Shark Depredation and Unwanted Bycatch in Pelagic Longline

Japan Pelagic Longline Fisheries
A5.10.7. Change in gear (hooks or leaders)
Most fishermen who have experience with nylon monofilament
leaders agreed that their use resulted in a lower shark catch, e.g. a
66% reduction was cited, due to biting off of the hook. Some interview
participants saw this as an advantage since it reduced the need to handle
large and dangerous sharks. In contrast, some fishermen preferred
wire leaders because they are more easily retrieved and repaired
and all fishermen specifically targeting sharks used wire leaders to
prevent bite off. Among fishermen who do not target sharks, enyo
fishermen targeting tuna used wire leaders until about 1990 but then
switched to nylon monofilament. This change was made to improve
the natural-looking movement of the bait on the hook which is
particularly important when targeting tuna. In the kinkai fleet,
targeting strategies and thus gear configuration, varied considerably:
wire leaders were used to opportunistically target tuna, billfish or
sharks; wire leaders were used to target billfish specifically; and a
mixture of wire and nylon monofilament leaders were used within
the same basket to target tuna. Engan fishermen not targeting sharks
reported using nylon monofilament leaders to target tuna and billfish.
All of the interviewed fishermen selected their leader material with
regard to its effectiveness in catching their target species. Since they
do not consider shark interactions a major issue they have never
contemplated changing the leader material to reduce depredation
or shark catch. No injuries associated with the snapping of nylon
monofilament branch lines by sharks during hauling were reported.
A few fishermen had experience with, or opinions on, circle hooks.
The results of field trials by NRIFSF have indicated that the catch rate
for blue sharks and the proportion of hooked blue sharks which were
dead did not differ significantly by hook type (Yokota et al. 2006a,
2006b). One enyo fisherman believed that circle hooks could reduce
shark and turtle interactions without causing a decline in tuna catches
while another said that hook shape would not affect shark catch rates.
The kinkai fisherman using mixed wire and nylon monofilament
leaders to target tuna stated that he is using circle hooks but they don’t
result in any change whatever in catches. Another kinkai fishermen
explained that smaller hooks will catch fewer sharks and the same
number of tuna and billfishes. An engan fisherman fishing offshore
for tuna, billfish and sharks had previously tried circle hooks but
had found them unsatisfactory since they reportedly did not attach
firmly and tended to lose bigeye tuna off the hook. One respondent
mentioned that the size of the circle hook used in Japan was smaller
than that in used in Hawaii because of differences in target species
and sizes.
A5.10.8. Most important factor in determining shark CPUE
The majority of participants named location (i.e. temperature,
position with regard to oceanic fronts, and latitude) rather than
depth, soak time, gear or any other factor as the most important
factor in determining shark interactions. As mentioned above,
interview participants consider that their fishing grounds are wellunderstood
and are comprised of distinct species assemblages that
can be easily targeted by skillful fishermen. Since this knowledge is
felt to be part of their intellectual capital, and in fact many fishermen
specifically target sharks, there was a general reluctance to provide
detailed information about targeting strategies and success rates.
A5.11. Incentives and Attitudes toward Reducing
Shark Bycatch and Depredation
As explained in several of the preceding sections, the interviewed
representatives of the Japanese longline fisheries do not consider
shark interactions a problem in their operations. This is due in
some cases to an ability to avoid sharks through skillful selection
of fishing grounds, and in many cases to the opportunity to utilize
sharks either in whole or in part at existing landing ports. When
depredation occurs it is almost always considered a natural and
unavoidable phenomenon and no evasive action is taken.
The utilization of shark fins, which has always been high, is now
accompanied by growing markets for shark meat. In some areas, e.g.
South Africa, the retention of shark meat is likely to be motivated
by finning regulations rather than price because the value of shark
meat is very low (< 1 USD per kg) relative to tuna. In Japan’s markets
the price of shark meat is >2 USD per kg and reportedly rising due
to a shortage in raw materials for surimi production. Still, the value
of shark meat is low relative to other species and, assuming other
species can be caught, several engan and kinkai fishermen believe
it will never be profitable to retain shark meat. Utilization of sharks
in Japan is closely related to whether the shark catch can be landed
in Kesennuma where there is strong market for fins and meat, and
a reportedly declining market for cartilage and skin 14 . Fishermen
explained that in Kii-Katsuura, where fishermen are primarily
landing tuna, the combination of unreliable supply of sharks and low
price for meat has prohibited the expansion of the shark meat market
while allowing several fin dealers to operate.
A few respondents felt that catches were generally stable but several
fishermen reported that shark numbers appear to be declining.
Various reasons for the perceived decline were given including a lack
of prey, a jump in fin prices in 2002 (from 600 to >2000 yen (5 to 17
USD) per kg), finning activities by other fleets, and recent abundant
swordfish catches which have resulted in lower retention rates for
hooked sharks. It should be noted that the opportunistic targeting
strategy of Japan’s engan and kinkai fisheries creates difficulties
when drawing conclusions about shark abundance from catch or
landings statistics.
While many interview participants knew of controls on finning in
other parts of the world, a few fishermen who finned sharks were
not aware of any regulation or controversy surrounding this issue.
Some fishermen who reportedly do not routinely fin sharks voiced a
strong opposition to finning regulations. Other respondents believed
that the issues of shark utilization and ecosystem balance were more
important than a ban on finning per se. In summary, Japanese
14
Fishermen in Kesennuma reported that only salmon shark livers are utilized (for fertilizer); all other shark livers are discarded at sea. There is no active market for shark teeth
or jaws in Kesennuma.
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