Behavioural Ecology of Lake Trout: From Movement Ecology to Bioenergetics

The movement patterns of most organisms are directed to maximizing the success of habitat exploitation, which can be quantified by examining population-level parameters such as size and age at maturity, and the population bioenergetics. Similarly, the behavioural decisions of organisms are influenced and regulated by abiotic and biotic variables. For example, in temperate aquatic organisms such as fish, habitat use is limited by environmental conditions such as temperature and dissolved oxygen concentration, but also biotic variables like prey type, quantity and quality influence the habitat selection. This research investigates the behavioural movements of Lake Trout (Salvelinus namaycush), a top predator fish, in four lakes that differ in the prey community that support them. The study was completed using a relatively new telemetry-transmitter that measures acceleration on two axes of the fish body; providing an added possibility for studying the bioenergetics of this species. This thesis is divided into three main studies. First, a calibration of the acceleration-transmitters to use it as proxy of energy expenditure in this species was completed. Laboratory and field-based experiments were performed to validate the use of this type of transmitter, and they demonstrated that transmitter-reported acceleration, fish swimming speed, and oxygen consumption increased in parallel, supporting previous findings on the topic. Second, the vertical movement of Lake Trout associated to the known distribution of their prey was examined in the four lakes of interest. The patterns of diel movement were well explained when the distribution of prey was considered. The data showed evidence that Lake Trout are able to track the diel vertical movement of their prey, which would provide a metabolic advantage. Third, the bioenergetics of the four lake-populations were assessed and associated to the quality of prey. In general, Lake Trout were found to swim more actively in lakes where their prey is small and frequently located outside their preferred habitat of cold and well-oxygenated waters. Lakes with pelagic prey fishes, which are the preferred prey for Lake Trout, showed the lowest values of swimming activity, and highest proportion of time spent inactive. In general, this study provided evidence supporting the hypothesis that Lake Trout behavioural movements are associated with the food web composition of the lakes where they live.Ph.D