Shark Depredation and Unwanted Bycatch in Pelagic Longline
Shark Depredation and Unwanted Bycatch in Pelagic Longline
Shark Depredation and Unwanted Bycatch in Pelagic Longline
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<strong>Shark</strong> <strong>Depredation</strong> <strong>and</strong> <strong>Unwanted</strong> <strong>Bycatch</strong> <strong>in</strong> <strong>Pelagic</strong> Longl<strong>in</strong>e Fisheries<br />
so that branch l<strong>in</strong>es become entangled, requir<strong>in</strong>g a substantial amount<br />
of time to correct as well as reduced catch of commercially valuable<br />
species. The average cost from damage <strong>and</strong> loss of gear to sharks is $19<br />
<strong>and</strong> $50 on typical tuna <strong>and</strong> swordfish sets, respectively.<br />
Fishers report hav<strong>in</strong>g an average of 3 commercially valuable fish<br />
species damaged from shark bites on a typical longl<strong>in</strong>e tuna set <strong>and</strong><br />
5 commercially valuable fish species damaged on a typical swordfish<br />
set. This can represent a loss of several thous<strong>and</strong>s of dollars depend<strong>in</strong>g<br />
on the size <strong>and</strong> species of fish that are damaged. On an especially bad<br />
set, as many as 50% of target species may be damaged to a degree<br />
that they cannot be sold. An average sized bigeye tuna weighs about<br />
79 lb, <strong>and</strong> typical price per lb is USD 3.50. An average sized swordfish<br />
weights 150 lb <strong>and</strong> typical price per lb is USD 4.50. Assum<strong>in</strong>g that<br />
average sized bigeye tunas are damaged by sharks <strong>in</strong> the tuna fishery<br />
<strong>and</strong> average sized swordfish are damaged <strong>in</strong> the swordfish fishery, <strong>and</strong><br />
assum<strong>in</strong>g tuna vessels make 15 trips per year <strong>and</strong> swordfish vessels<br />
make 12 trips per year, very roughly, annual costs for a vessel from<br />
shark depredation due to damage to fish <strong>in</strong> the tuna <strong>and</strong> swordfish<br />
fisheries is USD 393,750 <strong>and</strong> 688,500, respectively.<br />
Fig. A8.2. Hawaii longl<strong>in</strong>e crew demonstrat<strong>in</strong>g how they clip a loop of<br />
rope onto a branch l<strong>in</strong>e below the weighted swivel at the top of the wire<br />
leader to assist with remov<strong>in</strong>g a hook from a caught shark.<br />
would require more than one crew to use. Some sharks will twist <strong>and</strong><br />
sp<strong>in</strong> when hauled to the vessel, or the shark might close their mouth<br />
on the dehooker, which could result <strong>in</strong> the dehooker be<strong>in</strong>g dropped<br />
overboard. One respondent said that it would be too difficult to use<br />
a dehooker because it would not be possible to get enough slack <strong>in</strong><br />
the l<strong>in</strong>e to push the hook out when us<strong>in</strong>g the dehooker. The more<br />
sharks that they catch, the longer it takes them to haul the gear as they<br />
have to take time to remove caught sharks from the gear to discard<br />
them. Because sharks are on the sea surface dur<strong>in</strong>g haul<strong>in</strong>g, crew are<br />
concerned about hav<strong>in</strong>g branch l<strong>in</strong>es break if a shark pulls the l<strong>in</strong>e,<br />
<strong>and</strong> use of a dehooker might <strong>in</strong>crease the <strong>in</strong>cidence of this occurr<strong>in</strong>g<br />
if us<strong>in</strong>g a dehooker required br<strong>in</strong>g<strong>in</strong>g the shark close to the vessel. The<br />
crew will rebuild all branch l<strong>in</strong>es on which sharks were caught as the<br />
sharks tend to stretch the l<strong>in</strong>e <strong>and</strong> chafe the l<strong>in</strong>e from contact with<br />
their sk<strong>in</strong>, weaken<strong>in</strong>g it so that there is a risk of los<strong>in</strong>g a caught fish on<br />
a subsequent set if the gear were not rebuilt. Fishers also report that<br />
occasionally a caught shark will break the ma<strong>in</strong> l<strong>in</strong>e, <strong>and</strong> that it has<br />
taken them as long as two days to locate both ma<strong>in</strong> l<strong>in</strong>e segments, <strong>and</strong><br />
occasionally a caught shark, usually threshers, will pull the gear down<br />
Over half (58%) of respondents reported that shark <strong>in</strong>teractions are<br />
a problem more because of the amount of time they have to spend<br />
to remove the sharks from the gear <strong>and</strong> to repair <strong>and</strong> replace gear<br />
versus from the actual cost of lost <strong>and</strong> damaged gear <strong>and</strong> damaged<br />
fish. A quarter of the respondents feel that the problems from shark<br />
<strong>in</strong>teractions of time they have to spend to repair <strong>and</strong> replace da maged<br />
gear <strong>and</strong> to remove sharks from the gear <strong>and</strong> the actual cost from lost<br />
<strong>and</strong> damaged gear <strong>and</strong> damaged fish are about equal <strong>in</strong> scale. One<br />
respondent, who is a capta<strong>in</strong> of a tuna longl<strong>in</strong>e vessel who reported<br />
hav<strong>in</strong>g the lowest shark capture rate of <strong>in</strong>terviewed fishers, who stated<br />
that he sets his gear relatively deeper than other tuna vessels, <strong>and</strong> does<br />
not use wire trace on his branch l<strong>in</strong>es, responded that neither the time<br />
or cost result<strong>in</strong>g from shark <strong>in</strong>teractions are problematic.<br />
Most (75%) of <strong>in</strong>terviewed fishers would rather avoid catch<strong>in</strong>g sharks<br />
if they could even if there were no rules restrict<strong>in</strong>g their use of sharks,<br />
<strong>in</strong>clud<strong>in</strong>g restrictions on f<strong>in</strong>n<strong>in</strong>g. Most cited reasons for this response<br />
were that (i) they want to avoid the safety risk when a shark is hauled<br />
to the vessel <strong>and</strong> the l<strong>in</strong>e breaks <strong>and</strong> swivels hit the crew, (ii) the<br />
economic costs from shark <strong>in</strong>teractions would still exceed revenue<br />
from shark f<strong>in</strong>s <strong>and</strong> other parts, <strong>and</strong> (iii) they would rather avoid<br />
spend<strong>in</strong>g the time to deal with caught sharks <strong>and</strong> the damage they<br />
cause to their gear than receive the revenue from shark f<strong>in</strong>s <strong>and</strong> meat.<br />
Two thirds of respondents reported that, if regulations allowed, their<br />
revenue from catch<strong>in</strong>g sharks would still not become an economic<br />
advantage. The other third of respondents believe that their revenue<br />
from shark f<strong>in</strong>s would exceed economic costs from shark <strong>in</strong>teractions<br />
if the restrictions on f<strong>in</strong>n<strong>in</strong>g were removed.<br />
A8.7. Onboard Process<strong>in</strong>g of Reta<strong>in</strong>ed <strong>Shark</strong>s<br />
<strong>Shark</strong>s that will be reta<strong>in</strong>ed <strong>and</strong> l<strong>and</strong>ed are f<strong>in</strong>ned, the head is removed<br />
from the third gill, gutted, <strong>and</strong> put on ice with the rest of the reta<strong>in</strong>ed<br />
fish. If f<strong>in</strong>s are to be reta<strong>in</strong>ed, some fishers report freez<strong>in</strong>g them, while<br />
others will dry them near the eng<strong>in</strong>e.<br />
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