Shark Depredation and Unwanted Bycatch in Pelagic Longline

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Chapter 3 Shark Catch Rates and Disposition Table 3.1 summarizes the disposition of caught sharks for fisheries included in the study where this information is available. As discussed below, several of these entries are based on limited data from small sample sizes. For the Japan distant water, offshore and nearshore longline fisheries, the shark catch rates reported in Table 3.1 are based on logbook data. These data are thus the number of sharks that are recorded in vessel logbooks but these figures’ relationship to the actual number of sharks hooked and retained is expected to vary with logbook recording behavior (Clarke, this volume; Nakano and Clarke, 2006). The Italy Mediterranean large-scale longline swordfish fishery is the only fishery included in this study where there is a lack of a local market for shark fins, and as a result, fishers do not fin sharks (Piovano, this volume). The shark catch rates for the two Chile fisheries included in Table 3.1 are estimated from fisher interviews (Alfaro-Shigueto et al., this volume). Shark catch rates reported in the literature for the Chile longline swordfish fishery and artisanal longline mahi mahi and shark fishery are available only in weight per unit of effort (0.36 kg/hk and 0.28 kg/hk, respectively, 2005 (Barria and Donoso, 2006)), and not as number of sharks per unit of effort. In both fisheries, almost all caught sharks are retained (Alfaro- Shigueto et al., this volume). Blue and mako sharks are the main shark species caught. Carcasses and fins are usually retained, however, sometimes fins of blue sharks are only retained and carcasses are discarded, and occasionally sharks are released alive because they are small or to avoid contaminating the non-shark catch in the hold. For the Chile artisanal longline fishery during the mahi mahi season, vessels only retain shark carcasses that are caught during the last sets of a trip and only if space is available in the vessel hold. If the shark catch rate is high, blue shark carcasses may be discarded to make room for move valuable mako shark carcasses. For the Fiji longline tuna fishery, observer data from 1999 and 2002 to 2005 show that 78 - 90% of caught sharks were finned and the carcasses discarded (Secretariat of the Pacific Community unpublished data reported in Thomson, this volume). Statistics reported in Table 3.1 for the Peru artisanal longline mahi mahi and shark fishery are based on 2004 - 2006 onboard observer data taken only during the mahi mahi season from four ports for a total of 27 trips and 197 sets (Pro Delphinus, unpublished data; Mangel and Alfaro-Shigueto, this volume). The Peru artisanal longline fishery is similar to the Chile artisanal longline fishery in that almost all caught sharks are retained primarily for the sale of both their fins and meat (Mangel and Alfaro-Shigueto, this volume). Of 188 observed caught sharks, 30 were discarded (all released alive after retrieval of terminal tackle), 146 were retained whole, and fins only of 12 were retained (Pro Delphinus, unpublished data). Some fishers discard sharks smaller than about 50 cm long only when the shark is alive when hauled to the vessel (Mangel and Alfaro-Shigueto, this volume). The large number of “not available” entries and entries based on rough estimates in Table 3.1 suggests either that there is insufficient data collection and management measures for shark species or that relevant data are collected but have not been analyzed. For fisheries where there is high confidence in available shark catch rates, these range from 0.7 to 17 sharks per 1000 hooks. The location of fishing grounds and characteristics of fishing gear and methods are likely primary factors determining a fleet’s shark catch rate. Certain gear designs (e.g., use of a wire leader, use of squid for bait, and depth of baited hooks) contribute to high shark catch rates. Shallow-setting pelagic longline fisheries generally have higher shark catch rates than deeper-setting fisheries. The proportion of total catch comprised of sharks by number varies widely for the fisheries included in this study. In the Australia longline tuna and billfish fishery, sharks comprise about 27% of the 12
Shark Catch Rates and Disposition Table 3.1. Shark catch rate and disposition in 12 pelagic longline fisheries for the most current year for which data are avaiable (Megalofonou et al., 2005; Alfaro-Shigueto et al., this volume; Brothers, this volume; Clarke, this volume; Gilman, this volume; Mangel and Alfaro Shigueto, this volume; Petersen and Goren, this volume; Thomson, this volume). Pelagic Longline Fishery Shark Catch Rate (Number per 1000 hooks) Shark Retention (Fins and/or Carcass) (% of Total Number Caught Sharks) Australia Tuna and Billfish Longline Fishery 5.5 1 Not available Chile Artisanal Mahi Mahi and Shark Longline Fishery 24 2 > 99 2 Chile Longline Swordfish Fishery 8 2 > 99 2 Fiji Longline Tuna Fishery 1.1 78-90 Italy Mediterranean Industrial Longline Swordfish Fishery 0.74 Not available Japan Distant Water Longline Tuna Fishery 0.021 3 Not available Japan Offshore Longline Fishery 0.175 3 Not available Japan Nearshore Longline Fishery 0.020 3 Not available Peru Artisanal Longline Mahi Mahi and Shark Fishery during mahi season 0.99 84 South Africa Longline Tuna and Swordfish Fishery 4.0 80 USA - Hawaii tuna 2.2 2.1 USA - Hawaii swordfish 16.7 0.2 1 Rough estimate based on Australian Commonwealth Scientific and Research Organization unpublished data from a subset of the fleet and time period, possibly not representative (Brothers, this volume). 2 Rough estimate based on interview responses. 3 Based on number of sharks recorded in vessel logbooks (Clarke, this volume; Nakano and Clarke, 2006). total catch (Brothers, this volume). Observer data from 1999 found that sharks comprised > 25% of the total number of fish caught by Fiji longline tuna vessels (Swamy, 1999), while Secretariat of the Pacific Community observer program data for 1999 and 2002-2005 found that sharks comprised only 5.5% of the total number of caught fish (Thomson, this volume). From 1998-1999, sharks comprised about 18% of the total catch in the Italy Mediterranean industrial longline swordfish fishery (Megalofonou et al., 2005). In the Peru artisanal longline mahi mahi and shark fishery, during the mahi mahi season in the port of Ilo for 2005-2006, sharks comprise less than 1% of the total catch by number (Mangel and Alfaro-Shigueto, this volume). In the South Africa longline tuna and swordfish fishery, from 1998- 2005, sharks comprised 16.2% of the total number of caught fish (Petersen and Goren, this volume). In 2001, pelagic sharks comprised about 50% of the catch composition of swordfish sets and 16% for tuna sets in the Hawaii longline fishery (Ito and Machado, 2001). However, since 2004 the shark catch rate in the swordfish fishery dropped 36% when the fishery was required to switch from using J hooks with squid bait to wider circle hooks with fish bait (Gilman et al., 2006a). The results from this study are generally consistent with the literature, which shows that a large quantity of pelagic sharks is taken as bycatch in pelagic longline fisheries with tuna and swordfish as their primary target species (Bailey et al., 1996; Williams, 1997; Matsunaga and Nakano, 1999; Swamy, 1999; Francis et al., 2001; Beerkircher et al., 2002). For example, in the western Pacific, shark species account for the highest category of bycatch in tropical fisheries, where sharks comprise 27% of total bycatch, and in subtropical fisheries, where sharks are 18% of total bycatch (Bailey et al., 1996; Heberer and McCoy, 1997). In the U.S. Atlantic longline swordfish and tuna fisheries, sharks and rays constituted 25% of total catch between 1992 and 2003 (Abercrombie et al., 2005). Beerkircher et al. (2002) found that sharks comprised 15% of the total catch, comprised of 22 elasmobranch species, in the southeastern U.S. pelagic longine swordfish and tuna fisheries. Bonfil (2002) found that the same numbers of sharks are caught in directed fisheries as are caught as bycatch mostly in longline tuna fisheries. However, the recent development of longline directed shark fisheries, especially in the Pacific, may mean that directed shark fisheries are now catching more sharks (Chen et al., 2002; Stevens, 2002; Catarci, 2004; FAO, 2006; Alfaro-Shigueto et al., this volume; Mangel and Alfaro-Shigueto, this volume). For fisheries where information on shark catch composition is available, blue sharks comprise the largest proportion of shark catch. Blue sharks comprise 47% of total shark catch by number of fish in the Australia longline tuna and billfish fishery (Brothers, this volume); 49% in the Fiji longline tuna fishery (Thomson, this 13
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Page 9 and 10: Contents Summary and Conclusions 1
Page 11 and 12: Contents Appendix 3. Fiji Pelagic L
Page 13: Contents Appendix 8. USA Hawaii Lon
Page 19 and 20: Chapter 1 Introduction and Methods
Page 21 and 22: Introduction and Methods 1.2. Metho
Page 23 and 24: Fishing Gear and Operational Charac
Page 25: Fishing Gear and Operational Charac
Page 29 and 30: Chapter 4 National and Internationa
Page 31 and 32: National and International Measures
Page 33 and 34: Economic, Practical, Ecological and
Page 35 and 36: Economic, Practical, Ecological and
Page 37 and 38: Chapter 6 Industry Attitudes and Pr
Page 39 and 40: Industry Attitudes and Practices Lo
Page 41 and 42: Industry Attitudes and Practices Fi
Page 43 and 44: Chapter 7 Potential of Deterrents,
Page 45 and 46: Potential of Deterrents, Hotspot Av
Page 47 and 48: References Campana, S.E., L. Marks,
Page 49: References Neves dos Santos, M., Ga
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Appendix 5 Japan Pelagic Longline F
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Japan Pelagic Longline Fisheries Fi
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Appendix 6 Peru Artisanal Mahimahi
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Peru Artisanal Mahimahi And Shark L
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Appendix 7 South Africa Pelagic Lon
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South Africa Pelagic Longline Tuna
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Appendix 8 USA Hawaii-based Pelagic
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USA Hawaii-based Pelagic Longline S
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Appendix 9 USA Atlantic, Gulf of Me
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USA Atlantic, Gulf of Mexico and Ca
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Shark Depredation and Unwanted Bycatch in Pelagic Longline

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