When sharks attack humans, keeping the sharks safe can be the last thing on anyone’s mind. But after a dozen or so attacks in the waters around Cape Town since 2004, city authorities reacted not by embarking on a culling programme, but by calling in scientists to find ways to deter sharks without harming them.
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The result, according to researchers at the Southern African Shark and Ray symposium, held on 7–9 September on the shores of False Bay near Cape Town, has been a proliferation of research into shark-friendly safety measures. Promising trials of several technologies were presented at the conference — including orca-patterned deterrent surfboards and non-lethal shark nets.
And whereas in Western Australia sharks have been culled to prevent attacks on humans — actions roundly condemned by scientists, who point out that it can severely damage populations of threatened marine animals — Cape Town’s shark population has not been affected. “Scientists have worked with government in a very collaborative way,” says Alison Kock, chief researcher of Shark Spotters, a programme that monitors shark activity at popular Cape Town beaches.
In Australian trials, the high-contrast striped pattern of poisonous sea snakes has already been shown to deter sharks, and has been used to produce ‘shark-repellent’ ranges of wetsuits and surfboards. But Phil Richardson, a researcher from Human Wildlife Solutions, a consultancy firm in Cape Town, told the conference that he has found a better deterrent — the signature black-and-white belly pattern of killer whales (orcas; Orcinus orca).
Richardson, together with Mike Barron at the University of Pretoria, towed pairs of patterned decoys behind a boat in two shark hotspots, and filmed the sharks' responses. They found that sharks aborted their attacks most often on decoys with an orca belly pattern, avoiding these much more than plain black decoys or those painted with black-and-white checks. The study is part of Barron’s yet-to-be-completed master's thesis.
Orca-patterned decoys also seemed to confer a degree of protection on any decoy towed alongside it. “The sharks changed their mind about the attack when they saw the nearby orca pattern,” Richardson says. He has filed a South African patent for a sticker with the orca pattern that could be put on wetsuits or under surfboards.
Researchers also presented encouraging results from the first two years of a trial of a pioneering shark-exclusion net at Fish Hoek beach, where two of Cape Town’s four fatal attacks occurred over the past decade.
Leigh De Necker
Traditional shark nets — such as those employed in New South Wales and Queensland in Australia, and off the coast of Durban in South Africa — work by tangling up sharks that get close to the net and drowning them. But they also catch other species, such as turtles, rays and dolphins, and leave gaps so that beaches are not entirely enclosed.
Unlike those nets, Fish Hoek’s 350-metre-long net is taken in and out daily, and is moulded to the ocean floor to entirely cordon off the bay and prevent sharks from accessing the waters. It has a smaller mesh, which prevents creatures from being caught — sharks, rays, whales and dolphins visit the bay regularly, but none has been trapped in the net or swum inside it.
It has also been cost-effective at US$230 per deployment, says Sarah Waries, director of Shark Spotters, which manages the net. However, she notes that its use is limited to small, sheltered beaches, and that it protects mainly swimmers, not surfers, who risk encountering sharks more often because they spend more time in deeper water.
But a $500,000 six-month trial of an electromagnetic shark barrier that, in theory, could replace shark nets entirely has produced no useful data, researchers told the conference.
Surfers and swimmers often wear personal devices that emit electromagnetic fields to keep sharks away — a technology invented in the 1980s. From October 2014 to April 2015, South African researchers tested a 100-metre-long prototype barrier made up of many such devices, anchored to the ocean floor in two parallel lines near Glencairn, False Bay.
But bad weather conditions, large amounts of kelp and sand brought on by rough seas and a drop in shark activity in the bay meant not a single shark was seen close to the barrier during the trial, making it impossible to know whether the deterrent worked.
“It was just curveball after curveball,” says the trial's leader Paul von Blerk, a technology specialist at the KwaZulu-Natal Sharks Board, a shark-safety organization. He and his team are seeking funding for another electromagnetic barrier test — hoping that this time, the sharks will come to the party.
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