Biology & Evolution

Magnet barriers could save sharks

The great white shark.
The great white shark.

Every beat of your heart could attract a shark. It starts with an electrical impulse, which sets off a cascade of activity in the relatively small muscle that keeps you alive. That electric current goes hand in hand with a magnetic field and this changing field is how, even if you are not bleeding, a shark knows where to find you.

Scientists from the University of Stellenbosch are using this information to develop shark barriers that will protect swimmers from the marine predator and also save the sharks – as well as numbers of other marine creatures such as dolphins and sea turtles – from shark nets.

“Sharks play a critical role within the marine ecosystem,” said Craig O’Connell, a PhD candidate at the University of Massachusetts Dartmouth and a research fellow at Stellenbosch University.

“Beach nets are being utilised to maximise beachgoer safety; however, these nets are substantially and negatively affecting shark populations.”

The main threat to shark populations in South Africa and worldwide, however, is fishing. The International Union for Conservation of Nature now considers the great white shark, a shark often found in South African waters, a vulnerable species.

O’Connell and a team of researchers are working on magnetic barriers called SharkSafe rather than nets to keep sharks away from beaches, and to protect local sharks and other marine animals.

Their technology is based on the fact that sharks actually have a sixth sense: the ability to perceive magnetic fields.

’Sharks use sensory organs’
”[Sharks] can detect magnetic field emissions, either natural or produced by prey, or artificial – produced by submarine communication cables – relative to the Earth’s background geomagnetic fields,” said Dr Sean Fennessy, a senior scientist at the South African Association for Marine Biological Research.

“Sharks use sensory organs, called the ampullae of Lorenzini, concentrated in their heads to detect electromagnetic radiation. [They] reportedly have the greatest electrical sensitivity of any animal.”

The ampullae, first described by scientist Stefano Lorenzini in 1678, are a network of tiny jelly-filled pores that allow sharks to perceive electromagnetic and temperature changes.

The SharkSafe barrier involves placing magnets in Perspex tubes, which are disguised as a kelp forest. “The point is to mimic a kelp forest so that it [appeals] to the shark’s visual system and magnetic electro-sensory system,” O’Connell said.

He was speaking from a boat in Gansbaai, where the team is beginning the next phase of development.

“For the past three years, we [have been working on] a larger-scale barrier at Dyer Island [about 8km off Gansbaai] … It has been very successful: more than 60 sharks interacted with the barrier, and not one crossed it.”

Professor Conrad Matthee, principal investigator of the evolutionary genomics group at Stellenbosch University, has been providing logistical support for the project and has been involved in it since its inception.

He said: “The next stage is an exclusion barrier, where [the sharks] can never come in … [Engineers] are looking at the durability of the system and the materials, and measuring the wear and tear.”

O’Connell and partners are now testing this exclusion zone on great white sharks. He had previously tested it with other sharks, such as tiger and Zambezi sharks.

“We deployed an exclusion zone [a cubed area encased in magnetic fields created by the SharkSafe barrier], and put bait in the centre,” he said.

“Our thinking was that, if you can block a motivated shark, [the technology] is promising. Eleven bull sharks tried to get through the barrier, and they wouldn’t do it. We’re now in South Africa to test it on the next breed, the great white.”

‘Causes temporary discomfort’
Asked whether the amplified magnetic waves could hurt the sharks, O’Connell said: “We think it causes temporary discomfort. We think they use magnetic fields to navigate, and a stronger field will repel them.”

He likens it to walking down the road: “If a car hoots, you’d jump a bit. If a train sounded next to you, you’d jump a mile. That’s what these stronger magnets are doing. It’s a stimulus the sharks are not used to.”

Asked whether he enjoyed the seminal shark movie Jaws, O’Connell said: “Jaws did a lot of bad things. Growing up, I used to love the movie, but it negatively affected perceptions. They are beautiful creatures that deserve to be protected.” …

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