Shark Depredation and Unwanted Bycatch in Pelagic Longline

USA Hawaii-based Pelagic Longline Swordfish and Tuna Fisheries
A8.5. Economic, Social, and Ecological Effects,
Including Effects on Fishing Practices, from
Regulations Governing Shark Interactions
Of the twelve fishermen interviewed, nine were longlining based from
Hawaii, one was longlining based from California, and two were not
longlining in the U.S. prior to when the rules on shark finning came
into effect. Eight of the ten fishermen who were fishing in the U.S.
before the shark finning regulations came into effect used to fin sharks,
while two stated that they did not fin sharks when it was legal. The eight
fishers that used to fin sharks had received a total of between $400 -
$3000 per trip from the sale of shark fins (mean of $1,620 per trip, or
about $8,100 per crew per year, assuming three crew per vessel and
15 trips per year). Crew received the revenue from the sale of fins.
This is generally consistent with findings of McCoy and Ishihara (1999)
who report that, prior to the adoption of regulations on shark finning,
income from shark fins was retained by the crew except for some
vessels where owners, mostly on owner-operated vessels, retained a
share of the revenue from shark fins. Hamilton (1996) reports that
average annual wages for Hawaii longline crew was $22,000 based on
data from 1993-1995. McCoy and Ishihara (1999) estimate that in 1998
(prior to the adoption of regulations on shark finning) crew earned
an average annual income from shark fin sales of between $2,375 to
$2,850, 10-11% of their estimated annual wage. On some bad trips,
a crew’s revenue from shark fins could exceed their share from the
sale of the catch. In 1998 an estimated 38 t of dried shark fins with an
ex-vessel value of about $1 million was produced, of which about 95%
came from blue sharks (McCoy and Ishihara, 1999). In 1998, logbook
records show that of 97,080 sharks caught by the Hawaii longline
fleet, 58,444 sharks were finned (53,822 blue sharks, 579 mako, 1,357
thresher, and 2,686 other) (McCoy and Ishihara, 1999).
Most (66%) of the interviewed fishermen report occasionally retaining
one mako shark every two or three trips, if it is caught in the last
2-3 sets of the trip and space remains in the hold, and that they less
frequently retain a thresher shark. Two of the twelve fishermen report
that they now discard the fins of retained sharks because the vessel
owner or captain does not want to risk violating the shark regulations
or raise negative public perceptions. For vessels that do retain fins,
crew still receive the revenue from the sale of the fins, but this amounts
only to about $50 from the sale of one set of mako or thresher fins
every one to two trips. Revenue from shark meat is divided by the
vessel the same as any other landed fish. One captain reports that his
crew occasionally cleans and sells a mako jaw for about $25 a jaw.
Since the restrictions on finning came into effect, the revenue from
catching sharks is exceeded by the cost from shark depredation and
loss and damage to gear.
Only one fisherman reports changing his fishing methods as a result of
the adoption of shark finning restrictions; the captain of this longline
tuna vessel (F/V Garden Sun) now sets his main line shooter at a
faster speed to make the main line relatively more slack to increase
its setting depth, to target higher quality tuna, but also to reduce the
shark capture rate. All others report not having made any changes to
their fishing methods and gear as a result of the shark finning rule.
A8.6. Practices to Deal with Caught Sharks and
Costs from Shark Depredation and Gear Damage
Almost all Hawaii longline tuna vessels use ca. 45 cm-long wire
traces at the end of branch lines, located between the baited hook and
a weighted swivel, while swordfish vessels do not use a wire trace. As
a result, sharks that bite baited hooks in tuna gear tend to be retained
on the line, while about a quarter of sharks that bite baited hooks in
swordfish gear bite through the monofilament line and are not retained
on the line to be hauled to the vessel. Longline tuna vessels catch an
average of 9.5 sharks on a typical set. Longline swordfish vessels catch
an average of 25 sharks on a typical set.
The potential exists to increase post release survival prospects and
reduce fishing mortality of caught and discarded sharks through
improved handling and release practices by crew. For about 66% of
caught sharks, crew cut branch lines after bringing the shark as close to
the vessel hull as possible. For about 34% of caught sharks, when crew
are not too busy processing commercially valuable caught fish, they
will bring smaller sharks of species that are relatively easier to handle
or that are dead when hauled to the vessel and are small enough to
lift up onto the rail on the bulwark and remove the hook with a small
filet knife (Fig. A8.2). Crew report being able to occasionally yank
the hook out of a caught shark that is loosely-hooked. When the
crew cut the branch line to discard a shark, they will usually lose the
terminal tackle, including the hook, wire leader, swivel, and a bit of
monofilament line for tuna gear, and the hook, monofilament line, and
sometimes a lightstick and swivel for swordfish gear. Some crew on
tuna vessels report that they occasionally are able to bring the caught
shark close enough to the vessel hull to cut the wire leader to discard
a shark, thus retaining the swivel and part of the wire. If there are fish
on deck that need to be processed and preserved, crew may decide not
to spend time and effort handling sharks to retrieve terminal tackle
and cut branch lines containing sharks or dropping the entire branch
line containing the caught shark. Two fishers report that, when they
are busy processing commercially valuable species, they will place a
tarred rope with a knot at the end off the stern and will clip branch
lines containing sharks onto this rope so they can remove the sharks
from the gear after they have completed the haul and processed the
catch. At the end of the haul, about 75% of the sharks that are put on
the ‘shark line’ have fallen off the hooks, some of the lines break (and
the weighted swivels hit the stern of the vessel – this vessel has a high
bulwark so these flying weights do not pose a risk to the crew), while
the sharks remaining on the line at the end of the haul are usually dead.
One captain reports killing all caught sharks in an effort to minimize
future shark depredation, which is a practice also reported by McCoy
and Ishihara (1999), however observer data show that a very small
proportion of caught sharks that are alive when hauled to the vessel are
killed before discarding (Tables A8.7 and A8.8). Several respondents
reported catching the same shark as many as ten times in a single haul.
McCoy and Ishihara (1999) report that before restrictions on finning
were instituted, some Hawaii longline fishers had used a 220-volt
electrical line rigged to a gaff to stun sharks before landing. None of
the interviewed fishers report using a dehooker device to try to remove
a hook from a caught shark because they believe this would be more
dangerous or time consuming than their current practice, and that it
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