WILLIAM N. TAVOLGA
154
the possibility .that some of the sounds produced by swimming fishes are
of internal origin, i.e., produced by muscular and skeletal movements
within the animal.
The most intense of these sounds are emitted when the animal turns
rapidly or changes its velocity. In his review of fish propulsion, Nursall
(1962) pointed out that the main thrust in a swimming fish arises from
transverse movements of the contralateral waves. Turning is accomplished
by a unilateral wave as the head of the fish turns, and the caudal portion
is used as a fulcrum. It is clear that lateral displacement of the medium
will arise during straight-line swimming, and these will tend to be
rhythmic since the body movements are rhythmic. The turning of the
head will produce a strong displacement of the medium. These displacements will, of course, result in compression waves, which can be detected
as sound by most hydrophones.
Skudrzyk and Haddle (1963) defined flow noise as turbulences and
concomitant pressure fluctuations produced by the motion of a body
through water. This is primarily a near-field phenomenon and, as such,
would not be propagated over large distances. Although the above study
was concerned with the noise generated by the motion of rigid objects,
such as vessels, it is obvious that surface turbulence and eddies would be
produced by swimming fish.
The locomotion of fish, therefore, produces pressure and displacement
effects in three possible ways: the more or less rhythmic effects of undulatory movement; the turbulence generated by flow noise; and, possibly,
internally generated locomotor sounds.
D. Characteristics of Fish Sounds
It has long been recognized that a verbal description of a sound is
inadequate and often misleading. This problem has been especially
troubling to observers attempting to describe sounds of animals such as
birds and amphibians. With the advent of high fidelity tape recording
equipment, the problem of preserving the data seemed to be solved, although precautions still had to be taken against artifacts resulting from
overloaded amplifiers, incorrect equalization, and other electronic difficulties. Photographs of oscilloscope tracings of sounds were frequently
used, and these analyses are still especially valuable for short, rapidly
pulsed sounds. Fish (1954) presented her data on sounds of fishes in the
form of frequency analysis graphs that were made with an octave band
filter.
An important improvement over the octave band filter was the de-
154
the possibility .that some of the sounds produced by swimming fishes are
of internal origin, i.e., produced by muscular and skeletal movements
within the animal.
The most intense of these sounds are emitted when the animal turns
rapidly or changes its velocity. In his review of fish propulsion, Nursall
(1962) pointed out that the main thrust in a swimming fish arises from
transverse movements of the contralateral waves. Turning is accomplished
by a unilateral wave as the head of the fish turns, and the caudal portion
is used as a fulcrum. It is clear that lateral displacement of the medium
will arise during straight-line swimming, and these will tend to be
rhythmic since the body movements are rhythmic. The turning of the
head will produce a strong displacement of the medium. These displacements will, of course, result in compression waves, which can be detected
as sound by most hydrophones.
Skudrzyk and Haddle (1963) defined flow noise as turbulences and
concomitant pressure fluctuations produced by the motion of a body
through water. This is primarily a near-field phenomenon and, as such,
would not be propagated over large distances. Although the above study
was concerned with the noise generated by the motion of rigid objects,
such as vessels, it is obvious that surface turbulence and eddies would be
produced by swimming fish.
The locomotion of fish, therefore, produces pressure and displacement
effects in three possible ways: the more or less rhythmic effects of undulatory movement; the turbulence generated by flow noise; and, possibly,
internally generated locomotor sounds.
D. Characteristics of Fish Sounds
It has long been recognized that a verbal description of a sound is
inadequate and often misleading. This problem has been especially
troubling to observers attempting to describe sounds of animals such as
birds and amphibians. With the advent of high fidelity tape recording
equipment, the problem of preserving the data seemed to be solved, although precautions still had to be taken against artifacts resulting from
overloaded amplifiers, incorrect equalization, and other electronic difficulties. Photographs of oscilloscope tracings of sounds were frequently
used, and these analyses are still especially valuable for short, rapidly
pulsed sounds. Fish (1954) presented her data on sounds of fishes in the
form of frequency analysis graphs that were made with an octave band
filter.
An important improvement over the octave band filter was the de-