prerecorded advertisement calls (boatwhistles) of a marine species, the
oyster toadfish (Opsanus tau), in very shallow water sites (0.75–1.2 m) with
sandy-silt bottoms (water temperatures 24–27°C). All sounds were played
through a J-9 transducer. For pure tones, transmission loss was greatest
within the first 3 m from the transducer. For boatwhistles, transmission loss
was more gradual out to a distance of 5 m from the J-9 transducer, at which
point the signals were no longer detectable above background noise levels.
The boatwhistle’s fundamental frequency was attenuated more quickly
than either its second harmonic or the entire call. Hence, higher-frequency
components of the call were transmitted over a greater distance, consistent
with the predicted influence of water depth on cutoff frequency. Signal
attenuation values with distance doubling were about 10 dB more (approximately 30 * log 10 (r)) than that predicted for either spherical or cylindrical
spreading and similar to the range reported by Banner (1970) for continuous, random noise over a similar frequency range (see Section 10.3).
Figure 2.12 shows decrements in sound-pressure levels for the calls of
midshipman males at increasing distances from their nests. In this case,
sound levels were determined using calibrated amplifiers (Shure Brothers
Inc.) and a digital tape recorder (TEAC Corp.). Sound-pressure levels fall
off at a rate close to that predicted for spherical spreading, namely 6 dB per
distance doubling. Compared with the toadfish study summarized above,
these sounds were recorded in areas where nests are positioned in greater
water depths (~5 m) and have a harder substrate (rocky-gravel), both of
which may contribute to attenuation rates that are closer to theoretical
50
A.H. Bass and C.W. Clark
Figure 2.12. Transmission-loss profiles for the hum (total duration = 6 min; fundamental frequency = 109 Hz), growl (total duration = 1.93 sec; fundamental frequency
= 62.1 Hz), and grunt (total duration = 167 msec; fundamental frequency = 106 Hz)
from a single nest containing two type I males (28.0 cm and 18.0 cm standard length).
Also shown from top to bottom are curve fits for the growl, hum, and grunt, respectively. Nest temperature was 17.3°C (Brinnon, WA, June, 1999). Recordings courtesy of M. Marchaterre, Cornell University.
oyster toadfish (Opsanus tau), in very shallow water sites (0.75–1.2 m) with
sandy-silt bottoms (water temperatures 24–27°C). All sounds were played
through a J-9 transducer. For pure tones, transmission loss was greatest
within the first 3 m from the transducer. For boatwhistles, transmission loss
was more gradual out to a distance of 5 m from the J-9 transducer, at which
point the signals were no longer detectable above background noise levels.
The boatwhistle’s fundamental frequency was attenuated more quickly
than either its second harmonic or the entire call. Hence, higher-frequency
components of the call were transmitted over a greater distance, consistent
with the predicted influence of water depth on cutoff frequency. Signal
attenuation values with distance doubling were about 10 dB more (approximately 30 * log 10 (r)) than that predicted for either spherical or cylindrical
spreading and similar to the range reported by Banner (1970) for continuous, random noise over a similar frequency range (see Section 10.3).
Figure 2.12 shows decrements in sound-pressure levels for the calls of
midshipman males at increasing distances from their nests. In this case,
sound levels were determined using calibrated amplifiers (Shure Brothers
Inc.) and a digital tape recorder (TEAC Corp.). Sound-pressure levels fall
off at a rate close to that predicted for spherical spreading, namely 6 dB per
distance doubling. Compared with the toadfish study summarized above,
these sounds were recorded in areas where nests are positioned in greater
water depths (~5 m) and have a harder substrate (rocky-gravel), both of
which may contribute to attenuation rates that are closer to theoretical
50
A.H. Bass and C.W. Clark
Figure 2.12. Transmission-loss profiles for the hum (total duration = 6 min; fundamental frequency = 109 Hz), growl (total duration = 1.93 sec; fundamental frequency
= 62.1 Hz), and grunt (total duration = 167 msec; fundamental frequency = 106 Hz)
from a single nest containing two type I males (28.0 cm and 18.0 cm standard length).
Also shown from top to bottom are curve fits for the growl, hum, and grunt, respectively. Nest temperature was 17.3°C (Brinnon, WA, June, 1999). Recordings courtesy of M. Marchaterre, Cornell University.