(at the UK level) the magnitude of effect is also considered to be negligible, due to the very low at sea densities in this region.
12.6.1.6.3Impact significance
382. At the reference population level impacts on harbour and grey seal are assessed as minor adverse.
383. In the case of harbour seal (at the UK level) the impact is assessed as minor adverse.
384. Based on the definitions in Table 12.8, the impact would equate to the loss of less than one individual seal from the population, and therefore would not be detectable. Furthermore, the harbour seal region in this MU is currently increasing, and is therefore likely to be robust to the loss of more than one individual from the population.
385. The location of the East Anglia THREE site and offshore cable corridor are not in areas of high or medium risk as identified by SNCAs (2012). Therefore no further mitigation (above that described in section 12.3.2) is deemed necessary. However, best practice and industry guidelines will be followed during construction to minimise the potential impact.
386. The confidence in the data underpinning the sensitivity of seal species to this type of impact is considered to be medium to low.
12.6.2 Potential impacts during operation 387. Impacts assessed during the operational phase of the project have been agreed in consultation with Natural England (Table 12.1). The impacts assessed are underwater noise from turbines and vessels, impacts upon prey species, vessel interaction and physical barrier effects.
12.6.2.1 Impact 1: Underwater noise - turbines 388. Noise levels generated by operational wind turbines are much lower than those generated during construction activities. Operational wind turbine noise mainly originates from the gearbox and the generator and has tonal characteristics (Madsen et al. 2006; Tougaard et al. 2009b). However, recordings of underwater noise are only available from a small number of operational windfarm sites. The main contribution to the underwater noise emitted from the wind turbines is expected to be from acoustic transfer of the vibrations of the substructure into the water rather than from transmission of in-air noise from the turbines into the water column (Lidell 2003).
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 12 Marine Mammal Ecology Page 91
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