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

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Report No. 6945 BBN Systems and Technologies Corporation North Aleutian Basin The sources used in the SNC Model analysis for the North Aleutain Basin area are representative of existing fishing, transportation, and cultural activities plus hypothetical oil industry operations. As shown in Table 5.8A, the dominant sources in this area for the late spring - summer season are the tug/barges, outdrives, and hypothesized seismic array. Important secondary sources are small craft, trawlers (in transit) and hypothesized large dredge. Outdrives and other high-speed small craft are dominant sources, because of the large number in operation during peak fishing seasons. The larger tugs and fishing trawlers, while not as numerous, contribute significantly because they generally have relatively high RPM propellers which produce cavitation noise for most vessel operating conditions. The southern portion of this area along the Alaska Peninsula is in an active volcanic zone (Sec. 3.2.5). As a result, sporadic low frequency noise is produced by bottom motion during earthquake events. During these events, the noise levels at frequencies below 50 Hz can be signicantly louder than the source levels of the industrial sources listed in Table 5.8A, with the possible exception of the seismic array. Sporadic seismic noise has not been given a rating in Table 5.8A because high level events are relatively infrequent, typically less than 1 per year of Magnitude 4 or greater (Fig. 3.5). Four species - gray whale, harbor seal, harbor porpoise, and Steller sea lion - were considered, together with the five sources just discussed, in the SER model analysis for this area. The results in Table 5.8B and Fig. 5.5A show that the gray whale - seismic array encounter again has the highest SER rating, followed by the gray whales encountering the tug/barges and outdrives. The model was not run using the seismic array or trawler in relation to the other species since the pinnipeds and harbor porpoises were assumed to be generally located near shore during this season. As shown by the SER values, harbor porpoise have a higher potential for acoustic interaction than the other small marine mammals as a result of their more sensitive low frequency hearing. There is a resident population of sea otters in the southern part of this area. No hearing sensitivity data are available for this species. It is expected that their hearing is optimized for airborne rather than underwater sound since they spend most of their time at or above the surface. Observations of the behavior of sea otters in the presence of an operating air gun and support vessel were made as part of an acoustic disturbance study of migrating gray whales (Malme et al. 1984). No significant changes in behavior were observed for operation as close as 900 m (Riedman 1984). The SNC analysis for the late fall - early winter season in the Nprth Aleutian Planning Area is shown in Table 5.9A. The group of sources used for the previous analysis was considered again after making changes in TL values and in the expected number of sources. The SNC ratings for all of the sources are reduced somewhat compared to those for the spring - summer season due to higher short-range TL and an estimated smaller number of operational vessels and small craft. The hypothesized seismic array along with tug/barges and outdrives are the dominant sources. The estimated smaller number of outdrives
Report No. 6945 BBN Systems and Technologies Corporation TABLE 5.8A STANOARDIZED WISE COYTRlWTlOW -EL, North Aleutian Plwning Area, Surfsce Layer Condition Ref. areas wed in mdel (kmA2): Total overall, 149000 ; Coastal (c), 3600 ; Fishing (f), 34400 ; Airports (a), 78 Ref. Range, 300 n; Max. Effutiw Range; ship, aircraft (km)- 27 0.9 (a - estimated) Ref. 300 11 I(ov.Srct.Corr. Fluc. Equiv. Encntr. Exp. SWC ratings Source (area) Type Speed Ominant W, Hz Max 113 Oct,Hz D.Bnd. Mx 113 Area TravTim Corr. Level Prob. Nu. D.Bnd 11x 113 (kts) fmin f u Ls1.d frq. LP,& Lr1.a Lr2,cB &,dB Tt/Tr TfITr Lq.d Pa Y UICl,& WCZ Tug/Barge (c) mvng 10 100 12500 171 630 162 129 120 -11 1 1 118 9.4-03 5 105 % l e Twin Outdrv.(s)mvng 20 40 16000 167 500 156 125 114 -11 0.75 0.8 112 1.l-02 15 106 95 e t 13' Yhrler tc) mvng 20 630 6000 159 4000 153 117 111 -11 0.73 0.8 104 I.&-02 20 W 93 e l Trawltr(f) 5 40 1000 157 100 147 115 105 -11 1 1 104 5.lE-04 20 Y 74 Trawler (f) mvng 10 l Drillship Dredge (AQ.) fixed fixed Seismic Array movng 5 8. 757-200 (a) mvng 400 TABLE 5.88 STAWARDIZEO EXPOSURE RATlWO ,-EL, Yorth Aleutian Ptming Area, Surf ace Layer Condi tion Source Informtion from SWC Ilodcl, Ref. Rmge - 300 m a - estimated value (c) - coastal area source (f) - fishing area source WURCE Dominant BY, is1 Fsh SeimicArray 20 160 Tuin Outdrv.(c) 40 16000 Tuin Outdrv.(c) 40 16000 Twin Outdrv.(c) 40 16000 Twin Outdrv.(c) 40 16000 13' Haler (c) 630 6000 13' Haler (c) 650 8000 13' Haler (c) 630 13' Haler (c) 650 0000 TuglBarge (c) 100 12500 lug18arge (c) 100 12500 lug/llarge tc) 100 12500 Tug/B.rge (c) 100 12500 Trawlercf) 40 4000 NO. WCl N d C* 1 101 e 20 106 e 20 106 l 20 106 e 20 106 ZOW l 2 0 w l 20 w e 20 w 5 105 e 5 105 e 5 105 l 5 105 l 5 93 RECEIVER Ds e Gray Hele 0.02 e Harbor sea1 0.44 l Harbor Porp. 0.02 (1) e Stel.Sea Lion 0.21 e Gray Ilhalt 0.02 t Harbor Seal 0.44 l Harbor Porp. 0.02 (0 l Ste1.Sea Lion 0.21 e Gray male 0.02 Harbor Seal 0.44 Harbor Porp. 0.02 (1) l Stel.Sea Lion 0.21 e Gray Uhale 0.02 Harbor Porp. 0.02 Hearing BY, kMz Sensitivity Lr3 Wcff Frl Frh fr -,dB Ss,d cB kHz e e e e l e e 0.09 9 e 40 41 149 20 t 101 60 e 109 130 e l 113 30 l l 116 20 111 50 111 130 e 106 20 t e 105 20 l 104 63 113 130 l l 115 30 t t 119 20 103 130 KR, Ref. SER- Area SWCl e e e 222 205 101 a a l 162 158 52 a e a 186 171 65 e e a 1% 147 41 a c e 195 178 R e e l 154 150 51 a l l 175 158 59 e e e 1s 131 32 e e t 177 160 61 e e e 164 160 55 e t e 191 174 69 e e e 155 158 43 e e e 197 180 75 l a l 169 152 59 Note (11: Heering chareteristic for California sea. lion used for Steller sea lion.
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H BOWERS BAW I ALEUTIAN ARC 3 STGEC
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Report No. 6945 L 1 A. Baird's Beak
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on the ice. The single calves remai
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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. 3.1 7 REPRESENTATIVE R
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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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FIG. D. 1 HUMAN VOCALIZATION AND AU
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FIG. D. 3 ESTIMATED HEARING CHARACT
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