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

Report No. 6945
BBN Systems and Technologies Corporation
A major species of concern for the spring - summer condition in the
Shumagin area is the fin whale. Since no hearing sensitivity data are available
for this species, an assumption was made that the fin whale hearing
characteristic is similar to that of the gray whale. It'is probable that
their low frequency sensitivity is better that that of the gray whale since
their vocalization range extends to below 20 Hz. With this information, a
hearing sensitivity curve for this species was estimated by modifying the
previously developed gray whale curve as shown in Appendix D. This permitted
an SER analysis with results as shown in Table 5.10B and illustrated in Fig.
5.6A. The estimated SER ratings are somewhat higher than those obtained for
the gray whale in the North Aleutian Basin. This is a result of the extended
low frequency hearing range which was assumed to be appropriate for the fin
whale. The highest SER rating is obtained for the seismic array with the
large tanker somewhat lower. Though the SNC rating for the tanker is considerably
higher than that of the seismic array, the dominant output of the
tanker is at very low frequencies, estimated to be below the most sensitive
region of the whalesf hearing curve. While gray whales are present in this
area during migration periods, no specific SER analysis was done since the
values would be only slightly lower that those obtained for fin whales.
Other important species found in this region during the spring - summer
season are humpback whales, killer whales, and Steller sea lions. The SER
results for humpback whales are expected to be similar to those for fin whales
so a specifc analysis was not made for this'species. The SER ratings for
killer whales and Steller sea lions show that killer whales have the higher
potential response with SER ratings larger than those of the fin whale for
outdrive sources. The ratings for the Steller sea lion are medium to low for
all the sources considered.
The period for neutral gradient conditions in the Shumagin area would
extend from late fall through winter and into early spring since no ice forms
in this region. The SNC analysis for this period used the same sources as
shown in Table 5.10A with the numbers adjusted for TL changes and a somewhat
reduced vessel traffic during the winter period. The results of the SNC
analyis shown in Table 5.11A are similar to those obtained for the spring -
summer season with the large tanker being the dominant source and the
hypothetical seismic array and ferry/cargo vessels secondary sources.
The principal species of concern in this area during the winter season
include fur seals, Dallls porpoise, and Steller sea lion. No hearing
sensitivity data are available for Dallls porpoise so data from the harbor
porpoise were assumed to be similar. The results of the analysis, shown in
Table 5.11B and Fig. 5.6B, suggest that the probability of acoustic interaction
may be high for the fur seal and Dallfs porpoise with the large tanker
having the highest SER values. The Steller sea lion SER ratings are also
relatively high for the tanker. For the other sources, the seismic array -
fur seal encounter also has a relatively high SER value, but this encounter
may not occur very often in survey operations.