By Dan Klepal
The Cincinnati Enquirer

Douglas the manatee will soon be gone from the Cincinnati Zoo. But his time here may help his species live on.

During his four-year stay, Douglas participated in a study that could someday help save other manatees from their biggest threat in Florida waterways - collisions with motorboats.

Douglas will be released next month in the Florida Keys, where he will face other dangers as well: locks and dams that could crush him; water temperature changes and algae blooms that could make him sick; or fishing line, nets or hooks that could injure him.

But an apparent inability to hear oncoming motors causes the most harm to manatees. And that captured the curiosity of a Xavier University professor.

Chuck Grossman, along with an army of volunteers, has been studying manatee hearing in an attempt to figure out why the slow-moving sea cow doesn't get out of the way of motorboats.

Since 1974, nearly 1,200 manatees have been killed by boats; scores of others have been scarred by close encounters.

About 3,000 of the animals survive in the wild.

"Nobody seems to know why they can't hear the boats, which make quite a lot of noise," Grossman said. "Is it because of the frequencies, or is it because of how sound reflects off the water? No one is clear."

So Grossman enlisted a physics professor, a mathematician, a radio engineer and several of his students to work on his project.

They made a grid of parachute silk and placed it across the front of the zoo's 150,000-gallon tank. They rented two transducers from the U.S. Navy, once used to listen for Russian submarines, to record sounds at different frequencies. They then pumped sound into the tank while charting the movements of Douglas and Stoneman, the other manatee at the zoo.

It's early in the research, but so far the team has found that the manatees traveled 21/2 times farther away from the sound source during broadcast of audible tones, which mimic a British ambulance siren. This could mean that manatees might be better protected if boats carried certain kinds of sound projectors.

"We found they respond to mixed frequencies," Grossman said. "They identified the direction of the sound, turned and moved away."

Grossman and his team hope to expand their research to learn if other captive manatees respond to the same sounds. They are applying for permits to do a similar study at the Columbus Zoo, and plan on continuing their research in Cincinnati when a new manatee replaces Douglas.

If they find similar results during those studies, similar experiments in the wild will need to be done.

"It's so early on, all we know is they seem to respond," Grossman said. "But let's say they do, if we put projectors on every boat, would they care? If there was a siren sounding on every car on the expressway, would we know which to get away from?"

Tough questions, with answers that will be years in the making.

But Terri Roth, vice president of animal sciences for the Cincinnati Zoo, said she is glad to have the experiments performed at her facility.

The testing, some of which was done while the exhibits were open to the public, was beneficial for visitors, researchers and even the manatees.

"The more we can learn about animals while they're in captivity, the more justice we can do for them," she said.

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E-mail dklepal@enquirer.com