Shark Depredation and Unwanted Bycatch in Pelagic Longline

Shark Depredation and Unwanted Bycatch in Pelagic Longline Fisheries
To further assist in shark management, there has been considerable
effort devoted to providing appropriate species identification tools
e.g, Last and Stevens (1994), Daley et al (2005) that will help to
address the species identification deficiencies known to occur.
A1.8. National Regulations
A1.8.1. Regulated fishing effort
There are separate management plans, one for the south and west
and one for the eastern fisheries. Although the preferred method of
managing fisheries in Australia is by output controls in the form of
Individual Transferable Quota (ITQ) (AFFA 2003), input control by
Total Allowable Effort (TAE) was considered more satisfactory for
the eastern fishery. In the south and west, control is quota based via
ITQ’s applying to the four main target species, yellowfin, big eye,
albacore tuna and swordfish.
Fishing effort is controlled by a combination of input controls
that include limited entry, area restrictions (zoning), vessel size
restrictions and gear restrictions. Statutory rights (SFR) (granted
based on previous effort and amount caught) which equal a set
number of branchline clips are to be granted under the current
permit system in which there are at present 232 pelagic longline
entitlements (Hobday et al 2004). The number of effort units
expended is branchline clips multiplied by SAF (sub-area factor) i.e.
an effort unit can equal or exceed or be less than 1 to make fishing
in an area more or less attractive. This has potential as a means of
limiting impact on species, including sharks, essentially by providing
incentive for operators to fish or not fish in a certain area.
Daily SFR utilization by each vessel is monitored against an annual
limit (equivalent to hooks set) in each fishing season that commences
on 1 July and finishes on 30 June each year. The total allowable effort
(TAE) is equivalent to around 125, 000 hooks, (branchline clips) per
operator (for a re-structured fishery consisting of approximately 80
entitlements) annually or 7.8 million for the fishery, 0.8 of which
is to be assigned to fishing outside the EEZ of Australia. This Total
Allowable Effort (TAE) will be determined each fishing season with
consideration to the reference points for each primary species and
secondary species. (The effort can be divided into areas for instance
to maintain a species reference point). TAE is based on an estimate of
total take from all users of the fishery, reference points for scheduled
species, information about the sustainability of marine species in
the area, the precautionary principle and any decision made by the
Minister (of Fisheries) that may affect the TAE.
Obviously then, a limit on fishing effort does serve to limit catches
of sharks but the impact on individual species is uncertain, which is
one of the reasons that other measures to limit catches apply.
In 2006 an Australian government fishing permit buy-back incentive
to reduce the total number of permits by about 30% was instigated.
The impact of such a theoretical reduction in overall fishing effort
on sharks etc, remains unclear because this, as a consequence will
be dependent entirely upon which permits are acquired (inactive
permits, of which there are many do not catch sharks!).
It is possible that, following a period of management by TAE, the
preference for managing by ITQ of some or all species caught will be
re-considered. The potential impact of this on bycatch species such
as sharks is unclear. Consideration is also being given to imposing
bathometric related limits to the shores within which pelagic
longlining will be prohibited. Designed to assist managing longline
target species recreational fishing this restriction on pelagic
longlining could greatly affect shark bycatch in several ways: a
frequent comment by fishers surveyed (see this paper) was that
shark bycatch (by number) was far higher when lines were set or
inadvertently drifted over more inshore (shallower) waters. Putting
all longline fishing effort into more oceanic waters will alter species
composition and abundance of sharks caught, but considering the
other shark management prescriptions that already apply, this may
be a change of little concern.
A1.8.2. Retention limits per trip
There can be no doubt that the retention limit of 20 sharks per trip
imposed in 2004 (Hobday et al 2004) was a significant influence
on the fate of sharks caught. But perhaps without a finning ban
having also been imposed, the 20 sharks per trip limit may not have
altered the retention rate (and so altered conservation implication
of catches) much of those species that were being retained anyway.
This is because seldom would a vessel, on the average duration trip
(Table A1.1) actually catch this number of species whose flesh was
sufficiently valuable to make its retention desirable. Furthermore,
many operators only retain a shark that falls into this category if it is
already dead or dying, thus safely and relatively easily landed. Mako
and thresher sharks in particular fall into this category.
Once a vessel reaches its limit of 20 landed sharks, it is a requirement
that no more sharks are retained. In practice however, the fate of
sharks caught remains uncertain, dependent on whether an operator
pursues hook recovery (see method used to kill) from the sharks and
the method used to do this.
Any caught in excess of 20 no longer fall into the category of
byproduct but become bycatch and so the obligation of fishing
concession holders to keep this to a minimum, i.e. try not to catch
them in the first instance, applies.
But an additional consequence of a trip carcass retention limit is the
potential for high grading wherein a shark retained is subsequently
discarded in preference for larger or fresher, or more valuable species
encountered. This has obvious conservation implications further
complicated by the life history traits of such species wherein killing
larger individuals (sexually mature or at a late age) is perhaps most
detrimental. Fortunately, for sharks species with relatively high
meat value this is likely to be not a major issue simply because total
catch on each fishing trip is usually below maximum carcass limit
imposed. (See survey section).
Further catch limits or reference points may be established for
shark species following the required risk assessment of ecological
sustainability of catches, to be carried out for all secondary species
within 24 months of the management plan’s implementation (2005).
Shark catches may also be influenced by target species stock status
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