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 />
A2.9. Practices to Deal with Caught <strong>Shark</strong>s <strong>and</strong><br />
Costs from <strong>Shark</strong> <strong>Depredation</strong> <strong>and</strong> Gear Damage<br />
32% of mahi mahi longl<strong>in</strong>e vessels use a nylon monofilament at<br />
the end of the branch l<strong>in</strong>es, located between the baited hook <strong>and</strong> a<br />
weighted or un weighted swivel. Another 42% use only wire leaders<br />
at the end of the branch l<strong>in</strong>es, while 21% use a mix of wire leaders <strong>and</strong><br />
nylon monofilament. Wire leaders are mentioned as used to avoid<br />
shark damage or loss to gear. Fishermen do not believe use of wire<br />
leaders reduces target species capture.<br />
Two of three swordfish vessel respondents reported us<strong>in</strong>g wire<br />
leaders at the end of the branch l<strong>in</strong>es. One of the three respondents<br />
reported us<strong>in</strong>g nylon monofilament.<br />
Almost two thirds (63.8%) of respondents reported that sharks that<br />
bite baited hooks <strong>in</strong> mahi mahi gear bite through the monofilament<br />
l<strong>in</strong>e <strong>and</strong> are not reta<strong>in</strong>ed on the l<strong>in</strong>e to be hauled to the vessel.<br />
From this study (19 <strong>in</strong>terviews), respondents noted that vessels<br />
catch an average of 5.3 sharks on a typical mahi mahi set. The three<br />
respondents from swordfish vessels <strong>in</strong>dicated that they catch an<br />
average of 13.1 sharks on a typical set <strong>and</strong> only 6.7% of sharks bite<br />
through the monofilament l<strong>in</strong>e.<br />
Most (95.5) respondents, both mahi mahi <strong>and</strong> swordfish fishermen,<br />
will always reta<strong>in</strong> sharks that get caught <strong>in</strong> the fish<strong>in</strong>g gear. However,<br />
almost three quarters (72.2%) of mahi mahi fishermen did<br />
report discard<strong>in</strong>g the carcasses of some sharks. Discard sometimes<br />
occurs when catch<strong>in</strong>g blue sharks (<strong>in</strong> which case they reta<strong>in</strong> the f<strong>in</strong>s<br />
only) or when sharks are small (<strong>in</strong> which case they are released alive).<br />
One of the swordfish fishermen reported reta<strong>in</strong><strong>in</strong>g mako sharks only<br />
<strong>and</strong> not blues.<br />
Two mahi mahi fishermen report that for about 15% of caught sharks,<br />
the crew cut the branch l<strong>in</strong>es. One of these fishermen mentioned<br />
that he would only do that if a big blue shark was caught <strong>and</strong> hook<br />
has been swallowed. Responses among swordfish fishermen varied.<br />
One mentioned that the crew cut the branchl<strong>in</strong>es for 90% of caught<br />
sharks. The other two replied they would cut the branch l<strong>in</strong>e only<br />
for about 5-10% of caught sharks. These fishermen also mentioned<br />
that they cut the branch l<strong>in</strong>es either close to the hook or up to 2<br />
fathoms from it. The ma<strong>in</strong> reason given by one swordfish fisherman<br />
for cutt<strong>in</strong>g branchl<strong>in</strong>es was that when haul<strong>in</strong>g process has to be done<br />
fast they could not spend time h<strong>and</strong>l<strong>in</strong>g sharks.<br />
Two mahi mahi fishermen described ways of de hook<strong>in</strong>g sharks us<strong>in</strong>g<br />
a knife or a pair of pliers. One swordfish fisherman reported that he<br />
uses a wooden stick to retrieve hooks but only with small sharks.<br />
More than two thirds (68.4%) of mahi mahi fishermen report that<br />
sharks will either break the ma<strong>in</strong> l<strong>in</strong>e or bite through the nylon<br />
monofilament <strong>in</strong> the branch l<strong>in</strong>e thus los<strong>in</strong>g hooks. Two of three<br />
swordfish fishermen responded similarly. The average cost reported<br />
from damage <strong>and</strong> loss of gear due to sharks was $18.5 for a typical<br />
mahi mahi set.<br />
Fishermen reported hav<strong>in</strong>g an average of 5.5 mahi mahi fish <strong>and</strong><br />
3.3 swordfish damaged from shark bites on a typical longl<strong>in</strong>e set for<br />
artisanal <strong>and</strong> <strong>in</strong>dustrial vessels, respectively. This represents a loss of<br />
approximately $146 per mahi mahi set <strong>and</strong> $1063 per swordfish set,<br />
depend<strong>in</strong>g on the size of the fish that are damaged.<br />
Only 37% of mahi mahi fishermen considered shark <strong>in</strong>teractions to<br />
be problematic. Among those, more than a half (57%) reported that<br />
shark <strong>in</strong>teractions are a problem more because of the amount of time<br />
they have to spend repair<strong>in</strong>g <strong>and</strong> replac<strong>in</strong>g lost gear versus 14.3%<br />
who report the cost of lost <strong>and</strong> damaged gear as the ma<strong>in</strong> reason<br />
shark <strong>in</strong>teractions are a problem. Another 29% of respondents replied<br />
that shark damage is a problem because of both the time <strong>and</strong> cost of<br />
repairs. About half (47.4%) of respondents reported that neither time<br />
nor cost result<strong>in</strong>g from shark <strong>in</strong>teractions was problematic.<br />
Two of three swordfish fishermen reported that shark <strong>in</strong>teractions<br />
were not problematic. One reason for this response was that loss of<br />
gear <strong>and</strong> damage by sharks is considered part of their work. Only one<br />
fisherman replied that shark damage is a problem because of both the<br />
time <strong>and</strong> cost of repairs.<br />
Most (84.2%) <strong>in</strong>terviewed mahi mahi fishermen would not avoid<br />
catch<strong>in</strong>g sharks if they could. The most cited reasons for this were<br />
that sharks mean extra revenue because of their meat <strong>and</strong> high value<br />
f<strong>in</strong>s, <strong>and</strong> that there is noth<strong>in</strong>g to be done to avoid catch<strong>in</strong>g sharks<br />
s<strong>in</strong>ce they use wire leaders. Only 15.8% of respondents stated that<br />
they would avoid catch<strong>in</strong>g sharks because fish<strong>in</strong>g for mahi mahi is<br />
more profitable dur<strong>in</strong>g summer.<br />
For swordfish respondents, two replied that they would avoid<br />
catch<strong>in</strong>g sharks if they could because sharks are not well valued or<br />
for purposes of shark conservation. Only one fisherman stated that<br />
he would not avoid catch<strong>in</strong>g sharks unless there were regulations<br />
prohibit<strong>in</strong>g it.<br />
A2.10. Methods for Onboard Process<strong>in</strong>g<br />
of Reta<strong>in</strong>ed <strong>Shark</strong>s<br />
In the mahi mahi fishery, sharks that will be reta<strong>in</strong>ed <strong>and</strong> l<strong>and</strong>ed<br />
are usually f<strong>in</strong>ned. Animals are brought on board where they are<br />
immobilized by hitt<strong>in</strong>g them <strong>in</strong> the head with a wooden stick <strong>and</strong><br />
then cutt<strong>in</strong>g the head (48% of respondents). Only one respondent<br />
(4%) stated that he immobilizes sharks by cutt<strong>in</strong>g off the tip of the<br />
snout <strong>and</strong> pass<strong>in</strong>g a metal wire <strong>in</strong>to the bra<strong>in</strong>. Also, two fishermen<br />
(8%) mentioned the use of a de hooker for hooks removal. After<br />
immobilization the animal is gutted (sometimes at the completion<br />
of the haul - 12% of respondents) <strong>and</strong> is put on ice with the rest of<br />
the catch.<br />
Swordfish fishermen <strong>in</strong>dicated that they process sharks <strong>in</strong> a similar<br />
way. Two of three respondents <strong>in</strong>dicated that sharks were f<strong>in</strong>ned<br />
before be<strong>in</strong>g placed on ice.<br />
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