353. The diet of harbour porpoise over recent years is thought to reflect changes in the composition of food resources (section 12.5.3). Re-distribution of harbour porpoise between the 1995 SCANS and 2005 SCANS II surveys (Hammond et al. 2013) are thought to, in part reflect re-distribution of prey species, and over this time the size of the population did not change. However, there is limited data linking prey abundance to diet trends in this species, and the diet of harbour porpoise had large overlap with commercial fisheries catch (Santos and Peirce, 2003). However, harbour porpoise, have relatively high daily energy demands and need to consume between 4% and 9.5% of their body weight in food per day (Kastelein et al. 1997). If a harbour porpoise does not capture enough prey to meet its daily energy requirements it can rely on stored energy (primarily blubber) for three to five days, depending on body condition (Kastelein et al. 1997). Harbour porpoise are therefore considered to have medium sensitivity to this impact.
12.6.1.4.2Magnitude
354. The conclusions of the Chapter 11 Fish and Shellfish Ecology assessment are that during construction impacts will be minor adverse at worst, and not significant. The impacts are considered to be intermittent and temporary, but could occur over the East Anglia THREE site (and beyond in the case of noise impacts from pile driving) in a limited number of noise sensitive species. Based on this assessment, the magnitude of the effect on marine mammals is considered to be negligible for all species.
355. In the case of harbour seal (at the UK level) the magnitude of effect is still considered to be negligible (less than 1% of the South-east England MU) due to the very low at sea densities in this region.
12.6.1.4.3Impact significance
356. For grey seal, the combination of negligible magnitude of effect and low sensitivity provides an assessment of negligible impact, which is not significant.
357. The negligible magnitude of effect when combined with medium sensitivity in harbour seal and harbour porpoise concludes a negligible and non -significant impact.
358. In the case of harbour seal at the UK level, the assessment is also negligible impact.
359. No further mitigation measures are considered for this impact beyond those embedded measures presented Chapter 11 Fish and Shellfish Ecology and section 12.3.2.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 12 Marine Mammal Ecology Page 87
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