Shark Shields: Electric, Chemical Repellents Show Promise

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"The beach barriers would eliminate the capture of marine organisms," he said.

U.S. scientists are developing an alternative coastal deterrent, based on chemical signals.

The idea of using chemicals to ward off sharks is not new.

During World War II many U.S. servicemen were killed by sharks in the Pacific. The most infamous incident came in July, 1945, when the U.S.S. Indianapolis was torpedoed by the Japanese. Up to 80 deaths were attributed to sharks, which for five days picked off survivors as they floated on the ocean. In response, the U.S. Navy developed a life jacket which gave off a dye and chemicals that were supposed to repel and confuse feeding sharks. The jackets weren't a success.

Researchers are more hopeful for a repellent based on chemicals extracted and purified from dead sharks. The technique builds on those early, wartime experiments, says shark expert Sonny Gruber, a marine biologist at Florida's University of Miami.

He says substances extracted from shark carcasses can clear an area of sharks for up to 15 minutes with one small dose.

"One drop per minute will protect a tasty bait from actively feeding sharks," Gruber said. "When the drops stop, the bait is immediately taken."

The repellent is thought to act as a fright substance that warns other sharks to stay away.

Minnow Studies

In the 1940s Austrian biologist Carl von Frisch found that minnows contain a chemical in their skin which is released when a predator kills it. "This causes the school to break up," Gruber said. "This is the basic framework I am using."

The team is working on a device that would allow lifeguards to release the repellent rapidly in coastal waters if potentially dangerous sharks get too near a beach.

"We plan for our device to be used when a sighting occurs and/or when an attack is imminent or occurring, allowing a rescue to take place sooner—or to devoid the area of the sharks if required," said Eric Stroud, cofounder of the Oak Ridge Shark Lab in New Jersey.

"The requirement is that our device is deployable from shore," he added. The equipment is scheduled to be on the market in the spring of next year.

The repellent will also be marketed as a conservation tool, helping to cut the annual death toll of millions of sharks caught accidentally by commercial fishing vessels. The repellent would be applied to baits intended for tuna, swordfish, and other fish.

Stroud says tests with yellowfin tuna suggest they are not affected by the substance.

"The concept is that the fish do not detect the repellent and get caught, but the sharks are not [caught], because they are repelled," he said. "It's a careful balance of time-release and overpowering the bait odor to an approaching shark, while using as little chemical as possible."

There are also plans to develop surfboards equipped to carry shark repellent.

"I think this type of device would be a little farther out on the time line," Stroud said. "Extensive great white shark testing would need to be performed. …"

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