Shark Depredation and Unwanted Bycatch in Pelagic Longline

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Shark Depredation and Unwanted Bycatch in Pelagic Longline Fisheries Table A9.2. Summary of bycatch species in pelagic longline fishery, Marine Mammal Protection Act (MMPA) category, Endangered Species Act (ESA) requirements, data collection and management measures (modified from NMFS (2004)) Fishery/Gear Type Bycatch Species MMPA Category ESA Requirements Bycatch Data Collection Management Measures Pelagic Longline Bluefin tuna Billfish Undersize target species Marine mammals Sea turtles Seabirds Non-target finfish Prohibited shark species Large Coastal Shark species after closure Category I Jeopardy finding in 2000, Reasonable and Prudent Alternative implemented 2001 Permit requirement (1985); logbook requirement (SWO- 1985; SHK - 1993); observer requirement (1992), EFPs (2001, 2002, 2003) BFT target catch Requirements (1981); quotas (SWO - 1985; SHK - 1993); prohibit possession of billfish (1988); minimum size (1995); gear marking (1999); line clippers, dipnets (2000); MAB closure (1999); limited access (1999); limit the length of mainline (1996- 1997 only); move 1 nm after an interaction (1999); voluntary vessel operator workshops (1999); GOM closure (2000); FL, Charleston Bump, NED closures (2001); gangion length, corrodible hooks, dehooking devices, handling & release guidelines (2001); NED experiment (2001); VMS (2003) caught in U.S. PLL operations can be retained assuming adherence to accompanying regulations. These include large coastal sharks such as Carcharhinus plumbeus (sandbar shark), Galeocerdo cuvier (tiger shark) and Carcharhinus falciformis (silky shark) as well as pelagic sharks such as Isurus oxyrinchus (shortfin mako shark), Alopias vulpinus (common thresher shark), Lamna nasus (porbeagle shark), Carcharhinus longimanus (oceanic whitetip shark) and Prionace glauca (blue shark) (NMFS 2004). Importantly, there is yet a U.S./ICCAT management system in place for the sharks taken in international waters by non-U.S. vessels, where a high proportion of the shark landings in the Atlantic occur via foreign fleets (Crowder and Myers, 2002). A9.2. Incidental Shark Takes in the Atlantic A9.2.1. General takes according to species Although routinely caught in Atlantic PLL operations, shortfin mako, and common thresher sharks will not be addressed to the same degree here. Due to existing market values, these species and to a lesser extent select coastal species, represent the elasmobranchs more regularly landed when caught by U.S. domestic LL operations during open seasons. Although not necessarily targeted as the sole basis of trip as are tuna or swordfish (and thus still considered bycatch by definition), the incidental capture of these species is not viewed with same futility as is that of a tiger or blue shark. This also applies to trips where sharks are finned and remaining carcasses discarded by foreign fleets in international waters. Although landings and illegal finning are topics worthy of extensive attention, this report will proceed under the assumption that interactions are not desired. Many reports pertaining to the U.S. Atlantic PLL fishery, most notably those submitted to ICCAT, have addressed shark landings and bycatch since the mid-1990s, when the management of sharks began receiving heightened attention. The aforementioned POP and mandatory logbook data have been the dominant data sources for the bulk of this output, with several other sources providing valuable direct or ancillary data. Although widely diverse in aim and scope, relevant works are tabulated and summarized herein (Table A9.4). Documents related to the Canadian PLL industry and foreign fleets in the Atlantic are also represented. Although detailed synopses of each of these works are not germane to this report, selected principal findings warrant inclusion. Independent of region, blue sharks represent by far the most heavily captured shark in U.S. Atlantic PLL operations, constituting 17-32% of the universal catch reported in this fishery between 1987 and 1995 (Cramer, 1997C). This is consistent with the findings from fisheryindependent data sources that blue sharks represent by far the most 136
USA Atlantic, Gulf of Mexico and Caribbean Pelagic Longline Swordfish and Tuna Fisheries abundant pelagic shark in the Northwest Atlantic (Simpfendorfer et al., 2002). The species reportedly comprises 50% of the universal Northwest Atlantic PLL bycatch, a group of species not comprised exclusively of sharks (Crowder and Myers, 2001). A virtually unwanted species in tuna and swordfish operations, blue shark discards peaked at an estimated 29,000 individuals in 1993 (NMFS, 2006). As of 2000, predicted annual discards for the species were set at 1,575 metric tons (mt) based on POP data (Harrington et al., 2005). In comparison, silky shark discards (mt) were predicted to be (163); dusky (113); sandbar (40); bigeye thresher shark (39); and Sphyrna lewini (scalloped hammerhead) (32) (Harrington et al., 2005). In an analysis by Hoey and Moore (1999) of the POP data spanning 1990- 1997, the following positively identified shark species were captured in descending order by number while excluding all other factors: blue (19,264); silky (1,905); mako (1,726); dusky (1,122); hammerhead (multiple sp., 725); tiger (351); common thresher (348); sandbar (333); oceanic whitetip (262); Carcharhinus limbatus (blacktip) (92); and porbeagle (45). When taking into account the relative scarcity of blue sharks in more Southern tropical fishing zones (e.g. GOM), the magnitude of these disparities highlights both the comparative dominance of blue versus other shark species as bycatch in this fishery, and the disproportionate numbers of blue sharks taken in their prevalent take zones. It has been reported that Canadian observers may only be documenting blue shark catches brought on deck, a predicament not accounting for the leader bite-offs prior to boarding (DFO, 2002; Campana et al., 2005). Thus, blue shark catches may also be grossly underreported in that fishery, an outcome not implausible for the U.S domestic fishery as well. However, this species appears quite resilient to the rigors of longline capture. Low boarding (at-vessel) blue shark mortality has been observed, where dependent upon the study, 7-19% of the all blue shark discards were deemed alive at the time of release (e.g. Cramer 1997C; Campana et al., 2005). Logbook data have reported an oscillating but nevertheless declining trend in blue shark catch numbers during recent years (Crowder and Myers, 2001; NMFS, 2006). Thus, in studies equating catchability (CPUE) with indices of abundance, Atlantic blue sharks are among those species reported to have undergone considerable population declines (Baum et al., 2003). In accordance with previous arguments against treating CPUE as an index of abundance (Cooke and Beddington, 1984), the extent of the reported blue shark decline (~60% since 1986) postulated by Baum et al. (2003) has been questioned by several authors (e.g. Campana et al., 2005) on the basis that potential reasons for drops in CPUE aside from abundance declines were not accounted for. It is acknowledged, however, that the species has likely endured some level of decline in recent years (Brooks et al., 2005; Campana et al., 2006). Considering its comparatively high fecundity in relation to most other sharks, even a minimal decline would suggest that blue sharks, even if released alive, may be dying at a higher rate following PLL capture and discard than presumed. If the supposition is true that virtually all blue sharks are discarded alive with a high ultimate rate of survivability, the declines in abundance surmised by certain authors would only be conceivable due to a climb in natural mortality or an increase in landings of the species by non-U.S fleets in N. Atlantic high seas fisheries. This area warrants further investigation. Table A9.3. Shark species comprising U.S. Atlantic (domestic) management units (Bonfil, 1994). Large Coastal Sharks Small Coastal Sharks FAO Common Name Sandbar Blacktip Dusky Spinner Silky Bull Bignose Copper Galapagos Night Caribbean reef Tiger Lemon Sandtiger Bigeye sand tiger Nurse Scalloped hammerhead Great hammerhead Smooth hammerhead Whale Basking Great White Atlantic sharpnose Carribbean sharpnose Finetooth Blacknose Smalltail Bonnethead Sand devil Scientific Name Carcharhinus plumbeus Carcharhinus limbatus Carcharhinus obscurus Carcharhinus brevipinna Carcharhinus falciformis Carcharhinus leucas Carcharhinus altimus Carcharhinus brachyurus Carcharhinus galapagensis Carcharhinus signatus Carcharhinus perezi Galeocerdo cuvier Negaprion brevirostris Carcharias taurus Odontaspis noronhai Ginglymostoma cirratum Sphyrna lewini Sphyrna mokarran Sphyrna zygaena Rhincodon typus Cetorhinus maximus Carcharodon carcharias Rhizoprionodon terraenovae Rhizoprionodon porosus Carcharhinus isodon Carcharhinus acronotus Carcharhinus porosus Sphyrna tiburo Squatina dumeril Pelagic Sharks Shortfin mako Isurus oxyrinchus Longfin mako Porbeagle Thresher Bigeye thresher Blue Oceanic whitetip Sharpnose sevengill Bluntnose sixgill Bigeye sixgill Isurus paucus Lamna nasus Alopias vulpinus Alopias superciliosus Prionace glauca Carcharhinus longimanus Heptranchias perlo Hexanchus griseus Hexanchus vitulus 137
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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
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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
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Page 147 and 148: Appendix 9 USA Atlantic, Gulf of Me
Page 149: USA Atlantic, Gulf of Mexico and Ca
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Shark Depredation and Unwanted Bycatch in Pelagic Longline

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