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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Chapter 2<br />
Fish<strong>in</strong>g Gear <strong>and</strong> Operational Characteristics<br />
The scope of the 12 fisheries <strong>in</strong>cluded <strong>in</strong> this study ranged from smallscale<br />
domestic artisanal fisheries to modern mechanized <strong>in</strong>dustrial<br />
fleets of distant water fish<strong>in</strong>g nations. Some of these fisheries never<br />
target sharks <strong>and</strong> rarely reta<strong>in</strong> caught sharks, while <strong>in</strong> other fisheries<br />
sharks are occasionally an important <strong>in</strong>cidental catch species or can<br />
be an important target species.<br />
Table 2.1 summarizes the general gear <strong>and</strong> operational characteristics<br />
of each fishery <strong>in</strong>cluded <strong>in</strong> the study, focus<strong>in</strong>g on parameters that are<br />
likely to affect shark <strong>in</strong>teractions. For <strong>in</strong>stance, the number of hooks<br />
<strong>in</strong> a basket, float l<strong>in</strong>e length <strong>and</strong> branch l<strong>in</strong>e length will affect the<br />
depth of baited hooks when soak<strong>in</strong>g, which affects shark catch rates.<br />
The material used for the trace (leader) will affect shark retention<br />
on branch l<strong>in</strong>es. The type of bait used will affect shark catch rates.<br />
The <strong>in</strong>formation <strong>in</strong> Table 2.1 is <strong>in</strong>tended to provide a generalized<br />
characterization of the gear of each fishery. However, for some<br />
parameters, there may be large variability <strong>in</strong> fish<strong>in</strong>g gear <strong>and</strong> methods<br />
between vessels <strong>in</strong> a fleet <strong>and</strong> even for an <strong>in</strong>dividual vessel. For<br />
<strong>in</strong>stance, some vessels <strong>in</strong> the Fiji longl<strong>in</strong>e tuna fleet fish at grounds<br />
with<strong>in</strong> the Fiji Exclusive Economic Zone (EEZ), while larger vessels<br />
fish at grounds much more distant from their home port, on the high<br />
seas <strong>and</strong> <strong>in</strong> other nation’s EEZs, <strong>and</strong> these two categories of vessels<br />
have substantial differences <strong>in</strong> the gear characteristics (Thomson,<br />
this volume). In some fisheries, vessels will seasonally substantially<br />
alter their gear when they change their primary target species (e.g.,<br />
Chile <strong>and</strong> Peru artisanal longl<strong>in</strong>e mahi mahi <strong>and</strong> shark fisheries,<br />
Alfaro-Shigueto et al., this volume, Mangel <strong>and</strong> Alfaro-Shigueto, this<br />
volume; Japan offshore <strong>and</strong> nearshore pelagic longl<strong>in</strong>e tuna fisheries,<br />
Clarke, this volume). Gear characteristics may also vary substantially<br />
between seaports with<strong>in</strong> a fishery (Mangel <strong>and</strong> Alfaro-Shigueto, this<br />
volume; Japan offshore <strong>and</strong> nearshore pelagic longl<strong>in</strong>e tuna fisheries,<br />
Clarke, this volume). Due to the large <strong>and</strong> diverse nature of the fleets,<br />
<strong>and</strong> because the <strong>in</strong>formation is not available <strong>in</strong> many cases, it is not<br />
practical to summarize the Japanese distant water, offshore <strong>and</strong><br />
nearshore longl<strong>in</strong>e fisheries <strong>in</strong> Table 2.1. Available <strong>in</strong>formation for<br />
these fleets is presented <strong>in</strong> Appendix 5. The follow<strong>in</strong>g is a summary<br />
of the ma<strong>in</strong> gear <strong>and</strong> operational characteristics of each fishery<br />
<strong>in</strong>cluded <strong>in</strong> the study that affect shark catch rates:<br />
• Australia longl<strong>in</strong>e tuna <strong>and</strong> billfish fishery: There are about<br />
90 vessels, 15-30 m <strong>in</strong> length, <strong>in</strong> this year-round fishery. Trip<br />
length is typically four days or less. All but one of the vessels<br />
fish <strong>in</strong> waters off Australia’s east coast. Hooks are set at depths<br />
between 33-77 m. Regulations prohibit the use of a wire leader<br />
on branch l<strong>in</strong>es. A variety of fish species <strong>and</strong> squid are used for<br />
bait. About 11% of bait is caught by vessels <strong>and</strong> held aboard alive<br />
<strong>in</strong> circulat<strong>in</strong>g tanks for extended periods. Lightsticks are used.<br />
Gear soaks through the night.<br />
• Chile artisanal longl<strong>in</strong>e mahimahi <strong>and</strong> shark fishery <strong>and</strong><br />
longl<strong>in</strong>e swordfish fishery: (i) The artisanal fishery, with about<br />
131 vessels with lengths < 18 m, targets mahi mahi dur<strong>in</strong>g the<br />
austral summer when mahi mahi is more available <strong>and</strong> has a<br />
higher value than sharks, <strong>and</strong> targets sharks throughout the<br />
year. Trip length varies by season with mahi mahi-target<strong>in</strong>g trips<br />
typically last<strong>in</strong>g three to four days. The artisanal fishery, when<br />
target<strong>in</strong>g sharks, is restricted to grounds along Chile’s northern<br />
coast. Baited hooks are set at depths between 9-72 m. Wire leaders<br />
are used dur<strong>in</strong>g the shark season. Bait species <strong>in</strong>clude sard<strong>in</strong>e,<br />
mackerel <strong>and</strong> fly<strong>in</strong>g fish. Lightsticks are not used. Sett<strong>in</strong>g <strong>and</strong><br />
haul<strong>in</strong>g is conducted manually. Gear is set <strong>and</strong> soaks dur<strong>in</strong>g the day.<br />
(ii) The <strong>in</strong>dustrial <strong>and</strong> artisanal swordfish fishery has 16 vessels<br />
with lengths rang<strong>in</strong>g from 17-42 m. The fishery operates<br />
primarily from March to December. Vessels fish at grounds<br />
near Valparaiso <strong>and</strong> Concepcion at 80 o W longitude, between<br />
16-40 o S latitude. Baited hooks are set at depths between 58-70<br />
m. Wire leaders are typically used. Mackerel <strong>and</strong> squid are used<br />
for bait. Lightsticks are used. Gear soaks at night.