Seasonal depth and temperature use, and diel movements of lake trout (Salvelinus namaycush) in a subarctic lake

We conducted a multi-year acoustic telemetry study of lake trout (Salvelinus namaycush (Walbaum, 1792)) in a small subarctic lake to investigate depth and temperature occupancy, and vertical activity across seasons (summer, fall, and winter), diel periods (day, twilight, and night), and during summer periods of 24 h light (day and twilight). Analyses using generalized additive mixed models revealed a high degree of individual variation in depth occupancy independent of the factors hour of day, season, and diel period, whereas temperature occupancy and vertical activity were explained using the three combined factors. Habitats occupied were typically 9–20 m and 6–9.5 °C in summer, 1–3 m and 2–15 °C in fall during presumed spawning, and ≤6 m and <3 °C in winter. Lake trout exhibited partial diel migration where individuals displayed a variety of vertical migratory directions within and among seasons or diel period, including during periods of 24 h light. Fish were most vertically active during periods of daylight and in fall. During 24 h light, some lake trout performed crepuscular movements, whereas individual behaviour best explained modelled depth and temperature occupancy and vertical activity. The variety of vertical patterns among individuals and seasons suggests multifactor proximate causes of partial diel migration and crepuscular movements.