Page 10 - Acoustics Today

Fig. 2. The gulf toadfish swimbladder is lined with sonic muscles, which are the fastest known contracting vertebrate muscles. The oscillogram and spectrogram show field recordings from the Gulf of Mexico. Each pulse in the oscillogram corresponds to a sonic muscle contraction. (toadfish photo: USGS).
Amorim et al., 2008; gobies: Lugli and Fine, 2003). Yet certain areas with high fish diversity, like tropical rivers, remain little studied. Interestingly, many invasive species, such as the walking catfish, likely produce sounds, and passive acoustics may provide a method to study their distribution.
Pioneering efforts by William Mowbray and Marie Poland Fish led to the publication of the only text devoted to characterizing fish sounds (Fish and Mowbray, 1970). They produced a compendium of fish sounds by collecting species and placing them in tanks to record the sounds they made. The original tape recordings from the University of Rhode Island have been recovered by Rodney Rountree and many are now available online at FishBase and the MacCauley Library at Cornell University.
For many species, early studies resorted to handling the fish to get them to produce sounds. While this technique
identifies fishes that are capable of producing sounds, it may not reveal their full repertoire and will overlook species that don’t produce sounds when handled. Underwater video cam- eras linked to hydrophones have been essential for docu- menting sound production associated with courtship and spawning in many species such as damselfish, hamletfish, and groupers. These tools have enabled us to unravel the full repertoire of fish sounds with recordings made in natural sit- uations, where fish are more likely to engage in aggressive and courtship interactions. For example, the recordings of red hind grouper by Fish and Mowbray showed they would produce a single knock when handled. When recordings were made on a spawning aggregation site, red hind were found to produce longer distinctive sounds consisting of repetitive pulses that graded into hums (Mann et al., 2010) (See Fig. 3).
Fig. 3. Red hind grouper single pulse sound recorded when handling the fish (left) (Fish and Mowbray, 1970). A diver deploys a passive acoustic recorder at Mona Island, Puerto Rico to record red hind sounds. Sound recorded from a naturally behaving red hind showing a complex pulse structure (right).
Remote Sensing of Fish 9