1. Introduction

1. This Marine Mammal Technical Report presents a detailed baseline characterisation of the marine mammal ecology to inform the assessment of impact for the construction, operation and maintenance and decommissioning phases of the Array. The Ossian Array includes the offshore components of the offshore wind farm, e.g. wind turbines, Offshore Substation Platforms (OSPs) and inter-array/interconnector cabling and is hereafter referred to as the ‘Array’ (for more details about the Project Description see volume 1, chapter 3). Data were collated through a detailed desktop study of the existing resources available for marine mammals within the region, incorporating data from third party organisations as well as data from a 24-month programme of site-specific Digital Aerial Surveys (DAS) (March 2021 to February 2023). Additionally, Sea Mammal Research Unit (SMRU) provided telemetry maps and haul out counts for harbour seal Phoca vitulina and grey seal Halichoerus grypus which have also been used to inform baseline characterisation (Stevens, 2023).
2. The aim of this Technical Report is to provide a robust baseline characterisation of the marine mammals likely to be present within the marine mammal study areas (please see section 2), against which the potential impacts resulting from the development of the Array can be assessed.

2.             Study Area

2. Study Area

3. Marine mammals are highly mobile, wide-ranging species, with varying behaviour and ecology between species. To account for this and to provide wider geographic context, the marine mammal study area proposed for the purpose of baseline characterisation has been defined at two spatial scales ( Figure 2.1   Open ▸ ):

• Array marine mammal study area: an area encompassing the site boundary (within which the Array will be located) plus 8 km buffer ( Figure 3.1   Open ▸ ). The Array marine mammal study area corresponds with the aerial survey area, in which 24 months of DAS were conducted (see section 3.2.1 for more details).
• Regional marine mammal study area: an area encompassing the wider northern North Sea to account for the highly mobile nature of marine mammals. The boundaries of the northern North Sea are closely aligned with those of Marine Natural Areas (Wildlife Trusts, 2021). The regional marine mammal study area has informed the screening of internationally designated sites and has been used to identify projects included in the cumulative effects assessment.

4. The Array marine mammal study area and the regional marine mammal study area were presented in the Array Scoping Report (Ossian OWFL, 2023). Subsequently in the Ossian Array Scoping Opinion (MD-LOT, 2023), stakeholders recognised both study areas as appropriate to take forward to the Array EIA Report.
5. To assess population level impacts for a given species, species-specific Management Units (MUs) are presented in this Technical Report. The Special Committee on Seals (SCOS) and Inter-Agency Marine Mammal Working Group (IAMMWG) reports were used to define MUs for cetaceans and seals, respectively (SCOS, 2023, IAMMWG, 2022). Where the MU for a given species extends over a very large scale (e.g. the Celtic and Greater North Sea MU for minke whale Balaenoptera acutorostrata: Figure 5.12   Open ▸ ) the appropriate Small Cetaceans in European Atlantic waters and the North Sea survey (SCANS) IV block which overlaps with the Array marine mammal study area is provided for context.

Figure 2.1: Marine Mammal Study Areas

3.             Methodology

3. Methodology

3.1.        Desktop Study

3.1. Desktop Study

3.1.1.    Regional Data Sources

3.1.1. Regional Data Sources

6. Information on marine mammals within the regional marine mammal study area was collected through a detailed desktop review of existing studies and datasets, listed in Table 3.1   Open ▸ .

Table 3.1: Key Sources of Information for the Marine Mammal Baseline Characterisation

3.2.        Surveys

3.2. Surveys

3.2.1.    Site-Specific Surveys

3.2.1. Site-Specific Surveys

7. A summary of the site-specific surveys undertaken to inform the marine mammal assessment for the Array are outlined in Table 3.2   Open ▸ and presented in more detail in volume 3, appendix 10.2, annex A.
8. The DAS campaign for the Array commenced in March 2021 and continued monthly up to and including February 2023 to allow 24 months of data collection, including any additional surveys to account for delayed survey flights (see paragraph 22 for more details). The study area for the DAS campaign was delineated as the site boundary plus an 8 km buffer. The site boundary plus 8 km buffer is hereafter referred to as the ‘Array marine mammal study area’. The extent of the DAS area was presented in the Scoping Report (Ossian OWFL, 2023) and subsequently received approval from NatureScot in the Ossian Array Scoping Opinion (MD-LOT, 2023).
9. The surveys were conducted by HiDef Aerial Surveying Limited (hereafter ‘HiDef’). A total of 31 transects were spaced 2.5 km apart across the Array marine mammal study area, aligned in a broadly north-east to south-west orientation, perpendicular to the depth contours along the coast ( Figure 3.2   Open ▸ ). The total survey effort was approximately 5,439.85 km2, with a monthly mean of approximately 226.66 km2.

Table 3.2: Summary of Surveys Undertaken Across Array Marine Mammal Study Area

10. Marine mammal sightings from the DAS were analysed in line with the methodology consulted with the stakeholders via the Array Marine Mammal Methodology Note (volume 3, appendix 5.1, annex B) as well as Array Marine Mammal Consultation Note 1 (volume 3, appendix 5.1, annex D). The DAS results and data analysis methodology is presented in more detail in volume 3, appendix 10.2, annex A.

Figure 3.1: Digital Aerial Survey Transects Flown Over the Array Marine Mammal Study Area

3.2.2.    Historic Surveys of the Firth of Forth and Tay

3.2.2. Historic Surveys of the Firth of Forth and Tay

11. Historically, surveys have been carried out within the wider Firth of Forth and Tay area in inshore and offshore waters that do not overlap with the site boundary ( Figure 3.2   Open ▸ ). As some species are known to have distinct inshore and offshore populations (for example bottlenose dolphins, see paragraph 112), no conclusions on marine mammal distribution within the Array marine mammal study area can be made based on this historic survey data as the Array is located at considerable distance from the shore (80 km south-east of Aberdeen). However, given that marine mammals are wide ranging species, findings of historic surveys are considered in section 4.1.1 and presented for each species in section 5 to provide context for their abundance and distribution within the regional marine mammal study area.

                        TCE aerial surveys

12. A series of visual aerial surveys of offshore wind farm sites was commissioned between 2009
    and 2010 by TCE (hereinafter referred to as “TCE aerial surveys”). Surveys were carried out during 24 days between May and August 2009 (summer: nine survey days) and November 2009 and March 2010 (winter: 15 survey days) (Grellier and Lacey, 2011). The transect design of these visual aerial surveys of Scottish territorial waters was based on parallel flight tracks, equally spaced at approximately 5 km, in both inshore (up to 12 nm) and offshore (greater than 12 nm) areas (Grellier and Lacey, 2011, MacLeod and Sparling, 2011). Between five and 48 transects were flown in any one survey day and observed track length varied from 341 km to 1,116 km ( Figure 3.2   Open ▸ ).

                        Seagreen boat-based surveys

13. Visual boat-based surveys for marine mammals and seabirds were commissioned by Seagreen Wind Energy Limited and were carried out by ECON Energy between May 2010 and November 2011 (hereinafter referred to as “Seagreen boat-based surveys”). The surveys encompassed the Firth of Forth Round 3 Zone, which is approximately 2,850 km2 and approximately 25 km offshore of the Firth of Forth ( Figure 3.2   Open ▸ ). The monthly surveys followed transect lines distributed 3.7 km apart across four different routes (east, west, north and south), spaced at 300 m from each other (Sparling, 2012). Over the 19 surveys, a total of 17,017 km of survey effort was undertaken (Sparling, 2012).

                        Seagreen ornithology surveys

14. Incidental recordings of marine mammals were recorded during visual, boat-based ornithology surveys undertaken for what was previously known as the Seagreen Alpha/Bravo project area (and known since 2018 as ‘Seagreen’). Surveys were conducted in summer 2017 (May to August inclusive) with sea state ranging between one and four on the Douglas sea scale, resulting in excellent to average conditions for sighting marine mammals. A summary of the marine mammal incidental sightings was reported in the Seagreen Marine Mammal Baseline Technical Report (Seagreen Wind Energy Limited, 2018).

                        Berwick Bank aerial surveys

15. DAS of seabirds and marine mammals were commissioned by Berwick Bank Wind Farm Limited (hereinafter referred to as “Berwick Bank aerial surveys”). Surveys encompassed the Berwick Bank array area plus 16 km buffer ( Figure 3.2   Open ▸ ), covering a total area of 4,980 km2 through 37 transects spaced 2 km apart. Transects were surveyed to cover a total length of approximately 2,490 km each month, and data from two cameras (0.25 km combined width) were subsampled to provide a minimum target of 10.0% coverage of the total survey area. Surveys commenced in March 2019 and continued monthly up to and including April 2021 with an additional survey undertaken in both May 2020 and April 2021.

Figure 3.2: Surveys Conducted in the Wider Area of Firth of Forth and Tay

Table 3.3: Summary of Surveys Undertaken in the Wider Firth of Forth and Tay Area

3.3.        Assumptions and Limitations

3.3. Assumptions and Limitations

3.3.1.    Survey Timings

3.3.1. Survey Timings

16. Two historic surveys, namely TCE aerial surveys and Seagreen boat-based surveys, took place between 2009 and 2011 (section 3.2.2 provides further detail). These data are now more than ten years old, and it is possible that there may have been changes in the distribution and abundance of marine mammals in the wider Firth of Forth and Tay since these surveys were carried out. The most recent historic surveys for Berwick Bank (SSE Renewables, 2022) were conducted between March 2019 and April 2021 ( Table 3.3   Open ▸ ).
17. The site-specific DAS for the Array marine mammal study area have been conducted monthly between March 2021 and February 2023. Data collected represent a snapshot over a single survey day in each calendar month. This is a standard survey method applied for marine mammal data collection to inform the baseline for offshore wind developments. The differences in sighting rates between months may be due to seasonal changes and it may be possible to investigate seasonality of sightings based on aerial survey data. The environmental conditions also have the potential to influence these results and data collected over a short time frame (one day) does not allow this to be explored further.

3.3.2.    Marine Mammal Observers

3.3.2. Marine Mammal Observers

18. Boat-based surveys rely on marine mammal observers to record the number of marine mammals and accurately identify the individuals to species level. Ideally, a survey team, following a standard distance sampling approach, should consist of three people – one to monitor the track line, the second to monitor over distance and the third to write down sightings. The team is usually rotated to reduce the possibility of observer fatigue. The Seagreen boat-based survey adopted the use of only a single marine mammal observer which may have resulted in under-recording (Sparling, 2012).
19. There is less potential for under-recording during aerial surveys, e.g. DAS, as all observations within the transect strip length are recorded and can be investigated during the analysis of data.

3.3.3.    Weather Conditions

3.3.3. Weather Conditions

20. Boat-based surveys are often carried out to collect bird and marine mammal data simultaneously. However, seabird surveys can be carried out in Douglas sea states of up to four, whilst marine mammals are surveyed only in Douglas sea states of up to three. If bird surveys were carried out simultaneously, as in the case of the Seagreen boat-based surveys (Sparling, 2012), there is a risk that encounter rates may be biased downwards if portions of the survey were carried out in sea states above three. Harbour porpoise in particular are difficult to record; detection probability of harbour porpoises decreases by 50% between Beaufort sea state 0 and Beaufort sea state 3 and continues to decrease substantially as Douglas sea state values increases (Palka 1996).
21. Compared to boat-based surveys, sea state is less problematic for aerial surveys, e.g. DAS, as surveys can effectively be carried out in Douglas sea states of up to four for both marine mammals and birds (HiDef, pers. comm.).

3.3.4.    Delayed Surveys

3.3.4. Delayed Surveys

22. Logistical issues and/or downtime due to unsuitable weather conditions prevented DAS from being flown in two months: May 2021 and February 2022 during the Array marine mammal study area surveys. Potential data gaps were avoided by flying additional surveys as close in time as possible to those missed. Subsequently, the May 2021 survey was replaced by a supplementary flight on 09 June 2021, and the survey for February 2022 was conducted on 06 March 2022.

3.3.5.    Bias In Data

3.3.5. Bias In Data

23. Marine mammals spend most of their time underwater and therefore might be unavailable for detection at the surface and on the transect line. Undercounting as a result of this is known as ‘availability bias’ and is corrected for using an estimate of the probability that an animal is on the surface at any randomly chosen point in time. The resulting correction factor is used to estimate the total number of animals that may be present within the survey area. In the case of DAS, animals are available for detection if they are on the surface or just below the surface, as depth of detectability is dependent on water clarity. Data from historic surveys as well as DAS provide a count of the relative numbers of each species (or species group) within survey transects. However, sightings data from historic surveys as well as DAS do not allow for estimations of site-specific availability biases. Therefore, published correction factors, where considered to be appropriate, were applied to data to correct for availability bias to estimate absolute numbers. Correction factors applied to the site-specific DAS data in this Technical Report were consulted with stakeholders via the Array Marine Mammal Methodology Note (volume 3, appendix 5.1, annex B) and Array Marine Mammal Consultation Note 1 (volume 3, appendix 5.1, annex D) and are described in more detail in volume 3, appendix 10.2, annex A.
24. If a group of animals on the transect line is at the surface, they may not be detected due to various factors such as observation conditions or observer fatigue, known as ‘perception bias’. Given that some marine mammal species are known to actively avoid vessels, either by moving away or by diving, unquantifiable bias may be introduced into the data collected during boat-based surveys (Palka and Hammond, 2001). Perception bias is less of a limiting factor for aerial surveys since high-definition video or still imagery captures all animals on the surface and their detection is less influenced by the ability of an observer to detect an animal. For both boat-based and aerial surveys it can be challenging to record wide ranging or cryptic species, especially when making the snapshot count.

3.4.        Other Studies and Data Sources

3.4. Other Studies and Data Sources

3.4.1.    SCANS Surveys

3.4.1. SCANS Surveys

25. The first SCANS survey was conducted in summer 1994 to provide estimates of abundance and density of small cetaceans in the North Sea and European Atlantic continental shelf waters. The SCANS II surveys were completed in July 2005 and SCANS III in July 2016. All surveys comprised of a combination of vessel and aerial surveys. Both aerial and boat-based survey methodologies were designed to correct for availability and detection bias and to allow the estimation of absolute abundance. The original SCANS III data was published in Hammond et al. (2017), which has been revised following the discovery of some analytical errors and the updated version Hammond et al. (2021) is used for the purpose of this baseline characterisation. SCANS IV was carried out in summer 2022 and the results of surveys are presented in Gilles et al. (2023)
26. The Array is located in the SCANS II survey area V and SCANS III survey area R ( Figure 3.3   Open ▸ ), surveyed by boat and air, respectively. Due to the change in survey blocks used in the SCANS II and SCANS III surveys, direct comparison between the surveys for abundance and density estimation is not possible. Gilles et al. (2023) presented the North Sea divided in 13 blocks, NS-A to NS-M and the Array falls within the NS-D block. The boundaries and dimensions of SCANS III block R ( Figure 3.3   Open ▸ ) are closely aligned with SCANS IV block NS-D boundaries ( Figure 3.4   Open ▸ ) as the total surface areas differ by only 9 km2 (Hammond et al., 2021, Gilles et al., 2023).
27. The most recent data from SCANS III and SCANS IV has been referred to in section 5 indicating trends in species abundance across survey years where relevant (Hammond et al., 2021, Gilles et al., 2023).

                        SCANS III density surfaces

28. SCANS III data were used by Lacey et al. (2022) to provide information on summer distribution of recorded species by modelling the data in relation to spatially linked environmental features to generate density surface maps.
29. Lacey et al. (2022) presents density surface modelling for harbour porpoise, bottlenose dolphin, short-beaked common dolphin Delphinus delphis and minke whale. Density surface modelling used environmental covariates (which were selected as having the potential to explain additional variability in cetacean density) including depth, slope, aspect, distance from the coast, topography, sea level anomaly (i.e. the difference between recorded sea level and mean sea level) and sea surface temperature. Consecutive records made along the aerial survey transects were combined into 10 km segments of search effort to allow density estimates to be predicted to a spatial grid of 10 km x 10 km resolution.
30. Figures showing surfaces of predicted density and coefficient of variation (CV )of predicted density were produced for each species for SCANS-III, with patterns of predicted density influenced by model covariates, fitted smooth functions and spatial variation in the values of the covariates in the prediction grid (Lacey et al., 2022). To note, the density surfaces are for summer distributions only, as this is when SCANS-III was carried out. The figures allow density surfaces to be overlaid with the Array marine mammal study area for mean density outputs and are discussed in section 5 for relevant species.

Figure 3.3: SCANS III Survey Blocks

Figure 3.4: SCANS IV Survey Blocks

3.4.2.    Joint Cetacean Protocol (JCP) Phase III Analysis

3.4.2. Joint Cetacean Protocol (JCP) Phase III Analysis

31. The JCP Phase III analysis combined datasets from 38 sources, collected from boat-based and aerial platforms between 1994 and 2010. The total survey effort of over 1.05 million km was undertaken to estimate spatial and temporal patterns of abundance for seven species of cetaceans (paragraph 32) (Paxton et al., 2016). Developer areas were chosen based on best available information at this time of the areas of interest for renewable energy developments and referred to as “areas of commercial interest” (Paxton et al., 2016).
32. The following species were included in the analysis: harbour porpoise, minke whale, bottlenose dolphin, short-beaked common dolphin, Risso’s dolphin Grampus griseus, white-beaked dolphin and Atlantic white-sided dolphin Lagenorhynchus acutus. Density surface models were used to predict species density over a fine scale grid of 25 km2 resolution for one day in each season in each survey year. The data were divided into regions for which seasonal abundance in winter (January to March), spring (April to June), summer (July to September) and autumn (October to December) was estimated. The site boundary is situated just outside the “Firth of Forth area of commercial interest” ( Figure 3.5   Open ▸ ), however, this study is considered to provide context within the regional marine mammal study area.
33. It should be noted that, as stated by Paxton et al. (2016), the abundance estimates produced by the JCP Phase III modelling will be less reliable than those obtained from a well-designed dedicated abundance survey given the assumptions made when standardising the data and the spatial and temporal patchiness of the data available.

Figure 3.5: JCP Phase III Developers Areas

3.4.3.    JNCC Report 544: Harbour Porpoise Density

3.4.3. JNCC Report 544: Harbour Porpoise Density

34. Heinänen and Skov (2015) conducted a detailed analysis of the majority of the standardised JCP data resources to identify “discrete and persistent areas of high density” that might be considered important for harbour porpoise, with the goal of determining SACs for the species. Outputs of the analysis included distribution maps of density estimates for the waters around the UK, and the results are summarised in paragraphs 89, 90 and 98. The analysis grouped data into three subsets: 1994 to 1999, 2000 to 2005 and 2006 to 2011 to account for patchy survey effort. To explore whether distribution patterns differed between seasons, the study analysed summer (April to September) and winter (October to March) data separately. The analysis presented in Heinänen and Skov (2015) relied on extensive extrapolation of survey data over space and time. Any such extrapolation is sensitive to the covariates used in models and makes the assumption that these relationships hold true outside of the surveyed areas. Given the uneven survey effort over the modelled period, there was a large degree of uncertainty in modelled distributions.

3.4.4.    SCOS

3.4.4. SCOS

35. Natural Environment Research Council (NERC) provides scientific advice to government on matters related to the management of seal populations (under the Conservation of Seals Act 1970 and the Marine (Scotland) Act 2010). NERC has appointed SCOS to formulate this advice which is provided by SMRU through a series of scientific briefing papers and meetings and an annual report is produced. The annual report includes advice on matters related to the management of seal populations, including general information on British seals and information on their current status. Upfront sections of the report often address specific questions raised by regulators and stakeholders. The most recent publicly available SCOS report is SCOS (2023) which presents data collected and population estimates up to and including 2022.

3.4.5.    SMRU Seal Surveys

3.4.5. SMRU Seal Surveys

36. SMRU carries out surveys of harbour and grey seals in Scotland and on the east coast of England to contribute to the NERC’s statutory obligation under the Conservation of Seals Act 1970 through provision of scientific advice on matters related to the management of seal populations to the UK Government. SMRU surveys form the routine monitoring of seal populations around the UK. Most surveys are carried out in August from the air by either light aircraft or helicopter and record seals that are hauled out on shore. Although both species are surveyed during the month of August, on account of differences in the breeding behaviour of harbour and grey seals, these surveys correspond to different points in the two species’ annual cycles.
37. A SMRU report was commissioned to support the baseline assessment for the Array and associated Array marine mammal study area. The report provided a detailed account of grey and harbour seal haul outs and telemetry tracks within the vicinity of the Array as well as East Scotland and Northeast England seal MUs (Stevens, 2023) ( Figure 3.6   Open ▸ ).

                        Harbour seal

38. Surveys of harbour seals are carried out during the summer and early autumn months. There are two types of surveys conducted: breeding season counts and August moult counts. Given that there are no harbour seal breeding surveys conducted in the East Scotland or Northeast England seal MUs, these are not considered further in this report (Stevens, 2023). The main population surveys are carried out when harbour seals are moulting, during the first three weeks of August. The frequency of surveys differs by area (Stevens, 2023). In general, moult surveys are conducted annually in Lincolnshire and Norfolk (England), and in the Moray Firth and the Firth of Tay (Scotland). The remainder of the Scottish coast is surveyed approximately every four to five years, although there is considerable variation between areas. The most recent data available for the East Scotland and Northeast England seal MUs are from 2021 (Stevens, 2023).

                        Grey seal

39. In the UK, grey seals are surveyed during their breeding season (August to December), wherein pup counts are conducted at known breeding colonies. Most breeding colonies are surveyed by SMRU by fixed wing aerial vertical photography (Hebrides, Orkney, north Scotland the north-east Scotland and most of the Firth of Forth) while other colonies are surveyed by ground count by other organisations (including NatureScot, Natural England, Natural Resources Wales, National Trust, and Lincolnshire Wildlife Trust) (Stevens 2023). The grey seal pup production database contains data from 1996 to 2021 and includes 74 breeding colonies, 70 of which are in Scotland and one of which is in north-east England (though not all colonies have been surveyed consistently since 1989 and some smaller colonies are surveyed more sporadically than others). The most recent complete grey seal pup production survey (covering Orkney, Inner and Outer Hebrides and the North Sea colonies) was conducted in 2019. It should be noted that grey seal distribution during the breeding season is very different to their distribution at other times of the year.
40. Grey seals are also counted during SMRU’s harbour seal August moult surveys, however, counts of grey seals during the summer months can be highly variable and, although these counts are not used as a population index, they provide useful information on the summer and non-breeding season distribution of grey seals. The most recent data available for the East Scotland and Northeast England seal MUs are from 2021.

3.4.6.    Designated Seal Haul Out Sites

3.4.6. Designated Seal Haul Out Sites

41. Seal haul out sites are locations on land where seals come ashore to rest, moult or breed. In Scotland, seal haul out sites are designated under section 117 of the Marine (Scotland) Act 2010. The Protection of Seals (Designation of Haul-out Sites) (Scotland) Order 2014 laid in the Scottish Parliament on 26 June 2014 which, from 30 September 2014, makes it an offence to harass seals at these sites. Harassment involves any activity that “pesters, torments, troubles or attacks a seal on a designated haul-out site. In particular, it would include any action that causes a significant proportion of seals on a haul out site to leave that site either more than once or repeatedly or, in the worst cases, to abandon it permanently” (Marine Scotland, 2014).
42. The closest designated haul out site to the Array marine mammal study area, Kinghorn Rocks, is located approximately 157 km to the south-west ( Figure 3.6   Open ▸ ).

Figure 3.6: Seal MUs and Designated Sites

3.4.7.    Seal Telemetry Data

3.4.7. Seal Telemetry Data

43. SMRU has deployed telemetry tags on grey seals and harbour seals in the UK since 1988 and 2001, respectively. Tags are glued to the fur on the back of the seal’s neck and fall off with the fur during the annual moult, if not before. These tags transmit data on seal locations with the tag duration (number of days) varying between individual deployments. Data obtained during telemetry studies provide information on seal movement patterns away from their haul out sites, as well as data on the foraging behaviour of seals at sea, and demonstrate connectivity between areas.
44. Telemetry data presented in this report for harbour and grey seal (sections 5.3.1 and 5.3.2, respectively) draws on the SMRU commissioned study (Stevens, 2023), which presents an analysis of existing satellite data to describe the movements of harbour and grey seal within or in the vicinity of the Array marine mammal study area.

3.4.8.    Seal Usage Maps

3.4.8. Seal Usage Maps

45. Carter et al. (2022) presents the most up-to-date seal usage maps for UK waters. The study utilised a high-resolution GPS tracking dataset (114 grey and 239 harbour seals) and wide spatial coverage to model habitat preference and generate at-sea distribution estimates for the entire UK and Ireland populations of both species of seals. Additionally, the study provides SAC-specific estimates of at-sea distribution, demonstrating that hotspots of at-sea density cannot always be apportioned to the nearest SAC. The at-sea usage maps represent the number of grey and harbour seals estimated to be in the water in each 5 km x 5 km grid cell at any one time. Values in the Carter et al. (2022) report are presented as spatial predictions of relative density. Absolute densities were provided by the author (Carter, pers. comm.).

3.4.9.    Distribution Maps Of Cetacean and Seabird Populations In The North-East Atlantic

3.4.9. Distribution Maps Of Cetacean and Seabird Populations In The North-East Atlantic

46. Waggitt et al. (2020) collated and standardised data from 2.68 million km of cetacean and seabird surveys carried out in the north-east Atlantic between 1980 and 2018. The study consisted of three stages – collating survey data, linking differences among surveys with various parameters (platform type, transect design, observation method and weather) to calculate the variations in the surface area covered, and generating species distribution models. As a result, distribution maps were provided for 12 cetacean and 12 bird species at 10 km resolution and monthly frequency in the north-east Atlantic.

4.             Baseline Environment

4. Baseline Environment

4.1.        Marine Mammal Presence Within Study Areas

4.1. Marine Mammal Presence Within Study Areas

4.1.1.    Regional Marine Mammal Study Area

4.1.1. Regional Marine Mammal Study Area

47. The northern portion of the North Sea (delineated by Weir (2001) approximately between 57°N and 60°N) supports several species of cetaceans, with both numbers and species diversity decreasing towards the southern North Sea (Weir, 2001). There are 11 species of cetaceans and two species of pinnipeds that are regularly encountered within the regional marine mammal study area (Hammond et al., 2021, Weir, 2001, Hammond et al., 2013, NMPi, 2023). Weir (2001) suggested that due to the presence of pelagic species entering the waters of the northern North Sea in areas adjacent to the deep Atlantic and along the continental shelf edge, these areas attract a higher number of cetaceans (individuals and species) compared to the southern part of the northern North Sea. Given that the distribution of marine mammals is strongly influenced by the distribution of their prey, the distribution of marine mammals in the North Sea is variable. Nevertheless, some areas consistently support a higher number of species.
48. The east coast of Scotland and north-east of England support multiple haul out sites for grey seal and harbour seal (SCOS, 2023, Weir, 2001). Although densities of these species might be expected to be higher in the vicinity of haul outs at certain times of the year, Carter et al. (2022) reported that links between grey and harbour seal distribution at sea and use of land-based sites have not been researched in detail. One of the reasons for this is that grey seal exhibit partial migration and may move between regions for breeding and foraging, e.g. seals that breed in a given SAC do not necessarily forage nearby (Carter et al., 2022).
49. Within the waters of the east of Scotland, the more commonly recorded cetaceans include harbour porpoise, bottlenose dolphin, white-beaked dolphin and minke whale. Other species of cetacean have been recorded as occasional or rare visitors to this region ( Table 4.1   Open ▸ ).

Table 4.1: Summary of Cetacean Species Found in the Regional Marine Mammal Study Area. Sources: Weir (2001), Hammond et al. (2013), Hammond et al. (2021), NMPI (2023) and Citizen Projects (pers. comm.)

50. Data from historic surveys conducted within the Firth of Forth ( Table 3.3   Open ▸ ) demonstrated that several marine mammal species occur regularly in inshore and offshore waters. Harbour porpoise was the most frequently recorded cetacean during all historic surveys and was recorded in every month of the year. Species recorded during the historic surveys also included minke whale and white-beaked dolphin (both with seasonal occurrence during spring/summer months), grey seal (year-round) and harbour seal (with only a few sightings recorded to species level during the TCE and Berwick Bank aerial surveys).
51. Bottlenose dolphins were positively identified in historic TCE aerial surveys in inshore (within 12 nm) and offshore (beyond 12 nm) waters with only one encounter of one individual outside 12 nm (Grellier and Lacey, 2011). No bottlenose dolphins were encountered during Seagreen boat-based surveys between 2010 and 2011 (Sparling, 2012). The Berwick Bank aerial surveys also observed a relatively small number of bottlenose dolphin with two sightings and a total of seven individuals across two years of surveys. No bottlenose dolphin were observed during DAS.
52. Although there are no records of humpback whales in any of the historic surveys conducted in the Firth of Forth, data from citizen science projects[1],[2] suggest a recent increase in sightings of this species on the east coast of Scotland (section 5.2.2).

4.1.2.    Array Marine Mammal Study Area

4.1.2. Array Marine Mammal Study Area

53. Given that the extent of the Array marine mammal study area was covered by the DAS campaign, data from DAS is considered the most accurate to inform marine mammal presence and distribution in the vicinity of the Array.
54. During DAS, harbour porpoise was the most frequently recorded cetacean, followed by white-beaked dolphin. Minke whale were mostly encountered during the spring and summer months, but the number of animals encountered was small (12 individuals over 24-month survey period).
55. Only three individual sightings of short-beaked common dolphin were recorded, all during a single survey in July 2021. Studies predicted a significant northwards range expansion of short-beaked common dolphin within the next few decades (Lambert et al., 2011, van Weelden et al., 2021). There are accounts that show that this species has already expanded its range northward in UK waters (van Weelden et al., 2021, MacLeod et al., 2005), however, these studies are focussed on the south-west of Britain and north-west Scotland. Given the short-beaked common dolphin preference for tropical and warm temperate seas, it is still regarded as an occasional visitor on the east coast of Scotland and within the northern North Sea.
56. There were no records of bottlenose dolphins across the Array marine mammal study area over 24 months of DAS. Considering that the site boundary is located approximately 80 km south-east of Aberdeen, it lies outside of the main distributional range of the coastal east Scotland bottlenose dolphin population (refer to paragraph 121) and therefore lack of sightings offshore was anticipated.
57. Grey seal were the most recorded pinnipeds during monthly site-specific DAS, however only 18 sightings were recorded. There were only two records of harbour seal over 24 months of DAS. There is no evidence of hotspots or regular foraging areas for grey and harbour seal in the vicinity of the site boundary and therefore low numbers of both species within the Array marine mammal study area were to be expected.
58. More details about species accounts within the Array marine mammal study area is provided in section 4.2.

4.2.        DAS Results

4.2. DAS Results

59. This section provides an overview of the DAS campaign for the Array marine mammal study area. The DAS campaign commenced in March 2021 and survey flights were undertaken monthly, with a total of 24 months of data collected up until February 2023.

4.2.1.    Marine Mammal Counts

4.2.1. Marine Mammal Counts

60. A summary of marine mammal counts observed in each calendar month during the DAS campaign (i.e. number of marine mammals identified in DAS imagery, uncorrected for effort and availability bias) is presented in Table 4.2   Open ▸ Based on raw count data, harbour porpoise accounted for the highest number of sightings identified to species level across the Array marine mammal study area and was recorded in all but three survey months ( Table 4.2   Open ▸ ). White-beaked dolphin accounted for the second highest number of sightings and was recorded in seven months over the 24-month survey period, followed by grey seal with 18 individuals recorded over nine months. For both minke whale and harbour seal, the number and frequency of sightings, was very low ( Table 4.2   Open ▸ ). No bottlenose dolphin were observed during any of the surveys over 24 months.
61. There were also a number of cetacean sightings that could not be assigned to species level, although the numbers of these sightings were also low. Similarly, sightings classified as ‘seal species’ (due to the difficulty of identifying to species level from aerial survey data) occurred in 16 months.

Table 4.2: Monthly Raw Sightings Data (Number of Animals, Uncorrected for Effort) Across the Array Marine Mammal Study Area

1The May 2021 survey was replaced by a supplementary flight on 09 June 2021.

2 The survey for February 2022 was conducted on 06 March 2022.

4.2.2.    Density Estimates

4.2.2. Density Estimates

62. For those species where there were sightings in a sufficient number of surveys to allow for temporal trends in observations to be estimated (namely harbour porpoise, white-beaked dolphin, and grey seal), relative densities were calculated from the DAS count data ( Table 4.3   Open ▸ ). To provide estimates of relative density and associated variance, the data were analysed using a non-parametric bootstrap approach, with replacement (Buckland et al., 2001). Bootstrapping allows more robust estimates (e.g. mean or confidence limits (CL)) to be made from a data set when sample sizes are smaller than the optimum. This is achieved by repeatedly analysing random subsets of the data, and when bootstrapping is undertaken ‘with replacement’ this simply means that each data point may be included more than once when subsets of the data are generated. Non-parametric bootstrapping makes no assumptions about the data, in contrast to parametric bootstrapping which assumes that data follow a specific distribution. Density estimates with bootstrapping were undertaken for harbour porpoise, white-beaked dolphin, and grey seal on a monthly and seasonal basis. Other species observed in the DAS campaign did not occur in sufficient numbers to allow monthly or seasonal density estimates to be produced.
63. Research into temporal patterns of harbour porpoise density has identified two broad divisions in distribution, termed by Heinänen and Skov (2015) as ‘Summer’ (April to September) and ‘Winter’ (October to March). Similarly for grey seal, broad-scale seasonal patterns of density have been determined based upon potential changes in distribution between the breeding season (defined as September to December for this region (Marine Scotland, 2020; SCOS, 2020) and the non-breeding season (January to August). Pooling data into two bio-seasons allows the robustness of analyses to be improved where sample sizes in seasonal or monthly divisions may be small, while retaining greater resolution than pooling data by year or across the whole DAS campaign. As well as monthly and seasonal estimates, spatial density estimates for harbour porpoise and grey seal were also produced on a bio-seasonal basis.
64. It was not possible to produce model-based density estimates for other marine mammal species within the Array marine mammal study area due to low numbers of sightings. Model-based analysis was undertaken using the MRSea package (Scott-Hayward et al., 2013) in R statistical software (R Core Team, 2023) with environmental covariates used to predict species distributions.
65. Estimates of relative density and abundance were subsequently corrected for availability bias to provide an approximation of absolute density and abundance. Correction factors were derived from studies on dive behaviour of marine mammals and their availability at the surface (further detail of correction factors is provided in section 3.5 of volume 3, appendix 10.2, annex A).

Table 4.3: Estimated Densities Based on the DAS Data (March 2021 to February 2023). For Harbour Porpoise, Model-based Estimates are Shown in Parentheses

1 Bio-seasons for harbour porpoise are defined as winter (October to March) and summer (April to September).

2 Meteorological seasons were applied in modelling for white-beaked dolphin as winter (December to February) and summer (June to August).

3 Bio-seasons for grey seal are defined as breeding (August to December) and non-breeding (January to July).

4.3.        Legislation and Conservation Designations

4.3. Legislation and Conservation Designations

4.3.1.    Legal Framework

4.3.1. Legal Framework

66. The Conservation (Natural Habitats, &c.) Regulations 1994 (as amended)[3] make it an offence to disturb a cetacean intentionally or recklessly in Scottish inshore waters (within 12 nm of the coast). Improved protection for seals is provided in the Marine (Scotland) Act 2010. In the UK, all species of cetaceans (porpoises, dolphins, and whales) out to 12 nm are protected under the Wildlife and Countryside Act (1981).
67. Several marine mammal species present in the UK waters are listed in Annex II of the Habitats Directive (Council Directive 92/43/EEC on the conservation of natural habitats and of wild fauna and flora) as species whose conservation requires the designation of SACs. In Scotland, the Habitats Directive is translated into legal obligations by the Conservation (Natural Habitats, etc.) Regulations 1994 (as amended), the Conservation of Habitats and Species Regulations 2017, the Conservation of Offshore Marine Habitats and Species Regulations 2017, the Offshore Petroleum Activities (Conservation of Habitats) Regulations 2001 and the Wildlife and Countryside Act 1981 (Government, 2015). Annex II marine mammal species for which SACs are designated within Scottish waters include harbour porpoise, grey seal, harbour seal and bottlenose dolphin. Under Annex IV of the Habitats Directive, all cetacean species are afforded strict protection wherever they occur within a Member State’s territory, both inside and outside designated protected areas. Here, they are termed European Protected Species (EPS).
68. The Marine (Scotland) Act 2010 and The UK Marine and Coastal Access Act 2009 include provisions to designate Marine Protected Areas (MPAs) (within territorial and offshore waters, respectively). MPAs are areas of the sea with special controls to protect species and habitats, and to support the wider marine ecosystem. A total of 36 Nature Conservation MPAs (ncMPAs) have been designated in Scotland’s seas (NatureScot, 2023).

4.3.2.    Conservation Designations

4.3.2. Conservation Designations

69. There are several designated areas within the regional marine mammal study area that have marine mammals as notified interest features. The entire regional marine mammal study area has been screened to identify the European sites that require further consideration due to a likely connectivity with the Array ( Table 4.4   Open ▸ ; Figure 4.1   Open ▸ ). In addition to the SACs considered in Table 4.4   Open ▸ , the Southern Trench ncMPA has been included due to the proximity to the Array and its importance for minke whale.

Table 4.4: Relevant National and European Designated Sites for the Protection of Marine Mammals

70. Potential connectivity of the designated sites listed in Table 4.4   Open ▸ with the Array is provided on a species-specific basis in section 5.

Figure 4.1: Designated Sites for the Protection of Marine Mammals

                        Southern Trench ncMPA

71. The Southern Trench ncMPA lies approximately 66.9 km north-west of the Array marine mammal study area ( Figure 4.1   Open ▸ ), covers an area of approximately 2,536 km2 and was designated by Marine Scotland as a Nature Conservation MPA in 2020 (NatureScot, 2020). It is protected for containing persistently above average densities of minke whale, where both juvenile and adult whales are regularly observed feeding (NatureScot, 2020). Adjusted densities showed high densities of minke whale north of the coastline from Buckie to Fraserburgh in particular. Recent evidence has suggested some spatial separation or habitat partitioning by age-class, with juveniles showing a preference for the shallower, inshore waters with sandy gravel sediments, whilst adults showing preference for deeper, offshore waters with greater bathymetric slope (Robinson et al., 2023). This ncMPA lies within the Celtic and Greater North Seas (CGNS) MU for minke whale (IAMMWG, 2022).

                        Firth of Tay and Eden Estuary SAC

72. The Firth of Tay and Eden Estuary SAC lies approximately 113.7 km west of the Array marine mammal study area ( Figure 4.1   Open ▸ ), covers an area of approximately 155 km2 and comprises of two high quality estuarine areas, which are integral components of a large, geomorphologically complex area (JNCC, 2023a). The SAC supports a breeding colony of harbour seal. Adult harbour seals use sandbanks within this SAC as a haul out habitat to rest, pup and moult (JNCC, 2023a).
73. Between 1990 and 2002, the majority of the East Scotland seal MU harbour seal population was located in the Firth of Tay and Eden Estuary SAC. During this period, harbour seal counts in this SAC remained stable, representing approximately 85% of the East Scotland seal MU count (Stevens, 2023). The population within the SAC then declined rapidly from 2002 to 2021 to a count of 41 individuals, representing an approximate 95% decline in the population. As such, the SAC now accounts for approximately 16% of the haul out counts in the East Scotland seal MU. There is, however, recent evidence that this decline may be slowing (Stevens, 2023).

                        Berwickshire and North Northumberland Coast SAC 

74. The Berwickshire and North Northumberland Coast SAC ( Figure 4.1   Open ▸ ) extends over an area of 652 km2 and lies approximately 114 km from the Array marine mammal study area (JNCC, 2023b). The SAC features an extensive and diverse stretch of coastline in south-east Scotland and north-east England and hosts a range of Annex I habitats, including mudflats and sandflats not covered by seawater at low tide, large shallow inlets and bays, reefs as well as submerged and partially submerged sea caves (JNCC, 2023b).
75. This SAC is located within the East Scotland and Northeast England seal MUs and contains two large, discrete Annex II grey seal breeding populations at the Farne Islands and Fast Castle. The Farne Islands have been an important breeding site since the Middle Ages (SCOS, 2023), while Fast Castle is a recently established breeding site first colonised in the 1990s. The grey seal pup production at the Farne Islands and Fast Castle has shown a recent, rapid increase (Stevens, 2023). From 2014 to 2019, the mean estimated increase in grey seal pup production at Farne Islands was 53% (SCOS, 2022).

                        Southern North Sea SAC

76. The Southern North Sea SAC lies along the east coast of England ( Figure 4.1   Open ▸ ), predominantly in the offshore waters (88% of the site) of the central and southern North Sea. The SAC covers an area of 36,951 km2 and is located 130.7 km to the south-east of the Array marine mammal study area. It was designated for harbour porpoise (JNCC, 2023cc) and supports an estimated 17.5% of the UK North Sea MU population. The northern section of the SAC (approximately two-thirds of its total area) supports higher densities of porpoises during the summer season (April to September), whilst the southern section is recognised as an important area during the winter season (October to March) (JNCC, 2023cc).

                        Isle of May SAC 

77. The Isle of May SAC extends over an area of 3.5 km2 (JNCC, 2023d). The SAC is located approximately 130.9 km from the Array marine mammal study area ( Figure 4.1   Open ▸ ) and supports a breeding colony of grey seals (JNCC, 2023dd). It is located within the East Scotland SMU.
78. Grey seal pup production at the Isle of May SAC increased at a rate of 9.9% per year since surveys began (1979), before reaching an peak of approximately 2,000 pups in the late 1990s (SCOS, 2022). Although prior to the 1990s the Isle of May SAC was the dominant location for grey seal pup production within the East Scotland MU, pup production is now considered to be stable or potentially declining (Stevens, 2023).

                        Moray Firth SAC

79. The Moray Firth in north-east Scotland supports the only known resident population of bottlenose dolphin in the North Sea. The Moray Firth SAC is located approximately 176.5 km to the north of the Array marine mammal study area ( Figure 4.1   Open ▸ ) and covers an area of 1,512 km2 (JNCC, 2023ee). Bottlenose dolphins associated with the Moray Firth SAC are part of a Scottish east coast population of 224 animals that range south past Aberdeen to the Firths of Tay and Forth (Quick et al., 2014, Arso Civil et al., 2019). Data from site condition monitoring for the SAC suggest that the proportion of the east coast of Scotland bottlenose dolphin population that use the SAC has declined, although the overall population along the east coast is increasing (Cheney et al., 2018, Arso Civil et al., 2019, Arso Civil et al., 2021). The resident population of bottlenose dolphin from the Moray Firth SAC is now known to venture down the coast of east Scotland and England as far south as Scarborough, where there have been regular sightings in recent years (Hackett, 2022).

5.             Species Accounts

5. Species Accounts

80. The following section provides detailed baseline information for each of the key species identified as common within the Array and regional marine mammal study areas (see section 4.1). These are:

• harbour porpoise;
• bottlenose dolphin;
• white-beaked dolphin;
• minke whale;
• harbour seal; and
• grey seal.

81. Additionally, given increased frequency of sightings of humpback whale in the Firth of Forth, this species will also be accounted for in this section. However, it should be noted that there are no species-specific studies of these species in Scottish waters and therefore available desktop data is sparse.
82. Species-specific densities presented in this section were consulted on with stakeholders via the Array Marine Mammal Methodology Note (volume 3, appendix 5.1, annex B) and Array Marine Mammal Consultation Note 1 (volume 3, appendix 5.1, annex D).

5.1.        Odontocetes

5.1. Odontocetes

5.1.1.    Harbour Porpoise

5.1.1. Harbour Porpoise

                        Ecology

83. The harbour porpoise is a small odontocete (toothed whales) inhabiting coastal temperate and boreal waters of the northern hemisphere. It reaches a maximum length of 1.9 m (Bjørge and Tolley, 2009), with females growing to an average length of 1.6 m whilst males reach 1.45 m in length (Lockyer, 1995). Although the recorded longevity is 24 years, most individuals do not live past 12 years of age (Lockyer, 2013).
84. Harbour porpoise have a large extensible stomach (up to six times the relaxed size). They are capable of ingesting up to 90% of their daily energetic requirements in one hour and can feed again shortly afterwards (Kastelein et al., 2019a, Booth et al., 2023). Harbour porpoise feed on a wide range of fish species, but mainly small shoaling species from demersal or pelagic habitats (Santos and Pierce, 2003a). There are regional and seasonal differences in diet, interannual variation depending on the availability of prey species as well as variation according to individual age, with juveniles targeting smaller species such as gobies Gobiidae or smaller individuals of the same prey species targeted by adults (Santos and Pierce, 2003a). A harbour porpoise’s metabolic rate remains stable over seasonally changing water temperatures. Heat loss is deemed to be managed via cyclical fluctuations in energy intake to build up a blubber layer that offsets the extra cost of thermoregulation during winter (Rojano-Doñate et al., 2018).
85. Ransijn et al. (2019) produced energy maps for various harbour porpoise prey species and found that the energy available in the North Sea is highest in the summer and the main energic contributions were from sandeels Ammodytidae and whiting Merlangius merlangus. During the winter season European sprat Sprattus sprattus and Atlantic herring Clupea harengus also contributed to overall energy density (Ransijn et al., 2019). This study corroborated previous findings that predominant prey item of harbour porpoise during the summer off the east coast of Scotland is sandeel (Santos, 1998, Santos and Pierce, 2003b). Although harbour porpoise generally hunt alone or in small groups, this species can be seen in larger aggregations of 50 or more individuals, either during seasonal migrations or associated with increased concentrations of prey. Within these aggregations, segregation may occur, with females travelling with their calves and yearlings, and immature animals of each sex segregating into groups. The largest group of harbour porpoises recorded during DAS of the Array marine mammal study area consisted of 144 individuals (refer to volume 3, appendix 10.2, annex A).
86. The geographic range of harbour porpoise coincides with cool, high latitude waters. Because harbour porpoise have a greater body surface area to volume ratio than other, larger cetacean species, this causes them to potentially lose energy through radiation and conduction to the surrounding water (Kastelein et al., 2018, Kastelein et al., 2019b, Lambert, 2020). To maintain their body temperature and other energy needs, they need to feed frequently and consume enough prey per unit body weight (Rojano-Doñate et al., 2018). For this reason, porpoise may be susceptible to changes in the abundance of prey species or disturbance from foraging areas. Given that harbour porpoise are predated on by other odontocetes (killer whale) and pinnipeds (grey seal), they often flee when encountering predators (Kastelein et al., 2019a). As such, it can be anticipated that harbour porpoise have adaptive mechanisms over certain time scales and the time when harbour porpoise are not feeding may extend to up to 9 to 12 hours (Kastelein et al., 2019a). Recent studies in Iceland suggest that despite ecosystem changes in the study region, harbour porpoise show no long-term changes in trophic ecology, indicating that this species may be able to adapt to spatial changes in prey distribution or shift to other prey at similar trophic levels (Samarra et al., 2022).
87. The age of sexual maturation for the harbour porpoise is approximately three to four years and reproduction is strongly seasonal, with mating occurring between June and August (Lockyer, 1995). Gestation is ten to 11 months and there is a peak in birth rate around the British Isles during the months of June and July (Boyd et al., 1999).
88. Bycatch in fisheries is the predominant threat to harbour porpoise in the North Sea (Lusseau et al., 2023). Harbour porpoise are particularly vulnerable to being caught in bottom-set gill nets, due to their feeding behaviour. Other threats include prey depletion, pollution affecting the health of individuals, and acoustic and physical disturbance (Evans and Prior, 2012).

                        Distribution and occurrence

89. The harbour porpoise is widespread throughout the cold and temperate seas of Europe, including the North Sea, the Skagerrak, Kattegat, Irish Sea, the seas west of Ireland and Scotland, northwards to Orkney and Shetland and off the coasts of Norway (JNCC, 2023f). Heinänen and Skov (2015) found that in the North Sea MU the water depths and hydrodynamic variables are the most important factors predicting the presence of harbour porpoise. During summer, animals were predicted to avoid well-mixed areas showing preference for more stable areas. Studies indicated lower presence of harbour porpoise with lower salinity, reflecting an avoidance of estuarine water masses Heinänen and Skov (2015).
90. The Heinänen and Skov (2015) analysis concluded that in the summer months, harbour porpoise presence in the North Sea MU was best predicted by season, water depth and salinity of surface waters. In the winter months the presence of harbour porpoise was best predicted by the season, water depth and seabed surface sediments. In winter months a peak in presence was observed at water depths of 30 m to 40 m. Williamson et al. (2016) found that the proportion of hours with acoustic detection of harbour porpoise in muddy habitats within the Moray Firth increased during hours of darkness by 18%. Harbour porpoise detections also differed in response to depth in different sediment types between hours of darkness and daylight. In muddy areas with a water depth of between 50 m to 60 m, detections at night were almost double those during daylight hours. Therefore, it can be concluded that harbour porpoise use different types of habitats during hours of daylight and darkness and their distribution may change accordingly.
91. Harbour porpoise was the most commonly identified cetacean during TCE aerial surveys (Grellier and Lacey, 2011), Berwick Bank aerial surveys (SSE Renewables, 2022b) and Seagreen boat-based surveys (Sparling, 2012). During the TCE aerial surveys, a greater number of sightings were recorded offshore, with most individuals observed alone, although group size ranged from 0 to six individuals. The Berwick Bank aerial survey and Seagreen boat-based survey results showed that sightings occurred throughout the respective survey areas ( Figure 3.2   Open ▸ ). Harbour porpoise was also the most frequently recorded species of cetacean during Neart na Gaoithe boat-based surveys undertaken each month between November 2009 and October 2012 (Mainstream Renewable Power, 2019).
92. Harbour porpoise accounted for the highest number of sightings across all species in the DAS of the Array marine mammal study area, with a total of 839 animals recorded across 21 months. No clear spatial patterns were observed in the distribution of harbour porpoise sightings.
93. Based on the Seagreen boat-based survey data (Seagreen Wind Energy Limited, 2018), it seems that the morphological bank features such as Scalp Bank are particularly important for harbour porpoise. These areas may represent good foraging grounds due to the sandy banks providing good habitat for prey species such as sandeel and whiting, both of which have been recorded as important constituents of the diet of harbour porpoises on the east coast of Scotland, with the relative proportion of each of these in the diet changing seasonally (Santos and Pierce, 2003b).

                        Density/abundance

                        Published literature

94. Density and abundance estimates of harbour porpoise are available from various studies carried out across a broader area within the regional marine mammal study area. IAMMWG (2022) estimated abundance for the North Sea MU ( Figure 5.1   Open ▸ ) as 346,601 animals (CV = 0.09, 95% confidence interval (CI) = 289,498 to 419,967). The SCANS III data (Hammond et al., 2021) estimated the abundance of harbour porpoise within block R ( Figure 3.3   Open ▸ ) as 38,646 animals (CV = 0.29, 95% CI = 20,584 to 66,524). The abundance of harbour porpoise within SCANS IV block NS-D is comparable to this reported for SCANS III block R with a population of 38,577 individuals indicating no changes in harbour porpoise abundance (Gilles et al., 2023).
95. Hammond et al. (2021) reported densities for harbour porpoise across block R as 0.599 animals per km2. Recently modelled density surfaces using the SCANS III data (paragraph 29) (Lacey et al., 2022) gave a mean density of 0.763 animals per km2 and a maximum of 0.835 animals per km2 for the Array marine mammal study area ( Figure 5.2   Open ▸ ), with areas of higher density to the south-east of the Array marine mammal study area. The harbour porpoise density estimates for SCANS IV block NS-D are analogous to these reported for SCANS III block R at 0.5985 harbour porpoises per km2 (Gilles et al., 2023).

Figure 5.1: North Sea Management Unit

Figure 5.2: Harbour Porpoise Density Surface Derived From SCANS III Data (from Lacey et al. (2022))

96. Monthly predicted distribution maps of harbour porpoise from Waggitt et al. (2020) suggest that harbour porpoise densities are higher throughout autumn and summer months ( Figure 5.3   Open ▸ to Figure 5.5   Open ▸ ). Highest densities within the Array marine mammal study area were predicted in August with a mean of 0.604 animals per km2 ( Figure 5.4   Open ▸ ). The density of harbour porpoises increases towards the southern North Sea, south-east of the site boundary.
97. To provide additional context, JCP Phase III analyses estimated abundance for harbour porpoise in 2010 by season for the Firth of Forth area of commercial interest region (Paxton et al., 2016) ( Figure 3.5   Open ▸ ). Highest abundance of harbour porpoise was estimated for the winter months (January to March), with 7,000 (97.5% CI = 5,200 to 11,800) animals estimated. Abundance estimates for spring (April to June) and summer (July to September) were 3,500 (97.5% CI = 1,900 to 6,600) and 4,400 (97.5% CI = 2,900 to 6,800) animals respectively. The lowest abundance was estimated in autumn (October to December) with 2,500 (97.5% CI = 1,600 to 3,600) animals (Paxton et al., 2016). These equated to density estimates of 0.492 animals per km2 in the winter, 0.246 animals per km2 in the spring, 0.309 animals per km2 in the summer and 0.176 animals per km2 in the autumn (Paxton et al., 2016). These densities are lower than the ones reported by Waggitt et al. (2020), Hammond et al. (2021) and Lacey et al. (2022).
98. The Heinänen and Skov (2015) analysis concluded that the density estimates within the outer Firth of Forth and Firth of Tay region were predicted to be relatively low compared to other parts of the North Sea. The areas of persistent high densities are predicted in the outer Moray Firth. Paxton et al. (2016) corroborated this finding by reporting that the Firth of Forth and the east coast of Scotland was not associated with the highest density for this species, compared to other regions such as the west coast of Ireland or the Hebrides, and that higher abundance was correlated with the Moray Firth. The study reported the predicted abundance in the Firth of Forth as 1.4% (95% CI = 0.6 to 2.3) of the overall predicted number for the North Sea MU (based on estimates for summers 2007 to 2010).

Figure 5.3: Harbour Porpoise Density from January to April Based on Waggitt et al. (2020)

Figure 5.4: Harbour Porpoise Density from May to August Based on Waggitt et al. (2020)

Figure 5.5: Harbour Porpoise Density from September to December Based on Waggitt et al. (2020)

                        Surveys

99. Relative density estimates of harbour porpoise from DAS were corrected for availability bias using the most conservative conversion factor of 42.5% based on Teilmann et al. (2013) (refer to volume 3, appendix 10.2, annex A for more detail). The most robust method was developed by combining the data by bio-season specific to harbour porpoise (“winter” (October to March) and “summer” (April to September) seasons), as the most biologically relevant approach Heinänen and Skov (2015). Design-based approaches gave absolute densities of 0.062 and 0.651 animals per km2 for winter and summer respectively. The mean absolute density estimate across all transects and all monthly surveys for the 24-month survey period, with bootstrapping, was estimated as 0.357 animals per km2 (95% CLs = 0.200, 0.510; CV = 1.367). Mean absolute density from the model-based approach was 0.064 for winter (95% CL = 0.030 to 0.121, CV = 0.54) and 0.648 for summer (95% CL = 0.102 to 0.916, CV = 0.0.422).
100. Spatial modelling using linear models showed harbour porpoise density hotspots during winter in north-west and south-west of the Array marine mammal study area and during summer in the south-east of the Array marine mammal study area ( Figure 5.6   Open ▸ ). This is in line with findings presented by Waggitt et al. (2020) and Lacey et al. (2022) which show that the density of harbour porpoises increases towards the southern North Sea. This may be correlated with information provided previously for the Southern North Sea SAC in paragraph 76 as the northern part of this SAC, located south-east from the site boundary supports higher densities of porpoises during the summer season (April to September) (JNCC, 2023c).
101. Grellier and Lacey (2011) reported the mean density of harbour porpoise during the TCE aerial surveys ( Figure 3.2   Open ▸ ) as 0.080 (CV=0.11) individuals per km2. Summer density estimates were higher compared to winter estimates with 0.099 (CV=0.12) and 0.048 (CV=0.24) individuals per km2, respectively. The analysis indicated that depth was a significant predictor of occurrence, with fewer animals in shallow water. After correcting for availability, Mackenzie et al. (2012) estimated absolute abundance for the survey area (TCE aerial surveys and Seagreen boat-based surveys, Figure 3.2   Open ▸ ) across the survey period as 582 (95% CI = 581 to 1235; using a correction factor of 0.434). Relative mean monthly density using Berwick Bank aerial survey ( Figure 3.2   Open ▸ ) data was estimated as 0.127 (95% CI = 0.066 to 0.277) animals per km2 with a peak mean density during spring months of 0.826 (95% CI = 0.440 to 1.616) animals per km2 (SSE Renewables, 2022c).

Figure 5.6: Predicted Mean Relative Density of Harbour Porpoise for the ‘Winter’ (Top) and ‘Summer’ (Bottom) Bio-Seasons

                        Summary of the densities

102. Harbour porpoise are the most abundant marine mammal species within the North Sea with areas of higher density located in the southern North Sea. Comparison of key data sources for harbour porpoise is shown in Table 5.1   Open ▸ .
103. As presented in paragraph 99, Heinänen and Skov (2015) reported that pooling data according to temporal patterns of harbour porpoise distribution is the most biologically relevant approach to studying harbour porpoise abundance/densities. As such, the most precautionary estimates of harbour porpoise density from DAS presented in Table 5.1   Open ▸ are based on the “summer” bio-season (April to September).
104. Predicted estimates of mean density for the Array marine mammal study area from Waggitt et al. (2020) are comparable to the SCANS III block R and SCANS IV block NS-D estimates ( Table 5.1   Open ▸ ), but provide densities at a higher resolution (10 km x 10 km) and monthly frequency, rather than a single estimate over a wide area (as is the case with SCANS surveys which use large blocks). It should be noted that SCANS densities do not take into account variability in cetacean density associated with environmental covariates (such as depth, slope, distance from the coast). Additionally, both Gilles et al. (2023) and Hammond et al. (2021) highlight that the very short timeframe over which the SCANS surveys are conducted (summer) means that there is limited understanding of species distribution and abundance in other seasons.
105. Densities from Lacey et al. (2022) are derived from the same resolution as Waggitt et al. (2020) (10 km x 10 km) and are comparable to the design and model-based densities from DAS ( Table 5.1   Open ▸ ). It should be noted that Lacey et al. (2022) used SCANS III data alongside the environmental covariates such as depth and slope in the density surface modelling. As reported by Heinänen and Skov (2015) (see paragraph 90), the depth, amongst other parameters is an important predictor for harbour porpoise distribution. As such, studies that consider environmental factors are perhaps more robust when predicting harbour porpoise density.
106. When compared to studies analysing data from large scale surveys, such as SCANS, the results of the analysis of the site-specific DAS data are considered to be the most robust as these are based on the most recent data, collected regularly (monthly) over two years and over a specific area of interest (Array marine mammal study area). As such, it is considered that density estimates based on DAS data are the most appropriate to inform impact assessments and the absolute density of 0.651 animals per km2 will be taken forward to the assessment.

Table 5.1: Comparison of Density Estimates for Harbour Porpoise (DAS Design-Based Density Will Be Taken Forward to the Assessment)

                        Seasonality

107. Across datasets, harbour porpoise counts were consistently higher during the summer months. During the TCE aerial surveys ( Figure 3.2   Open ▸ ) harbour porpoises were recorded nearly three times as often in summer (2.01 sightings per 100 km) compared to winter (0.70 sightings per 100 km) (Grellier and Lacey, 2011). The same pattern of higher encounter rates during summer months was also recorded during the Seagreen boat-based surveys (Sparling, 2012). The Seagreen boat-based surveys in summer 2017 recorded the highest counts of harbour porpoise between May and July (Seagreen Wind Energy Limited, 2018).
108. Similarly, analysis of Berwick Bank aerial survey data suggest highest encounter rates during spring each year (April and May) and lowest during winter and autumn (from November 2019 to March 2020 and from October 2020 to February 2021) (SSE Renewables, 2022a).
109. The monthly encounter rate for harbour porpoise from Array marine mammal study area DAS data varied across months with the encounter rate for summer (specifically July 2021, April 2022, June 2022, and July 2022) estimated to be considerably higher compared to other seasons of the year ( Table 4.2   Open ▸ ).

5.1.2.    Bottlenose Dolphin

5.1.2. Bottlenose Dolphin

                        Ecology

110. Bottlenose dolphin are members of the family Delphinidae, which are odontocete cetaceans found in temperate and tropical waters worldwide. This species is the largest of the beaked dolphins and ranges in size from 1.9 m to 3.8 m. Bottlenose dolphin can live, on average, between 20 to 30 years. On average, males reach sexual maturity at ten to 12 years and females at five to ten years. Mating occurs during the summer months, with gestation taking 12 months and calves suckling for 18 to 24 months. Females generally reproduce every three to six years (Mitcheson, 2008)
111. The distribution of this species is influenced by factors such as tidal state, weather conditions, resource availability, life cycle stage, or season (Hastie et al., 2004) and there is variation in the patterns of habitat use, even within a population. Typical prey items in Scottish waters include cod Gadus morhua, saithe Pollachius virens, whiting, salmon Salmo salar and haddock Melanogrammus aeglefinus (Santos et al., 2001).
112. Bottlenose dolphin are more frequently seen in groups rather than individually, although group size in coastal populations may be smaller than offshore populations. It should be noted that very little is known about offshore populations (Rogan et al., 2018) and this assessment will focus on coastal bottlenose dolphin population. Mean group size across the SCANS III survey areas was 5.25 individuals (Hammond et al., 2021). Robinson et al. (2017) reported that in the outer Moray Firth observed group sizes varied between two and 70 animals.

                        Distribution and occurrence

113. Based on the data collected in 1980s and early 1990s, the Moray Firth SAC boundary is thought to encompass the core area of occurrence of the resident, coastal population of bottlenose dolphins in the North Sea.
114. Acoustic occupancy rates and habitat modelling in the East Coast Marine Mammal Acoustic Study (ECOMMAS) highlighted that the waters between Stonehaven and Aberdeen are also a potential area of high occupancy (Palmer et al., 2019). It is worth noting that the ECOMMAS study did not deploy any hydrophone stations on the north-east English coast. Quick et al. (2014) established that a high proportion of bottlenose dolphins from the Coastal East Scotland population use both the Tayside and Fife area as well as the Moray Firth SAC, over a range of temporal scales. These findings were corroborated by Arso Civil et al. (2019) who reported that that more than half of the estimated CES population was consistently using the St Andrews Bay and the Tay estuary. The data collected during boat-based trips between Moray Firth and Fife Ness (during summers 2017 to 2019) show that the Tay estuary area and adjacent waters continue to be used by more than half of the total estimated population every summer (Arso Civil et al., 2021). The same study suggested that it is likely that changes in the distribution range are continuing with a further southern range expansion. Ongoing citizen science projects suggest that some members of this population are relocating from Scottish waters into waters off the coast of eastern England (as far as south of Scarborough, Figure 5.7   Open ▸ ) (Hackett, 2022).
115. North East Cetacean Project (NECP) is a community engaging people involved in marine mammal watching. Citizens can share their whale, dolphin, porpoise and other interesting marine wildlife sightings anywhere from the Humber to the Scottish Border (NECP, 2021). Another project which combines research and citizen science photo-identification data, specifically of bottlenose dolphins, is called Citizen Fins (Citizen Fins, 2023). This collaboration allows for photo identification work to match photos taken by citizens in England with the East Coast Scotland Bottlenose Dolphin Photo-ID Catalogue. Many individuals from the East Coast Scotland population were positively identified from the Northumberland coast at numerous locations, including Cresswell, Beacon Point, King Edward's Bay (Tynemouth), Whitburn Beach and Roker Beach (Citizen Fins, 2023). As such, the results of photo-identification analysis suggest that animals found off the north-east coast of England are not a separate, isolated population from those in the Moray Firth SAC. Although historic accounts suggest that bottlenose dolphins are not new to the area between Firth of Forth and Withernsea (Bloom, 1991), the data detailed in the Sea Watch Foundation's National Whale and Dolphin Watch reports have revealed an influx of animals in the last decade (Hackett, 2022, Sea Watch Foundation, 2023). Photo-identification study and analysis of sightings data conducted by Hackett (2022) corroborated these findings and showed that annual sightings of bottlenose dolphins along north-east England have steadily increased since 2019. Sixteen post-construction surveys were undertaken between March and October 2018 for the Blyth Offshore Demonstrator project, located 5 km off the coast of Blyth, Northumberland (EDF Renewables, 2019). Bottlenose dolphins were recorded on two separate surveys, noting that no bottlenose dolphins were recorded during preconstruction surveys carried out between March and October 2016 (EDF Renewables, 2019).
116. The ECOMMAS C-POD study (Palmer et al., 2019) found that broadband acoustic occupancy rates throughout the survey were generally higher for C‐PODs closer to the shoreline which corroborates findings of Thompson et al. (2015) suggesting the bottlenose dolphins are more likely to be observed in coastal waters, within 5 km of shore and therefore are unlikely to be present in the offshore areas that may be exposed to significant construction noise from offshore wind farms. These results were corroborated by Quick et al. (2014) which reported that dolphins were mostly encountered in waters less than 30 m deep, generally in waters between 2 m and 20 m and within 2 km from the coast. Paxton et al. (2016) also describes bottlenose dolphin distribution as coastal.
117. Bottlenose dolphins were recorded in low numbers during the Berwick Bank aerial surveys, with one and six individuals encountered in October 2019 and April 2021, respectively (SSE Renewables, 2022a). However, there were no records of bottlenose dolphins in the offshore waters during three years (2009 to 2012) of boat-based surveys within the Neart na Gaoithe Offshore Wind Farm area (Mainstream Renewable Power, 2019). There were also no records of bottlenose dolphins during the Seagreen boat-based surveys, which took place approx. 25 km offshore (Sparling, 2012). No bottlenose dolphins were recorded during DAS of the Array marine mammal study area.

                        Density/abundance

                        Published literature

118. Cheney et al. (2013) reported that the population estimate of bottlenose dolphin for the Coastal East Scotland MU ( Figure 5.7   Open ▸ ) is 195 individuals (95% CI = 162 to 253) based on photo ID counts between 2006 and 2007. Following this publication, Cheney et al. (2018) estimated that the bottlenose dolphin population on the east coast of Scotland is increasing and varied from 129 (95% CI = 104 to 155) in 2001 to 189 (95% CI = 155 to 216) in 2015. IAMMWG (2022) published the most up-to-date bottlenose dolphin population estimate for Coastal East Scotland MU of 224 individuals (based on Arso Civil et al. (2021). Cheney et al. (2018) reported that the proportion of the population that uses the Moray Firth SAC has declined due to an overall increase in population size and expansion of range.
119. The SCANS III estimated abundance for block R ( Figure 3.3   Open ▸ ) was 1,924 bottlenose dolphins (95% CI = 0 to 5,408) (Hammond et al., 2021). This is a much higher estimate than the abundance estimate for the Coastal East Scotland population derived from the dedicated photo-identification surveys described in paragraph 118 (Cheney et al., 2018). However, studies for the Coastal East Scotland population are focussed on inshore waters, and SCANS III results were obtained through large-scale surveys, including offshore waters. Studies suggest that inshore and offshore populations are often ecologically and genetically discrete (Cheney et al., 2013).
120. Hammond et al. (2021) reported densities for bottlenose dolphin across block R as 0.0298 animals per km2. Recently modelled density surfaces using the SCANS III data (refer to paragraph 29) (Lacey et al., 2022) gave a mean density of 0.00303 animals per km2 and a maximum of 0.00432 animals per km2 for the Array marine mammal study area ( Figure 5.8   Open ▸ ), with density maps showing higher areas of density in the inshore waters close to the Firths of Forth and Tay estuaries. There were no bottlenose dolphin sightings in block NS-D during the SCANS IV survey and therefore SCANS IV density values for bottlenose dolphins within this block are not available (Gilles et al., 2023).

Figure 5.7: Coastal East Scotland Management Unit and Southern Limit of Bottlenose Dolphin Sightings

Figure 5.8: Density Surface Maps From SCANS III Data for Bottlenose Dolphin Based on Lacey et al. (2022)

121. To capture the patchiness in coastal distribution of bottlenose dolphins and estimate density, an analysis of ECOMMAS data has been provided as a part of the Berwick Bank marine mammal technical report (SSE Renewables, 2022a). The analysis considered the most up-to-date coastal population size based on Arso Civil et al. (2021), distributional range between the Moray Firth and Firth of Forth as presented in Cheney et al. (2013), coastal distribution within 5 km from the shore (Palmer et al., 2019, Arso Civil, 2014, Oudejans et al., 2015) and depth preference of 2 m to 20 m (Quick et al., 2014). Assuming even distribution of 50% population of bottlenose dolphin between Peterhead and the Farne Islands, excluding the outer Firth of Tay, a density of 0.197 animals per km2 was calculated. In order to reflect the relative importance of the outer Firth of Tay in terms of bottlenose dolphin distribution, the habitat preference map for bottlenose dolphins in the Firth of Tay and adjacent areas as modelled by Arso Civil et al. (2019) was used. Four distinct segments were identified on the habitat preference maps: Fife Ness to St Andrews, Outer Firth of Tay, Arbroath, and Montrose; a number of bottlenose dolphins was estimated for each of the segments. The density within the Firth of Tay and 2 m to 20 m depth contour was estimated as 0.294 animals per km2. It should be noted that this analysis did not consider individuals from the Coastal East Scotland bottlenose dolphin population that range further south and along the Northumberland coast (refer to paragraph 115 for more detail).
122. Predicted distribution maps of bottlenose dolphin at monthly scales by Waggitt et al. (2020) demonstrated bottlenose dolphin densities to be consistently low throughout the year ( Figure 5.9   Open ▸ to Figure 5.10   Open ▸ ). Highest densities within the Array marine mammal study area were predicted in August with a maximum of 0.00271 animals per km2 ( Figure 5.10   Open ▸ ). However, as a limitation authors of this study highlight that small and isolated sub-populations would have little influence on these broad scale models and that there may have been substantial changes in populations across the study period. As such, density estimates provided by Waggitt et al. (2020) may not be a true reflection of densities for the Coastal East Scotland bottlenose dolphin population due to its small size and recent southward expansion.

Figure 5.9: Bottlenose Dolphin Density from January to April Based on Waggitt et al. (2020)

Figure 5.10: Bottlenose Dolphin Density from May to August Based on Waggitt et al. (2020)

Figure 5.11: Bottlenose Dolphin Density from September to December Based on Waggitt et al. (2020)

                        Surveys

123. Given that no bottlenose dolphins were recorded during DAS of the Array marine mammal study area, design or model-based density and abundance estimates for this species are not available. Similarly, low numbers of bottlenose dolphins were recorded during the historic surveys in the wider Firth of Forth and Tay areas and therefore there are no density estimates, that were informed by these surveys.

                        Summary of the densities

124. Overall, bottlenose dolphins are present across the northern North Sea, however, only the coastal population, distributed within the 2 m to 20 m depth contour and approximately 2 km from the shore, is well documented in literature. Comparison of key data sources for bottlenose dolphin is shown in Table 5.2   Open ▸ .
125. As presented in paragraph 123, design or model-based density and abundance estimates for bottlenose dolphin based on DAS are not available.
126. Predicted estimates of mean density for the Array marine mammal study area from Waggitt et al. (2020) are comparable to the Lacey et al. (2022) estimate and are provided at the same resolution (10 km x 10 km). Densities published by Hammond et al. (2021) are an order of magnitude higher, however these are based on one estimate for a large block ( Figure 3.3   Open ▸ ) that covers both inshore and offshore waters. As presented in paragraph 116, the distribution of bottlenose dolphins within the Coastal East Scotland MU is restricted to coastal areas within 2 km to 5 km of the shore and therefore the density within these areas is expected to be higher than offshore.
127. As such, it is considered that densities presented in Hammond et al. (2021) may not be representative of the offshore waters, where the Array marine mammal study area is located. Lacey et al. (2022) maps reflect coastal distribution of CES bottlenose dolphin population. Moreover, it should be noted that Lacey et al. (2022) used SCANS III data alongside the environmental covariates such as depth and slope (refer to section 3.4.1 for more details) in the density surface modelling. As described in paragraph 116, depth is an important predictor for bottlenose dolphin distribution. Therefore, studies that consider the environmental conditions allowing to discriminate among different habitats (e.g. shallow vs deep) are preferrable to be used when predicting bottlenose dolphin density. As such, density estimates reported by Lacey et al. (2022) are considered more appropriate to use to reflect densities of bottlenose dolphins in offshore waters where the site boundary is located and a density of 0.00303 animals per km2 will be taken forward to the assessment.

Table 5.2: Comparison of Main Data Sources Densities for Bottlenose Dolphin (Lacey et al. (2022) Density Will Be Taken Forward to the Assessment)

                        Seasonality

128. Thompson et al. (2011) reported that in the Moray Firth, three times as many individuals occurred within inshore waters in the summer compared to the winter months. Paxton et al. (2016) suggested that within the Firth of Forth bottlenose dolphins are more abundant during spring and summer. Similarly, photo-identification study and analysis of sightings data conducted by Hackett (2022) showed that although sightings of bottlenose dolphins between Firth of Forth and Withernsea are recorded year-round, the rates at which bottlenose dolphins are being seen are three to seven times higher during summer than other seasons. It has been suggested that this seasonal inshore occurrence of bottlenose dolphin may be linked to periods when animals move into warmer shallow waters to calve and nurse their young during the summer months. Breeding in bottlenose dolphins is usually seasonal and varies with location but in the Moray Firth the peak calving period is in the late summer (Culloch and Robinson, 2008). Other driving factors may also include seasonal distribution of prey species. Seasonal trends in offshore populations are unknown.

5.1.3.    White-Beaked Dolphin

5.1.3. White-Beaked Dolphin

                        Ecology

129. The white-beaked dolphin belongs to the family Delphinidae (oceanic dolphins) in the suborder Odontoceti. It is a robust species that can grow up to 3.5 m for males and 3.05 m for females. Adults become sexually mature at a length of approximately 2.6 m and at approximately 12 to 13 years of age (Reeves et al., 1999). The mating season for white-beaked dolphin is in July and August with the gestation period lasting about 11 months (Culik, 2010).
130. Little is known about the reproductive behaviour of this species and whilst it was thought that births often occur offshore in the northern North Sea (Evans, 1991), there is also evidence to suggest that females move into inshore waters to give birth (Canning et al., 2008, Weir et al., 2007).
131. The white-beaked dolphin is considered to be of Least Concern on the International Union for Conservation of Nature (IUCN) Red List of species. However, there are concerns about the potential impact of climate change causing a reduction in its range (MacLeod et al., 2005). In general, white-beaked dolphin is only found in waters cooler than around 18˚C and is most common in waters below about 13˚C (Tetley and Dolman, 2013). It has been suggested that due to the increase in sea surface temperature (SST) between 1948 and 2003, the suitable habitat of white-beaked dolphins in Scottish waters decreased, which resulted in reduced species presence (van Weelden et al., 2021, MacLeod et al., 2005).
132. The white-beaked dolphin is known to have a broad diet (Samarra et al., 2022), however, the main prey species for this species in Scottish waters is whiting and in lesser extent other clupeids Clupeidae (e.g. herring), gadoids (e.g. haddock and cod) and shad (Alosa spp.) (Canning et al., 2008). Although the distribution and abundance of prey species affects the distribution and abundance of white-beaked dolphin, this species tends to be influenced by temperature with larger numbers and group sizes associated with cooler temperatures (Evans, 1991, Canning et al., 2008, Weir et al., 2007). Recent studies in Iceland demonstrate that despite ecosystem changes in the study region, white-beaked dolphin showed no long-term changes in trophic ecology, suggesting that it adapts to spatial changes in prey distribution or shifts to other prey at similar trophic levels (Samarra et al., 2022).

                        Distribution and occurrence

133. The white-beaked dolphin inhabits the temperate and subarctic waters of the North Atlantic (Schick et al., 2020). It is the second most numerous cetacean in the North Sea, recorded more frequently in the western sector of the central and northern North Sea across to western Scotland and is generally sighted in small groups of three to four animals (Reid et al., 2003).
134. In the north-east Atlantic white-beaked dolphins are generally restricted to shelf waters and prefer waters less than 120 m deep (Tetley and Dolman, 2013) . However, Weir et al. (2009) suggested that individuals were encountered in significantly deeper waters around Scotland, with a range from 106.5 m to 134.5 m and with no sightings in waters of less than 70 m. This indicates the preference of white-beaked dolphins to inhabit open waters located outside of the immediate coastal zone. Moreover, other habitat variables, such as slope and seabed aspect, were thought to be important factors in driving occurrence (Tetley and Dolman, 2013). White-beaked dolphins are capable of long-range regional movements, although individuals can also show repeated inter-annual site fidelity.
135. During the TCE aerial surveys, white-beaked dolphins were encountered in both, inshore and offshore waters, although most encounters were recorded offshore ( Figure 3.2   Open ▸ ) with group sizes ranging from one to six individuals (Grellier and Lacey, 2011). During Seagreen boat-based surveys, white-beaked dolphins occurred most often in groups: with a mean group size of three and a maximum group size of 15 individuals (Sparling, 2012) with most sightings further offshore. A peak in sightings and therefore density, was apparent to the north-east of the survey area. During the Berwick Bank aerial surveys, white-beaked dolphins were most often in the south-east of the Berwick Bank survey area ( Figure 3.2   Open ▸ ). No clear patterns in distribution of white-beaked dolphin across the Array marine mammals study area can be concluded based on DAS sightings (refer to volume 3, appendix 10.2, annex A for more detail).

                        Density/abundance

                        Published literature

136. The relevant MU for white-beaked dolphins is the CGNS MU ( Figure 5.12   Open ▸ ) which has an estimated population size of 43,951 animals (CV = 0.22, 95% CI = 28,439 to 67,924) . The SCANS III estimated abundance for block R ( Figure 3.3   Open ▸ ) was 15,694 white-beaked dolphins (CV=0.48, 95% CI = 3,022 to 33,340) (Hammond et al., 2021). The SCANS IV reported white-beaked dolphin abundance within block NS-D of 5,149 individuals representing approximately one-third of the SCANS III estimates for block R indicating a reduction in white-beaked dolphin abundance (Gilles et al., 2023).
137. Hammond et al. (2021) reported densities for white-beaked dolphin across block R as 0.243 animals per km2. Recently modelled density surfaces using the SCANS III data (refer to paragraph 29) (Lacey et al., 2022) gave a mean density of 0.120 animals per km2 and a maximum of 0.181 animals per km2 for the Array marine mammal study area ( Figure 5.13   Open ▸ ), with density maps showing higher areas of density in the offshore waters north of the site boundary. The SCANS IV surveys reported lower white-beaked dolphin density of 0.0799 animals per km2 for block NS-D when compared to SCANS III block R (Gilles et al., 2023).
138. The JCP Phase III analysis provided estimated abundances for white-beaked dolphin in 2010 by season for the Firth of Forth area of commercial interest ( Figure 3.5   Open ▸ ). Highest abundance was estimated in the spring months with 1,760 animals (97.5% CI = 620 to 4,530) with lower estimates in all other seasons; summer with 720 animals (97.5% CI = 360 to 1,840), autumn with 540 animals (97.5% CI = 220 to 1,130) and winter with 410 animals (97.5% CI = 170 to 1,110) (Paxton et al., 2016). This equated to density estimates between 0.029 individuals per km2 in winter and 0.124 individuals per km2 in summer and therefore were lower compared to the mean density estimate for SCANS-III block R (0.243 animals per km2) as described previously. Additionally, the study reported predicted abundance of white-beaked dolphins in the Firth of Forth as a percentage of the predicted number from CGNS MU, based on estimates for summers 2007 to 2010 as 4.6% (97.5% CI = 0.1 to 5.9).
139. Predicted distribution maps of white-beaked dolphin at monthly scales by Waggitt et al. (2020) demonstrated white-beaked dolphin densities to be relatively low throughout the year ( Figure 5.14   Open ▸ to Figure 5.16   Open ▸ ). Highest densities within the Array marine mammal study area were predicted in August with a maximum of 0.131 animals per km2 ( Figure 5.15   Open ▸ ).

Figure 5.12: Celtic and Greater North Seas Management Unit

Figure 5.13: Density Surface Maps From SCANS III Data for White-beaked Dolphin Based on Lacey et al. (2022)

Figure 5.14: White-beaked Dolphin Density from January to April Based on Waggitt et al. (2020)

Figure 5.15: White-beaked Dolphin Density from May to August Based on Waggitt et al. (2020)

Figure 5.16: White-beaked Dolphin Density from September to December Based on Waggitt et al. (2020)

                        Surveys

140. Relative density estimates of white-beaked dolphin from DAS of the Array marine mammal study area were corrected for availability bias using the conversion factor of 18% based on Rasmussen et al. (2013) (refer to volume 3, appendix 10.2, annex A for more detail). White-beaked dolphin were not observed in sufficient numbers for robust modelling, and as such their density within the Array marine mammal study area can only be estimated via design-based methods. Given seasonality of white-beaked dolphin sightings and higher number of records during summer, design-based density estimates were calculated across four seasons, with absolute densities of 0.024 and 0.057 animals per km2 for winter and summer respectively.
141. After correcting for availability, Mackenzie et al. (2012) estimated absolute abundance for the TCE aerial and Seagreen boat-based survey areas across the survey period as 293 (95% CI = 267 to 1,055). An availability bias correction for white-beaked dolphin was unavailable, therefore, this study applied a value for bottlenose dolphin (0.11). Absolute density estimates presented in Mackenzie et al. (2012) for the TCE aerial and Seagreen boat-based surveys had high uncertainty and ranged from zero to one individual per km2 in a single grid cell over the survey period. Mean monthly density of white-beaked dolphin estimated from Berwick Bank aerial surveys was 0.009 (95% CI = 0.003 to 0.017) animals per km2 (SSE Renewables, 2022a). Correcting this for availability bias based on a bio-logging study in Iceland (Rasmussen et al., 2013) gave an absolute density of 0.05 (CV = 1.40, 95% CI = 0.017 to 0.094) animals per km2.

                        Summary of the densities

142. Overall, white-beaked dolphins are abundant in the central and northern North Sea. Comparison of key data sources for white-beaked dolphin is shown in Table 5.3   Open ▸ .
143. Predicted estimate of mean density for the Array marine mammal study area from Waggitt et al. (2020) are comparable to the Lacey et al. (2022) estimate and are provided at the same resolution (10 km x 10 km). Densities published by Hammond et al. (2021) are the highest, however these are based on one estimate for a large block ( Figure 3.3   Open ▸ ) and do not take into account variability in cetacean density associated with environmental covariates (such as depth, slope, distance from the coast). As described in paragraphs 131 and 134, temperature and depth are important predictors for white-beaked dolphin distribution. Therefore, studies that take into account the environmental conditions allowing to discriminate among different habitats (e.g. shallow vs deep) are preferrable when predicting white-beaked dolphin density, such as Lacey et al. (2022) and/or Waggitt et al. (2020).
144. As presented in paragraph 140, given the relatively high number of white-beaked dolphin sightings over 24 months of the DAS, it was possible to analyse the data and provide site-specific design-based density estimates. To provide the most precautionary figure, the design-based absolute density estimates from the DAS presented in Table 5.3   Open ▸ are based on summer meteorological season (June to August).
145. The calculated absolute density of 0.057 animals per km2 is approximately an order of magnitude lower when compared to density values from Waggitt et al. (2020) and Lacey et al. (2022). Although the reasons for such discrepancies are unknown, it can be hypothesised that the abundance of white-beaked dolphins on the east coast of Scotland may be lower compared to historic accounts due to rising sea surface temperature (van Weelden et al., 2021). The white-beaked dolphin is endemic to the colder waters of the North Atlantic and prefer water temperatures ranging from 8°C to 13°C (MacLeod et al., 2008). A number of studies have suggested that the abundance of white-beaked dolphins in the UK waters is declining as a result of increases in local water temperature (van Weelden et al., 2021, MacLeod et al., 2005, MacLeod et al., 2008, MacLeod  et al., 2007, Lambert et al., 2014). Findings from SCANS IV surveys conducted in 2022 also suggest a decline in the number of white-beaked dolphins on the east coast of Scotland with an estimated density of 0.0799 animals per km2 for block NS-D (Gilles et al., 2023) compared to the density of 0.243 animals per km2 for block R during SCANS III surveys carried out in 2016 (Hammond et al., 2021). Given that Waggitt et al. (2020) use the data collated between 1980 and 2018, the authors highlighted that the density estimates based on this study may not reflect recent changes in distribution over the study period. Therefore, to ensure that the density estimate is precautionary (with respect to corrected density estimates based on DAS of the Array marine mammal study area) and based on the most recent data and methodology that accounts for the habitat characteristic, it is considered that density estimates based on Lacey et al. (2022) are the most appropriate to use and a density of 0.120 animals per km2 will be taken forward to the assessment

Table 5.3: Comparison of Main Data Sources Densities for White-beaked Dolphin (Lacey et al. (2022) Density Will Be Taken Forward to the Assessment)

                        Seasonality

146. Grellier and Lacey (2011) reported that during the TCE aerial surveys sightings of white-beaked dolphins were more common in summer than in winter. These results were corroborated by the Seagreen boat-based survey results, where the highest rates of white-beaked dolphins were seen in the summer months (Sparling, 2012). The Seagreen bird surveys in summer 2017 recorded white-beaked dolphins on two of the five surveys in June and July (Seagreen Wind Energy Limited, 2018). White-beaked dolphin sightings were recorded during the Berwick Bank aerial surveys during summer months only, between June and September each year, with peak sightings in September 2020 (SSE Renewables, 2022a). During DAS, white-beaked dolphin encounters took place between March and September. These seasonal peaks are in line with Weir et al. (2007), who reported that the presence of white-beaked dolphins within the coastal North Sea area in Aberdeenshire is strictly seasonal, as animals were recorded only between June and August, with a peak in occurrence during August.

5.2.        Mysticetes

5.2. Mysticetes

5.2.1.    Minke Whale

5.2.1. Minke Whale

                        Ecology

147. Minke whale is the smallest mysticete (baleen whale) found in UK waters, measuring 7 m to 10 m when fully grown, with females usually slightly longer than males. Minke whales typically live up to 60 years and reach sexually maturity at the age of five to eight years (males) and six to eight years (females). In the northern hemisphere, mating occurs between October to March and the gestation period lasts approximately ten months, with the peak birth period between December and January (Sea Watch Foundation, 2012). Calves usually nurse for a period of four to six months.
148. Minke whales tend to be observed either solitarily or in pairs or threes. However, in higher latitudes, including northern Scotland, larger groups of ten to 15 individuals can be observed, particularly in areas of high prey density (Anderwald and Evans, 2007). The largest group of minke whales recorded during DAS of the Array marine mammal study area consisted of five individuals (recorded in July 2022; refer to volume 3, appendix 10.2, annex A for more detail). This species mostly inhabits continental shelf waters, occurs in depths of less than 200 m and can often be seen close to land. Minke whale follow prey distribution and sandeel are the key food resource throughout the North Sea, with sprat, shad and herring also preferred prey items (Robinson and Tetley, 2005). Samples taken from the stomach contents of specimens within the North Sea determined that in UK waters the dominant prey items were sandeels, followed by clupeids and to a lesser extent mackerel Scomber scombrus (Robinson and Tetley, 2007). Around Scotland (including the Moray Firth) the primary constituent (70% of the diet of minke whales was sandeel (Tetley et al., 2008) as well as herring and sprat (Robinson et al., 2021). A recent study in Moray Firth, Scotland, has shown that juveniles tend to exploit passive (low energy) feeding methods, targeting low-density patches of inshore prey, while adult minke whales use a range of active entrapment specialisations, exhibiting seasonal flexibility in targeted prey with interindividual variation (Robinson et al., 2021). Regional differences exist with respect to diet (Eerkes-Medrano et al., 2021).

                        Distribution and occurrence

149. Minke whale is the most frequently sighted mysticete species in UK waters and is particularly common around the Northern Isles and in regions of the North Sea (Weir, 2001, Robinson et al., 2007). By far the most sightings within continental shelf waters occur between May and September, with peak numbers from July to September, depending on the region (Evans et al., 2003). Although there are no obvious latitudinal trends in migration and distribution based on the Sea Watch database (Sea Watch Foundation, 2023), sightings in the north and east of Scotland have increased since the 1990s (Evans et al., 2003), most likely due to an increase in prey availability. The Moray Firth in particular attracts above average densities of minke whale relative to the adjacent and wider North Sea waters (Paxton et al., 2014), likely due to rich feeding grounds during summer and autumn months, with the Southern Trench ncMPA designated for the species along the southern coast of the outer Moray Firth. The boundaries of the Southern Trench ncMPA enclose deep shelf waters (~200 m in depth) and core frontal systems, which concentrates nutrients and plankton attracting fish species, and geodiversity features (such as burrowed mud) provides optimal nursery areas.
150. Robinson et al. (2009) analysed data from boat-based studies in the Moray Firth (2001 to 2006) and reported that spatial and temporal distribution of minke whales was highly variable and non-uniform. Monthly encounter rates were highly inconsistent from one year to the next, with annual encounter frequencies ranging from 0 to 0.042 individuals per km2 across the six year study period. Robinson et al. (2009) highlighted that such variability is common in studies of baleen whales on their feeding grounds. Robinson et al. (2021) reported that in 2006, disproportionate numbers of both adult and juvenile minkes were sighted inshore within the Moray Firth study area. This coincided with the introduction of the European Union (EU)-wide ban on the North Sea sandeel fishery and therefore it has been hypothesised that minke whales were profiting from high densities of sandeel prey.
151. Following the Geographic Information System (GIS) analyses of sightings data, Robinson et al. (2009) estimated that over 70% of the whales recorded in the Moray Firth study area occurred in steeply sloped areas at depths of between 20 m and 50 m. The arrival of whales each year appeared to be synchronised with the emergence of sandeels into the water column to feed, and in the GIS results over 66% of the whale encounters showed a clear spatial preference for sandy-gravel sediments (i.e. optimal sandeel habitat). The study proved strong correlation of the sediment type with the distribution of whales. Robinson et al. (2021) corroborated the fact that occurrence of minke whales on their feeding grounds is linked to the environmental variables which influence the distribution of their prey. The study reported that the benthic slope, water depth and proximity to shore were found to be significant predictors for the occurrence of adult minke whales, whilst proximity to shore, water depth and sediment-type were the most important predictors for juveniles (Robinson et al., 2021). More recently, Robinson et al. (2023) suggested that the partitioning between the age-classes in the Southern Trench ncMPA was largely based on the differing proximity of animals to the shore, with juveniles showing a preference for the shallower, gentler seabed slopes, and adults preferring deeper offshore waters with greater slope. Both adults and juveniles show a similar preference for sandy gravel sediment types (optimal sandeel habitat).
152. During the historic TCE aerial surveys (Grellier and Lacey, 2011) minke whales were encountered throughout the survey area, with slightly more sightings in the northern part of the survey area ( Figure 3.2   Open ▸ ). Minke whales were mostly recorded as single animals, although three animals were sighted together in May 2010 and two in June 2011. During the Berwick Bank aerial surveys, minke whales were recorded throughout the surveyed area ( Figure 3.2   Open ▸ ) (SSE Renewables, 2022a). Given that minke whales were recorded in four months only during DAS of the Array marine mammal study area, no clear pattern in their distribution across the Array marine mammal study area can be concluded (refer to volume 3, appendix 10.2, annex A for more detail).

                        Density/abundance

                        Published literature

153. All minke whales in UK waters are considered to be part of the CGNS MU ( Figure 5.12   Open ▸ ). Based on the most up to date estimates, the abundance of minke whales in this MU is 20,118 animals (CV = 0.18, 95% CI = 14,061 to 28,786) (IAMMWG, 2022). The SCANS III estimated abundance for block R ( Figure 3.3   Open ▸ ) was 2,498 minke whales (CV = 0.61, 95% CI = 604 to 6,791) (Hammond et al., 2021). SCANS IV reported minke whale abundance within block NS-D of 2,702 individuals indicating an increase in minke whale abundance when compared to SCANS III results for block R (Gilles et al., 2023).
154. Hammond et al. (2021) reported densities for minke whale across block R as 0.0387 animals per km2. Recently modelled density surfaces using the SCANS III data (refer to paragraph 29) (Lacey et al., 2022) gave a mean density of 0.0284 animals per km2 and a maximum of 0.0358 animals per km2 for the Array marine mammal study area ( Figure 5.17   Open ▸ ), with density maps showing higher areas of density in the offshore waters east of the site boundary. The SCANS IV surveys reported relatively higher minke whale density of 0.0419 animals per km2 for block NS-D when compared to SCANS III block R (Gilles et al., 2023).
155. The JCP Phase III analyses presented abundances for minke whales in 2010 by season for the Firth of Forth area of commercial interest region ( Figure 3.5   Open ▸ ) estimated highest abundance in the summer months at 360 (97.5% CI = 140 to 990) animals, with low estimates in all other seasons (20 animals during autumn and winter). This equates to density estimates between 0.025 individuals per km2 and 0.001 individuals per km2. Additionally, the study reported predicted abundance of minke whales in the Firth of Forth as a percentage of the predicted number from CGNS MU ( Figure 5.13   Open ▸ ), based on estimates for summers 2007 to 2010 as 1.4% (97.5% CI = 0.6 to 2.3).

Figure 5.17: Density Surface Maps from SCANS III Data for Minke Whale Based on Lacey et al. (2022)

                        Surveys

156. Minke whales were recorded in four months during DAS and due to low numbers of sightings (refer to volume 3, appendix 10.2, annex A for more detail), design or model-based density and abundance estimates for this species are not available.
157. Based on the sightings data from the TCE aerial surveys and Seagreen boat-based surveys, Mackenzie et al. (2012) reported the absolute abundance as 594 individuals for the survey area but also showed a high level of uncertainty due to the low number of sightings (95% CI = 483 to 2,695). An availability bias correction factor was applied to this analysis for minke whale at 0.04 (Mackenzie et al., 2012).
158. The greatest number of minke whales counted from the Seagreen bird surveys was 13 animals in July 2017. No minke whales were sighted during the June survey and only one animal per survey was recorded in May and August (Seagreen Wind Energy Limited, 2018). Mean monthly density of minke whale based on the Berwick Bank aerial survey data was estimated as 0.007 (95% CI = 0.004 to 0.010) animals per km2 (SSE Renewables, 2022a). Correcting this for availability bias using dive profile data from a visual tracking study in Iceland (McGarry et al., 2017), provided an absolute density of 0.016 (95% CI = 0.009 to 0.023) animals per km2 (SSE Renewables, 2022a).

                        Summary of the densities

159. Overall, minke whales are widely distributed in the northern North Sea. Comparison of key data sources for minke whale is shown in Table 5.4   Open ▸ .
160. As presented in paragraph 156, due to low numbers of minke whale sightings during DAS, design or model-based density and abundance estimates for this species are not available.
161. The predicted estimate of mean density for the Array marine mammal study area from Waggitt et al. (2020) are lowest when compared to the Lacey et al. (2022) and Hammond et al. (2021) estimates. Densities published by Gilles et al. (2023) are the highest, followed by densities published by Hammond et al. (2021) ( Table 5.4   Open ▸ ). However, SCANS III and SCANS IV densities are based on one estimate for large blocks and do not take into account variability in cetacean density associated with environmental covariates (such as depth, slope, distance from the coast). Furthermore, both Gilles et al. (2023) and Hammond et al. (2021) highlight that the very short timeframe over which the SCANS surveys are conducted (summer) means that there is limited understanding of species distribution and abundance in other seasons. It should be noted that Lacey et al. (2022) used SCANS III data alongside the environmental covariates such as depth and slope (refer to section 3.4.1 for more detail) in the density surface modelling. As described in paragraph 151, depth and slope are important predictors for minke whale distribution. As such, studies that consider the environmental conditions allowing to discriminate among different habitats (e.g. shallow vs deep) are preferrable to be used when predicting minke whale density. As such, it is considered that densities presented in Lacey et al. (2022) are the most appropriate to use for the specific area of interest (Array marine mammal study area) and a density of 0.0284 animals per km2 will be taken forward to the assessment.

Table 5.4: Comparison of Main Data Sources Densities for Minke Whale (Lacey et al. (2022) Density Will Be Taken Forward to the Assessment)

                        Seasonality

162. Robinson et al. (2009) reported that in the Moray Firth, minke whales were encountered each month with a peak in annual occurrence from July to August (using sightings data from boat-based surveys carried out between May and October, 2001 to 2006). The distribution of whales showed a progressive inshore movement of animals across the summer and autumn months and then a progressive return to offshore waters again towards the end of the study period at which time whales were evidently less abundant, although the timing of this inshore-offshore movement was clearly variable from one year to the next. The results of this study suggest that while sandeels in the Moray Firth are highly targeted by minke whales in summer months, offshore populations of pelagic herring and sprat may also be equally or sometimes even more accessible to foraging whales at certain periods across the summer or from one year to the next, explaining the seasonal inshore-offshore movements and inter-annual variability of animals. Robinson et al. (2021) reported that there were seasonal differences in prey items with sandeels being targeted by juveniles and adults across all study months (May to October), herring preferentially targeted by adults from early July and sprat between late August to October.
163. The presence of minke whale pulse trains was recorded across ten sites localised between the southern edge of St. Abbs and northern Moray Firth from 2016 to 2018 (Risch et al., 2019). Across all sites and all years, minke whale pulse trains were first detected in late May and detections generally declined at the end of October. During autumn and spring, minke whale pulse train detections showed strong diel periodicity, with calling rates being lowest during daylight and highest during the night. Diel variation in baleen whale vocalisations has also been attributed to prey distribution, with reduced vocalisation rates during active feeding and an increase in vocalisations in a social context at hours of lowest prey availability (Risch et al., 2019).
164. The results of the analysis of sightings data from Seagreen boat-based surveys are in line with previous studies of Aberdeenshire coastal waters that reported minke whales to be highly seasonal (Sparling, 2012). Encounter rates were highest in the spring and summer and relatively low in autumn and winter. A similar pattern was reflected in the Neart na Gaoithe boat-based surveys and Berwick Bank aerial surveys, with sightings recorded only between May and November (Mainstream Renewable Power, 2019) and between April and September (SSE Renewables, 2022a), respectively. During DAS of the Array marine mammal study area, minke whale were only recorded in April 2022, June 2022, and July 2021/2022.

5.2.2.    Humpback whale

5.2.2. Humpback whale

                        Ecology

165. The humpback whale is a medium-sized mysticete of the Balaenopteridae family, which includes all the rorquals and is found in all oceans of the world (Johnson and Wolman, 1984). At maturity, the humpback whale reaches lengths of up to 17 m and weighs approximately 40 tonnes (HWDT, 2023). Humpback whales are easy to distinguish from other baleen whales due to their distinctive appearance with exceptionally long flippers, which are one-fourth to one-third of their total body length (Johnson and Wolman, 1984, HWDT, 2023).
166. The behaviour of humpback whale varies according to the season (HWDT, 2023). During breeding periods in the tropics, humpbacks fast, relying on their large fat reserves built up during feeding season (Rizzo and Schulte, 2009). Male whales sing long, complex songs during the breeding season, presumably to attract females and warn off rival males. These songs are known to vary between populations and change over time (HWDT, 2023). Humpback whales are normally seen as solitary individuals or in small groups of up to seven animals, and long-term associations are rare. They can dive for up to 40 minutes and raise their tail fluke when making a deep dive (HWDT, 2023). There are no studies on the prey presence within the Scottish waters, however, humpback whales were reported to prefer sprat and herring in the Celtic Sea (Ryan et al., 2014).
167. Following a severe decline due to commercial whaling, humpback whale populations in the North Atlantic region have been undergoing steady recovery during the latter part of the twentieth century (Johnson and Wolman, 1984, O’Neil et al., 2019). In the western North Atlantic, entanglement in static fishing gear, namely crab and lobster creels (pots), is currently considered to be the largest source of anthropogenic mortality and injury for this species (Ryan et al., 2016, Leaper et al., 2022).

                        Distribution and occurrence

168. Humpback whales are known for travelling long annual migration distances (Rizzo and Schulte, 2009). During summer, they spend their time in high latitudes, feeding as much as they can to create a great blubber layer, but do not mate. In winter, they travel to low latitude areas, in tropical waters, where they mate and calve, fasting for long periods such as weeks or even months (Rizzo and Schulte, 2009). Studies focussing on humpback whales in feeding areas found preferences for areas of upwelling, high chlorophyll-a concentration and frontal areas with changes in temperature, depth and currents, where prey can be found in high concentration (Meynecke et al., 2021). Preferred calving grounds were identified as shallow, warm and with slow water movement to aid the survival of calves (Meynecke et al., 2021). Although they favour inshore waters and continental shelf areas, humpback whales travel through open waters during their migration (HWDT, 2023).
169. Ramp et al. (2015) investigated the temporal variation in the occurrence of humpback whales in a North Atlantic summer feeding ground, the Gulf of St. Lawrence (Canada), from 1984 to 2010 using a long-term study of individually identifiable animals. The study found that humpback whales shifted their date of arrival at a previously undocumented rate of more than one day per year earlier over the study period and that the departure date also shifted earlier (Ramp et al., 2015). The analysis revealed that the trend in arrival was strongly related to earlier ice break-up and rising SST, likely triggering earlier primary production. The findings presented by Ramp et al. (2015) suggest that further changes to humpback whale distribution or annual life cycle may occur with ongoing climatic changes.
170. The first match from the British Isles to any breeding ground was made when a humpback whale photographed off the Shetland Islands, Scotland in 2016 was identified as having been seen off Guadeloupe in 2015 (Jones et al., 2017). The calculated great-circle distance between these sighting locations is approximately 6,900 km. As reported by Ryan et al. (2022), humpback whales in Scottish waters have been matched with both recovering (western North Atlantic) and non-recovering (Cape Verde) breeding populations. In 2022, the 100th humpback whale was added to the Scottish Humpback ID Catalogue (HWDT, 2022a).

                        Density/abundance

                        Published literature

171. There is little information that exists on the historical distribution and abundance of humpback whales in Scottish waters prior to commercial whaling. A few sources indicate that they were present in low densities (O’Neil et al., 2019, Weir et al., 2001). Based on archived logbooks detailing landings at Scottish shore-based whaling stations, most humpback whale catches were to the north of Shetland, although several were taken to the west of the Outer Hebrides at the continental shelf edge (Ryan et al., 2022). Of the baleen whale landings, humpback whales comprised a very small proportion of the total, e.g. approximately 0.7% of the entire catch (Ryan et al., 2022).
172. Although all records of humpback whale presence, including visual, acoustic and strandings, remain relatively low, there have been increasing records for this species in Scotland and the wider eastern North Atlantic region since the mid-1980s (O’Neil et al., 2019, Evans and Waggitt, 2023). The first confirmed record of a humpback whale in the Firth of Forth, occurred in February 2003, with further records from August 2006, October 2012, and August 2017. Opportunistic sightings by citizen science projects in recent years suggest an increase in occurrence in inshore waters (Hague, 2023). Some individuals from the Firth of Forth were matched with records off the Scottish west coast (Isle of Coll, Hebrides) (HWDT, 2022b). Based on photographs made by citizen scientists between January 2017 and March 2018 in the Firth of Forth, O’Neil et al. (2019) reported that individuals present in the Firth of Forth had been previously photographed in Svalbard, Norway. The same study provided the first confirmed record of an individual humpback whale returning to the Firth of Forth in consecutive years (O’Neil et al., 2019). It has been suggested that the Firth of Forth may represent a migratory stopover, or a feeding or recovery opportunity en-route of a longer migration (O’Neil et al., 2019).
173. No contemporary density or abundance estimate exists for humpback whales in Scottish waters and SCANS surveys did not detect any between 1994 and 2022 (Hammond et al., 2021, Gilles et al., 2023, Hammond et al., 2013, Hammond et al., 2002).

                        Surveys

174. Humpback whales were not recorded in any of the historical surveys that took place within the wider Firth of Forth and Tay (refer to Table 3.3   Open ▸ and Figure 3.2   Open ▸ ) nor the DAS surveys of the Array marine mammal study area (refer to volume 3, appendix 10.2, annex A for more detail).

                        Seasonality

175. Over recent years, most of the sightings in the Firth of Forth were reported in winter, between December and March (O’Neil et al., 2019, Hague, 2023).

5.3.        Pinnipeds

5.3. Pinnipeds

5.3.1.    Harbour Seal

5.3.1. Harbour Seal

                        Ecology

176. Harbour seal typically weigh between 80 kg to 100 kg and is the smaller of the two species of pinniped that breed in the UK (SCOS, 2022). Harbour seal become sexually mature at four to six years old for males and three to five years of age for females (Lowry, 2016). Harbour seal are long-lived animals with individuals estimated to live to between 20 and 30 years (SCOS, 2022).
177. Harbour seals are central place foragers and come ashore in sheltered waters, often on sandbanks and in estuaries as well as rocky areas (SCOS, 2022). This species requires haul out sites on land for resting, moulting, and breeding, and disperse from these sites to forage at sea. In order to reduce time and energy searching for prey, animals are likely to travel directly to areas of previously or predictably high foraging success (Bailey et al., 2014). Harbour seals persist in discrete metapopulations and tend to stay within 50 km of the coast (Carter et al., 2022), although most foraging trips are over shorter ranges (Russell and McConnell, 2014). Harbour seal are generalist feeders and their diet varies both seasonally and from region to region (Hammond et al., 2005). The analysis of stable isotopic composition and concentration of mercury and selenium ions in blood of harbour seals from the North Sea demonstrated that harbour seals diet is comprised of 30% juvenile cod, 29% of plaice Pleuronectes platessa and 23% of monkfish Lophius piscatorius as well as European hake Merluccius merluccius and haddock (Damseaux et al., 2021).
178. Harbour seal breed in small groups scattered along the coastline. Pups are born in June and July having moulted their white coats prior to birth. During lactation, females spend much of their time in the water with their pups and, although they will forage during this period, distances travelled at this time are more restricted than during other periods (Thompson, 1994). In recent years, a very limited number of breeding season surveys have been carried out on behalf of NatureScot in areas designated as SACs for harbour seals in Scottish waters (Stevens, 2023). Given that there are no harbour seal breeding surveys conducted in the East Scotland or Northeast England seal MUs, these are not considered further in this report.
179. The annual moult of harbour seals in Scotland occurs in August and that is when the greatest and most consistent numbers of harbour seals are hauled out ashore (SCOS, 2022). As such, the main harbour seal population surveys are carried out when seals are moulting.

                        Distribution and occurrence

180. Harbour seals are found around the coasts of the North Atlantic and North Pacific from the subtropics to the Arctic (SCOS, 2022). The largest population of harbour seals in Europe is in the Wadden Sea and currently, approximately 32% are found in the UK (SCOS, 2022). Harbour seals are widespread around the west coast of Scotland and throughout the Hebrides and Northern Isles. On the east coast, their distribution is more restricted with concentrations in the major estuaries of the Thames, The Wash, the Firths of Forth and Tay, and the Moray Firth.
181. Major declines have now been documented in several harbour seal populations along the east coast of England and around Scotland (SCOS, 2022). The pattern of declines is not universal, e.g. the decline following 1998 phocine distemper virus outbreak in England affected mostly the Wash population but had limited impact elsewhere (SCOS, 2022). A sudden change in the East Scotland seal MU population trend was observed in 2002 and the nature of this change remains unknown (Stevens, 2023). As previously described for the Firth of Tay and Eden Estuary SAC in section 4.3.2, between 1990 and 2002, the majority of the East Scotland seal MU population was located in this SAC. At this time counts in the SAC remained stable, representing approximately 85% of the East Scotland seal MU count (Stevens, 2023). The population within the SAC then declined rapidly and monotonically from 2002 to 2021 to a count of 41 individuals, representing an approximate 95% decline. As such, now the SAC accounts for approximately 16% of the haul out counts in the East Scotland seal MU. Such rapid population decline appears to be restricted to the SAC, and there is now evidence that this decline may be slowing (Stevens, 2023). There has also been a redistribution of harbour seals within the East Scotland seal MU and additional groups of harbour seals are located in the Firth of Forth, Montrose Basin and around the Aberdeenshire coast ( Figure 5.18   Open ▸ ). Within the Northeast England seal MU, harbour seal haul outs were primarily recorded at Lindisfarne in north Northumberland and within the Tees Estuary (near Middlesbrough) ( Figure 5.18   Open ▸ ).

Figure 5.18: August Harbour Seal Haul Out Counts (2021) based on Stevens (2023)

182. The telemetry data confirmed that harbour seal usage within the Array marine mammal study area is very limited. A total of 46 harbour seals were tagged in the East Scotland seal MU between 2001 and 2018 and no seals were tagged in the Northeast England seal MU (Stevens, 2023). A further four harbour seals that were tagged elsewhere entered the seal MUs of interest ( Figure 5.19   Open ▸ , please refer to volume 3, appendix 10.2, Annex B for more details). In total, there were 50 harbour seals tracked within the seal MUs of interest and of these, four had telemetry track data recorded within the Array marine mammal study area ( Figure 5.20   Open ▸ ) (Stevens, 2023). All four of these were tagged within the Firth of Tay and Eden Estuary SAC, thus showing connectivity between the SAC and the Array marine mammal study area ( Figure 5.20   Open ▸ ). None of these individuals showed connectivity with harbour seal SACs outside of the East Scotland seal MU (Stevens, 2023). The Firth of Tay and Eden Estuary SAC is located approximately 113.7 km from the Array marine mammal study area. Given that average foraging range of harbour seal is 50 km and that only 8% of all harbour seals tagged in the East Scotland seal MU showed connectivity with the Firth of Tay and Eden Estuary SAC, it is concluded that there is limited connectivity with the SAC.
183. Harbour seal tracks were recorded in the central and southern part of the Array marine mammal study area ( Figure 5.20   Open ▸ ). No clear patterns in distribution of harbour seal across the Array marine mammals study area can be concluded based on DAS sightings as only a single individual was recorded on two occasions (two harbour seals in total; refer to volume 3, appendix 10.2, annex A for more detail).

Figure 5.19: Telemetry Tracks of Harbour Seals that Entered the Seal MUs of Interest

Figure 5.20: Telemetry Tracks of Harbour Seals with Connectivity to the Array Marine Mammal Study Area

                        Density/abundance

                        Published literature

184. The main population surveys are carried out when harbour seals are moulting, during the first three weeks of August. The most recent August haul-out count for the whole of Scotland is for the count period 2016 to 2019 and 2021, where a total of 26,378 harbour seals were counted (Stevens, 2023). For England and Wales, in 2021 a further 3,659 harbour seals were counted and in Northern Ireland 818 were counted. This results in a total count of 30,855 harbour seals in the UK during the period 2016 to 2021 equating to an estimated population of approximately 42,854 harbour seals in the UK (excluding the Republic of Ireland) (Stevens, 2023).
185. In the East Scotland seal MU, the population has been in decline since the 1996 to 1997 survey period where the highest counts of 764 individuals were recorded. In the 2016 to 2019 survey block, the haul out counts within the East Scotland seal MU had increased for the first time since the decline, to 343 (when compared to 224 in 2011 to 2015) but have since declined again in the most recent 2021 surveys to 262 (Stevens, 2023). The current scaled population estimate for the East Scotland seal MU is 364 harbour seals (Stevens, 2023). In the Northeast England seal MU, harbour seal haul out counts are low, with the most recent haul-out count of 89 harbour seals for the 2021 count period resulting in a population estimate of 124 harbour seals (Stevens, 2023). There were sudden declines in the population noted in 1988 and 2002 and phocine distemper virus is considered to be the cause of these declines (Stevens, 2023).
186. Mean harbour seal at sea usage within the Array marine mammal study area is very low, with mean usage of 0.000016 animals per 5 x 5 m grid cell, equating to a density of 0.00000064 animals per km2 (Carter et al., 2022) ( Figure 5.21   Open ▸ ). The peak count of harbour seal within grid cells overlapping the Array marine mammal study area is 0.000303 harbour seals, which, assuming uniform density within a grid cell is a density of 0.00001212 animals per km2.

                        Surveys

187. A single harbour seal was recorded on two occasions during DAS, in April 2021 and May 2022 (refer to volume 3, appendix 10.2, annex A for more detail) and as such, design or model-based density and abundance estimates for these species are not available.
188. Seagreen boat-based surveys show that harbour seals were seen in low numbers during most months in 2010, with the only exceptions being October and November when no harbour seals were recorded (Sparling, 2012). However, it should be noted that the Seagreen boat-based surveys were conducted in the areas closer to the shorelines and Firths of Forth and Tay, where the harbour seal usage is higher ( Figure 3.2   Open ▸ , Figure 5.19   Open ▸ ). No harbour seals were recorded during the Seagreen boat-based surveys in 2017 (Seagreen Wind Energy Limited, 2018). Only three sightings of harbour seal were made over the 25 months of Berwick Bank aerial survey (SSE Renewables, 2022a).

Figure 5.21: Mean Harbour Seal at Sea Usage Based on Carter et al. (2022)

                        Summary of the densities

189. Harbour seals normally feed within 50 km around their haul out sites and therefore their presence in the offshore waters is limited ( Table 5.5   Open ▸ ). Due to low numbers of harbour seal sightings during DAS, design or model-based density and abundance estimates for this species are not available. As previously described in paragraph 186, Carter et al. (2022) reports mean density of harbour seal across the Array marine mammal study area as 0.00000064 animals per km2.
190. Following feedback received in the Ossian Array Scoping Opinion from MD-LOT and NatureScot (MD-LOT, 2023), harbour seal was scoped into the assessment and a thorough review of its distribution and ecology within the regional marine mammal study area was carried out in section 5.3.1. However, considering relatively short foraging ranges, low numbers of harbour seals detected during DAS, low at-sea harbour seal usage ( Figure 5.21   Open ▸ ) and a limited connectivity with the Array marine mammal study area based on the telemetry data ( Figure 5.19   Open ▸ , Figure 5.20   Open ▸ ), the potential for effects on harbour seal populations on the east coast of Scotland is very low. Therefore, in the Array marine mammal consultation note 1 (Ossian OWFL, 2023c) the Applicant invited the stakeholders to reconsider their position on the advice provided with regard to including harbour seals in the assessment of potential impacts as a result of the construction, operation and maintenance and decommissioning of the Array. The Applicant suggested to exclude this species from further analysis in the marine mammal Array EIA Report Chapter. As such, no harbour seal density is presented here as being taken forward to the assessment.

Table 5.5: Comparison of Main Data Sources Densities for Harbour Seal

                        Seasonality

191. No clear patterns in seasonality of harbour seal can be concluded based on DAS and historic survey sightings ( Figure 3.2   Open ▸ ) due to low numbers of animals identified to species level (refer to volume 3, appendix 10.2, annex A for more detail).

5.3.2.    Grey Seal

5.3.2. Grey Seal

                        Ecology

192. Grey seal is the larger of the two pinniped species which occur around the British Isles. Males weigh up to 300 kg and females weigh up to 200 kg. The average lifespan for this species is between 20 to 30 years, however, females tend to live longer than males. Females mature at between three and five years old and males around six years, although they are probably not socially mature until eight years old (Hall and Thompson, 2009).
193. Grey seals breed, rest, moult and engage in social activity when they gather in colonies on land (known as haul outs). Haul out events occur also at sea on exposed sandbanks, but their frequency is low, and their duration is on average shorter than those events on land (Russell and Lonergan, 2012).
194. Female grey seals tend to return to the same breeding site at which they were born in order to give birth. Preferred breeding locations in the UK include remote, uninhabited islands or coasts and in small numbers in caves (SCOS, 2022). These sites allow females with young pups to move inland away from busy beaches and storm surges. Seals may also breed on exposed, cliff-backed beaches but these locations limit the opportunity to avoid storm surges and it may result in higher levels of pup mortality (SCOS, 2022). In the UK, grey seals breed in the autumn, but there is a clockwise cline in the mean birth date around the UK (SCOS, 2022). The majority of pups in south-west Britain are born between August and October; in north and west Scotland pupping occurs mainly between September and late November; in east Scotland between August and December and in eastern England pupping occurs mainly between early November to mid-December. Grey seal give birth to a single, white-coated pup which is weaned over a period of 17 to 23 days (SCOS, 2022). Pups shed their white natal coat (lanugo) and develop their first adult coat, with moult occurring at the time of weaning after which pups remain on the breeding colony for up to two to three weeks before going to sea. Following this, the female comes into oestrus and mating occurs, after which adult females return to sea to forage and build up fat reserves.
195. Along the Scottish coast, grey seals exhibit an offshore foraging behaviour (Damseaux et al., 2021). Wyles et al. (2022) studied the influence of geomorphological features of the seabed on at-sea behaviour of grey seal. The study found that features such as slopes, foot slopes and hollows attract grey seal individuals as these may host prey aggregations, and/or lead to increased prey capture success. Grey seal have a selective diet. A study on the diet of grey seals in Scottish waters found that 50% of prey items were plaice and sole Solea solea and 46% of prey items were sandeels (Damseaux et al., 2021). Hammond et al. (2005) also highlighted that grey seal diet comprises primarily sandeels, gadoids and flatfish, in that order of importance, but varying seasonally and from region to region. Gosch (2017) also reported that there are significant regional and temporal differences in the diet of grey seal. Seals in shallow waters show a preference for demersal and groundfish species such as cephalopods and flatfish, whilst seals foraging in deeper waters, over sandy substrates, will target pelagic and benthopelagic species such as blue whiting Micromesistius poutassou and sandeels (Gosch, 2017).
196. Grey seals tend to forage in the open sea, returning to land regularly to haul out. Foraging trips can be wide-ranging, however, tracking studies have shown that most foraging is likely to occur within 100 km of a haul out site (SCOS, 2022). During breeding season grey seal tend to forage within 20 km from the breeding site (pers. comm. with NatureScot).

                        Distribution and occurrence

197. Globally, grey seal concentrate in three regions: eastern Canada and the north-east USA, around the coast of the UK, especially in Scottish coastal waters, and the Baltic Sea. All populations are known to be increasing, however, numbers are still relatively low in the Baltic where the population was reduced by human exploitation and pollution (SCOS, 2022, Galatius et al., 2020).
198. The nearest designated haul out sites for grey seals from the Array marine mammal study area are Kinghorn Rocks and Inchmickery and Cow and Calves (designated for harbour and grey seal) and Fast Castle, Inchkeith and Craigleith (seasonal grey seal haul out sites) ( Figure 3.6   Open ▸ ). The closest site, Fast Castle, is located approximately 113 km from the Array marine mammal study area.
199. In the East Scotland seal MU, grey seal haul out sites are concentrated around sites in the Firth of Forth and the Tay and Eden estuaries as well as further north around Peterhead and Fraserburgh ( Figure 5.22   Open ▸ ). Within the Northeast England seal MU, the largest concentrations of haul outs can be found along the north Northumberland coast and within the Tees Estuary ( Figure 5.22   Open ▸ ).

Figure 5.22: Most Recent August Grey Seal Haul Out Counts (2015, 2016, 2018, 2021). Note That Not All Sites Were Surveyed Each Year

200. A total of 105 grey seals of all age were tagged in the seal MUs of interest ( Figure 3.6   Open ▸ ) between 1990 and 2014, 74 in the East Scotland seal MU and 31 in the Northeast England seal MU (Stevens, 2023). Of these, 84 were adults ( Figure 5.23   Open ▸ ). A further 33 adult grey seals that were tagged elsewhere entered the seal MUs of interest (refer to the volume 3, appendix 10.2, annex B for more detail). In total, there were 101 adult grey seals tracked within the seal MUs of interest and of these, 18 were tracked within the Array marine mammal study area (Stevens, 2023). Fifteen of these individuals (five female and ten male) that showed use of the Array marine mammal study area also showed connectivity with at least one grey seal SAC ( Figure 5.24   Open ▸ ). Connectivity with only the Isle of May SAC was observed in two adult grey seals, with only the Berwickshire and North Northumberland Coast SAC in nine adult grey seals, and with both SACs in four adult grey seals (Stevens, 2023). Given that only approximately 2% of all grey seals tagged in the seal MUs of interest showed connectivity with the Isle of May SAC, it is concluded that there is limited connectivity with the SAC.
201. Connectivity was also noted between the Humber Estuary SAC (one male of unknown age), the Faray and Holm of Faray SAC (one adult male) and the Monach Islands SAC (one adult male). Given that these last three SACs are located at further distances from the Array marine mammal study area, there are lower levels of expected connectivity and therefore these SACs will not be considered further.
202. Adult grey seals tracks were recorded throughout the Array marine mammal study area, with a higher density of tracks in the south of the Array marine mammal study area ( Figure 5.23   Open ▸ , Figure 5.24   Open ▸ ). No clear patterns in distribution of grey seal across the Array marine mammals study area can be concluded based on DAS sightings (refer to volume 3, appendix 10.2, annex A for more detail).

Figure 5.23: Telemetry Tracks of Adult Grey Seals Tagged in the Seal MUs of Interest

Figure 5.24: Telemetry Tracks of Adult Grey Seals with Connectivity to the Array Marine Mammal Study Area and SACs

203. The movement data was also obtained from the telemetry tags on 45 pup and juveniles, with 37 individuals tagged in the seal MUs of interest ( Figure 5.25   Open ▸ ). It is important to note that pup and juvenile movements may not be representative of the typical movement patterns of adult grey seals, since recently weaned pups are known to disperse widely to haul out locations far from their birth colony location (Stevens, 2023). Of these 45 grey seal pups, 13 were tracked within the Array marine mammal study area, 11 of which were also tracked inside a grey seal SAC ( Figure 5.26   Open ▸ ). Connectivity with only the Isle of May SAC was observed in two grey seal pups, with only the Berwickshire and North Northumberland Coast SAC in five grey seal pups, and with both SACs in four grey seal pups. No connectivity was observed between these grey seal pups and any SAC outside the East Scotland and Northeast England seal MUs.
204. During the Seagreen boat-based surveys grey seals were recorded in the highest numbers over sandy shallow banks such as Scalp Bank, Marr Bank, Wee Bankie and Berwick Bank, which are thought to be important areas for sandeels, a key prey item of grey seal (Sparling, 2012). During the Berwick Bank aerial surveys grey seals were recorded throughout the surveyed area ( Figure 3.2   Open ▸ ) with the mean encounter rate of 0.011 animals per km (95% CI = 0.014 to 0.007; unidentified seal sightings were precautionarily assigned to grey seal due to their prevalence in the region).

Figure 5.25: Telemetry Tracks of Grey Seal Pups Tagged in the Seal MUs of Interest

Figure 5.26: Telemetry Tracks of Grey Seal Pups with Connectivity to the Array Marine Mammal Study Area and SACs

                        Density/abundance

                        Published literature

205. Grey seals encountered during harbour seal August moult surveys are counted during SMRU surveys as these provide useful information on their summer distribution. However, at this time of year, grey seal numbers at haul outs can be more variable from day to day and therefore are not an accurate reflection of grey seal abundance in each region. The UK wide grey seal population is estimated using a population model that combines regional pup production estimates and August haul-out counts scaled to population estimates (Stevens, 2023).
206. In 2019, total UK pup production was estimated at 67,850 (95% CI = approximately 60,500 to 75,100) based primarily on estimates from less frequently aerial surveyed colonies as well as ground count data (Stevens, 2023). Pup production in Scotland in 2019 was estimated at 54,050 individuals, equating to approximately 79.7% of all pups born in the UK. The overall trend in pup production in the East Scotland seal MU has been increasing in recent years, however, the distribution of pup production appears to be changing (Stevens, 2023). Prior to the 1990s, the Isle of May SAC was the dominant location for pup production but since 2012, pup production estimates at the Isle of May have been overtaken by the Fast Castle colony (Stevens, 2023). Pup production estimates at the Isle of May are now considered to be stable or potentially declining (SCOS, 2023). In the Northeast England seal MU, pup production comes entirely from the Farne Islands, where the pup production has been showing a rapid increasing trend (Stevens, 2023).
207. Grey seal August counts are estimated to be stable in the East Scotland seal MU and increasing in the Northeast England seal MU ( Figure 5.27   Open ▸ ) (Stevens, 2023). The most recent August grey seal counts took place in 2021 in both East Scotland and Northeast England MU and resulted in a scaled August population estimates of 10,783 and 25,913 grey seals, respectively (SCOS, 2023).
208. The UK total grey seal population size at the start of the 2022 breeding season was estimated to be 162,000 grey seals of which 129,100 (approximately 80%) were in Scotland (Stevens, 2023).

Figure 5.27: August Haul Out Counts of Grey Seals Within Seal MUs of Interest

209. Mean grey seal at sea usage within the Array marine mammal study area is low, as the hotspots are located closer to the shore and in the vicinity of the Berwickshire and Northumberland Coast SAC, Firth of Forth, Tay and Eden Estuary and north of Aberdeen ( Figure 5.28   Open ▸ ). The average value of the mean at sea usage within the Array marine mammal study area was estimated at 4.49 animals per 5 x 5 km grid cell, equating to a density of 0.180 animals per km2 (Carter et al., 2022).

                        Surveys

210. Grey seal were not observed during DAS in sufficient numbers for robust modelling to be undertaken, and as such their density can only be estimated via design-based methods. Peaks in grey seal presence occurred in winter. As such, the most precautionary grey seal densities calculated across the Array marine mammal study area were estimated for winter with 0.033 (95% CI = 0.014 to 0.054) animals per km2.
211. Seasonal density estimates estimated from Berwick Bank aerial surveys highlighted that mean monthly densities of grey seal were highest during spring months. The absolute density was estimated as 0.276 animals per km2 with a peak mean density during spring months of 0.321 (SSE Renewables, 2022a). However, it should be noted that Berwick Bank aerial surveys took place at a distance closer to the shore ( Figure 3.2   Open ▸ ), where grey seal usage is higher compared to the Array area ( Figure 5.28   Open ▸ ). These densities are therefore higher than seasonal design-based estimates from DAS data with 0.034 animals per km2 (estimate based on data during non-breeding season (refer to Table 4.3   Open ▸ ).

Figure 5.28: Mean Grey Seal at Sea Usage Based on Carter et al. (2022)

                        Summary of the densities

212. The east coast of Scotland and northern England provide important breeding and haul out habitats for grey seal (SCOS, 2023). Comparison of key data sources for grey seal is shown in Table 5.6   Open ▸ .
213. To provide the most precautionary figure, the design-based absolute density estimates from the DAS presented in Table 5.6   Open ▸ are based on the non-breading bio-season (September to December). However, the predicted estimate of mean density for the Array marine mammal study area from Carter et al. (2022) of 0.180 animals per km2 is higher than the absolute density of 0.034 animals per km2 based on DAS data ( Table 5.6   Open ▸ ). Given uncertainties associated with identification of seals to species level based on aerial survey data, the density of 0.180 animals per km2 based on Carter et al. (2022) will be taken forward to the assessment.

Table 5.6: Comparison of Main Data Sources Densities for Grey Seal. Densities In Bold Will Be Taken Forward to the Assessment in the EIA (Carter et al. (2022) Density Will Be Taken Forward to the Assessment)

                        Seasonality

214. Grey seal sighting rates during Seagreen boat-based surveys were lowest over the autumn and winter (Seagreen Wind Energy Limited, 2018). During the Berwick Bank aerial survey grey seals were recorded every month, except one (SSE Renewables, 2022a). Based on DAS sightings, grey seals were most abundant in summer (June) (refer to volume 3, appendix 10.2, annex A for more detail).
215. Higher encounter rates of grey seals at sea during summer are likely to be related to the capital breeding habit of grey seals and possibly indicative of a period of intense foraging where adult seals are at-sea gaining energy reserves prior to the breeding season. During autumn (August to December) grey seals aggregate to breed at traditional colonies between August and December and therefore the number of seals might be expected to be low as a large proportion of the population will be hauled out to breed.

6.             Summary

6. Summary

216. Data gathered through a desktop review (publicly available sources as well as commercial survey results) and DAS found that the northern North Sea supports a number of different marine mammal species with internationally important populations of certain species occurring within the vicinity of the Array marine mammal study area. Key marine mammals identified within the regional marine mammal study area include harbour porpoise, bottlenose dolphin, white-beaked dolphin, minke whale, grey seal, and harbour seal. Humpback whales were identified through citizen science projects as occasional visitors, recorded in the vicinity of the Firth of Forth mostly over winter months.
217. Where possible, species-specific density estimates were generated using DAS data gathered during 24 months of surveys across the site boundary plus 8 km buffer. Where it was not possible to estimate densities due to low sightings rates, data were sought from published sources including regional studies of key species. A summary of the densities for each species that will be taken forward to the assessment in the EIA are provided in Table 6.1   Open ▸ . It should be noted that due to paucity of data on abundance and density of humpback whale in the North Sea, the assessment of impacts on this species in the EIA will be qualitative. In the EIA process, population-level effects will be considered for a given species-impact pathway and with respect to the species-specific MUs ( Table 6.1   Open ▸ ). Where relevant, the assessment will also be compared at a smaller scale against SCANS IV block NS-D population estimates (Gilles et al., 2023).
218. Sites designated for the conservation of internationally important Annex II marine mammal populations within the regional marine mammal study area include the Firth of Tay and Eden Estuary SAC designated for harbour seal, the Berwickshire and North Northumberland Coast SAC and Isle of May SAC designated for grey seal, the Moray Firth SAC designated for bottlenose dolphin and the Southern North Sea SAC designated for harbour porpoise. Following a comprehensive assessment of potential connectivity in section 5, only sites presented in Table 6.1   Open ▸ will be considered further in the EIA process.

Table 6.1: Summary of Marine Mammal Receptors to be Considered in the Marine Mammal Array EIA Report Chapter Together with Relevant Densities, Reference Populations and Designated Sites

1 Design-based density estimates from DAS data (refer to volume 3, appendix 10.2, annex A for more detail).

2 Densities based on Lacey et al. (2022) maps.

3 Carter et al. (2022) maps.

7.             References

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