Shark Depredation and Unwanted Bycatch in Pelagic Longline

Japan Pelagic Longline Fisheries
Interview respondents used a variety of cold storage techniques
including ice, cold water freezer “pools”, standard freezers and ULT
freezers. Those vessels with ULT equipment and cold water freezers
stated that the use of this technology avoided any concerns regarding
urea contamination of tunas and billfishes from sharks. One enyo
fishermen using ULT technology explained, however, that sharks
were often separated from other fish for ease of unloading. In this
case, the shark storage area was located in the area where the bait was
kept. As the cruise progressed, the bait was depleted and by the end
of the cruise the area could store 10-20 mt of sharks.
Those vessels using standard freezers and ice potentially faced urea
contamination problems and thus often stored sharks in special ways.
One kinkai freezer vessel retained only thresher shark carcasses
because he stated the urea content in this species (only) was low
enough to avoid contamination. Blue shark fins were also stored in
the freezer but in a separate area. Vessels landing in Kesennuma often
retained whole sharks and thus had extensive experience in storing
carcasses. Many of these fishermen used ice or bait to separate sharks
from other fish in different compartments of the hold. Others used
created layers in the hold by placing sharks at the bottom and other
fish on top of the sharks. A combination of these two approaches was
described in detail as follows:
“At first the sharks and swordfish are put in separate compartments
of the hold divided by planks. When the first compartment
containing sharks is about a third to a half full, a thick ice layer
is place on top of the sharks and swordfish are transferred from
the separate hold to the top of the shark hold. This kind of storage
continues as long as there is space to temporarily store the swordfish
separately. Near the end of the cruise new swordfish are placed
directly onto the top of one of the nearly full compartments and the
last available compartment is used exclusively for sharks.”
In summary, none of the interviewed fishermen noted insurmountable
problems associated with the storage of shark products, either
fins or whole carcasses, in their holds. Those fishermen who retained
whole sharks did so without the need to remove the fins on board,
and through a variety of measures were able to prevent urea contamination
of tuna and billfishes.
A5.8. Practices Employed to Reduce Shark Capture
and Depredation
As described above, only one fisherman recalled a situation in which
special measures were taken to avoid shark catch and depredation
(i.e. the Uruguay example). None of the other respondents admitted
taking special evasive action. Most believed that if the goal was to
catch tuna or billfish and minimize shark catches, this could best
be achieved by a good understanding of which areas and techniques
to deploy. In other words, the fishermen believed that the issue was
simply a matter of proper targeting: in Japan those who involuntarily
caught large numbers of sharks were generally considered to be
inept 12 . Depredation was believed to be an inherent and unavoidable
cost of fishing, and thus no fishermen had ever tried to minimize or
avoid its impacts.
A5.9. Reasons for Discontinuing any Methods
Attempted to Reduce Shark Interactions
Other than avoidance of shark catches by changing fishing grounds,
no special methods for reducing shark interactions have ever be
applied by the interview participants. Therefore, no experience with
discontinuing methods was cited.
A5.10. Perceptions on Efficiency and Commercial
Viability of Strategies to Reduce Shark Interactions
As described above, Japanese longline fishermen interviewed for
this study have never applied any explicit strategies with regard to
shark interactions. The following discussion is thus based largely
on fishermen’s prospective opinions rather than experience with
individual strategies. It is useful to note that the vast majority of
interview respondents stated either that there is no need for them to
avoid sharks and/or that it is impossible to avoid sharks.
A5.10.1. Avoiding areas with sharks
Although most fishermen stated that they make no special effort to
avoid shark interactions, this strategy was often cited as potentially
the most effective in achieving this aim. The success of this technique
will depend on the ability of the fishing master to determine which
areas have the lowest numbers of sharks. The interview participants
unanimously agreed that skillful fishing masters could easily control
their shark interactions using an avoidance method. However,
there was also a view that some low level of shark interaction was
inevitable, even in the most optimal areas. It is probable that the
acceptable threshold for shark interactions in Japanese longline
fisheries is higher than in other fisheries which are tightly controlled
by finning regulations and in which there are limited or no markets
for shark products.
A5.10.2. Refraining from chumming or bait/offal disposal
At present, no interview respondents chum during sets. According to
some of the older fishing masters in Kesennuma, bags of bait used to
be hung between branch lines and chumming was practiced in order
to increase shark catches, but both methods were discontinued due to
a combination of ineffectiveness and intensive manpower demands.
12
Some interview participants acknowledged key differences between fishing conditions off Japan and those in Hawaii. For example, these respondents stated that for various
reasons including sea temperature conditions, sharks and tuna/billfish occur in more distinct and separate areas near Japan than off Hawaii where such populations are
frequently mixed.
97