9.5 Assessing the Impact of Underwater Noise on Marine Fauna from Marine Impact Piling
9.5.1 Introduction 49. When considering the potential impacts of noise on sensitive marine receptors the noise exposure process may be divided into several components:
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noise emission from the source (requiring the characterisation of the source, for example whether it is continuous or pulsed in nature, its frequency characteristics etc.);
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• •
50.
the sound transmission process (which will depend on boundary conditions and environmental conditions for a given source;
the ambient noise level; and
the hearing sensitivity and behavioural context of the subject or receiver at the location where the sound is detected.
This section highlights the potential impacts of underwater noise on marine receptors and describes the available internationally accepted impact criteria for marine mammals and fish, in the context of windfarm construction. A summary of impact criteria adopted in this assessment, and based on the review below, is provided at the end.
9.5.2 Effect of Sound on Marine Fauna 51. Underwater sound can potentially have a negative impact on marine mammals and fish ranging from changing their acoustic habitat to scaring them away and even causing physical injury. In general, biological damage as a result of sound is either related to a large pressure change (barotrauma) or to the total quantity of sound energy received by a receptor. Barotrauma injury can result from exposure to a high intensity sound even if the sound is of short duration, such as an explosion. However, when considering injury due to the energy of an exposure, the duration of the exposure becomes important. For example, a continuous source operating at a given pressure level has a higher energy and is therefore considered more damaging (Southall et al. 2007) than an intermittent source reaching the same pressure level. The harmful effects of high-level underwater sound can be summarised as lethal, physical injury and hearing impairment. Other ways in which sound or noise can be detrimental to the marine mammals and fish is by causing behavioural disturbance and masking.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Appendix 9.1 Underwater Noise Modelling 16
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