New Shark Repellent Uses Chemical Signals
for National Geographic News
|July 29, 2004|
Researchers say they have developed a shark repellent that uses apparently natural chemical signals to shift the animals from hunting mode to flight mode. If it proves to be effective and environmentally safe to use, it could soon become standard-issue for everyone who comes into contact with the marine predatorsfrom surfers to commercial fishers.
Eric Stroud is a chemist and cofounder of the New Jersey based Oak Ridge Shark Lab. He began looking for an effective repellent during 2001, when some well-publicized incidents caused a media feeding frenzy known as the Summer of the Shark (in fact, that season recorded below-average statistics of shark-human encounters).
"As a chemist I was wondering what was being done as far as a repellent," Stroud recalled. "I began looking through a lot of past research and ended up in the area of semiochemicals. That seemed to be promising."
Semiochemicals are chemical "messengers" used in natural behavior and communication between individualsthough the chemicals' exact roles are not completely understood.
Animals or even plants may emit different semiochemicals (including pheromones) which serve as sexual attractants, repellents to potential predators, or inducements to flight mode. A flower, for example, may mimic sexual attractants to draw pollinating insects, while other animals may emit scents that deter predators.
Semiochemicals are currently used in animal-control industries like insect management. They can be used as attractants to lure bugs into traps or as repellents to keep them away.
Semiochemicals are also common in the lives of aquatic animals, said Samuel H. Gruber. "Doc" Gruber is a marine biologist at Florida's University of Miami and a leading shark researcher with decades of hands-on experiences. "Certain kinds of fishes, like minnows, release something when attacked that tells the rest of the school to disperse quickly," he said.
Stroud and assistant Mike Herrmann believed that sharks might possess a similar avoidance chemical that sometimes warns other sharks to stay away. Their task was to isolate that chemical." We took that as our direction and began to investigate the molecular chemistry of shark tissues," Stroud said.
The hands-on results from tests at Gruber's Bimini Biological Field Station in the Bahamas, and elsewhere, have been very promising.
To date, six different species have been effectively repelled by the mixture, which was dropped from a boat into a chum-filled sea of feeding sharks.
"They stop feeding, go into alarm mode, and they rapidly leave," Stroud explained. "Once they detect this, we suspect by olfactory senses, there's definitely a behavioral change, and they either go deep or leave the area.
"I think it's not a question of [affecting the] gills or of pain, it seems to be a signal," Gruber said. "When the shark gets the signal its behavior looks reflexive."
In all tests so far, the chemical has proven nontoxic to sharks.
Fish feeding in the area appear to be totally unaffected, yet sharks detect the substance in even minute proportions.
In the controlled environment of lab tanks, sharks have responded to even 0.1 part per millionfor example, they would likely respond to 12 ounces of the chemical in an Olympic-size swimming pool.
The semiochemical is even strong enough to awaken lab sharks from tonic immobility, an induced, "death-feigning" state during which researchers can go so far as to perform surgery without arousing the animal.
Shark repellents have been in development for decadeswith only limited success. Researchers have tried (and continue to try) everything from chemicals and cages to audio signals and electric fields.
During World War II widespread ocean combat and casualties led to large numbers of human-shark interactions. The Navy issued a chemical repellent called Shark Chaser to protect sailors and airplane pilots.
Sharks also caused operational difficulties. Future chef Julia Child helped the wartime Office of Strategic Services (OSS), the forerunner to today's CIA, cook up repellents that would prevent sharks from prematurely detonating anti-submarine explosives.
None of these wartime repellents was particularly effective.
In the mid-1970s, marine biologist Eugenie Clark tested a natural repellent from acidic protein secretions of the flounder-like Red Sea Moses sole. Gruber also worked on the project in Israel, Egypt, and Japan. However, effective, natural supplies of the secretion were limited and synthetic versions proved expensive and unstable.
In the early 1980s Cold War developments renewed the Navy's lapsed interest in repellents.
"It came to light that the submarine fleet was being challenged by sharks," Gruber recalled. "We had subs, as did the Soviets, cruising around the Atlantic listening for each other with towed sonar arrays, and from time to time they experienced what was called the 'million dollar bite.'
The costly chomp occurred when sharks bit, and damaged, trailing arrays or listening devices known as hydrophonesin these cases, big rubber tubes about 2 inches (5 centimeters) in diameter and half a mile (800 meters) long.
"The sharks were really biting into these things," Gruber recalled, noting that the problem spurred his first involvement in the development of chemical repellents.
In the 1990s the Natal Sharks Board of South Africa developed and patented electronic repellent technology employed by professional divers on their cages.
Australian-based SeaChange Technology currently markets the technology on their Shark Shield line of electronic repellent products for divers, swimmers, and surfers. While some hail the devices as effective, they lack the possible range of uses a semiochemical repellent could offer.
Semiochemical repellent could find its way into everything from clothing to fishing tackle.
The substance could be a boon for longline commercial fishing operations like swordfish boatsand for the sharks that they inadvertently catch.
"To make longline fishing a little more selective, to reduce the horrific bycatch, which is sometimes three or five wasted sharks for each targeted speciesthat would be fantastic," Gruber said.
Though the product must be tested on more species, recreational applications may soon include incorporating the chemical into bathing suits, sunblock, and wet suits.
While the chance of attack will always be very small, those who spend time in the water may breathe a bit easier knowing that they are chemically less appealing to sharks.
Yet the biggest beneficiary may turn out to be the sharks themselves. Helping them avoid human encounters may be critically important to their survival.
For more shark news, scroll down.
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