Andrew P. Aitken ^{1, 2}

Supervisors: Professor Charles Griffiths¹ and Geremy Cliff²

1 Zoology Department, University of Cape Town, Rondeboch, 7700, Cape Town, South Africa.
² Natal Sharks Board, Private Bag 2, Umhlanga Rocks 4320, KwaZulu-Natal, South Africa

September 2003

ABSTRACT

The general biology and catch statistics of the tiger shark Galeocerdo cuvier were investigated from catches in the shark nets that protect the bathing beaches of KwaZulu-Natal (KZN), South Africa. Between 1978 and 2001, a total of 1133 tiger sharks were caught in the nets, with an annual mean of 47. There was no evidence to suggest any long-term decrease in either catch or catch rate. The catch consisted primarily of juvenile sharks and a strongly skewed sex ratio was apparent with more females than males being caught (2.2 females: 1 male). Little seasonal variation was evident in the geographical distribution of small (<2m) tiger sharks. Large (>2 m) tiger sharks appear to undergo a southward range extension into northern KZN waters during the summer months. Diet analyses indicated that tiger sharks in KZN are extremely opportunistic predators that feed on a wide variety of prey items. The infrequent occurrence of sardines in the diet indicated that G. cuvier is not directly associated with the winter sardine (Sardinops sagax) run.

An investigation into tiger shark diving at Aliwal Shoal revealed that ecotourism operations that allow divers to observe feeding sharks have become increasingly popular. An extensive literature review revealed that there is no published scientific evidence that links the baiting or feeding of sharks to an increased frequency of attack on either divers involved with the feeding or other ocean users elsewhere. Field observations, photographic data and telemetry data, suggest that mature female tiger sharks may be resident in the area for the first five months of the year, and that some individuals may return on an annual basis.

Interactive marine experiences with charismatic megafauna in the form of whale sharks Rhincodon typus have also become popular and several locations around the world now offer dedicated whale shark diving. In South Africa whale shark diving is largely the result of opportunistic encounters with whale sharks while dive boats at Sodwana Bay in northern KZN are traveling to and from dive sites. Aerial surveys were carried out from October 2001 to September 2002 to investigate the viability of a dedicated whale shark diving industry in northern KZN. Only ten whale sharks were seen in thirteen surveys and revealed that it is not possible to offer any dedicated diving at present. Poor whale shark sightings from aerial surveys were mirrored by reports from other sources such as local dive operators. Aerial surveys should be repeated to determine the inter-annual fluctuations in whale shark numbers and to help in the global assessment of whale shark stocks.