ABSTRACT. Ashmore Reef

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1 ABSTRACT The life cycle of sea turtles is complex and is not yet fully understood. For most species, it involves at least three habitats: the pelagic, the demersal foraging and the nesting habitats. This study investigated the ecology of green and hawksbill sea turtles foraging on two dissimilar reefs in northwestern Australia. Aspects of this study included: species, size and sex composition, population size, growth rates, health assessment, available food resources~ diet, short-tenn movements, foraging behaviour and the analysis of blood chemistry. It focused on an assemblage of green and hawksbill turtles on an inshore terrigenous reef (Fog Bay) and a population of green turtles on a shelf-edge platform reef (Ashmore Reef) in north-western Australia. The two reefs were approximately 800 km apart. Turtles were captured by hand, individually tagged, measured and examined before release. The significant contributions to our knowledge of sea turtle biology are presented for each locality as well as those of a more universal application. Fog Bay 1048 captures were made of 891 individuals Fog Bay contained 62% green and 38% hawksbill turtles. Size structure was dominated by immature turtles: mean size of greens 48.1 cm eel, mean size of hawksbills 48.7 cm eel. At least 99.4 % of greens and 86.1 % ofhawksbills were under adult size Species and size composition varied over temporal and spatial scales Sex ratios of both species were biased toward females Both species occurred in high densities: 200 green/km 2 and 60 hawksbills/km 2 Green turtles grew at approximately 1.5 cm eel/year while hawksbills grew at 2.5 cm eel/year Natural and anthropogenic factors impacted on the health of these turtles The foraging area was dominated by algae and sponges The diet of the green turtles was dominated by algae The diet of the hawks bill turtles comprised algae and sponge Both turtle species showed diet selection Overlap occurred between foraging niches Both species demonstrated short and long term fidelity to feeding sites Fog Bay is a critical developmental habitat for green and hawksbill turtles. Ashmore Reef 371 captures were made of335 individuals 11

2 Ashmore Reef contained 95% green, 3.5% loggerhead turtles and 1.5% hawksbill turtles Size structure was dominated by immature greens: Mean size 54.9 cm eel. At least 93 % were under adult size Species and size composition showed temporal and spatial variability Green turtles occurred in a high density: 40 green/krn 2 Green turtles grew over more than twice as fast (4 cm eel/year) as green turtles in Fog Bay Natural and anthropogenic factors impact on the health of these turtles The foraging area and the diet of green turtles was dominated by seagrass Green turtles showed both short and long term fidelity to feeding sites Ashmore Reef is a critical developmental habitat for green turtles General The concept of developmental migration has been expanded to include oceanic islands, smaller scale movements into overlapping habitat, and habitats of mixed sized individuals Current methods of population estimates are insufficient to cope with large population sizes in homogenous habitat with high turnover rates Comparative study areas are useful to examine processes within foraging areas More than one capture technique is recommend to remove capture bias Blood chemistry has the potential for use in health and nutritional studies in sea turtles when the diet is known Further studies in more geographically and ecologically diverse habitats are required to better understand the spatial and temporal variability of processes operating within developmental habitats. Such studies would provide valuable comparisons and would assist in population modelling and management of sea turtles. 111

3 CONTENTS ABSTRACT II CONTENTS... VI CHAPTER GENERAL INTRODUCTION & BACKGROUND LITERATURE... 1 GENERAL INTRODUCTION... I BACKGROUND SEA TURTLE LITERATURE... 3 Taxonomy... 3 Life History... 4 Global Distribution and Abundance...;...:... 7 Hawksbill Turtles... 7 Green Turtles... 7 Distribution of Sea Turtles in the Northern Territory -A Regional Perspective... 7 Green Turtle... 9 Hawksbill turtle...'... 9 Conservation Status...:... JO Biological Status... I I Green Turtle Hawksbill Turtle CHAPTER STUDY AREA AND GENERAL METHODS STUDY AREA Fog Bay - Primary Study Site... I 6 Geographic Location and Physical Features History Climate Tides Marine Plants Sea Turtles Ashmore Reef- Comparative Study Site... I 9 Physical Features History Climate Tides Marine Plants Sea Turtles... :~ GENERAL METHODS Sampling Period Fog Bay Ashmore Reef Catch Sectors and Areas and Seasons Fog Bay Ashmore Reef Season Capture ofturtles Fog Bay Ashmore Reef Tags and Tagging General Measurements Gender vi

4 Data Management and Analyses CHAPTER DEVELOPMENTAL HABITATS & DEVELOPMENTAL POPULATIONS INTRODUCTION A Review of the Concept of Developmental Migration Definitions of Developmental Habitat and Developmental Migration Developmental Habitat Developmental Migration Current Knowledge and Evidence for Developmental Migration METHODS Species Composition Size Class Composition Analysis Maturity Gender Recruitment Morphometric. Measurements RESULTS Species Composition Fog Bay Ashmore Reef Size Structure... : Fog Bay - Green Turtles Fog Bay - Hawksbill turtles Ashmore Reef - Green and Hawksbill Turtles Comparisons of Populations... : Maturity Fog Bay Ashmore Reef Recruitment Size Indication of Emigration Size Gender Fog Bay Ashmore Reef Morphology DISCUSSION Species Composition Size Structure Recruitment Size Emigration Size Gender Morphology The Concept of Developmental Habitat and Developmental Migration Origin ofrecruits Destination ofemigrants Mechanisms that Drive Developmental Migration Problems in Defining Developmental Migration and Developmental Habitats A Problem of Scale in Defining Migration and Habitat Implementing For aging Studies The Importance of Studies in Developmental Habitat CONCLUSION CHAPTER POPULATION ESTIMATES INTRODUCTION... I 02 Relative Estimates Vll

5 Absolute Estimates... I 03 Strip-Transect Surveys Mark Recapture Studies... I 04 Predictive Models using Existing Frequency of Catch Data Recapture rates and length of study METHODS Mark-Recapture Strip -Transects... I 08 Biomass... I 09 Assessment of Population Estimates for Each of the Populations Predictive Models Using Existing Frequency of Catch Data... 1 JO RESULTS Population Estimates Hawksbill Turtles Fog Bay... I I I Green Turtles Fog Bay... I 11 Green Turtles Ashmore Reef...., Hawksbill Turtles at Ashmore Reef Predictive Models Using Frequency of Catch Data Recapture Rates and Length of Study DISCUSSION Hawksbill Turtles Fog Bay Green Turtles Assessment of Methods Frequency of Capture Jolly-Seber - mark-recapture Boat Strip-Transects Proportion of Recaptures to Captures - Implications for For aging Studies... I 19.CONCLUSION FIGURE 30 GRAPH TO PREDICT PROGRESSIVE RECAPTURES AT GIVEN CUMULATIVE CAPTURES CHAPTER GROWTH RA TES INTRODUCTION Importance of Growth Studies... ; Growth Factors Aims METHODS Growth Models Comparisons between populations RESULTS... :: I Growth Rates - Curved Carapace Hawksbill Turtles - Fog Bay Green Turtles - Fog Bay Green Turtles - Ashmore Reef Between Species Comparison - Hawksbi/ls and Greens in Fog Bay Within Species Comparison - Greens at Fog Bay and Ashmore Reef DISCUSSION Comparisons between Green Turtles from Fog Bay and Ashmore Reef Hawksbill and Green Turtlesfrom Fog Bay Growth Rates Compared with Other Studies Green Turtles Hawksbill Turtles CONCLUSION CHAPTER Vlll

6 HEALTH,CONDITION AND MORTALITY INTRODUCTION METHODS RESULTS FogBay... /46 Cachectic Myopathy Parasites Fibropapillomatosis Boat Strike Traditional Hunting Commercial Fishing Marine Debris Predation Unknown Ashmore Reef.... I 5 I Cachectic Myopothy l Fibropapillomatosis... : Harvest Marine Debris Predation Unknown Deformities DISCUSSION CONCLUSION CHAPTER AVAILABLE FOOD RESOURCES INTRODUCTION FogBay Ashmore Reef Food Availability and Diet Selection METHODS Terminology Identification General Description of Habitat and Food Resources Food Resources Study-Fog Bay: Temporal and Spatial Variation (Part 1 Diet Selectivity Study)l69 RESULTS Description of Habitat FogBay Ashmore Reef Food Resources Study- Fog Bay: Temporal and Spatial Variation (Part I Diet Selectivity Studyl73 Algae Sponges... : Seagrass DISCUSSION Fog Bay Algae and Seagrasses Sponges Ashmore Reef Food Resources Study- Fog Bay: Temporal and Spatial Variation (Part I Diet Selectivity Study)/77 Algae Sponges Importance of Algal and Seagrass Ecosystems Conclusion CHAPTER DIET: BREADTH, NICHE OVERLAP AND SELECTION IX

7 INTRODUCTION Diet of Sea Turtles Green turtle..., Hawksbill Breadth of diet Interspecific Competition and Niche Overlap Diet Selection Sampling Techniques Available Aims METHODS Diet Techniques Used in This Study Preservation and Analysis Breadth of Diet... 2 I 0 Niche Overlap Between Hawksbill and Green Turtles... 2 JO Diet Selection... ~ RESULTS... : Diet Green Turtles -Ashmore Reef l Green Turtles - Fog Bay Hawksbill Turtles - Fog Bay Dietary Breadth Niche Overlap Diet Selectivity - Fog Bay... 2 I 2 Green Turtles Hawksbill Turtles DISCUSSION Green Turtles Hawksbi/1 Turtles... 2 I 5 Dietary Breadth Niche Overlap Diet Selection.... : Food Availability Physical Limitations Nutrient Composition Secondary Compounds General CONCLUSION CHAPTER FORAGING BEHAVIOUR AND MOVEMENT INTRODUCTION METHODS... ~: General Foraging Behaviour Short and Long Term Fidelity Homing Ability Homing Ability Detected by VHF Tracking Detailed Foraging Movements RESULTS General Behaviour Foraging Behaviour..., Activity Foraging Habitat Fidelity Tag and Release at Same Location Homing Ability... : Translocation Experiment- Mark-Recapture Translocation Experiment - VHF tracking X

8 Detailed Foraging Movements DISCUSSION Feeding Behaviour Fidelity Homing '. 248 Detailed Movements and Tracking Success CONCLUSION CHAPTER ANALYSIS OF BLOOD CHEMISTRY - A RESEARCH TOOL FOR FORAGING TURTLES?259 INTRODUCTION Blood Chemistry and Reference Values Uses of Blood Chemistry for Wild Animals - Background Diseased, Sick and Malnourished Animals..., l Nutritional Studies and Growth Reference Values and General Investigation Nutritional Assessment Health Assessment METHODS General Reference Values Correlations Gender New recruits and resident turtles Use of Discriminant Analysis to determine similarity between populations Health Assessment Comparison Between Healthy and Clinically Sick Turtles Comparison of Healthy Turtles With and Without Internal Cysts Nutritional Assessment Comparison Between Green Turtles from Ashmore Reef and Fog Bay Comparison Between Hawksbill and Green Turtles in Fog Bay RESULTS General Reference Values Correlations Gender Comparison Between New Recruits and Resident Turtles Overall Comparisons Between Foraging Populations Health Assessment Comparison Between Healthy and Clinically Sick Turtles Comparison Between Healthy Turtles With Internal Cysts and Without Internal Cysts Nutritional Assessment Comparison Between Green Turtles from Ashmore Reef and Fog Bay Comparison Between Hawksbill and Green Turtles in Fog Bay DISCUSSION General Reference Values Overall Comparisons Between Foraging Populations Correlations Gender New Recruits Health Assessment Comparison Between Healthy and Clinically Sick Turtles Comparison Between Clinically Healthy Turtles With and Without Internal Cysts Nutrition Comparison between green turtles from Ashmore Reef and Fog Bay Comparison between hawksbill and green turtles in Fog Bay Assessment of Blood Chemistry as a Research Tool CONCLUSION Xl

9 CHAPTER GENERAL DISCUSSION The Complexity of Foraging Ecology Goals, Techniques and Logistics of Conducting Foraging Studies Implications for Management of Sea Turtles in North-Western Australia CONCLUSION REFERENCES APPENDIX WATER TEMPERATURE METHODS Fog Bay... : Subtidal..., Interti.dal Ashmore Reef RESULTS Fog Bay Subtidal Intertidal Ashmore Reef DISCUSSION APPENDIX ANNOTATED REFERENCES TO OTHER BLOOD CHEMISTRY STUDIES Analysis of Blood Chemistry of Other Wild Species Blood Chemistry Analysis Used on Different Species of Sea Turtles APPENDIX DESCRIPTION OF BLOOD PARAMETERS BLOOD PARAMETERS Elements - Electrolytes and Metals Enzymes Nutrients or Metabolites Xll