Free-Ranging Energetics of Bottlenose Dolphins

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The bottlenose dolphin, Tursiops truncatus is likely the most extensively studied small cetacean, yet very little is know about their physiological ecology. Virtually all studies concerning the energetic expenditures of Odontocete cetaceans have been performed either on captive animals or on trained animals doing open-ocean respirometry. Thus far there have been no direct field studies of the energy requirements of any free- ranging cetacean. This project represents the next phase in a continuing program designed to elucidate the metabolic and behavioral adjustments which occur during normal seasonal cycles in dolphins. Over the previous 3 years, measurements have been made of the changes in the insulative blubber stores of dolphins in Sarasota Bay, FL, as well as measurements of metabolism and water and energy flux in captive dolphins. The next phase is to measure the free-ranging foraging energetics of these animals. The Sarasota Bay dolphin community iis ideal for these studies as it is possible to repeatedly recapture known individual dolphins. This capability allows one to correlate seasonal changes in energy expenditure, measured using the double-labelled water technique, with changes in the animals insulative capability and foraging costs. In previous research, blubber thickness was found to vary seasonally. However, it has not been possible to separate whether these changes in blubber thickness were related solely to seasonal changes in the animals energy stores (i.e., are they responding to changes in prey availability and composition) or whether these changes are in response to variations in the ambient water temperature. In addition, data derived from this study will provide the first direct measurement of the at-sea metabolic rate of a small cetacean. Measurement of cetacean foraging energetics will increase our understanding of the costs and efficiencies of various foraging modes in the marine environment.