Shark Depredation and Unwanted Bycatch in ... - ProDelphinus

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Shark Depredation and Bycatch in Pelagic Longline Fisheries Page 28 shows some of the tools used by longline fishermen to assist with immobilizing and retrieving terminal tackle from sharks. The survival of sharks that are not finned, that are deeply hooked (where the shark has swallowed the hook) and have hooks removed by fishers pulling the hook out likely depends on where they were hooked and how much damage is done by pulling out the hook. In these cases of deeply hooked sharks, as is believed to be the case for sea turtles (Gilman et al., 2006a), prospects for shark post release survival might be improved by having fishers cut the line as close to the shark as safely possible. Fig. 6.1. Some of the tools used by longline fishermen to immobilize and retrieve terminal tackle from sharks. Hawaii longline fisherman demonstrating how he clips a loop of rope onto a branch line below the weighted swivel at the top of the wire leader to assist with removing a hook from caught sharks (left); ring and electrical cord of a “shocker” device used by a Japanese nearhshore longline fishermen to immobilize sharks (middle); Chilean fisherman’s improvised dehooker (right) (photos by E. Gilman, J. Mangel, T. Miyamoto). A large proportion of sharks caught in longline gear that is released after removal of the hook from the mouth are expected to survive. Research conducted by the U.S. National Marine Fisheries Service Pacific Islands Fisheries Science Center using pop-up satellite archival tags found that 97.5% of pelagic sharks released after capture on longline gear survived (1 of 40 captured sharks died), while a study by the U.S. National Marine Fisheries Service Southwest Fisheries Science Center found that 94% of 17 tagged shorfin mako sharks survived beyond two months after release (U.S. National Marine Fisheries Service, 2005). Some vessels in the Australia longline fishery are known to use firearms to safely and efficiently kill caught sharks to retrieve terminal tackle, while some vessels in the Australia and Hawaii fisheries will kill caught sharks in an effort to avoid the inconvenience of their recapture. However in the Hawaii fisheries, observer data show that a very small proportion of caught sharks that are alive when hauled to the vessel are killed before discarding (Gilman, this volume). This is also the case in the Peru longline mahi mahi and shark fishery (Pro Delphinus, unpublished data; Mangel and Alfaro-Shigueto, this volume). Some vessels in the Hawaii longline fleet report that, when they are busy processing commercially valuable species on deck, they will place a tarred rope with a knot at the end off the stern and will clip branch lines containing sharks onto this rope so they can remove the sharks from the gear after they have completed the haul and processed the catch. The majority of sharks placed on this line will have fallen off before the end of the haul, while most sharks remaining on the line when it is retrieved are dead. In the Italy Mediterranean industrial longline swordfish fishery, some fishermen reported that, in the past when shark capture rates were higher, they would routinely kill all caught sharks in order to reduce local shark abundance, which they believed would result in an increase in their swordfish catch by reducing shark predation on the swordfish (Piovano, this volume). Reducing such practices that result in the mortality of discarded sharks would contribute to preventing the unsustainable exploitation of sharks. A few of the interviewed fishers report killing all caught sharks in order to prevent the inconvenience of recapturing them, reduce shark depredation, and in one case, to reduce shark populations to reduce the likelihood of being killed by a shark if he ever has to abandon ship (Brothers, this volume; Gilman, this volume; Thomson, this volume). While this attitude was not held by the majority of the fishers
Page 29 Shark Depredation and Bycatch in Pelagic Longline Fisheries interviewed, it is useful to identify as a potential obstacle to introducing new techniques to improve the post-release survival prospects of caught sharks that are discarded. While circle hooks may result in a higher shark CPUE than J and Japan tuna style hooks (Section 6.2.3), because fish caught on circle hooks are more likely to be hooked in the mouth versus swallowing the hook, removal of circle hooked sharks is easier and may result in reduced injury to the shark than sharks caught on other hook types. None of the interviewed pelagic longline fishermen use dehookers to discard live sharks. Only two fishers, one from the Chile artisanal mahi mahi and shark longline fishery and one from the Peru artisanal mahi mahi and shark longline fishery, report that they use a dehooker to recover hooks from sharks when these are onboard and already dead (Alfaro-Shigueto et al., this volume; Mangel and Alfaro-Shigueto, this volume). The Peruvian fisher possessed the dehooker initially for the purpose of releasing sea turtles. A benefit of using a dehooker might include reduced time to retrieve terminal tackle. The U.S.-based company Aquatic Release Conservation produces a 0.8 m long “Big Game” and a 0.4 m long “Bite Block” dehooker, which are designed to remove hooks from sharks brought onboard. For sharks that are too large to bring onboard, this company also produces a 2.4 m long and 3.7 m long dehooker on a pole. The effect of dehookers on the post-release survival prospects of sharks compared to crew cutting a hook from the shark or cutting the branch line and leaving a hook and trailing line attached to the shark has not been assessed. Almost all of interviewed fishers from all fisheries included in the study, except South Africa where all the fishers thought use of a dehooker would reduce shark injury, believe that it would be inefficient to use dehookers to remove sharks from gear, either because this would increase the safety risk, or because it is simply not feasible to use this device to remove sharks. Some caught sharks will twist and spin when hauled to the vessel, which could cause the dehooker to be lost overboard and be a hazard for crew to handle before being lost overboard. Because sharks may be on the sea surface when being hauled, some fishers were concerned that the incidence of having branch lines break if a shark pulls the line would increase with use of a dehooker because to use a dehooker requires bringing the shark close to the vessel. Gear soak time also likely affects the proportion of caught sharks that are alive when hauled to the vessel. Changes to fishing gear and methods that reduce soak time could contribute to reducing fishing mortality of discarded sharks. 6.2.5. Reduce retention of sharks on branch lines Retention of sharks on branch lines with wire leaders or other durable material is substantially higher than in gear with no wire leader where nylon monofilament is connected directly to the hook (Chapter 4) (e.g., Williams, 1997). For instance, an owner-operator of a vessel in the Japan nearshore pelagic longline fishery who seasonally will target sharks stated that he does not use a wire leader (nylon monofilament is used through to the hook) when he is targeting tunas and billfish because he believes that this gear design maximizes the catch of these target species. He uses a 1 m wire trace at the hook during seasons when he targets sharks (Clarke, this volume). Also, fishers in the Chile and Peru artisanal longline mahi mahi and shark fisheries will add a wire leader to increase shark catch rates (Alfaro- Shigueto et al., this volume; Mangel and Alfaro-Shigueto, this volume).
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Page 55 and 56: Appendix 1, Australia Page 41 Of th
Page 57 and 58: Appendix 1, Australia Page 43 A1.4.
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Page 79 and 80: Appendix 1, Australia Page 65 The f
Page 81 and 82: Appendix 1, Australia Page 67 Shott
Page 83 and 84: Appendix 2, Chile Page 69 Captures
Page 85 and 86: Appendix 2, Chile Page 71 Landings
Page 87 and 88: Appendix 2, Chile Page 73 Table A2.
Page 89 and 90: Appendix 2, Chile Page 75 Fig. A2.5
Page 91 and 92: Appendix 2, Chile Page 77 A summary
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Appendix 2, Chile Page 79 Prices ar
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Appendix 2, Chile Page 81 Two of th
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Appendix 2, Chile Page 83 A2.14.6.
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Appendix 2, Chile Page 85 Fig. A2.1
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Appendix 2, Chile Page 87 A2.17. Re
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Appendix 3, Fiji Page 89 • Robert
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Appendix 3, Fiji Page 91 The data i
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Appendix 3, Fiji Page 93 Table A3.4
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Appendix 3, Fiji Page 95 A3.7.2. Pr
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Appendix 3, Fiji Page 97 Table A3.1
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Appendix 3, Fiji Page 99 of whale d
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Appendix 4, Italy Page 101 A4.2. Fl
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Appendix 4, Italy Page 103 Branch l
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Appendix 4, Italy Page 105 catch sp
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Appendix 4, Italy Page 107 Table A4
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Appendix 5, Japan Page 111 Appendix
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Appendix 5, Japan Page 113 A5.2. Hi
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Appendix 5, Japan Page 115 SEA SURF
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Appendix 5, Japan Page 117 A5.3.1.
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Appendix 5, Japan Page 119 period (
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Appendix 5, Japan Page 121 Catch ('
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Appendix 5, Japan Page 133 Japanese
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Appendix 6, Peru Page 135 Appendix
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Appendix 6, Peru Page 137 While the
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Appendix 6, Peru Page 139 Pro Delph
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Appendix 6, Peru Page 141 Table A6.
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Appendix 6, Peru Page 143 Revenue f
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Appendix 6, Peru Page 149 Fig. A6.1
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Appendix 7, South Africa Page 151 A
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Appendix 8, Hawaii Page 163 Table A
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Appendix 8, Hawaii Page 165 Average
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Appendix 8, Hawaii Page 167 regulat
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Table A8.7. Shark capture statistic
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Appendix 8, Hawaii Page 171 A8.4. M
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Shark Depredation and Bycatch in Pe
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