The Response of Humpback Whales (Megaptera Novaeangliae) to Offshore Seismic Survey Noise: Preliminary Results of Observations About a Working Seismic Vessel and Experimental Exposures

Abstract

During October to November 1996 WMC Petroleum conducted the Robert 3D seismic survey to the northeast of North West Cape, off Exmouth Western Australia. The survey used one of two 2678 cui (44 L) air-gun arrays of source level 258 dB re 1µPa2−m p−p below the array (77 bar-m), operating every eight s for 33.4 days of continual operation. Tracklines ran east-west across the path of southerly migrating humpback whales. Before the seismic survey began aerial surveys determined that humpbacks moving through the seismic area were distributed uniformly seaward of the 20 m depth contour. Based on observations made from the operating Geco Resolution there did not appear to be any gross changes in the migratory path of humpback whales through the seismic area. Whales approaching the operating Geco Resolution began avoidance manoeuvres at 5−8 km and mostly kept a standoff range of 3−4 km. Some whales approached the vessel closer. Experiments were carried out in Exmouth Gulf where the movements and behaviour of humpback pods were monitored before, during and after an approach with a 20 cui air-gun (0.33 L) of horizontal source level 227 dB re 1µPa2−m p−p. The levels at which avoidance manoeuvres began during these trials was approximately 159 dB re 1µPa2 p−p, which is roughly equivalent to the received level of the 2678 cui array at 5 km, at 162 dB re 1µPa2 p−p. General avoidance of the 20 cui air-gun was observed at 1 km, or a level of 168 dB re 1µPa2 p−p, which was roughly equivalent to the level of the 2678 cui array at 3 km at 170 dB re 1µPa2 p−p, which was the general minimum humpback standoff range observed from this array. Whales were observed to move closer to the operating 20 cui and 2678 cui air-gun/array. It is speculated that these whales were mostly males intent on investigating or passing quickly by the appropriate air-gun/array.

Broad-band calibration of marine seismic sources used by R/VPolarsternfor academic research in polar regions

“…Rather, the signal duration and energy play an important role, whether and to what extent hearing effects like temporary or permanent threshold shifts (TTS, PTS) are induced. In agreement with Finneran et al (2002a,b) he recommended, that both a maximum received peak pressure and a maximum received sound exposure level (SEL) should be used to mitigate the sound exposure of marine mammals, and a 90 per cent energy approach should be used to determine the signal duration (McCauley et al 1998;Blackwell et al 2004). In agreement with Finneran et al (2002a,b) he recommended, that both a maximum received peak pressure and a maximum received sound exposure level (SEL) should be used to mitigate the sound exposure of marine mammals, and a 90 per cent energy approach should be used to determine the signal duration (McCauley et al 1998;Blackwell et al 2004).…”

“…Most of the field studies describe short-term reactions of baleen whales to seismic surveys in shallow waters (Reeves et al 1984;Richardson et al 1986Richardson et al , 1995Ljungblad et al 1988;McCauley et al 1998McCauley et al , 2000Moore & Clarke 2002), whereas field studies on toothed whales (Goold & Fish 1998;Madsen et al 2006;Stone & Tasker 2006) and underwater pinnipeds (Harris et al 2001) are rare. Most of the field studies describe short-term reactions of baleen whales to seismic surveys in shallow waters (Reeves et al 1984;Richardson et al 1986Richardson et al , 1995Ljungblad et al 1988;McCauley et al 1998McCauley et al , 2000Moore & Clarke 2002), whereas field studies on toothed whales (Goold & Fish 1998;Madsen et al 2006;Stone & Tasker 2006) and underwater pinnipeds (Harris et al 2001) are rare.…”

“…Therefore, longer windows, which include 90 per cent of the total signal energy (McCauley et al 1998;Blackwell et al 2004;Madsen 2005), or which have a constant length of 200 ms , or of 0.5 or 1 s (Tolstoy et al 2004) have been used to assess the total impact of sound sources on marine mammals. Therefore, longer windows, which include 90 per cent of the total signal energy (McCauley et al 1998;Blackwell et al 2004;Madsen 2005), or which have a constant length of 200 ms , or of 0.5 or 1 s (Tolstoy et al 2004) have been used to assess the total impact of sound sources on marine mammals.…”

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“…Por esta razão, faz-se necessário o profundo conhecimento prévio dos hábitos daqueles espécimes observados para conferir maior nível de certeza na interpretação dos comportamentos registrados durante a presença de sísmicas marítimas. As constatações realizadas por McCauley et al (1998McCauley et al ( , 2000, por exemplo, registraram tanto comportamentos de afastamento, quanto de aproximação do navio fonte. Malme et al (1986), por sua vez, evidenciaram que espécimes de Eschrichtius robustus afastaram-se de determinados níveis de pulsos sonoros, enquanto Gailey et al (2007) não observaram alterações significativas nos movimentos da mesma espécie quando expostas as sísmicas marítimas.…”

“…Certamente estudos realizados com uma mesma população em momentos diferentes com a presença e ausência da prospecção sísmica podem oferecer resultados mais consistentes sobre a influência da atividade naquela população, a exemplo do realizado por Goold (1996), McCauley et al (1998 e, mais recentemente, por Yazvenko et al (2007a Apesar dos estudos realizados até o momento confirmarem a existência de algum efeito das aquisições sísmicas sobre os cetáceos, ainda não está claro de que maneira estes efeitos podem afetar significativamente a biologia das espécies expostas e como eles podem afetá-las em níveis populacionais. Somente com estudos de longo prazo e com metodologias ajustadas para este fim será possível avançar nesse sentido.…”