High degree of individual repeatability found in the annual migrations of walleye (Sander vitreus) in eastern Lake Ontario

Adult walleye (Sander vitreus) conduct annual migrations from riverine spawning sites in the Bay of Quinte into the eastern basin of Lake Ontario to forage. Although fidelity to spawning river is quite high for these fish across the Laurentian Great Lakes, very little is known about the repeatability of site selection along the entirety of their annual migration. This study used multiple years of acoustic telemetry (2018–2020) to assess the within-individual repeatability of the timing associated with major migratory events (spawning river entry and departure, main lake entry and departure), as well as the average monthly spatial distribution of individuals throughout the year. Fine-scale sequence analysis was used to combine these two metrics to assess the within and among individual sequence dissimilarity in the population. Within-individual repeatability was high across most timing and spatial measures, and the sequence dissimilarity within individual sequences was significantly less than that among individuals. Sex and size were not significantly related to sequence dissimilarity, while individuals from the Trent River displayed more dissimilarity than those from the Napanee River. The high level of within-individual annual repeatability in migrations was demonstrated not only during spawning activity, but at a daily level throughout the entire year. This research shows that walleye possess the ability to orient themselves and navigate across long distances in a highly repeatable manner at all times of the year. Future work will be required to better understand the underlying mechanisms and drivers behind these abilities.