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Thermoregulation in the Leatherback Sea Turtle (Dermochelys Coriacea)

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Thermoregulation in the Leatherback Sea Turtle (Dermochelys Coriacea) Thermoregulation in the leatherback sea turtle (Dermochelys coriacea ) by Brian Lee Bostrom B.Sc., The University of British Columbia, 2005 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Zoology) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) August 2009 © Brian Lee Bostrom, 2009 ABSTRACT Adult leatherback turtles ( Dermochelys coriacea ) exhibit thermal gradients between their bodies and the environment of ≥ 8 °C in sub-polar waters and ≤ 4 °C in the tropics. There has been no direct evidence for thermoregulation in leatherbacks although modelling and morphological studies have given an indication of how thermoregulation may be achieved. Using a cylindrical model of a leatherback I investigated the extent to which heat production by muscle activity during variation of swim speed could be used in a leatherback’s thermal strategy. Drag force of a full scale cast of a leatherback was measured in a low velocity wind tunnel to obtain an estimate of the metabolic cost needed to offset drag. It is apparent, from this modelling, that heat flux from the body and flippers, activity and body and water temperatures are important variables to measure in order to fully classify the thermoregulatory response of live leatherbacks. Using captive juvenile leatherbacks of 16 and 37 kg I show for the first time that leatherbacks are indeed capable of thermoregulation. In cold water (< 25 °C), flipper stroke frequency increased, heat loss through the plastron, carapace and flippers was minimized, and a positive thermal gradient of up to 2.3 °C was maintained between body and environment. In warm water (25 – 31 °C), turtles were inactive and heat loss through their plastron, carapace and flippers increased, minimizing the thermal gradient (0.5 °C). In juvenile leatherbacks, heat gain is controlled behaviourally through activity while heat flux is regulated physiologically, presumably by regulation of blood flow distribution. Using a scaling model, I show that a 300 kg adult leatherback is able to maintain a maximum thermal gradient of 18.2 °C in cold sub-polar waters. Thus, by employing both physiological and behavioural mechanisms, adult leatherbacks are able to ii keep warm while foraging in cold sub-polar waters and to prevent overheating in a tropical environment, greatly expanding their range relative to other marine turtles. iii TABLE OF CONTENTS Abstract ................................................................................................................................... ii Table of Contents .................................................................................................................. iv List of Tables ......................................................................................................................... vi List of Figures ....................................................................................................................... vii List of Abbreviations ............................................................................................................ ix Acknowledgements ............................................................................................................... xi Co-authorship Statement ................................................................................................... xiii 1 General Introduction ............................................................................... 1 1.1 References ....................................................................................................... 7 2 Exercise Warms Adult Leatherback Turtles ...................................... 10 2.1 Introduction .................................................................................................. 10 2.2 Materials and Methods ................................................................................ 14 2.2.1 Heat production .................................................................................. 14 2.2.1.1 Parameters and variables of the heat gain equation ............. 15 2.2.1.1.1 Resting metabolic rate .............................................. 15 2.2.1.1.2 Aerobic efficiency .................................................... 16 2.2.1.1.3 Drag force ................................................................. 16 2.2.1.1.4 Propeller efficiency .................................................. 17 2.2.2 Heat loss ............................................................................................. 18 2.2.2.1 Parameters and variables of the heat loss equation .............. 18 2.2.2.1.1 Surface area .............................................................. 18 2.2.2.1.2 Insulation .................................................................. 19 2.2.2.1.3 Cost of ingesting gelatinous prey ............................. 19 2.2.3 Results ................................................................................................ 20 2.2.3.1 Turtle drag ............................................................................ 20 2.2.3.2 Surface area .......................................................................... 21 2.2.4 Predictions from the model ................................................................ 21 2.2.4.1 Metabolic rate ....................................................................... 21 2.2.4.2 Temperature gradient ........................................................... 22 2.3 Discussion ...................................................................................................... 23 2.3.1 Test of the model ................................................................................ 27 2.4 Figures ........................................................................................................... 31 2.5 References ..................................................................................................... 36 iv 3 Behaviour & Physiology: The Thermal Strategy of Leatherback Turtles ......................................................................... 41 3.1 Introduction .................................................................................................. 41 3.2 Materials and Methods ................................................................................ 43 3.2.1 Materials ............................................................................................. 43 3.2.1.1 Animals and husbandry ........................................................ 43 3.2.2 Methods .............................................................................................. 44 3.2.2.1 Temperature regime ............................................................. 44 3.2.2.2 Instrumentation ..................................................................... 45 3.2.2.2.1 TB and TW recording ................................................. 45 3.2.2.2.2 Heat flux recording ................................................... 45 3.2.2.2.3 Activity recording ..................................................... 46 3.2.3 Data recording and analysis ................................................................ 46 3.2.3 Calculations ........................................................................................ 47 3.2.4.1 Surface area .......................................................................... 47 3.2.4.2 Total heat transfer rate .......................................................... 48 3.2.4.3 Thermal admittance of the plastron ...................................... 48 3.3 Results ........................................................................................................... 49 3.3.1 Thermal gradient ................................................................................ 49 3.3.2 Swimming activity .............................................................................. 49 3.3.3 Heat loss ............................................................................................. 50 3.3.4 Surface area ........................................................................................ 51 3.3.5 Total heat loss ..................................................................................... 51 3.3.6 Fraction of heat loss through the body and carapace ......................... 52 3.4 Discussion ...................................................................................................... 52 3.4.1 Physiological and behavioural responses to warm and cold water .... 53 3.4.2 Effect of body mass on thermal gradients .......................................... 57 3.5 Tables ............................................................................................................. 60 3.6 Figures ........................................................................................................... 61 3.7 References ..................................................................................................... 66 4 General Discussion ................................................................................. 68 4.1 Other Sea Turtles ......................................................................................... 73 4.2 Final Conclusions ......................................................................................... 75 4.3 References ..................................................................................................... 77 Appendix A ..........................................................................................................................
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