For most marine mammals, many marine fish, and possibly some shellfish, sound is important for communication, locating mates, searching for prey, avoiding predators and hazards, and for short- and long-range navigation. Noise at inappropriate volume and frequency can mask biologically relevant signals; it can lead to a variety of behavioural reactions; hearing organs can be adversely affected, and at very high levels, sound can injure or even kill marine life. Man-made sound sources of primary concern are explosions, shipping, seismic surveys, offshore construction and offshore industrial activities and sonars of various types, including military sonar, which has previously been implicated in deaths of beaked whales.

There is currently not enough evidence to provide a quantitative assessment of underwater noise in UK waters, but increasing activity in constructing, for example, offshore wind farms, is likely to have raised local noise levels while the developments were underway. Further large-scale developments of offshore wind farms are likely in the future. The management of subsurface noise emitted from shipping is currently the subject of international debate within the International Maritime Organization and we expect further guidance on this issue in the future.

Meanwhile, this area requires considerably more research. Future studies should focus on mapping and modelling ambient noise, observational and experimental studies, and developing frameworks for assessing noise related risks. The UK Marine Monitoring and Assessment Strategy (UKMMAS) community will eventually need to develop a monitoring programme regarding underwater noise to meet the requirements of the EU Marine Strategy Framework Directive.