Eric Stroud and colleague demonstrate the effect of magnetised rare-earth metals on a lemon shark. Video courtesy of PRI’s The World
An American chemist says he’s found a substance – several, in fact – that can repel some of the most fearsome predators in the ocean. He wants to use his discovery to protect them, and us.
Eric Stroud stands on a pier on the island of North Bimini in the Bahamas. He looks down into the turquoise water.
A couple of eagle rays and barracudas swim by.
“The current is ripping through here right now,” he says. “The tide is going out. So any scent that’s put here goes right to the outside of the channel, and that’s where the big sharks are right now.”
Stroud is setting up an experiment. He unwraps 20lbs (9kgs) of frozen sardines, drops them into a mesh bag tied to the pier, and tosses the bag into the water. He’s hoping to attract a large bull shark.
“It’s a fairly dangerous shark,” he explains. “It can be aggressive, especially when provoked or cornered.”
If a bull shark does turn up, he’ll throw a large baited hook into the water. But it’s not your typical fishhook. In fact, if all goes well, this hook won’t catch any sharks.
For more than a decade, Stroud has been working to develop shark repellents.
He used to work as a chemist in the pharmaceutical industry. Then, in the summer of 2001, he and his wife went on a cruise to Bermuda.
“We hit bad weather, and we were trapped in a cabin, and on the news was shark bite after shark bite,” he says. “It seemed like everyone that stepped in the ocean in Florida was getting attacked by a shark that summer.”
That’s when his wife suggested he turn his talents to developing shark repellents. When they got home to New Jersey, he set up several small pools in his basement, and filled them with small sharks.
He watched how the sharks fed, swam, and behaved. Then, one day, he accidentally dropped a large magnet from his workbench. He noticed some small nurse sharks dart away.
“That night, we put magnets into the water and couldn’t believe the nurse sharks were extremely distressed and stayed away from them,” he says.
Stroud thinks that was the moment he discovered that magnets repel sharks.
He demonstrates the effect at the Bimini Biological Field Station in the Bahamas. He stands waist-deep in water, just offshore, in a fenced-in pen in the sea. Several young Lemon sharks glide around the perimeter. One of Stroud’s assistants captures one of them and slowly rotates it onto its back underwater. This puts the shark into a sleep-like state.
Then Stroud takes a magnet and spins it as he moves it towards the shark. The shark darts away suddenly. “There you go,” he says. “Look at that beautiful bend away from the magnet like he’s repelled by it”.
Sharks possess electrical sensors, called the ampullae of Lorenzini, that look like tiny freckles on their snouts. Biologists believe sharks use these sensors to detect the heartbeats of their prey and to navigate using the Earth’s magnetic field.
Stroud suspects the spinning magnet overwhelms these electrical sensors.
“It’s probably something like a bright flashlight across your eyes,” he says. “It’s just temporarily blinding, and you’re startled. And it’s not pleasant.” …