Shark Depredation and Unwanted Bycatch in Pelagic Longline

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Shark Depredation and Unwanted Bycatch in Pelagic Longline Fisheries Table A5.2. Number of vessels by size class, 1993-2003. (MAFF, 2005 (most recent data=2003)). Total Engan Kinkai Enyo 10 t 50 mt 200 mt 1993 1,829 131 181 478 18 254 85 682 1994 1,823 147 187 485 21 234 75 674 1995 1,704 87 179 472 20 202 78 666 1996 1,614 104 154 453 17 183 63 640 1997 1,573 105 158 435 11 169 64 631 1998 1,555 100 165 447 11 153 56 623 1999 1,473 103 160 440 6 146 51 567 2000 1,418 126 165 441 3 142 45 496 2001 1,461 142 197 438 4 141 45 494 2002 1,447 144 198 144 298 135 44 484 2003 1,390 128 198 154 287 119 44 460 Fig. A5.5. Recorded shark catch and total catch (i.e. all species) by vessel class in the Japanese longline fleet, 1993-2003. (MAFF, 2005 (most recent data=2003)). Fig. A5.6. The effect of filtering Japanese longline fishery logbooks, 1971-2002, using a reporting rate of 80% (i.e. discarding records from vessels which did not report shark catches for at least 80% of all sets in a single cruise). 90
Japan Pelagic Longline Fisheries Table A5.3. Effort by vessel class, 1993-2003. Engan (days at sea) Source: MAFF (2005) Source: MAFF (2003) Calculated (see text for assumptions) Kinkai (cruises) Enyo (cruises) Kinkai (sets) Enyo (sets) Engan (hooks) Kinkai (hooks) Enyo (hooks) 1993 104,173 1,600 2,041 37,426 154,106 104,173 74,852 308,212 1994 103,538 1,712 2,127 31,785 148,725 103,538 63,570 297,450 1995 101,658 1,435 2,009 28,113 141,744 101,658 56,226 283,488 1996 102,087 1,322 2,026 29,163 146,440 102,087 58,326 292,880 1997 108,097 1,233 1,961 25,396 148,716 108,097 50,792 297,432 1998 105,496 1,173 1,712 22,898 143,208 105,496 45,796 286,416 1999 107,304 1,092 1,423 22,973 127,200 107,304 45,946 254,400 2000 109,088 1,066 1,252 23,228 119,677 109,088 46,456 239,354 2001 110,638 1,036 1,220 22,161 124,614 110,638 44,322 249,228 2002 43,056 4,528 1,148 na na 43,056 na na 2003 46,403 4,443 1,045 na na 46,403 na na deep (7-20 hpb) showed a striking pattern. In a recent analysis, an analytical filter was applied to remove data from fishermen who do not always accurately record shark catches (Nakano and Clarke 2006). The filter works by assuming that at least 80% of all sets in a single cruise should record at least one shark and excludes data from cruises which do not meet this criterion. In other words, the number of sets in a cruise passing the filter can be used as a rough indication of the frequency of shark catches and when the frequency is too low the reporting is suspect. When the effect of the filter was examined separately for shallow and deep sets, the percentage of shallow sets passing the filter remained consistently above 25% from 1971-1985 and from 1985 until 2002 more than 90% of the shallow sets passed the filter (Fig. A5.6). In contrast, during the same period (1971-2002) the proportion of deep sets passing the filter ranged from 7-26%. These data seem to suggest that the depth of the set may determine the shark catch rate. However, when the location of shallow and deep sets was examined it was revealed that proximity to Japanese ports is confounded with hooks per basket (a proxy variable for depth). Therefore, it may be location and not depth which is responsible for the observed trends. In particular, as the fishery developed (see Section A5.2) the location of the deep sets moved farther and farther offshore, coincident with the expansion of the enyo fleet’s targeting of bigeye tuna. Within the small subset of the deep sets that remained in nearshore waters (i.e. waters between 15-40ºN and 140-160ºE) a high percentage (80%) passed the filter (i.e. frequently recorded at least one shark per set) between 1971-1992 The shallow sets, which had a high rate of passing the filter were predominantly made in inshore waters (15-50ºN and east of 180ºE) which are the fishing grounds of the kinkai fleet. This finding reinforces and partially explains the finding of disproportionately high shark catches in the kinkai fleet. Given the available data, we cannot determine whether there is causality between the higher kinkai shark catch rates and a) the proximity to a market for sharks in Japanese ports and/or b) the effect of setting hooks at shallow depths. Fig. A5.6 indicates that a very high proportion of shallow sets record catching sharks, whereas a very low proportion of deep sets record catching sharks (Source: NRIFSF unpublished data). A5.3.3. Calculation of nominal shark CPUE Effort for the three longline fleets are currently published (MAFF 2005) in units of cruises for enyo and kinkai fleets, and days at sea for the engan fleet (Table A5.3, Columns 1-3). In previous years (e.g. MAFF 2003), effort for the enyo and kinkai fleets was published in units of sets (Table A5.3, Columns 4-5). If one assumes that each engan day at sea represents one set of on average 1,000 hooks, and each kinkai and enyo set represents on average 2,000 hooks, an approximate number of hooks fished by each fleet can be calculated (Table A5.3, Columns 6-8) thereby providing a common unit of effort for all three fleets. Combining the effort data in Table A5.3 with the annual shark catch data in Fig. A5.5a (i.e. year-by-year, fleet-specific shark catch divided by effort) produces nominal catch per unit effort (CPUE) figures for sharks over the years 1993-2003. The engan and enyo fleets have a similar nominal shark CPUE of 0.020 (sd=0.0022) for engan, and 0.021 (sd=0.0090) for enyo. The nominal shark CPUE in 3 For an unknown reason, in 1993 the percentage of deep sets in nearshore waters which pass the filter drops suddenly below 20% and remains at this low level until 2002. While it may be possible that deep set longline operations changed abruptly in 1993, it is also possible that the introduction of new logbook reporting formats in 1993 may also be a factor. 91
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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
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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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