Introduction to Acoustics

Frequency (Hz)
150
100
50
0
0
a) b) c)
Underwater Acoustics 5.8 Acoustics and Marine Animals 199
100 200 300 400 500 600 700 800 900
Time (sec from 14:01 GMT)
70 80 90 100 110
120
130
Fig. 5.59 Whale spectrogram power spectral density are in units of dB re 1 µPa 2 /Hz. The blue-whale broadband signals
denoted by (a), (b)and(c) are designated “type A calls”. The FM sweeps are “type B calls”. The multiple vertical energy
bands between 20 and 30 Hz have the appearance of fin-whale vocalizations [5.109]
Marine mammal sounds span the spectrum from
10–200 000 kHz. Examples are: blue (see spectrogram
in Fig. 5.59) and fin whales in the 20 Hz region with
source levels as high as 190 dB, Wedell seals in the
1–10 kHz region producing 193 dB levels; bottlenose
dolphin, 228 dB in a noisy background, sperm whale
clicks are the loudest recorded levels at 232 dB. A list of
typical levels is shown in Table 5.4. Most of the levels
listed are substantial and strongly suggest acoustics as
a modality for monitoring marine mammals. Thus, for
example, Fig. 5.60 shows the acoustically derived track
of a blue whale over 43 days and thousands of kilometers
as determined from SOSUS arrays (see Introduction
to this chapter) in the Atlantic Ocean.
The issues mostly dealt with in marine mammal
acoustics are: understanding the physiology and behavior
associated with the production and reception of
sounds, and the effects that manmade sounds have on
marine mammals from actual physical harm to causing
changes in behavior. Physical harm includes actual
Table 5.4 Marine-mammal sound levels
Source Broadband source level
(dB re 1 µPa at 1 m)
Sperm whale clicks 163–223
Beluga whale echo-location click 206–225 (peak to peak)
White-beaked dolphin 194–219 (peak to peak)
echo-location clicks
Spinner dolphin pulse bursts 108–115
Bottlenose dolphin whistles 125–173
Fin whale moans 155–186
Blue whate moans 155–188
Gray whale moans 142–185
Bowhead whale tonals, moans and 128–189
song
Humpback whale song 144–174
Humpback whale fluke and flipper 183–192
slap
Southern right whale pulsive call 172–187
Snapping shrimp 183–189 (peak to peak)
Part A 5.8