Underwater noise pollution poses a global threat to marine life and is a growing concern for policymakers and environmental managers. Evidence is mounting of noise‐induced habitat loss, heightened physiological stress, masking of biologically important sound (e.g. for communication, predator/prey detection), auditory injury, and in extreme cases, direct or indirect mortality (Popper et al., 2014; Southall et al., 2007). Initial studies focused on charismatic megafauna (particularly marine mammals), but in recent years effects have been discovered in other taxa and at lower trophic levels, including various fish species (Popper et al., 2014), functionally important marine crustaceans (Solan et al., 2016) and zooplankton (McCauley et al., 2017).
Projected growth in the blue economy is expected to bring an expansion in noise‐generating activities, notably the construction of offshore wind turbines and other marine infrastructure, geophysical surveys using seismic airguns or sub‐bottom profilers, sonar usage and vessel traffic. With increasing awareness of the potential cumulative impact of these and other activities on marine ecosystems, managers are faced with tough choices over how best to alleviate pressure on the marine environment from multiple stressors and industrial sectors. Unlike other marine pollutants such as microplastics or persistent organic pollutants, underwater noise is ephemeral and quickly disperses in the environment. If effective, interventions to reduce noise pollution could lead to a rapid easing of this pressure on acoustically sensitive organisms.
Current measures to manage underwater noise pollution largely involve requiring environmental impact assessments (EIAs) for major inshore and offshore projects, in accordance with legislation for protected species or habitats (e.g. EU Habitats Directive, US Marine Mammal Protection Act). If acoustically sensitive species may be present and potentially harmful noise levels are expected, modelling is carried out to estimate the possible extent of adverse effects. On this basis, regulators may grant or decline consent, or require additional mitigatory action to be taken. However, many EIAs for underwater noise do not apply scientifically credible methods, and regulators often lack the expertise to critically assess consent applications (Farcas, Thompson, & Merchant, 2016). Furthermore, while in some northern European countries noise abatement technologies are being routinely deployed (e.g. for pile driving of offshore wind farms in Germany, Denmark, Norway, Sweden and the Netherlands), in other jurisdictions it is rare for the effect of reducing technologies to be assessed (and consequently recommended or required as a condition of consent), and the consideration of cumulative effects remains inadequate (Willsteed, Gill, Birchenough, & Jude, 2017; Wright & Kyhn, 2015).
Our purpose in this article is to set out clear guiding principles for assessing the impact of underwater noise, providing developers, regulators and policymakers with a robust, science-based framework to address this emerging threat. Based on our experience of advising these stakeholders and of conducting assessments, we identify shortcomings in current practice (and suggest remedies), and propose concrete steps to improve the compatibility of individual EIAs with cumulative effects assessments. We also promote an adaptive approach to EIA which enables regulators to consider the benefits of additional noise reduction measures, rather than the assessment being presented as a fait accompli. Our aim is to encourage more rigorous and informative assessments, and to help orient newcomers to this rapidly evolving area.