Shark Depredation and Unwanted Bycatch in Pelagic Longline

USA Hawaii-based Pelagic Longline Swordfish and Tuna Fisheries
sharks as the meat from these species are the only ones that are
marketable, although occasionally a vessel will retain carcasses of
blue and other shark species. For example, in 2004, 44.7% (830) and
13.7% (717) of the total number of caught mako and thresher sharks
were retained, respectively, while only 2.0% (1,303) and 6.9% (210)
of the total number of caught blue and ‘other’ sharks were retained,
respectively, in 2004 (Western Pacific Regional Fishery Management
Council, 2005a). In 2004 the average price per pound (whole weight)
for shark meat was $0.17, down from $0.32 in 2003 (Western Pacific
Regional Fishery Management Council, 2005a).
Table A8.7 includes statistics from observer data on the proportion
of caught sharks that are alive vs. dead when hauled to the vessel
and the condition of discarded sharks in Hawaii-based longline
swordfish sets for the period that these data have been collected
from 2004-2006, during which time there has been 100% observer
coverage. Table A8.9 provides the same statistics for the Hawaii-based
longline tuna fishery, with information on the condition of sharks
when hauled to the vessel starting in 2003. Over 89% of sharks caught
in swordfish gear and over 93% of sharks caught in tuna gear are alive
when the gear is retrieved. In swordfish gear, < 0.82% of sharks that
are hauled to the vessel alive are discarded dead, while in tuna gear
< 4.3% of sharks hauled alive are discarded dead. Hawaii-based longline
crew have not been killing a large proportion of sharks caught
alive before discarding them. However, information on the types of
injuries of discarded sharks is not available, which might provide an
indication of their post release survival prospects.
A8.4. Management Framework Relevant to Shark
Interactions
In 2000 the U.S. Congress and State of Hawaii passed legislation
restricting shark finning practices. Federal regulations implementing
the Shark Finning Prohibition Act came into effect on 13 March
2002 (U.S. National Marine Fisheries Service, 2002). The federal
Act amended the Magnuson-Stevens Fishery Conservation and
Management Act to prohibit (i) any person aboard a U.S. fishing
vessel from ‘finning sharks’, defined as taking a shark, removing fins,
and returning the remainder of the shark to the sea; (ii) any person
from possessing shark fins aboard a U.S. fishing vessel without the
corresponding carcasses; (iii) any person from a U.S. fishing vessel
from landing shark fins without the corresponding carcasses; (iv)
any person on a foreign fishing vessel from engaging in shark finning
in the U.S. EEZ, from landing shark fins without the corresponding
carcasses into a U.S. port, and from transshipping shark fins in the
U.S. EEZ; and (v) the sale or purchase of shark fins taken in violation
of these prohibitions (U.S. National Marine Fisheries Service, 2002).
The Act states that any shark fins landed from a fishing vessel or
found onboard a fishing vessel were taken, held or landed in violation
of the Act if the total weight of shark fins exceeds 5% of the total
dressed weight of shark carcasses landed or found on board (U.S.
National Marine Fisheries Service, 2002, 2005b). The aims of the Act
are to (i) prevent unsustainable levels of shark catch, which is now a
risk due to the demand for shark fins, and (ii) prevent the waste of
usable shark meat (U.S. National Marine Fisheries Service, 2002).
To achieve these aims, there is an unstated assumption that the ban
on finning will reduce shark fishing mortality.
From 1999 through 2004 the Hawaii longline fleet, especially the
swordfish component, was subject to area and temporal closures
that were intended to protect sea turtles. In April 2004, the swordfish
component of the Hawaii longline fishery was authorized to resume
after being closed for over two years, but is subject to measures limiting
effort, requiring the use of specific types of hook and bait, capping
annual turtle interactions, requiring 100% observer coverage, and
other measures. Measures designed to reduce the capture of seabirds
by Hawaii longline vessels were first required in 2001. These seabird
and sea turtle avoidance measures affect the fishing methods, gear, and
effort of the fleet, and may affect shark interactions. As part of rules
that are intended to reduce sea turtle interactions, Hawaii longline
vessels that are deep-setting to target tuna are prohibited from using
light sticks, must use float lines that are > 20 m in length, and have an
annual cap on effort of 2,120 sets targeting swordfish (Western Pacific
Regional Fishery Management Council, 2005b). Also, as part of rules
designed to reduce turtle interactions, Hawaii longline vessels that are
shallow-setting to target swordfish must use 18/0 or larger circle hooks
with a 10o offset and can use only ‘mackerel-type bait’ when fishing
North of the equator (Western Pacific Regional Fishery Management
Council, 2005b). As part of rules intended to reduce seabird interactions
that might affect shark interactions, shallow-setting swordfish vessels
that are stern-setting must (i) set only at night, (ii) dye fish bait blue,
and (iii) discharge fish, offal, or spent bait from the opposite side of
the vessel from where longline gear is being set or hauled, or otherwise
they can set their gear from the side of the vessel and attach weights
> 45 g within 1 m of the hook (Western Pacific Regional Fishery
Management Council, 2005b). To comply with seabird regulations
that might affect shark interactions, deep-setting vessels targeting
tuna that are stern setting must, when fishing North of 23 degrees
N. latitude, (i) use blue-dyed bait; (ii) discard offal, spent bait, and
fish during setting and hauling; and (iii) attach weights > 45 g within
1 m of the hook, or otherwise side set with a minimum of 45 g weights
attached on branch lines within 1 m of the hook (Western Pacific
Regional Fishery Management Council, 2005b).
All Hawaii-based longline vessels are required to have a VMS unit
onboard, which is a satellite transponder that provides ‘real-time’
position updates and the track of the vessel movements. There is 100%
onboard observer coverage of shallow-setting swordfish longline
vessels, and about 20% observer coverage of the tuna longline fleet
(Western Pacific Regional Fishery Management Council, 2005b).
The Hawaii longline fishery is limited entry, vessels cannot exceed
30.8 m in length, and as part of rules adopted to manage turtle
mortality, there is a cap on the annual swordfish effort of 2,120 sets
targeting swordfish (Western Pacific Regional Fishery Management
Council, 2005b). In early 1991 longline fishing was prohibited within
50 nm of the Northwestern Hawaiian Islands to prevent interactions
between endangered populations of Hawaiian monk seals. An
additional longline exclusion zone was established in mid 1991
50-75 nm around the Main Hawaiian Islands to prevent gear conflicts
between longliners and smaller fishing boats targeting pelagic species
(Western Pacific Regional Fishery Management Council, 2005b).
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