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

Report No. 6945
BBN Systems and Technologies Corporation
vice versa. Each successive research effort on most of these species expands
knowledge to such an extent that it is reasonable to assume that their full
repertoires have not yet been documented.
Nonvocal sounds made by marine mammals include tail and flipper slaps,
breaching sounds, jaw claps, bubble noises and underwater blow noises (Pryor
1986). Some marine mammals produce sounds inadver ;ently when engaged in other
activities. When baleen whales are feeding, the baleen may rattle as water
passes through it (Watkins and Schevill 1976). Ringed seals produce noise
when they scratch the ice to keep dive- holes open (Cummings et al., 1984).
2.2.1 Toothed whales--calls and echolocation signals
The vocalizations made by toothed whales can be classified into two
general groups: pure tone whistles and pulsed sounds. Pulsed sounds include
the high frequency clicks used in echolocation, low frequency clicks used for
communication, and complex grunts, screams, barks, quacks, squawks, blares
and moans.
Basic whistle types include trills, and sounds that are unmodulated,
ascending, descending, or wavering in frequency. A whistle can consist of one
such call type uttered singly or as a continuous series of the same or mixed
call types. Over the duration of a whistle, the amplitude of ascending and
descending call types can vary. Wavering frequency calls can be superimposed
on ascending/descending type whistles. Whistles can be continuous or have a
variable number bl-eaks and segments within one whistle. For any one species,
initial, final and peak frequencies may vary, as can the duration and intensity.
Whistles do not rise above 20 kHz and the lower frequency limit can be
as low as 260 Hz (Table 2.7). Source levels for whistles have rarely been
recorded. A sound pressure level of 180 dB re 1 uPa at 1 m has been measured
for pilot whale whistles. They may serve as identification calls and for
communication (Caldwell and Caldwell 1977 ; Herman and Tavolga 1980 ; Tyack
1986). The whistle repertoires of the white whale, pilot whale and Pacific
white sided dolphin are well developed.
Pulsed tones have been recorded only from the white whale and killer
whales. Most vocalizations made by the killer whale are pulsed tones (Ford
and Fisher 1983). These are complex and are used for identification and
coordination of group behavior (Ford and Fisher 1983; Hoelzel and Osborne
1986). Pulsed tones contain most of their energy tslow 8 kHz (Table 2.7). In
the white whale, pulsed tones as well as some whistles were associated with
social interaction situations (Sjare and Smith 1986b). Source levels of these
pulsed calls are unknown.
Non-echolocation click type signals made by the sperm whale are used for
social communication and the coordination of group behavior (Watkins and
Schevill 1977; Watkins et al. 1985). They have the same functions as the
whistles and pulsed tones of other species. The 2 kHz low frequency clicks
uttered by the harbor porpoise also may be used for communication. Other
species that do not whistle or make pulsed sounds may use moderate frequency
clicks for communication. Sperm whale clicks have most of their energy below