Shoo, Sharks!

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.

Scientists had tested whether magnets could repel sharks in the past. The magnets were fixed to fishhooks. But the tests had mixed results. Sometimes the magnets repelled sharks. They seemed to attract sharks other times. 

Raoult thought magnets would work better in traps. These large cages hold bait. The traps have three openings. They’re shaped like funnels. They allow fish to swim in. But they can’t easily get out. 

Raoult tested his idea on 1,015 traps. His team used ice pop-sized magnets. They glued them to one-third of the traps. Four magnets were placed around each cage’s openings (see Testing Traps, below). A shark would try to get the bait. But first they’d have to swim through the ring of magnets. That made the traps different from hooks fitted with magnets.

The team also set up two control groups. They served as standards. The team could compare their results against them. The team fitted one-third of the traps with pieces of metal. They weren’t magnetic. But they were the same size as the magnets on the other traps. They would tell Raoult why the objects affected sharks. Was it their shape or because they were magnetic? The team left the last third of the traps unchanged.

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.

Each of the 1,015 traps was placed on the seafloor. They sat there for a single night. This was done over eight months. Raoult’s team then studied the fish caught in the traps.  

Raoult found that traps with magnets caught 30 percent fewer sharks. The same traps also caught 30 percent more fish. Raoult thinks he knows why. Sharks entering traps likely scare 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.