Protective gill-nets (shark nets) have been successful in reducing the
frequency of shark attacks on the coast of KwaZulu-Natal (KZN), South Africa,
since 1952. This is achieved primarily through a local reduction in numbers of
large sharks. Yet the nets are non-selective in terms of shark species caught
and take a by-catch of dolphins, sea turtles, batoids and teleosts. Baited
lines, or drumlines, as used in the Queensland shark control programme, were
tested as possible alternatives to gill-nets. They demonstrated greater
species selectivity for sharks and also a reduced by-catch of non-shark
animals. The shark catch included the three species responsible for most shark
attacks on the KZN coast, Carcharhinus leucas,
Galeocerdo cuvier and
Carcharodon carcharias. The probability of the bait
being scavenged, or a shark being caught, was modelled in relation to a number
of physical environmental factors. Although there was insufficient variability
in the effort data for a quantitative comparison of catch rates between nets
and drumlines, the results suggested that an optimal solution may be to deploy
a combination of nets and drumlines.
