The risers on the cable are clearly visible at low tide

Testing a shark repellent cable at Glencairn

Signage at Glencairn explaining the test
Signage at Glencairn explaining the test

Perhaps you have noticed some new signage and a little wooden hut at Glencairn beach, where an exciting test – of an electronic cable to repel great white sharks – is underway. The cable is a massively scaled up version of the Shark Shield technology with which many surfers and lifesavers will be familiar. The Shark Shield has been subjected to scientific testing, and is effective in certain circumstances.

The risers on the cable are clearly visible at low tide
The risers on the cable are clearly visible at low tide

The cable is a collaboration between the KwaZulu Natal Sharks Board (who would like an alternative to the gill nets and drum lines currently used to harvest sharks and other marine life off South Africa’s north coast), and the Institute for Maritime Technology (IMT) in Simon’s Town, a division of ARMSCOR. Shark Spotters and the City of Cape Town are assisting with the testing phase, which started in November and will continue until the end of March 2015. A permit has been obtained from the Department of Environmental Affairs.

The cable is 100 metres long, and is situated at the northern end of Glencairn beach. Cape Town is an ideal location to test things like this, because Shark Spotters has ten years of shark spotting data that will give a baseline measure for “normal” white shark activity without the cable. When something new (the cable) is introduced into the environment, changes in behaviour relative to the baseline data can be ascribed to its presence. Fish Hoek was originally mooted as an ideal beach to run the test, but the trek net fishermen were concerned for their fishing opportunities and so the test was moved to Glencairn.

The cable is off the end of Glencairn beach
The cable is off the end of Glencairn beach

The cable emits a low frequency electrical pulse that – it is hoped – will repel sharks. The electrical output of the cable poses no threat to swimmers or surfers, but for obvious reasons people are requested to keep clear of it for the duration of the experiment. The cable has electrodes on either side of it, supported by vertical risers that are marked by small orange buoys (so the cable runs down the middle of the rows of buoys in the pictures). At high tide the buoys are below the surface, but Tony took the boat past at low tide and photographed them sticking out of the water.

Shark Spotters will be monitoring the cable from the mountain above Glencairn, and a video feed will also be used to closely analyse the movements of any sharks that approach the cable. The risers on the cable (marked by the orange buoys in the photographs on this page) are semi-rigid, designed to minimise the risk of entanglement of any marine life. As it is the end of whale season in False Bay, there is not much risk of a whale visiting this location. Despite that, a boat and crew are on constant standby should an entanglement situation arise.

There is a full report on the testing phase, with an artist’s impression of the cable underwater, on the Sharks Board website, including a list of frequently asked questions (which should set your mind at ease). There’s also a great post at Round About South that includes pictures of the study area, and of the cable from the KZNSB document.

It’s important to note that this is an experiment, and no additional protection from white sharks is offered or guaranteed while the cable is in the water.

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Clare

Lapsed mathematician, creator of order, formulator of hypotheses. Lover of the ocean, being outdoors, the bush, reading, photography, travelling (especially in Africa) and road trips.

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