similar environment in near-by areas. This was assumed to be due to decreased fishing and vessel activity and increased food availability (Scheidat et al. 2011).
451. The impacts are likely to be localised in occurrence, they will be temporary, and limited to this phase of the development. The 25 year operational lifespan could be considered permanent in the context of marine mammal life history. However, individual marine mammals will not be continually impacted due to their highly mobile nature.
452. The magnitude of effect is considered to be negligible. To reflect the long-duration of this development phase in relation to marine mammal life history the magnitude of effect is revised up on level in the assessment to low.
12.6.2.6.3Impact significance
453. For all species at the reference population level, and at the UK level for harbour seal, the impact is assessed as negligible.
454. The confidence in the data underpinning the sensitivity to this type of impact is considered to be medium.
12.6.3 Potential impacts during decommissioning 455. Decommissioning impacts are to be assessed have been agreed in consultation with Natural England (Table 12.1). The impacts are underwater noise (vessel noise, seabed preparation and foundation and cable removal), impacts on prey species, vessel interactions (ship strikes and ducted propellers).
456. It is not possible to provide details of the methods that will be used during decommissioning at this time. However, is it expected that the activity levels will be comparable to the construction phases (with the exception of pile driving noise).
457. A detailed decommissioning plan will be provided prior to decommissioning that will give details of the techniques to be employed and any relevant mitigation measures.
12.6.3.1 Impact 1: Underwater noise - vessels, seabed preparation and foundation and cable removal
458. The level of noise expected during each of the decommissioning phase is based on the worst case scenario (Table 12.2). Section 12.6.1.2 and section 12.6.1.3 provide details of the noise impacts during construction (other than pile driving).
459. Explosives will not be used during decommissioning.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 12 Marine Mammal Ecology Page 99
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