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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Australia Longl<strong>in</strong>e Tuna <strong>and</strong> Billfish Fishery<br />
reta<strong>in</strong> <strong>in</strong>dividuals <strong>in</strong> already dead or near-so condition). The third<br />
category <strong>in</strong>to which sharks that are caught fall is that of bycatch<br />
whereby operators have no <strong>in</strong>cl<strong>in</strong>ation to reta<strong>in</strong> any, <strong>and</strong> take the<br />
safest <strong>and</strong> quickest means of discard<strong>in</strong>g them. However, all or most<br />
survey respondents agreed that their attitude to the sharks that they<br />
catch is largely a f<strong>in</strong>ancial consideration, <strong>in</strong> that if it was economically<br />
worthwhile with established markets <strong>and</strong> unrestrict<strong>in</strong>g regulations,<br />
sharks would become a bycatch species of importance to the extent<br />
that some operators would actually target them more with appropriate<br />
gear changes. Regardless, most respondents were of the op<strong>in</strong>ion that<br />
shark-specific regulations have had little or no impact on the nature of<br />
<strong>and</strong> extent of their <strong>in</strong>teractions with sharks. This is because they would<br />
seldom have the opportunity to exceed the exist<strong>in</strong>g 20 shark per trip<br />
retention limit of species that are of sufficient value to make retention<br />
worthwhile (unless those species with little or no market value were to<br />
become economically attractive to reta<strong>in</strong>).<br />
In Australia it would seem that the shark-specific management<br />
prescriptions, particularly those of f<strong>in</strong>n<strong>in</strong>g <strong>and</strong> a per-trip retention limit<br />
has altered the way <strong>in</strong> which sharks are h<strong>and</strong>led by 50% of operators,<br />
but the regulations do not preclude rout<strong>in</strong>e kill<strong>in</strong>g of the sharks that are<br />
caught. Also, irrespective of the current attitude to f<strong>in</strong>n<strong>in</strong>g, historical<br />
data do suggest that without specific regulations prevent<strong>in</strong>g this, sharks<br />
would be killed for their f<strong>in</strong>s alone by many operators.<br />
us<strong>in</strong>g wire. For example, operators become proficient at reta<strong>in</strong><strong>in</strong>g all<br />
their fish<strong>in</strong>g gear when a shark is caught because the wire from the<br />
hook to a 45g or 60g swivel (about 600mm or less away), allows for<br />
greater control with much improved safety. (Wire is more likely to not<br />
part from the fish under tension <strong>and</strong> be<strong>in</strong>g less elastic (compared to<br />
nylon under tension) is not so dangerous). Thus, sharks are generally<br />
released <strong>in</strong> good health alongside the vessel with the fish<strong>in</strong>g gear<br />
recovered <strong>and</strong> un-damaged. Also <strong>in</strong> parts of Australia the daily gear<br />
damage because wire cannot be used is considered economically <strong>and</strong>/<br />
or operationally unacceptable. But one reason given for a preference<br />
not to use wire, if free to do so was that shark h<strong>and</strong>l<strong>in</strong>g time <strong>and</strong><br />
<strong>in</strong>creased difficulties <strong>in</strong> discard<strong>in</strong>g sharks are unacceptable.<br />
Half the respondents do not consider any effort to reta<strong>in</strong> sharks or<br />
recover the gear (hook) from sharks is worth it because economic<br />
loss from this will always exceed the little revenue derived from<br />
retention of sharks. (Table A1.4) (Aside from the associated risks to<br />
crew from h<strong>and</strong>l<strong>in</strong>g sharks). In fact, potential <strong>in</strong>jury to crew (less<br />
of a consideration if firearms are used to kill fish) was an important<br />
consideration dictat<strong>in</strong>g the fate of sharks caught.<br />
Table A1.4 . Summary of op<strong>in</strong>ions expressed by survey respondents on<br />
how to m<strong>in</strong>imize or <strong>in</strong>crease shark catches.<br />
In the Australian fishery, where an accepted <strong>and</strong> widespread method<br />
used to kill fish is with a firearm, most operators were of the op<strong>in</strong>ion<br />
that this practice alone can result <strong>in</strong> the death of significantly more<br />
sharks that are not <strong>in</strong> any way utilized. Several operators, whilst<br />
personally dis<strong>in</strong>cl<strong>in</strong>ed to do so, <strong>in</strong>dicated that other operators do kill<br />
all sharks, if only to safely recover hooks that are otherwise lost as<br />
each shark is cut free. But on many vessels, (over 1/3 of the fleet)<br />
the safety concerns associated with firearms aboard outweigh any<br />
perceived safety or operational advantages of firearms use (57% of<br />
respondents).<br />
Strategy<br />
Set on the cold side of a thermocl<strong>in</strong>e<br />
Light stick use (esp blue)<br />
Intermediate ma<strong>in</strong>l<strong>in</strong>e floats<br />
Circle hooks (mouth hook only)<br />
Live bait use<br />
Fewer<br />
<strong>Shark</strong>s<br />
X<br />
X<br />
X<br />
More<br />
<strong>Shark</strong>s<br />
X<br />
X<br />
Of the respondents, over half would elect to use wire traces to<br />
some degree if free to do so (use of wire traces is not permitted<br />
<strong>in</strong> the fishery). Reasons for this preference varied from this be<strong>in</strong>g<br />
considered a necessity <strong>in</strong> lower latitudes ow<strong>in</strong>g to:<br />
Set hooks deeper<br />
Talk to other vessels<br />
Larger bait size<br />
X<br />
X<br />
X<br />
• The extent of gear damage <strong>and</strong> therefore lost fish<strong>in</strong>g efficiency<br />
caused by sharks, lancetfish, snake mackerel <strong>and</strong> marl<strong>in</strong>, if wire<br />
is not used; <strong>and</strong><br />
• The fact that sharks here are an economically viable target catch.<br />
More oily bait (pilchards)<br />
Use wire trace<br />
Discharge burley dur<strong>in</strong>g set<br />
X<br />
X<br />
(maybe)<br />
Elsewhere, operators considered that <strong>in</strong>termittent wire use could<br />
deliberately allow for capture of a specific <strong>in</strong>dividual shark (as opposed<br />
to it be<strong>in</strong>g able to bite through a nylon trace), which would otherwise<br />
cause considerable economic loss by bit<strong>in</strong>g off hooks or destroy<strong>in</strong>g,<br />
caught target fish. Several respondents were of the op<strong>in</strong>ion that if wire<br />
use was widespread, then with more sharks caught, larger numbers<br />
<strong>in</strong> total would die. It is perhaps worthy to note that <strong>in</strong> other fisheries<br />
where firearms are not the selected method used to despatch fish on<br />
hooks <strong>and</strong> where wire traces are permitted <strong>and</strong> widely used, there<br />
are some advantages, <strong>and</strong> not just disadvantages, to sharks from<br />
‘J’ hook use<br />
Shorter sets<br />
Use artificial baits (limited data)<br />
Firearms to dispatch fish<br />
Avoid known high shark densities<br />
Set <strong>and</strong> haul hooks <strong>in</strong> daytime<br />
X<br />
X<br />
X<br />
X<br />
X<br />
X<br />
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