Shark shields: Electrical and chemical repellents show promise

Recent shark attacks in Florida have sparked the now customary feeding frenzy in the media. Before Florida it was South Africa, where last month a medical student was eaten by a 16-foot (5-meter) great white near Cape Town.

Shark-conservation groups point out that you're more likely to be killed by a falling coconut than a shark. Nevertheless, coconuts don't have multiple rows of big, razor-sharp teeth, nor can they swallow you whole.

If our fear of sharks doesn't reflect the actual chances of being attacked, how do we put our minds at ease? When will it seem safe to go back in the water?

Scientists are developing coastal shark deterrents aimed at reducing both the risk of attacks and the perceived risk of attacks. The new tools include electronic beach shields and chemical repellents. Ironically, such deterrents could also help save sharks from even deadlier killers—humans.

Researchers are working on an electronic beach defense system aimed at preventing potential man-eaters from approaching people sporting in the surf. A prototype of this technology was used to safeguard triathletes competing in Sydney Harbour during the 2000 Olympics.

The electronic-shield project is a joint effort of the Natal Sharks Board in South Africa and SeaChange Technology.

SeaChange Technology, an Australian company, has already developed a range of personal shark-deterrent devices for professional divers and others. The equipment has proved effective against great white sharks, according to Natal Sharks Board biologist Sheldon Dudley.

The devices tap into the heightened sensitivity that sharks have to electrical fields. Dudley says humans and other marine creatures aren't bothered by low-level underwater electric signals, but sharks are.

"Our goal is to develop a beach barrier using similar technology," the biologist added.

Shark Shields
Some have criticized the proposed shark shields. For instance, Andy Cobb, of the Germany-based conservation group Sharkproject, described them as "unacceptable," saying they would cause unnecessary harassment of sharks.

But Dudley argues that electronic barriers are preferable to shark nets, which currently guard South Africa's more vulnerable beaches. He says these nets catch both sharks and marine animals that pose no threat to humans.

"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. …"

Source: news.nationalgeographic.com