The cryptic and transboundary nature of ghost gear in the Maldivian Archipelago Item Type Thesis or dissertation Authors Stelfox, Martin Citation Stelfox, M. (2019). 'The cryptic and transboundary nature of ghost gear in the Maldivian archipelago'. Unpublished PhD Thesis. Derby: University of Derby. Publisher University of Derby Rights Attribution-NonCommercial-ShareAlike 4.0 International Download date 06/10/2021 14:39:16 Item License http://creativecommons.org/licenses/by-nc-sa/4.0/ Link to Item http://hdl.handle.net/10545/625352 UNIVERSITY OF DERBY The cryptic and transboundary nature of ghost gear in the Maldivian Archipelago Martin Richard Stelfox Doctor of Philosophy 2020 1 Sensitivity: Internal THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK 2 Sensitivity: Internal Contents Appendices ................................................................................................................................. 6 Figures........................................................................................................................................ 7 Tables ......................................................................................................................................... 9 Abbreviations ........................................................................................................................... 10 Abstract .................................................................................................................................... 12 Preface...................................................................................................................................... 14 Acknowledgements .................................................................................................................. 17 General Introduction ................................................................................................................ 19 Chapter 1: A review of ghost gear entanglement amongst marine mammals, reptiles and elasmobranchs .......................................................................................................................... 27 1.1 Abstract .................................................................................................................................... 28 1.2 Introduction ............................................................................................................................. 28 1.2.1 Supply and demand – A brief look at global fishing pressure ............................................. 29 1.2.2 When does fishing gear become ALDFG ............................................................................ 30 1.2.3 What factors affect ghost fishing rates ................................................................................ 30 1.2.4 The cyclical nature of ghost fishing and the role of bio-fouling .......................................... 32 1.3 Material and Method............................................................................................................... 34 1.4 Results ...................................................................................................................................... 35 1.4.1 The effects of ghost fishing on marine mammals, reptiles and elasmobranchs ................... 35 1.4.2 Gear types........................................................................................................................... 43 1.4.3 Bias in results ..................................................................................................................... 43 1.5 Discussion ................................................................................................................................. 47 1.5.1 Cetaceans and ghost fishings .............................................................................................. 47 1.5.2 Pinnipeds and ghost fishing ................................................................................................ 48 1.5.3 Manatee and dugong and ghost fishing .............................................................................. 49 1.5.4 Marine turtles and ghost fishing ......................................................................................... 49 1.5.5 Elasmobranchs and ghost fishing ....................................................................................... 51 1.5.6 Management and mitigation ............................................................................................... 52 1.6 Conclusion ................................................................................................................................ 54 Chapter 2: Statistical approaches to understanding the source and impact of ghost gear entanglement of Lepidochelys olivacea in the Maldivian Archipelago ............................... 73 3 Sensitivity: Internal 2.1 Abstract .................................................................................................................................... 74 2.2 Introduction ............................................................................................................................. 75 2.3 Material and method ............................................................................................................... 78 2.3.1 Logistic regrression ............................................................................................................ 80 2.3.2 Building classifiers with rare events ................................................................................... 81 2.3.3 Dealing with rare events ..................................................................................................... 82 2.3.4 Assigning fishing nets to fisheries ....................................................................................... 83 2.4 Results ...................................................................................................................................... 84 2.4.1 Logistic regression ............................................................................................................. 85 2.4.2 Random forest model predictions ....................................................................................... 87 2.4.3 Ghost net clustering ............................................................................................................ 89 2.5 Discussion ................................................................................................................................. 91 2.5.1 Causes of turtle entanglement ............................................................................................. 91 2.5.2 Impact on sea turtles ........................................................................................................... 93 2.5.3 Potential origin of nets ....................................................................................................... 95 2.5.4 Solutions and mitigation: Gear traceability ........................................................................ 97 2.5.5 Solutions and mitigation: Ghost net prevention .................................................................. 98 2.6 Conclusion ................................................................................................................................ 99 Chapter 3: Minimum drift times infer trajectories of ghost nets found ............................... 120 3.1Abstract ................................................................................................................................... 121 3.2 Introduction ........................................................................................................................... 122 3.3 Materials and method ........................................................................................................... 125 3.3.1 Study Site .......................................................................................................................... 125 3.3.2 Experimental assessment of bioaccumilation on floating nets and buoys ......................... 126 3.3.3 Ghost net data................................................................................................................... 129 3.3.4 Lagrangian modelling ...................................................................................................... 129 3.3.5 Fishery interaction ........................................................................................................... 130 3.4 Results .................................................................................................................................... 130 3.4.1 Experimental assessment of bioaccumilation on floating nets and buoys ......................... 130 3.4.2 Ghost net age estimates and their putative origin ............................................................. 138 3.4.3 Putative origin for ghost nets without drift time estimates ................................................ 140 3.4. Possible fisheries responsible for ghost nets in the Maldives ............................................. 143 3.5 Discussion ............................................................................................................................... 146 3.5.1 Biofouling communities and ghost gear ageing ................................................................ 146 3.5.2 Lagrangian simulations .................................................................................................... 148 3.5.3