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

Report No. 6945
BBN Systems and Technologies Corporation
disturbance response data are needed for other species before a broader based
testing of the procedure can be performed.
Chukchi Sea
Table 5.4A shows the model results for the summer 50% ice cover condition.
The sources considered were based on assumed'oil exploration and
drilling activity, together with representative commercial cargo barge and
near-shore small craft activity. The dredge example used was the AQUARIUS, a
transfer dredge which had the highest noise output of the examples obtained
for the study. The two drill rigs considered were a drillship (EXPLORER 11)
and a drilling barge (KULLUK). The icebreaker example used was based on the
ROBERT LEMEUR, an ice-breaking supply vessel, for which source level data are
available. The noise level output of larger Polar-Class icebreakers is
estimated to be significantly higher. (See Sec. 3.3.1 for details of noise
characteristics from these sources.)
The loudest sources in terms of maximum level at the reference range
(300 m) are the seismic array, icebreaker, dredge, and drilling barge. These
sources are considered to found operating anywhere within the entire planning
area with equal probability. The cargo barges operate primarily along the
coast in a coastal zone which is assumed to extend offshore to a range of
4 km. An estimated coastal zone area is used in determining the Pe value for
this source.
The sources selected for use with the SER ~ocel because of their high SNC
ratings were the seismic array, icebreaker, KULLUK., and the commercial tug/
barge combination. Although the received level ratings for the tug/barge type
of source are lower than those of several other sources such as the drillship,
the SNC rating is high because of its high probability of encounter. The
output level and spectrum for the dredge are similar to those of the KULLUK so
the results of the model analysis for the KULLUK can also be considered to
apply to the dredge. The review of mammal distribution in Section 2 indicated
that three species to be found in the Chukchi during the summer season in
relatively large numbers are gray whales, walruses, and white whales. The
results of the SER Model analysis using the four dominant sources and these
three species are shown in Table 5.4B.
The results of the SER analyses shown in Table 5.4B have been also
plotted in bar graph form to illustrate the relationships between the SNC1,
SER(ref) , and SER(area) values. The resulting graph is shown in Fig. 5.3.
Figure 5.3 is an SER rating comparison for the Chukchi Sea area. It is
based on values from Tables 5.4B and 5.5B for summer and winter seasons in
this area. The information presented allows a comparison of the acoustic
influence potential of the various major source and species interactions that
are possible in this area. Only the dominant sources and the species of
greatest population density and/or greatest importance are considered.