A New Tool for Evaluating Predator-Prey Balance in Southern U.S. Reservoirs

Gizzard shad dominate the prey biomass in many southern U.S. reservoirs.  Previous studies suggest prey limitation frequently occurs in these systems, indicating that fisheries managers need tools to evaluate the production potential of the populations they manage.  Bioenergetics modeling was used to quantify age-0 gizzard shad abundance necessary to sustain multiple piscivore species under a wide range of growth rates, population sizes, mortality rates and diets.  Resulting piscivore consumption rates were used to evaluate the community-wide piscivore demand for gizzard shad.  Gizzard shad biomass at the 50^th percentile of published values was insufficient to support seven piscivore species in 64% of the simulations, suggesting that above-average prey biomass is required to support multiple piscivore populations at high abundance and growth rates.  To help guide management, estimates of the gizzard shad biomass needed to sustain piscivore communities are provided for management situations in which coarse-scale (low, medium or high) growth, population size and percent of shad in diet data are available.  These published data can be used as a simple tool to estimate prey abundance required to meet piscivore demand under current conditions or to evaluate the prey required to support targeted population characteristics based on proposed management goals.