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Migratory Behaviour and Spatial Dynamics of Large Sharks and Their Conservation Implications

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Migratory Behaviour and Spatial Dynamics of Large Sharks and Their Conservation Implications University of Plymouth PEARL https://pearl.plymouth.ac.uk 04 University of Plymouth Research Theses 01 Research Theses Main Collection 2017 Migratory behaviour and spatial dynamics of large sharks and their conservation implications Lea, James Simon Eaton http://hdl.handle.net/10026.1/8334 University of Plymouth All content in PEARL is protected by copyright law. Author manuscripts are made available in accordance with publisher policies. Please cite only the published version using the details provided on the item record or document. In the absence of an open licence (e.g. Creative Commons), permissions for further reuse of content should be sought from the publisher or author. Migratory behaviour and spatial dynamics of large sharks and their conservation implications by James Simon Eaton Lea A thesis submitted to the University of Plymouth in partial fulfilment for the degree of DOCTOR OF PHILOSOPHY School of Marine Science and Engineering Faculty of Science In collaboration with the Marine Biological Association and the Guy Harvey Research Institute July 2016 This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with its author and that no quotation from the thesis and no information derived from it may be published without the author's prior consent. 1 2 Migratory behaviour and spatial dynamics of large sharks and their conservation implications by James Simon Eaton Lea A thesis submitted to the University of Plymouth in partial fulfilment for the degree of DOCTOR OF PHILOSOPHY School of Marine Science and Engineering Faculty of Science In collaboration with the Marine Biological Association and the Guy Harvey Research Institute January 2017 3 4 Migratory behaviour and spatial dynamics of large sharks and their conservation implications James Simon Eaton Lea Abstract Determining the dynamic nature of animal movement has been an important component in a wider understanding of animal population ecology. Generally, this is because temporal change in the density of a population at a specific geographic location is not only a function of births and deaths but also of movements, including migration. The increased availability of remote telemetry and biologging systems in recent years has enabled many studies tracking marine predators, such as turtles, seabirds and marine mammals, but a general understanding of spatial dynamics in large sharks remains less well developed. This is in part due to few studies having achieved sufficiently long-term, multi-year tracks to detect changes in movement behaviour over time. Determining the timing, repeatability and potential motivations for movements of large sharks is necessary to understand the ecological and evolutionary role of such behaviour more generally in marine predators. Furthermore, given global concerns of declining shark populations, a detailed appreciation of shark movements can reveal the extent 5 of overlap with area-focused human activities (e.g. fishing), as well as inform assessments of population trends and spatial management options. In order to demonstrate how shark migratory behaviour and spatial dynamics can vary dramatically depending on the species and location, with subsequent contrasting conservation implications, the present work used long- term, remote telemetry to reveal detailed patterns in shark movement behaviour at two very different geographical scales: broad-scale movements of larger species that encompass ocean basins, versus fine-scale movements of reef-associated species at a remote atoll. First, using satellite telemetry, it was revealed for the tiger shark Galeocerdo cuvier, that adult males undertake annually repeated, roundtrip migrations of over 7,500 km in the northwest Atlantic. Second, acoustic telemetry was used to determine the fine-scale spatial dynamics of a multi- species shark assemblage at a small, remote atoll in the Seychelles, Indian Ocean, where a number of species displayed perennial residency. While the fine-scale movements of reef sharks in the Seychelles suggest an MPA of moderate size may be an effective management option, the long-distance migrations of the tiger sharks in the Atlantic reveal that conservation efforts targeting them must account for dynamic fisheries interactions over large geographical scales, potentially requiring time-area closures to be effective. Examining the long-term movement behaviour of different shark species over contrasting geographical scales has emphasised the importance of understanding spatial dynamics when informing management decisions, and has contributed to a wider understanding of the population ecology of these species. 6 Contents Abstract ........................................................................................................................................ 5 Contents ........................................................................................................................................ 7 Figures ......................................................................................................................................... 11 Tables .......................................................................................................................................... 19 Acknowledgements .................................................................................................................... 21 Author’s Declaration .................................................................................................................. 24 1 General Introduction .......................................................................................................... 27 1.1 The Value of Sharks ..................................................................................................... 27 1.2 Population Declines .................................................................................................... 33 1.3 Movements and Management ................................................................................... 36 1.4 Genetics ...................................................................................................................... 41 1.5 Origins of the Present Study ....................................................................................... 42 1.6 Aims and Objectives .................................................................................................... 43 2 General Methods ................................................................................................................ 46 2.1 Study Sites ................................................................................................................... 46 2.1.1 Challenger Bank, Bermuda .................................................................................. 46 2.1.2 D’Arros and St Joseph, Seychelles ....................................................................... 47 2.2 Telemetry Techniques ................................................................................................. 50 2.2.1 Satellite Telemetry .............................................................................................. 51 2.2.2 Acoustic Telemetry ............................................................................................. 52 2.3 Shark Capture and handling ........................................................................................ 55 2.4 Track Analysis .............................................................................................................. 61 7 2.4.1 Satellite Tag Geolocation ..................................................................................... 61 2.4.2 Acoustic Network Analysis .................................................................................. 64 3 Migratory behaviour and philopatry of tiger sharks Galeocerdo cuvier in the Atlantic Ocean........................................................................................................................................... 66 3.1 Introduction ................................................................................................................. 66 3.2 Methods ...................................................................................................................... 69 3.3 Results ......................................................................................................................... 72 3.4 Discussion .................................................................................................................... 86 3.4.1 Repeated long-distance migration ...................................................................... 86 3.4.2 Partial migration .................................................................................................. 89 3.4.3 Conservation implications ................................................................................... 90 4 Ontogeny of environmental influences on tiger shark Galeocerdo cuvier distribution and movement behaviour ................................................................................................................. 92 4.1 Introduction ................................................................................................................. 92 4.2 Methods ...................................................................................................................... 95 4.2.1 Spearman’s Rank Correlation .............................................................................
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