Researchers will conduct experiments off Hawai'i this fall on a new chemical shark repellent that could prove valuable in minimizing the unintended catching of sharks by the state's longline fishery, and help protect and rescue swimmers at attack sites.

"We are developing a product that lifeguards can use for shark attacks," said Eric Stroud, research chemist and founder of SharkDefense. He has identified 12 natural and synthetic compounds — eight affecting a shark's taste mechanism and four its sense of smell — that are effective against tiger sharks, the shark most often involved in Hawai'i attacks.

The repellent, based on one or more of these compounds, could be useful in post-attack situations when sharks are lingering, thereby keeping lifeguards away from a bleeding victim.

"Most of the time, people bleed to death from severe attacks. If we can drive the sharks away and lifeguards can get to them sooner, we could save some lives," Stroud said.

Ralph Goto, who oversees O'ahu's lifeguard program, said his water safety personnel are not expected to put their own lives at undue risk and would be justified in staying away from a victim if sharks were present. He expressed cautious interest in the repellent.

"It sounds interesting. I'd like to learn more about it. But it's got to be effective all the time. Ninety-nine percent of the time isn't good enough," Goto said.

SharkDefense, a New Jersey company, intends to market a product for lifeguards in Florida next spring, after completing additional research in which various combinations of compounds are to be tested on several shark species.

The repellent is also generating interest from the longline fishing community, which wants to reduce the loss of gear and the unwanted catch of sharks. Yonat Swimmer, a marine biologist and turtle researcher with NOAA Fisheries in Honolulu, said federal researchers will use the repellent during longlining tests in Hawai'i waters later this year.

The repellent's compounds appear to affect only sharks. Other fish are not apparently bothered by them. That is why researchers hope it can provide a way to keep sharks away from longline hooks and bait.

"We tested it in Panama with tuna, and we know they're not going to be bothered by it." They eat bait treated with the repellent, Stroud said.

SharkDefense plans to experiment with different techniques, including soaking bait in repellent or using a repellent-soaked sponge that releases the compounds steadily.

"The key is to find a delivery mechanism," Stroud said. "It looks really good right now at the small scale, but we haven't seen it on the huge scale."

Fishery biologists with NOAA Fisheries have asked SharkDefense to try also to develop a turtle repellent, so that longliners' unintended catch of endangered and threatened sea turtles can be reduced.

"It could be an excellent way to develop a turtle-friendly fishery," Swimmer said. For longliners, she said, keeping sharks and turtles away from the bait could keep their gear fishing more effectively for the primary catch — generally tuna and swordfish.

But environmental groups are concerned that improving the efficiency of longlining — even if it successfully avoids the unwanted catch of sharks and turtles — misses a point they've been trying to make.

"If you're not catching a shark, who can criticize that? But in doing that, you're not going to be addressing the fact that longlining is not a sustainable form of fishing. It is industrial fishing that is taking more fish out than the populations can sustain," said Earthjustice attorney Paul Achitoff.

The shark repellent's 12 compounds are derived from those found in rotting shark meat.

"It builds on the observation that when fishermen hung out rotting shark, other sharks left the area," Stroud said.

In tests so far, Stroud maintains the repellent has never failed to drive away sharks. In tests in the Caribbean, he said, even hungry sharks avoided bait as long as the compound was in sufficient concentration in the water around it.

"They will get away from it if there is a persistent amount of (shark repellent). As it is diluted, they will come back," Stroud said.

Other products have also been shown to work against sharks. Sodium lauryl sulfate, a common soap compound, repels the predator fish, but only when sprayed directly into a shark's mouth.

Developers of a World War II shark repellent used by the Navy tried to mimic the smell of rotting sharks. Initial testing of early repellents may have falsely yielded promising results, not because of the effect on sense of smell or taste, but because a cloud of dye released with the repellent made people less attractive as targets.

Researchers have also noted that sharks are repelled by certain electrical fields, Stroud said, noting that in experiments involving carefully controlled electrical fields, sharks appear to be convinced that any object inside the field is not food.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.