How to spook a shark: New tech keeps them away from fishing lines

Bill Kearney, South Florida Sun Sentinel on Feb 11, 2026

Published in Outdoors

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FORT LAUDERDALE, Fla. — The delicious tuna and swordfish that ends up on plates across South Florida puts a dent in more than just your wallet — catching them puts a dent in global shark populations.

It’s common for sharks to get hooked on commercial tuna and swordfish longlines, which can stretch across vast areas of sea — 20 to 60 miles — and be rigged with thousands of baited hooks. Once hooked, the sharks often die on the line, or cause damage to expensive gear.

To address the issue, researchers at Florida Atlantic University have developed a device that repels sharks but not tuna and swordfish.

The device, which clamps onto the line just above the hook and pairs zinc and graphite in seawater, creates a small electric field about the size of a beachball around the hook, and rattles approaching sharks.

Sharks use an organ around their snout and head called the ampullae of Lorenzini to sense subtle electrical fields produced by prey.

Though they’re attracted to low electrical fields emitted by smaller fish, they are repelled by the strength of the field from the device.

“Basically, we are producing an electric field that is well outside the range of anything that these sharks would naturally encounter,” said FAU’s Stephen Kajiura, senior author of the study. “It’s something that is startling to them or unusual, and they say, ‘What the heck is that?’ And they basically say, ‘I’m going to leave now.’ ”

Meanwhile, the commercially valuable tuna and swordfish lack the organ and are thus unbothered.

In a recent field study, FAU tested the device on two sets of sharks: Bottom-dwelling dogfish in New England waters and open-ocean sharks in the Gulf. The device reduced the bycatch of the open-ocean sharks by 62% to 70% but didn’t reduce catches of tuna or swordfish at all.

Things turned out a bit differently with the bottom-dwelling dogfish.

“These guys swarm by the hundreds in these schools and they will just Hoover up the bottom,” Kajiura said. The dogfish ignored the electrical field and ate the bait anyway.

The difference offered insights. Dogfish have fewer electroreceptors than many open-water species such as blacktips and oceanic whitetips, which are susceptible to longlines meant for tuna and swordfish.

The most sensitive sharks to the device were in the order Carcharhiniformes, which includes oceanic white-tip sharks and blue sharks. He said that if it works on these sharks, it probably works on many of the other 270 species in that family.

Kajiura said the program is about both conservation and economics. Shark bycatch causes costly loss of gear and adds risk to crew members who must handle and release sharks that are still alive.

Kajiura said that blue sharks are of great concern “because they are occupying so many hooks. Blue sharks are not a particularly threatened or endangered shark in any way,” he said, “but it’s a concern for the fishermen because it reduces their profitability if you’ve got all these sharks on the line.” Species that are of concern would be oceanic white tip sharks and makos, he said.

Longlining is legal in most federal waters two to 300 miles offshore.

But it was made illegal from Georgia down to the Keys in 2001, to protect both sailfish and swordfish. At the time, commercial fishers had learned that swordfish, which swim deep during daylight hours, often ascend to near the surface to feed at night, making them susceptible to nocturnal longlining techniques.

“Shark bycatch is a widespread and pressing problem, both in the United States and around the world,” said the study. “The scope of shark bycatch, from small coastal fisheries to large international fleets, makes it a global conservation challenge with serious ecological consequences.”

Kajiura said FAU is working with pelagic longline fishermen to come up with a design that would be easy for them to implement.

“I think if we can demonstrate to the fisherman that if you spend the extra $3 per hook to get this device, it’s going to keep the sharks off and make you more profitable, then there’ll be widespread adoption. But we need the data. And that’s what we’re working on right now.”