Analysis and Ranking of the Acoustic Disturbance Potential of ...

Report No. 6945
BBN Systems and Technologies Corporation
16 kHz (Table 2.7). Low to moderate frequency click sounds made by other
species -have lower limits of 40 Hz to 2 kHz (Table 2.7).
Echo-location clicks from toothed whales are the highest frequency sounds
produced by any marine mammals. In the white whale they range from 40 to 120
kHz (Au e$ al. 1985, 1987) and in the harbor porpoise they range from 100 to
160 kHz (Mdhl and Anderson 1973). The sound intensity of echolocation clicks
has been reported to range from 132 to 222 dB re 1 pPa at 1 m (Table 2.7).
Moreover, these signals are highly directional and, at least in the white
whale and bottlenose dolphin, have beamwidths (to the -3, dB points) of 5 to 12
degrees from the major axis (Au et al. 1986, 1987). Source levels and
frequencies are variable within as well as between species; toothed whales
apparently adjust their click frequencies and levels for optimum echolocation
capabilities under varying environmental conditions ( Au et al. 1985). When
echolocating, the white whale usually emits a series of about 16 to 42 clicks
(Au et al. 1985). In the white whale the typical interclick interval for the
main-echolocating clicks is 44 ms (Au et al. 1985). Typical click durations
for odontocetes are less than' 1 ms and can be as low as 35 ps (Popper 1980).
2.2.2 Baleen whales
Most sounds made by fin, blue, minke and sei whales (genus ~alaeno~tera)
are low in frequency and of moderate intensity. Most vocalizations are below
3 kHz and have source levels of 15 1 to 188 dB re 1 pPa at 1 m (Table 2.8) .
The fin whale produces a repeated stereotyped 20 Hz call during winter that
could be a display associated with reproduction (Watkins 1981; Watkins et al.
1987). .These calls have been recorded from most ice free waters in winter,
but not specifically from the Bering Sea (Watkins et al. 1987). The
significance and uses of other calls are unknown.
Some moderate to high frequency click sounds have been recorded in the
presence of blue, fin and minke whales (Beamish and Mitchell 1971, 1973;
Beamish 1979; Thompson et al. 1979). Frequencies were 3.3 to 31 kHz and
source levels were 130 to 159 dB re 1 pPa at 1 m (Table 2.8). Beamish and
Mitchell (1973) raised the possibility that baleen whales use echolocation.
However, other researchers have not recorded these click sounds and believe
that there is no evidence to show that baleen whales use echolocation (Norris
1981 ; Watkins 1981).
Humpbacks are very vocal when on their southern wintering grounds. The
songs and social sounds produced in late fall and winter have been well
studied (Tyack 1981; Payne and Guinee 1983). Humpbacks do not sing and are
less vocal when on their summering grounds in the Gulf of Alaska (Thompson et
al. 1986). During summer, sounds are generally in the 20 to 2000 Hz range
with intensities of 144 to 192 dB re 1 uPa at 1 m (Thompson et al. 1986).
Gray whales are vocal when migrating and when on their southern wintering
grounds (Fish et al. 1974; Norris et al. 1977; Dahlheim et al. 1984). Sounds
made on the summer feeding grounds in the Bering Sea are similar to those made
while on the wintering grounds (Moore and Ljungblad 1984). The behavioral
significance of the sounds is unknown (Dahlheim et al. 1984; Moore and
Ljungblad 1984). On both the summering and wintering grounds, frequencies of