Movement Ecology of Potamodromous Top Predator in a Large Lake: Synchrony and Coexistence of Distinct Migratory Patterns 

Abstract Migrations are a key component of the life-histories of many highly mobile animals. The study of potamodromous migrations occurring within large lakes have lagged and are poorly understood for most species. This is an issue for restoration efforts and adaptive management, as understanding the movement of species, and underlying patterns and mechanisms are essential for identifying key habitat and quantifying the species role in the ecosystem. Using acoustic telemetry, this study quantified the spatio-temporal movements and migratory patterns of lake trout (Salvelinus namaycush), an iteroparous, potamodromous predator in Lake Ontario, the 13th largest lake by volume in the world that is highly managed and supports a diverse fish community of native and non-native species. Over 2.5 years (December 2016 to April 2019), the movements of 41 lake trout were quantified across a large array of 196 acoustic receivers in Lake Ontario. Individual analysis revealed annual convergence in the fall at a location other than the spawning grounds, followed by synchronized migrations to spawning sites. Consistent with divergent migrations, out-migration was asynchronous, stretching over a longer period of time than pre-spawning movements and across multiple routes. At least two groups of individuals with distinct migratory behaviors, i.e. contingents, were identified in the population. These results illustrate the presence of contingents and provide key information on migratory patterns, convergence points and routes in a potamodromous top predator population in a large lake. Thus, we provide evidence that contingents with different behavior used different habitats across seasons. As such, this study informs management on the potential success and implications of employing different rehabilitation strategies, such as diversifying a species’ population through selective strain stocking in large deep lakes to aid reestablishment across habitats. This knowledge would improve modelling of community dynamics, understanding of nutrient cycling, and overall ecosystem function of large lakes.