Many marine organisms, including most marine mammals (whales, dolphins, porpoises and pinnipeds), many marine fish species, and even some invertebrates, use sound for a variety of purposes, for example in communication, to locate mates, to search for prey, to avoid predators and hazards, and for short- and long-range navigation (for reviews see for example Tyack & Clark 2000; Popper et al. 2001; Würsig & Richardson 2002; Popper et al. 2004). Depending on the intensity (sound pressure level) at the source, the pitch (frequency) and the distance between source and receiver, sound can potentially affect marine organisms in various ways. In this regard, it is also important to consider the cumulative effect when a sound source is long-lasting or repeated in time (Richardson et al. 1995).
Concerns on the potential adverse effects of anthropogenic noise on marine life have been raised from within the scientific community since the 1970s, and research on the topic expanded in the 1980s (e.g. Payne & Webb 1971; Richardson et al. 1985). During the last decade the topic has been investigated extensively by a number of scientific institutions, governmental agencies and intergovernmental bodies, with major reviews dealing with the effects of sound on fish and marine mammals (e.g. Richardson et al. 1995; Würsig & Richardson 2002; Popper et al. 2004; Hastings & Popper 2005; Hildebrand 2005; ICES 2005; NRC 2003, 2005; Wahlberg & Westerberg 2005; Thomsen et al. 2006; Madsen et al. 2006; Southall et al. 2007; Nowacek et al. 2007). These studies have documented both the presence and absence of physiological effects and behavioural responses of marine mammals, fish, and even invertebrates to various sound signals and have set the scene for discussions among scientists, stakeholders and policy makers on how to address potential impacts of underwater noise and how to develop meaningful mitigation measures within regulatory frameworks.