Shark Depredation and Unwanted Bycatch in Pelagic Longline

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