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

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Report No. 6945 BBN Systems and Technologies Corporation ;ER RATING COMPARISON, SHUMAGIN AREA Surface Layer Conditions SNCl SER(ref)- OSER(area) Outdrlvo SER RATING COMPARISON, SHUMAGIN AREA, Neutral Gradient Conditions SNC1 SER(ref) OSER(area) - Solsmlc Arrav Figure 5.6. SER Rating Comparison, Shumagin Area. A. Surface Layer Conditions B. Neutral Gradient Conditions
Report No. 6945 BBN Systems and Technologies Corporation An analysis was not performed for gray whales and fin whales which may be in this area during part of the winter. Because of their assumed good hearing sensitivity at low frequencies, the SER values which would be obtained for these species would be high and similar to those obtained for the spring - summer period, with some changes due to different population dens it ies . 5.3 Zone of Influence Estimates for Major Noise Sources Observations on whale behavior as related to quantified acoustic exposure levels have been obtained for a few species such as the gray (Malme et al. 1983, 1984) ; bowhead (Richardson et al. 1985; Ljungblad et al. 1989) ; humpback (Malme et al. 1985) ; and white whales (Aubrey et al. 1986). These studies have used movement away from a sound source (avoidance) as one of the main indicators of a desire to reduce sound exposure. Analyses of response data obtained from playback experiments and tests using air gun sources have provided estimates of the probability of avoidance for a limited set of industrial noise sources. The disturbance criteria are usually given in terms of the sound exposure level which will produce avoidance behavior in 50% of the animals exposed. For playback experiments with gray whales the sound level which produced a 50% probability of avoidance was found to vary within a range of 117 to 125 dB depending on the playback stimulus. The stimuli used were recordings of a drillship, drilling platform, semi-submersible platform, production platform and helicopter. The effective level of the playback signal was determined using the dominant bandwidth of the signal as defined previously in Section 3. Studies of the behavioral responses of bowhesd whales to playback of drillship and dredge noise and to noise from nearby boats have developed a somewhat different criterion (Richardson et al. 1985; Miles et al. 1987). In these studies the ratio of the received level in the strongest 1/3 octave band of the stimulus signal to the ambient noise in the same band was used as the primary measurement parameter. It was found that, while individual responses were highly variable, a S/N ratio of 30 dB caused about 50% of bowhead whales to exhibit avoidance behavior during drillship and dredge noise playbacks. Reactions to boats seemed to occur at lower S/N ratios. In developing the estimates of the range at which a 50% probability of avoidance would occur for the major noise sources determined in this study, we have considered both the constant effective level criterion, using 120 dB as representing an average avoidance level for the various sources, and the 30 dB S/N criterion using the highest 1/3 octave band in the signal. As shown by the SER ratings determined in the previous section, the gray whale is the species that is potentially the most impacted by the major underwater sound sources considered. This is a result of the assumed high sensitivity of this species to low frequency sound and its high abundance relative to most other baleen whales in Alaskan waters. Presumably the hearing characteristics of the bowhead, humpback, and fin whales are comparable to the assumed characteristic of the gray whale, and as a result they also are potentially more influenced by the low frequency noise sources considered here than are the pinnipeds and odontocetes.
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Report No. 6945 L 1 A. Baird's Beak
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Table 2.8. Characteristics of Under
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FIG. 3.2 NOISE SPECTRA IN SHALLOW W
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Adapted From K.H. Jacob (1986) Cali
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FIG. 3.8 ESTIMATED OVERALL SOUND LE
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FIG. 3. Q UNDERWATER NOISE SPECTRA
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FIG- 3.1 1 STATISTICAL ANALYSIS OF
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FIG- 3-12 STATISTICAL ANALYSIS OF C
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-- Alr Gun Array + Vlbrosels -* Ice
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FIG. 3.14 REPRESENTATIVE SHIPS AND
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FIG. 3-18 REPRESENTATIVE CULTURAL S
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FIG. 4.1 CORRECTION TO 300 M REFERE
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A. 6. ~la~onca 011shwe. mm I C. MSI
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FIG. D. 1 HUMAN VOCALIZATION AND AU
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FIG. D. 3 ESTIMATED HEARING CHARACT
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