9.5.2.3 Behavioural 54. At levels where the underwater sound wave may not directly injure animals or cause hearing impairment, the underwater sound may have the potential to cause behavioural disturbance. Studies of the behavioural response of marine species to sound describe a variety of different behavioural reactions, and a general consensus for criteria has been slow to emerge. There are a number of factors which are likely to influence the response of the animal and require careful consideration when establishing the applicability of a given criteria for an impact assessment. Whilst it is widely acknowledged that hearing sensitivity of the animal is a key factor (Finneran and Schlundt 2011; Terhune 2013 and Nedwell et al. 2007b), the context of the exposure is also likely to have an influence, in addition to the level of the underlying ambient noise (i.e. the perceived signal-to-noise ratio). Clearly, the frequency characteristics of the source need to be taken into account, as does the type of sound exposure (Southall et al. 2007). For this assessment, the criteria have been based on published observations of animals exposed to real sound sources (and in the far-field of the sound source), which are similar in characteristics to those being assessed, and in open water environments (tank based exposures are generally expected to be performed with background noise levels which are significantly lower than those present in the North Sea for example). This assessment follows the framework followed by Southall et al. (2007) for behavioural disturbance.


9.5.2.4 Auditory Masking 55. Auditory masking occurs when an unwanted sound or noise may partially or entirely reduce the audibility of a signal which occurs in the same critical hearing band, even if the signal level is above the absolute hearing threshold. Auditory masking can reduce the ability of an animal to communicate or detect predators. For sonar equipped animals, masking can also reduce their ability to hunt and navigate. However, the short pulse length and relatively low repetition rate of hammer strikes used for marine piling reduce the likelihood of this sound masking out the short, higher frequency vocalisations of marine mammals. Even at larger distances where the pulse length might be lengthened due to multi-paths, the high frequency noise levels should be sufficiently reduced. It should also be noted that the predominant acoustic energy generated during marine impact piling is well below the frequencies used for communication and echolocation in odontocetes and so there is no cross- over at levels which might cause significant masking in the critical hearing bands (Thomsen et al. 2006). This may not be true for fish which are most sensitive at lower frequencies or for pinnipeds, for example, that can vocalise at frequencies which overlap with marine impact piling (Thomsen et al. 2006). An operational wind


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm Appendix 9.1 Underwater Noise Modelling 18


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