Use of physiological telemetry as a method of estimating metabolism of fish in the natural environment

One of the most difficult components to measure in the energy budgets of natural fish populations is the energy released in metabolism. Telemetry of physiological correlates of metabolism, such as heart rate, can (with calibration) enable direct measurements of metabolism and simultaneous observations of behavior in the natural environment. Heart rate is a good indicator of metabolic rate for northern pike Esox lucius and was used to obtain information on metabolism, activity, and food intake in the natural environment. Mean field metabolic rates were 1.5 times standard metabolic rate. Activity metabolism accounted for 5-10% of total metabolism and was approximately an order of magnitude greater than estimates based on mean swimming speed derived from location tracking. Feeding metabolism was 15-25% of total metabolism. Even when the full metabolic rate calibration is not considered, physiological telemetry can provide useful information on patterns of energy expenditure of direct relevance to bioenergetics modeling. Heart rate telemetry of spawning Atlantic salmon Salmo salar demonstrated that females expended large amounts of energy during upstream movement and redd cutting, but exhibited prolonged periods of inactivity and low energy expenditure. In contrast, males displayed higher sustained metabolic costs and greater up and downstream movements than females. Metabolism can be standardized with respect to minimum and maximum limits, enabling useful comparisons between species and environmental conditions. This technique was used to demonstrate that patterns of energy expenditure vary with fish species, lifestyle, stage of life cycle, and environmental conditions. Because of recent technological advances, physiological telemetry should become an increasingly useful tool for improving and validating bioenergetics models.