Dead-shark extract found to make potent shark repellant
Private researchers say they finally have found a potent repellent to drive away sharks, after testing off Bimini island in the Bahamas. It's a goal that's eluded scientists for decades.
If proven effective, the repellent one day might protect divers, surfers and swimmers.
But researchers say that would require much more study. First they hope it can protect sharks — in decline worldwide due to overfishing — by keeping them away from nets and reducing the numbers caught needlessly by long-line commercial fishermen.
The researchers hope to make a slow-dissolving repellent for use in baits and fishing nets, and to guard equipment on submarines and oil-exploration vessels that sharks have damaged in the past.
"You introduce this chemical, and they all leave," said lead researcher Eric Stroud, a 30-year-old chemical engineer from Oak Ridge, N.J. "It works very, very well."
Stroud is doing is study under $500,000 in private financing, has a patent on the product and hopes to market it.
The repellent, called A-2 because it was the second recipe tried, is derived from extracts of dead sharks that Stroud gathered at New Jersey fish markets and piers. Fishermen and scientists have long noted sharks stay away if they smell a dead shark.
Tests have found the repellent effective on three species: the Caribbean reef, blacknose, nurse and lemon sharks. Studies are needed on other species such as the great white, mako and oceanic whitetip.
"We have something that really works, but research remains," said Samuel Gruber, a University of Miami marine biologist and shark expert who is helping conduct tests at the Bimini Biological Field Station.
Gruber said the repellent seems to carry a chemical messenger that triggers a flight reaction. He said more studies are needed to pinpoint the active molecule among a dozen or so.
A dose of 4 fluid ounces is enough to scare away feeding sharks, Stroud said, keeping them away from a fish head for two hours with just a few drops per minute. The repellent, though nontoxic, is apparently so disagreeable to sharks it can revive them from semiconsciousness. Some species slip into a hypnotic state if turned belly-up, and tests found the repellent brought captive sharks out of that trance.
Anti-shark items on the market now include cages, steel mesh suits and a device called the Shark Shield, which when worn by divers or surfers emits an electric field. The device's Australian maker acknowledges it can't guarantee total effectiveness.
In most cases, the danger of attack is extremely slight. The International Shark Attack File, at the Florida Museum of Natural History, recorded 55 unprovoked attacks worldwide last year, including four deaths.
Although researchers first began looking — unsuccessfully — for a shark repellent during World War II to protect American service members in the South Pacific, Stroud decided to join the hunt after several 2001 shark attacks drew widespread attention, including one that nearly killed a boy near Pensacola, Fla.
University of Maryland shark expert Eugenie Clark, who has been searching for a dependable repellent for more than three decades, said the latest findings could be a welcome way to reduce accidental killing of sharks, though she is skeptical of human use, saying few would be carrying the repellent at the rare moment it's needed.
"I'd be happy to see somebody work it out, but I don't see it as a practical solution," she said.