Barriers to natural recruitment of stocked Walleye (Sander vitreus) in the Hamilton Harbour Area of Concern

Walleye (Sander vitreus) are an ecologically, culturally, and commercially important cool-water predator. While historically common in the Hamilton Harbour Area of Concern, naturally reproducing Walleye were largely extirpated by the 1970s. Stocking of Walleye in the early 2010s, with an objective of re-establishing a native top-predator to increase piscivore biomass, led to strong adult year classes. Here we briefly summarize the state of knowledge on factors limiting Walleye recruitment in other freshwater systems, compare these factors to the current conditions within Hamilton Harbour, and explore multiple lines of evidence to identify potential recruitment bottlenecks. Based on electrofishing, acoustic telemetry, egg collection, and habitat surveys, stocked Walleye are spawning and producing fertilized eggs in suitable habitat, but the absence of swim-up fry in larval tows16 and young-of-year (YOY) in fall electrofishing surveys indicates an early life-stage recruitment bottleneck. There are few direct management actions that will likely promote Walleye recruitment in the near-term since recruitment appears limited in these early life phases due to interacting factors such as water quality, sedimentation, wind and wave transport, and predation. Fall monitoring for YOY Walleye, particularly in alternating years with stocking, is recommended as the best method for detecting natural recruitment.