What's All The Noise About Manatee Hearing?

Recently, there have been some questions about the need for additional regulatory measures to protect manatees. These questions have been raised by some members of the boating community who maintain there is a simple solution to the problem of high manatee mortality from watercraft collisions. They believe the solution lies not in regulatory measures, but in a study by Edmund Gerstein and Joe Blue from Florida Atlantic University.

Gerstein and Blue’s study shows that a manatee’s optimal hearing range is in a higher frequency range. Some boaters interpret the results of the study to mean that manatees can’t hear boat motors, and that is why so many watercraft mortalities occur. In reality, however, manatees have a wide range of hearing and we know that they can hear boats. The Gerstein and Blue study also shows that manatees are able to hear in all frequencies -- including those of a boat motor going at slow speed. In addition, videotape from the Florida Marine Research Institute clearly documents manatees reacting to the sound of approaching boats at various speeds.

Gerstein has concluded in earlier reports that a sonic device for boats should be developed, and he would like to test it in the next phase of his research. Boaters are also encouraging the development of the device as a solution to the problem of high watercraft mortality. However, there are many problems associated with the application of a sonic device. First, the manatee will have to have at least one negative encounter with a boat that has the device in order for a manatee to associate the sound with a speeding boat. In other words, the manatee will have to get hit by a fast-moving boat with the device, survive the encounter, and hopefully make the connection the next time it hears the device. This is negative reinforcement conditioning, and Save the Manatee Club is opposed to it for obvious practical as well as ethical reasons. Second, even if the manatee does associate the boat with the sound, there is a problem associated with the possibility of numerous boats that might carry the device. If multiple boats bearing the device approach from different directions, the manatee would likely not know how to react.

In addition, what happens if a boat doesn’t have a device? Manatees could develop a false sense of security -- if they don’t hear the sound, then they don’t need to be concerned. Finally, there are also concerns about putting more noise into an already noisy environment and how these additional sounds will affect manatees and other aquatic species.

Save the Manatee Club believes that we already have a solution to the problem of high manatee mortality from watercraft collisions. That solution is to slow boats down in areas of frequent manatee use.

Members of the Manatee Technical Advisory Council are appointed by the Governor of Florida to provide recommendations on manatee-related issues. Read MTAC's Recommendations on Acoustic Technology
as a Manatee Protection Strategy
.