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

Report No. 6945
BBN Systems and Technologies Corporation
The SNC ratings for the area show that the seismic array dredge,
tug/barges and outdrives are the dominant sources with small craft,
represented by the "whaler", and dredges rating as strong secondary sources.
The review of marine mammal distribution in Section 2 showed that gray whales
and walruses are important species in this area during the late spring and
summer season. These species were used together with the five important
sources determined above as the basis for the SER analysis shown in Table
5.6B, and illustrated by the graphs in Fig. 5.4A.
The results of the SER analysis show that, in this region as well as in
the Chukchi, gray whales are potentially the species which may be most
influenced by the noise sources. In this case the seismic source shows the
most potential for causing reactions with tug/barge operations having the
second highest SER rating. The SER ratings for the outdrives and the tugs are
strongly influenced by assumptions about the number operating. The assumed
values are based on general information from the region but are not derived
from specific on-site data. The SER values for walrus while not as high as
those for gray whales, show a moderate potential for acoustic influence since
the SER values are generally more than 50 dB higher than the SNC values for
the input sources. The seismic array again has the highest SER rating. This
conclusion is subject to revision if hearing data for the walrus become
available since it is based on the assumption that walrus hearing characteristics
are similar to those for California sea lions.
The results of the model analysis for the late fall - early winter
conditions in Norton Basin are shown in Table 5.7A. An icebreaker source has
been added to the group of sources considered in the previous analysis. The
numbers of the multiple sources operating have been reduced to reflect the
probable seasonal effect. The resulting SNC ratings show that a seismic array
retains its dominance followed by the icebreaker, coastal dredge, tug/barges,
and outdrives. The estimated reduction in the number of outdrives and tugs
operating has reduced their SNC ratings to less than that of the dredge.
Important species present in the area during the late fall - early winter
season are ringed seal and walrus. These species have been used together with
the dominant four sources listed previously as the basis for the SER analysis
(the SER results for outdrives are expected to be similar to those for the .
tug/barges).
The results, presented in Table 5.7B and in the graphs in Fig.
5.4B, show that the highest rating is for the ringed seal - seismic array
encounter, with lower values occurring for the ringed seal - icebreaker and
ringed seal - dredge encounters. The ringed seal - seismic array encounter
may not occur very frequently in the real world because of the need for
seismic vessels to operate well clear of ice covered areas as opposed to the
propensity of ringed seals to seek out ice-covered areas. The ringed seal -
icebreaker encounter, with a relatively high SER rating, is much more probable
and the ri2ged seal - dredge encounter less likely. The SER results for
walrus show a moderate interaction potential for the seismic array and icebreaker
encounters which are lower than the ratings given the ringed seal
encounters. The area SER ratings for all species are based on assumed density
values and may be subject to revision when more information becomes available.