1.10. Marine Mammals

  1. The marine mammal assessment focuses on the marine mammal communities within the vicinity of the Array. The northern North Sea is an important area for marine mammals, supporting many species of cetaceans (dolphins, whales and porpoises) and two species of seal. The distribution of marine mammals is strongly influenced by the distribution of their prey (i.e. mostly fish) and their occurrence is often unpredictable due to their highly mobile nature.
  2. The marine mammal ecology in the vicinity of the marine mammal study area was characterised through a detailed desktop review of existing studies and datasets, alongside site-specific data. Data from the Digital Aerial Survey (DAS), undertaken by using digital cameras on aircraft flying over the site, demonstrated that four of the five key marine mammal species were sighted within the marine mammal study area, and these included: harbour porpoise, white-beaked dolphin, minke whale and grey seal. Of the cetaceans, harbour porpoise was the most frequently recorded species and, during site-specific aerial surveys, was sighted in every month of the year (across two years of surveys). Minke whale and white-beaked dolphin were found to be seasonal visitors to the region (summer months). Bottlenose dolphins, which primarily move along inshore areas, are part of an east coast of Scotland resident population and were not sighted in the DAS throughout the survey. Grey seals haul-out on shore in coastal areas and make foraging trips out to sea. Seals were recorded regularly during site-specific aerial surveys, with most species identified as grey seal.
  3. A number of potential impacts on marine mammal receptors, associated with the construction, operation and maintenance, and decommissioning phases of the Array, were identified:
  • injury and disturbance from underwater noise generated during piling, UXO clearance and site-investigation surveys (including geotechnical surveys);
  • injury and disturbance from underwater noise generated during vessel use and other noise producing activities;
  • injury due to collision with vessels;
  • effects on marine mammals due to EMFs from subsea electrical cabling in the water column;
  • injury and disturbance from underwater noise generated during the operation of floating wind turbines and anchor mooring lines;
  • effects on marine mammals due to entanglement associated with the Array; and
  • effects on marine mammals due to altered prey availability.
  1. With the proposed designed in measures in place, most of these impacts result in effects of minor adverse significance, which is not significant in EIA terms.
  2. The assessment did, however, identify the potential effect of moderate adverse significance (significant in EIA terms) on harbour porpoise (injury) as a result of clearance of UXOs by full detonation of the munition (injury), therefore, secondary mitigation was proposed. For UXOs, the proposed approach is to clear the munitions using small, shaped donor charges that would neutralise the explosive material and therefore not lead to full detonation. Since there is a small, inherent risk of an accidental full detonation could occur, additional mitigation was proposed via use of an Acoustic Deterrent Device (ADD) and soft start charges (very small scare charges) and although there remains some residual effect (i.e. potential risk of injury to harbour porpoise), the numbers are likely to be very small in the context of the North Sea reference population and therefore the residual impact was determined to be of minor adverse significance, which is not significant in EIA terms. Whilst the proposed approach is to avoid the use of full detonation, a European Protected Species (EPS) licence will be applied for on the basis that such detonation could occur.
  3. Cumulative impacts arising from the Array together with other projects and plans were assessed and predicted to result in effects of minor adverse significance (not significant in EIA terms) upon marine mammals within the regional marine mammal study area for most impacts. As per the Array alone assessment, the assessment of cumulative effects identified the potential effect of moderate adverse significance (significant in EIA terms) on harbour porpoise (injury) as a result of clearance of UXOs by full detonation of the munition (injury), therefore, secondary mitigation was proposed as noted in paragraph 145 which reduced the residual significance to minor adverse significance (not significant in EIA terms).
  4. No transboundary effects with regard to marine mammals from the Array on the interests of other EEA states were predicted.