Shark Depredation and Unwanted Bycatch in Pelagic Longline

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Shark Depredation and Unwanted Bycatch in Pelagic Longline Fisheries livers from which oil for squalene can be extracted being discarded. Targeted shark fisheries in Australia are worth an estimated AU$42 million annually. Observer coverage in Australian fisheries in which sharks are caught has been limited to a small percent of the total fishing effort and cannot be relied upon to provide accurate estimates of the incidental shark catch. Furthermore, in the data are species identification problems (Rose and McLaughlin 2001). Likewise these problems and that of under-reporting catch exist in the obligatory logbook records of fishers. Furthermore, stock assessments have only been undertaken for six species of sharks that are subjected to target fishing. Compared to the challenges of managing shark bycatch in nontarget fisheries (Barker and Schluessel 2004), managing targeted shark resources is fairly easy. There is evidence in Australia from fisheries in which sharks are both target and non-target catch, of biomass reduction to very low levels being caused. (Graham et al 2001). For exploited demersal sharks, this pattern is consistent with worldwide trends (Shotton 1999) and is considered to reflect their susceptibility to fishing pressure as a consequence of their life history and biological attributes. Aside from seemingly typical stock status uncertainties, especially in pelagic longline fisheries, there has been substantial overfishing to as low as 18% of virgin (unfished) biomass for some species. A1.3. Introduction to the Australian Pelagic Longline Fishery A1.3.1. Target species The main species targeted by pelagic longlining in Australia are bigeye, yellowfin, and albacore tuna and broadbill swordfish. Their combined catch rate is around 15 fish per 1000 hooks. Frequent retained bycatch (incidental catch) consists mostly of striped marlin, dolphinfish, spearfish, rudderfish, Rays bream, oilfish as well as pelagic sharks (Hobday et al., 2004; Dambacher, 2005). Excluding sharks, the combined catch rate of these incidental catch species is around 5.5 fish per 1000 hooks. This species composition of catch is very similar to that of many other of the world’s pelagic longline fisheries with a high likelihood therefore of similarities in fishing equipment and how it is used. This is an important aspect for understanding bycatch issues and potential mitigation options across fisheries. According to recent fishery statistics (ABARE, 2005) the gross value of production in the pelagic longline fishery was around AU$55 million, 3.8 million being from species that may have included sharks in 2003/04. Sharks inhabit Australian waters from the far northern tropical waters to cool temperate southern waters, all of which are subjected to pelagic longline fishing. It is this situation alone that has produced such a diverse range of attitudes to handling or utilization of sharks caught, in responding to the changes in shark species and their abundance encountered. A1.3.2. Management regime For the majority of present fishing effort management is by Total Allowable Effort (TAE), an input control, although because the preferred management method in Australia’s fisheries is by Individual Transferable Quota (ITQ) this could be applied in the future. A1.3.3. Size of fleet Currently (2006) there are between 80 and 90 vessels in the fishery, all but one of which are operating on Australia’s east coast with the majority of these based at the port of Mooloolabah. Vessels operate from 12 or more ports scattered along about 3500 km of the east coast. This fleet has rapidly declined from a peak of around 120 vessels in only the past year or so. Further reduction in fishing effort is expected. A1.3.4. Vessel type Most vessels are between 15 - 30 m in length and are either generalpurpose inshore vessels or purpose-built ones capable of high seas fishing. A1.3.5. Crew Maximum number recorded from a sample of 35 vessels was 6, the minimum 2, with an average of 4 per vessel. A1.3.6. Fishing gear Boats use monofilament mainlines set through stern-mounted line shooters from typical commercially produced mainline reels (spools) with two-section monofilament branchlines set manually off the vessel’s stern and retrieved again into the hook boxes via hydraulic branchline (snood) pullers. All vessels are equipped with the latest in electronics equipment. A1.3.7. Bait type Squid and pelagic fish species are used for bait, including pilchards, jack mackerel, yellowtail scad, blue mackerel (and other mackerel), anchovy, redbait, tooth-whiptails and redfish. Approximately 11% of bait is caught by vessels and held aboard alive in circulating tanks for extended periods. A1.3.8. Target catch Although approximately 100 species (including fishes) have been recorded as taken in the fishery, the main catch is yellowfin, bigeye, and albacore tuna, broadbill swordfish and striped marlin. These constitute approximately 60% of all fish caught with main incidental species constituting an additional 23%. A1.3.9. Shark catch With an average catch rate of between 1.3 and 5.5 sharks per thousand hooks, approximately 12,000 - 50,000 sharks may be caught annually. The current practice is for the majority of sharks to be discarded alive. A1.3.10. Catch storage The fishery is a fresh fish fishery (as opposed to frozen at sea). The catch is kept on ice, in ice slurry, brine, or brine spray systems. 38
Australia Longline Tuna and Billfish Fishery A1.3.11. Trip length Trip length is generally around 4 days, but frequently shorter. The longest trip (based on information from 178 trips during which at least one set occurred) was 30 days. A1.3.12. Daily fishing pattern The typical fishing pattern is a set of 950 hooks commenced in the late afternoon at around 3 pm. Setting takes about 3.5 hours, after which the vessel drifts until line hauling commences in the early morning around 5 am. Hauling takes about 8 hours. A1.3.13. Market The majority of the catch is exported to the Japanese market. A1.4. Shark Species Encountered by Pelagic Longline Vessels in Australian Waters Of the 166 species of sharks that occur in Australian waters, almost half of which are endemic to Australia (Last and Stevens 1994), fewer than 12 are commonly caught by pelagic longliners (Stevens and Wayte 1998). Blue sharks are caught in greatest numbers, with oceanic white tips, porbeagle, short fin mako, thresher spp., silky and crocodile sharks also being frequently caught. Less frequently caught are hammerhead, tiger, dogfish (family squalidae) and longfin mako sharks. There is uncertainty in the species composition of shark catch due to observer identification inaccuracies that can arise due to similarities in appearance between species. In addition to the ‘true’ sharks, a further 130 chondrichthyans, 117 rays and 13 chimaeras occur here. At least several species of pelagic rays are caught regularly on pelagic longlines. For instance, approximately 1500 rays are estimated by Dambacher (2005) to be caught annually. In total, about 80 fish species have been recorded in catches of Australian pelagic longlining (Hobday et al 2004). A1.5. Shark Catch Rates in Australian Pelagic Longline Fisheries Extrapolation of observed blue shark catch rates from total fishery effort by foreign longline vessels fishing in Australian waters up until their exclusion in 1997 indicates that around 86,000 or 1,100 tons (approx 0.1% of the estimated world catch of this species (Bonfil 1994)) were being caught annually. This species comprised 84.7% of the total shark catch. Catch rates and total catches by species are largely a consequence of changes with latitude in species abundance (Stevens 1992) and over 80% of the fishing effort in this instance was South of 30° South latitude. Catch rates of the same species in New Zealand and Australia from similar latitudes were not the same. For example, blue shark CPUE in New Zealand was typically < 15 blue sharks per 1000 hooks, but could occasionally be as high as 114 (Francis et al 2000) while in Australia, the average blue shark catch rate was 5.5 per 1000 hooks, occasionally exceeding 100 (Steven 1992, Stevens and Wayte 1999). For other less frequently caught species, catch rates were less than 0.5 individuals per 1000 hooks (Stevens and Wayte 1998). For shortfin makos, the observed catch rate was 0.2 per 1000 hooks or some 3,100 each season (3.3% of all sharks species caught). The porbeagle catch rate was 0.5, with about 4,800 caught (South of 39 o South latitude) representing 5.5% of all species caught. At a time when, although finning had been banned, there were no restrictions on the quantity of sharks being retained or perhaps killed in order to recover hooks, at least 75% of sharks caught were released alive: Between 1991 and 1998, from observation of 9% of fishing effort, 25,000 of 32,314 blue whalers, 1,100 of 1,894 porbeagles and 38 of 44 crocodile sharks were released alive (the status of a further 11% was unknown) (Hobday et al 2004). But, the extent to which the presence of an observer may have influenced the fate of sharks caught must be considered. Catch rates on Australia’s east coast varied from around 1.3 sharks per 1000 hooks between 10 and 30 degrees south latitude, to around 7.7 between 40 to 50 degrees south. The best estimate of the catch rate average of all shark species in the fishery was around 5.5 per 1000 hooks. This is a rough estimate based on Australian Commonwealth Scientific and Research Organization unpublished data from a subset of the fleet and time period, and is possibly not representative of the entire fleet. Most recently, data collected from 4% (402 sets) of observed fishing effort by Dambacher (2005) indicate that in 2004/05 discarded shark catch rate was around 1.3/1000 hooks, (this figure derived from patchy data with respect to area and season). Of the 504 individuals of 17 species (sharks and rays) observed discarded, 84% were alive. The three most commonly caught were blue whaler (47%) pelagic ray (17%) and Mako (10%), with the next most abundant at around 3% being Hammerhead, Manta ray and Oceanic white-tip. If these data could be reliably used to calculate total annual catch, it would be around 12,000 sharks (1.2/1000 hooks) representing 4.6%, by number of all fish caught in the fishery. However from these data it is not possible to ascertain what actual proportion of sharks caught were either retained or discarded. Although there is some degree of uncertainty about the accuracy of shark catch rate overall, even if this was 5.5 per 1000 hooks as has been suggested, vessels would seldom reach their maximum trip limit (even if they kept every shark). It is possible therefore that aside from shark retention rates perhaps declining simply because of the influence of legislation on attitude, the restrictions of the legislation alone may in fact have had little bearing on shark conservation. But it is necessary to remember that without regulations shark catch can be dramatically increased deliberately and can vary substantially from day to day. The biological implications of catches are potentially complicated by the fact that, at least for blue sharks, whilst known to have an extreme but variable distribution throughout tropical and temperate waters, they display very apparent sex and size segregation. Furthermore the impact of this fishery on pelagic sharks cannot be calculated due to the restricted time series of catches and effort data (Stevens and Wayte 1998). There was no consistent trend apparent even for the species caught in greatest numbers, the blue shark. This species of shark is however considered likely to be the most resilient to fishing pressure. Although Stevens and Wayte (1998) state that at the time the majority of pelagic sharks are finned and the carcasses discarded, no data 39
Page 3 and 4: Shark Depredation and Unwanted Byca
Page 5: Shark Depredation and Unwanted Byca
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 and 26: Fishing Gear and Operational Charac
Page 27 and 28: Shark Catch Rates and Disposition T
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
Page 99 and 100: Appendix 5 Japan Pelagic Longline F
Page 101 and 102: Japan Pelagic Longline Fisheries Fi
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Japan Pelagic Longline Fisheries mo
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Japan Pelagic Longline Fisheries Ta
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Japan Pelagic Longline Fisheries is
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Japan Pelagic Longline Fisheries ta
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Japan Pelagic Longline Fisheries In
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Japan Pelagic Longline Fisheries A5
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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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