Distribution and movement of European grayling in a subarctic lake revealed by acoustic telemetry

Knowledge of the horizontal and vertical distribution and habitat use of fish in lakes provides insights into the ecology, evolution and conservation of a species. Using high-resolution, high-frequency sampling, we provide an account of the distribution and movements of adult European grayling, Thymallus thymallus, in a recently colonised subarctic lake. We evaluated summer home range size, daily and seasonal patterns in vertical movement and vertical distribution of individuals relative to the summer thermocline. There was an allometric relationship between body size and home range area. Individuals showed diverse patterns of daily movement and some clear circadian cycles, likely mediated by light. All individuals that were monitored during the winter under ice were within 2m of the surface. Most fish associated with the thermocline during the period for which we were able to estimate its centre point. We propose that the patterns we observed are primarily driven by foraging opportunity and that foraging tactics differ between individuals and seasons.