Habitat-dependent metabolic costs for a wild cold-water fish.

Bioenergetics models for fishes are useful for understanding ecological processes (e.g., survivorship, growth, and reproduction) and can also inform fisheries management. Yet, current bioenergetics models are unable to ascertain direct energetic costs associated with standard and active metabolism for wild, free-swimming fishes. The use of telemetry with accelerometer sensors, calibrated in the laboratory using swim tunnel respirometers, have made it possible to estimate field metabolic activity in wild fish. Our objectives were to determine seasonal thermal habitat use and habitat-dependent metabolic costs associated with standard, active, and maximum metabolism in a ~1400 ha multibasin lake in Québec, Canada. We implanted 47 wild, free-swimming Lake Trout (Salvelinus namaycush) with either acoustic transmitters equipped with temperature and depth sensors or an acceleration sensor. Three sets of water temperature loggers (one set for each basin) were deployed at 2, 4, 6, 10, and 18 or 20 m to measure seasonally available thermal habitat. Thermal profiles of lake water temperature varied among basins with the thermocline being ~5 m in the smallest basin (north basin) and ~7.5 m in the largest basin (east basin). Thermal habitat used by Lake Trout varied seasonally, coupled with seasonal and basin differences in standard and maximum metabolism. Daily active metabolism loosely followed seasonal changes in thermal habitat use but was largely unaffected by differences in thermal habitat use among capture basins. The theoretical scope-for-activity followed seasonal trends and was estimated to range between 47% and 74% of theoretical aerobic scope. Our observations suggest that available thermal habitats influence Lake Trout thermal habitat use, and thus metabolic costs associated with swimming. These changes in thermal habitats could have metabolic consequences for individuals in a population, resulting in altered fitness metrics (i.e., survival, growth, and/or reproduction). Reductions in the volume and availability of optimal thermal habitats for Lake Trout are likely to occur under climate change scenarios. Our study indicates that the species can adjust metabolic costs throughout the year even when thermal habitats appear to be limiting, which may inform future evidence-based management decisions. [ABSTRACT FROM AUTHOR]