Shark Depredation and Unwanted Bycatch in Pelagic Longline

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Shark Depredation and Unwanted Bycatch in Pelagic Longline Fisheries No special procedures for bait or offal disposal in present day operations were cited. Therefore, in practice, excess bait and offal are disposed overboard while hooks are still in the water but no adverse effects are reported. Contrary to expectations, two fishermen insisted that discarding shark heads and guts into the water will deter other sharks from approaching the area. This opinion met with skepticism when raised with subsequent interview participants and one fishermen claimed that this technique was likely to have the opposite effect. A5.10.3. Changing target depth and soak time Several fishermen believe that fishing at depths below 50-100 m will result in lower shark catches and rates of depredation. Some interview participants claimed that their lack of shark interaction problems was related to their use of deep sets (and nylon leaders), but none of the respondents decided their fishing depth based on this factor alone. As mentioned above, soak time was not considered an important factor for sharks. Some fishermen mentioned that longer soak times could lead to higher shark catches and more depredation. However, one kinkai respondent explained that soak time is determined by the crew rotation schedule and thus there is little experience in this fishery with varying soak time (usually about 9-10 hours). In a related issue, many participants believed that the number of sharks in an area will decline with repeated sets. One respondent claimed that shark catch in a subsequent set would equal only half that of the previous set in the same area, and that a third set’s shark catch would be even lower. A5.10.4. Chemical and electrical deterrents Several of the interview participants targeted sharks during all or part of their operations and for this reason declined to comment on shark deterrent measures. All interview participants who stated an opinion on such deterrents cited concerns that such techniques would not be effective. Other articulated concerns included adverse environmental impacts (in the case of chemicals) and undesirable deterrent effects on target species. One fishermen believed there might be potential to use underwater sound waves as a deterrent. Although not related to the interview program, an electrical shark avoidance device was tested in a coastal midwater trawl fishery in the Sea of Japan (Ishikawa Prefecture) in 2004 (personal observation). The purpose of the device was to deter predation by sharks on the cod end of the trawl during hauling. The device, mounted on the fishing vessel, emitted an electrical pulse into the waters in the immediate vicinity. It was believed by fishermen to be effective based on observations of sharks suddenly moving away from the cod end and the vessel once the electrical pulse was emitted. This example provides a useful illustration of electrical deterrents for sharks but the effectiveness of the device is yet to be fully proven, and it would have to be substantially modified before being applied to longline fisheries. A5.10.5. Artificial bait and other changes to bait type or attraction A variety of bait types were used by the interview participants but in all cases the choice of bait was for the purpose of attracting target species while minimizing cost, not for repelling sharks or other bycatch. The majority of interviewed fishermen believe that squid, especially small-sized squid, might be a preferred bait for sharks. These respondents also expressed the possibility that the rubbery texture of squid makes it less likely to fall off the hook or for fish to bite it off the hook and thus the use of squid bait could lead to higher shark catches. One former fishing master listed bait types in descending order of preference by sharks: squid, mackerel, good quality herring, horse mackerel, saury, scad and poor quality herring. Squid is also a useful bait for billfishes and tuna, especially bigeye tuna, but one box of squid bait costs approximately three times as much as a box of mackerel bait and contains fewer pieces when compared to other bait. For this reason, many fishermen do not often use squid bait and those that do use it alternate squid with other bait in a pattern within the same basket. Based on this information, avoidance of squid bait, if possible, might be useful in reducing shark hooking rates. Interview participants had no experience with artificial bait but generally doubted its effectiveness based on a belief that sharks will take any bait. In support of this opinion, one fisherman cited his experience of seeing oceanic whitetip sharks eating plastic. Only one fishermen who had read about artificial bait trials seemed hopeful about their prospective use. Lightsticks are never used in the Japanese longline fleet due to cost. For this reason, respondents generally had no opinions on the effect of lightsticks on shark catch rates. However, one fishermen said that the use of lightsticks would have no effect on sharks. A5.10.6. Reducing injury to discarded sharks Use of a de-hooking device or other methods of freeing hooked sharks while retrieving the gear seemed unreasonable to most interview participants due to the widespread utilization of shark catches, either whole or in part. The only sharks which are reportedly released are extremely large sharks, which cannot be safely handled and require cutting the leader, and very small sharks, for which retention is not cost-effective and which can be de-hooked without serious risk to crew. In both cases, special de-hooking technology was not considered necessary. Under current practices, crew injuries from sharks were considered rare events and not of particular concern, however, if more careful de-hooking procedures were followed for the sake of minimizing mortality to sharks, concerns about crew injuries may increase. In contrast to the experience of fishermen in other longline fleets, Japanese longline fishermen did not believe that releasing sharks alive would lead to more sharks being hooked multiple times. In addition to fishermen very rarely seeing sharks with old hooks in their mouths, one fishermen cited results from a recent NRIFSF experimental fishing survey in which sharks released alive did not return to the area to bite hooks again 13 . 13 NRIFSF scientists subsequently stated that this claim is not supported by their survey records. 98
Japan Pelagic Longline Fisheries A5.10.7. Change in gear (hooks or leaders) Most fishermen who have experience with nylon monofilament leaders agreed that their use resulted in a lower shark catch, e.g. a 66% reduction was cited, due to biting off of the hook. Some interview participants saw this as an advantage since it reduced the need to handle large and dangerous sharks. In contrast, some fishermen preferred wire leaders because they are more easily retrieved and repaired and all fishermen specifically targeting sharks used wire leaders to prevent bite off. Among fishermen who do not target sharks, enyo fishermen targeting tuna used wire leaders until about 1990 but then switched to nylon monofilament. This change was made to improve the natural-looking movement of the bait on the hook which is particularly important when targeting tuna. In the kinkai fleet, targeting strategies and thus gear configuration, varied considerably: wire leaders were used to opportunistically target tuna, billfish or sharks; wire leaders were used to target billfish specifically; and a mixture of wire and nylon monofilament leaders were used within the same basket to target tuna. Engan fishermen not targeting sharks reported using nylon monofilament leaders to target tuna and billfish. All of the interviewed fishermen selected their leader material with regard to its effectiveness in catching their target species. Since they do not consider shark interactions a major issue they have never contemplated changing the leader material to reduce depredation or shark catch. No injuries associated with the snapping of nylon monofilament branch lines by sharks during hauling were reported. A few fishermen had experience with, or opinions on, circle hooks. The results of field trials by NRIFSF have indicated that the catch rate for blue sharks and the proportion of hooked blue sharks which were dead did not differ significantly by hook type (Yokota et al. 2006a, 2006b). One enyo fisherman believed that circle hooks could reduce shark and turtle interactions without causing a decline in tuna catches while another said that hook shape would not affect shark catch rates. The kinkai fisherman using mixed wire and nylon monofilament leaders to target tuna stated that he is using circle hooks but they don’t result in any change whatever in catches. Another kinkai fishermen explained that smaller hooks will catch fewer sharks and the same number of tuna and billfishes. An engan fisherman fishing offshore for tuna, billfish and sharks had previously tried circle hooks but had found them unsatisfactory since they reportedly did not attach firmly and tended to lose bigeye tuna off the hook. One respondent mentioned that the size of the circle hook used in Japan was smaller than that in used in Hawaii because of differences in target species and sizes. A5.10.8. Most important factor in determining shark CPUE The majority of participants named location (i.e. temperature, position with regard to oceanic fronts, and latitude) rather than depth, soak time, gear or any other factor as the most important factor in determining shark interactions. As mentioned above, interview participants consider that their fishing grounds are wellunderstood and are comprised of distinct species assemblages that can be easily targeted by skillful fishermen. Since this knowledge is felt to be part of their intellectual capital, and in fact many fishermen specifically target sharks, there was a general reluctance to provide detailed information about targeting strategies and success rates. A5.11. Incentives and Attitudes toward Reducing Shark Bycatch and Depredation As explained in several of the preceding sections, the interviewed representatives of the Japanese longline fisheries do not consider shark interactions a problem in their operations. This is due in some cases to an ability to avoid sharks through skillful selection of fishing grounds, and in many cases to the opportunity to utilize sharks either in whole or in part at existing landing ports. When depredation occurs it is almost always considered a natural and unavoidable phenomenon and no evasive action is taken. The utilization of shark fins, which has always been high, is now accompanied by growing markets for shark meat. In some areas, e.g. South Africa, the retention of shark meat is likely to be motivated by finning regulations rather than price because the value of shark meat is very low (< 1 USD per kg) relative to tuna. In Japan’s markets the price of shark meat is >2 USD per kg and reportedly rising due to a shortage in raw materials for surimi production. Still, the value of shark meat is low relative to other species and, assuming other species can be caught, several engan and kinkai fishermen believe it will never be profitable to retain shark meat. Utilization of sharks in Japan is closely related to whether the shark catch can be landed in Kesennuma where there is strong market for fins and meat, and a reportedly declining market for cartilage and skin 14 . Fishermen explained that in Kii-Katsuura, where fishermen are primarily landing tuna, the combination of unreliable supply of sharks and low price for meat has prohibited the expansion of the shark meat market while allowing several fin dealers to operate. A few respondents felt that catches were generally stable but several fishermen reported that shark numbers appear to be declining. Various reasons for the perceived decline were given including a lack of prey, a jump in fin prices in 2002 (from 600 to >2000 yen (5 to 17 USD) per kg), finning activities by other fleets, and recent abundant swordfish catches which have resulted in lower retention rates for hooked sharks. It should be noted that the opportunistic targeting strategy of Japan’s engan and kinkai fisheries creates difficulties when drawing conclusions about shark abundance from catch or landings statistics. While many interview participants knew of controls on finning in other parts of the world, a few fishermen who finned sharks were not aware of any regulation or controversy surrounding this issue. Some fishermen who reportedly do not routinely fin sharks voiced a strong opposition to finning regulations. Other respondents believed that the issues of shark utilization and ecosystem balance were more important than a ban on finning per se. In summary, Japanese 14 Fishermen in Kesennuma reported that only salmon shark livers are utilized (for fertilizer); all other shark livers are discarded at sea. There is no active market for shark teeth or jaws in Kesennuma. 99
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Shark Depredation and Unwanted Byca
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Contents Summary and Conclusions 1
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Contents Appendix 3. Fiji Pelagic L
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Contents Appendix 8. USA Hawaii Lon
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Chapter 1 Introduction and Methods
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Introduction and Methods 1.2. Metho
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Fishing Gear and Operational Charac
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Fishing Gear and Operational Charac
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Shark Catch Rates and Disposition T
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Chapter 4 National and Internationa
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National and International Measures
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Economic, Practical, Ecological and
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Economic, Practical, Ecological and
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Chapter 6 Industry Attitudes and Pr
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Industry Attitudes and Practices Lo
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Industry Attitudes and Practices Fi
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Chapter 7 Potential of Deterrents,
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Potential of Deterrents, Hotspot Av
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References Campana, S.E., L. Marks,
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References Neves dos Santos, M., Ga
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Page 99 and 100: Appendix 5 Japan Pelagic Longline F
Page 101 and 102: Japan Pelagic Longline Fisheries Fi
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Page 115 and 116: Appendix 6 Peru Artisanal Mahimahi
Page 117 and 118: Peru Artisanal Mahimahi And Shark L
Page 127 and 128: Appendix 7 South Africa Pelagic Lon
Page 129 and 130: South Africa Pelagic Longline Tuna
Page 135 and 136: Appendix 8 USA Hawaii-based Pelagic
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Page 147 and 148: Appendix 9 USA Atlantic, Gulf of Me
Page 149 and 150: USA Atlantic, Gulf of Mexico and Ca
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Shark Depredation and Unwanted Bycatch in Pelagic Longline

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