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

Report No. 6945
BBN Systems and Technologies Corporation
2.4.4 Dredging and marine construction
Dredges constitute some of major sources of underwater sound in certain
nearshore areas. Fraker (1977a,b) observed that white whales reacted less to
stationary dredges than to moving tug-barge combinations that emitted similar
sound levels. White whales sometimes approached as close as 400 m from an
operating dredge. Bowhead whales also were observed within 800 m of a suction
dredge during aerial surveys, and industry personnel have reported that they
sometimes were seen considerably closer than that (Richardson et a1 . 1985a, b ,
MS). Underwater noise from the dredge was clearly detectable out to distances
of several kilometers, indicating that the white whales and bowheads may
tolerate considerable dredge noise. However, underwater playback experiments
using recorded sound from the same dredge showed that bowhead whales exhibited
strong avoidance reactions when exposed to received broadband noise levels of
122-131 dB re 1 vPa, or 21-30 dB above the ambient noise levels at the times
of the experiments (Richardson et al. 1985b, MS).
Insofar as we are aware, no quantitative data are available on reactions
of other species of cetaceans or of pinnipeds to dredging and construction
activities.
2.4.5 Offshore drilling and production facilities
Several anecdotal accounts have been published ,about the occurrence of
various marine mammals (mainly cetaceans) near drilling and production sites
(Richardson et al. 1989). In addition, controlled studies have been done to
determine the sensitivity of white, gray, humpback and bowhead whales to
underwater playbacks of drilling and ( in some species ) product ion sounds.
White whales have often been seen within 100 m of artificial islands that
were "operationalw and presumably drilling (Fraker 1977a,b; Fraker and Fraker
1979). Reactions of white whales to underwater playbacks of recorded sounds
from a semisubmersible drillship have been tested in both the field (Stewart
et al. 1983) and in captivity (Awbrey et al. 1986). Stewart et al.
demonstrated avoidance reactions, but did not measure the sound levels that
elicited avoidance. Awbrey et al. found that captive white whales were
briefly startled by the onset of semisubmersible noise, but later swam within
1 m of the sound projector where the received noise level was at least 153 dB
re 1 pPa. Overt behavior was not markedly affected by exposure to strong
semisubmersible noise, and plasma catecholamine levels were not affected,
suggesting that the animals were not stressed. These results may be another
example of the degree to which white whales can adapt to repeated or ongoing
man-made noise when it is not associated with negative consequences (see
"Ships and Boats" section, above).
Bowhead whales whose behavior seemed normal have been seen within 10-
20 km of drillships on several occasions, and on two occasions were as close
as 8 and 4 km while the ship was drilling (Richardson et al. 1985a,b, MS).
Industry personnel have reported closer sightings. Broadband sound levels
4 and 10 km from one of the drillships involved were 118 and 109 dB re
1 vPa, respectively, or 20 and 11 dB above the average background.leve1 in the