Monitoring and mitigation of sound exposure from seismic surveys for a feeding whale population
Seismic surveys are an essential tool in the search for and periodic assessment of hydrocarbon deposits for oil and gas production. Airgun arrays, which are to date the overwhelmingly predominant sound source for these surveys, generate a high level of low-frequency pulses which can cause disturbance to marine life, particularly species with good low-frequency hearing such as baleen whales (Southall et al., 2007). Despite numerous studies (see Nowacek et al., 2007 for a review), substantial data gaps remain in terms of impacts of seismic surveys on cetacean physiology, behaviour and population dynamics. There is broad acceptance, however, of the need to mitigate the exposure of animals to noise from seismic surveys, especially for endangered populations or species (Nowacek et al., 2013). The northeastern shelf of Sakhalin Island, Russia, is an important feeding ground of a critically endangered population of grey whales (Eschrichtius robustus) which convene annually in the region near the mouth of Piltun lagoon. Sakhalin Energy Investment Company Ltd (Sakhalin Energy) operates two platforms in the Piltun-Astokhskoye licence area. In 2010 and 2015, Sakhalin Energy conducted repeat (4D) seismic surveys to characterize changes to the subsurface from hydrocarbon production at the two platforms, required for efficient positioning of new wells; the original 3D data had been acquired in 1997. In 2015 the surveyed region was approximately twice as large as in 2010, and another operator (Exxon Neftegas Limited or ENL) also conducted seismic surveys to the immediate north and south of the Piltun-Astokhskoye area on a co-ordinated schedule.