Modeling Vertical Movements of Lake Erie Fishes: Comparing Different Movement Rules and Different Measurement Scales with Field Observations

Continued climate change is expected to increase hypoxia in downstream (coastal) ecosystems via increased temperature and nutrient runoff, which may differentially impact fishery resources.  We developed a spatially-explicit, one-dimensional, individual-based model to examine these climate-driven impacts on four ecologically and economically important fishes of central Lake Erie that vary in trophic position, feeding guild, and thermal preferences: walleye (Sander vitreus), yellow perch (Perca flavescens), rainbow smelt (Osmerus mordax), and emerald shiner (Notropis atherinoides).  Within the model, fish vertical dynamics are based on the biotic and abiotic environment experienced by individuals.  We altered the relative influences of light, temperature, hypoxia, prey availability, and predator presence on the movement rules of fish, and determined the vertical responses of species, age groups, and individuals.  We then compared these predicted responses to existing hydroacoustic and trawl data.  Predicted distributions matched observed data well and among-individual variation in vertical position was high.  Collectively, our simulations suggest that growth and survival of rainbow smelt are strongly, deleteriously affected by increased temperature and hypoxia, whereas the impacts on other species are relatively weak.  Accurately representing individual variation in behavior, while preserving emergent population trends, is a necessary challenge in the forecasting of impacts on vertically migrating fishes.