River discharge as a predictor of Lake Erie yellow perch recruitment

We have found that Maumee River discharge during spring (March-May) is a strong predictor of yellow perch recruitment to age-2 (high discharge leads to strong recruitment events).  The mechanisms underlying this relationship, however, are enigmatic.  Owing to the recent oligotrophication of Lake Erie, and the increased importance of Maumee River phosphorus inputs to west basin phosphorus dynamics, our primary hypothesis is that Maumee River discharge benefits yellow perch via phosphorus inputs that stimulate zooplankton production for larvae and young juveniles.  Our hypothesis is supported by the fact that springtime Maumee River discharge is positively related to: 1) springtime phosphorus inputs; 2) west basin age-  yellow perch abundance in August (i.e., thus, regulation occurs during the larval/early juvenile stage); and 3) May-June west-basin copepod zooplankton biomass.  However, Maumee River discharge also is highly correlated with total suspended solid inputs (sediments).  Thus, Maumee River discharge may also benefit yellow perch by reducing predation mortality on larvae (via enhanced turbidity).  Herein, we propose to use innovative field, lab, experimental, and modeling approaches to explore the relative importance of both hypothesis by contrasting larval yellow perch foraging, growth, and survival inside and outside of the Maumee River plume in the west basin.  Ultimately, we seek to provide Lake Erie Committee agencies with knowledge of the relative roles of oligotrophication-driven zooplankton availability and predation mortality in regulating yellow perch recruitment.  In so doing, we also seek to substantiate use of Maumee River discharge as a means to provide early forecasts of yellow perch recruitment to the fishery.