Scientists out to get an earful from fish

Songs possible clues to oil-spill effects

— For the past 30 years, a Vero Beach, Fla., scientist has spent many spring and summer evenings recording the love songs of fish. And researchers hope his findings can help determine the effects of the spreading BP oil spill on marine creatures in the Gulf.

“Spawning is the most important thing a fish can do,” said Grant Gilmore, senior scientist at Estuarine Coastal and Ocean Science, a private research institution. “If you don’t have spawning sites, you don’t have fish.”

In the 1970s, Gilmore - then with Harbor Branch Oceanographic Institute in Fort Pierce - stuck a hydrophone in the water at night on a pier where fishermen were catching small silver perch.

The sound was like pistons pumping.

Then he put the hydrophone in a bucket full of the perch.

“My God, what a sound! I had to turn down the volume of my headphones,” he said.

In the ensuing years, Gilmore identified the species of fish crooning in the night and found they were mostly males trying to attract mates.

Male fish, he said, produce sounds with their gas bladders, which have vibrating sonic muscles.

Females home in on the sounds they like best. Each species has its own frequency.

“It’s like birds - he’s got to sing his heart out to win her over,” Gilmore said.

The love-struck male and receptive female meet on the surface, where she ejects thousands of eggs and he releases sperm.

Egg and sperm mix and float through the water column for a few days before settling in the sea grass at the bottom to grow.

Gilmore has mapped nearly two dozen spawning sites in the Indian River Lagoon, an estuary that stretches from Florida’s Palm Beach County north to Volusia County.

He found that fish such as spotted sea trout, silver perch, catfish and black drum return to the same areas year after year to spawn, usually in deeper channels and holes instead of shallow sea-grass beds - and always at night.

“During the day, if you sat there, you wouldn’t hear anything,” he said. “To me, it’s basic acoustics. It’s calmer at night so the sound will travel further.”

Another important finding: Changes in water quality - such as sudden large pulses of fresh water cascading into the estuary - will send spawning fish packing.

“They opened one of the locks at Vero - no sound, no eggs,” Gilmore said. “You can observe the impacts on spawning just from listening to fish.”

One of Gilmore’s colleagues, University of South Florida research scientist Jim Locascio, hopes to apply the science of fish sounds to damage assessment from the spreading Deepwater Horizon oil spill.

Locascio is drafting a proposal to the Florida Institute of Oceanography to place a network of hydrophones in passes, bays, channels and edges of sea-grass beds in the path of the Gulf oil spill using funds from BP.

He already has deployed three recorders at Riley’s Hump, a prolific spawning area west of the Dry Tortugas.

“Sound is a proxy for spawning,” Locascio said. “We can go in areas of Louisiana, Alabama, Mississippi and Florida and put recorders in habitats that are typical of reproduction at certain times of the year. The acoustic data would demonstrate whether habitat is healthy enough to support fish spawning. We don’t need before-and-after.”

Locascio said it’s a costeffective technique - $3,000 to $5,000 per listening station - with software that allows data collection for up to years at a time, depending on battery life.

“It gives you a lot of data,” he said.

Front Section, Pages 9 on 07/25/2010

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