1. Marine Mammal Mitigation Plan

1.1. Introduction

  1. This outline Marine Mammal Mitigation Plan (MMMP) has been prepared by Ossian Offshore Wind Farm Limited (Ossian OWFL), a joint venture partnership between SSE Renewables (SSER) Limited, Copenhagen Infrastructure Partners, and Marubeni Corporation (hereafter referred to as “the Applicant”), to support the Array Environmental Impact Assessment (EIA) Report for the Ossian Array (hereafter referred to as “the Array”).
  2. The Array is located off the east coast of Scotland, approximately 80 km south-east of Aberdeen from the nearest point ( Figure 1.1   Open ▸ ). The Array covers an area of approximately 859 km2 and comprises up to 265 floating wind turbines and up to 15 Offshore Substation Platforms (OSPs). Inter-array cables will connect the wind turbines to each other and to the OSPs, while interconnector cables will connect the OSPs to each other. 
  3. This outline MMMP presents a summary of findings as assessed in the Array EIA Report on the effects of underwater noise during piling (floating foundations), Unexploded Ordnance (UXO) clearance, and pre-construction geophysical surveys, on marine mammals. Piling and UXO clearance have the potential for impact during the construction phase, and geophysical surveys have the potential for impact during both the construction and operation and maintenance phase. This outline MMMP presents mitigation protocols to minimise the risk of injury to marine mammals. This outline MMMP is informed by the following sections of the Array EIA Report:
  • volume 2, chapter 10: Marine Mammals;
  • volume 3, appendix 10.1: Underwater Noise Technical Report; and
  • volume 3, appendix 10.2: Marine Mammal Technical Report.
  1. Whilst the assessment of injury in the EIA is based upon the dual metric approach, advice received from NatureScot in response to Marine Mammal Consultation Note 2 (volume 3, appendix 5.1, annex E) advised that “pre-piling mitigation should be based on the instantaneous risk for permanent threshold shift (PTS) onset” and therefore the injury ranges from the Peak Sound Pressure Level (SPLpk) metric form the basis for mitigation (and define the mitigation zone) in this outline MMMP.


Figure 1.1:
Array Area for Ossian Offshore Wind Farm

Figure 1.1: Array Area for Ossian Offshore Wind Farm

1.2. Purpose of the MMMP

  1. This outline MMMP has been prepared to secure mitigation strategies which seek to ensure there is no injury to marine mammals as a result of the following activities associated with the Array:
  • underwater noise during piling;
  • UXO clearance; and
  • site investigation surveys (geophysical).
  1. Information presented in this outline MMMP is based on volume 2, chapter 10 of the Array EIA Report which considers the potential impacts of the Array during the construction, operation and maintenance, and decommissioning phases. The maximum design scenario (MDS) informing the assessment of potential impacts on marine mammals as a result of elevated underwater noise during piling, UXO clearance, and geophysical site investigation surveys is presented in Table 10.16 of volume 2, chapter 10 of the Array EIA Report.
  2. This outline MMMP has been prepared in accordance with the following guidance and it is considered that compliance with these will reduce the risk of injury to marine mammals:
  • Joint Nature Conservation Committee (JNCC) (2010a), Statutory nature conservation agency protocol for minimising the risk of injury to marine mammals from piling noise;
  • JNCC (2010b), Guidelines for minimising the risk of injury to marine mammals from using explosives; and
  • JNCC (2017), Guidelines for minimising the risk of injury to marine mammals from geophysical surveys.
  • These measures may encompass, but are not restricted to, the following:
  • Establishment of a designated mitigation zone;
  • Monitoring of mitigation zone through visual observation using qualified and trained Marine Mammal Observers (MMO2);
  • Utilisation of a Passive Acoustic Monitoring (PAM) System;
  • Deployment of Acoustic Deterrent Devices (ADDs);
  • Establishment of communication channels between MMO2, PAM and ADD operators; and
  • Implementation of a soft start and ramp up procedures.
  1. The development of mitigation measures and emerging and evolving technologies for marine mammal monitoring will be actively monitored. Where it is identified that such measures or technologies would be appropriate for implementation as part of the Array, this MMMP will be updated accordingly.

1.3. Target Species

  1. Marine mammals were characterised based on their abundance and densities at a regional scale (regional marine mammal study area) and local scale (Array marine mammal study area), as detailed in volume 2, chapter 10.
  2. Digital aerial surveys (DAS) commenced in March 2021 and continued monthly up to and including February 2023. DAS identified that harbour porpoise Phocoena phocoena was the most commonly sighted marine mammal in the Array marine mammal study area. Other marine mammals that were regularly sighted in the surveys include grey seal Halichoerus grypus, minke whale Balaenoptera acutorostrata and white-beaked dolphin Lagenorhynchus albirostris. These species use sound for many aspects of their lives and are sensitive to underwater noise, which can cause permanent damage to their ear tissue. A detailed account on the effects of underwater noise on the marine mammal species presented in this outline MMMP can be found in volume 2, chapter 10.
  3. All of the marine mammal species which would potentially be affected by the Array are protected by international legislation and/or are important from a conservation perspective at an international or national context (volume 2, chapter 10). Therefore, the value of marine mammal Important Ecological Features (IEF) at the Array was designated as International ( Table 1.1   Open ▸ ).

 

Table 1.1:
Marine Mammal IEFs and their Importance Within the Marine Mammal Regional Study Area

Table 1.1 Marine Mammal IEFs and their Importance Within the Marine Mammal Regional Study Area

 

1.4. Measures Adopted As Part of the Array

  1. As part of the Array design process, a number of designed in measures have been proposed to reduce the potential for injury and/or mortality on marine mammals ( Table 1.2   Open ▸ ). As there is commitment to implementing these measures, they are considered inherently part of the design of the Array and represent a standard industry practice for this type of development. As part of designed in measures, a commitment to up to 30 minutes of ADD deployment is included.
  2. Secondary mitigation measures, such as extended use of ADDs (over 30 minutes) may be implemented and are further discussed in section 1.6, however these are not considered to be a designed in measure.

 

Table 1.2:
Designed in Measures Adopted as Part of the Array

Table 1.2: Designed in Measures Adopted as Part of the Array