if predatory fish are forage limited and to what extent abiotic variables influence the lesser condition of predators in these stocked fisheries.  We physically divided the experimental waters into control and treatment basins, and the treatment basin received additions of forage fish.  Treatment effects were minimal across waters, however, responses varied based on inherently different abiotic and biotic characteristics of each.  Diet and stable isotope analyses indicate that resident predators were unable to utilize stocked forage fish. These analyses, along with metrics of condition and bioenergetics models, suggest that the supplemental forage further increased competition for resources among stocked and held-over predators.  Growth and condition of predators stocked at the outset of the experiment was limited by the presence of crayfish in two reservoirs; diet breadth of the predators was narrower in these systems.  This study confirms the delicate nature and variable management needs of fisheries within artificial aquatic systems and highlights the complexities of trying to manage these food webs.