Sufficient scientific data exist to conclude that seismic airguns used in geophysical exploration have a low probability of directly harming most marine life, except at close range where physical injury is a real danger. While the use of airguns in some conditions does not appear to disturb animals, in other conditions it can result in moderate to extreme behavioral responses and/or acoustic masking over large areas (see reviews by: Clark et al., 2009; D.P. Nowacek et al., 2007; Southall et al., 2007 and original research by Miller et al., 2009, Castellote et al., 2012 and Cerchio et al., 2014). Additionally, recent studies have reported the presence of sound energy from seismic surveys over vast ranges of nearly 4000 km (Nieukirk et al., 2012), and while the potential for effects have not even been investigated at such ranges, the presence of the signals must be taken into account when evaluating overall potential for impacts. Most documented responses to seismic exploration or other intermittent human activities involving loud sounds include apparently temporary changes in behavior, but a detailed scientific understanding of the prevalence and implications of these effects remains limited. Recent efforts to include acoustic disturbance into an understanding of population level consequences are, however, promising (e.g., Harwood et al., 2011).
The European Union has recognized ocean noise as an indicator of environmental quality under its Marine Strategy Framework Directive (EU 2008), and it is in the process of developing targets for achieving good environmental status for ocean noise and acute noise-producing activities; additionally, in 2014, the EU identified seismic survey noise as a factor in the preparation of environmental impact assessments (EIA). Similarly, the United States recognizes underwater noise in the preparation of environmental impact statements for oil and gas development in the regions under its jurisdiction, particularly the Gulf of Mexico, Atlantic Ocean, and Arctic Ocean (e.g., BOEM 2014). These efforts, which are still in development, are indicative of the stage and scale of efforts needed to address these critical issues.
While mitigation measures to reduce immediate potential impacts (primarily direct harm) have understandably been the historical focus of operational protocols, measuring and understanding reactions in a systematic way is in fact an important aspect of any responsible development program. However, a distinction must be made between (i) understanding the potential impacts of discrete activities of a single company or seismic survey over a relatively short time period and (ii) the general industrialization of biologically important area(s), which can result in more severe and sustained impacts on marine life (e.g., gray whales, Eschrichtius robustus, in response to noise in breeding lagoons; Gard, 1974). Another important distinction is between the terms ‘mitigation’ and ‘monitoring’. For the purposes of the current paper, mitigation will be interpreted as the efforts devoted to implementing safeguards (e.g., minimizing immediate impacts to marine wildlife) during a single seismic survey, while monitoring refers to the collection of information during a survey that can be used later to test for impacts potentially caused by the survey and to design future mitigation efforts.
We have recently learned a valuable lesson with respect to baseline data. The fact that insufficient data existed for many Gulf of Mexico species, cetacean and otherwise, because of limited sampling prior to the Deepwater Horizon disaster bespeaks a broad failure on the part of management. This failure is limiting our ability to assess the true impacts of the Gulf disaster in retrospect, and therefore it is also limiting our ability, and perhaps also our willingness, to anticipate and plan for future prevention and remediation. Unfortunately, the inadequacy of baseline biological data from the U.S. Gulf of Mexico is not unusual. In fact, many places around the world where significant seismic exploration is ongoing or is projected to occur suffer from similar, or worse, baseline data shortfalls. Given the international and transboundary nature of noise from marine seismic surveys, their ubiquity as well as growth, and the presence of numerous other sources of ocean noise, a responsible path forward should focus on the creation of legally binding international commitments for the management and minimization of noise and international standards for monitoring and mitigation.