Monthly differences in the movement ecology of lake whitefish (Coregonus clupeaformis) in eastern Lake Ontario.

Lake whitefish are a cold-water species that holds cultural and economic importance throughout the Great Lakes region. Anthropogenic stressors over the last 60 years (e.g., invasive species, habitat degradation, and pollution) have caused significant declines in their populations. Furthermore, there is limited knowledge on the spatial ecology and habitat use of the species in Lake Ontario. Therefore, we used acoustic telemetry to quantify horizontal and vertical habitat use by lake whitefish over a 3-year period (2021-2024) in Lake Ontario. We also evaluated seasonal changes in bottom-oriented versus suspended behaviours. Lake whitefish were heavily concentrated along the central Duck-Galloo Ridge and in 20-30 m during periods of stratification (June to September), while their distribution shifted to the south shore of Prince Edward County and 10-25 m during isothermal conditions (non-stratified; October to May) and for spawning. During the isothermal period, lake whitefish exhibited a predominantly bottom-oriented behaviour; during stratification, they exhibited both suspended and bottom-oriented behaviours. These differences in vertical and horizontal distribution may be driven by changes in thermal habitats and/or prey; however, further exploration is needed. Ongoing ecological change may influence lake whitefish distribution and behaviours, necessitating changes to monitoring and/or management that accounts for observed behaviours.