Shark Depredation and Unwanted Bycatch in Pelagic Longline

Shark Depredation and Unwanted Bycatch in Pelagic Longline Fisheries
A2.14.5. Reducing the attractiveness of baited hooks to
sharks, such as by using artificial baits, using or not using
light sticks, or avoiding a bait type known to result in high
shark catch rates
Over a quarter (26.3%) of mahi mahi fishermen believe that avoiding
bait types known to result in high shark catch rates would reduce
shark interactions. About two thirds (63%) of respondents replied
that these strategies would not be effective. Of these, two fishermen
(16.7%) replied that shark interactions occur even when not using bait
types typically employed for shark capture. Three respondents (25%)
believe artificial bait would not be economically viable for mahi mahi
capture since bait type for this target species is captured fresh before
the setting of the longline. Two of three swordfish fishermen replied
that they believe these strategies would reduce shark captures.
A2.14.6. Reducing injury to hooked sharks that you will discard
Almost a quarter (25.1%) of all respondents with mahi mahi as
target species reported discarding small sharks alive. Of these, three
quarters (75%) did not indicate a way to reduce injury to hooked
sharks that they will discard, while the remainder replied that the use
of dehookers will not reduce injury to hooked sharks for discarding.
One respondent (5.3%) mentioned that he uses a dehooker to recover
hooks from sharks when these are on board and already dead.
No swordfish fishermen reported discarding sharks alive. However,
one of them said that they would discard blue sharks due low storage
capacity. It is unclear whether or not they fin those sharks before
discarding.
A2.14.7. Reducing shark retention by avoiding a specific
size or type of hook, or by not using wire leaders on branch
lines
Of mahi mahi fishemen, only one respondent (5.3%) replied that
the size of the hook would affect the shark catch rate. About 36.8%
(among whom there were fishermen that use both nylon and wire
leaders) replied that shark retention is or would be reduced by not
using a wire leader on their branch lines. Three fishermen (15.7%)
that use wire leaders believe that using nylon monofilament would
mean an increase in gear loss from sharks. Some respondents use
nylon monofilament only because they believe that using wire leaders
would decrease their target species capture during the summer. Wire
leaders are used during shark season to increase shark capture.
Two swordfish fishermen indicated that not using wire leaders will
reduce shark retention.
A2.14.8. Will the economic impact of sharks be reduced
from using a wire leader on branch lines
Most respondents (73.7%) that fish for mahi mahi believe that
the economic impact of sharks is or would be reduced by using a
wire leader on branch lines. Among those respondents were all of
the ones that use wire leaders and two thirds of fishermen that use
nylon monofilament. One of the latter stated that he will not switch
to wire leader because it would reduce his target species capture.
However, another fisherman that use wire leaders mentioned that
target species capture remains the same as if using nylon monofilament.
All three swordfish fishermen interviewed believe that the cost from
damage to gear is or would be reduced by using wire traces on branch
lines.
A2.14.9. Most important factor that affects shark CPUE
Over two thirds (68%) of mahi mahi fishermen believe that altering
fishing position in relation to certain water temperatures alone will
result in a high shark catch rate. The other third (32%) replied that
a combination of different factors results in a high shark catch rate.
Half of these respondents did not specify these factors. Equal amount
of respondents replied (1) that altering fishing position and setting
gear deeper will increase shark CPUE, (2) that time of month was an
important factor along with altering fishing position in shark capture,
or (3) that it is certain water temperatures together with time of the day
that are the most important factors affecting shark CPUE. Respondents
based their answer on their fishing practices during shark season.
According to all swordfish fishermen, it is a combination of different
factors that will affect shark CPUE, but they did not specify these factors.
A2.15. Incentives and Attitudes on Reducing Shark
Bycatch and Depredation
In general, both swordfish and mahi mahi fishermen interviewed
(95%) are not interested in reducing shark bycatch. Forty-seven
percent and 33.3% of mahi mahi and swordfish fishermen,
respectively, are interested in reducing shark depredation.
The most common reason given by mahi mahi fishermen for not
wanting to reduce shark interactions is because of the high value for
shark meat and fins. Swordfish fishermen also mentioned that they
do not want to avoid catching shark because it is profitable. Only
one fisherman from a swordfish vessel replied that he wants to avoid
shark interactions because they are not his target species.
Over two thirds (68.4%) of respondents believe, in the absence
of restrictions on finning sharks, that bycatch during mahi mahi
season would not mean a decline of shark populations. Two mahi
mahi fishermen (9.1%) replied that shark bycatch during summer
time is not high enough to threaten shark populations. Another two
fishermen blamed industrial vessels for declines in shark populations
due to finning aboard these vessels.
About 72% of respondents stated that their general feelings about
sharks are that they are economically important. For them, sharks
mean mostly extra income. One swordfish fisherman (4.5% of
respondents) mentioned that it is sometimes annoying having many
sharks in the line. Six (27.3%) respondents stated that sharks should
be under sustainable management program. They believe shark
populations have declined within the past years and that penalties,
bans, and more control over industrial vessels should be enforced for
conservation purposes.
A2.16. Supporting Figures
Figs. A2.8 – A2.16 provide images of the fisheries described in this
contribution.
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