reported in Southall et al. (2007) for high-frequency cetaceans (this category includes the harbour porpoise), in this assessment possible avoidance thresholds are considered to approximate to the severity scoring of 5-6 (Southall et al. 2007). This type of behavioural response has the ability to affect foraging, reproduction or survival, should an individual respond, but not all individuals that are exposed to this level or noise will respond. Sensitivity of harbour porpoise to this type of impact is considered medium.
12.6.1.1.2Magnitude
12.6.1.1.2.1 Lethal effects 266. The predicted noise levels in close proximity to the pile are comparable to those estimated for the onset of auditory injury and mortality and would only be expected at noise levels substantially above those necessary to cause auditory injury. The pile driving installation is thus unlikely to result in radiated noise levels sufficient to cause instantaneous mortality in marine mammals beyond a few metres from the pile.
267. As a result of the establishment of mitigation zones through the MMMP, there should be no marine mammals within a few metres of the pile. Therefore, the potential magnitude of effect is no change.
12.6.1.1.2.2 Auditory injury (PTS onset) 268. Table 12.14 summarises the PTS onset ranges for each species and species group for a range of hammer energies. The 1,400kJ hammer was the lowest modelled hammer energy. Although this is greater than the hammer energy at the start of the soft start (400kJ) the impact ranges for PTS onset are shown to be less than 500m at the higher energy. Therefore, the establishment of a mitigation zone out to at least 500m (following current JNCC 2010a guidelines) would prevent exposure of individuals to noise thresholds which could lead to instantaneous onset of PTS.
269. Using the 3,500kJ hammer energy, the maximum range of instantaneous PTS onset is less than 1km for harbour porpoise (and less than 500m in all other species). The establishment of a mitigation zone out to the maximum range of PTS onset in harbour porpoise (currently assessed as up to 1kmusing the 3,500kJ hammer) though the development of a MMMP, is included as embedded mitigation, and has been agreed during consultation (Table 12.1). Table 12.14 confirms that mitigation out to this range will also prevent an injury offence to other EPS which may be rare or occasional visitors to the East Anglia Zone. The exact range of the mitigation zone will be confirmed during development of the MMMP post consent, once pile driving parameters have been refined within the project design envelope. The range may be less than 1km as currently assessed.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 12 Marine Mammal Ecology Page 72
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