GREAT LAKES FISHERY COMMISSION 2014 Project Completion Report1 A COUPLED PHYSICAL-BIOLOGICAL MODEL TO FORECAST LARVAL YELLOW PERCH DISTRIBUTIONS, GROWTH RATES, AND POTENTIAL RECRUITMENT IN LAKE ERIE

Yellow perch (Perca flavescens; YP) is an economically and ecologically important species across the Great Lakes, which demonstrates variable recruitment to the fishery that we hypothesized is regulated by physical processes operating during early life stages. Previous research has found recruitment success is positively correlated with Maumee River inflow during spring, with individuals that use the Maumee River plume (MRP) as larvae contributing disproportionately to the new year-class. Research also has identified water turbidity as a key regulator of larval recruitment success because it reduces the ability of predators to forage on planktivorous fish such as larval YP. However, uncertainty in predicting the plume dynamics, as well as its effect on movement, predation risk, consumption, growth, and survival of YP larvae remains a major impediment to fully understanding and forecasting recruitment to the fishery in this system. To address these important questions, we built a coupled biophysical model of western Lake Erie. This model coupled general linear models developed to accurately predict YP growth and length (r2 = 0.84) with a physical (hydrodynamics and sediment) model that uses a flexible, unstructured grid to capture current dynamics, even in shallow nearshore areas. Using the biophysical model, we (a) evaluated the interactive effects of river discharge and wind-driven currents on the creation and expansion of high-quality nursery habitat within the MRP, (b) determined the relative importance of advection-caused loss of YP larvae to the observed disproportionate recruitment of MRP individuals relative to non-MRP individuals and (c) identified mechanistic linkages between physical processes and YP year-class strength. Our analysis found that the MRP area is most strongly influenced by Maumee River discharge and wind strength and direction, with larger plumes occurring at high discharge events when winds were from the E and NE. Other factors such as the Detroit River discharge and sediment input, local and distant wind forcing, wave climate and sediment resuspension can also influence MRP dynamics at a smaller scale. Advection of MRP and non-MRP YP out of the western basin was unimportant whether larvae exhibited an active swimming behavior or not (mean # particles lost < 5 %). This retention of larvae in the basin is likely due to an anticyclonic circulation pattern that is commonly exhibited in the basin that could help retain larvae. Further model and empirical analysis suggested, however, that in order to remain in the MRP (i.e., not simply the basin), larvae are required to exhibit an active swimming behavior. Finally, our results suggest the mechanisms influencing YP survival are dependent upon average plume size during the spring and on water temperature during early May. Year-classes that experienced low water temperature during May of their first year of life recruited at higher levels (>20 million 2-year olds) and were positively related to the size of the plume, modeled retention of larvae in the plume and modeled survival rates. Year-classes that experienced high water temperatures during May of their first year of life recruited at low levels (<20 million 2-year olds) regardless of the size of the plume, modeled retention of larvae in the plume and modeled survival rates. The causes behind these different relationships may be due to a match-mismatch with prey and predators, or differences in larval quality between cold and warm early springs. In conclusion, these results suggest that the size of the MRP, a high quality habitat for larval YP, is largely determined by wind forcing and river discharge, and that the size of the plume, in addition to spring water temperature, can be used to predict the number of these fish that survive to enter the fishery at age-2. Managers may therefore want to continue updating our hydrodynamics model with recent years to help forecast future year-classes.