The IUCN/SSC Shark Specialist Group
Shark News 4: July 1995
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Shark control measures: the Natal Sharks Board and shark conservation
Sheldon Dudley
Introduction
Shark control measures exist to reduce the likelihood of an encounter
between a large shark and a recreational user of the nearshore zone.
This is achieved by locally reducing numbers of large sharks. The
world's three major shark control programmes, which were introduced
in response to public demand, are located in New South Wales (NSW)
and Queensland, Australia, and in KwaZulu/Natal, South Africa. The
programmes are controversial in both the scientific and the
environmental arenas. The views of respondents to a recent opinion
survey of members of the American Elasmobranch Society illustrate
the controversy: of 65 respondents, 39 (60%) believed that shark
control "is never justified -the Ocean is a wilderness area, and people
who enter it do so at their own risk". AES President Don Nelson, in a
plenary address to the Society's annual meeting in June 1994
expressed the personal opinion that it is "unethical to cleanse a
wilderness area of its natural inhabitants to make it safer than natural
for human use". Nelson did, however, concede that "certain well
defined bathing beaches" might be excluded from the wilderness.
If one includes a prohibition of economic activity in one's
definition of wilderness, the existence of commercial fishing
immediately precludes the ocean from being considered a
wilderness area. Be this as it may, I believe that to regard the ocean
as a wilderness with regard to shark control but not recreational
angling is inconsistent. Ethically, shark control differs little from
angling in that both consist of the exploitation of marine resources for
the benefit of human recreation. In the case of both angling and shark
control, however, it is the function of scientists and managers to try
to ensure that the utilisation of those resources is sustainable.
A meshing crew services a shark net off Durban. Photo: Natal Sharks Board.
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Current practice
The current modus operandi of the Natal Sharks Board (NSB), the
organisation which runs the KwaZulu/Natal programme, entails the
permanent maintenance of large-mesh (50 cm stretched) set-nets off
a number of bathing beaches. Three 213 m x 6.2 m nets are used to
provide protection at most beaches, although some beaches have
more. The nets are not a
barrier to sharks; about 35%
of the catch consists of sharks
moving offshore from within
the protected area. The nets
have an impressive record
in terms of reducing the
number of shark attacks at
netted beaches. Between
1906 and the time nets were
introduced in the 1950s and
1960s, there were 38 attacks
resulting in either a fatality
or a non-fatal but serious
injury (e.g. limb amputation).
Since nets were installed,
and despite increasing
bather numbers, there have
been no fatalities and only
three serious injuries.
The nets take an annual
catch of some 1,345 large sharks of 14 species, of which about 13%
are tagged and released. About 901 (whole weight) of shark is killed
annually. There is a by-catch of some 80 dolphins (three species, 3%
released), 380 rays (about ten species, 71 % released), 70 turtles (five
species, 36% released) and, because the mesh size is large, only a few
teleosts.
Investigations to date indicate that the effect of the nets on shark
numbers is localised and that the catches are sustainable, although
the dynamics of this multi-species, constant-effort, constant-locality
fishery are not well understood. Despite this apparent sustainability,
the NSB attempts to minimise mortalities by releasing all live
animals and by temporarily lifting the nets during the annual
'sardine run', the winter influx of pilchard Sardinops sagax shoals
which are accompanied by large numbers of sharks and dolphins.
The NSB is also in the process of trying to determine whether
fishing effort can be reduced without substantially reducing bather
safety. A reduction in effort would have the dual benefit of reducing
both catches and operating costs.
Investigations into effort reduction
The first step in the investigation into effort reduction was to conduct
a comparison of the three major shark control programmes. Large-
mesh set-nets are used in all three and in Queensland baited lines, or
drumlines, are used as well. In NSW,the fishing gear is intermittently
deployed off each protected beach for a total of about nine nights per
month in an eight month season. In Queensland, the gear is
continuously deployed offeach beach in a 10-12 month season. In
KwaZulu/Natal, deployment is continuous at each beach throughout
the year. The monthly fishing effort, expressed as standard (100 m) net
days per beach, deployed in season at a NSW beach and at a
Queensland beach, is about 14% and 30% respectively of that
deployed at a KwaZulu/Natal beach. The same three shark species
are believed to have been responsible for most of the attacks in the
three regions - the bull, or Zambezi, shark Carcharhinus leucas, the
great white shark Carcharodon carcharias and the tiger shark
Galeocerdo cuvier. While there are differences between the regions
in terms of both shark distribution and the nearshore physical
environment, these don't appear to have led to the differences in
levels of effort. There is, therefore, an a priori case for considering
effort reduction in the KwaZulu/Natal programme.
A workshop was held at the NSB headquarters near Durban on
29 November 1994 at which scientists from the NSB and other
institutions discussed ways of determining the extent to which effort
could be reduced. A number of proposals were put forward concerning
ways of improving current understanding of the relationship between
near-shore shark densities and the number of nets.
Additional experimentation
In addition to considering net reduction, the NSB is conducting two
sets of experiments with the objective of reducing the by-catch both
of small sharks and of other animals. Experiments with nets with a
larger (70 cm) mesh size have been running for several years and the
results are promising, the larger mesh continuing to catch sharks of a
size considered to be potentially dangerous but at the same time
taking fewer of the smaller sharks. Secondly, bailed drumlines
similar to those used in Queensland, have been successful in catching
large bull and tiger sharks but it is too early to compare catch rates
with those of sharks taken in the nets. Very little non-shark by-catch
is taken on the lines.
A third set of experiments aimed specifically at reducing the by-
catch of dolphins entails the incorporation of air-filled floats into a
number of nets in an attempt to improve the acoustic visibility of the
nets to dolphin sonar.
Low catch rates dictate that all the experiments will have to run
for some time in order to accumulate a statistically adequate sample.
A final research project consists of the development of an electrical
shark repellent as an alternative means of providing bather protection.
Although the repulsion of sharks using electricity is not a new
concept, the NSB is hopeful that it may be able to develop a practical
and affordable device.
In summary, the Natal Sharks Board is committed to carrying out
its mandate of protecting bathers from shark attack, but is also
committed to ongoing research into methods of reducing mortalities
of marine organisms.
Sheldon Dudley
Natal Sharks Board, Private Bag 2,
Umhlanga Rocks, 4320, Republic of South Africa
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