Distinct diel and seasonal behaviours in rainbow trout detected by fine-scale acoustic telemetry in a lake environment.

The fine-scale behavioural activities of rainbow trout (Oncorhynchus mykiss) in nature are not well understood, but are of importance for identifying interactions with the ecosystem and of interest to conservationists and recreational anglers. We have undertaken a high-resolution acoustic telemetry study to identify the distinct movement patterns of 30 rainbow trout in a freshwater lake, specifically examining swim speed, area of movement, and site preference in both summer and winter. Activity levels were reduced in winter compared with summer across all fish, but ranking of individuals was consistent. In summer, 16/30 fish displayed diel movement, in which they travelled to a different area of the lake at dawn and returned at dusk, while other fish maintained their site preference regardless of the time of day or swam more randomly throughout the lake. These patterns were minimized in winter, where there was a reduction in cross-lake movement under ice and only 4/30 fish displayed diel movement. Winter conditions may limit the capability (physiological limitations) and (or) motivation (prey availability) for diel behaviours observed in summer. [ABSTRACT FROM AUTHOR]