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An Analysis of Fish Bycatch in the California Large Mesh Drift Gillnet Fishery

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An Analysis of Fish Bycatch in the California Large Mesh Drift Gillnet Fishery AN ANALYSIS OF FISH BYCATCH IN THE SIO/SWFSC CALIFORNIA LARGE MESH DRIFT GILLNET FISHERY 2016 Capstone Project by: Gwendal Le Fol Committee: Dr. Stephen Stohs (Chair) (SWFSC, NOAA) Dr. Heidi Dewar (SWSFC, NOAA) Brian Stock (SIO) Dr. Stuart Sandin (SIO) Gwendal Le Fol (MAS-MBC) –Capstone Report 2016 Committee Signatures: Stephen Stohs (Chair) Heidi Dewar Brian Stock Stuart Sandin 1 Gwendal Le Fol (MAS-MBC) –Capstone Report 2016 Contents Table of Acronyms .................................................................................................................... 4 Introduction ................................................................................................................................ 5 Background ............................................................................................................................ 5 Purpose ................................................................................................................................... 9 Project Origin ....................................................................................................................... 10 Methodology ............................................................................................................................ 11 The data ................................................................................................................................ 11 Analysis using R ............................................................................................................... 13 Findings ................................................................................................................................... 15 Bycatch ranks ....................................................................................................................... 15 1990-1997 (included): ...................................................................................................... 15 1998-2000 (included): ...................................................................................................... 17 2001-2013 (included): ...................................................................................................... 17 Biomass ................................................................................................................................ 19 Trends in discards in the CA DGN fishery .......................................................................... 19 Overall discards ................................................................................................................ 19 Discard disposition ........................................................................................................... 21 Discussion ................................................................................................................................ 21 Future steps .............................................................................................................................. 23 Bootstrapping ....................................................................................................................... 23 Removing the effect of latitude that already existed pre-PLCA .......................................... 23 Comparison with other fisheries .......................................................................................... 23 Assess the magnitude of catches in relation to stock biomass ............................................. 23 Explore the effects of environmental variables .................................................................... 24 Conclusion ............................................................................................................................... 24 Annexes ..................................................................................................................................... 26 Annex A: Bibliography (cited as well as general sources of information) .......................... 26 Annex B: 1990-1997 CA DGN catch rankings .................................................................... 30 Annex C: 1998-2000 CA DGN catch rankings .................................................................... 32 Annex D: 2001-2013 CA DGN catch rankings ................................................................... 34 Annex E: 1990-2013 CA DGN catch rankings .................................................................... 36 Annex F: Overall catch trends (CPUE) of individual species that account for the top 98.16 % of catches between 2001 and 2013. Tables ranked in order of importance in terms of catch numbers between 1990 and 2013. .......................................................................... 38 Common mola .................................................................................................................. 38 Broadbill swordfish .......................................................................................................... 38 Albacore tuna .................................................................................................................... 38 Shortfin mako shark .......................................................................................................... 39 2 Gwendal Le Fol (MAS-MBC) –Capstone Report 2016 Blue shark ......................................................................................................................... 39 Opah .................................................................................................................................. 39 Skipjack ............................................................................................................................ 40 Common thresher shark .................................................................................................... 40 Pacific mackerel ............................................................................................................... 40 Bluefin tuna ...................................................................................................................... 41 Bonito ............................................................................................................................... 41 Bullet mackerel ................................................................................................................. 41 Yellowfin tuna .................................................................................................................. 42 Bigeye thresher shark ....................................................................................................... 42 Annex G: 1990 to 2000 (included) North of Point Conception catch rankings ....................... 43 Annex H: 1990 to 2000 (included) South of Point Conception catch rankings ....................... 45 3 Gwendal Le Fol (MAS-MBC) –Capstone Report 2016 Table of Acronyms Acronym Definition CA California CDFW California Department of Fish and Wildlife CPUE Catch Per Unit Effort DGN Drift Gill Net EEZ Exclusive Economic Zone ESA Endangered Species Act FMP Fisheries Management Plan HMS Highly Migratory Species MMPA Marine Mammal Protection Act NGO Non-Governmental Organization NMFS National Marine Fisheries Service NOAA National Oceanic and Atmospheric Administration PFMC Pacific Fisheries Management Council POCTRP Pacific Offshore Cetacean Take Reduction Plan PLCA Pacific Leatherback Conservation Area SFA Sustainable Fisheries Act SIO Scripps Institution of Oceanography 4 Gwendal Le Fol (MAS-MBC) –Capstone Report 2016 Introduction The California Large Mesh Drift Gillnet fishery (CA DGN fishery) has targeted swordfish (Xiphias gladius) within the exclusive economic zone (EEZ) off the West Coast of the United States since the late 1970s. Since its inception a number of regulatory changes have been implemented to reduce the take of non-target species. Concerns over marine mammal interactions led to the implementation of the Federal Fisheries Observer Program in 1990 to support compliance with the Marine Mammal Protection Act (MMPA). Observer information is used by the National Marine Fisheries Service (NMFS) to inform stock assessments, help construct fishery management plan regulations, develop bycatch reduction devices, and identify the need for protective regulations for protected species1. The implementation of gillnet extenders in 1998 under the Pacific Offshore Cetacean Take Reduction Plan (POCTRP) and the establishment of the Pacific Leatherback Conservation Area (PCLA) in 2001 have since contributed to reducing marine mammal and sea turtle interactions for this fishery into compliance with the MMPA and Endangered Species Act (ESA). The tremendous dataset collected by fisheries observers since 1990 is rich with information on finfish catch and discards in the CA DGN fishery. This component of the fishery remains largely under-studied in the context of the gear modifications and spatial closures that were originally intended to benefit marine mammals, sea turtles and sharks. This research project therefore aims to explore the fish catch and discard characteristics and disposition of fish species in the CA DGN fishery, using an approach based on biomass wherever possible. In addition, catch trends of various species will be described graphically in order to begin drawing a picture of the fishery’s impact on the major species that constitute its catch. The overall aim of this project is to provide an overview of catch and bycatch composition in the CA DGN fishery. Background Drift gillnets
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