New Shark Repellent Uses Chemical Signals

Brian Handwerk
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 predators—from 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 individuals—though 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.

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