Shark repellent cable
The KZNSB received a permit from the Department of Environmental Affairs (DEA) to test the shark repellent cable. The cable, 100 metres long is currently being tested in Cape Town. It is installed parallel to the shore at Glencairn beach since October 2014 and is activated on certain days during daylight hours.
The cable emits a low frequency pulsed electronic signal, which has been shown to repel white sharks. If successful, it will provide the basis to develop a barrier system that can protect bathers without killing or harming sharks or any other marine animals.
The KZNSB has long been investigating the use of new technology to provide alternatives to its current programme of shark nets and drumlines deployed along the KZN coast. The organisation has a legal duty both to protect bathers against shark attack in the province and to minimise the environmental impact of its operations. Technology developed by the KZNSB in the 1990s is already used in the Shark Shield personal shark repellent device that divers and other water users in several countries wear to reduce their risk of shark attack.
A major investment by the KwaZulu-Natal Department of Economic Development, Tourism and Environmental Affairs (DEDTEA) has enabled the KZNSB to undertake further research and development of this technology. In 2012, the Institute for Maritime Technology (IMT), a Division of Armscor SOC Ltd, in Simon’s Town was contracted to design and build a demonstrator cable. The specialist engineering and technical team at IMT first built a short cable that was tested for sea-worthiness. After medical evaluation showed that the electronic pulse emitted was expected to be well within conservative safety limits, a full-length demonstrator cable was constructed.
The system is now being tested in open water. The experiment has the full support of DEA, SanParks, the City of Cape Town, SharkSpotters and other stakeholders.
The system consists of a main cable fixed to the sea floor, with vertical ‘risers’ supporting the electrodes that are fitted on either side of the cable. The risers are semi–rigid and are kept upright by small sub-surface buoys.
There are continuous monitoring of the cable and the area where it is deployed. This is done by means of a video camera high above the beach and by Shark Spotters who will track the movements of any sharks sighted near the cable. The video footage and the records kept by the Shark Spotters are analysed by KZNSB scientists to see how the signal emitted by the cable affects white sharks.
The testing period was chosen to coincide with the end of the whale season, to minimise the risk of whale encounters, and the peak white shark season, to maximise the number of possible white shark encounters. Nevertheless the system has been specially adapted for False Bay to prevent whale entanglements by employing semi-rigid risers, not just rope or wires. In addition, a specialised team is on standby in case a whale does approach the area.
Divers and boat crews from the KZNSB and IMT monitor and maintain the cable system to ensure it functions as planned.
Questions and answers
Q. Is this shark repellent cable safe for humans?
A. The electronic shark repellent cable has been subjected to extensive safety evaluation by a medical and scientific team. The same form of pulsed electronic signal has been used within personal shark diver protection devices for many years. The pulse from these devices has been at higher intensities than those expected in the cable, without any reported events.
The safety evaluation has included a review of known relevant research and literature. It has also involved direct research on certain aspects of the field’s effects. The International Electrotechnical Commission refers to a minimum charge expected to cause risk of Ventricular Fibrillation of the
heart (the main life-threatening effect of shock) as being of the order of 20 000 micro Coulombs. The cable system is calculated to deliver less than 200 micro Coulombs even with direct contact. Simply put, it would be expected that 100 times the charge produced by the cable would be needed to cause a life-threatening shock. Accordingly, the evidence currently to hand suggests a high level of safety for the average member of the public and even direct contact is unlikely to cause harm. Users of pacemakers are advised to maintain a five-metre distance from the installation due to possible problematic interference in certain unusual subgroups.
Q. What happens if a person touches the cable?
A. The main cable is on the sea floor in water six metres deep but if anyone touched it nothing would happen as the cable itself is insulated. There are vertical electrodes (‘risers’) emerging from the cable and if someone touched the small part of an electrode that is exposed, they might experience a tingling sensation.
Q. How close can a person approach the cable?
A. t is recommended that people stay at least five metres away from the cable to avoid unintentional contact and obstruction of the experiment.
Q. Has anyone been injured by this technology?
A. No. This technology has been used for many years in personal shark repellent devices. The Shark Shield device that uses this technology developed by the Sharks Board is commercially available. It has been shown to be safe in a series of tests and the research team is not aware of any reports of injury related to its use.
Q. What effect will the cable have on white sharks?
A. The purpose of the testing is to find out how the pulse or signal emitted from the cable acts as a barrier to white sharks. These sharks are highly sensitive to electromagnetic fields. If a shark experiences any discomfort it is able to move away from the cable.
Q. What effect will the cable have on other marine life?
A. No effects have been observed on any other mobile marine animals exposed to the signal, particularly fish and seals.
Q. Will this installation pose a threat to whales?
A. The cable has been specifically designed to minimise the likelihood of a whale becoming entangled. There are likely to still be a few whales in the vicinity at the start of the experiment. Should any whale approach the cable it will be switched off. An inflatable boat stationed at Fish Hoek beach will be deployed to herd the whale from the location. Mr. Mike Meyer, Chairman of the SA Whale Disentanglement Network, is informed and updated about any whale and its behaviour in the Glencairn area.
Q. How does the cable work?
A. The cable emits a low-frequency, low-power electronic field into the immediate area around the cable, which has been proved to repel white sharks.
Q. How is this system different from other barriers that have been tested?
A. This system uses an active low-power pulsed electronic field in sea water. It does not use magnets and it does not provide a physical barrier to sharks or other marine animals.
Q. Why is the KZNSB doing research in the Western Cape?
A. The demonstrator cable that IMT has built is designed to repel white sharks, which are most commonly found in the waters off the Western Cape. These sharks, unlike Zambezi (bull) and tiger sharks, often swim at the surface in daylight hours, so it is far easier to monitor their movements and responses to the cable/barrier. If these tests are successful, further research will need to be conducted against other species and in different conditions.
Q. Why was Glencairn chosen?
A. The area lends itself to testing of this nature due to the high frequency of shark sightings in the area in shark season and the high ground that Elsie’s Peak provides for surveillance purposes. It is also close to the IMT offices in Simon’s Town.
Q. Is this cable visible from the beach?
A. All that will be visible is two parallel rows of small floats at the surface that are used to support the risers attached to the cable.