Surf Board56

During my work in South Africa last February, I was asked to help in the investigation of a surfboard accident with a great white shark (Carcharodon carcharias). An analysis showed that the shark had attacked and grabbed the surfer from behind and then returned at least twice. Unfortunately in this case the surfer died. Based on available details of the incident, I concluded that the surfer could not have been bitten by accident but that other factors must have played a role. Part of my work as advisor for the "Global Shark Attack File (GSAF)" of the Shark Research Institute in Princeton, New Jersey, USA (also see the report in Shark Info 1/99), includes investigating and testing possible causes for such accidents in addition to examining and analyzing the sequence of events in such cases. When I returned to South Africa in May to work on another project I also used the opportunity to test some initial theories on the cause of this latest fatal event, the type of accident which is usually explained by saying that the shark mistook the surfboard for a seal.
Important Considerations

Our tests were intended to consciously provoke attacks by white sharks to enable an analysis of the factors which triggered the above incident. Past accident statistics show that white sharks usually bite surfers who sit or rest quietly on their board, i.e. who do not actively move away. If one accepts the hypothesis that sharks mistake surfers for seals, then sharks will find a dummy resting motionless in the water interesting and sooner or later will grab or attack it. In order to increase the sharks' curiosity we selected a dummy resembling a seal rather than a surfboard, considering that seals are the white shark's preferred prey. The dummy was black (not colored as most surfboards are) and was made of multilayered rubber.

As an alternative to the immobile dummy, a second experiment was made in which we pulled the dummy at a constant speed of 5 knots (9.26 km) per hour at a distance of 15 m behind the boat.