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Ken Kiefer 2/Image Source/Getty Images

Shoo, Sharks!

Can magnets keep sharks away from fish traps?

By Alessandra Potenza
From the May/June 2020 Issue
Other Focus Areas: Earth and Space Science; Human Impacts
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A shark with openings on its snout.

Ken Kiefer 2/Image Source/Getty Images

Sharks have tiny openings in their snouts that let them sense the pull of magnets.

Ecologist Vincent Raoult drives a boat and smiles.

Courtesy of Troy Gaston

Vincent Raoult

Sharks are the ocean’s top predators. But every year, an estimated 20 million sharks die after getting caught in traps and nets meant for other fish. That’s one reason many shark species are at risk of dying out.

Vincent Raoult is an ecologist at the University of Newcastle in Australia. In 2017, fishers asked him to help keep sharks out of their traps. Raoult had a clever idea for a solution: magnets! 

Sharks have tiny openings in their snouts. These openings allow sharks to sense magnetic fields, areas near a magnet affected by its pull. Scientists think sharks can detect the magnetic field produced by Earth’s iron core. That might help them navigate the oceans.  

The strong pull produced by magnets is disturbing to sharks. “It’s like a really bad smell,” Raoult says. Could fitting fish traps with magnets repel, or drive away, sharks? Raoult set out to investigate.

Magnet Power

In the past, researchers had tested whether magnets attached to fishhooks could repel sharks. The tests had mixed results. Sometimes, the magnets worked. Other times, they seemed to attract sharks. 

Raoult thought magnets would work better in certain fish traps. These large cages contain bait. Three openings shaped like funnels allow fish to swim in but not easily escape. 

Raoult tested his idea with 1,015 traps. On one-third of the traps, he and his team glued four ice pop-sized magnets around each opening (see Testing Traps, below). A shark would have to swim through the ring of magnets to reach the bait. That made the traps different from hooks fitted with magnets.

The team also prepared two control groups. These served as standards against which the team could compare their results. They fitted one-third of the traps with pieces of nonmagnetic metal the same size as the magnets. This group would tell Raoult whether the pieces of metal were affecting sharks because of their shape instead of their magnetism. Finally, the team left the last third of the traps unchanged.

Test Time

Over eight months, each of the 1,015 traps was placed on the seafloor for a single night. Raoult’s team then identified the fish caught in the traps.  

Raoult found that the traps with magnets caught 30 percent fewer sharks. The same traps also caught 30 percent more fish. Raoult thinks that may be because when sharks entered the traps, they scared the other fish away. 

Raoult hopes magnets will be used worldwide to repel sharks. The cost is only $10 per trap. “It benefits the sharks and it benefits the fishers,” he says.

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