Assessing potential barriers to migratory Walleye in the Sandusky River, Ohio

ObjectiveThe Sandusky River, Ohio, is one of the major Lake Erie tributaries that supports migratory Walleye Sander vitreus reproduction. Following the construction of the Ballville Dam in 1913, Walleye spawning was limited to an area downstream near Fremont, Ohio. After the removal of the dam in 2018, several natural and human-made features were identified that may impede Walleye passage by collecting woody debris and altering flow conditions. In this study, we use hydrologic modeling and migratory sampling to understand the spatial and temporal dynamic nature of the blockages caused by the remaining anthropogenic and natural barriers.MethodsWe created a fine-scale Hydrologic Engineering Center's River Analysis System (HEC-RAS) model to examine these potential natural and human-made barriers to Walleye passage during spawning. Using our model, we compared swim speeds (10 min maintained and burst) of small, medium, and large Walleye under three flow scenarios with five levels of blockage to assess whether the area was passable. Further, we conducted electrofishing surveys during annual spawning runs from 2020 to 2021 to assess Walleye presence upstream and downstream after dam removal.ResultOur model predicted that Walleye were able to pass the barriers under most of the scenarios by maintaining burst swim speed. Additionally, we captured Walleye above the former dam site in 2021, suggesting that Walleye can access newly available spawning habitat during certain river conditions.ConclusionRemoving the Ballville Dam restored fish passage, increased access to spawning habitat, and could improve Walleye production in the Sandusky River. Following the removal of a long-standing dam, installation of ice control structures and presence of natural barriers on the Sandusky River has changed flow and created selective barriers to migratory Walleye. Our study uses velocity models and presence of Walleye to further understand the nature of these dynamic barriers.Impact statement