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

Report No. 6945
BBN Systems and Technologies Corporation
Although much speculation about some features of baleen whale hearing is
possible, empirical measurements are highly desirable. It is technically
feasible to obtain an audiogram from a beached or restrained baleen whale
(Ridgway et al. 1981; Ridgway and Carder 1983). Empirical data are necessary
before any confident predictions about mysticete auditory capabilities are
possible.
2.4 Reactions of Marine Mammals to Man-Made Noise*
Reactions or lack of reactions of various marine mammals to different
types of man-made sounds have been mentioned in many studies. Studies
reported prior to 1983 were reviewed by Richardson et al. (1983). An updated
version of that review considering. studies done up to mid-1988 will soon be
available (Richardson et al. 1989). Similarly, Johnson et al. ( 1989) reviewed
literature and unpublished information about disturbance reactions of Alaskan
pinnipeds. However, relatively few of the studies have provided specific
information about the threshold sound levels, signal-to-noise ratios, or
spectral characteristics at which marine mammals start to react. Some studies
have provided information about reaction distances. In cases where sound
attenuation rates can be estimated as a function of distance, these "distance
threshold" data can provide approximate information about threshold sound
levels at which reactions can be expected to begin.
This section 'summarizes selected studies of behavioral reactions of
marine mammals to man-made noise, emphasizing the few studies in which the
threshold of responsiveness was reported in terms of the received sound level
.~t which behavioral reactions began. Studies in which the threshold reaction
distance was reported are mentioned when the data may be specific enough to
allow reasonably reliable estimates of sound levels as a function of distance.
This is most likely to be true in the case'of airborne sound propagation,
e.g., from passing aircraft to pinnipeds hauled out on land or ice. For more
details about all of the topics summarized below, the reader is referred to
the more comprehensive reviews of Richardson et al. (1983, 1989) and Johnson
et al. (1989).
2.4.1 Aircraft
Reactions of marine mammals to aircraft have been reported in many
studies, but it was rarely documented whether the reaction was attributable to
sound, vision or some other stimulus. Almost none of these reports have
provided data on sound levels received by the mammals; some reports have
provided estimates of the distances at which the mammals first react. These
distances are quite variable, apparently depending on factors such as aircraft
type, distance and altitude at closest approach, and flight pattern (straight
line, circling, passing directly overhead vs. to the side, etc.).
Pinnipeds--Seals, sea lions and walruses that haul out on land or ice are
probably the most sensitive marine mammals with respect to aircraft. These
pinnipeds often rush into the water when disturbed by a passing aircraft.
*W. John Richardson, LGL Ltd.