160
WILLIAM N. TAVOLGA
were given by Moulton ( 1958), Tavolga ( 1960), and Winn ( 1964) in
spectrograms. In the majority of species, the sounds consist of single
pulses with a duration of 20-100 msec each. Some forms characteristically
produce a train of such pulses, and the repetition rates are probably
species-specific. Sounds of the black grouper, Mycteroperca bonaci,
usually occur in volleys of 4 or 5 pulses each, while other species normally emit one sound pulse at a time (Tavolga, 1960). Squirrelfish,
Holocentmcs, produce rattling volleys of up to 20 pulses in quick succession (Winn and Marshall, 1963). Many species of croakers and drumfish
also produce such trains of pulses, and Winn (1964) classified such
emissions as “iixed-interval signals.” He proposed that this kind of temporal patterning can serve as a primitive means of communication.
Long, sustained tones are unusual. The boat-whistle sounds of toadfish vary from 350 to 450 msec in length, and occasional yelps of the gafftopsail catfish may reach 500 msec in duration (Tavolga, 1960).
The low-pitched pulses of many species are extremely difficult to
distinguish from one another on the basis of acoustical characteristics
alone. Harmonic structure is greatly affected by the conditions of recording and the equipment used. There is little known as to the consistency with which certain species produce characteristic pulse trains.
The problem of identification of sound sources, therefore, is one that will
require considerably more data than are now available.
3. HYDRODYNAMIC AND SWIMMING SOUNDS
The character of sounds produced by the motion of fishes through the
water has only recently been recognized and described. Thus far, Moulton (1960b) has been the only investigator to report any spectral analyses
on such sounds. He has found that the sounds are nonharmonic with the
dominant frequencies extending far below 100 Hz.
The main sound output from individual or schooling fish occurred
when there was a rapid change in direction or speed. The sound resembled a low roar or that of a wooden mallet striking the side of a boat
under water. Such sounds could be detected from single predatory fish
such as jacks or barracuda (Fig. 15). Sounds of veering schools of sardines, herrings, and anchovies were of lower amplitude and appeared
to have more high frequency components (Tavolga, 1964b).
The pressure fluctuations produced by flow noise are affected by a
wide variety of factol’s such as surface roughness, shape, and velocity.
The predominant frequencies, upon spectral analysis, are in the range
below 500 Hz, and the frequencies below 100 Hz are least affected by
changes in the above variables (Skudrzyk and Haddle, 1963).
WILLIAM N. TAVOLGA
were given by Moulton ( 1958), Tavolga ( 1960), and Winn ( 1964) in
spectrograms. In the majority of species, the sounds consist of single
pulses with a duration of 20-100 msec each. Some forms characteristically
produce a train of such pulses, and the repetition rates are probably
species-specific. Sounds of the black grouper, Mycteroperca bonaci,
usually occur in volleys of 4 or 5 pulses each, while other species normally emit one sound pulse at a time (Tavolga, 1960). Squirrelfish,
Holocentmcs, produce rattling volleys of up to 20 pulses in quick succession (Winn and Marshall, 1963). Many species of croakers and drumfish
also produce such trains of pulses, and Winn (1964) classified such
emissions as “iixed-interval signals.” He proposed that this kind of temporal patterning can serve as a primitive means of communication.
Long, sustained tones are unusual. The boat-whistle sounds of toadfish vary from 350 to 450 msec in length, and occasional yelps of the gafftopsail catfish may reach 500 msec in duration (Tavolga, 1960).
The low-pitched pulses of many species are extremely difficult to
distinguish from one another on the basis of acoustical characteristics
alone. Harmonic structure is greatly affected by the conditions of recording and the equipment used. There is little known as to the consistency with which certain species produce characteristic pulse trains.
The problem of identification of sound sources, therefore, is one that will
require considerably more data than are now available.
3. HYDRODYNAMIC AND SWIMMING SOUNDS
The character of sounds produced by the motion of fishes through the
water has only recently been recognized and described. Thus far, Moulton (1960b) has been the only investigator to report any spectral analyses
on such sounds. He has found that the sounds are nonharmonic with the
dominant frequencies extending far below 100 Hz.
The main sound output from individual or schooling fish occurred
when there was a rapid change in direction or speed. The sound resembled a low roar or that of a wooden mallet striking the side of a boat
under water. Such sounds could be detected from single predatory fish
such as jacks or barracuda (Fig. 15). Sounds of veering schools of sardines, herrings, and anchovies were of lower amplitude and appeared
to have more high frequency components (Tavolga, 1964b).
The pressure fluctuations produced by flow noise are affected by a
wide variety of factol’s such as surface roughness, shape, and velocity.
The predominant frequencies, upon spectral analysis, are in the range
below 500 Hz, and the frequencies below 100 Hz are least affected by
changes in the above variables (Skudrzyk and Haddle, 1963).