David Mann
University of South Florida
College of Marine Science
140 7th Avenue South
St. Petersburg, FL 33701
727-553-1192
dmann@marine.usf.edu

Program Summary
Sound is an ideal way for animals to communicate in the ocean. Sound attenuates little in the ocean, is directional, and is very useful where there is no light. It is not surprising then that many fishes have evolved the ability to produce sounds by drumming the swimbladder with specialized muscles or bones. While many fishes are known to produce sound, most have not been studied.

Identifying Sound Producing Fishes
One goal of my laboratory is to identify sounds produced by fishes and to document the behaviors that accompany sound production. One species that we are intensively studying, the Gulf toadfish (Opsanus beta), produces a call that sounds like a fog horn known as the ‘boatwhistle’. This call is used to attract females to nests that the male has prepared. The toadfishes are a good example of how much basic information about sounds has yet to be gathered. While there are 69 species of toadfishes, the sounds of only six species have been recorded and analyzed.

Underwater datalogger and housing used to record fish sounds. The assembled device is shown on the left. The datlogger (in black) and batteries in green are shown on the right.

Ecology of Sound Production
Since many fish sounds are associated with reproduction, they can be used to measure the time and place of spawning. We are using passive acoustics to identify spawning periodicity for several species in Sarasota Bay and Charlotte Harbor in southwestern Florida. One thrust of these studies is the development of instrumentation for passive acoustic detection in the field. For example, we have programmed an advanced digital signal processing datalogger to automatically detect and record toadfish calls. Figure 1 shows the calls of the gulf toadfish produced over a one night period (they appear as horizontal red bands on the graph). This type of device will be useful for fisheries bioacoustics once measures of sound production have been ground-truthed against data of interest to fisheries managers, such as when and where fish spawn and the size of spawning aggregations.

Figure 1. Spectrogram of a series of automatically-detected toadfish (Opsanus beta) calls plotted one after another (the calls appear as the red lines moving across the image).

Effects of Noise on Fishes
One final area of research that we are undertaking is to study the impacts of noise on sound-producing fishes. Great emphasis has been recently placed on understanding the impacts of anthropogenic noise from boats, geologic exploration (from air guns), and scientific research on cetaceans (whales and dolphins). Yet, very few studies have investigated the impact of noise on fishes, especially sound-producing fishes. Figure 2 shows a recording of the sound from an outboard boat in Charlotte Harbor, FL. This sound includes the same frequencies as fish sounds. The range over which sound-producing fishes could attract mates could be severely limited by increased levels of background noise.

Figure 2. Sounds produced by a small outboard boat recorded in Charlotte Harbor, FL. Most of the sounds are between 100 and 2500 Hz, which are in the same range as most fish sounds.

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