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

Report No. 6945
BBN Systems and Technologies Corporation
Sperm, right, fin, sei, and minke whales and Dall's and harbor porpoise
are found in the Bering Sea in summer. Dall's and the harbor porpoise and
minke whales range into the Chukchi Sea. Cuvier's beaked, Bering sea beaked
and Baird's beaked whales summer in the Bering Sea. Cuvier's beaked and the
Bering Sea beaked whale are year round residents. All of these species
vocalize and can be expected to make some contribution to ambient noise
levels.
Fall and Winter - In fall, Alaskan marine mammals migrate to their winter
grounds. Because much of the spring time vocalization is related to reproductive
activities, the contribution of marine mammal sounds to ambient noise
would be expected to be lower in fali than in spring. Apart from bowhead and
a few white whale recordings made in fall during several studies, there are no
specific reports of sounds made by Alaskan marine mammals during fall. There
is insufficient information from other areas to establish the nature and rates
of vocalizations in fall.
Bowheads, walruses, white whales, bearded, ribbon, ringed, northern fur,
harbor and spotted seals and Steller sea lions all winter in the Bering Sea
near or south of the ice edge. Minke whales, Dall's porpoise and the harbor
porpoise winter in the open water of the Bering sea. Winter distribution of
walruses and other species depends on ice conditions. Ringed seals and a few
bearded seals are the only inhabitants of the winter fast ice in the Chukchi
and Beaufort Seas. Vocal behavior of Alaskan species in winter has not been
studied.
2.3 Marine Manrmal Hearing*
The hearing ability of a marine mammal is a complex function of several
specific abilities or parameters:
1. The intensity of sound that is barely audible in the absence of
ambient noise. This absolute hearing threshold varies with
frequency, and the curve relating the threshold intensity to
frequency is called the audiogram. Some species are more sensitive
than others, and the frequency of peak hearing sensitivity varies
among species.
2. The signal-to-noise (S/N) ratio that is required to detect a sound
signal in the presence of background noise. This is called the
"critical ratio" and is also a function of frequency.
3. The ability to localize the direction from which a sound is arriving.
Animals with good localization abilities should be able to detect
signals at a lower S/N ratio than animals with poor localizaticn
abilities, provided that the noise source masking the signal is not
omnidirectional, and that signal and noise are not arriving from the
same direction.
*W.J. Richardson, LGL Ltd.