1. Introduction

1.1.        The Purpose of this Report to Inform Appropriate Assessment

1.1. The Purpose of this Report to Inform Appropriate Assessment

1. This Report to Inform Appropriate Assessment (RIAA) has been prepared by RPS and Niras on behalf of Ossian Offshore Wind Limited (Ossian OFWL) (hereafter referred to as the ‘Applicant’). The purpose of this RIAA is to support the Habitats Regulations Appraisal (HRA) of the Array in the determination of the implications for European sites. This RIAA builds upon the Array HRA Stage One Likely Significant Effects (LSE2) Screening Report (Part 1, appendix 1A) and the subsequent joint Environmental Impact Assessment (EIA) Scoping and LSE1 Screening advice received in the Ossian Array Scoping Opinion (Marine Directorate – Licensing Operations Team (MD-LOT) (2023)).
2. This RIAA assesses whether the Array could have an adverse effect, either alone, or in-combination with other plans or projects, on the integrity of any European site. This report will provide the Competent Authority with the information required to undertake an HRA Stage Two Appropriate Assessment.
3. The scope of this RIAA Part 2 SAC Assessments covers all relevant SACs and qualifying interest features where a LSE2 has been identified in the Array HRA Stage One LSE2 Screening Report (Part 1, appendix 1A), due to the potential impacts arising from the Array. This includes ‘offshore’ European sites and features.
4. There were no SACs designated for Annex I habitats or Annex II European otter Lutra lutra advanced to the RIAA stage, and therefore these are not included in this assessment.

1.2.        Structure of the RIAA

1.2. Structure of the RIAA

5. As detailed in section 1.5 of Part 1, for clarity and ease of navigation, the RIAA is structured and reported in the below ‘Parts’, as follows:

• Executive Summary and Conclusion;
• Part 1: Introduction;
• Part 2 Special Area of Conservation (SAC) Assessments; and
• Part 3: Special Protection Area (SPA) and Ramsar Site Assessments.

1.3.        Structure of this Document

1.3. Structure of this Document

6. As stated in paragraph 5, this document constitutes Part 2 of the RIAA, and presents the assessment of the implications of the Array on SACs.
7. This document is structured as follows:

• Section 1: Introduction, which details the purpose and structure of the RIAA and this Part 2 document;
• Section 2: Consultation, which provides a summary of relevant consultation undertaken to date, the responses provided, and how these have been addressed in this Part of the RIAA;
• Section 3: Summary of the HRA Stage One LSE2 Screening conclusions for SACs;
• Section 4: Information to inform the Appropriate Assessment, which includes the Maximum Design Scenario (MDS), information on designed in measures, and an outline of the baseline data on the SACs;
• Section 5: Assessment of adverse effects on integrity on designated sites for Annex II diadromous fish both alone and in-combination with other plans and projects;
• Section 6: Assessment of adverse effects on integrity on designated sites for Annex II marine mammals both alone and in-combination with other plans and projects;
• Section 7: Overall summary of this Part of the RIAA; and
• Section 8: References.

2.             Consultation

2. Consultation

8. Consultation has been undertaken with statutory stakeholders with regards to the relevant Annex I habitats and Annex II diadromous fish and marine mammal features of SACs. A summary of all relevant consultation undertaken to date is presented in Table 2.1   Open ▸ .

Table 2.1: Summary of Key Consultations on Relevant to Part 2 of the RIAA

3.             Summary of HRA Stage One LSE Screening Conclusions for Special Areas of Conservation

3. Summary of HRA Stage One LSE Screening Conclusions for Special Areas of Conservation

9. This section summarises all pathways for potential LSE2 on Annex II diadromous fish and marine mammal features of SACs (arising alone or in-combination with other plans and projects).

3.1.        Screening Outcomes for the Array Alone

3.1. Screening Outcomes for the Array Alone

10. The potential for LSE2 as a result of the Array alone has been identified following the HRA Stage One LSE2 Screening with respect to 12 SACs ( Figure 3.1   Open ▸ and Table 3.1   Open ▸ ).
11. There were no SACs designated for Annex I habitats or Annex II European otter advanced to the RIAA stage.

3.1.1.    Annex II Diadromous Fish

3.1.1. Annex II Diadromous Fish

12. Nine SACs designated for Annex II diadromous fish and dependent features were advanced to the RIAA. These are as follows (presented in increasing distance from the closest point on the site boundary):

• River Dee SAC;
• River South Esk SAC;
• Tweed Estuary SAC;
• River Tweed SAC;
• River Tay SAC;
• River Spey SAC;
• Berriedale and Langwell Waters SAC;
• River Teith SAC; and
• River Oykel SAC

13. Standard data forms for all SACs are available from the JNCC (2024c).
14. A summary of these nine SACs for which LSE2 was identified for Annex II diadromous fish features, alongside corresponding impact pathways for each phase of the Array, are presented in Table 3.1   Open ▸ . No updates relating to Annex II diadromous fish have been made to the HRA Stage One LSE2 Screening outcomes.
15. Some of the nine SACs advanced to the RIAA are also designated for Annex II river lamprey, however, as stated in the Array HRA Stage One LSE2 Screening Report, this species was not considered as the marine phase of their life cycle is restricted to the coastal/estuarine environment. Given the distance of the site boundary offshore (approximately 80 km from the nearest coastline), interactions between river lamprey and activities associated with the Array are not anticipated.
16. Some of the SACs are also designated for Annex II freshwater pearl mussel Margaritifera margaritifera, which will not be directly affected by the Array as it is restricted to freshwater environments but has the potential to be indirectly impacted due to its symbiotic life cycle with Atlantic salmon Salmo salar. The freshwater pearl mussel relies on Atlantic salmon, the host species during a critical parasitic phase of its life cycle, where its larvae attach to the gills of Atlantic salmon in mid to late summer and drop off in spring (Taeubert et al., 2017). Therefore, there could be an indirect effect upon the freshwater pearl mussel feature of European sites, should the Atlantic salmon population be adversely affected by the Array.

3.1.2.    Annex II Marine Mammals

3.1.2. Annex II Marine Mammals

17. Three SACs designated for Annex II marine mammals were advanced to the RIAA. These are as follows (presented in increasing distance from the closest point on the site boundary):

• Berwickshire and North Northumberland Coast SAC;
• Southern North Sea SAC; and
• Moray Firth SAC.

18. Standard data forms for all SACs are available from the JNCC (2024c).
19. A summary of the three SACs for which LSE2 was identified for Annex II marine mammal features, alongside corresponding impact pathways for each phase of the Array, are presented in Table 3.1   Open ▸ .
20. Since the Array EIA Scoping Report (Ossian OWFL, 2023) and Array HRA Stage One LSE2 Screening Report (Part 1, appendix 1A) were published, there have been some minor changes to the impacts associated with marine mammals. Firstly, the impact of ‘Operational noise from anchor mooring lines’ was assessed as such in the Array HRA Stage One LSE2 Screening Report. This has since been updated to ‘Injury and disturbance from underwater noise generated during the operation of floating wind turbines and anchor mooring lines’ and has been assessed accordingly in this Part of the RIAA and in the Array EIA Report (Ossian OWFL, 2024). Secondly, the potential impact of injury and disturbance due to site-investigation surveys (including geophysical surveys), has since been included in the Array EIA Report, and has been carried forward for assessment in this Part of the RIAA. At the time of writing the Array HRA Stage One LSE2 Screening Report, site-investigation survey activities (including geophysical) were to be submitted in a separate application (Part 1, appendix 1A). Any potential impacts as a result of site-investigation (including geophysical) survey activities were therefore out with the scope of the Array HRA Stage One LSE2 Screening Report. They have since been included as part of the Application, and therefore, the potential impact of ‘injury and disturbance due to site-investigation surveys (including geophysical surveys)’ has been considered as a potential impact at the HRA Stage Two Appropriate Assessment in the construction and operation and maintenance phases, as per the approach taken in the Array EIA Report.
21. Following a comprehensive assessment of potential connectivity as well as feedback from NatureScot, Natural England and MD-LOT provided as part of the Ossian Array Scoping Opinion and LSE2 Screening feedback ( Table 2.1   Open ▸ ), the Isle of May SAC, which is designated for grey seal, has not been carried forward for Appropriate Assessment. This deviates from the Array HRA Stage One LSE2 Screening Report, wherein the potential for LSE2 on this SAC was proposed.
22. No other updates relating to Annex II marine mammals have been made to the HRA Stage One LSE2 Screening outcomes.

3.2.        Screening Outcomes for the Array In-Combination with other Plans and Projects

3.2. Screening Outcomes for the Array In-Combination with other Plans and Projects

3.2.1.    Annex II Diadromous Fish

3.2.1. Annex II Diadromous Fish

23. A precautionary approach to the selection of relevant European sites for Annex II diadromous fish was adopted in the Array HRA Stage One LSE2 Screening Report. This involved the use of a large buffer of 100 km and screening in all SACs which flowed into the Firth of Forth and the Moray Firth (Part 1, appendix 1A). Due to this approach, all SACs relevant for Appropriate Assessment, particularly due to the potential for disruption to migration (i.e. barriers to migration) to/from natal rivers, have been identified. Therefore, there is no potential for connectivity between the site boundary and Annex II diadromous fish from any additional SACs beyond those identified as relevant in the Array HRA Stage One LSE2 Screening Report.
24. This screening approach was adopted for both Atlantic salmon (and freshwater pearl mussel by proxy) and sea lamprey Petromyzon marinus, however with the caveat that there is little information on their spatial distribution of sea lamprey out with rivers and estuaries. Therefore, the screening approach was highly precautionary for sea lamprey.
25. No potential impact pathways were identified between the Array and any additional sites designated for Annex II diadromous fish. Therefore, there is no potential for in-combination effects at any sites apart from those which are screened in for HRA Stage Two Appropriate Assessment (i.e. those listed in paragraph 12).

3.2.2.    Annex II Marine Mammals

3.2.2. Annex II Marine Mammals

26. A precautionary approach to selection of relevant European sites for Annex II marine mammals was adopted in the Array HRA Stage One LSE2 Screening Report (Part 1, appendix 1A).  Marine mammals are highly mobile animals with the potential to forage over wide areas. Therefore, all European sites for marine mammal features with a range that overlaps with the site boundary were considered. The screening area extended to the relevant marine mammal MUs and Seal Management Units (SMU) for each species, as defined by the Inter Agency Marine Mammal Working Group (IAMMWG) for cetaceans (IAMMWG, 2022, 2023), and by the Special Committee on Seals (SCOS) for grey seal (SCOS, 2023). For grey seal, the site boundary is located within the East Scotland Seal SMU, borders the Northeast England Seal SMU, and is within the vicinity of the Moray Firth Seal SMU. Thus, any European sites that are located within the East Scotland Seal MU were considered, and a precautionary buffer of 100 km was used to identify SACs within the adjacent SMUs which had the potential for connectivity with the Array.
27. There were 19 transboundary sites identified within the search areas outlined above. However, all relevant impact pathways were considered extremely weak, given the distance between the site boundary and the sites (from 246 to 687 km depending on the site) (Part 1, appendix 1A). As a result, only negligible effects would be apparent and could not contribute, in any material way, to an in-combination effect. As such, LSE2 associated with planned projects or other activities in the vicinity of the site boundary are also not anticipated for marine mammal features of any transboundary site.
28. No potential impact pathways were identified between the Array and any additional sites designated for Annex II marine mammals. Therefore, there is no potential for in-combination effects at any sites apart from those which are screened in for HRA Stage Two Appropriate Assessment (i.e. those listed in paragraph 17).

Figure 3.1: Location of all European Sites Designated for Annex II Diadromous Fish and Marine Mammals for which an Appropriate Assessment is Required

Table 3.1: Summary of all SACs for which the Potential for LSE2 could not be Discounted, and for Which Information to Support an Appropriate Assessment is Presented

4.             Information To Support the Appropriate Assessment

4. Information To Support the Appropriate Assessment

4.1.        Introduction

4.1. Introduction

29. As described in Part 1 of this RIAA, a European site is progressed to the Appropriate Assessment stage (Stage Two of the HRA process) where it is not possible to exclude an LSE2 on one or more of its qualifying interest features with regards to the site’s conservation objectives. European sites and potential impacts of the Array that require an Appropriate Assessment are therefore those for which LSE2 could not be ruled out during the HRA Stage One LSE2 Screening exercise and following consultation.
30. Information to help inform the Appropriate Assessment for SACs is provided in sections 4.2 to 4.6. The information provided includes a description of the SACs under consideration, their qualifying interest features, and an assessment of the implications of the Array for the site in view  of the conservation objectives of each site and considering any adverse effect on site integrity. A cross-referencing approach has been adopted to aide readability and reduce repetition where relevant, but this has been carefully carried out to ensure that all information required for a robust HRA of each site is presented. 

4.2.        Maximum Design Scenarios

4.2. Maximum Design Scenarios

31. All SAC assessment presented in this Part of the RIAA have been based on a realistic Maximum Design Scenario (MDS), which was derived from the Project Design Envelope (PDE). The final design will be no greater than the parameters set out in the MDS, and in some instances, may be less. An overview of the MDS considered for the assessment of potential impacts on Annex II diadromous fish and Annex II marine mammals is presented per potential impact (see sections 5.3 and 6.3 respectively). This MDS is consistent with that used for the fish and shellfish and marine mammal assessments in the Array EIA Report (Ossian OWFL, 2024).

4.3.        Designed in Measures

4.3. Designed in Measures

32. As part of the project design process, a number of designed in measures have been included in the Array and are committed to be delivered by the Applicant as part of the Array. These designed in measures are integrated into the project description for the Array and are not considered as mitigation measures intended to specifically avoid or reduce effects on European sites.
33. Measures intended specifically to avoid or reduce effects on European sites were not considered during the HRA Stage One LSE2 Screening exercise but are included within the HRA Stage Two Appropriate Assessment for determination of Adverse Effects on Integrity. Where relevant, this Part of the RIAA indicates whether adverse impacts on European sites are likely and if so, whether those effects can be avoided through the introduction of mitigation measures that avoid or reduce the impact. These measures are referred to as secondary mitigation and may be taken from the relevant chapters of the Array EIA Report (Ossian OWFL, 2024) or, where necessary, may have been developed specifically to comply with HRA requirements. Where the latter is the case, this has been made clear throughout.

4.4.        Baseline Information

4.4. Baseline Information

34. Baseline information on the SACs identified for further assessment within the HRA Stage Two Appropriate Assessment has been collated through a comprehensive review of existing desktop studies and datasets. Key desktop data sources are presented in sections 5.2 and 6.2 for Annex II diadromous fish and marine mammals, respectively. Further baseline information is presented within the respective topic chapters in the Array EIA Report and accompanying technical reports for fish and shellfish and marine mammals (Ossian OWFL, 2024).

4.5.        Conservation Objectives and Conservation Advice

4.5. Conservation Objectives and Conservation Advice

35. The Statutory Nature Conservation Bodies (SNCBs) have produced conservation advice for European sites under their statutory remit. Their conservation advice provides supplementary information on European sites and their features, and although the content provided is similar, the format of the advice provided varies between the different SNCBs.
36. Given the location and scale of the Array, European sites with the potential to be impacted fall under the remit of the Joint Nature Conservation Committee (JNCC), NatureScot, and/or Natural England. For example, the conservation advice for the Berwickshire and North Northumberland Coast SAC was developed jointly by NatureScot and Natural England but is hosted on Natural England’s Designated Site System as an interactive Conservation Advice Package (CAP). Further, the CAP for the Southern North Sea SAC has been jointly developed by Natural England and the JNCC but is hosted on JNCC’s website in the form of a ‘Conservation Objectives and Advice on Operations’ document. The Tweed Estuary SAC is under Natural England’s remit and therefore conservation advice is hosted on Natural England’s Designated Site System. However, the River Tweed SAC is located within the remit of both the Scottish Borders and Northumberland local authorities, and the CAP was produced by NatureScot and is hosted on the NatureScot sitelink system.
37. For those European sites under the statutory remit of NatureScot, CAP documents have been produced for all terrestrial SACs (many of the river SACs screened in for Annex II diadromous are considered terrestrial), while Conservation and Management Advice (CMA) documents cover marine SACs. These documents contain revised and updated conservation objectives for the features of each European site, site-specific clarifications, advice for the conservation objectives to be achieved, and advice on management required to achieve said conservation objectives. At the time of writing, the River Teith SAC was the only site which does not have a CAP, CMA document, or conservation advice documents such as those detailed in paragraph 36.
38. Conservation objectives of European sites set the framework for establishing appropriate conservation measures for each feature and provide a framework against which plans or projects can be assessed. The conservation objectives present the essential elements needed to ensure that the Favourable Conservation Status (FCS) of a qualifying habitat or species is maintained or restored at the site. The integrity of the site will be maintained if all the conservation objectives are met.
39. Within the NatureScot CAPs and CMAs, the conservation objectives comprise overarching objectives (objectives 1 and 2) that apply to all features of the site, and additional objectives (2a, 2b and 2c) that have been written for each feature. Site-specific supplementary advice is provided for each objective.
40. It is recognised in the conservation advice that if any feature of the European site is in unfavourable condition, the integrity of the site is deemed to be compromised and the overarching objective is therefore to restore site integrity. NatureScot guidance, however, states that with the ‘new style’ conservation objectives it is not expected that plans or projects must include measures that lead to restoration of features (where restore objectives are in place) in order to gain approval from a competent authority. Instead, a plan or project should not prevent site integrity from being able to be restored where necessary. This means that a plan or project should not prevent a feature from being able to be restored. HRAs should, therefore, focus on and consider if the plan or project is likely to undermine the conservation objectives of the site.

4.6.        Approach to the In-Combination Assessment

4.6. Approach to the In-Combination Assessment

41. The approach taken for the assessment of in-combination impacts has been partly informed by the Cumulative Effects Assessment (CEA) carried out for relevant topics in the Array EIA Report (Ossian OWFL, 2024). The methodology for the in-combination assessment is compliant with HRA guidance and is summarised in the following paragraphs.
42. The in-combination assessment has assessed potential impacts associated with the Array together with other relevant plans, projects and activities. In-combination effects are defined as the combined effect of the Array with the effects from a number of different plans or projects, on the same receptor or resource.
43. The screening undertaken for the CEA in the Array EIA Report has been used to inform the list of projects and plans relevant to the in-combination assessment. This involved a staged process that considered the level of detail available for projects, plans and activities, as well as the potential for interactions on a conceptual, physical and temporal basis. See volume 3, appendix 6.4 of the Array EIA Report for further details on the screening process).
44. The in-combination assessment presents relevant in-combination impacts of projects according to a tiered approach. This approach provides a framework for placing relative weight upon the potential for each project/plan to be included to ultimately be realised, based upon the project/plan’s current stage of maturity and certainty in the projects’ parameters. All projects/plans screened in via the previously described screening process have been allocated into one of the three Tiers for the in-combination assessment. It is worth noting that data collection is assessed against the source of this data (i.e. data confidence) to verify its accuracy and reliability. Where quantitative assessment has not been practicable, a mix of qualitative and quantitative or wholly qualitative assessment has been undertaken.
45. The tiered approach which has been utilised within the in-combination assessment employs the following tiers:

• Tier 1 assessment – Array with Proposed offshore export cable corridor(s) and Proposed onshore transmission infrastructure and all plans/projects which became operational since baseline characterisation, those under construction, and those with consent and submitted but not yet determined;
• Tier 2 assessment – All plans/projects assessed under Tier 1, plus projects with a Scoping Report; and
• Tier 3 assessment – All plans/projects assessed under Tier 2, which are reasonably foreseeable, plus those projects likely to come forward when an Agreement for Lease (AfL) has been granted.

46. The specific projects scoped into the in-combination assessment for Annex II diadromous fish and Annex II marine mammals are presented in sections 5.4 and 6.4, respectively. There will be no in-combination effects with the Proposed onshore transmission infrastructure for Annex II diadromous fish and marine mammals, as all onshore works are above MHWS. Therefore, there is no receptor-impact pathway, and the Proposed onshore transmission infrastructure component of Ossian has not been considered further within the in-combination assessment. However, the Proposed offshore export cable corridor(s) is included in the Tier 1 assessment, due to a potential receptor impact pathway for both Annex II diadromous fish and marine mammals.
47. To note, whilst the Proposed offshore export cable corridor(s) is in Tier 1 for the in-combination assessment, due to uncertainty in the final grid connection design and location details of the Proposed offshore export cable corridor(s), it was not possible to undertake a full detailed quantitative assessment at the time of writing.
48. All of the potential impacts included for the alone assessment (see Table 3.1   Open ▸ ) were brought forward to the in-combination assessment. Some of the potential impacts considered within the Array alone assessment are specific to a particular phase of development. The potential for in-combination effects with other plans or projects requires spatial or temporal overlap with the Array during certain phases of development, therefore potential impacts associated with a certain phase have been omitted from further consideration where no plans or projects were identified to have the potential for in-combination effects during that phase.
49. The in-combination assessment for each Tier generally follows the same methodology for each impact as the alone assessment, in order to conclude the potential for an adverse effect of integrity of the SACs.   

5.             Assessment of Potential Adverse Effects on Integrity: Annex II Diadromous Fish

5. Assessment of Potential Adverse Effects on Integrity: Annex II Diadromous Fish

5.1.        Introduction

5.1. Introduction

50. This section provides background information and an explanation for the approach taken to assess the potential impacts of the Array on European sites designated for Annex II diadromous fish.
51. As stated in section 3.1, the potential for LSE2 was identified for the Annex II diadromous fish features of nine SACs, which are listed in Table 5.1   Open ▸ and illustrated in Figure 5.1   Open ▸ .

Table 5.1: European Sites Designated for Annex II Diadromous Fish Features for which an Appropriate Assessment is Presented

Figure 5.1: Location of European Sites Designated for Annex II Diadromous Fish for which an Appropriate Assessment is Required

52. LSE2s on the SACs presented in Table 5.1   Open ▸ were identified for the construction and operation and maintenance phases of the Array, and these are outlined in Table 5.3   Open ▸ A range of designed in measures have been committed to as part of the Array, these are presented, where relevant, in section 5.3.

Table 5.2: Potential For Impact to Annex II Diadromous Fish

53. The Stage Two Appropriate Assessment (considering effects of the Array both alone and in-combination) for European sites designated for Annex II diadromous fish are presented in section 5.3 and 5.4 respectively. A summary of Assessments undertaken within this Part of the RIAA is provided in section 7.
54. Freshwater pearl mussel has been considered within this section (specifically as a qualifying feature of the River Dee SAC, River South Esk SAC, River Spey SAC, and the River Oykel SAC) because the larval stage of its life cycle is reliant on salmonid species, such as Atlantic salmon (see paragraph 16). The potential for adverse effects to freshwater pearl mussel, if they occur at all, would be indirect and would occur as a result of direct effects on Atlantic salmon, which are a relevant host species for freshwater pearl mussel within the SACs assessed.

5.2.        Baseline

5.2. Baseline

55. Baseline information on the relevant screened in Annex II diadromous fish and freshwater pearl mussel features has been gathered through a comprehensive desktop study of existing datasets and materials. Full detail is provided in volume 2, chapter 9 and volume 3, appendix 9.1 of the Array EIA Report (Ossian OWFL, 2024).
56. Within the Array EIA Report, a broad fish and shellfish ecology study area was defined and agreed with SNCBs for the purposes of the baseline characterisation. It encompassed a buffer of 100 km around the site boundary and included the Firth of Forth. A buffer of 100 km was used as it represented a precautionary Zone of Influence (ZoI) of potential impacts due to underwater noise. The fish and shellfish ecology study area provides wider context for the spatially and temporally variable Annex II diadromous fish species and encompasses a potential area in which they may migrate to and from the various SACs assessed in this Part of the RIAA ( Figure 5.1   Open ▸ ). Based on feedback from SNCBs, an additional three SACs in the Moray Firth (and therefore out with the fish and shellfish ecology study area) have been brought forward for Appropriate Assessment ( Figure 5.1   Open ▸ , see Table 2.1   Open ▸ ).

5.2.1.    River Dee SAC

5.2.1. River Dee SAC

                        Site description

57. At its closest point, the River Dee SAC is located 80.57 km north-west from the site boundary. The entire length of the River Dee is designated as a SAC due to its importance for Atlantic salmon and freshwater pearl mussel. The River Dee originates in the Cairngorms and flows through southern Aberdeenshire to reach the North Sea at Aberdeen. The site covers an area of 2,334.48 ha and is designated for the following Annex II diadromous fish features: Atlantic salmon and freshwater pearl mussel (NatureScot, 2020c). 

                        Feature accounts

                        Atlantic salmon

58. As a diadromous species, Atlantic salmon live in both freshwater and marine environments throughout their life cycle. Adult Atlantic salmon spawn in the rivers that they were born in (referred to as ‘natal rivers’) from November to December, and females lay their eggs in gravel depressions known as ‘redds’. These are immediately fertilised by a male, and the female will cover the fertilised eggs with gravel (NatureScot, 2023a). The eggs typically hatch in early spring and are known as ‘fry’ when they reach around 3 cm in length. They develop into ‘parr’ once they develop markings on their sides, and live in the river for two to three years before migrating to the sea as ‘smolts’ and ‘post-smolts’ (NatureScot, 2023a). After one to three years at sea, adult Atlantic salmon migrate back to their natal river to spawn again. Individuals that only spend one year at sea, before migrating back to spawn are referred to as ‘grilse’, which reach 2 kg to 3 kg in weight (Malcolm et al., 2010, NatureScot, 2023a, Scottish Government, 2019). Individuals that spend two to three years at sea before returning to spawn are referred to as ‘multi-sea-winter salmon’ and are typically larger than grilse as they’ve spent more time feeding in marine environments (usually off the coast of Greenland) (Malcolm et al., 2010, NatureScot, 2023a, Scottish Government, 2019). Around 90% to 95% of Atlantic salmon will die after spawning, but those which survive may spawn again (NatureScot, 2023a).
59. Malcolm et al. (2015) used metadata to assess the timing of smolt emigration across Scotland. This suggested that most fish leave rivers between mid-April and the end of May. These results do not include the period spent by smolts in the coastal environment after leaving their natal rivers. There was also evidence that smolt emigration is becoming earlier (by around 1.5 days per decade over a period of around 50 years) (Malcolm et al., 2015).
60. Various cues are involved during their return migration to their natal rivers; in earlier phases, sun position and Earth’s magnetic field seem to play a role in oceanic orientation (Hansen et al., 1998). Tidal phase and time of day have also been suggested as important factors for their upstream migration (Smith et al., 1997). Migration upstream of estuaries have also been observed to be nocturnal, occurring during ebb tides (Smith et al., 1997). In the final phase of the upstream migration, olfactory cues direct Atlantic salmon up the river (Hasler et al., 1983). For smolts migrating downstream, migratory activity has been identified to be associated with night time while daytime was utilised more for prey detection and predator avoidance  (Hedger et al., 2008). Upon reaching the North Sea, the post-smolts are transported by water currents towards northern Norway and then into the Norwegian Sea (Jonsson et al., 1993). Further evidence from Atlantic salmon from the east coast of Scotland (i.e. from the River Dee, River Tay and River North Esk) recaptured in Greenland and the Faroe Islands waters showed that smolts emigrated west to feed and grow (Malcolm et al., 2010).
61. This is further supported by evidence from the Moray Firth (Gardiner et al., 2018b, Newton et al., 2019, Newton et al., 2017), which suggests that smolts migrating from their rivers in the Moray Firth head directly across the North Sea relatively rapidly. Newton et al. (2017) also showed the majority remained predominantly within the upper 1 m of the water column during migration. Mortality of smolts was considered mainly attributable to predation and there was a strong relationship between group survival, early migration and group size.  It is thought that this route, rather than moving in a coastal direction upon leaving their natal rivers, allows them to take advantage of east flowing currents which cross the North Sea. This fast progress away from the coast limits exposure to predators occurring close to the coast. Similar evidence of a rapid easterly migration out into the North Sea has also been shown for the River Dee in Aberdeenshire (Gardiner et al., 2018a). Therefore, it could be assumed that smolts from other east coast rivers (e.g. the River Tay, River Dee, River South Esk, River Tweed, and River Teith) would move in a similar fashion.
62. Between 2018 to 2021, a tagging study was conducted on juvenile Atlantic salmon and sea trout migrating from the River Dee (River Dee Trust et al., 2023). Atlantic salmon were found to travel at an average speed of 0.45 m/s from the river mouth to around 4 km offshore, before dropping to 0.24 m/s between 4 km to 20 km offshore (River Dee Trust et al., 2023). Individuals mostly swam within the top 3 m of the water column and swam in an easterly direction in the first 4 km, before following a south-easterly trajectory. This pattern was consistent over the three years of the study, suggesting that this is a regular migratory route and that Atlantic salmon must make a northerly course adjustment at some point in their migration to reach higher latitude feeding grounds in the Norwegian Sea (River Dee Trust et al., 2023). The authors concluded that this easterly and south-easterly migratory trajectory suggests that Atlantic salmon could be present in offshore areas of the North Sea.
63. Atlantic salmon numbers have declined throughout their geographic range, including in Scottish rivers (JNCC, 2024e, NatureScot, 2020c). The most recent wild Atlantic salmon total rod catch data reported 42,204 individuals in 2022, the fourth lowest record since the start of the statistics on salmon fisheries in Scotland by Marine Scotland in 1952 (Scottish Government, 2023). This is an increase from the 35,693 recorded in 2021 (Scottish Government, 2022), but still provides evidence of the population declines of Atlantic salmon in Scotland.
64. Atlantic salmon are of considerable cultural and conservation importance (Hindar et al., 2011). The species is subject to many pressures in both marine and freshwater environments. These include pollution, the introduction of non-native salmon stocks, physical barriers to migration, exploitation from netting and angling, physical degradation of spawning and nursery habitat, and increased marine mortality (Oslo Paris Convention (OSPAR) Commission (2024)). Since 2016, as a result of the Salmon Conservation Regulations, Atlantic salmon caught in coastal waters must be released. This was implemented to prevent the killing of Atlantic salmon in coastal waters and estuaries to protect stocks that were in poor conservation status.
65. Alongside other salmonids (such as sea trout Salmo trutta), Atlantic salmon are host species for the parasitic larval phase of freshwater pearl mussel. Freshwater pearl mussel are strictly freshwater species and have seen population declines throughout their UK range. A decline in Atlantic salmon stocks is one of the factors corresponding to this population decline. As stated in paragraph 16, the potential impact s to Atlantic salmon can directly affect populations of Annex II freshwater pearl mussel, which has been assessed alongside Atlantic salmon in this Part of the RIAA.

                        Freshwater pearl mussel

66. Freshwater pearl mussels are long-lived freshwater molluscs that live in beds of clear, well-oxygenated, and fast-flowing rivers that are free of turbidity and pollution (JNCC, 2024d). They burrow into sandy substrates, often between boulders and pebbles (JNCC, 2024d). During their parasitic larval stage, they are dependent upon a healthy population of salmonids (young Atlantic salmon or sea trout) which act as host species (Taeubert et al., 2017). Freshwater pearl mussel larvae attach to the gills of salmonid fish in mid to late summer and drop off the following spring. When they detach from their hosts they must land in sandy or gravelly substrates to settle and grow to adulthood (JNCC, 2024d). In suitable conditions they can live for over 100 years and grow up to 20 cm.
67. They are filter feeders, and are therefore particularly vulnerable to pollution and other changes in water quality (NatureScot, 2023b). Other threats to freshwater pearl mussels include hydrological alterations (including river engineering and abstractions), habitat degradation of river beds and banks, illegal fishing, and availability of host salmonids (JNCC, 2024d, NatureScot, 2023b).
68. The freshwater pearl mussel is widely distributed in Europe and north-eastern North America, but has suffered serious decline and is threatened with extinction or is highly vulnerable in every part of its former range (JNCC, 2024d, NatureScot, 2023b). It is listed as ‘critically endangered’ in Europe by the International Union for the Conservation of Nature and Natural Resources (IUCN) (Moorkens, 2011). The species was formerly widespread throughout western and northern parts of the UK. However, England and Wales are each now believed to support only a single recruiting population. In Northern Ireland the species formerly occurred widely in several catchments but is now restricted to a few sites (NatureScot, 2023b). Many UK rivers now contain only scattered individuals, with no juvenile mussels recorded; such populations may become extinct due to lack of recruitment. Despite serious declines in both range and total population, Scotland is the remaining European stronghold for the species, supporting functional populations in over 50 rivers, mainly in the Highlands. Of the 26 SACs designated for freshwater pearl mussel, 19 are in Scotland, and four of these are included in this Part of the RIAA (e.g. the River Dee SAC, River South Esk SAC, River Spey SAC, and River Oykel SAC).

                        Conservation objectives

69. Conservation objectives for the River Dee SAC have been developed by NatureScot as part of a CAP (NatureScot, 2020c). Conservation objectives for all qualifying features of this SAC are:

• to ensure that the qualifying features of the River Dee SAC are in favourable condition and make an appropriate contribution to achieving FCS; and
• to ensure that the integrity of the River Dee SAC is restored by meeting objectives 2a, 2b, 2c for each qualifying feature (and 2d for freshwater pearl mussel) (NatureScot, 2020c).

70. Conservation objectives for freshwater pearl mussel are as follows:

• 2a. Restore the population of freshwater pearl mussel as a viable component of the site;
• 2b. Restore the distribution of freshwater pearl mussel throughout the site;
• 2c. Restore the habitats supporting freshwater pearl mussel within the site and availability of food; and
• 2d. Restore the distribution and viability of freshwater pearl mussel host species and their supporting habitats (NatureScot, 2020c).

71. Conservation objectives for Atlantic salmon are as follows:

• 2a. Restore the population of Atlantic salmon, including range of genetic types, as a viable component of the site;
• 2b. Restore the distribution of Atlantic salmon throughout the site; and
• 2c. Restore the habitats supporting Atlantic salmon within the site and availability of food (NatureScot, 2020c).

72. The overarching conservation objectives detailed in paragraph 69 are related to the species-specific conservation objectives 2a to 2c for Atlantic salmon and 2a to 2d for freshwater pearl mussel. Therefore, the assessment of the Array alone and in-combination with other plans and projects focuses on the individual species-specific conservation objectives. This allows a proportionate approach, as by demonstrating that potential impact s associated with the Array alone and in-combination with other plans and projects will not have an adverse effect on the species-specific conservation objectives (2a to 2c/2d), the overarching conservation objectives will therefore not be impaired.

                        Condition assessment

73. The condition of Atlantic salmon was assessed in 2011, and in 2014 for freshwater pearl mussel (NatureScot, 2020c). The outcomes of these feature condition assessments were as follows:

• freshwater pearl mussel: unfavourable – declining; and
• Atlantic salmon: favourable – maintained.

74. Freshwater pearl mussel was assessed as being in unfavourable condition due to the low number and density of freshwater pearl mussels present. This is due to low levels of juvenile recruitment, water flow, river morphology, the presence of filamentous algae, and water quality at the SAC (NatureScot, 2020c).

5.2.2.    River South Esk SAC

5.2.2. River South Esk SAC

                        Site description

75. At its closes point, the River South Esk SAC is located 107.13 km west from the site boundary. The site is located in Angus in Eastern Scotland and covers 471.85 ha. The site is designated solely for Atlantic salmon and freshwater pearl mussel (NatureScot, 2020e).

                        Feature accounts

                        Atlantic salmon

76. The ecology of Atlantic salmon is as described above in section 5.2.1, and not repeated here. The SAC supports a large, high-quality Atlantic salmon population. The River South Esk has a strong nutrient gradient along its length, rising in the nutrient-poor Grampians and flowing for half of its length through the rich agricultural lands of Strathmore. The high proportion of the South Esk which is accessible to salmon and the range of ecological conditions in the river allows it to support the full range of life-history types found in Scotland, with sub-populations of spring, summer salmon and grilse all being present (JNCC, 2024g).

                        Freshwater pearl mussel

77. The ecology of freshwater pearl mussel is as described above in section 5.2.1, and not repeated here,. This species is abundant in the River South Esk and is highest in the middle reaches of the river where they attain densities > 20 m2. The conservation importance of the site is further increased by the abundance of juveniles which comprise approximately 20% of the population. The presence of juvenile freshwater pearl mussels >20 mm long indicates that there has been successful recruitment since monitoring began in 1996 (JNCC, 2024g).

                        Conservation objectives

78. Conservation objectives for the River South Esk SAC have been developed by NatureScot as part of a CAP (NatureScot, 2020e). Conservation objectives for all qualifying features of the SAC are:

• to ensure that the qualifying features of the River South Esk SAC are in favourable condition and make an appropriate contribution to achieving FCS; and
• to ensure that the integrity of the River South Esk SAC is restored by meeting objectives 2a, 2b, 2c for each qualifying feature (and 2d for freshwater pearl mussel) (NatureScot, 2020e).

79. Conservation objectives for freshwater pearl mussel are as follows:

• 2a. Restore the population of freshwater pearl mussel as a viable component of the site;
• 2b. Restore the distribution of freshwater pearl mussel throughout the site;
• 2c. Restore the habitats supporting freshwater pearl mussel within the site and availability of food; and
• 2d. Restore the distribution and viability of freshwater pearl mussel host species and their supporting habitats (NatureScot, 2020e).

80. Conservation objectives for Atlantic salmon are as follows:

• 2a. Restore the population of Atlantic salmon, including range of genetic types, as a viable component of the site;
• 2b. Restore the distribution of Atlantic salmon throughout the site; and
• 2c. Restore the habitats supporting Atlantic salmon within the site and availability of food (NatureScot, 2020e).

81. The overarching conservation objectives detailed in paragraph 78 are related to the species-specific conservation objectives 2a to 2c for Atlantic salmon and 2a to 2d for freshwater pearl mussel. The assessment of the Array alone and in-combination with other plans and projects focuses on the individual species-specific conservation objectives. This allows a proportionate approach, as by demonstrating that potential impacts  associated with the Array alone and in-combination with other plans and projects will not have an adverse effect on the species-specific conservation objectives (2a to 2c/2d), the overarching conservation objectives will therefore not be impaired.

          Condition assessment

82. The condition of Atlantic salmon was assessed in 2011, and in 2009 for freshwater pearl mussel (NatureScot, 2020e). The outcomes of these feature condition assessments were as follows:

• freshwater pearl mussel: unfavourable – no change; and
• Atlantic salmon: unfavourable – recovering. 

83. Freshwater pearl mussel was assessed as being in unfavourable condition due to the low number and density of freshwater pearl mussels present. This is due to low levels of juvenile recruitment, biological oxygen demand, and disturbance of mussel beds through largely historical fishing (NatureScot, 2020e).

5.2.3.    Tweed Estuary SAC

5.2.3. Tweed Estuary SAC

                        Site description

84. At its closest point, the Tweed Estuary SAC is located 128.65 km south-west from the site boundary. The site, located in Northumberland, encompasses the Tweed Estuary, a long and narrow estuary discharging into the North Sea. The site covers an area of 155.93 ha.  The site is designated for Annex I habitats and Annex II river lamprey and sea lamprey (with the latter being applicable to this Part of the RIAA) (Natural England, 2018).

                        Feature accounts

                        Sea lamprey

85. The sea lamprey is a primitive, jawless fish which resembles an eel. It is the largest of the three lamprey species found in the UK (with the other two being river lamprey and brook lamprey Lampetra planeri) (NatureScot, 2023c). As a diadromous species, the sea lamprey requires both freshwater and marine habitats during different phases of its life cycle. Adults require estuaries and easily accessible rivers with clean gravel substrates in which to spawn. Hatched larvae are referred to as ammocoetes, which drift downstream with the current and settle in nursery habitats with fine, soft substrate in well-oxygenated and slow-flowing freshwater (NatureScot, 2023c). Sea lamprey ammocoetes may remain in their freshwater nurseries for up to eight years before the metamorphose into adults and migrate to the marine environment, where they are parasitic predators on a range of different fish species (Hume, 2017; Maitland, 2003). These prey species include large fish, such as salmonids, but sea lamprey have been recorded as a parasitic predator on at least 54 different fish and marine mammal species (Silva et al., 2014). Sea lamprey remain at sea for 18 to 24 months, before migrating upstream into freshwater spawning habitats between April and May. They spawn in May and June, and die after spawning (JNCC, 2023c). During spawning, they have preference for warm waters (JNCC, 2023c). In contrast to Atlantic salmon (see paragraph 58), there is no evidence of homing behaviour to natal rivers in sea lamprey (Scottish Government, 2019).
86. Sea lamprey are rarely captured in coastal and estuarine waters, suggesting that they are solitary hunters and widely dispersed at sea, and can be found at considerable depths (up to 4,099 m) (Scottish Government, 2019). As they are parasites during the adult marine phase of their life cycle, their distribution at sea is largely dictated by their host species (Scottish Government, 2019). As such it is not expected that they will be particularly attracted to structures associated with offshore wind developments. However, this is not certain, as there is limited information available on the utilisation of the marine environment by sea lamprey. It is a possibility that sea lamprey will be present in the vicinity of the Array.
87. The sea lamprey occurs over much of the Atlantic coastal area of western and northern Europe (from northern Norway to the western Mediterranean) and eastern North America, and is reasonably widespread in UK rivers (JNCC, 2023c). However, sea lamprey has declined in parts of its UK range and has become extinct in a number of rivers. It appears to reach its northern limit of distribution in Scotland and does not occur north of the Great Glen (see section 5.2.6) (JNCC, 2023c).
88. The Tweed Estuary SAC, together with the River Tweed SAC (see section 5.2.4), was designated for its significant presence of sea lamprey (Natural England, 2018). Sea lamprey migrates through the Tweed Estuary to reach freshwater spawning grounds in the main River Tweed and its tributaries in late May and June. Downstream juvenile migration occurs in July to September (Maitland, 2003). Given the difficulty in surveying sea lamprey larvae, they were only recorded in the lower part of the main river in the Tweed catchment in a 2004 dataset (NatureScot, 2020a). It is unclear whether or not this reflects the actual distribution of sea lamprey or whether it is due to the difficulties of sampling sea lamprey as reports of spawning and adults were historically more widespread over the catchment (NatureScot, 2020a). The 2004 dataset also presented evidence for three years of spawning sea lamprey in the lower Tweed (NatureScot, 2020a). However, a more recent survey in 2013 did not find any records of sea lamprey ammocoetes (Campbell, 2013).
89. Sea lamprey use the Tweed Estuary for migration and feeding between their freshwater spawning grounds and coastal waters. Man-made features such as weirs and dams, as well as polluted sections of the River Tweed may impede migration (Natural England, 2018). Within the adjacent freshwater River Tweed SAC (see section 5.2.4), sea lamprey need clean gravel for spawning, and marginal silt or sand for juveniles to burrow in (Natural England, 2018).

                        Conservation objectives

90. The conservation objectives for the Tweed Estuary SAC were developed by Natural England (2018). These high-level objectives ensure that, subject to natural change, the integrity of the site is maintained or restored as appropriate, and that the site contributes to achieving the FCS of its qualifying features, by maintaining or restoring:

• the extent and distribution of qualifying natural habitats and habitats of the qualifying species;
• the structure and function (including typical species) of qualifying natural habitats;
• the structure and function of the habitats of the qualifying species;
• the supporting processes on which qualifying natural habitats and the habitats of qualifying species rely;
• the populations of each of the qualifying species; and
• the distribution of qualifying species within the site (Natural England, 2018).

91. The second conservation objective: ‘the structure and function (including typical species) of qualifying natural habitats’ is only relevant to the Annex I habitat features of the Tweed Estuary SAC and is therefore not included further in this assessment on Annex II diadromous fish features.
92. Supplementary advice on conservation objectives (last updated on 09 May 2023), provide the site-specific attributes and targets specific to the sea lamprey feature of the site. All targets for the sea lamprey feature have been set as ‘Maintain’ by Natural England, using expert judgement based on knowledge of the sensitivity of the feature to activities that are occurring/have occurred on the site (Natural England, 2023b). A summary of the conservation targets for sea lamprey are as follows:

• maintain the unrestricted usage of the estuary by adult and juvenile sea lamprey including for migratory passage and juvenile development;
• maintain the reproductive and recruitment capability of the species;
• maintain the presence and spatial distribution of the species and their ability to undertake key life cycle stages and behaviours;
• maintain connectivity of estuarine features to surrounding rivers, freshwater, marine and coastal habitats, to ensure larval dispersal and recruitment, maintain nursery grounds for mobile species, and to allow movement of migratory species;
• maintain the extent and spatial distribution of the following supporting habitats: water column;
• maintain the abundance of preferred food items required by the species;
• maintain the natural physico-chemical properties of the water;
• maintain all hydrodynamic and physical conditions such that natural water flow is not significantly altered or constrained;
• reduce aqueous contaminants to levels equating to High Status according to Annex VIII and Good Status according to Annex X of the Water Framework Directive (WFD), avoiding deterioration from existing levels. This target was set using the Environmental Agency 2019 water body classifications data;
• maintain the dissolved oxygen concentration at levels equating to High Ecological Status (specifically ≥ 5.7 mg/L (at 35 salinity) for 95% of year) avoiding deterioration from existing levels. This target was set using the Environmental Agency 2019 water body classifications data;
• maintain water quality at mean winter dissolved inorganic nitrogen levels where biological indicators of eutrophication (opportunistic macroalgal and phytoplankton blooms) do not affect the integrity of the site and features, avoiding deterioration from existing levels. This target was set using the Environmental Agency 2019 water body classifications data; and
• maintain natural levels of turbidity (e.g. concentrations of suspended sediment, plankton and other material) in areas where this species is, or could be present (Natural England, 2023b).

                        Condition assessment

93. The condition of the Tweed Estuary SAC’s features had not been assessed at the time of writing (Natural England, 2018).

5.2.4.    River Tweed SAC

5.2.4. River Tweed SAC

                        Site description

94. At its closest point, the River Tweed SAC is located 133.40 km south-west from the site boundary. The site, located in Eastern Scotland and Northumberland and Tyne and Wear encompasses 3,742.62 ha of the River Tweed’s catchment and 1,285 km of watercourse (NatureScot, 2020h). The site is designated for Annex I habitats and Annex II species, including diadromous fish species relevant to this assessment: Atlantic salmon and sea lamprey.

                        Feature accounts

                        Atlantic salmon

95. The ecology of Atlantic salmon is as described above in section 5.2.1, and not repeated here,. The River Tweed supports a very large, high-quality population of Atlantic salmon, with sub-catchments in both Scotland and England. The river is the best example in the UK of a large river showing a strong nutrient gradient along its length, with oligotrophic conditions in its headwaters, and nutrient-rich lowland conditions just before it enters the sea at Berwick (JNCC, 2024k). The river supports the full range of salmon life history types, with sub-populations of spring, summer salmon and grilse all being present  (JNCC, 2024k). Research by Gauld (2014) and Gauld et al. (2016) suggested that Atlantic salmon mainly spawn in the main lower stretches of the channel of the River Tweed. The extensive system supports a significant proportion of the Scottish salmon resource. In recent years, the salmon catch in the River Tweed is the highest in Scotland, with up to 15% of all salmon caught (JNCC, 2024k).

                        Sea lamprey

96. The ecology of sea lamprey is as described above in section 5.2.3, and not repeated here,. In the English waters of the River Tweed SAC, sea lamprey are believed to spawn in the lower reaches of the main river although features such as weirs and dams may impede migration to spawning grounds (Natural England, 2022). Sea lamprey seems to be relatively poor at ascending obstacles to migration (in comparison to river lamprey), and are frequently restricted to the lower reaches of rivers (Natural England, 2022). Within the River Tweed SAC, there are excellent examples of the features that sea lamprey needs for survival, including areas of silt, sand, gravel and cobbles in the middle to lower reaches of the river which provide suitable spawning and nursery habitat (Natural England, 2022).

                        Conservation objectives

97. The River Tweed SAC crosses the border between England and Scotland. Management of the River Tweed SAC is shared by Natural England and NatureScot and conservation objectives for the site have been published by both SNCBs (Natural England, 2022, NatureScot, 2020h). In this assessment, both sets of conservation objectives have been consulted as the features being assessed are diadromous fish, and therefore may migrate to and from the English or Scottish parts of the SAC.
98. A CAP for the River Tweed SAC has been developed by NatureScot (NatureScot, 2020h). Conservation objectives for Atlantic salmon and sea lamprey are:

• to ensure that the qualifying features of the River Tweed SAC are in favourable condition and make an appropriate contribution to achieving FCS; and
• to ensure that the integrity of the River Tweed SAC is restored by meeting objectives 2a, 2b, 2c for each qualifying feature (NatureScot, 2020h).

99. Conservation objectives for Atlantic salmon are as follows:

• 2a. Maintain the population of Atlantic salmon, including range of genetic types, as a viable component of the site;
• 2b. Maintain the distribution of Atlantic salmon throughout the site; and
• 2c. Maintain the habitats supporting Atlantic salmon within the site and availability of food (NatureScot, 2020h).

100. Conservation objectives for sea lamprey are as follows:

• 2a. Maintain the population of the lamprey species’ as viable components of the site;
• 2b. Maintain the distribution of the lamprey species throughout the site; and
• 2c. Maintain the habitats supporting the lamprey species within the site, and availability of food (NatureScot, 2020h).

101. The overarching conservation objectives detailed in paragraph 98 are related to the species-specific conservation objectives 2a to 2c for Atlantic salmon and sea lamprey. The assessment of the Array alone and in-combination with other plans and projects focuses on the individual species-specific conservation objectives. This allows a proportionate approach, as by demonstrating that potential impacts associated with the Array alone and in-combination with other plans and projects will not have an adverse effect on the species-specific conservation objectives (2a to 2c), the overarching conservation objectives will therefore not be impaired.
102. Conservation objectives and related supplementary advice developed by Natural England apply to those parts of the SAC lying in England (Natural England, 2022). The high-level objectives for the site are:

• to ensure that the integrity of the site is maintained or restored as appropriate, and ensure that the site contributes to achieving the FCS of its Qualifying Features, by maintaining or restoring:

–           the extent and distribution of qualifying natural habitats and habitats of qualifying species;

–           the structure and function (including typical species) of qualifying natural habitats;

–           the structure and function of the habitats of qualifying species;

–           the supporting processes on which qualifying natural habitats and the habitats of qualifying species rely;

–           the populations of qualifying species; and

–           the distribution of qualifying species within the site (Natural England, 2022).

103. The second conservation objective: ‘the structure and function (including typical species) of qualifying natural habitats’ is only relevant to the Annex I habitat features of the River Tweed SAC and is therefore not included further in this assessment on Annex II diadromous fish features.
104. Supplementary advice on conservation objectives (published on 31 August 2022) (Natural England, 2022) provides the site-specific attributes and targets specific to the Atlantic salmon and sea lamprey features of the SAC. Conservation targets for Atlantic salmon are summarised here:

• restore the population to that expected under un-impacted conditions, allowing for natural fluctuations;
• maintain juvenile densities at those expected under un-impacted conditions throughout the site, taking into account natural habitat conditions and allowing for natural fluctuations;
• restore the distribution of spawning to reflect un-impacted conditions through the site, and avoid reductions in existing levels;
• maintain or where necessary restore the distribution and continuity of the feature and its supporting habitat, including where applicable its component vegetation types and associated transitional vegetation types, across the site;
• maintain or where necessary restore the total extent of the habitats which support the feature at 156.20 km (the entire length of the English portion of the river), including habitat mosaics, supply of coarse and fine sediment, water flows, underlying soil types, water quality, vegetation, and thermal regime;
• the movement of other characteristic biota should not be artificially constrained;
• maintain or where necessary restore the feature's ability, and that of its supporting habitat, to adapt or evolve to wider environmental change, either within or external to the site;
• ensure non-native species categorised as 'high-impact' in the UK under the WFD are either rare or absent but if present are causing minimal damage to the feature;
• maintain or, where necessary, restore concentrations and deposition of air pollutants to at or below the site-relevant Critical Load or Level values given for this feature of the site;
• ensure exploitation (e.g. netting or angling) of Atlantic salmon is undertaken sustainably without compromising any components of the population, including multi-sea winter fish and seasonal components of the adult run;
• ensure fish stocking introductions do not interfere with the ability of the river to support self-sustaining populations of the feature; and
• maintain a sufficient proportion of all aquatic macrophytes to allow them to reproduce in suitable habitat and unaffected by river management practices (Natural England, 2022).

105. Natural England (2022) conservation targets for sea lamprey are summarised here:

• maintain or where necessary restore juvenile densities at those expected under unimpacted conditions throughout the site, taking into account natural habitat conditions and allowing for natural fluctuations;
• maintain or where necessary restore the abundance of the population to a level which is close to that expected under unimpacted conditions throughout the site (subject to natural habitat conditions and allowing for natural fluctuations), whilst avoiding deterioration from its current level as indicated by the latest mean peak count or equivalent;
• maintain or where necessary restore the distribution and continuity of the feature and its supporting habitat, including where applicable its component vegetation types and associated transitional vegetation types, across the site;
• maintain or where necessary restore the total extent of the habitats which support the feature at 156.20 km (the entire length of the English portion of the river), including habitat mosaics, nutrient regimes, supply of coarse and fine sediment, water flows, underlying soil types, water quality, vegetation, and thermal regime;
• the movement of other characteristic biota should not be artificially constrained;
• all exploitation (e.g. netting or angling) of sea lamprey should be undertaken sustainably without compromising any components of the population;
• ensure fish stocking/introductions do not interfere with the ability of the river to support self-sustaining populations of the features;
• all intakes and discharges likely to trap a significant number of individuals of characteristic species are being adequately screened;
• ensure non-native species categorised as 'high-impact' in the UK under the WFD are either rare or absent but if present are causing minimal damage to the feature;
• maintain or, where necessary, restore concentrations and deposition of air pollutants to at or below the site-relevant Critical Load or Level values given for this feature of the site; and
• maintain the feature's ability, and that of its supporting processes, to adapt or evolve to wider environmental change, either within or external to the site (Natural England, 2022).

                        Condition assessment

106. The condition of Atlantic salmon was assessed in 2011, and in 2018 for sea lamprey (NatureScot, 2020h). The outcome of the feature condition assessment was as follows:

• Atlantic salmon: favourable – maintained; and
• sea lamprey: unfavourable – declining (NatureScot, 2020h).

107. Sea lamprey was assessed as being in unfavourable condition at this SAC due to a restricted distribution within the Tweed catchment. The Mertoun weir at St Boswells is potentially a significant obstacle for sea lamprey, although other fish species are largely successful at migrating upstream of the structure (NatureScot, 2020h). Despite the presence of a fish pass, river flow rates over the weir, particularly during upstream migrations, may not be suitable for the species. As a result, sea lamprey may be largely restricted to the lower Tweed. Better evidence is required to provide a true picture of sea lamprey distribution at this SAC and the impacts of the Mertoun weir on this (NatureScot, 2020h).
108. Although the conservation objectives for sea lamprey are phrased in order to ‘maintain’ the species’ population, distribution and habitats (paragraph 100), the condition assessment concluded the sea lamprey feature of this SAC to be in unfavourable declining condition (paragraph 106). Therefore, the conservation objectives for the sea lamprey feature of this SAC have been assessed throughout as ‘maintained or restored’ to account for this condition assessment.

5.2.5.    River Tay SAC

5.2.5. River Tay SAC

                        Site description

109. At its closest point, the River Tay SAC is located 162.32 km west from the site boundary. The site comprises the longest river in Scotland, originating in western Scotland, flowing easterly across the Highlands before becoming tidal at the Firth of Tay. The River Tay drains a very large catchment, and has the greatest flow of all UK rivers (JNCC, 2024i). The site covers an area of 9,461.63 ha. The site is designated for Annex I habitats and Annex II species including diadromous fish species relevant to this assessment: Atlantic salmon and sea lamprey (NatureScot, 2020g).

                        Feature accounts

                        Atlantic salmon

110. The ecology of Atlantic salmon is as described above in section 5.2.1, and not repeated here,. The River Tay supports a high-quality Atlantic salmon population, with rod catch returns showing that it is consistently one of the top three salmon rivers in Scotland (JNCC, 2024i). In 1999 the catch was 7,230 fish, over 10% of the Scottish total (JNCC, 2024i). There is considerable ecological variety in the River Tay catchment, resulting in the SAC supporting the full range of salmon life history types found in Scotland, with adult salmon entering the River Tay throughout the year to spawn in different parts of the catchment (JNCC, 2024i).
111. As stated in paragraph 63, Atlantic salmon numbers have declined throughout their geographic range, including in Scottish rivers. At the River Tay, the proliferation of small scale hydro schemes, Invasive Non Native Species (INNS) such as the North American signal crayfish Pacifastacus leniusculus, and diffuse pollution from agriculture are having a notable impact upon the Atlantic salmon population (NatureScot, 2020g).

                        Sea lamprey

112. The ecology of sea lamprey is as described above in section 5.2.3, and not repeated here,. At the River Tay, the main issues that may affect sea lamprey are obstructions to passage (e.g. from hydro-schemes), diffuse pollution, and river engineering (NatureScot, 2020g).

                        Conservation objectives

113. Conservation objectives for the River Tay SAC have been developed by NatureScot as part of a CAP (NatureScot, 2020g). Conservation objectives for all qualifying species features are:

• to ensure that the qualifying features of River Tay SAC are in favourable condition; and
• to ensure that the integrity of the River Tay is maintained by meeting objectives 2a, 2b and 2c for each qualifying feature and make an appropriate contribution to achieving FCS (NatureScot, 2020g).

114. Conservation objectives for Atlantic salmon are as follows:

• 2a. Maintain the population of Atlantic salmon, including range of genetic types, as a viable component of the site;
• 2b. Maintain the distribution of Atlantic salmon throughout the site; and
• 2c. Maintain the habitats supporting Atlantic salmon within the site and availability of food (NatureScot, 2020g).

115. Conservation objectives for sea lamprey are as follows:

• 2a. Maintain the population of sea lamprey as viable components of the site;
• 2b. Maintain the distribution of sea lamprey throughout the site; and
• 2c. Maintain the habitats supporting sea lamprey within the site, and availability of food (NatureScot, 2020g).

116. The overarching conservation objectives detailed in paragraph 113 are related to the species-specific conservation objectives 2a to 2c for Atlantic salmon and sea lamprey. The assessment of the Array alone and in-combination with other plans and projects focuses on the individual species-specific conservation objectives. This allows a proportionate approach, as by demonstrating that potential impacts s associated with the Array alone and in-combination with other plans and projects will not have an adverse effect on the species-specific conservation objectives (2a to 2c), the overarching conservation objectives will therefore not be impaired.

                        Condition assessment

117. The condition of sea lamprey was assessed in 2007 and Atlantic salmon condition was assessed in 2011. The outcomes of these feature condition assessments were as follows:

• Atlantic salmon: favourable – maintained; and
• sea lamprey: favourable – maintained (NatureScot, 2020g).

5.2.6.    River Spey SAC

5.2.6. River Spey SAC

                        Site description

118. At its closest point, the River Spey is located 181.56 km north-west from the site boundary. The site, located in the Highlands and flowing into the Moray Firth, encompasses a total of 5,759.72 ha (NatureScot, 2020f). The site is designated for Annex II species, including diadromous fish features relevant to this assessment: Atlantic salmon, freshwater pearl mussel, and sea lamprey (NatureScot, 2020f).

                        Feature accounts

                        Atlantic salmon

119. The ecology of Atlantic salmon is as described above in section 5.2.1, and not repeated here. The River Spey supports one of Scotland’s largest Atlantic salmon populations, with little evidence of modification by non-native stocks. Adults spawn throughout the whole length of the river, and good quality nursery habitat is found in abundance in the main river and numerous tributaries. The population includes fish of all ages including migrating smolts and returning adults (JNCC, 2024h). However, the Atlantic salmon population within the River Spey has shown a decrease in the spring multi-sea winter fish since 1952 (NatureScot, 2020f).

                        Freshwater pearl mussel

120. The ecology of freshwater pearl mussel is as described above in section 5.2.1, and not repeated here,. The River Spey is a large Scottish river which supports a freshwater pearl mussel population in its middle to lower reaches. In parts of the SAC, extremely dense mussel colonies have been previously been recorded and the total population was once estimated at several million (JNCC, 2024h).
121. In the River Spey, Atlantic salmon seem to be the most used host species for freshwater pearl mussel larvae (NatureScot, 2020f). Within the River Spey SAC, it is likely that freshwater pearl mussels have an artificially low population due to historic unsustainable fishing (NatureScot, 2020f).

                        Sea lamprey

122. The ecology of sea lamprey is as described above in section 5.2.3, and not repeated here,. The River Spey represents the most northern part of the sea lamprey’s range in the UK, as the species is absent from rivers north of the Great Glen, and the River Spey is virtually at its northern limit (JNCC, 2024h). Recent surveys show that sea lamprey larvae are widely distributed throughout the middle and lower reaches of the river, where the particularly fast-flowing waters of the River Spey provide ideal spawning conditions for this species (JNCC, 2024h).

                        Conservation objectives

123. Conservation objectives for the River Spey SAC have been developed by NatureScot as part of a CAP (NatureScot, 2020f). Conservation objectives for all qualifying species features are:

• to ensure that the qualifying features of River Spey SAC are in favourable condition and make an appropriate contribution to achieving FCS; and
• to ensure that the integrity of the River Spey SAC is restored by meeting objectives 2a, 2b and 2c for each qualifying feature (and 2d for freshwater pearl mussel) (NatureScot, 2020f).

124. Conservation objectives for Atlantic salmon are as follows:

• 2a. Restore the population of Atlantic salmon, including range of genetic types, as a viable component of the site;
• 2b. Restore the distribution of Atlantic salmon throughout the site; and
• 2c. Restore the habitats supporting Atlantic salmon within the site and availability of food (NatureScot, 2020f).

125. Conservation objectives for freshwater pearl mussel are as follows:

• 2a. Restore the population of freshwater pearl mussel as a viable component of the site;
• 2b. Restore the distribution of freshwater pearl mussel throughout the site;
• 2c. Restore the habitats supporting freshwater pearl mussel within the site and availability of food; and
• 2d. Restore the distribution and viability of freshwater pearl mussel host species and their supporting habitats (NatureScot, 2020f).

126. Conservation objectives for sea lamprey are as follows:

• 2a. Maintain the population of sea lamprey as a viable component of the site;
• 2b. Maintain the distribution of sea lamprey throughout the site; and
• 2c. Maintain the habitats supporting sea lamprey within the site and availability of food (NatureScot, 2020f).

127. The overarching conservation objectives detailed in paragraph 123 are related to the species-specific conservation objectives 2a to 2c for Atlantic salmon and sea lamprey and 2a to 2d for freshwater pearl mussel. The assessment of the Array alone and in-combination with other plans and projects focuses on the individual species-specific conservation objectives. This allows a proportionate approach, as by demonstrating that potential impacts s associated with the Array alone and in-combination with other plans and projects will not have an adverse effect on the species-specific conservation objectives (2a to 2c/2d), the overarching conservation objectives will therefore not be impaired.

                        Condition assessment

128. The condition of Atlantic salmon and sea lamprey were assessed in 2011 and freshwater pearl mussel condition was assessed in 2014. The outcomes of these feature condition assessments were as follows:

• Atlantic salmon: unfavourable – recovering;
• freshwater pearl mussel: unfavourable – declining; and
• sea lamprey: favourable – maintained (NatureScot, 2020f).

129. Atlantic salmon was assessed as being in unfavourable condition at this SAC due to a decline in the number of salmon in the river, especially the spring salmon component of the population. The main issues include marine survival, water abstraction, dams and weirs, predation, and invasive non-native species. Marine mortality of adult salmon was also suggested as potentially contributing to the decline, but the scope of the CAP only covered measures that can be taken within the SAC (NatureScot, 2020f).
130. Freshwater pearl mussel monitoring in the River Spey SAC showed a significant apparent decrease in mussel density between 2000 and 2014. The small and isolated populations in the upper Spey were not recruiting and some appeared to have disappeared. Mussels are not successfully recruiting at an adequate density to maintain the population upstream of Grantown on Spey. As a result the site is in unfavourable condition for this feature (NatureScot, 2020f). The lack of recruitment in the upper Spey may be due to fine sediment causing anoxic conditions in the river gravels, which immature mussels cannot tolerate. Another issue could be poor water quality as there is lower flow in the upper river, and therefore less dilution (NatureScot, 2020f). Further, water crowfoot Ranunculus fluitans has been found to impact freshwater pearl mussels in the middle and lower Spey. This occurs through entanglement of mussels within the roots of water crowfoot, and smothering due to trapped sediment within these roots (NatureScot, 2020f).

5.2.7.    Berriedale and Langwell Waters SAC

5.2.7. Berriedale and Langwell Waters SAC

                        Site description

131. At its closest point, the Berriedale and Langwell Waters SAC is located 219.57 km north-west from the site boundary. The site, located in the Highlands and flowing into the Moray Firth, encompasses 58.25 ha (JNCC, 2024a). The site is designated solely for Atlantic salmon.

                        Feature accounts

                        Atlantic salmon

132. The ecology of Atlantic salmon is as described above in section 5.2.1, and not repeated here,. The Berriedale and Langwell Waters SAC support small, but high-quality Atlantic salmon populations. The SAC is comprised of two comparatively small rivers and only supports a small proportion of the Scottish Atlantic salmon resource. However, their long history of low management intervention means that they score highly for naturalness. Recent records indicate that the full range of Atlantic salmon life-history types return to the river, with grilse, spring and summer salmon all being caught (JNCC, 2024a).

                        Conservation objectives

133. Conservation objectives for the Berriedale and Langwell Waters SAC have been developed by NatureScot as part of a CAP (NatureScot, 2020b). Overarching conservation objectives for this SAC are:

• to ensure that the qualifying feature of Berriedale and Langwell Waters SAC is in favourable condition and makes an appropriate contribution to achieving FCS;
• to ensure that the integrity of Berriedale and Langwell Waters SAC is maintained by meeting objectives 2a, 2b and 2c for Atlantic salmon (NatureScot, 2020b).

134. Specific Atlantic salmon conservation objectives for Atlantic salmon are as follows:

• 2a. Maintain the population of Atlantic salmon, including range of genetic types, as a viable component of the site;
• 2b. Maintain the distribution of the species throughout the site; and
• 2c. Maintain the habitats supporting the species within the site and availability of food (NatureScot, 2020b).

135. The overarching conservation objectives detailed in paragraph 133 are related to the species-specific conservation objectives 2a to 2c for Atlantic salmon. The assessment of the Array alone and in-combination with other plans and projects focuses on the individual species-specific conservation objectives. This allows a proportionate approach, as by demonstrating that potential impacts s associated with the Array alone and in-combination with other plans and projects will not have an adverse effect on the species-specific conservation objectives (2a to 2c), the overarching conservation objectives will therefore not be impaired.

                        Condition assessment

136. The condition of Atlantic salmon was assessed in 2011 as:

• Atlantic salmon: favourable – maintained (NatureScot, 2020b).

5.2.8.    River Teith SAC

5.2.8. River Teith SAC

                        Site description

137. At its closest point, the River Teith SAC is located 244.19 km south-west from the site boundary. The river begins in Loch Lomond and the Trossachs National Park and flows through Stirling and into the Firth of Forth. The SAC encompasses 1,289.33 ha and is designated for Annex II diadromous fish species, including Atlantic salmon and sea lamprey, which are relevant to this assessment (NatureScot, 2015).

                        Feature accounts

                        Atlantic salmon

138. The ecology of Atlantic salmon is as described above in section 5.2.1, and not repeated here,. Atlantic salmon are present as a qualifying feature of this SAC, but not a primary reason for site selection. This, in combination with no CAP available for this site, results in a lack of site-specific information about this species. However, it is noted in Standard Data From for this SAC that it is considered to support a significant presence of Atlantic salmon (JNCC, 2015).

                        Sea lamprey

139. The ecology of sea lamprey is as described above in section 5.2.3, and not repeated here,. The River Teith in eastern Scotland represents part of the sea lamprey’s eastern range. The River Teith is the most significant tributary of the River Forth and young sea lampreys have been recorded throughout the lower reaches of the main river. The conservation importance of the River Teith is increased by the fact that, unlike many British rivers, it supports populations of all three lamprey species (including river lamprey and brook lamprey which are out with the scope of this RIAA) (JNCC, 2024j).

                        Conservation objectives

140. A CAP has not yet been published for the River Teith SAC. However, conservation objectives for all qualifying species have been defined to avoid deterioration of their habitats or significant disturbance to the qualifying species, thus ensuring that the integrity of the site is maintained, and that the site makes an appropriate contribution to achieving FCS for each of the qualifying species. The following conservation objectives are to be maintained in the long term for the qualifying species:

• the population of the species, including range of genetic types for Atlantic salmon, as a viable component of the site;
• the distribution of the species within site;
• the distribution and extent of habitats supporting the species;
• the structure, function and supporting processes of habitats supporting the species; and
• there is no significant disturbance of the species (NatureScot, 2015).

141. Conservation objectives specific to Atlantic salmon and sea lamprey (e.g. 2a, 2b, and 2c) were not provided  (NatureScot, 2015).

                        Condition assessment

142. As stated in paragraph 37, there was no CAP available for the River Teith SAC at the time of writing, and therefore no condition assessments were available for Atlantic salmon and sea lamprey.

5.2.9.    River Oykel SAC

5.2.9. River Oykel SAC

                        Site description

143. At its closest point, the River Oykel is located 259.33 km north-west from the site boundary. The site is in the Highlands and flows into the Moray Firth. The SAC encompasses 921.46 ha and is designated solely for Annex II Atlantic salmon and freshwater pearl mussel (NatureScot, 2020d).

                        Feature accounts

                        Atlantic salmon

144. The ecology of Atlantic salmon is as described above in section 5.2.1, and not repeated here,. As stated in paragraph 63, Atlantic salmon numbers have declined throughout their geographic range, including in Scottish rivers. In the River Oykel, potential pressures to Atlantic salmon include: overexploitation, loss of habitat connectivity, habitat degradation, climate change-related changes to surface water temperature and hydrology, built development (such as hydropower on the River Cassley and a weir on the Tutim Burn which is a barrier to salmon reaching apparently suitable habitat upstream) and direct and diffuse pollution and inappropriate stocking with young salmon in the past (NatureScot, 2020d).

                        Freshwater pearl mussel

145. The ecology of freshwater pearl mussel is as described above in section 5.2.1, and not repeated here,. The River Oykel supports a high-quality freshwater pearl mussel population with high densities recorded at some locations, including a bed numbering several thousand individuals. There is also evidence of non non-surveyed populations in deep water that may increase the conservation importance of the river (JNCC, 2024f).

                        Conservation objectives

146. Conservation objectives for the River Oykel SAC have been developed by NatureScot as part of a CAP (NatureScot, 2020d). Conservation objectives for all qualifying species features are:

• to ensure that the qualifying features of River Oykel SAC are in favourable condition and make an appropriate contribution to achieving FCS; and
• to ensure that the integrity of the River Oykel SAC is restored by meeting objectives 2a, 2b, 2c for both features (and 2d for freshwater pearl mussel) (NatureScot, 2020d).

147. Conservation objectives for Atlantic salmon are as follows:

• 2a. Restore the population of Atlantic salmon, including range of genetic types, as a viable component of the site;
• 2b. Maintain the distribution of Atlantic salmon throughout the site; and
• 2c. Maintain the habitats supporting Atlantic salmon within the site and availability of food (NatureScot, 2020d).

148. Conservation objectives for freshwater pearl mussel are as follows:

• 2a. Restore the population of freshwater pearl mussel as a viable component of the site;
• 2b. Restore the distribution of freshwater pearl mussel throughout the site;
• 2c. Restore the habitats supporting the freshwater pearl mussel within the site and availability of food; and
• 2d. Maintain the distribution and viability of freshwater pearl mussel host species and their supporting habitats (NatureScot, 2020d).

149. The overarching conservation objectives detailed in paragraph 146 are related to the species-specific conservation objectives 2a to 2c for Atlantic salmon and 2a to 2d for freshwater pearl mussel. The assessment of the Array alone and in-combination with other plans and projects focuses on the individual species-specific conservation objectives. This allows a proportionate approach, as by demonstrating that potential impacts associated with the Array alone and in-combination with other plans and projects will not have an adverse effect on the species-specific conservation objectives (2a to 2c/2d), the overarching conservation objectives will therefore not be impaired.

                        Condition assessment

150. The condition of Atlantic salmon was assessed in 2011 and freshwater pearl mussel condition was assessed in 2015. The outcomes of these feature condition assessments were as follows:

• Atlantic salmon: favourable – recovered;
• freshwater pearl mussel: unfavourable – no change (NatureScot, 2020d).

151. Freshwater pearl mussel has been assessed as being in unfavourable condition at this SAC due to the low number and density of individuals present, low levels of juvenile recruitment, water quality, water flow and disturbance of mussel beds through illegal pearl fishing (NatureScot, 2020d).

5.3.        Assessment of the Adverse Efects of the Array Alone

5.3. Assessment of the Adverse Efects of the Array Alone

5.3.1.    Underwater Noise Generated during Piling and UXO Clearance

5.3.1. Underwater Noise Generated during Piling and UXO Clearance

152. The LSE2 assessment during the HRA Stage One process identified that during the construction phase, LSE2 could not be ruled out for the impact of underwater noise generated during piling and UXO clearance. This relates to the following sites and relevant Annex II diadromous fish features:

• River Dee SAC;

–           Atlantic salmon; and

–           freshwater pearl mussel.

• River South Esk SAC;

–           Atlantic salmon; and

–           freshwater pearl mussel.

• Tweed Estuary SAC;

–           sea lamprey.

• River Tweed SAC;

–           Atlantic salmon; and

–           sea lamprey.

• River Tay SAC;

–           Atlantic salmon; and

–           sea lamprey.

• River Spey SAC;

–           Atlantic salmon;

–           freshwater pearl mussel; and

–           sea lamprey.

• Berriedale and Langwell Waters SAC;

–           Atlantic salmon.

• River Teith SAC; and

–           Atlantic salmon; and

–           sea lamprey.

• River Oykel SAC;

–           Atlantic salmon; and

–           freshwater pearl mussel.

153. The MDS and designed in measures considered for the assessment of underwater noise during piling and UXO clearance are shown in Table 5.3   Open ▸ and Table 5.4   Open ▸ , respectively.

Table 5.3: MDS Considered for the Assessment of Potential Impacts to Annex II Diadromous Fish due to Underwater Noise Generated during Piling and UXO Clearance in the Construction Phase of the Array Alone

Table 5.4: Designed In Measures Considered for the Assessment of Potential Impacts to Annex II Diadromous Fish to Underwater Noise Generated during Piling and UXO Clearance in the Construction Phase

                        Information to support the assessment

                        Hearing sensitivity of Annex II diadromous fish

154. Underwater noise can potentially have an adverse impact on various fish species ranging from physical injury and mortality to behavioural effects. Peer reviewed guidelines have been published by the Acoustical Society of America (ASA) and provide directions and recommendations for setting criteria (including injury and behavioural criteria) for fish. These guidelines (Popper et al., 2014) provide the most relevant and best available guidelines for impacts of underwater noise on fish species (see volume 3, appendix 10.1 of the Array EIA Report for further detail).
155. The Popper et al. (2014) guidelines broadly group fish into the following categories according to the presence or absence of a swim bladder and on the potential for that swim bladder to improve the hearing sensitivity and range of hearing:

• Group 1: Fishes lacking swim bladders (e.g. elasmobranchs and flatfish). These species are only sensitive to particle motion, not sound pressure and show sensitivity to only a narrow band of frequencies;
• Group 2: Fishes with a swim bladder but the swim bladder does not play a role in hearing (e.g. salmonids and some Scombridae). These species are considered to be more sensitive to particle motion than sound pressure and show sensitivity to only a narrow band of frequencies;
• Group 3: Fishes with swim bladders that are close, but not connected, to the ear (e.g. gadoids and eels). These fishes are sensitive to both particle motion and sound pressure and show a more extended frequency range than Groups 1 and 2, extending to about 500 Hz; and
• Group 4: Fishes that have special structures mechanically linking the swim bladder to the ear (e.g. clupeids such as herring Clupea harengus, sprat Sprattus sprattus and shads Alosa spp.). These fishes are sensitive primarily to sound pressure, although they also detect particle motion. These species have a wider frequency range, extending to several kHz and generally show higher sensitivity to sound pressure than fishes in Groups 1, 2 and 3.

156. Sea lamprey are considered to be a Group 1 species, and therefore has relatively low sensitivity to underwater noise (Popper et al., 2014). Lamprey species are known to have relatively simple ear structures (Popper et al., 1987), with very few responses to auditory stimuli noted overall (Popper, 2005), except a slight swimming speed increase and decrease in resting behaviour when exposed to continuous low frequency noise of 50 to 200 Hz (Mickle et al., 2018). This suggests a low vulnerability to impacts of noise overall. In contrast, Group 4 hearing specialist fish, such as herring, possess an otic bulla; a gas filled sphere that is connected to the swim bladder, which enhances hearing ability. This anatomy is not present in sea lamprey, although the gas filled swim bladder in Atlantic salmon may be involved in their hearing capability (Popper et al., 2014). While there is no direct link to the inner ear, Atlantic salmon are able to detect lower noise frequencies and as such are considered to be a Group 2 species, and therefore have a higher hearing sensitivity to sea lamprey, but comparatively low with respect to Group 3 and Group 4 species (Popper et al., 2014).
157. Freshwater pearl mussel may only be indirectly affected by underwater noise as they are a freshwater-resident species, and piling will only occur within the site boundary, which is around 80 km offshore. Therefore, the effects of underwater noise upon freshwater pearl mussel assessed in this section are limited to indirect effects, due to potential disruption to Atlantic salmon migration.

                        Overview of underwater noise modelling conducted for the Array

158. Piling and UXO clearance activities may lead to injury and/or disturbance to Annex II diadromous fish species. The MDS ( Table 5.3   Open ▸ ) considers the reasonable worst case scenario from underwater noise generated during piling based on the greatest hammer energy. This scenario is represented by the installation of up to 265 semi-submersible floating wind turbine foundations, with up to six anchors per foundation and one 4.5 m diameter pile per anchor (1,590 piles) for wind turbines, and up to three large and 12 small jacket foundations (total 216 piles) for OSPs, with all piles assumed to be installed via impact piling as the most precautionary scenario.
159. For wind turbines, piling was assumed to take place over a period of up to eight hours per pile with up to eight piles installed in each 24 hour period. OSP foundations will take place over 25 hours for up to three piles (maximum duration of up to eight hours per pile) with up to eight piles installed in each 24 hour period. A maximum duration of 1,728 hours of piling activity, over a maximum of 72 months over eight years, may take place during the construction phase, based on the maximum duration of the piling phase.
160. Underwater noise modelling was undertaken for both single piling and concurrent piling (i.e. piling at more than one location simultaneously). To ensure a precautionary assessment, modelling of a concurrent piling scenario based on a 3,000 kJ hammer energy for the wind turbine foundation piles and 4,400 kJ hammer energy for the OSP jacket piles has been undertaken, alongside single piling scenarios, using the maximum 4,400 kJ hammer energy for the OSP jacket piles. These are discussed further below in relation to injurious effects with relevant contours also presented and discussed in the context of potential behavioural effects on Annex II diadromous fish (specifically disruption and barriers to migration). 
161. If required, UXO clearance (including detonation) will be completed prior to the construction phase (pre-construction). The MDS ( Table 5.3   Open ▸ ) assumes clearance of up to 15 UXOs within the site boundary, with a maximum of 698 kg NEQ. The UXO clearance campaign will involve subsonic combustion with a single donor charge of up to 0.025 kg NEQ for each clearance event, and up to 0.5 kg NEQ to neutralise residual explosive material at each location. Total duration of UXO clearance campaigns is eight days, with up to two detonations within 24 hours although it is noted that this may not always be required.
162. To understand the magnitude of noise emissions from piling and UXO clearance during construction activity, underwater noise modelling has been undertaken considering the key design parameters summarised above. Compared to piling, UXO detonations will be single, isolated events of very short duration; as such, potential behavioural effects upon Annex II diadromous fish will be extremely short lived and reversible. Full detail on the underwater noise modelling is provided in volume 3, appendix 10.1 of the Array EIA Report, and is summarised in terms of injury and disturbance in paragraphs 163 to 185.

                        Injury from piling (permanent and temporary)

163. The Popper et al. (2014) guideline criteria for the onset of mortality, recoverable injury, and Temporary Threshold Shift (TTS) due to impulsive piling are presented in Table 5.5   Open ▸ . A dual criteria approach has been adopted in the guidelines to account for the uncertainties associated with the effects of underwater noise on fish. This includes two parameters for assessment: Cumulative Sound Exposure Level (SELcum) and SPLpk.
164. It should be noted that the SPLpk thresholds for mortality and potential mortal injury and recoverable injury are the same ( Table 5.5   Open ▸ ). The data on mortality and recoverable injury used by Popper et al. (2014) are derived from Halvorsen et al. (2011), Halvorsen et al. (2012a), and Halvorsen et al. (2012b), based on 960 sound events at 1.2 second intervals. The same Single Strike SEL (SELss) was used throughout these Halvorsen et al. piling studies, therefore, the same peak level was derived (SPLpk) as part of the criteria by Popper et al. (2014).

Table 5.5: Criteria for the Onset of Mortality, Recoverable Injury, and TTS due to Impulsive Piling for Relevant Annex II Diadromous Fish Species (Popper et al., 2014)

165. To inform the assessment on Annex II diadromous fish, predicted injury ranges associated with the installation of one 4.5 m diameter pile have been presented. This modelling resulted in the greatest predicted injury ranges and therefore forms the focus of the assessment for injury, noting that in most cases, the maximum hammer energy would not be reached during piling. The metrics presented are for SELcum for fleeing fish and static fish ( Table 5.6   Open ▸ ) and SPLpk ( Table 5.7   Open ▸ ). A swim speed of 0.5 m/s was used to model fleeing fish (Popper et al., 2014).
166. For the SELcum metric, the injury ranges presented indicate that mortality and recoverable injury may occur out to ranges of tens of metres, based on the MDS for fleeing receptors (e.g. 15 m to 20 m for sea lamprey and 32 m to 110 m for Atlantic salmon ( Table 5.6   Open ▸ ). If modelled as static receptors, the mortality and recoverable injury ranges increased to the low hundreds of metres for sea lamprey and up to 2,300 m for Atlantic salmon ( Table 5.6   Open ▸ ). For both species, the TTS ranges were 8,380 m as fleeing receptors and 13,200 m as static receptors ( Table 5.6   Open ▸ ). Practically, the risk of injury will be considerably lower due to the hammer energies being lower than the absolute maximum modelled (3,000 kJ). The expected fleeing behaviour of fish when exposed to high levels of noise and the implementation of soft starts mean that it is likely that fish will have ample time to vacate the areas in which injury may occur prior to noise levels reaching the maximum modelled; however there are uncertainties as to whether all fish species will flee from piling noise and as such static receptors were also modelled, noting these are likely to be highly precautionary ranges.
167. For peak pressure noise levels when piling energy is at its maximum for the wind turbine foundation pile installation, mortality and recoverable injury may occur within approximately 266 m and 414 m of the piling source for sea lamprey and Atlantic salmon, respectively ( Table 5.7   Open ▸ ).
168. When piling for OSP foundations (i.e. maximum hammer energy of 4,400 kJ; Table 5.8   Open ▸ ), greater injury ranges are predicted than for single piling of wind turbine foundations. Using the SELcum metric for fleeing fish, mortality and recoverable injury may occur out to ranges between 25 m and 31 m for sea lamprey and 112 m and 1,440 m for Atlantic salmon ( Table 5.8   Open ▸ ). If modelled as static receptors, the mortality and recoverable injury ranges increase to 855 m and 1,220 m, respectively, for sea lamprey and 2,440 m and 5,120 m for Atlantic salmon ( Table 5.8   Open ▸ ). For both species, the TTS ranges were 21,100 m as fleeing receptors and 26,960 m as static receptors ( Table 5.8   Open ▸ ). Modelling using the peak SPL metric showed a similar pattern with mortality and recoverable injury to ranges of up to 615 m for sea lamprey and up to 1,055 m for Atlantic salmon under the maximum hammer energy of 4,400 kJ ( Table 5.9   Open ▸ ).
169. Based on the two noise criteria (SELcum and SPLpk), injury will occur in the range of tens to hundreds of metres ( Table 5.6   Open ▸ to Table 5.9   Open ▸ ), with larger injury ranges predicted for the maximum hammer energy of 4,400 kJ used during OSP jacket pile installation. However, the modelling has been informed by the maximum hammer energies within the MDS, which, in most cases, will not be reached. Additionally, injury ranges at the start of each piling sequence will be much smaller than those presented here, due to soft starts; at 660 kJ for OSP foundations and 450 kJ for foundation piles.

Table 5.6: Potential Mortality, Injury, and TTS Ranges for Single Wind Turbine Foundation Pile Installation at 3,000 kJ based on the SELcum Metric for Fleeing and Static Annex II Diadromous Fish

Table 5.7: Potential Mortality and Injury Ranges for Single Wind Turbine Foundation Pile Installation at 3,000 kJ based on the SPLpk Metric for Annex II Diadromous Fish

Table 5.8: Potential Mortality, injury, and TTS Ranges for Single OSP Jacket Pile Installation at 4,400 kJ Based on the SELcum Metric for Fleeing and Static Annex II Diadromous Fish

Table 5.9: Potential Mortality and Injury Ranges for Single OSP Jacket Pile Installation at 4,400 kJ based on the SPLpk Metric for Annex II Diadromous Fish

170. The MDS considers the potential for up to two pile installation vessels operating concurrently ( Table 5.3   Open ▸ ). The potential SELcum injury ranges for Annex II diadromous fish due to impact driving of piles have been modelled as following the same piling plans with all phases starting at the same time. For injury, the MDS is that of two adjacent piles, separated by a distance of 950 m in order to assume the maximal overlap of noise propagation contours leading to the maximum generated noise levels. Conversely, for disturbance, the maximum separation between two piling locations would lead to the larger area ensonified at any one time and therefore the greatest disturbance (discussed in paragraph 176 et seq.).
171. As per the MDS, there is potential for two vessels to be piling concurrently at one wind turbine and one OSP foundation ( Table 5.3   Open ▸ ). Injury ranges for concurrent piling of OSP jacket installation at 4,400 kJ and wind turbine foundation installation at 3,000 kJ at each site are given in Table 5.10   Open ▸ . The peak metric will remain the same as the single installation case ( Table 5.7   Open ▸ and Table 5.9   Open ▸ ). For all other piling scenarios, injury ranges would be smaller; the full range of modelled scenarios are given in volume 3, appendix 10.1 of the Array EIA Report. As expected, these show that for this precautionary cumulative piling scenario, injury ranges are similar or slightly larger than the single piling scenarios for fleeing fish, but considerably larger (e.g. double the ranges) for static fish.

Table 5.10: Potential Mortality, Recoverable Injury, and TTS Ranges for Concurrent OSP Jacket Piling (4,400 kJ) and Wind Turbine Foundation Piling (3,000 kJ) based on the SELcum­ Metric for Fleering and Static Annex II Diadromous Fish

                        Injury from UXO clearance

172. Underwater noise modelling was undertaken for UXO clearance. The criteria used in this underwater noise assessment for explosives are given in Table 5.11   Open ▸ following Popper et al. (2014). The recoverable injury and TTS criteria are categorised in relative terms as ‘high’, ‘moderate’, or ‘low’ at three distances from the source: ‘near’ (i.e. in the tens of metres), ‘intermediate’ (i.e. in the hundreds of metres), or ‘far’ (i.e. in the thousands of metres), as shown in Table 5.11   Open ▸ . It is important to note that these criteria are qualitative rather than quantitative.

Table 5.11: Criteria for the Onset of Mortality, Recoverable Injury, and TTS due to UXO Clearance for Relevant Annex II Diadromous Fish Species (Popper et al., 2014)

173. Modelling was undertaken for a range of orders of detonation, from the maximum high order detonation (698 kg) to low order detonations (e.g. deflagration and clearance shots), which will be used as mitigation to reduce noise levels. Table 5.12   Open ▸ details the injury ranges in relation to various orders of detonation. The method of low order has been committed to ( Table 5.4   Open ▸ ), and as such will be the dominant method of UXO clearance, although higher order detonations may also occur if low order is not successful or unintentionally as part of the low order process.
174. The predicted injury ranges for low and high order disposal order detonations of UXOs are presented in Table 5.12   Open ▸ and demonstrate the effectiveness of the low order methods to reduce the risk of injury (i.e. injury ranges of tens of metres for low order, but up to 930 m for high order detonations).
175. Due to a combination of dispersion (i.e. where the waveform elongates), multiple reflections from the sea surface, and seabed and molecular absorption of high frequency energy, the noise is unlikely to still be impulsive once it has propagated more than a few kilometres. Consequently, caution should be used when interpreting any results with predicted injury ranges in the order of tens of kilometres. Furthermore, the modelling assumes that the UXO acts like a charge suspended in open water whereas it is likely to be partially buried in the sediment. In addition, it is possible that the explosive material will have deteriorated over time meaning that the predicted noise levels are likely to be over-estimated. Overall, these factors mean that the results should be treated as precautionary potential impact ranges and are likely to be significantly lower than predicted.

Table 5.12: Potential Impact Ranges for UXO Clearance Activities, based on the Criteria Presented in Table 5.11   Open ▸

                        Behavioural disturbance (including TTS as a proxy)

176. Behavioural reactions of fish to underwater noise have been found to vary between species and depend on hearing sensitivity. Typically, fish sense noise via particle motion in the inner ear which is detected from noise-induced motions in the fish’s body. The detection of sound pressure is restricted to those fish which have air filled swim bladders; however, particle motion (induced by noise) can be detected by fish without swim bladders (e.g. sea lamprey). Further, the presence of a swim bladder does not necessarily mean that the fish can detect pressure. Some fish have swim bladders that are not involved in the hearing mechanism and can only detect particle motion (e.g. Atlantic salmon).
177. Popper et al. (2014) provides qualitative behavioural criteria for fish from a range of noise sources. The behavioural criteria categorise the risks of effects as ‘high’, ‘moderate’, or ‘low’ at three distances from the source: ‘near’ (i.e. in the tens of metres), ‘intermediate’ (i.e. in the hundreds of metres), or ‘far’ (i.e. in the thousands of metres). It is important to note that the Popper et al. (2014) criteria for disturbance due to noise are qualitative rather than quantitative, due to a lack of agreed quantitative behavioural response thresholds (e.g. as set out for injury above). Consequently, a source of noise of a particular type (e.g. piling) would be predicted to result in the same potential impact, no matter the level of noise produced or the propagation characteristics. The behavioural criteria for piling operations are summarised in Table 5.13   Open ▸ for the relevant Annex II diadromous fish hearing groups and indicate a high to moderate risk of behavioural effects in the near and intermediate fields (i.e. up to hundreds of metres) and a low risk of behavioural effects in the far field (i.e. thousands of metres). As noted above, these criteria were developed for piling in general, with no consideration of piling characteristics, propagation, site specific considerations etc. 

Table 5.13: Potential Risk for the Onset of Behavioural Effects in Relevant Annex II Diadromous Fish from Piling (Popper et al., 2014)

178. Additional studies have examined the behavioural effects of the sound pressure component of impulsive noise (including piling operations) on a range of fish species. For example, Mueller-Blenkle et al. (2010) recorded behavioural responses of cod Gadus morhua and sole Solea solea to sounds similar to those produced during marine piling, with variation noticed across specimens (i.e. depending on the age, sex, condition etc. of the fish, as well as the possible effects of confinement in cages on the overall stress levels in the fish). This study concluded that it was not possible to find a clear relationship between the level of exposure and the extent of the behavioural response, although an observable behavioural response was reported at 140 dB to 161 dB re 1 μPa SPLpk for cod and 144 dB to 156 dB re 1 μPa SPLpk for sole (Mueller-Blenkle et al., 2010). Regardless, these thresholds should not be interpreted as the level at which an avoidance reaction will be elicited, as the study was not able to show this.
179. Further, a study by Pearson et al. (1992) examined the effects of geophysical survey noise on caged rockfish Sebastes spp. and observed a startle or “C-turn response” at peak pressure levels beginning around 200 dB re 1 μPa. This response was less common with the larger fish. Studies by McCauley et al. (2000) exposed various fish species in large cages to seismic airgun noise and assessed behaviour, physiological and pathological changes. The study observed that:

• a general fish behavioural response was to move to the bottom of the cage during periods of high level exposure (greater than rms levels of around 156 dB to 161 dB re 1 μPa; approximately equivalent to SPLpk levels of around 168 dB to 173 dB re 1 μPa);
• a greater startle response was seen in small fish to the above levels;
• a return to normal behavioural patterns was noticed some 14 to 30 minutes after airgun operations ceased;
• no significant physiological stress increases attributed to air gun exposure; and
• some preliminary evidence of damage to the hair cells was noticed when exposed to the highest levels, although it was determined that such damage would only likely occur at short range from the source (McCauley et al., 2000).

180. Post construction monitoring at the Beatrice Offshore Wind Farm concluded that there were no evidence of adverse effects on sandeel (Ammodytidae) and cod populations between pre and post construction levels over a six year period (Beatrice Offshore Wind Farm Limited, 2021a, 2021b). Based on these studies, it can therefore be assumed that noise impacts associated with installation of an offshore wind development are temporary and that fish communities (specifically cod and sandeel in this case) show a high degree of recoverability following construction.
181. With specific reference to diadromous fish, Harding et al. (2016) failed to produce physiological or behavioural responses in Atlantic salmon when subjected to noise similar to piling. However, the noise levels tested were estimated at <160 dB re 1µPa (rms), below the level at which injury or behavioural disturbance would be expected for Atlantic salmon. Nedwell et al. (2006) used the slightly less sensitive sea trout as a model for comparison to Atlantic salmon, and found no significant behavioural response from piling activities, with modelling suggesting a similar response in Atlantic salmon and sea trout. Bagočius (2015) reported physical impacts on migrating salmonids exposed to piling noise of 218 dB re 1μPa2s (SEL), although at these high noise levels, it would be expected that avoidance reactions would occur, to avoid injury.
182. Noting that there are no published or agreed thresholds for behavioural effects on fish from piling operations, a risk based approach has been undertaken using published literature on the behavioural responses of fish to underwater noise (paragraphs 181 to 180). Based on these studies, modelling has been presented using the 160 dB (SPLpk) noise contour to assess behavioural responses in fish species in general and, for the purposes of this report in Atlantic salmon and sea lamprey ( Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ). It is unlikely that species will experience behavioural disturbance beyond this noise contour, based on the described studies which demonstrated behavioural responses (including avoidance) at levels above this threshold. It’s likely that 160 dB re 1 μPa (SPLpk) is over conservative, given that Atlantic salmon and sea lamprey are at the lower end of the sensitivity spectrum (i.e. hearing groups 1 and 2). The 160 dB (SPLpk) contour is presented on Figure 5.2   Open ▸ and Figure 5.3   Open ▸ for the maximum north and south piling locations using the maximum hammer energy of 4,400 kJ (noting all other hammer energies will result in smaller contours). The extent of the 160 dB (SPLpk) contour should be noted, particularly in terms it’s considerable distance offshore, and its relatively small area of effect in terms of the availability of habitat in the North Sea. While the 150 dB (SPLpk) does extend closer to the shore, particularly for the northern location ( Figure 5.2   Open ▸ ), behavioural disturbance is highly unlikely at this level (based on the studies outlined above). 
183. In addition to this site specific noise modelling has considered criteria presented in the Washington State Department of Transport (WSDOT) Biological Assessment Preparation for Transport Projects Advanced Training Manual (WSDOT, 2011) in this assessment for estimating the distances at which behavioural effects may occur due to noise from impulsive piling (as set out see volume 3, appendix 10.1 of the Array EIA Report). The manual suggests an unweighted sound pressure level of 150 dB re 1 μPa (SPLroot mean square (rms)) as the criterion for onset of behavioural effects, based on work by Hastings (2002). Sound pressure levels in excess of 150 dB re 1 μPa (rms) are expected to cause temporary behavioural changes, such as elicitation of a startle response, disruption of feeding, or avoidance of an area. The document notes that levels exceeding this threshold are not expected to cause direct permanent injury but may indirectly affect the individual fish (such as by impairing predator detection). It is important to note that this threshold is for onset of potential effects, and not necessarily an ‘adverse effect’ threshold.
184. The underwater noise modelling (using the WSDOT (2011) 150 dB re 1 μPa (rms) criterion for the onset of behavioural effects) suggests behavioural responses may extend up to 33 km for single pin piling with a hammer energy of 3,000 kJ (representative of the MDS for wind turbine foundation installation).  For a hammer energy of 4,400 kJ (thus representative of the MDS for OSP installation), this range was modelled out to a maximum range of 49 km from piling activity; noting these ranges will be highly conservative for the less sensitive diadromous species considered here. In some cases (e.g. previous offshore wind projects), TTS has been used as a proxy for behavioural disturbance. The maximum TTS values for single piling with hammer energy of 3,000 kJ were 13.20 km ( Table 5.6   Open ▸ ), 26.96 km for a hammer energy of 4,400 kJ for OSP installation ( Table 5.8   Open ▸ ), and 45.10 km for concurrent piling ( Table 5.10   Open ▸ ). These ranges are therefore, of a similar magnitude (i.e. low tens of kilometres) as those ranges reported for the WSDOT criteria summarised above for the two maximum hammer energies and are likely representative of the absolute maximum ranges of behavioural disturbance to diadromous fish species. The 160 dB (SPLpk) contour presented in Figure 5.2   Open ▸ and Figure 5.3   Open ▸ also extends to the low tens of kilometres from the piling location, further strengthening the conclusion that significant behavioural responses (i.e. those that may lead to disruption of migration or barrier effects) are unlikely beyond this range. As described in paragraph 171, the peak metric will remain the same for both single and consecutive piling. As the single piling scenarios presented in Figure 5.2   Open ▸ and Figure 5.3   Open ▸ are based on the peak metric, potential disturbance ranges will not increase the risk of barrier effects under consecutive piling scenarios.
185. Due to the distance between the Array and the coast (approximately 80 km), these behavioural impacts are unlikely to cause barrier effects to diadromous species as they migrate along the east coast of Scotland, due to the relatively limited area around piling events where noise levels are high enough to cause behavioural responses in the context of the wider fish and shellfish ecology study area (as illustrated in Figure 5.2   Open ▸ and Figure 5.3   Open ▸ and extrapolated from the information presented in paragraph 176 et seq.).

Figure 5.2: Modelled 10 dB SPLpk Noise Contours for Piling Hammer Energy of 4,400 kJ at the North Location

Figure 5.3: Modelled 10 dB SPLpk Noise Contours for Piling Hammer Energy of 4,400 kJ at the South Location

                        Summary of underwater noise modelling

186. Sea lamprey and Atlantic salmon close to piling operations may experience injury or mortality. However, diadromous fish species tend to be highly mobile and are unlikely to be particularly reliant on the marine environment within the fish and shellfish ecology study area other than to pass through during migration. Therefore, piling is unlikely to result in significant mortality of Annex II diadromous species. The use of soft start piling procedures (see Table 5.4   Open ▸ ) will allow many individuals in close proximity to piling to flee the ensonified area and will also reduce the overall acoustic energy entering the marine environment, therefore reducing the likelihood of injury and mortality.
187. Atlantic salmon and sea lamprey may experience behavioural effects in response to piling noise, including a startle response, disruption of feeding, or avoidance of an area. As discussed in paragraphs 176 et seq., these would be expected to occur at ranges up to low tens of kilometres, depending on the maximum hammer energies. Due to the distance of the site boundary from the Scottish coast (approximately 80 km), potential behavioural impacts are highly unlikely to cause barrier effects to diadromous species as they migrate along the east coast of Scotland, due to the relatively limited area around piling events where noise levels are high enough to cause behavioural responses (as demonstrated in Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ).

                        Construction phase

                        River Dee SAC

Atlantic salmon

188. As outlined in paragraphs 163 to 175, Atlantic salmon within close proximity to piling operations may experience injury or mortality due to underwater noise from piling or UXO clearance. However, Atlantic salmon are highly mobile, and may only use the fish and shellfish ecology study area to pass through during migration (noting that at-sea behaviour is largely unknown). Therefore, it is unlikely that this impact will result in significant mortality or injury to the Atlantic salmon feature of this SAC. Further, as presented in Table 5.4   Open ▸ , the designed in measure of soft start piling procedures will allow individuals in close proximity to piling to move away from the ensonified area and reduce the total amount of acoustic energy entering the marine environment. In addition, the designed in measure of low order UXO disposal will reduce the noise levels and their potential for injury in the vicinity of UXO clearance operations. Overall, these two designed in measures further reduce the likelihood of injury and mortality.
189. As outlined in paragraphs 176 et seq., underwater noise during piling would result in behavioural responses in the vicinity of the Array, although these may occur out to a range in the low tens of kilometres, and thus not represent a significant barrier to migration to and from the SAC, particularly in terms of the vast availability of habitat in the North Sea and distance between the coast and the site boundary ( Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ). The behavioural disturbance modelling results are also highly precautionary as they were modelled against the maximum hammer energy, which will not realistically occur over the duration of the piling programme. Further, the potential underwater noise impacts will be short term and intermittent in nature during the construction phase (i.e. piling occurring over up to 602 days over eight years). As such, there is negligible risk of disruption to migration.

Freshwater pearl mussel

190. Adult freshwater pearl mussel are confined to freshwater environments, and there is therefore no pathway for direct effects associated with this impact. However, there is potential for indirect impacts on the larval stage of freshwater pearl mussel if Atlantic salmon (their host species) are impacted. As detailed in paragraphs 188 to 189, underwater noise in the construction phase will not lead to significant mortality or injury to Atlantic salmon and is unlikely to result in barriers to migration. Therefore, it can also be concluded that there will be no indirect impact to freshwater pearl mussel.

Conclusion

191. Adverse effects on the qualifying Annex II diadromous fish features of the River Dee SAC which undermine the conservation objectives of the SAC will not occur as a result of underwater noise during construction activities. Potential effects from these activities on the relevant conservation objectives (as presented in paragraphs 69 to 71) are discussed in turn below in Table 5.14   Open ▸ .

Table 5.14: Conclusions Against the Conservation Objectives of the River Dee SAC from Underwater Noise Generated during Piling and UXO Clearance in the Construction Phase of the Array Alone

192. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the River Dee SAC as a result of underwater noise generated during piling and UXO clearance with respect to the construction phase of the Array alone.

                        River South Esk SAC

Atlantic salmon

193. As outlined in paragraphs 163 to 175, Atlantic salmon within close proximity to piling operations may experience injury or mortality due to underwater noise from piling or UXO clearance. However, Atlantic salmon are highly mobile, and may only use the fish and shellfish ecology study area to pass through during migration (noting that at-sea behaviour is largely unknown). Therefore, it is unlikely that this impact will result in significant mortality or injury to the Atlantic salmon feature of this SAC. Further, as presented in Table 5.4   Open ▸ , the designed in measure of soft start piling procedures will allow individuals in close proximity to piling to move away from the ensonified area and reduce the total amount of acoustic energy entering the marine environment. In addition, the designed in measure of low order UXO disposal will reduce the noise levels and their potential for injury in the vicinity of UXO clearance operations. Overall, these two designed in measures further reduce the likelihood of injury and mortality.
194. As outlined in paragraphs 176 et seq., underwater noise during piling would result in behavioural responses in the vicinity of the Array, although these may occur out to a range in the low tens of kilometres, and thus not represent a significant barrier to migration to and from the SAC, particularly in terms of the vast availability of habitat in the North Sea and distance between the coast and the site boundary ( Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ). The behavioural disturbance modelling results are also highly precautionary as they were modelled against the maximum hammer energy, which will not realistically occur over the duration of the piling programme. Further, the potential underwater noise impacts will be short term and intermittent in nature during the construction phase (i.e. piling occurring over up to 602 days over eight years). As such, there is negligible risk of disruption to migration.

Freshwater pearl mussel

195. Adult freshwater pearl mussel are confined to freshwater environments, and there is therefore no pathway for direct effects associated with this impact. However, there is potential for indirect impacts on the larval stage of freshwater pearl mussel if Atlantic salmon (their host species) are impacted. As detailed in paragraphs 193 and 194, underwater noise in the construction phase will not lead to significant mortality or injury to Atlantic salmon and is unlikely to result in barriers to migration. Therefore, it can also be concluded that there will be no indirect impact to freshwater pearl mussel.

Conclusion

196. Adverse effects on the qualifying Annex II diadromous fish features of the River South Esk SAC which undermine the conservation objectives of the SAC will not occur as a result of underwater noise during construction activities. Potential effects from these activities on the relevant conservation objectives (as presented in paragraphs 78 to 80) are discussed in turn below in Table 5.15   Open ▸ .

Table 5.15: Conclusions Against the Conservation Objectives of the River South Esk SAC from Underwater Noise Generated during Piling and UXO Clearance in the Construction Phase of the Array Alone

197. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the River South Esk SAC as a result of underwater noise generated during piling and UXO clearance with respect to the construction phase of the Array alone.

                        Tweed Estuary SAC

Sea lamprey

198. As for Atlantic salmon, the underwater noise modelling suggested that sea lamprey within close proximity to piling operations and UXO clearance may experience injury or mortality. However, sea lamprey are also highly mobile, and may only use the fish and shellfish ecology study area to pass through during migration (noting that the at-sea behaviour and habitat use of sea lamprey is largely unknown). Therefore, this impact is unlikely to result in significant mortality or injury to sea lamprey. Further, as presented in Table 5.4   Open ▸ , the soft start piling procedures designed in measure will allow many individuals in close proximity to piling to move away from the ensonified area and will also reduce the overall acoustic energy entering the marine environment. In addition, the designed in measure of low order UXO disposal will reduce the noise levels and the potential for injury in the vicinity of UXO clearance operations. Overall, these two designed in measures further reduce the likelihood of injury and mortality.
199. As outlined in paragraphs 176 et seq., underwater noise during piling would result in behavioural responses in the vicinity of the Array, although these would extend out the low tens of kilometres, and thus not represent a significant barrier to migration to and from the SAC, particularly in terms of the vast availability of habitat in the North Sea and distance between the coast and the site boundary ( Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ). The behavioural disturbance modelling results are also highly precautionary as they were modelled against the maximum hammer energy, which will not realistically occur over the duration of the piling programme. Further, the potential underwater noise impacts will be short term and intermittent in nature during the construction phase (i.e. piling occurring over up to 602 days over eight years). As such, there is negligible risk of disruption to migration.

Conclusion

200. Adverse effects on the qualifying Annex II diadromous fish features of the Tweed Estuary SAC which undermine the conservation objectives of the SAC will not occur as a result of underwater noise during construction activities. Potential effects from these activities on the relevant conservation objectives (as presented in paragraph 90 to 92) are discussed in turn below in Table 5.16   Open ▸ .

Table 5.16: Conclusions Against the Conservation Objectives of the Tweed Estuary SAC from Underwater Noise Generated during Piling and UXO Clearance in the Construction Phase of the Array Alone

201. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the Tweed Estuary SAC as a result of underwater noise generated during piling and UXO clearance with respect to the construction phase the Array alone.

                        River Tweed SAC

Atlantic salmon

202. As outlined in paragraphs 163 to 175, Atlantic salmon within close proximity to piling operations may experience injury or mortality due to underwater noise from piling or UXO clearance. However, Atlantic salmon are highly mobile, and may only use the fish and shellfish ecology study area to pass through during migration (noting that at-sea behaviour is largely unknown). Therefore, it is unlikely that this impact will result in significant mortality or injury to the Atlantic salmon feature of this SAC. Further, as presented in Table 5.4   Open ▸ , the designed in measure of soft start piling procedures will allow individuals in close proximity to piling to move away from the ensonified area and reduce the total amount of acoustic energy entering the marine environment. In addition, the designed in measure of low order UXO disposal will reduce the noise levels and their potential for injury in the vicinity of UXO clearance operations. Overall, these two designed in measures further reduce the likelihood of injury and mortality.
203. As outlined in paragraphs 176 et seq., underwater noise during piling would result in behavioural responses in the vicinity of the Array, although these may occur out to a range in the low tens of kilometres, and thus not represent a significant barrier to migration to and from the SAC, particularly in terms of the vast availability of habitat in the North Sea and distance between the coast and the site boundary ( Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ). The behavioural disturbance modelling results are also highly precautionary as they were modelled against the maximum hammer energy, which will not realistically occur over the duration of the piling programme. Further, the potential underwater noise impacts will be short term and intermittent in nature during the construction phase (i.e. piling occurring over up to 602 days over eight years). As such, there is negligible risk of disruption to migration.

Sea lamprey

204. As for Atlantic salmon, the underwater noise modelling suggested that sea lamprey within close proximity to piling operations and UXO clearance may experience injury or mortality. However, sea lamprey are also highly mobile, and may only use the fish and shellfish ecology study area to pass through during migration (noting that the at-sea behaviour and habitat use of sea lamprey is largely unknown). Therefore, this impact is unlikely to result in significant mortality or injury to sea lamprey. Further, as presented in Table 5.4   Open ▸ , the designed in measure of soft start piling procedures will allow many individuals in close proximity to piling to move away from the ensonified area and will also reduce the overall acoustic energy entering the marine environment. In addition, the designed in measure of low order UXO disposal will reduce the noise levels and their potential for injury in the vicinity of UXO clearance operations. Overall, these two designed in measures further reduce the likelihood of injury and mortality.
205. As outlined in paragraphs 176 et seq., underwater noise during piling would result in behavioural responses in the vicinity of the Array, although these would extend out the low tens of kilometres, and thus not represent a significant barrier to migration to and from the SAC, particularly in terms of the vast availability of habitat in the North Sea and distance between the coast and the site boundary ( Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ). The behavioural disturbance modelling results are also highly precautionary as they were modelled against the maximum hammer energy, which will not realistically occur over the duration of the piling programme. Further, the potential underwater noise impacts will be short term and intermittent in nature during the construction phase (i.e. piling occurring over up to 602 days over eight years). As such, there is negligible risk of disruption to migration.

Conclusion

206. Adverse effects on the qualifying Annex II diadromous fish features of the River Tweed SAC which undermine the conservation objectives of the SAC will not occur as a result of underwater noise during construction activities. Potential effects from these activities on the relevant conservation objectives (as presented in paragraphs 99 to 101) are discussed in turn below in Table 5.17   Open ▸ .

Table 5.17: Conclusions Against the Conservation Objectives of the River Tweed SAC from Underwater Noise Generated during Piling and UXO Clearance in the Construction Phase of the Array Alone

207. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the River Tweed SAC as a result of underwater noise generated during piling and UXO clearance with respect to the construction phase of the Array alone.

                        River Tay SAC

Atlantic salmon

208. As outlined in paragraphs 163 to 175, Atlantic salmon within close proximity to piling operations may experience injury or mortality due to underwater noise from piling or UXO clearance. However, Atlantic salmon are highly mobile, and may only use the fish and shellfish ecology study area to pass through during migration (noting that at-sea behaviour is largely unknown). Therefore, it is unlikely that this impact will result in significant mortality or injury to the Atlantic salmon feature of this SAC. Further, as presented in Table 5.4   Open ▸ , the designed in measure of soft start piling procedures will allow individuals in close proximity to piling to move away from the ensonified area and reduce the total amount of acoustic energy entering the marine environment. In addition, the designed in measure of low order UXO disposal will reduce the noise levels and their potential for injury in the vicinity of UXO clearance operations. Overall, these two designed in measures further reduce the likelihood of injury and mortality.
209. As outlined in paragraphs 176 et seq., underwater noise during piling would result in behavioural responses in the vicinity of the Array, although these may occur out to a range in the low tens of kilometres, and thus not represent a significant barrier to migration to and from the SAC, particularly in terms of the vast availability of habitat in the North Sea and distance between the coast and the site boundary ( Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ). The behavioural disturbance modelling results are also highly precautionary as they were modelled against the maximum hammer energy, which will not realistically occur over the duration of the piling programme. Further, the potential underwater noise impacts will be short term and intermittent in nature during the construction phase (i.e. piling occurring over up to 602 days over eight years). As such, there is negligible risk of disruption to migration.

Sea lamprey

210. As for Atlantic salmon, the underwater noise modelling suggested that sea lamprey within close proximity to piling operations and UXO clearance may experience injury or mortality. However, sea lamprey are also highly mobile, and may only use the fish and shellfish ecology study area to pass through during migration (noting that the at-sea behaviour and habitat use of sea lamprey is largely unknown). Therefore, this impact is unlikely to result in significant mortality or injury to sea lamprey. Further, as presented in Table 5.4   Open ▸ , the designed in measure of soft start piling procedures will allow many individuals in close proximity to piling to move away from the ensonified area and will also reduce the overall acoustic energy entering the marine environment. In addition, the designed in measure of low order UXO disposal will reduce the noise levels and their potential for injury in the vicinity of UXO clearance operations. Overall, these two designed in measures further reduce the likelihood of injury and mortality.
211. As outlined in paragraphs 176 et seq., underwater noise during piling would result in behavioural responses in the vicinity of the Array, although these would extend out the low tens of kilometres, and thus not represent a significant barrier to migration to and from the SAC, particularly in terms of the vast availability of habitat in the North Sea and distance between the coast and the site boundary ( Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ). The behavioural disturbance modelling results are also highly precautionary as they were modelled against the maximum hammer energy, which will not realistically occur over the duration of the piling programme. Further, the potential underwater noise impacts will be short term and intermittent in nature during the construction phase (i.e. piling occurring over up to 602 days over eight years). As such, there is negligible risk of disruption to migration.

Conclusion

212. Adverse effects on the qualifying Annex II diadromous fish features of the River Tay SAC which undermine the conservation objectives of the SAC will not occur as a result of underwater noise during construction activities. Potential effects from these activities on the relevant conservation objectives (as presented in paragraphs 113 to 115) are discussed in turn below in Table 5.18   Open ▸ .

Table 5.18: Conclusions Against the Conservation Objectives of the River Tay SAC from Underwater Noise Generated during Piling and UXO Clearance in the Construction Phase of the Array Alone

213. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the River Tay SAC as a result of underwater noise generated during piling and UXO clearance with respect to the construction phase of the Array alone.

                        River Spey SAC

Atlantic salmon

214. As outlined in paragraphs 163 to 175, Atlantic salmon within close proximity to piling operations may experience injury or mortality due to underwater noise from piling or UXO clearance. However, Atlantic salmon are highly mobile, and may only use the fish and shellfish ecology study area to pass through during migration (noting that at-sea behaviour is largely unknown). Therefore, it is unlikely that this impact will result in significant mortality or injury to the Atlantic salmon feature of this SAC. Further, as presented in Table 5.4   Open ▸ , the designed in measure of soft start piling procedures will allow individuals in close proximity to piling to move away from the ensonified area and reduce the total amount of acoustic energy entering the marine environment. In addition, the designed in measure of low order UXO disposal will reduce the noise levels and their potential for injury in the vicinity of UXO clearance operations. Overall, these two designed in measures further reduce the likelihood of injury and mortality.
215. As outlined in paragraphs 176 et seq., underwater noise during piling would result in behavioural responses in the vicinity of the Array, although these may occur out to a range in the low tens of kilometres, and thus not represent a significant barrier to migration to and from the SAC, particularly in terms of the vast availability of habitat in the North Sea and distance between the coast and the site boundary ( Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ). The behavioural disturbance modelling results are also highly precautionary as they were modelled against the maximum hammer energy, which will not realistically occur over the duration of the piling programme. Further, the potential underwater noise impacts will be short term and intermittent in nature during the construction phase (i.e. piling occurring over up to 602 days over eight years). As such, there is negligible risk of disruption to migration.

Freshwater pearl mussel

216. Adult freshwater pearl mussel are confined to freshwater environments, and there is therefore no pathway for direct effects associated with this impact. However, there is potential for indirect impacts on the larval stage of freshwater pearl mussel if Atlantic salmon (their host species) are impacted. As detailed in paragraphs 214 and 215, underwater noise in the construction phase will not lead to significant mortality or injury to Atlantic salmon and is unlikely to result in barriers to migration. Therefore, it can also be concluded that there will be no indirect impact to freshwater pearl mussel.

Sea lamprey

217. As for Atlantic salmon, the underwater noise modelling suggested that sea lamprey within close proximity to piling operations and UXO clearance may experience injury or mortality. However, sea lamprey are also highly mobile, and may only use the fish and shellfish ecology study area to pass through during migration (noting that the at-sea behaviour and habitat use of sea lamprey is largely unknown). Therefore, this impact is unlikely to result in significant mortality or injury to sea lamprey. Further, as presented in Table 5.4   Open ▸ , the designed in measure of soft start piling procedures will allow many individuals in close proximity to piling to move away from the ensonified area and will also reduce the overall acoustic energy entering the marine environment. In addition, the designed in measure of low order UXO disposal will reduce the noise levels and their potential for injury in the vicinity of UXO clearance operations. Overall, these two designed in measures further reduce the likelihood of injury and mortality.
218. As outlined in paragraphs 176 et seq., underwater noise during piling would result in behavioural responses in the vicinity of the Array, although these would extend out the low tens of kilometres, and thus not represent a significant barrier to migration to and from the SAC, particularly in terms of the vast availability of habitat in the North Sea and distance between the coast and the site boundary ( Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ). The behavioural disturbance modelling results are also highly precautionary as they were modelled against the maximum hammer energy, which will not realistically occur over the duration of the piling programme. Further, the potential underwater noise impacts will be short term and intermittent in nature during the construction phase (i.e. piling occurring over up to 602 days over eight years). As such, there is negligible risk of disruption to migration.

Conclusion

219. Adverse effects on the qualifying Annex II diadromous fish features of the River Spey SAC which undermine the conservation objectives of the SAC will not occur as a result of underwater noise during construction activities. Potential effects from these activities on the relevant conservation objectives (as presented in paragraphs 123 to 126) are discussed in turn below in Table 5.19   Open ▸ .

Table 5.19: Conclusions Against the Conservation Objectives of the River Spey SAC from Underwater Noise Generated during Piling and UXO Clearance in the Construction Phase of the Array Alone

220. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the River Spey SAC as a result of underwater noise generated during piling and UXO clearance with respect to the construction phase of the Array alone.

                        Berriedale and Langwell Waters SAC

Atlantic salmon

221. As outlined in paragraphs 163 to 175, Atlantic salmon within close proximity to piling operations may experience injury or mortality due to underwater noise from piling or UXO clearance. However, Atlantic salmon are highly mobile, and may only use the fish and shellfish ecology study area to pass through during migration (noting that at-sea behaviour is largely unknown). Therefore, it is unlikely that this impact will result in significant mortality or injury to the Atlantic salmon feature of this SAC. Further, as presented in Table 5.4   Open ▸ , the designed in measure of soft start piling procedures will allow individuals in close proximity to piling to move away from the ensonified area and reduce the total amount of acoustic energy entering the marine environment. In addition, the designed in measure of low order UXO disposal will reduce the noise levels and their potential for injury in the vicinity of UXO clearance operations. Overall, these two designed in measures further reduce the likelihood of injury and mortality.
222. As outlined in paragraphs 176 et seq., underwater noise during piling would result in behavioural responses in the vicinity of the Array, although these may occur out to a range in the low tens of kilometres, and thus not represent a significant barrier to migration to and from the SAC, particularly in terms of the vast availability of habitat in the North Sea and distance between the coast and the site boundary ( Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ). The behavioural disturbance modelling results are also highly precautionary as they were modelled against the maximum hammer energy, which will not realistically occur over the duration of the piling programme. Further, the potential underwater noise impacts will be short term and intermittent in nature during the construction phase (i.e. piling occurring over up to 602 days over eight years). As such, there is negligible risk of disruption to migration.

Conclusion

223. Adverse effects on the qualifying Annex II diadromous fish features of the Berriedale and Langwell Waters SAC which undermine the conservation objectives of the SAC will not occur as a result of underwater noise during construction activities. Potential effects from these activities on the relevant conservation objectives (as presented in paragraph 133) are discussed in turn below in Table 5.20   Open ▸ .

Table 5.20: Conclusions Against the Conservation Objectives of the Berriedale and Langwell Waters SAC from Underwater Noise Generated during Piling and UXO Clearance in the Construction Phase of the Array Alone

224. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the Berriedale and Langwell Waters SAC as a result of underwater noise generated during piling and UXO clearance with respect to the construction phase of the Array alone.

                        River Teith SAC

Atlantic salmon

225. As outlined in paragraphs 163 to 175, Atlantic salmon within close proximity to piling operations may experience injury or mortality due to underwater noise from piling or UXO clearance. However, Atlantic salmon are highly mobile, and may only use the fish and shellfish ecology study area to pass through during migration (noting that at-sea behaviour is largely unknown). Therefore, it is unlikely that this impact will result in significant mortality or injury to the Atlantic salmon feature of this SAC. Further, as presented in Table 5.4   Open ▸ , the designed in measure of soft start piling procedures will allow individuals in close proximity to piling to move away from the ensonified area and reduce the total amount of acoustic energy entering the marine environment. In addition, the designed in measure of low order UXO disposal will reduce the noise levels and their potential for injury in the vicinity of UXO clearance operations. Overall, these two designed in measures further reduce the likelihood of injury and mortality.
226. As outlined in paragraphs 176 et seq., underwater noise during piling would result in behavioural responses in the vicinity of the Array, although these may occur out to a range in the low tens of kilometres, and thus not represent a significant barrier to migration to and from the SAC, particularly in terms of the vast availability of habitat in the North Sea and distance between the coast and the site boundary ( Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ). The behavioural disturbance modelling results are also highly precautionary as they were modelled against the maximum hammer energy, which will not realistically occur over the duration of the piling programme. Further, the potential underwater noise impacts will be short term and intermittent in nature during the construction phase (i.e. piling occurring over up to 602 days over eight years). As such, there is negligible risk of disruption to migration.

Sea lamprey

227. As for Atlantic salmon, the underwater noise modelling suggested that sea lamprey within close proximity to piling operations and UXO clearance may experience injury or mortality. However, sea lamprey are also highly mobile, and may only use the fish and shellfish ecology study area to pass through during migration (noting that the at-sea behaviour and habitat use of sea lamprey is largely unknown). Therefore, this impact is unlikely to result in significant mortality or injury to sea lamprey. Further, as presented in Table 5.4   Open ▸ , the designed in measure of soft start piling procedures will allow many individuals in close proximity to piling to move away from the ensonified area and will also reduce the overall acoustic energy entering the marine environment. In addition, the designed in measure of low order UXO disposal will reduce the noise levels and their potential for injury in the vicinity of UXO clearance operations. Overall, these two designed in measures further reduce the likelihood of injury and mortality.
228. As outlined in paragraphs 176 et seq., underwater noise during piling would result in behavioural responses in the vicinity of the Array, although these would extend out the low tens of kilometres, and thus not represent a significant barrier to migration to and from the SAC, particularly in terms of the vast availability of habitat in the North Sea and distance between the coast and the site boundary ( Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ). The behavioural disturbance modelling results are also highly precautionary as they were modelled against the maximum hammer energy, which will not realistically occur over the duration of the piling programme. Further, the potential underwater noise impacts will be short term and intermittent in nature during the construction phase (i.e. piling occurring over up to 602 days over eight years). As such, there is negligible risk of disruption to migration.

Conclusion

229. Adverse effects on the qualifying Annex II diadromous fish features of the River Teith SAC which undermine the conservation objectives of the SAC will not occur as a result of underwater noise during construction activities. Potential effects from these activities on the relevant conservation objectives (as presented in paragraphs 140 to 141) are discussed in turn below in Table 5.21   Open ▸ . As stated in paragraphs 140 to 141), a CAP has not yet been published for the River Teith SAC, and therefore, only the overarching conservation objectives for all qualifying species features are presented in Table 5.21   Open ▸ for Atlantic salmon and sea lamprey combined. The assessment has therefore been undertaken with regard to the available conservation objectives for the site (NatureScot, 2015).

Table 5.21: Conclusions Against the Conservation Objectives of the River Teith SAC from Underwater Noise Generated during Piling and UXO Clearance in the Construction Phase of the Array Alone

230. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the River Teith SAC as a result of underwater noise generated during piling and UXO clearance with respect to the construction phase of the Array alone.

                        River Oykel SAC

Atlantic salmon

231. As outlined in paragraphs 163 to 175, Atlantic salmon within close proximity to piling operations may experience injury or mortality due to underwater noise from piling or UXO clearance. However, Atlantic salmon are highly mobile, and may only use the fish and shellfish ecology study area to pass through during migration (noting that at-sea behaviour is largely unknown). Therefore, it is unlikely that this impact will result in significant mortality or injury to the Atlantic salmon feature of this SAC. Further, as presented in Table 5.4   Open ▸ , the designed in measure of soft start piling procedures will allow individuals in close proximity to piling to move away from the ensonified area and reduce the total amount of acoustic energy entering the marine environment. In addition, the designed in measure of low order UXO disposal will reduce the noise levels and their potential for injury in the vicinity of UXO clearance operations. Overall, these two designed in measures further reduce the likelihood of injury and mortality.
232. As outlined in paragraphs 176 et seq., underwater noise during piling would result in behavioural responses in the vicinity of the Array, although these may occur out to a range in the low tens of kilometres, and thus not represent a significant barrier to migration to and from the SAC, particularly in terms of the vast availability of habitat in the North Sea and distance between the coast and the site boundary ( Figure 5.2   Open ▸ and Figure 5.3   Open ▸ ). The behavioural disturbance modelling results are also highly precautionary as they were modelled against the maximum hammer energy, which will not realistically occur over the duration of the piling programme. Further, the potential underwater noise impacts will be short term and intermittent in nature during the construction phase (i.e. piling occurring over up to 602 days over eight years). As such, there is negligible risk of disruption to migration.

Freshwater pearl mussel

233. Adult freshwater pearl mussel are confined to freshwater environments, and there is therefore no pathway for direct effects associated with this impact. However, there is potential for indirect impacts on the larval stage of freshwater pearl mussel if Atlantic salmon (their host species) are impacted. As detailed in paragraphs 231 and 232, underwater noise in the construction phase will not lead to significant mortality or injury to Atlantic salmon and is unlikely to result in barriers to migration. Therefore, it can also be concluded that there will be no indirect impact to freshwater pearl mussel.

Conclusion

234. Adverse effects on the qualifying Annex II diadromous fish features of the River Oykel SAC which undermine the conservation objectives of the SAC will not occur as a result of underwater noise during construction activities. Potential effects from these activities on the relevant conservation objectives (as presented in paragraphs 146 to 148) are discussed in turn below in Table 5.22   Open ▸ .

Table 5.22: Conclusions Against the Conservation Objectives of the River Oykel SAC from Underwater Noise Generated during Piling and UXO Clearance in the Construction Phase of the Array Alone

235. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the River Oykel SAC as a result of underwater noise generated during piling and UXO clearance with respect to the construction phase of the Array alone.

5.3.2.    Effects due to EMFs from Subsea Electrical Cabling

5.3.2. Effects due to EMFs from Subsea Electrical Cabling

236. The LSE2 assessment during the HRA Stage One process identified that during the operation and maintenance phase, LSE2 could not be ruled out for potential effects to Annex II diadromous fish from EMFs generated by subsea electrical cables. This relates to the following sites and relevant Annex II diadromous fish features:

• River Dee SAC;

–           Atlantic salmon; and

–           freshwater pearl mussel.

• River South Esk SAC;

–           Atlantic salmon; and

–           freshwater pearl mussel.

• Tweed Estuary SAC;

–           sea lamprey.

• River Tweed SAC;

–           Atlantic salmon; and