W l L L l A M N. IAVULLm
1x5
Marshall ( 1962), Moulton ( 1963), Protasov ( 1965), Schevill et al. ( 1962),
Schneider ( 1961), and Tavolga ( 1960, 1965, 1967~). Two international
symposia on marine bioacoustics covered many aspects of the field,
including sound production in fishes, cetaceans, and other marine organisms ( Tavolga, 1964a, 1967a).
A serious problem encountered in obtaining recordings of aquatic
animals under natural conditions is that the listener is often working
blindly and thus the identification of the sound producer often becomes
impossible. A major approach to the solution of this problem has been
to accompany sonic observations with visual observations by means of
underwater television. A unique installation of this sort is now located
off Bimini, Bahamas (Steinberg et al., 1962; Steinberg and Koczy, 1964;
Kronengold et al., 1964). This system has been undergoing constant improvement and modification and has provided a large body of data on
sonic species of fish (Cummings et al., 1964, 1966; Steinberg et al., 1965).
B. Underwater Acoustics
Any study of sound production or sound detection in fishes necessitates an understanding of the acoustic properties of water as a medium.
Since water is much denser than air, the velocity of sound in water is
almost 1500 meters/sec while in air it is about 330 meters/sec. In air,
sound velocity is affected slightly by humidity, temperature, and barometric pressure. In water, temperature and pressure are independent
variables in shallow areas, while at greater depths pressure affects the
temperature. The curves that relate sound velocity to depth, therefore,
become quite complex (Albers, 1965; Tschiegg and Hays, 1959; MacKenzie, 1960) (Fig. 1). Salinity increases sound velocity, and in the
oceans sound velocity may attain 1540 meters/sec.
As a corollary to this almost fivefold difference in sound velocity, c,
between air and water, the wavelengths, h, of underwater sounds are
almost five times the length of those in air for the same frequency, f, i.e.,
Since water is about a thousand times denser than air, more input
energy is required to initiate the propagation of sound in water. However, once the sound is propagated, the acoustic energy will be transmitted faster in water. This transmission is further enhanced by the
reflection of sound from the water surface (up to 99.9% is reflected back),
from the sea bottom, and from interfaces that are formed by layers of
water at different temperatures (Vigoreux, 1960; Albers, 1965).
If we measure the sound level under ideal conditions, that is, with
h = c / f .
1x5
Marshall ( 1962), Moulton ( 1963), Protasov ( 1965), Schevill et al. ( 1962),
Schneider ( 1961), and Tavolga ( 1960, 1965, 1967~). Two international
symposia on marine bioacoustics covered many aspects of the field,
including sound production in fishes, cetaceans, and other marine organisms ( Tavolga, 1964a, 1967a).
A serious problem encountered in obtaining recordings of aquatic
animals under natural conditions is that the listener is often working
blindly and thus the identification of the sound producer often becomes
impossible. A major approach to the solution of this problem has been
to accompany sonic observations with visual observations by means of
underwater television. A unique installation of this sort is now located
off Bimini, Bahamas (Steinberg et al., 1962; Steinberg and Koczy, 1964;
Kronengold et al., 1964). This system has been undergoing constant improvement and modification and has provided a large body of data on
sonic species of fish (Cummings et al., 1964, 1966; Steinberg et al., 1965).
B. Underwater Acoustics
Any study of sound production or sound detection in fishes necessitates an understanding of the acoustic properties of water as a medium.
Since water is much denser than air, the velocity of sound in water is
almost 1500 meters/sec while in air it is about 330 meters/sec. In air,
sound velocity is affected slightly by humidity, temperature, and barometric pressure. In water, temperature and pressure are independent
variables in shallow areas, while at greater depths pressure affects the
temperature. The curves that relate sound velocity to depth, therefore,
become quite complex (Albers, 1965; Tschiegg and Hays, 1959; MacKenzie, 1960) (Fig. 1). Salinity increases sound velocity, and in the
oceans sound velocity may attain 1540 meters/sec.
As a corollary to this almost fivefold difference in sound velocity, c,
between air and water, the wavelengths, h, of underwater sounds are
almost five times the length of those in air for the same frequency, f, i.e.,
Since water is about a thousand times denser than air, more input
energy is required to initiate the propagation of sound in water. However, once the sound is propagated, the acoustic energy will be transmitted faster in water. This transmission is further enhanced by the
reflection of sound from the water surface (up to 99.9% is reflected back),
from the sea bottom, and from interfaces that are formed by layers of
water at different temperatures (Vigoreux, 1960; Albers, 1965).
If we measure the sound level under ideal conditions, that is, with
h = c / f .