For years, people have been searching for a chemical substance that repels sharks.

During World War II, the U.S. Navy created "Shark Chaser," a mixture of copper acetate and black dye made to smell like a rotting shark; scientists later determined it was ineffective.

In 1972, University of Maryland professor Eugenie Clark determined that a fish swimming in the Red Sea, known as the Moses sole, secreted a natural shark repellent. Researchers including the University of Miami's Samuel Gruber and a team of Israeli and Egyptian scientists worked on replicating the milky liquid but gave up once they realized it worked only when injected directly into a shark's mouth.

The Navy remained intent upon finding a solution, however, especially once sharks began their "million-dollar bite": snapping acoustic lines that U.S. submarine operators towed underwater to eavesdrop on Russian operations. Gruber continued to work on the project for the Navy, but a final answer eluded him, despite the fact that even Hollywood pretended it existed, with Batman saving the day in a 1966 episode while surfing by employing a "bat shark repellant."

An American inventor believes he has grasped it.

Eric Stroud, a research chemist who heads the Oak Ridge, N.J.-based company Shark Defense, comes to Bimini to test a chemical substance he believes will drive sharks away from dangerous fishing lines and, perhaps, also protect people. Working with Gruber, who directs the Bimini Biological Field Station, a shark-research facility, Stroud has determined that a synthetic liquid replicating the scent of rotting sharks prompts them to flee when it is released into the water.

Stroud, who used to work for pharmaceutical companies, entered the scene after the "summer of the shark" in 2001, when the national media were riveted on a series of 50 shark attacks off U.S. coasts.

In the spring of 2003, Stroud came to Bimini to test his formula -- a combination of a dozen compounds known as A2 -- on the shark species that thrive in the area, including blacknose, bull, Caribbean reef, lemon, nurse and tiger sharks.

"We were thinking of saving the sharks first, and the human product came afterwards," Stroud said.

Stroud -- who hopes to launch his first commercial product early next year, in the form of a time-released device fishermen can attach to their longlines so sharks do not become tangled in them -- now spends his time fielding calls from lifeguards, surfers and other water sports enthusiasts hoping to avert catastrophe.

"Nobody is really too interested in conservation," he said. "They're all saying, 'What are you doing for the humans?' " The number of shark attacks off U.S. coasts has risen over time, as more people have flocked to the water. In late June, doctors amputated the leg of a 16-year-old boy attacked by a shark while fishing off the Florida Panhandle two days after a shark killed a teenage girl at another beach 80 miles away.

U.S. shark attacks rose from 18 in 1990 to 52 in 2000, before dropping to 30 last year, according to the International Shark Attack File at Florida's Museum of Natural History. George Burgess, who directs the museum's Florida program for shark research, estimated that, worldwide, sharks kill five to seven people a year.

"We're talking about a small number of people who are dying," Burgess said. "Shark attacks are largely a human phenomenon, not a shark phenomenon, simply because the number of attacks are a product of the number of people in the water."

Experts say swimmers and surfers can take several steps to avoid shark attacks, including remaining close to shore, staying out of the water at dusk and dawn and while bleeding, and avoiding steep drop-offs in the water and areas where bait fish congregate.

It takes less than a pint of Stroud's repellent, which smells slightly sweet, to scare off a group of sharks. "They just have to get a whiff of it, that's all," said Michael Herrmann, Stroud's business partner and an electrical engineer by training.

Stroud has successfully tested the substance on tuna in Panama to make sure they will approach fishing lines despite the repellent, because fishermen will not use it if it scares off commercially targeted species.

Ellen Peel, president of the Billfish Foundation, a sport fishing conservation group, said the fishing industry has an incentive to use such a repellent because sharks can eat commercially desirable fish near longlines as well as occupy needed hooks.

Christofer Boggs, a biologist at the National Oceanic and Atmospheric Administration's Pacific Islands Fisheries Science Center in Honolulu, has been working with Shark Defense. He said that although Stroud deserves credit for developing a chemical shark repellent that works, "getting it to work on longline gear is a challenge." Longlines can stretch across 60 miles of ocean, and the repellent must be released around every hook: 800 to 2,500 sites for a single longline.

As Boggs put it, "It's not time to crow."

Gruber, who has studied sharks for about three decades, estimates the repellent could save as many as 50,000 a night worldwide. According to NOAA officials, nearly 124,000 sharks were caught accidentally off U.S. coasts in 2003, although some were released alive.

"Do I think it will save a lot of people? No," Gruber said of Stroud's repellent. "What I believe this could be beneficial in is protecting sharks. You cannot protect yourselves against a shark attack, short of staying out of the water."

Still, Stroud and Herrmann are hoping to minimize the public safety threat that sharks can pose. They are developing a prototype that beach lifeguards could throw in the water just after a shark attack, as a rescue cannot be attempted when a shark is still in the area.

"The first thing a rescuer has to determine is: Is it safe to approach the water? In a shark attack, it is not safe for a rescuer to approach unless they have a boat," said B.J. Fisher, director of health and safety for the American Lifeguard Association.

Fisher's association has endorsed Shark Defense's repellent, and other groups are urging the company to develop different applications. Surfers have suggested they incorporate it into surfboard wax, and swimmers are seeking a suntan lotion that provides shark protection, as well.

Herrmann cautioned, however, that Shark Defense may not be able to sell such a product, which could take years to gain approval by several government agencies. "It's going to take significantly more research to determine if you could incorporate this substance into suntan lotion, or in a sponge within a child's bathing suit. That's in the future."

Researcher Karl Evanzz contributed to this report.