Lake Ecotype Influences Metabolic Costs in Lake Trout

Daily foraging activities constitute a large part of energy-requiring events in aquatic organisms and, consequently, they are a major component of metabolic costs. In addition, the metabolic costs of foraging activities are related to the food web structure of the lakes. In Lake Trout, for example, the energy spent in feeding behaviour may be diverted from other metabolic processes such as growth and reproduction. For this study we were interested in describing the metabolic costs by Lake Trout in different lake ecotypes. We used acoustic telemetry to track four populations of this fish with various availability of pelagic prey: piscivorous populations, where Lake Trout had pelagic prey available, and non piscivorous populations, where littoral fish and/or mega-zooplankton (Mysis) were part of Lake Trout diet. Additionally, we used activity transmitters, which are good estimators of the metabolic demands of swimming in fish. In general, we found that non piscivorous Lake Trout populations had higher average metabolic costs than piscivorous populations. This was associated with the increased swimming demand for Lake Trout in lakes where their prey field was outside their thermal preferences or represented low energy prey compared to lakes where lake trout had access to larger rewarding prey fish.