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Underwater acoustic technology proves a reliable research tool

by Kathy Hagood
Brevard Technical Journal

Fish ecologist Dr. Grant Gilmore periodically takes groups out on the Indian River Lagoon and the Banana River after sunset to listen to what seems at first to be an underwater cacophony.

After Gilmore lowers a hydrophone into the water, the "click, click, click" of snapping shrimp projecting through his speaker system is ubiquitous. Soon, other sounds emerge, such as the slow and low thump of black drum mating calls.

On a recent trip, Gilmore accompanied Space Coast Birding & Wildlife Festival participants on a Space Coast Nature Tours pontoon boat to listen to the sounds of fish in Haulover Canal and nearby waterways.

The group learned how to distinguish the calls of the various fish they heard.

"We're still not sure what the fish are talking about, but we know it's related to mating," Gilmore said. "The choice of mates is based on calls. The most robust male calls lure the most females."

Underwater acoustic monitoring has enabled Gilmore and other environmental researchers and agencies learn about the spawning habits and whereabouts of fish such as black drum, red drum, grouper and spotted sea trout. The data has been used by environmental protection agencies to manage fisheries.

"Fish reproduction is critical to keeping our fisheries viable," Gilmore said.

Area fisheries provide food, jobs and recreation activities to area residents. They also draw tourists who boost the local economy.

Gilmore currently is working on a project to monitor fish, boating and diver activity on an artificial reef about nine and a half miles off the coast of Cape Canaveral.

The Florida Fish and Wildlife Conservation Commission has contracted him to record sounds produced on and around the reef. Volunteer divers will be placing hydrophones in key positions, then volunteer boaters and divers will participate in planned activities so that recordings of man-made and fish sounds on and near the reef can be made.

"The state wants to be able to determine if reefs are being overfished or underfished and how to better manage the reefs," Gilmore said.

Gilmore has been monitoring fish activity with underwater acoustic technology for almost three decades. He first heard about underwater acoustics in 1973, when he saw a hydrophone demonstration by a colleague at Harbor Branch Oceanograhic Institute in Fort Pierce.

"It captured my imagination because I knew it would serve as a great tool for monitoring fish behavior," Gilmore said.

Hydrophone technology was developed between the World Wars as the military sought to locate the whereabouts of enemy ships and submarines. After World War II the U.S. Navy contracted Marie Poland Fish and William Mowbray to record sounds from fish of the U.S. Atlantic coast and the Caribbean Islands. and catalogue them. Their work, which spanned 1950 to 1970, was published as "Sounds of Western North Atlantic Fishes: A Reference file of Biological Underwater Sounds," and greatly influenced marine scientists like Gilmore.

Gilmore first obtained a hydrophone in 1975, and began to listen to fish. Over the years he's used the hydrophone to record the sounds of 95 percent of the 200 sound-producing fish species in the Indian River Lagoon.

"We've shown over and over again that the level of the calls and spawning in the Indian River is directly related," Gilmore said.

When water quality periodically deteriorates, such as in the case of a major storm that produces an infusions of runoff into the river, calling activity and spawning lessens.

"The fish instinctively know when the water will allow for the viability of the eggs and don't waste their efforts when the water quality is bad," Gilmore said.

Gilmore left Harbor Branch after 27 years to create a marine fisheries program at Kennedy Space Center. He served as a senior scientist for the center's environmental research contractor, Dynamac and then ASRC Aerospace Corp.

During his time at KSC, Gilmore worked with NASA, NOAA and other agencies to monitor the surrounding fisheries of the Merritt Island National Wildlife Refuge and the Oculina Reef system for about five years.

"But after the Columbia accident, the focus shifted and there was less money for research. My program got axed," said Gilmore, who recently founded his own Vero Beach-based consulting company, Estuarine, Coastal and Ocean Science Inc.

Program managers at NASA decided to limit their environment monitoring for the wildlife refuge areas to marine mammals and species like indigo snakes and gopher tortoises. The spaceport provides data to government agencies for the protection of wildlife at the refuge.

"I understand their need to cut costs, but if you ask the person on the street whether they think it's more important to monitor indigo snakes or grouper, I think they'd choose the fish," Gilmore said.

Gilmore continues his marine research as a private consultant. His dream is to see government agencies and others fund permanent systems for ongoing acoustic monitoring in the Indian River and on the Oculina Reef.

"This technology is proven and provides reliable data," Gilmore said. "It's an easy way for us to keep track of vital areas and detect problems in early stages before it's too late to save a population," Gilmore said.