Fish Talk
by Victoria Parsons

Scientists listening to sounds that range from clicks and rumbles to squeaks and squeals are learning how and when fish use habitat in Tampa Bay and Charlotte Harbor. Like something from a James Bond film, researchers "bug" areas where they expect fish to spawn with underwater microphones and digital tape recorders.

Many species of fish - including silver perch, red drum and sea trout - have drumming muscles on their swim bladders that make distinct noises, says Dr. David Mann, a bioacoustic researcher at the University of South Florida. Trained listeners can distinguish which fish are present and - at least for some fish - what they're doing.

"The goal is to understand the process of spawning and settlement of larvae," Mann explains. "Right now, it's a big black box. We don't know where fish are coming from, what their mating patterns are or where the eggs and larvae go."

Research in Charlotte Harbor is showing that some fish spawn in habitat where they are seldom seen, he adds, possibly indicating a need for enhanced habitat protection for some species.

In some ways, listening in on fish raises more questions than it answers. For instance, high levels of fresh water that surge into estuaries after storms may push spawning fish into saltier water. "We hear a racket close to shore and then it's silent after a major storm event," he said. "We think it's lower salinity but it could be related to lunar cycles or changes in currents and tides." Other bioacoustic research underway at USF focuses on learning more about what fish, dolphin and manatees can actually hear using the same technologies as human infants being tested for deafness. "Fish are tested mainly in the lab, but manatees and dolphin are tested in situ, or in the field."

Understanding what and how manatees hear is critical, Mann said. "We think they hear boat engines, but we don't know if they can hear 40 boat engines and not know which way to go when they need to come up for air."

Listening to manatee sounds also may help researchers develop new ways to protect them, he adds. While other researchers are focused on creating warning devices for boats, Mann worries that manatees would need to be hit at least once to connect the noise with danger. On the other hand, devices that magnified the sounds manatees make may soon be used to warn boaters that the slow-moving marine mammals are present.

For more information and samples of fish sounds, visit USF's College of Marine Science