Shark Depredation and Unwanted Bycatch in Pelagic Longline

Shark Depredation and Unwanted Bycatch in Pelagic Longline Fisheries
A2.9. Practices to Deal with Caught Sharks and
Costs from Shark Depredation and Gear Damage
32% of mahi mahi longline vessels use a nylon monofilament at
the end of the branch lines, located between the baited hook and a
weighted or un weighted swivel. Another 42% use only wire leaders
at the end of the branch lines, while 21% use a mix of wire leaders and
nylon monofilament. Wire leaders are mentioned as used to avoid
shark damage or loss to gear. Fishermen do not believe use of wire
leaders reduces target species capture.
Two of three swordfish vessel respondents reported using wire
leaders at the end of the branch lines. One of the three respondents
reported using nylon monofilament.
Almost two thirds (63.8%) of respondents reported that sharks that
bite baited hooks in mahi mahi gear bite through the monofilament
line and are not retained on the line to be hauled to the vessel.
From this study (19 interviews), respondents noted that vessels
catch an average of 5.3 sharks on a typical mahi mahi set. The three
respondents from swordfish vessels indicated that they catch an
average of 13.1 sharks on a typical set and only 6.7% of sharks bite
through the monofilament line.
Most (95.5) respondents, both mahi mahi and swordfish fishermen,
will always retain sharks that get caught in the fishing gear. However,
almost three quarters (72.2%) of mahi mahi fishermen did
report discarding the carcasses of some sharks. Discard sometimes
occurs when catching blue sharks (in which case they retain the fins
only) or when sharks are small (in which case they are released alive).
One of the swordfish fishermen reported retaining mako sharks only
and not blues.
Two mahi mahi fishermen report that for about 15% of caught sharks,
the crew cut the branch lines. One of these fishermen mentioned
that he would only do that if a big blue shark was caught and hook
has been swallowed. Responses among swordfish fishermen varied.
One mentioned that the crew cut the branchlines for 90% of caught
sharks. The other two replied they would cut the branch line only
for about 5-10% of caught sharks. These fishermen also mentioned
that they cut the branch lines either close to the hook or up to 2
fathoms from it. The main reason given by one swordfish fisherman
for cutting branchlines was that when hauling process has to be done
fast they could not spend time handling sharks.
Two mahi mahi fishermen described ways of de hooking sharks using
a knife or a pair of pliers. One swordfish fisherman reported that he
uses a wooden stick to retrieve hooks but only with small sharks.
More than two thirds (68.4%) of mahi mahi fishermen report that
sharks will either break the main line or bite through the nylon
monofilament in the branch line thus losing hooks. Two of three
swordfish fishermen responded similarly. The average cost reported
from damage and loss of gear due to sharks was $18.5 for a typical
mahi mahi set.
Fishermen reported having an average of 5.5 mahi mahi fish and
3.3 swordfish damaged from shark bites on a typical longline set for
artisanal and industrial vessels, respectively. This represents a loss of
approximately $146 per mahi mahi set and $1063 per swordfish set,
depending on the size of the fish that are damaged.
Only 37% of mahi mahi fishermen considered shark interactions to
be problematic. Among those, more than a half (57%) reported that
shark interactions are a problem more because of the amount of time
they have to spend repairing and replacing lost gear versus 14.3%
who report the cost of lost and damaged gear as the main reason
shark interactions are a problem. Another 29% of respondents replied
that shark damage is a problem because of both the time and cost of
repairs. About half (47.4%) of respondents reported that neither time
nor cost resulting from shark interactions was problematic.
Two of three swordfish fishermen reported that shark interactions
were not problematic. One reason for this response was that loss of
gear and damage by sharks is considered part of their work. Only one
fisherman replied that shark damage is a problem because of both the
time and cost of repairs.
Most (84.2%) interviewed mahi mahi fishermen would not avoid
catching sharks if they could. The most cited reasons for this were
that sharks mean extra revenue because of their meat and high value
fins, and that there is nothing to be done to avoid catching sharks
since they use wire leaders. Only 15.8% of respondents stated that
they would avoid catching sharks because fishing for mahi mahi is
more profitable during summer.
For swordfish respondents, two replied that they would avoid
catching sharks if they could because sharks are not well valued or
for purposes of shark conservation. Only one fisherman stated that
he would not avoid catching sharks unless there were regulations
prohibiting it.
A2.10. Methods for Onboard Processing
of Retained Sharks
In the mahi mahi fishery, sharks that will be retained and landed
are usually finned. Animals are brought on board where they are
immobilized by hitting them in the head with a wooden stick and
then cutting the head (48% of respondents). Only one respondent
(4%) stated that he immobilizes sharks by cutting off the tip of the
snout and passing a metal wire into the brain. Also, two fishermen
(8%) mentioned the use of a de hooker for hooks removal. After
immobilization the animal is gutted (sometimes at the completion
of the haul - 12% of respondents) and is put on ice with the rest of
the catch.
Swordfish fishermen indicated that they process sharks in a similar
way. Two of three respondents indicated that sharks were finned
before being placed on ice.
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