A curtain of shark-repelling “seaweed” is on trial near some of Cape Town’s most popular beaches.
The SharkSafe barrier is made up of magnetic rods that mimic the tall stems of kelp forests. Sharks avoid swimming through thick kelp and are sensitive to magnetic impulses.
By dressing up and arranging magnetic rods to look like a kelp forest, the inventors aim to deter the predators with a “double whammy” repellent that has proved successful at trial sites.
Results from a four-year trial in Gansbaai — considered one of the world’s white shark hotspots — found sharks do not cross the barrier, even when offered fish as bait.
In Glencairn the developers want to see how the barrier withstands wave action in relatively shallow water and on the deep sand seafloor.
And so far so good, according to Stellenbosch University marine biologist Sara Andreotti.
“It survived a recent storm that was one of the most powerful in years,” she said.
“The tests conducted from 2012 to 2016 on sharks in Gansbaai were done using underwater remote baited surveillance systems. In other words, we tried to attract the sharks to swim through the barrier by positioning the baits in the middle of the SharkSafe protected area, and then filmed their behaviours.
“In Glencairn we are not testing on sharks, and we are also not providing a safe enclosure. We are only working on the engineering and robustness aspects by anchoring a few rods at different depths.”
• 90: Fatal shark attacks recorded in SA in the past 170 years
• 2021: The most recent attack, which claimed the life of a 38-year-old body boarder in Chintsa, Eastern Cape
• 1852: The earliest recorded attacks, following the sinking of HMS Birkenhead off Danger Point, Gansbaai
— IN NUMBERS
The test site is between the locations of previous fatal shark attacks in Fish Hoek and Simon’s Town. It is metres from the wreck of the Clan Stuart (1914), a popular diving site.
The rods are anchored to the seafloor and extend to the surface, sticking out about 1m at low tide and visible to passing motorists.
“When a large SharkSafe barrier installation is built, to provide a safe enclosure multiple magnets are inserted inside the [outermost] pipes only and form a continuous magnetic field,” Andreotti said.
“Sharks start feeling the magnetic field at about 2m from the barrier, and this becomes overwhelming to them within 1m.”
She said sharks' “sixth sense” allows them to hunt prey by following electric impulses.
“It is suspected they also use this sense for migration.”
The barrier is designed to be an alternative to nets and drum lines that typically kill a large number of sharks and other species.
“Only about 12% of sharks caught in these large shark nets can survive,” said Andreotti.
The magnetic barrier will cost more to install than nets but will ultimately work out cheaper because it does not require as much maintenance.
Marine biologist Lynton Burger, a SharkSafe Barrier director and shareholder, said the concept is a viable eco-friendly alternative.
“I’m really excited about the potential of this SA-born solution to the global problem, particularly in countries like Australia where they are killing hundreds of sharks in shark nets and drum-lines,” he said.
Simon Elwin, a marine mammal expert and co-director of Sea Search Research & Conservation, said he would welcome any nonfatal shark attack mitigation measure.
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