6. SOUND PRODUCTION AND DETECTION
157
Such sounds have been described verbally as rasps, scratches, clicks,
chirps, and scrapes.
The second category of stridulatory sounds are those in which the
swim bladder plays some part in determining the quality of the sound.
Verbally, the sounds have been called grunts, croaks, thumps, knocks,
etc. The frequency range is generally from 1000 to 8000 Hz, and the predominant frequencies are below 1000 Hz. Comparison of the analyses
made by Fish (1954), Moulton (1958), and other authors shows a considerable divergence of data as to frequency range and predominant
pitch. It is probable that the different types of equipment, different methods of eliciting the sonic behavior, and, most important, the different
conditions under which recordings were made can account for the discrepancies in the data.
2. SWIM BLADDER SOUNDS
Sounds produced by the vibration of muscles around or attached to
the swim bladder are usually recognizable by their harmonic structure.
If accompanied by stridulation, the harmonics can sometimes be partially
masked in a spectrogram, but to the ear these sounds seem vibrant and
possess a tonal quality. A number of parameters of such sounds can be
defined and measured by the use of spectrographic and oscillographic
analysis. The fundamental and predominant frequencies usually can be
determined. If the sound is a sustained call, its duration usually varies
within narrow limits. Often the sound consists of a number of rapidly
repeated pulses, and in such instances it is necessary to know the duration
of each pulse, the pulse repetition rate, and the usual number of pulses
within the sound complex.
The number and relative strengths of harmonics is extremely variable.
In studies on the sounds of marine catfish (Tavolga, 1962), it became
evident that the harmonic components could be varied by changing the
character of the surroundings, the type of hydrophone, the distance from
the second source, and the recording and analyzing levels. The hypothesis
was advanced that the actual emitted sound was virtually a pure tone.
In the process of listening to the boat whistle calls of toadfish, Opsanus
tau (Fig. 12), Tavolga ( 1964b) recorded a long series of sounds emitted
by single individuals that remained in the same position for many hours.
Several environmental variables were found to affect the number and
relative intensities of harmonics, e.g., the distance of the hydrophone from
the sound source was of prime importance. Schneider (1967) found that
the construction material of an aquarium tank affected the quality of the
recorded sounds of Therapon.
The midshipman, Porichthys notutus, is also a member of the toadfish
157
Such sounds have been described verbally as rasps, scratches, clicks,
chirps, and scrapes.
The second category of stridulatory sounds are those in which the
swim bladder plays some part in determining the quality of the sound.
Verbally, the sounds have been called grunts, croaks, thumps, knocks,
etc. The frequency range is generally from 1000 to 8000 Hz, and the predominant frequencies are below 1000 Hz. Comparison of the analyses
made by Fish (1954), Moulton (1958), and other authors shows a considerable divergence of data as to frequency range and predominant
pitch. It is probable that the different types of equipment, different methods of eliciting the sonic behavior, and, most important, the different
conditions under which recordings were made can account for the discrepancies in the data.
2. SWIM BLADDER SOUNDS
Sounds produced by the vibration of muscles around or attached to
the swim bladder are usually recognizable by their harmonic structure.
If accompanied by stridulation, the harmonics can sometimes be partially
masked in a spectrogram, but to the ear these sounds seem vibrant and
possess a tonal quality. A number of parameters of such sounds can be
defined and measured by the use of spectrographic and oscillographic
analysis. The fundamental and predominant frequencies usually can be
determined. If the sound is a sustained call, its duration usually varies
within narrow limits. Often the sound consists of a number of rapidly
repeated pulses, and in such instances it is necessary to know the duration
of each pulse, the pulse repetition rate, and the usual number of pulses
within the sound complex.
The number and relative strengths of harmonics is extremely variable.
In studies on the sounds of marine catfish (Tavolga, 1962), it became
evident that the harmonic components could be varied by changing the
character of the surroundings, the type of hydrophone, the distance from
the second source, and the recording and analyzing levels. The hypothesis
was advanced that the actual emitted sound was virtually a pure tone.
In the process of listening to the boat whistle calls of toadfish, Opsanus
tau (Fig. 12), Tavolga ( 1964b) recorded a long series of sounds emitted
by single individuals that remained in the same position for many hours.
Several environmental variables were found to affect the number and
relative intensities of harmonics, e.g., the distance of the hydrophone from
the sound source was of prime importance. Schneider (1967) found that
the construction material of an aquarium tank affected the quality of the
recorded sounds of Therapon.
The midshipman, Porichthys notutus, is also a member of the toadfish