Shark Depredation and Unwanted Bycatch in Pelagic Longline
Shark Depredation and Unwanted Bycatch in Pelagic Longline
Shark Depredation and Unwanted Bycatch in Pelagic Longline
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<strong>Shark</strong> <strong>Depredation</strong> <strong>and</strong> <strong>Unwanted</strong> <strong>Bycatch</strong> <strong>in</strong> <strong>Pelagic</strong> Longl<strong>in</strong>e Fisheries<br />
volume); > 70% of total shark catch by number for Japan longl<strong>in</strong>e<br />
fisheries (Clarke, this volume); 57% for the Peru artisanal mahi mahi<br />
<strong>and</strong> shark longl<strong>in</strong>e fishery (Pro Delph<strong>in</strong>us, unpublished data); 69%<br />
for the South Africa longl<strong>in</strong>e tuna <strong>and</strong> swordfish fishery (Petersen<br />
<strong>and</strong> Goren, this volume); <strong>and</strong> 82% <strong>and</strong> 92% for the U.S.A. Hawaii<br />
longl<strong>in</strong>e tuna <strong>and</strong> swordfish longl<strong>in</strong>e fisheries, respectively (Gilman,<br />
this volume).<br />
Identify<strong>in</strong>g effective <strong>and</strong> commercially viable methods to reduce<br />
unwanted shark bycatch <strong>in</strong> longl<strong>in</strong>e fisheries would contributes<br />
to reduc<strong>in</strong>g shark fish<strong>in</strong>g mortality. Increas<strong>in</strong>g discards of blue<br />
sharks <strong>in</strong> pelagic longl<strong>in</strong>e fisheries would likely reduce fish<strong>in</strong>g<br />
mortality of this species, as blue sharks are usually alive when<br />
hauled to the vessel (Beerkircher et al., 2002; Gilman, this volume;<br />
Mangel <strong>and</strong> Alfaro-Shigueto, this volume; Thomson, this volume).<br />
Beerkircher et al. (2002) found that the condition of sharks<br />
caught <strong>in</strong> pelagic longl<strong>in</strong>e gear (dead versus alive when hauled<br />
to the vessel) varied widely by species, where for example, blue<br />
sharks had a relatively low 12.2% mortality, while silky sharks<br />
(the most dom<strong>in</strong>ant species of shark by number caught <strong>in</strong> the<br />
observed southeastern U.S. pelagic longl<strong>in</strong>e swordfish <strong>and</strong> tuna<br />
fisheries, 31.4% of elasmobranch catch) had a 66.3% mortality.<br />
Gilman (this volume) found that over 89% of sharks caught <strong>in</strong> the<br />
Hawaii-based longl<strong>in</strong>e swordfish fishery <strong>and</strong> over 93% of sharks<br />
caught <strong>in</strong> the Hawaii-based longl<strong>in</strong>e tuna fishery are alive when the<br />
gear is retrieved. Mangel <strong>and</strong> Alfaro-Shigueto (this volume) found<br />
that 87% of sharks caught <strong>in</strong> the Peru artisanal mahi mahi <strong>and</strong> shark<br />
longl<strong>in</strong>e fishery were alive when gear was retrieved. Thomson (this<br />
volume) analyzes Secretariat of the Pacific Community observer<br />
program data from 2002-2005 for the Fiji longl<strong>in</strong>e tuna fishery <strong>and</strong><br />
found that over 94% of blue sharks <strong>and</strong> over 84% of comb<strong>in</strong>ed species<br />
of sharks were alive when hauled to the vessel.<br />
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