Florida International University FIU Digital Commons FIU Electronic Theses and Dissertations University Graduate School 3-29-2011 Habitat Use and Foraging Ecology of a Batoid Community in Shark Bay, Western Australia Jeremy Vaudo Florida International University, [email protected] Follow this and additional works at: http://digitalcommons.fiu.edu/etd Recommended Citation Vaudo, Jeremy, "Habitat Use and Foraging Ecology of a Batoid Community in Shark Bay, Western Australia" (2011). FIU Electronic Theses and Dissertations. Paper 367. http://digitalcommons.fiu.edu/etd/367 This work is brought to you for free and open access by the University Graduate School at FIU Digital Commons. It has been accepted for inclusion in FIU Electronic Theses and Dissertations by an authorized administrator of FIU Digital Commons. For more information, please contact [email protected]. FLORIDA INTERNATIONAL UNIVERSITY Miami, Florida HABITAT USE AND FORAGING ECOLOGY OF A BATOID COMMUNITY IN SHARK BAY, WESTERN AUSTRALIA A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in BIOLOGY by Jeremy Vaudo 2011 iii To: Dean Kenneth Furton choose the name of dean of your college/school College of Arts and Sciences choose the name of your college/school This dissertation, written by Jeremy Vaudo, and entitled Habitat Use and Foraging Ecology of a Batoid Community in Shark Bay, Western Australia, having been approved in respect to style and intellectual content, is referred to you for judgment. We have read this dissertation and recommend that it be approved. _______________________________________ John P. Berry _______________________________________ James W. Fourqurean _______________________________________ Philip K. Stoddard _______________________________________ Joel C. Trexler _______________________________________ Michael R. Heithaus, Major Professor Date of Defense: March 29, 2011 The dissertation of Jeremy Vaudo is approved. _______________________________________ choose the name of dean of your college/school Dean Kenneth Furton choose the name of your college/school College of Arts and Sciences _______________________________________ Interim Dean Kevin O’Shea University Graduate School Florida International University, 2011 ii ACKNOWLEDGMENTS The work presented in this dissertation would not be possible if it was not for the help of a multitude of people. I thank my parents for putting up with and fostering my dream of being a marine biologist, supporting me over the years, and collecting all my publications. Maybe someday they will actually read them. I owe a great deal to my Master’s adviser Chris Lowe. His guidance early in my graduate career set me up to run with the opportunities I was presented at FIU. It was also Chris that suggested I contact Mike Heithaus about doing a PhD, which brought me to where I am today. I thank Philip Stoddard, Joel Trexler, Jim Fourqurean, and Michael McClain for help in the early shaping of this project and providing a critical eye to my work. Aaron Wirsing also provided valuable discussion and advice, while in the field. I also thank John Berry for joining my committee after Michael McClain took a position in Europe. Working at a remote field site on the opposite side of the world presents a variety of challenges. I am indebted to Robert Black, Rory McAuley and Kim Gray of Fisheries Western Australia, the staff of Western Australia’s Department of Environment and Conservation’s Shark Bay District, the Shark Bay Fish Factory, Monkey Mia Wildsights and everyone at the Monkey Mia Dolphin Resort for logistical support. Derek Burkholder dealt with most of the organizational details for field assistants. I thank everyone that helped in the collection of data, especially Dave Heithaus, Kirk Gastrich, Meagan Dunphy-Daly, Pat Heithaus, Ray Heithaus, Jordy Thomson and Derek Burkholder. iii Special thanks also go to Dave Heithaus, Capes, Scotty, Sparks, Grant, Sylvie, Sam, Nicola, Cally, Shannon, Chris and the people of Shark Bay, who kept me sane during the long and often windy field seasons. Finally, I would like to thank Mike Heithaus. He believed in my project ideas and allowed me to run with them. In my time at FIU, Mike has been not only a mentor, but also a friend. Mike always made me feel like a colleague rather than just a student. Funding was provided by a Florida International University Presidential Fellowship and Dissertation Year Fellowship to J. Vaudo, a grant from the National Geographic Expeditions Council to J. Vaudo, National Science Foundation grants OCE0526065 and OCE0745606 to M. Heithaus, and Florida International University’s College of Arts and Sciences. Permission to use Chapters II, III and IV were provided by Elsevier Inc., Springer, and Inter-Research, respectively. With kind permission from Springer Science+Business Media: Marine Biology, Spatiotemporal variability in a sandflat elasmobranch fauna in Shark Bay, Australia, volume 156, 2009, pages 2579–2590, Jeremy J. Vaudo and Michael R. Heithaus. iv ABSTRACT OF THE DISSERTATION HABITAT USE AND FORAGING ECOLOGY OF A BATOID COMMUNITY IN SHARK BAY, WESTERN AUSTRALIA by Jeremy Vaudo Florida International University, 2011 Miami, Florida Professor Michael R. Heithaus, Major Professor Worldwide declines in populations of large elasmobranchs and the potential cascading effects on marine ecosystems have garnered considerable attention. Far less appreciated are the potential ecological impacts of changes in abundances of small to medium bodied elasmobranchs mesopredators. Crucial to elucidating the role of these elasmobranchs is an understanding of their habitat use and foraging ecology in pristine conditions. I investigated the trophic interactions and factors driving spatiotemporal variation in abundances of elasmobranch mesopredators in the relatively pristine ecosystem of Shark Bay, Australia. First, I describe the species composition and seasonal habitat use patterns of elasmobranch mesopredator on the sandflats of Shark Bay. Juvenile batoids dominated this diverse community and were extremely abundant in nearshore microhabitats during the warm season. Stomach content analysis and stable isotopic analysis revealed that there is a large degree of dietary overlap between common batoid species. Crustaceans, which tend to be found in seagrass habitats, dominated diets. Despite isotopic differences between many species, overlap in isotopic niche space was high and there was some degree of individual specialization. I then, investigated the v importance of abiotic (temperature and water depth) and biotic (prey and predator abundance) factors in shaping batoid habitat use. Batoids were most abundant and tended to rest in shallow nearshore waters when temperatures were high. This pattern coincides with periods of large shark abundance suggesting batoids were seeking refuge from predators rather than selecting optimal temperatures. Finally, I used acoustic telemetry to examine batoid residency and diel use of the sandflats. Individual batoids were present on the sandflats during both the warm and cold seasons and throughout the diel cycle, suggesting lower sandflat densities during the cold season were a result of habitat shifts rather than migration out of Shark Bay. Combined, habitat use and dietary results suggest that batoids have the potential to seasonally impact sandflat dynamics through their presence, although foraging may be limited on the sandflats. Interestingly, my results suggest that elasmobranch mesopredators in pristine ecosystems probably are not regulated by food supply and their habitat use patterns and perhaps ecosystem impacts may be influenced by their predators. vi TABLE OF CONTENTS CHAPTER PAGE PREFACE................................................................................................................1 I. INTRODUCTION ...................................................................................................2 Literature Cited........................................................................................................6 II. HIGH TROPHIC LEVEL CONSUMERS: ELASMOBRANCHS.........................7 Synopsis ...................................................................................................................8 Introduction..............................................................................................................8 Elasmobranchs As Prey .........................................................................................10 Elasmobranchs As Predators..................................................................................17 Competition And Resource Partitioning................................................................28 Metabolism, Digestion And Feeding Periodicity...................................................31 Elasmobranch Impacts On Prey And Community Structure .................................38 Elasmobranch Impacts On Nutrient Dynamics......................................................44 Elasmobranchs As Facilitators Of Trophic Interactions........................................46 Trophic Interactions of Elasmobranchs In Coastal Ecosystems............................47 Conclusions............................................................................................................66 Literature Cited......................................................................................................68 III. SPATIOTEMPORAL VARIABILITY IN A SANDFLAT ELASMOBRANCH FAUNA IN SHARK BAY, AUSTRALIA..........................99