6.3. Marine Mammals

6.3.1. Introduction

This section of this Scoping Report presents the relevant marine mammal data sources and baseline description within the Array and considers the scope of assessment on marine mammals from the construction, operation and maintenance, and decommissioning of the Array.

6.3.2. Study Area

Marine mammals are highly mobile, wide-ranging species, with varied behaviour and ecology between species. To account for this and provide wider geographic context, the marine mammal study area proposed for the purpose of baseline characterisation and subsequent Array EIA Report has been defined at two spatial scales:

Array marine mammal study area: this includes the area covered by the site-specific aerial surveys (March 2021 to February 2023). The preliminary results of these surveys provided an indication of the marine mammal species currently present within potential impact footprints associated with the Array (i.e. the potential Zones of Influence (ZoI)). The Array marine mammal study area encompasses the site boundary plus an 8 km buffer, which is based on the buffer implemented in the site-specific aerial surveys. The Array marine mammal study area is shown in Figure 6.4 Open ▸ ; and
Regional marine mammal study area: this area encompasses a larger range due to the highly mobile and wide-ranging nature of marine mammal species and is illustrated in Figure 6.4 Open ▸ and Figure 6.5 Open ▸ . Management Units (MUs) were used to inform the regional marine mammal study area at appropriate scales for each species, with cetacean MUs defined by the Inter Agency Marine Mammal Working Group (IAMMWG, 2015) and seal MUs provided by the Special Committee on Seals (SCOS, 2021). For species in which MUs extend over a very large scale (e.g. the Celtic and Greater North Sea MU for minke whale Balaenoptera acutorostrata and white-beaked dolphin Lagenorhynchus albirostris, and North Sea MU for harbour porpoise Phocoena phocoena) the appropriate Small Cetaceans in European Atlantic waters and the North Sea survey (SCANS)-III block which overlaps with the Array (block R) will be utilised. The different MUs for the target species are presented in Figure 6.5 Open ▸ .

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Figure 6.4: Marine Mammal Study Areas

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Figure 6.5: Management Units for Relevant Marine Mammal Species in the Vicinity of the Array

6.3.3. Baseline Environment

The marine mammal baseline environment of the Array is summarised briefly in this section, with a detailed description provided in Appendix 8. The baseline environment was characterised through an extensive desktop review of key datasets, the preliminary results from the site-specific aerial surveys undertaken (data available between March 2021 to September 2022 at the time of writing) and the results from site-specific surveys for nearby offshore wind farms (such as Seagreen 1 (formerly known as Seagreen Alpha and Bravo) and Berwick Bank Offshore Wind Farms). Seagreen 1 and Berwick Bank Offshore Wind Farms are 50.72 km and 56.77 km away from the site boundary, respectively.
Four marine mammal species were identified as being likely to occur within the Array marine mammal study area and/or the regional marine mammal study area either seasonally or year-round, dependant on species. These species are:

harbour porpoise;
minke whale;
white-beaked dolphin; and
grey seal Halichoerus grypus.

Additionally, there were four common dolphins Delphinus delphis and three harbour seal Phoca vitulina recorded in total from two sightings each. These were classed as rare or occasional visitors to the area and will not be carried forward in the assessment (refer to Appendix 8 for further details).

Harbour porpoise

The Array marine mammal study area is located within the North Sea MU for harbour porpoise (IAMMWG, 2022), which has an estimated abundance of 346,601 individuals (CV: 0.09, 95% CI: 289,498 to 419,967) based on estimates from the SCANS-III survey (Hammond et al., 2017, 2021).
The SCANS-III density estimate was 0.599 individuals per km2 (CV: 0.287) for survey Block R (Hammond et al., 2017, 2021). The predicted density surface of harbour porpoise in the Array marine mammal study area is between 0.5 to 1.2 animals per km2 (Appendix 3 by Lacey and Hammond in Hague et al., 2020).
Sightings data between 1980 and 2018, collated by Waggitt et al. (2020), report year-round abundance of harbour porpoise, with increased density in the summer months. This is consistent with the results of the site-specific aerial surveys conducted for the nearby Berwick Bank Offshore Wind Farm, which reported higher densities during spring and summer than in autumn and winter (SSER, 2022). Additionally, harbour porpoise were the most abundant marine mammal recorded during the site-specific surveys for the Array, with a total of 825 individuals sighted thus far between March 2021 to September 2022. They were the only species to be observed in all months, with the highest number of individuals observed in July 2021 (n=187).
Given their recorded abundance in the literature and recent site-specific surveys for the Array and nearby offshore wind farms, harbour porpoises are considered likely to occur within the Array marine mammal study area and regional marine mammal study area year-round.

Minke whale

All minke whales in UK waters are part of the Celtic and Greater North Seas MU (IAMMWG, 2022). This MU has an estimated abundance of 10,288 individuals in the UK portion (CV: 0.26, 85% CI: 6,210 to 17,042) and 20,118 individuals in the entire MU (CV: 0.18, 95% CI: 14,061 to 28,786) based on estimates from the SCANS-III survey (Hammond et al., 2017, 2021) and ObSERVE survey (Rogan et al., 2018).
The SCANS-III density estimate was 0.0387 individuals per km2 (CV: 0.614) for survey Block R (Hammond et al., 2017, 2021). The predicted density surface of minke whale in the Array marine mammal study area is between 0.03 to 0.05 animals per km2 (Appendix 3 by Lacey and Hammond in Hague et al., 2020).
Minke whales are considered to be seasonal visitors to the northern North Sea, as they are mainly present in Scottish waters in the summer (Hague, et al., 2020, Waggitt et al., 2020). This is consistent with the preliminary results of the site-specific surveys for the Array which recorded minke whales in the summer only, with sixteen individuals recorded across June and July in 2021 and 2022. Similarly, they were only observed in the summer months in site-specific aerial surveys for Berwick Bank Offshore Wind Farm and Firth of Forth Round 3 Zone surveys (Sparling, 2012, SSER, 2022). Therefore, minke whales are considered likely to occur regularly in the summer months within the Array marine mammal study area and the regional marine mammal study area.

White-beaked dolphin

All white-beaked dolphins in UK waters are part of the Celtic and Greater North Seas MU (IAMMWG, 2022). This MU has an estimated abundance of 34,025 individuals in the UK portion (CV: 0.28, 85% CI: 20,026 to 57,807) and 43,951 individuals in the entire MU (CV: 0.22, 95% CI: 28,439 to 67,924) based on estimates from the SCANS-III survey (Hammond et al., 2017, 2021) and ObSERVE survey (Rogan et al., 2018).
The SCANS-III density estimate was 0.243 individuals per km2 (CV: 0.484) for Block R (Hammond et al., 2017, 2021). The predicted density surface of white-beaked dolphin in the Array marine mammal study area is between 0.05 to 0.2 animals per km2 (Appendix 3 by Lacey and Hammond in Hague et al., 2020).
Waggitt et al. (2020) report year-round abundance of white-beaked dolphins in the Array marine mammal study area and regional marine mammal study area, with an increase in abundance in the summer months. This is consistent with the preliminary results of the site-specific surveys as individuals were observed between March to October, with highest numbers recorded in June and July (n=18 and 19, respectively). White-beaked dolphins were the second most abundant marine mammal observed during the site-specific surveys thus far, with a total of 72 individuals sighted across ten surveys. Given the literature and observations during recent site-specific surveys for the Array and other nearby offshore wind farms, white-beaked dolphins are considered likely to occur regularly (mostly likely in the summer months) within the Array marine mammal study area and regional marine mammal study area.

Grey seal

The Array marine mammal study area is situated within the East Scotland MU, with potential overlap with the Northeast England MU and Moray Firth MU (SCOS, 2021). This overlap with further away MUs is due to extensive offshore foraging trips undertaken by grey seals (McConnell et al., 2001; Jones et al., 2015; SCOS, 2021).
The most recent population estimate of grey seals in Scotland at the start of the breeding season (before pups are born) was 120,800 individuals in 2020, and 157,300 in the wider UK (SCOS, 2021). The most recent estimated pup production from 2019 was 54,050 pups in Scotland and 67,850 in the wider UK (SCOS, 2021). The overall pup production in the wider UK increased by <1.5% per year between 2016 and 2019, with increases mainly limited to North Sea colonies along the east coast of Scotland and England (SCOS, 2021).
August haul out counts for the East Scotland MU have increased from 2,328 individuals during the 1996-1997 survey to 3,683 in the 2016-2019 survey (Morris et al., 2021), accounting for 14% of grey seals hauled out in Scotland and 9% of grey seals hauled out in the UK. August haul out counts for the Moray Firth MU population increased from 551 individuals in the 1996-1997 survey to 1,917 in the 2011-2015 survey, with a decrease to 1,657 in the 2016-2019 survey (Morris et al., 2021). There are infrequent counts for the Northeast England MU, with grey seals primarily present in the Northumberland and The Tees areas. These counts show a significant increase from 613 individuals in the 1996-1997 period to 6,565 in the 2016-2019 period (SMRU, 2022b).
Grey seals were observed year-round during the site-specific surveys for the Array, with a total of 26 individuals recorded over ten surveys. Given their recorded abundance in the literature and recent site-specific surveys for the Array and nearby offshore wind farms, grey seals are considered likely to occur year-round within the Array marine mammal study area and regional marine mammal study area.

Designated sites

The Array marine mammal study area does not overlap with any protected sites that have been designated for marine mammal features. Numerous sites have been identified as occurring within the vicinity of the regional marine mammal study area and are presented in greater detail in Apx. Table 8.2 and Apx Figure 8.6 Open ▸ . These include six Special Areas of Conservation (SACs) and one Marine Protected Area (MPA):

Southern Trench MPA;
Berwickshire and North Northumberland Coast SAC;
Firth of Tay and Eden Estuary SAC;
Isle of May SAC;
Southern North Sea SAC;
Moray Firth SAC; and
Dornoch Firth and Morrich More SAC.

The closest designated site is the Southern Trench MPA, which is situated 66.9 km from the site boundary and is designated for minke whales. All other sites are over 100 km from the site boundary.
The LSE Screening Report will include a full screening of National and European designated sites with qualifying marine mammal interest features, that may be impacted by the Array. Any relevant sites and/or features screened into the marine mammal assessment will be assessed in the marine mammal chapter of the Array EIA Report. The information to support the assessment of transboundary European sites and features will be presented in the Report to Inform Appropriate Assessment (RIAA).

6.3.4. Potential Array Impacts

A number of potential impacts which may occur during the construction, operation and maintenance, and decommissioning phases of the Array in the absence of designed in measures on marine mammals have been identified in Table 6.11 Open ▸ .

Table 6.11: Potential Impacts Identified for Marine Mammals in the Absence of Designed In Measures

Potential Impact	Justification
Construction
Injury and disturbance from subsea noise generated during UXO clearance	Marine mammals are sensitive to increased subsea noise generated during UXO clearance, which can lead to behavioural disturbance, auditory injury (temporary threshold shift (TTS) or permanent threshold shift (PTS)), and in worst cases, death.
Injury and disturbance from subsea noise generated during piling	Marine mammals are sensitive to increased subsea noise generated during piling procedures, which can lead to behavioural disturbance, auditory injury (TTS or PTS), and in worst cases, death.
Disturbance due to pre-construction surveys (including geophysical surveys)	There is potential for behavioural disturbance and/or displacement of marine mammals during pre-construction surveys (such as geophysical site investigation surveys).
Disturbance due to vessel use	The presence of vessels and their activities associated with the construction phase (e.g. dredging) could result in behavioural disturbance and/or displacement of marine mammals.
Injury due to collision with vessels	Increased vessel traffic in the area during the construction phase could result in injury and/or death of marine mammals due to colliding with vessels.
Effects on marine mammals due to accidental release of pollutants	There is a risk of pollution being accidentally released from vessels and equipment involved during construction activities.
Effects on marine mammals due to increased SSCs and associated sediment deposition	There is potential for an increase in SSC and associated deposition during construction activities, such as foundation instillation and seabed preparation. Disturbance could be indirect (affecting prey species) or direct (affecting visibility).
Effects on marine mammals due to altered prey availability	Availability of prey (such as fish, crustaceans, cephalopods, etc.) may be affected during the construction phase due to a combination of other impacts.
Operation and Maintenance
Disturbance due to vessel use and vessel activities	The presence of vessels and their activities associated with the operation and maintenance phase (e.g. repairs to the turbine structures) could result in behavioural disturbance and/or displacement of marine mammals.
Effects on marine mammals due to entanglement associated with the Array	The presence of anchor mooring lines and inter-array cables may cause entanglement of animals in itself (primary entanglement), and lost or discarded fishing gear and other marine debris have the potential to become snagged and cause secondary entanglement of marine wildlife.
Injury due to collision with vessels	Increased vessel traffic in the area during the operation and maintenance phase could result in injury and/or death of marine mammals due to colliding with vessels.
Disturbance due to geophysical surveys	There is potential for behavioural disturbance and/or displacement to marine mammals during geophysical surveys during the operation and maintenance phase.
Effects on marine mammals due to accidental release of pollutants	There is a risk of pollution being accidentally released from vessels and equipment involved during operational and maintenance activities.
Injury and disturbance due to operational noise from turbines and anchor mooring lines	Marine mammals are sensitive to subsea noise, which can cause behavioural and/or injurious effects (TTS or PTS), and in worst cases, death. Increased subsea noise could occur due to the operation of wind turbines and from anchor mooring lines, which may affect marine mammal receptors.
Effects on marine mammals due to EMF from subsea electrical cabling	The subsea electrical cabling produces EMFs which may affect marine mammal interactions and ecology (e.g. prey/predator relationships may be affected due to the effect of EMF on fish). These potential effects could occur due to changes in background EMFs inhibiting or interfering with marine mammal behaviours.
Effects on marine mammals due to altered prey availability	Availability of prey (such as fish, crustaceans, cephalopods, etc.) may be affected during the operation and maintenance phase due to a combination of other impacts.
Decommissioning
Disturbance due to vessel use and vessel activities	The presence of vessels and their activities associated with the decommissioning phase could result in behavioural disturbance and/or displacement of marine mammals.
Injury due to collision with vessels	Increased vessel traffic in the area during the decommissioning phase could result in injury and/or death of marine mammals due to colliding with vessels.
Effects on marine mammals due to accidental release of pollutants	There is a risk of pollution being accidentally released from vessels and equipment involved during decommissioning activities.
Effects on marine mammals due to increased SSCs and associated sediment deposition	There is potential for an increase in SSC and associated deposition during decommissioning activities, such as turbine removal. Disturbance could be indirect (affecting prey species) or direct (affecting visibility).
Effects on marine mammals due to altered prey availability	Availability of prey (such as fish, crustaceans, cephalopods, etc.) may be affected during the decommissioning phase due to a combination of other impacts.

6.3.5. Designed In Measures

The following designed in measures have been considered in the identification of potential impacts that have been scoped into the Array assessment, including how these can reduce potential for impact ( Table 6.13 Open ▸ ):

the development of and adherence to an appropriate Code of Construction Practice (CoCP);
the development of and adherence to an EMP (including a Marine Pollution Contingency Plan (MPCP));
the development of and adherence to a VMP; or equivalent to be consulted upon with stakeholders post-consent;
the development of and adherence to a Marine Mammal Mitigation Plan (MMMP) to outline the additional mitigation to be implemented for piling and UXO clearance;
the development of and adherence to a Piling Strategy (or equivalent, after consultation with stakeholders) which will set out the mitigation measures including soft-start and ramp-up measures;
implementation of soft-start and ramp-up measures for piling and UXO clearance;
use of low order deflagration (ideally, and where possible) for UXO clearance; and
implementation of a Decommissioning Programme.

The significance of effects on marine mammal receptors will inform the extent of additional mitigation required. This significance will be assessed using the best available evidence (such as information from other offshore wind farms) and will be consulted and agreed upon with the statutory consultees throughout the consultation process.

6.3.6. Relevant Consultations

A summary of the key points of agreement with relevant stakeholders and Statutory Nature Conservation Bodies (SNCBs) during the Array Scoping workshop undertaken in November 2022 is presented in Table 6.12 Open ▸ .

Table 6.12: Summary of Key Consultation on the Scoping Assessment for the Array

Date	Consultee(s)	Type of Consultation	Summary of Consultation	Where Addressed
17 November 2022	NatureScot, MS-LOT, MSS	Scoping workshop	The requirement for further information regarding scoping out EMFs and operational noise from turbines was discussed. In addition, scoping out impacts due to UXO and geophysical and other pre-construction surveys was agreed upon due to the alternate licenses to be sought for these activities.	Table 6.14 Open ▸
17 November 2022	NatureScot, MS-LOT, MSS	Scoping workshop	Scoping in effects on marine mammals due to operational noise of anchor mooring lines was discussed, as was the inclusion of both primary and secondary entanglement in the scoping assessment. Finally, the potential to scope out injury to marine mammals due to collision with vessels was proposed, however it has been decided to scope in this potential impact during this revision whilst feedback is sought from stakeholders as agreement was not reached during the pre-Scoping workshop.	Table 6.13 Open ▸

6.3.7. Potential Impacts After the Implementation of Designed in Measures

Table 6.13 Open ▸ outlines the impacts which have been scoped into the Array assessment alongside a description of any additional data collection (e.g. site-specific surveys) and/or supporting analyses (e.g. modelling) that will be required to enable a full assessment of the impacts.
Table 6.14 Open ▸ describes the potential impacts to marine mammals that have been scoped out of the assessment presently.

Table 6.13: Impacts Proposed to be Scoped In to the Array Assessment for Marine Mammals. Project Phase Refers to Construction (C), Operation and Maintenance (O) and Decommissioning (D) Phase of the Array

Impact	Project Phase			Justification (including consideration of designed in measures)	Data Collection and Analysis Required to Characterise the Baseline Environment for the EIA	Summary of Proposed Approach to Assessment
Impact	C	O	D			Summary of Proposed Approach to Assessment
Injury and disturbance from subsea noise generated during UXO clearance				Marine mammals are sensitive to increased subsea noise generated during UXO clearance. Although UXO detonation works will be consented under a separate licensing regime, impacts from the works are scoped in here to ensure a pragmatic assessment of impacts to marine mammals is carried out. This separate license application will include designed in measures, such as the use of low order deflagration for UXO clearance wherever possible, and the development of a MMMP that is informed by the most recent guidance (JNCC, 2010b) and the outcomes of subsea noise modelling. Within the MMMP, additional mitigation will be outlined as required, such as the use of a defined mitigation zone, MMOs, PAM, ADDs and soft-start charges.	Confirmation on the number and sizes of UXOs to be cleared, and their associated charges, within the site boundary. Aerial survey data will be used to calculate density estimates, where data allows, for each species within the impact footprint.	A detailed noise modelling assessment will be undertaken to quantitively assess the risk of auditory injury and disturbance due to UXO clearance and to define a sufficient mitigation zone.
Injury and disturbance from subsea noise generated during piling				Marine mammals are sensitive to increased subsea noise generated during piling. Designed in measures include the development of piling soft-start and ramp up measures, a defined mitigation zone based on the noise modelling assessment and the development of an MMMP. Within the MMMP, additional mitigation will be outlined, such as the use of Marine Mammal Observers (MMOs), Passive Acoustic Monitoring (PAM), and ADDs.	Site-specific digital aerial survey data will be used to calculate density estimates, where data allows, for each species within the impact footprint. See Appendix 9 for full details of site-specific surveys.	A detailed noise modelling assessment will be undertaken to quantitively assess the risk of auditory injury and disturbance and to define a sufficient mitigation zone. Specific modelling parameters are unavailable at the time of writing, however this modelling will likely investigate scenarios such as the potential numbers of piling locations and the two furthest piling locations. The most recent guidance and thresholds presented in Southall et al. (2019) will be used to assess the risk of permanent auditory injury, in terms of PTS. This risk will be based on the dual metric approach: cumulative sound exposure level (SELCUM) and peak sound exposure level (SPLPEAK). The assessment of disturbance will be based on the good practice methodology available at the time and the most recent guidance documents, such as those provided by the JNCC. Noise contours at appropriate intervals will likely be generated from the noise modelling and overlain on species density surfaces to predict the number of animals potentially affected. To understand the ecological consequences of piling on marine mammals, the assessment will also use population modelling (iPCoD) and the potential for short-term and long term effects.
Disturbance due to vessel use and vessel activities				The impact of vessel use and vessel activities (such as dredging, rock placement, and trenching within the construction phase, operation and maintenance phase, and decommissioning activities) may result in behavioural disturbance and/or displacement of marine mammals. The designed in measure for this impact is the implementation and adherence to a VMP, and a decommissioning plan.	Not applicable for this impact	Comparative noise modelling for non-piling activities that also produce noise will be undertaken to inform a qualitative assessment of non-piling noise producing activities, such as geophysical surveying, rock placement and vessel movement.
Injury due to collision with vessels				There is likely to be increased vessel traffic during the construction, operation and maintenance, and decommissioning stages, which could increase the risk of collisions with marine mammals. The designed in measure for this impact is the implementation and adherence to a VMP (or equivalent).	Not applicable for this impact	A qualitative assessment will be undertaken, based on the best available and most recent literature at the time of writing.
Effects on marine mammals due to altered prey availability				Changes in abundance and distribution of prey species (such as fish, crustaceans, cephalopods, etc.) may occur due to activities in the construction, operation and maintenance, and decommissioning phases. These changes may affect the ability of marine mammals to forage. There are no designed in measures applicable to this impact.	Not applicable for this impact	There will be no specific modelling required for this impact, although the assessment will be based on the results of the subsea noise modelling assessment, Physical Processes assessment, and the resulting impact assessment carried out for fish and shellfish receptors.
Effects on marine mammals due to entanglement associated with the Array	×		×	The presence of anchor mooring lines may cause entanglement of animals in itself (primary entanglement), and lost or discarded fishing gear and other marine debris have the potential to become snagged and cause secondary entanglement of marine wildlife. Floating offshore wind is in its infancy so there is no data currently available to assess this impact. Therefore, both primary and secondary entanglement will be scoped in. There are no designed in measures relevant for this impact.	Not applicable for this impact	Desk-based study of data as it emerges to undertake a qualitative assessment.
Injury and disturbance due to operational noise from anchor mooring lines				Subsea noise produced by anchor mooring lines in the operation and maintenance phase has the potential to cause injury and disturbance to marine mammals. This impact is scoped in as a precaution due to the paucity of information regarding the levels of subsea noise produced by the anchor mooring lines of floating offshore wind turbines. There are no designed in measures relevant for this impact.	Not applicable for this impact	Subsea noise modelling to determine potential elevations in noise during operation.

Table 6.14: Impacts Proposed to be Scoped Out of the Array Assessment for Marine Mammals

Impact	Justification
Construction
Disturbance due to pre-construction and geophysical surveys	Pre-construction surveys (including geophysical surveys) during the construction phase, and annual geophysical surveys conducted during the operation and maintenance phase may result in behavioural disturbance and displacement of marine mammals. However, in order to achieve a proportionate EIA, this impact will not be considered further within the EIA as full geophysical and geotechnical surveys are expected to be completed in 2023 and it will be subject to a separate license. The separate license application will include designed in measures for this impact, such as the development of an MMMP following recent JNCC guidance (JNCC, 2017). The MMMP will contain additional mitigation measures, such as mitigation zones, MMOs, PAM, ADDs and soft-start charges.
Effects on marine mammals due to accidental release of pollutants	The impact of pollution released during accidental spills and contaminant releases could reduce species survival rates, either as a result of direct mortality of marine mammals or through a reduction in prey availability (scoped in). Designed in measures for this impact are the development and adherence to an EMP, including a MPCP, and an appropriate CoCP during the construction phase. With these measures in place and based on evidence from nearby Berwick Bank Offshore Wind Farm consent application (SSER, 2022), it is considered unlikely that a major incident affecting any species at population level will occur. SSER (2022) predicted that any impact would be of a local spatial scale, short term, intermittent and medium reversibility within the context of regional populations, and therefore not significant in EIA terms. This is considered to be applicable to the Array, where construction, operation and maintenance, and decommissioning will be of a comparable scale and within close proximity. Therefore, it is proposed that this impact is scoped out of the EIA.
Effects on marine mammals due to increased SSC and associated deposition	Increased SSC and associated deposition can disrupt water quality, which could have direct and indirect effects on marine mammals. Indirect impacts could include negative effects on prey species and reduced prey availability (scoped in). Direct impacts would include impaired visibility, thereby reducing foraging ability. However, marine mammals are known to forage in areas where water conditions are turbid and visibility is low. As harbour porpoises and harbour seals have been observed foraging in these conditions (Pierpoint, 2008; Marubini et al., 2009; Hastie et al., 2016), it is unlikely that low light levels, increased turbidity and murky water associated with increased SSC will adversely impact marine mammal foraging ability. Although these conditions may compromise visual ability, marine mammals are able to use other senses to navigate their surroundings. For example, seals can detect water movements and hydrodynamic trails with their mystacial vibrissae (i.e., whiskers; Dehnhardt et al., 2001; Grant et al., 2013) and odontocetes are well known for their use of echolocation to detect their surroundings and forage. Increased SSC and its associated effects on water quality generated during the construction and decommissioning stages of the Array are expected to have a localised maximum impact range. Sediments are likely to dissipate within one tidal cycle. Overall, the ZoI of increased SSC and associated deposition will be small, particularly in the context of the regional marine mammal study area, the duration of effects will be short term, and marine mammal receptors are not considered to be sensitive to increases in SSC. Therefore, it is proposed that this impact is scoped out of the EIA.
Operation and Maintenance
Effects on marine mammals due to accidental release of pollutants	As above for the construction phase.
Effects on marine mammals due to EMF from subsea electrical cabling	While the effects of EMF on fish and shellfish receptors are documented, there is no evidence of EMF related to offshore wind farms having any negative impact on marine mammals (Copping, 2018; Copping et al., 2020). Furthermore, there are no regulatory thresholds or guidelines that define acceptable levels of EMF emissions into the marine environment (Copping et al., 2020). There is no evidence that seals can detect or respond to EMF, however some cetacean species, may be sensitive and/or able to detect variations in magnetic fields (Normandeau, 2011; Czech-Damal et al., 2012; Hüttner et al., 2022). Until recently, the Guiana dolphin Sotalia guianensis was the only marine mammal species demonstrated to respond to EMFs (Czech-Damal et al., 2012, 2013). The Guiana dolphin possesses an electroreceptive system, which involves vibrissal crypts on their rostrum to detect weak electrical fields generated by their prey fish (Czech-Damal et al., 2012). As the Guiana dolphin only occurs in Central and South American waters, it is not present within the scope of this assessment. However, recent experimental evidence suggests that adult bottlenose dolphins possess many basic morphological similarities in their vibrissal crypts to Guiana dolphins and can perceive as equally low electrical fields (Hüttner et al., 2022). The authors suggest that bottlenose dolphins use electroreception to detect benthic prey at short ranges and suggest that as this ability has now been observed in two dolphin species, it may be widespread within odontocetes (Hüttner et al., 2022). However, the effects of EMFs from subsea cabling are attenuate below background levels within metres from the cable itself (Hutchinson, et al., 2021). As marine mammals have wide spatial distribution and are variable within the water column, the impacts (if any) from EMF will be minimal. Therefore, it is proposed that this impact is scoped out of the EIA.
Injury and disturbance due to operational noise from turbines	Previous studies on fixed foundation wind turbines have demonstrated that operational noise produced by turbines will have negligible effects on marine mammals (Teilmann et al., 2006a, 2006b; Cefas, 2010; Brasseur et al., 2012; Tougaard et al., 2020) and the noise generated has been demonstrated to be much lower than levels associated with construction activities (such as piling; Madsen et al., 2006). There is less information available on the operational noise levels of floating offshore wind turbines, however any effects on marine mammals are likely to be minimal as noise generated from the turbines is likely to be of low frequency and at low levels (Farr et al., 2021). Similarly, a subsea noise desk study for the Hywind Scotland pilot park of floating offshore wind turbines concluded that injury and disturbance due to operational noise of the turbines was unlikely to occur (Xodus, 2015). Therefore, it is proposed that this impact is scoped out of the EIA.
Disturbance due to geophysical surveys	As above for the construction phase.
Decommissioning
Effects on marine mammals due to accidental release of pollutants	As above for the construction phase.
Effects on marine mammals due to increased SSC and associated deposition	As above for the construction phase.

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