Underwater Noise

Marine mammals, many fish species and even some invertebrates communicate using sound to find mates, to search for prey, to avoid predators and hazards, and for navigation.

Many of the human activities that take place in the OSPAR Maritime Area generate sound and contribute to the general background level of noise in the sea. Anthropogenic sound sources are categorised as impulsive or continuous (ambient). Impulsive sound sources include percussive pile driving for inshore and offshore construction (e.g. windfarms) seismic surveys (using airguns) to inspect subsea oil and gas deposits, explosions, and some sonar sources. Continuous sound sources are mainly from shipping. Sound is referred to as ‘noise’ only when it has the potential to cause negative impacts on marine life.

Underwater sound from anthropogenic sources has the potential to mask biological signals and to cause behavioural reactions, physiological effects, injuries and mortality in marine animals.

Levels and frequencies of anthropogenic and naturally occurring sound sources in the marine environment. Specturum Noise Level ("Acoustic intensity per Hertz") versus Frequency (measured in Hertz or "cycles per second").

Impacts depend on both the nature of the sound and the acoustic sensitivity of the organism. There are difficulties in quantifying the extent and scale of the impacts, as there is great variability in the characteristics of the sounds, the sensitivities of different species and the scale of noise-generating activities. Ambient or background noise is not range-dependent and remains constant irrespective of location. The perception of localised noise sources reduces with increasing distance from each source, eventually becoming indistinguishable from ambient noise.

Monitoring and Assessment