RIVER DISCHARGE DRIVES SURVIVAL OF LARVAL WALLEYE

Walleye (Stizosredion vitreum) in Lake Erie have historically experien ced large fluctuations in recruitment success, which have important im plications for walleye population dynamics as well as food web interac tions, Because walleye year class strength in Lake Erie likely is set during the larval life stage, we explored factors underlying larval su rvival during out-migration in the Maumee and Sandusky rivers, Ohio's primary walleye spawning tributaries. To evaluate our expectation that survival of larval walleye would be positively related to discharge, we estimated daily larval production and used otoliths to estimate hat ch dates of larvae surviving out-migration. Comparing daily larval pro duction and survival distributions demonstrated strong temporal patter ns of larval survival that were unrelated to daily larval production p atterns. Daily survival varied greatly during the larval hatch (simila r to 4 wk), with short, discrete periods (4-7 d) of high survival acco unting for 75-84% of total survivors. Contrary to our original expecta tions, larval survival was inversely related to river discharge (P < 0 .05). As river discharge increased, the amount of suspended sediments increased (r(2) > 0.6, P < 0.001), likely directly increasing larval m ortality. Post-out-migration densities of larval walleye in Maumee and Sandusky bays were correlated strongly (Maumee Bay: r(2) = 0.99, Sand usky Bay: r(2) = 0.94) with Ohio Division of Wildlife estimates of lat e summer juvenile abundance of Lake Erie walleye (which historically h ave been correlated strongly with year class strength). Because high d ischarge events during the larval hatch likely reduce survival, variab ility in river discharge underlies variability of walleye year class s trength. Managers could mitigate these effects by reducing exploitatio n of spawning walleye and improving watershed characteristics to reduc e discharge fluctuations and suspended sediments.