Electric fence may stop sharks from taking a bite

2015-01-29 07:58


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Cape Town - Dozens of people are attacked by sharks every year. Fear among tourists is rife and industry profits are taking a hit. A new underwater electric fence - developed and trialled in South Africa - aims to stop sharks from getting close to bathers.

Nasief Jaffer, a 24-year-old surfer, emerges from the ocean, surfboard expertly tucked under one arm. He is at Muizenberg beach, one of South Africa's top holiday destinations.

A black flag featuring the white outline of a shark is flapping in the wind behind him. "Caution", the flag indicates. "Shark spotting conditions are poor."

Apparently unperturbed by the disclaimer, the 24-year-old shrugs. "I go surfing several times a week - I trust the shark spotters," he says.

The Shark Spotters are a beach safety organization that aims to protect swimmers and surfers from attacks on Cape Town's popular southern peninsula.

The Atlantic Ocean around Cape Town is home to the largest Great White population in the world.

The most dangerous and aggressive of all sharks, one specimen can weigh over 2 000kg, reach more than 6m in length and pounce at 56km/h.

For 10 hours each day, shark spotters take up positions on mountains overlooking nine popular beaches, searching the water for predators. If they see a shark, they alert a colleague on the beach, who sounds a siren and raises a white flag. Within minutes, everyone clears out of the water.


But the Shark Spotter programme, although lauded as a success, has a major weakness: human error.

"It's a high-responsibility job. It's very stressful, especially on days with poor visibility," says shark spotter Liesel Lott, while scanning the ocean with binoculars.

Pressure mounts during the summer, the sharks' in-shore hunting season. "We are expecting to sight sharks every day this time of year," says Shark Spotters field manager Monwabisi Sikweyiya.

Over the past decade, more than 1 700 sharks were spotted near the beaches of Cape Town's southern peninsula alone, most of them Great Whites. Some swim as close as 50m to the shore.

"I had no idea. My guide book only talks about whales," says Glenda Gordon, a tourist from London who is walking along Muizenberg beach. "I certainly won't go swimming now."

National conservation and research organsation Sharks Board records an average of six shark attacks per year in South Africa. That might not sound like much, but every accident raises fears - and memories of Steven Spielberg's iconic movie Jaws.

"Shark attacks have huge impact on tourism," says Sharks Board chief scientist Geremy Cliff. "Any incident is adverse publicity and has economic consequences."

On South Africa's east coast, nets prevent the predators from coming too close to the shore. But the meshwork catches not only sharks - which drown when immobilised - it also kills other sea animals including dolphins, turtles and rays.

'It's a world first'

As a result, the Sharks Board has spent the past three years developing an environmentally friendly solution to keep sharks at bay: an underwater electric fence that harms neither humans, sharks or any other marine animal.

The fence consists of a cable fixed to the sea floor from which vertical cables rise to the surface. The cables emit a low frequency signal, creating an electric fence that repels sharks whose noses are extremely sensitive to electricity.

If humans accidentally touch the cable, they only feel a tingling sensation.

Two 100m-long prototypes have been installed at Glencairn beach, 12km from Muizenberg. A high-definition camera on a peak opposite the bay films water activity to show if the fence effectively repels sharks.

"It's a world first. The design stretched our technical capability," says Claude Ramasami, project manager at the Institute for Maritime Technology that developed the fence.

Installing electricity safely in water, an ever shifting sea bottom, the force of the waves pounding the equipment and corrosion all add to the difficulty, Ramasami says.

By the end of March, the Sharks Board hopes to have sufficient data to prove the electric fence is working.

"If we're successful, it could be installed around the globe," says Sharks Board project manager Paul Von Blerk who is overseeing the trial phase.

Initial data already indicates positive results, he adds.

This would, for example, make bathing safer in the United States, which recorded 47 unprovoked shark attacks in 2013, or in Australia, where 10 accidents were reported in the same year, according to the International Shark Attack File of the Florida Museum of Natural History.

Even hardened surfers like Jaffer say they would welcome the protection of an electric fence. "I'd feel much safer," he admits.

Read more on:    cape town  |  environment  |  marine life

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