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Research sounds out tarpon at Boca Grande

How many fish are there in the sea?

Scientists may be able to answer that age-old question if research conducted this week in this world-famous tarpon hot spot proves successful.

A team of biologists from the Florida Marine Research Institute in St. Petersburg has set up a series of underwater loudspeakers, or transducers, on the rocky bottom of this 80-foot deep pass.

"The transducers send sound waves up toward the surface," Dr. Roy Crabtree said. "The tarpon show up as black dots on graph paper similar to the way a commercial fish finder works."

Crabtree, the state's leading tarpon researcher, said he repeatedly is asked by recreational anglers if there are as many tarpon today as there were 10 or 20 years ago.

"Without an accurate population estimate, we won't be able to answer that question in the future," Crabtree said.

State officials will use information gathered during the $50,000 study to help determine whether state regulations for tarpon are working.

The technique, commonly referred to as hydro-acoustics, has been used to successfully gauge baitfish populations, which in recent months have come under strict protection in the Tampa Bay area.

Earlier this week, a team of state and commercial scuba divers battled heavy current and murky water to place seven rented transducers at strategic spots on the ocean floor.

"At certain times, I could barely see my hand outstretched in front of my face," said Joe Kimmel, the lead state diver on the project. "The most obvious things on the bottom are old anchors, fishing line and lots of beer cans."

Tarpon have historically congregated in Boca Grande Pass to feast on the thousands of "pass crabs" flushed from Charlotte Harbor on the outgoing tide.

During the summer months, when fishing hits its peak, hundreds of boats line up gunwale to gunwale to pull the silver kings from the 12-fathom hole.

"Boca Grande is the perfect spot to conduct a study like this," Crabtree said, "because any big fish that shows up on the chart has to be a tarpon."

Boca Grande also is known for large hammerhead sharks, which have been known to bite hooked tarpon in half in front of onlooking anglers. But sharks, which do not have an air-filled swim bladder like other fish, register a "sound reflection" different from tarpon, so there is little danger of skewed count.

Recreational anglers and commercial charter boat captains, fearing their lines might tangle on the thousands of feet of cable strewn across the bottom, have expressed concern the study might interfere with fishing.

"We checked all the cable to make sure that it laid flat, so the chances of somebody snagging it are pretty slim," Kimmel said.

Once biologists determine how many tarpon congregate in the pass, the next step will be to figure out how long the average fish stays by tagging some fish with sonic transmitters.

"If we know that there are 5,000 tarpon in the pass and the average fish stays there for two days, by the end of the season, that is a lot of fish," Crabtree said.

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