Abstract
A 4D seismic survey was conducted in 2010 near the feeding grounds of gray whales off Sakhalin Island, Russia. To minimize disruptions to the whales’ feeding activity and enhance understanding of the potential impacts of seismic surveys on gray whales Eschrichtius robustus, an extensive monitoring and mitigation plan (MMP) was developed. Typically, mitigation plans involve observers on seismic vessels to monitor for the presence of marine mammals in an exclusion zone so as to prevent physical injury to the animals. Due to the protected status of western gray whales, an additional protection zone based on a behavioural disturbance threshold of exposure of 156 dB re μPa2-s per pulse was applied for whales within their feeding habitat defined by the estimated 95% abundance contour. Real-time radio-transmitting acoustic recorders were deployed along this contour to verify modelled acoustic footprints within the feeding grounds. Shore- and vessel-based observation teams monitored for the presence and activity of whales. A real-time GIS workflow tracking procedure was developed that integrated acoustic and whale positioning data to determine if sound levels at a whales’ position within the feeding area exceeded the behavioural threshold, in which case a shut-down of the seismic source was implemented. Additionally, behaviour and distribution surveys were conducted before, during and after the seismic survey to evaluate the effectiveness of the MMP. No large changes in whale movement, respiration, or distribution patterns were observed during the seismic survey. This could be interpreted to mean that the MMP was effective in reducing the sound exposure and behavioural responses of gray whales to seismic sounds. KEY WORDS: Seismic · Mitigation · Western gray whale · Eschrichtius robustus · Sakhalin · Piltun · Sea of Okhotsk · Anthropogenic disturbance
Highlights
Anthropogenic sound can have physiological and behavioural impacts on marine mammals, as well as affect their ability to communicate, navigate and forage (Richardson et al 1995, Nowacek et al 2007, Southall et al 2007)
(1) Careful planning in development and implementation of the monitoring and mitigation plan (MMP) by a multi-disciplinary technical team of both independent and company-contracted scientists led to an effective plan that appears to have met the objective of reducing risks to gray whales from the seismic survey (IUCN 2010c, Nowacek et al 2013)
(4) the shape of the A-zone was different for each A-line, the A-zone used in this MMP was static, in the sense that it was independent of the location of the seismic source in relation to the position of an observed whale
Summary
Anthropogenic sound can have physiological and behavioural impacts on marine mammals, as well as affect their ability to communicate, navigate and forage (Richardson et al 1995, Nowacek et al 2007, Southall et al 2007). The exact impacts of seismic surveys on cetacean auditory systems, behaviour and population dynamics depend on many factors and are generally not well understood, the need for mitigation measures to prevent adverse effects is broadly accepted. This is true when the sound exposures occur over a prolonged period and/or originate from multiple sources in critical habitat of endangered species. Sakhalin Energy Investment Company is developing oil and gas reserves from 2 platforms located in the Piltun-Astokh license area on the northeastern Sakhalin shelf, Russian Federation (Fig. 1). The survey was conducted from 17 June to 2 July 2010
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