An Assessment of Sea Turtle, Marine Mammal and Seabird Bycatch in the Wider Caribbean Region by Rhema Hyacinth Bjorkland Departm
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An Assessment of Sea Turtle, Marine Mammal and Seabird Bycatch in the Wider Caribbean Region by Rhema Hyacinth Bjorkland Department of Environment Duke University Date:_______________________ Approved: ___________________________ Larry Crowder, Supervisor ___________________________ Scott Eckert ___________________________ Pat Halpin ___________________________ Song Qian ___________________________ Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Environment in the Graduate School of Duke University 2011 ABSTRACT An Assessment of Sea Turtle, Marine Mammal and Seabird Bycatch in the Wider Caribbean Region by Rhema Hyacinth Bjorkland Department of Environment Duke University Date:_______________________ Approved: ___________________________ Larry Crowder, Supervisor ___________________________ Scott Eckert ___________________________ Pat Halpin ___________________________ Song Qian ___________________________ An abstract of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Environment in the Graduate School of Duke University 2011 Copyright by Rhema Hyacinth Bjorkland 2011 Abstract Sea turtles, marine mammals and sea birds are vulnerable to higher mortality rates as a direct function of incidental capture (bycatch) in marine fisheries. Their migratory behavior exposes them to multiple fishing gear types and fishing practices and efforts to understand the rates of interaction between these taxa and fishing necessarily entails analysis of data over large spatial areas (ocean-basin) and multiple types of fishing activities. The acquisition the requisite data, however, requires considerable resources and many regions in the world are data-poor with respect to bycatch, including the Wider Caribbean Region (WCR) in the west central Atlantic Ocean basin. This dissertation presents the results of multiple strategies used to assess sea turtle, marine mammal and seabird bycatch in the WCR, with a particular focus on sea turtle bycatch. The research incorporated a synthetic review of the literature, expert consultation, statistical techniques, and geospatial analyses to assess the bycatch seascape for the region. I conclude that sea turtle bycatch in the WRC is significantly linked to turtle rookeries, especially those on the continental land mass and in the southern section of the Caribbean basin, in large part because of the near shore artisanal nature of the fisheries and the importance of these habitats for foraging and reproduction. The limited information on marine mammal bycatch does not permit robust inferences, but it clearly identifies threats to at least one vulnerable marine iv mammal species, the tucuxi ( Sotalia fluviatilis ). Information on seabird bycatch was even more limited; the most vulnerable seabird populations occur in the higher latitudes (temperate zones) while the seabird populations in the WCR face significant threats from habitat loss and over-exploitation. This dissertation proposes specific recommendations for improving and advancing the information base for a regional, ecosystem-level management and mitigation of bycatch. v Dedication To my parent, Jim and Hyacinth Kerr and to my husband Ronald. vi Contents Abstract ......................................................................................................................................... iv List of Tables .................................................................................................................................. x List of Figures ............................................................................................................................ xiii Acknowledgements ................................................................................................................... xix 1. Overview ............................................................................................................................... 1 2. Sea turtle, marine mammal bycatch in the wider Caribbean ......................................... 4 2.1 Introduction ....................................................................................................................... 4 2.1.1 Overview of Caribbean fisheries ............................................................................... 7 2.1.2 Overview of sea turtles, marine mammals, and seabirds in the Caribbean ....... 9 2.2 Methods ........................................................................................................................... 12 2.2.1 Study area ................................................................................................................... 12 2.2.2 Synthesis of existing literature ................................................................................. 13 2.2.3 Consultation/ interviews .......................................................................................... 15 2.2.4 Longline fisheries catch rates ................................................................................... 15 2.3 Results .............................................................................................................................. 18 2.3.1 Recent historical information on bycatch ............................................................... 18 2.3.2 Bycatch information since 1990 ............................................................................... 19 2.3.2.1 Longline fisheries ............................................................................................... 19 2.3.2.2 Trawl fisheries .................................................................................................... 33 2.3.2..3 Gillnet fisheries ................................................................................................. 37 vii 2.3.2.4 Other net gear (Beach seines, purse seines, cast nets, weirs and pound nets) .................................................................................................................................. 44 2.3.2.5 Trap fisheries: ..................................................................................................... 45 2.4 Discussion ................................................................................................................... 49 3. The spatial overlap between breeding leatherback sea turtles ( Dermochelys coriacea ) and nearshore fisheries. Bycatch in the Trinidad drift gillnet fisheries. ............................. 54 3.1 Introduction ..................................................................................................................... 54 3.1 Materials and methods .................................................................................................. 64 3.3. Results ............................................................................................................................. 81 3.4 Discussion ........................................................................................................................ 92 4. Sea turtle bycatch in the Venezuelan industrial pelagic longline fishery. ............... 100 4.1 Introduction ................................................................................................................... 100 4.2 Methods ......................................................................................................................... 109 4.2.1 Data ........................................................................................................................... 109 4.2.2 Bycatch in relation to environmental covariates ................................................. 111 4.2.3 Spatio-temporal analyses ....................................................................................... 115 4.3 Results ............................................................................................................................ 116 4.3.1Spatio-temporal ........................................................................................................ 116 4.3.2 Bycatch and environmental correlates ................................................................. 134 4.4 Discussion ...................................................................................................................... 141 5. Regional strategies for mitigating and monitoring sea turtle bycatch in the Wider Caribbean Region ...................................................................................................................... 148 5.1 Introduction ................................................................................................................... 148 viii 5.2 Major themes ................................................................................................................. 148 5.3 Closing the gap: observations and recommendations ............................................ 151 Appendix A:............................................................................................................................... 160 Appendix B ................................................................................................................................ 164 APPENDIX C ............................................................................................................................. 170 Bibliography .............................................................................................................................. 189 Biography ..................................................................................................................................