Knowledge Bank

Walleye (Stizostedion vitreum) in Lake Erie have historically experienced large fluctuations in recruitment success, which have important implications for walleye population dynamics as well as food web interactions. Because walleye year class strength in Lake Erie likely is set during the larval life stage, we explored factors underlying larval survival 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 hatch dates of larvae surviving out migration. Comparing daily larval production and survival distributions demonstrated strong temporal patterns of larval survival that were unrelated to daily larval production patterns. Daily survival varied greatly during the larval hatch (~4 wk), with short, discrete periods (4-7 d) of high survival accounting for 75-84% of total survivors. Contrary to our original expectations, larval survival was inversely related to river discharge (P < 0.05). As river discharge increased, the amount of suspended sediments increased (r2 > 0.6, P < 0.001), likely directly increasing larval mortality. Post-out-migration densities of larval walleye in Maumee and Sandusky bays were correlated strongly (Maumee Bay: r2 = 0.99, Sandusky Bay: r2 = 0.94) with Ohio Division of Wildlife estimates of late summer juvenile abundance of Lake Erie walleye (which historically have been correlated strongly with year class strength). Because high discharge events during the larval hatch likely reduce survival, variability in river discharge underlies variability of walleye year class strength. Managers could mitigate these effects by reducing exploitation of spawning walleye and improving watershed characteristics to reduce discharge fluctuations and suspended sediments.