chapter  7
22 Pages

Metabolism, Energetic Demand, and Endothermy

ByJohn K. Carlson, Kenneth J. Goldman, and Christopher G. Lowe

CONTENTS 7.1 Introduction .................................................................................................................................. 203 7.2 Methods of Metabolic Rate Estimation....................................................................................... 204

7.2.1 Respirometry ................................................................................................................... 204 7.2.1.1 Annular/Circular Respirometers ...................................................................... 204 7.2.1.2 Swim Tunnel Respirometers............................................................................ 205

7.2.2 Biotelemetry .................................................................................................................... 206 7.2.2.1 Muscle Temperature Telemetry ....................................................................... 206 7.2.2.2 Heart Rate Telemetry ....................................................................................... 207 7.2.2.3 Swimming Speed Telemetry............................................................................ 208 7.2.2.4 Tailbeat Frequency Telemetry.......................................................................... 209

7.3 Estimates and Comparisons of Metabolic Rate........................................................................... 209 7.3.1 Standard Metabolic Rate................................................................................................. 209 7.3.2 Maximum Metabolic Rate .............................................................................................. 210 7.3.3 Specific Dynamic Action ................................................................................................ 211 7.3.4 Anaerobic Metabolism.................................................................................................... 211

7.4 Energetic Costs of Swimming ..................................................................................................... 211 7.4.1 Swimming Efficiency...................................................................................................... 211 7.4.2 Critical Swimming Speed and Sustainable Swimming.................................................. 213 7.4.3 Cost of Transport ............................................................................................................ 213

7.5 Endothermy .................................................................................................................................. 214 7.5.1 Background ..................................................................................................................... 214 7.5.2 Indirect Calorimetry: Endotherms vs. Ectotherms......................................................... 215 7.5.3 Indirect Evidence of Higher Metabolic Rates in Endothermic Sharks ......................... 216

7.6 Environmental Effects on Metabolism ........................................................................................ 216 7.6.1 Temperature..................................................................................................................... 216 7.6.2 Salinity............................................................................................................................. 217 7.6.3 Dissolved Oxygen ........................................................................................................... 217 7.6.4 Time of Day .................................................................................................................... 218

7.7 Conclusions and Future Directions.............................................................................................. 218 References .............................................................................................................................................. 219

7.1 Introduction Despite the ecological significance of elasmobranchs as top-level predators in most marine ecosystems (Cortés, 1999), information on their energetics and metabolism is meager. Metabolism is an important component of an organism’s daily energy budget and may account for its greatest, yet most variable proportion (Lowe, 2001). It was hypothesized that sharks had lower metabolic rates than comparable teleosts because most of the original work on the metabolic rate of sharks focused on relatively inactive,

cooler-water sharks such as spotted dogfish, Scyliorhinus canicula (Piiper and Schumann, 1967; Metcalf and Butler, 1984) and spiny dogfish, Squalus acanthias (Brett and Blackburn, 1978). Over time, better techniques have evolved that allow study of more active elasmobranch species that were typically considered difficult to work with in captivity. These advances in technology have expanded our knowledge of ecology, activity level, morphology, cellular physiology, and kinematics of elasmobranchs that exhibit a wide range of lifestyles, indicating that elasmobranchs have metabolic rates comparable to teleost fishes of similar size and lifestyle.