Shark Depredation and Unwanted Bycatch in Pelagic Longline

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Shark Depredation and Unwanted Bycatch in Pelagic Longline Fisheries Table A9.5. Quarterly CPUE (numbers per 1,000 hooks) and significant relationships observed in the pelagic longline fishery off the southeastern U.S., 1992–2000 (Beerkircher et al., 2002). Table A9.6. Overall nominal CPUE (numbers caught per 1,000 hooks) off the south eastern U.S. Data for 1981–83 are from Berkeley and Campos (1988); 1992–2000 data are from (Beerkircher et al., 2002). CPUE CPUE Species QTR 1 QTR 2 QTR 3 QTR 4 Quarterly relationship(s) P Species 1981-83 1992-2000 Silky 5.38 3.22 3.16 4.28 4>2 0.001 Silky 11.22 3.49 Dusky 1.50 3.09 1.94 1.10 Dusky 0.47 1.64 Night 1.48 1.62 0.30 0.28 1,2>3,4 0.0001 Night 10.75 1.36 Blue 1.29 1.51 0.09 0.41 1,2>3,4 0.0001 Blue 0.60 1.05 Unidentified 0.58 1.04 0.63 0.62 Unidentified 0.87 0.66 Tiger 0.57 0.64 0.93 0.87 Tiger 0.60 0.64 Scalloped hammerhead 0.63 0.83 0.78 0.62 Scalloped hammerhead 13.37 0.48 Oceanic whitetip 0.16 0.16 0.51 0.90 4>3>1,2 0.0001 Oceanic whitetip 0.87 0.32 Rays 0.28 0.09 0.45 0.49 4,3,1>2 0.0001 Sandbar 0.07 0.28 Sandbar 0.21 0.59 0.30 0.07 2>1,4 0.0002 Bigeye thresher 0.67 0.20 Bigeye thresher Shortfin mako 0.23 0.26 0.26 0.16 0.41 0.19 0.18 0.16 1>2,3,4 0.01 Shortfin mako 0.00 0.19 Table A9.7. Ranked order of sharks by species (blue and shortfin mako) or general categories designated by Hoey and Moore (1999), taken by pelagic LL between 1990 and 1997 by region. Derived from data in Hoey and Moore (1999). Geographic Zone* Rank I Rank II Rank III NED Blue shark Other pelagic sharks Large coastals NEC Blue shark Large coastal sharks Mako sharks MAB Blue shark Large coastal sharks Mako sharks SAB Large coastal sharks Blue sharks Other pelagic sharks FEC Blue sharks (< 20,000 lbs) Mako sharks Other pelagic sharks GOM Mako sharks (~20,000 lbs) Other sharks Other pelagic sharks WNCA† Blue shark (< 50,000 lbs) Mako sharks Other pelagic sharks CAR Blue sharks (< 15,000 lbs) Large coastal sharks Other pelagic sharks TROPa Blue sharks ~ 20,000 lbs) Other sharks Large coastal sharks 142
USA Atlantic, Gulf of Mexico and Caribbean Pelagic Longline Swordfish and Tuna Fisheries if encompassing more areas, was derived for the aggregate of shark species captured in PLL operations from 1992-2000 (Beerkircher et al., 2002). As referenced, silky sharks are second only to blue sharks in the total number of catches in this fishery. However, in assessments of the SAB and FEC exclusively, silky sharks were the predominant species taken (Beerkircher et al., 2002). Dusky and night sharks also exceeded blue sharks for CPUE and overall catch numbers. Quarterly deviations in CPUE also exist for several species with silky shark catch rates the highest in the 1st and 4th quarters of the year (Table A9.5). Comparable to the aforementioned declines in blue shark and alternate species CPUE in recent years, these authors also report a 1992-2000 decline when weighed against 1981 to 1983 estimates taken from Berkeley and Campos (1988) (Table A9.6). These downward trends may reflect shifts in abundance but could also be indicative of spatial and gear factors that have served to reduce catchability (Beerkircher et al., 2002). Based on the catch disposition figures derived by Hoey and Moore (1999), rankings of the highest weight of shark species caught by area have been tabulated (Table A9.7). Greater resolution of these rankings reveals that apart from the MAB, NEC and NED, a shark species or group never exceeded 100,000 pounds in a given area during the collective years covered in the report (1990-1997). In over half of the areas, the most captured shark by weight didn’t exceed ~ 20,000 lbs. Because in rare instances, disproportionately high numbers of sharks were caught when fishermen shifted to directed shark fishing (Hoey and Moore, 1999), the degree of shark bycatch (excluding shortfin makos) was likely even lower than the figures allude. However, the magnitude of overall catch weight, data only representative of when observers were present, is secondary. What is most germane is that fishing in certain regions will lead to increased shark encounters. Moreover, despite constituting the primary aggregate of bycatch species in the PLL fishery (e.g. Beerkircher et al., 2002), shark catches aside from those of blue sharks, do not appear exorbitantly high in U.S. domestic operations; at least when compared to the catches by foreign fleets. A9.2.3. Shark depredation In addition to being captured as bycatch, sharks are also responsible for removing baits and gear (bite-offs) and inflicting damage upon other catch already hooked and thus less able to avoid predation. Depredation thus represents a major nuisance to fishermen. To the detriment of industry, POP data indicates that of all damage between 1990 and 1997 (4% of total observed catch), 68% occurred on catches of swordfish, yellowfin and bigeye tuna collectively (Hoey and Moore, 1999). Although damaged catch has been reported in assessments of catch disposition by several authors (e.g. Hoey and Moore, 1999; Beerkircher et al., 2004; Diaz, 2006; Kerstetter and Graves, 2006B), the available data are not usually resolvable to a level where possible to definitively identify the depredating species (Lawrence Beerkircher, personal communication). The point of interaction is rarely observed to enable positive identification. In addition to sharks, cetaceans (Hoey and Moore, 1999) are also responsible for damaging catch and pilfering baits and gear. In fact, depredation by marine mammals could equal or even exceed that done by sharks in certain areas such as the MAB (Lawrence Beerkircher, personal communication). To facilitate the ability to distinguish between the depredating species, NMFS is implementing a new data collection protocol requiring more comprehensive reporting details in early 2007 (Lawrence Beerkircher, personal communication). However, even if able to distinguish between damage done by sharks and other animals, interspecific identification of the depredating animal will likely remain impossible. If such data are deemed as important, accounting for auxiliary factors such as the CPUE, abundance, distribution, and behavioral tendencies of potentially depredating species may strengthen the ability to identify the source species. Importantly, depredations on target or alternative catch may not always be accounted for. In cases where soak times are protracted, animals that die or are weakened from stressors experienced while hooked are much easier targets for scavenging species such as blue sharks (Ward et al., 2004). Thus, reducing soak-times is a straightforward method that could possibly mitigate both shark catch rates and depredation. A9.3. Potential Strategies to Reduce Shark Interactions and Mortality A9.3.1. That related to other taxa or fisheries A comprehensive Atlantic PLL Take Reduction Plan (APLTRP) was recently submitted to NOAA (2006). Although not directly addressed, it is conceivable that some of the measures intended by the Take Reduction Team (TRT) to reduce the number of serious injury interactions with pilot whales and Risso’s dolphins could also be successfully applied to sharks. The applicable proposals described in the APLTRP include proper handling protocols; mandatory mainline, gear and bait requirements to be discussed in greater detail shortly; and additional time-area closures. There are also existing regulations applying to the Atlantic and GOM bottom longline fishery that may be effective tools in increasing post-release survival for sharks taken by PLL (APLTRT, 2006). These include the rapid release of non-retained species with an immediate retrieval of gear remaining deployed; the use of line-cutters and dip-nets for release purposes; and the maintenance of seawater flow across the gills (as must be maintained in sawfish caught by bottom longline). However, these should be viewed as techniques that could potentially reduce the detrimental effects from, rather then the rates of, interactions. A9.3.2. That related to pelagic operations POP data, as previously reported upon by Hoey and Moore (1999), have revealed sets yielding disproportionately high shark catches. In some instances, PLL fishermen have reportedly altered operative strategies in order to land increased numbers of sharks. Alternatively, a particular set of conditions may translate into higher catch rates. Independent of whether or not intended however, these particular sets can be analyzed for environmental and operative factors that may have contributed to the higher catch rates. Accounting for such variables could prove beneficial to industry if deriving measures to help circumvent high numbers of shark interactions, or to enhance survivorship of discards. 143
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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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Appendix 5 Japan Pelagic Longline F
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Japan Pelagic Longline Fisheries Fi
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Japan Pelagic Longline Fisheries mo
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Shark Depredation and Unwanted Bycatch in Pelagic Longline

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