(IMARES) exposing fish larvae to prolonged piling activity (Bolle et al. 2011 and 2012) is also considered to inform the fish assessment.
28.
For behavioural disturbance, in the absence of internationally accepted criteria, a two-level generic behavioural disturbance criteria was used based on extensive observational studies of the response of caged fish to seismic airguns by Curtin University in Australia (McCauley et al. 2000a and 2000b) and some previous studies in Canada on the startle response of fish to seismic shooting (Pearson et al. 1992).
9.4.3.4 Assessment of other noise sources 29.
Other noise sources, including operational wind turbines and surface vessels are considered, in Appendix 9.1, using information available in the peer-reviewed literature to inform the likely noise levels and the potential for impact on marine fauna.
9.5 Existing Environment – Underwater Noise 30.
9.6 Potential Impacts – Underwater Noise 31.
Underwater ambient noise levels are subject to substantial variability depending on a number of natural and anthropogenic factors. Ambient noise and its contributors are considered in Appendix 9.1.
The underwater noise assessment detailed in Appendix 9.1 provides an assessment of the likely underwater noise conditions during the different phases of the East Anglia THREE project, including the assessment of the potential for injury and behavioural disturbance to sensitive marine receptors.
32.
Underwater noise from impact piling is known to result in significant peak pressure levels and SEL and will be distinguishable above ambient noise over distances of several tens of kilometres froma source (Thomsen et al. 2006; Nedwell et al. 2007; Bailey et al. 2010). Foundation types which rely on impact piling are considered the worst case in terms of the resulting underwater noise; other foundation types are therefore not considered in this aspect of the assessment.
33.
The injury and behaviour criteria outlined in Appendix 9.1 have been applied to the outputs of the underwater noise modelling to predict the potential impact ranges during pile driving for a maximum hammer blow energy of 3,500kJ with the following conclusions:
At the onset of piling, the potential for instantaneous auditory injury (PTS onset) of marine mammals may be expected to be mitigated by a 500m mitigation zone employed during the pre-piling watch provided the hammer
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 9 Underwater Noise Page 9
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