Michael L. Fine
We (Fine and collaborators) have studied various aspects of acoustic communication (sound production and hearing) in the oyster toadfish, channel catfish and several sciaenid species. Highlights include:
Our current and future emphasis will focus on understanding mechanisms of sound production, acoustic radiation and propagation of fish sounds. This information will aid in interpreting data from passive acoustics. In some species, for instance, sound frequency varies with fish size, but in others it is size independent. We have demonstrated that the toadfish advertisement call has a mildly directional pattern (several dB greater behind the fish), which correlates with its unusual heart shape (Fig. 1). Depending on the radiation of sounds from sciaenid fishes, their amplitude (a function of fish size and distance) might also vary with the fishs profile relative to the hydrophone.
Historically, the fish swimbladder has been characterized as a pulsating, resonant underwater bubble, which provides an omnidirectional (monopole) acoustical source useful in sound production and hearing. We contend that the classic beliefs about swimbladder acoustic function may not apply to all fishes. Fish sonic muscles are the fastest in vertebrates, something that does not seem necessary for exciting a resonant structure, i.e. ringing a bell or tapping a crystal wine glass. Recent work on the toadfish sonic muscle-swimbladder system provides evidence against the classic conceptions: its radiation pattern is directional, damping is rapid (Fig. 2), equivalent to an automobile shock absorber, a device that inhibits resonance, and sonic muscles drive it in an inefficient quadrupole fashion (Fig. 1) rather than as a pulsating monopole. Examination of swimbladder displacement, velocity and acceleration indicates that peak acoustic pressure occurs at the velocity maximum (Fig. 3). Therefore, rapid movement of the bladder appears to be necessary to generate an audible sound. Finally, deflating the bladder does not affect the toadfish audiogram (see Hong Yan), arguing against its classic role in audition.
It is our goal to provide similar information on species of interest for passive acoustics to aid in interpretation of calls recorded in the field.