In the aftermath of white shark encounters, a traumatised public often calls for the implementation of mitigating measures to stop or at least decrease the risk of further incidences. Various measures ranging from shark hunting expeditions, the installation of shark nets or the closure of certain beaches have been proposed by a wide cross section of society, but a rational, scientifically sound assessment of possible mitigation measures is rarely presented.
1. Shark capture devices, such as shark nets or drum lines, will have reduced effectiveness in minimizing risk to bathers in the inshore waters of Cape Town, because the more transient – or migratory – nature of white sharks in False Bay. Shark nets do not form physical barriers between bathers and sharks but rather act as fishing nets that kill sharks – and many other species – thereby reducing the density of more localized or residential sharks like Zambezi or Tiger sharks. White Sharks appear to be much more migratory and cover vast distances – some venture as far as Australia. Removed individuals would simply be replaced by others and would not be effective in reducing local white shark numbers.
2. During the winter and spring months the waters of Cape Town are home to a large population of southern right whales that use our inshore areas for calving and mating, while several species of dolphins occur year round. The installation of shark nets would result in unacceptably high levels of bycatch and entanglement of these marine mammals and other marine species. Shark nets would also suffer serious maintenance problems due to entanglement with prolific kelp.
3. Exclusion nets have been used with success in certain parts of the world. These nets do not capture sharks (or other marine species) and form a physical barrier between sharks and water users. Exclusion nets are, however, only effective in small areas that have very calm sea conditions and are not an option for surfers, kayakers or divers. The possibility of using exclusion nets in certain areas in False Bay to create a safe swimming zone is currently being investigated.
4. The use of sonar, to warn bathers of the presence of sharks, and the use of an electric field, as a shark shield to protect large areas, is currently still being developed by organizations like the Natal Sharks Board. Should this technology become available, it could potentially be used in parts of False Bay (e.g. Fish Hoek).
5. The best available mitigating measure at present to decrease the risk of white shark encounters in Cape Town is the Shark Spotter Programme. However, the limitations of the programme need to be clearly understood by ocean users. For example, only beaches with nearby high vantage points are suitable for shark spotting and when water clarity decreases so does the effectiveness of the spotters. Although human error and fatigue appear to be low, these should also be recognized as possible constraints.
6. Since deaths resulting from white shark bites usually result from loss of blood and subsequent shock, fast emergency response time and expert handling of a patient following a bite can drastically increase survival statistics. If sealed and dedicated shark trauma kits are readily available at all beaches and lifesavers, rescue workers, shark spotters as well as water users, are trained in emergency response and trauma medical aid, then deaths from white shark bites can be dramatically reduced.