Marine Environmental Research
Behavioural reactions of bowhead whales to seven 30–40 min underwater playbacks of recorded drillship and dredge noise were determined in 1982–1984. Some (but not all) bowheads oriented away when received noise levels and spectral characteristics were comparable to those several kilometres from actual drillships and dredges. During some playback tests, call rates decreased, feeding ceased, and cycles of surfacing, respiration and diving may have changed. Sensitivity of various whales to noise differed. Roughly half responded when the received level of noise was about 115 dB re 1 μPa on a broadband basis, or about 110 dB in one 13-octave band (20–30 dB above ambient). Such levels occurred 3–11 km from a drillship and dredge in the Canadian Beaufort Sea. Bowheads occasionally were seen < 5 km from actual drillships and dredges, where received noise levels were at least as high as during our brief playbacks. Thus, some bowheads may habituate to prolonged noise exposure. Alternatively, only the less sensitive individual whales may occur < 5 km from drillships and dredges.
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