Site conclusion
764 In conclusion, with reference to the conservation objectives set for the Annex II diadromous fish features of this site and the information presented in sections 12.3, 12.4 and 12.5.6, it can be concluded beyond all reasonable scientific doubt that there will be no Adverse Effect on Integrity on the River Teith SAC in respect of the sea lamprey, river lamprey and Atlantic salmon qualifying interests.
765 This finding is in relation to potential impacts associated with the Proposed Development during construction, decommissioning and operation and maintenance, acting alone and or in-combination.
13 Appraisal of Adverse Effects on Integrity: Marine Mammals
13.1 Introduction
766 The Screening exercise (at Stage One of the HRA process) as updated in response to consultation on the HRA Screening Report (SSE Renewables, 2021b) (see volume 2, chapter 10 of the Offshore EIA Report) identified LSEs on the following five European sites designated for Annex II marine mammal features (as summarised in Table 9.1 Open ▸ ):
- Berwickshire and North Northumberland Coast SAC (grey seal);
- Isle of May SAC (grey seal);
- Firth of Tay and Eden Estuary SAC (harbour seal);
- Southern North Sea SAC (harbour porpoise); and
- Moray Firth SAC (bottlenose dolphin).
767 This section explains the approach taken to assessing the potential impacts of the Proposed Development on European sites designated for Annex II marine mammal features and presents the Stage Two assessments for the above sites. Broadly, the potential effects to these sites are as follows (and addressed explicitly in the sections below):
768 During the construction and decommissioning phases:
- Underwater noise: direct injury or mortality and/or behavioural changes due to exposure to underwater noise generated by construction activities namely:
– piling;
– clearance of UXO;
– pre-construction surveys; and
– vessels and other vessel activities.
- Changes in prey availability: potential changes in distribution, abundance and migration patterns, community structure, susceptibility to disease due to changes in prey availability.
769 During the operation and maintenance phase:
- Underwater noise: behavioural changes due to exposure to underwater noise generated by vessels and other vessel activities; and
- Changes in prey availability.
770 The Stage Two assessments (considering effects both alone and in-combination) for sites designated for Annex II marine mammals are presented in this chapter. Integrity matrices summarising the assessments for the site are provided in Table 15.8 through to Table 15.12 in section 1514. A summary of all Appropriate Assessments undertaken within this report is provided in the concluding section of this report (see section 14).
13.2 Assessment Information
13.2.1 Maximum Design Scenarios
771 The maximum design scenario relevant to Annex II marine mammal features are set out in Table 13.10 Open ▸ Table 13.10 Open ▸ , Table 13.39 Open ▸ and Table 13.41 Open ▸ in this section. An overview of the maximum design scenario for all receptor groups is provided in Table 11.1 Open ▸ in section 11.
13.2.2 Designed-in measures
772 Designed-in measures relevant to Annex II marine mammal features are set out in Table 11.3 Open ▸ and in Table 13.11 Open ▸ and Table 13.40 Open ▸ in this section.
1.1.1. Baseline Information
773 The key data sources are presented within the volume 3, appendix 10.2 of the Offshore EIA Report and summarised below. The following information has informed the assessments:-
- Existing studies and dataset (see Table 4.1 in volume 3, appendix 10.2 of the Offshore EIA Report);
- Surveys (see section 4.2 in volume 3, appendix 10.2 of the Offshore EIA Report); and
- Digital Aerial Surveys (DAS) for the Proposed Development (see volume 3, appendix 10.2, annex A of the Offshore EIA Report).
774 Detailed European site information is presented in appendix A.
13.2.3 Conservation Objectives
775 The conservation objectives for sites designated for Annex II marine mammal features identified for Stage Two assessment are provided in section 13.6. Where Supplementary Advice to the conservation objectives, or site-specific conservation advice describes minimum targets for qualifying features in more detail, this detail is provided in appendix A and/or referenced within the relevant Stage Two Appropriate Assessments.
13.2.4 Species Accounts
776 This section introduces the distribution and abundance/densities of the relevant Annex II marine mammal features in the region. Site-specific populations, distributions, and abundances are provided in each assessment of adverse effects in sections 13.4 and 13.6.
777 For the purposes of marine mammal characterisation, two appropriate marine mammal study areas were defined:
- Proposed Development marine mammal study area: this is an area encompassing the Proposed Development array area and the Proposed Development export cable corridor plus a (approximate) 16 km buffer, including the area to the north and south of the proposed landfall location. This combined area was surveyed by the 2019 to 2021 DAS (see Figure 4.3 in the volume 3, appendix 10.2 of the Offshore EIA Report). It should be noted that the Proposed Development marine mammal study area has been defined based on the Proposed Development array boundaries at the time of the Scoping phase (SSE Renewables, 2021b). The Proposed Development array area has been subsequently amended. As The refinements resulted in a reduction of the Proposed Development array area, the Proposed Development marine mammal study area encompasses larger buffer and is therefore considered to remain representative and conservative for the current assessment. Given that the Proposed Development marine mammal study area has not been realigned to the current Proposed Development boundary, the buffer encompassing the Proposed Development array area may be equal to or greater than 16 km in some locations, including to the north-west, south-west and south-east of the Proposed Development array area; and
- Regional marine mammal study area: marine mammals are highly mobile and may range over large distances and therefore, to provide a wider context, the desktop review considers the marine mammal ecology, distribution and density/abundance within the wider northern North Sea. The Regional marine mammal study area also informs the assessment where the Zone of Influence (ZoI) for a given impact (e.g. underwater noise) may extend beyond the Proposed Development marine mammal study area.
778 Regional marine mammal study area boundaries were discussed with NatureScot and MSS during Road Map Meeting 1 and Road Map Meeting 2 (volume 3, appendix 10.3 of the Offshore EIA Report).
Grey seal
779 Telemetry data for grey seals tagged on the east coast of Scotland confirmed usage of the Proposed Development marine mammal study area (Sinclair, 2021). In total, 46 adult grey seals have been tagged in the East Scotland MU between 1990 and 2013, with a further 23 tagged in the Northeast England MU between 1991 and 2008 (Sinclair, 2021). Of the 69 adult grey seals tagged on the east coast of Scotland, 59 of these had telemetry tracks within the Proposed Development marine mammal study area.
780 The tagging data illustrated connectivity between the Proposed Development marine mammal study area and SACs with marine mammal notified interest features. A high proportion of tagged individuals were tracked between the Proposed Development marine mammal study area and the Berwickshire and North Northumberland Coast SAC (73%) and Isle of May SAC (41%) (Sinclair, 2021). A very small proportion of tagged seals (two to 3%) had telemetry tracks within the Faray and Holm of Faray SAC, the Humber Estuary SAC, the North Rona SAC and the Monach Islands SAC. Given that these four SACs are located at large distances from the Proposed Development array area (>298 km), there are lower levels of expected connectivity between these SACs and the Proposed Development. As highlighted in Table 8.1 Open ▸ , sites screened into this assessment were agreed through consultation with stakeholders. As with the tagged adult grey seals, there was also connectivity demonstrated between the Proposed Development marine mammal study area and SACs for pups/juveniles. Tracks were recorded between the Proposed Development marine mammal study area and the Berwickshire and Northumberland Coast SAC and Isle of May SAC; a small number (5% of tagged animals) were also recorded within the Humber Estuary SAC (298 km from the Proposed Development array).
781 Historic Seagreen Firth of Forth Round 3 boat-based surveys (2010 – 2011) recorded highest numbers of grey seals over sandy shallow banks such as Scalp Bank, Marr Bank, Wee Bankie and Berwick Bank, which are thought to be important areas for sandeel, a key prey item of grey seal (Sparling, 2012).
782 Grey seals were also recorded throughout the Proposed Development marine mammal study area during the DAS. Assuming that all seal species were grey seal, the mean encounter rate was 0.011 animals per km (95% CI = 0.014 to 0.007).
783 Mean grey seal at sea usage in the vicinity of the Proposed Development is variable, with hot spots at Berwickshire and North Northumberland Coast SAC, Firth of Forth, Tay and Eden Estuary and North of Aberdeen (Carter et al., 2020). Carter et al. (2020) used the most up-to-date Sea Mammal Research Unit (SMRU) telemetry data and habitat preference models to estimate at-sea seal usage and, as agreed through consultation with key stakeholders, these data were deemed most appropriate for grey seal surface density calculations (see Figure 6.25 in volume 3, appendix 10.2 of the Offshore EIA Report). Within the Proposed Development array area, the average value (of the mean at sea usage) within grid cells was estimated at 30.3 (95% CI = 15.9 to 43.1) animals per 5 x 5 km grid cell, equating to a density of 1.2 (95% CI = 0.64 to 1.7) animals per km2.
784 Density values from Carter et al., (2020) within the Proposed Development export cable corridor are generally lower than those estimated for the Proposed Development array area. There is, however, a single cell overlapping the Proposed Development export cable corridor closest to the shore with an estimated density of 108.87 (95% CI = 46.5 to 188.6) grey seals per 5 x 5 km grid cell, equating to 4.35 (95% CI = 1.9 to 7.5) grey seals per km2.
Harbour seal
786 Harbour seal populations along the east coast of Scotland have generally declined since the early 2000s (Special Committee on Seals (SCOS), 2020). Populations in the Firth of Tay and Eden Estuary SAC are continuing to decline although this is considered to be localised to the SAC and not reflective of the wider East Scotland MU population (SCOS, 2020). For example, while this MU has shown a large decline in numbers since the 1996 to 1997 count period, the most recent haul-out count in the 2016 to 2019 period (343) was higher than that in the 2011 to 2015 count period (224) suggesting that the MU population overall may be starting to increase in recent years. The main population surveys are carried out when harbour seals are moulting, during the first three weeks of August. The most recent harbour seal August moult count for the East Scotland MU is 343 (2016 to 2019 count period; SCOS, 2020). The population in this MU is mainly concentrated in the Firth of Tay and Eden Estuary SAC and in the Firth of Forth.
787 Mean harbour seal at sea usage in the vicinity of the Proposed Development is low, with the main area of usage within the Firth of Forth (Carter et al., 2020). Within the Proposed Development array area the average value (of the mean at sea usage) is estimated at 0.003 (95% CI = 0.0002 to 0.039) animals per 5 x 5 km grid cell, equating to a density of 0.0001 (95% CI = 0.00008 to 0.0016) animals per km2. The peak count of harbour seals within grid cells overlapping the Proposed Development array area was 0.05 (95% CI = 0.0002 to 0.01) animals per km2. This peak density aligned with the peak density previously reported by Russell et al. (2017) across the Proposed Development array area. A density of 0.0005 (94% CI = 0.00003 to 0.04) animals per km2 is representative of the mean densities of harbour seal along the Proposed Development export cable corridor.
Harbour porpoise
788 Harbour porpoises are widely distributed throughout the North Sea and through the Regional Marine Mammal study area. Heinänen and Skov (2015) found that in the North Sea MU (Figure 6.4 in volume 3, appendix 10.2 of the Offshore EIA Report) the water depths and hydrodynamic variables are the most important factors for the probability of presence of harbour porpoise. During the summer period (i.e. April to September) animals seem to avoid well-mixed areas showing preference for more stable areas (in terms of temperature differences). Studies indicated an avoidance of estuarine water masses.
789 Based on spatio-temporal modelling using species and environmental data, Heinänen and Skov (2015) concluded that during the summer period, harbour porpoises avoid muddy sediments and hard substrate areas. A study using long term passive acoustic data revealed however, that within the Moray Firth, harbour porpoise occurred in both sandy and muddy habitats (Williamson et al., 2016). The study also found that the proportion of hours with acoustic detection in muddy habitats increased during the night by 18% (Williamson et al., 2016). Porpoise detections also differed in response to depth in the different sediment types during hours of darkness and day-time periods. In muddy, deeper areas (50 m to 60 m) detections at night were nearly double those during the day. Therefore, it can be assumed that harbour porpoises use different types of habitats during the day and at night and therefore their distribution may shift accordingly.
790 The Heinanen 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 (October to March), the presence of harbour porpoise was best predicted by the season, water depth and the seabed surface sediments. For the winter months the modelling showed a peak in presence was observed at water depths of 30 to 40 m and that animals seemed to avoid waters with high current speeds as well as avoiding areas with muddy substrates.
791 Harbour porpoise was the most commonly identified cetacean during historic aerial surveys in the Forth and Tay Offshore Wind Developers Group (FTOWDG) region (Grellier and Lacey, 2011) and Seagreen Firth of Forth Round 3 boat-based surveys (Sparling, 2012). Harbour porpoises were distributed across the survey area (Figure 6.1 in volume 3, appendix 10.2 of the Offshore EIA Report), but there were a greater number of sightings offshore, most often seen singly although group size ranged from one to six individuals. Harbour porpoise was also recorded on all boat-based surveys and in all parts of the site (particularly near morphological bank features such as Scalp Bank to the north of the Proposed Development array area running down to the centre of the Proposed Development array area; Figure 6.2 in volume 3, appendix 10.2 of the Offshore EIA Report). 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 et al., 2004).
792 DAS survey data showed that harbour porpoise was distributed throughout the Proposed Development marine mammal study area. Sightings occurred throughout the survey area, however, the presence of harbour porpoise in May 2019 and June 2019 is more evident in the south-east of the Proposed Development array area. The spatial density maps produced using MRSea showed that during spring, the eastern half of the survey area appeared to be favoured by harbour porpoise. The highest encounter rate of harbour porpoise during the DAS was 0.212 individuals per km in April 2021. Mean monthly encounter rate was calculated as 0.037 (95% CI = 0.011 to 0.062). Harbour porpoise also had the second greatest overall encounter rate (0.013 sightings per km) from all marine species recorded during historic aerial surveys in the FTOWDG region (Grellier and Lacey, 2011).
794 Harbour porpoise was the most common cetacean species encountered during historic aerial surveys with the mean density of 0.080 (CV=0.11) individuals per km2 (Grellier and Lacey, 2011). Summer density estimates were calculated to be 0.099 (CV=0.12) individuals per km2, and winter 0.048 (CV=0.24) individuals per km2. These density estimates were minimum estimates based on inherent negative bias due to the survey methodology (Mackenzie et al., 2012). Therefore, spatially explicit density surfaces were generated using all FTOWDG aerial and Round 3 boat-based sightings (Mackenzie et al., 2012, section 5.2). When all data across all years were pooled, depth was a significant predictor of occurrence, with fewer animals in shallow water. The data showed a great deal of variation in the spatial distribution of harbour porpoise across the survey years, with the main predictor of density being survey methodology. The likely explanation for variation in densities across the survey area may relate to changes in prey distribution. After correcting for availability, Mackenzie et al. (2012) estimated absolute abundance for the survey area (aerial and boat-based) across the survey period as 582 (95% CI = 581 to 1235). The correction factor (i.e. probability of an animal being available to be seen at the sea surface) for harbour porpoise was 0.434 (McKenzie et al., 2012). 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 (Neart na Gaoithe, 2018).
795 Seasonal densities estimated from the DAS data highlighted that in spring months there were more harbour porpoise within the Proposed Development marine mammal study area. Mean monthly density was estimated as 0.127 (95% CI = 0.066 to 0.277) animals per km2. Correcting this for availability bias based on tagged porpoises in the Baltic/North Sea (Teilman et al., 2013) mean monthly density was estimated as 0.299 (95% CI = 0.155 to 0.652) animals per km2 with a peak mean density during spring months of 0.826 (95% CI = 0.440, 1.616) animals per km2 ( Table 13.1 Open ▸ ). Corrected abundance of harbour porpoise within the Proposed Development marine mammal study area ranged between 460 animals in winter and 4,108 animals in spring.
Table 13.1: Harbour Porpoise Modelled Absolute Density Estimates by Season for Proposed Development Array Area Including Lower Confidence Intervals (LCI) and Upper Confidence Intervals (UCI)[8]
796 Comparison of harbour porpoise encounter rate during different seasons based on the historic aerial surveys in the FTOWDG region showed that 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 boat-based surveys (Sparling, 2012). Boat-based surveys for Seagreen in summer 2017 recorded the highest counts of harbour porpoise between May and July (Seagreen Technical Report, 2018). These findings are different to JCP Phase III results, as the study reported highest densities of harbour porpoise during winter months (Paxton et al., 2016).
797 Similarly, a temporal trend emerged from the DAS, with highest encounter rates during spring months each year (April and May,). Harbour porpoise encounter rate was lowest during winter and autumn (from November 2019 to March 2020 and from October 2020 to February 2021). MRSea modelling corroborated the above as the results showed highest densities during spring months and lowest densities during winter (see volume 3, appendix 10.3, annex A of the Offshore EIA Report).
Bottlenose dolphin
798 The Moray Firth SAC boundary encompassed the core area of occurrence of the resident population of bottlenose dolphins in the North Sea based on the data collected in 1980s and early 1990s. However, studies have shown that the population of bottlenose dolphins off the east coast of Scotland is highly mobile with individuals ranging from Moray Firth to Firth of Forth (Quick et al., 2014; Cheney et al., 2018; Arso Civil et al., 2019; Arso Civil et al., 2021). Therefore, this range was established as the main distributional range of the population (Quick et al., 2014; Cheney et al., 2013).
799 Acoustic occupancy rates and habitat modelling in the East Coast Marine Mammal Acoustic Study (ECOMMAS) highlighted that the waters between Stonehaven and Aberdeen are a potential area of high occupancy (Palmer et al., 2019). Instruments deployed in the Stonehaven group showed the second highest acoustic occupancy rates behind the Cromarty group (area close to Moray Firth). Quick et al. (2014) established that a high proportion of bottlenose dolphins from the east coast of Scotland population use both the Tayside and Fife area and the Moray Firth SAC, over a range of temporal scales. The same study reported that most encounters occurred at the entrance of the Tay (35 to 46% of the east coast of Scotland population) and that bottlenose dolphins were only seen on the north side of the Forth, mostly between Anstruther and Fife Ness. These findings were corroborated by Arso Civil et al. (2019) who reported that the east coast population expanded its distribution range since more than a half of the estimated population was consistently using the St Andrews Bay and the Tay estuary. The ECOMMAS study reported that between 2013 and 2015 there was relatively low number of detections at the St. Andrews survey location nearest the bay and it has been suggested that this area may represent habitat associated with rest or socializing rather than foraging, therefore there are fewer clicks to detect (Palmer et al., 2019). The most recent data collected during boat-based trips between Moray Firth and Fife Ness (during summers 2017 to 2019) shows that the Tay estuary area and adjacent waters continues to be used by more than a half of the total estimated population every summer (in 2019 approx. 53.5%; Arso Civil et al., 2021). This study also reported that the number of animals estimated to be using this area has increased by around 4.3% per year between 2009 and 2019, although it decreased between 2017 and 2019. The author suggested that it is likely that changes in the distribution range are continuing with a further southern range expansion (Arso-Civil et al., 2021). In 2007 there was one confirmed sighting of a group near Whitley Bay and the Tyne river mouth (Cheney et al., 2013) and there are ongoing citizen science projects, which has resulted in bottlenose dolphin sightings being reported as far as the Farne Islands (Chronic Live, 2020). However, C‐PODs deployed at St. Abbs had very low (<5%) broadband occupancy rates for all survey years (2013 to 2015). There is currently no reported survey effort to the south of the Firth of Forth that would indicate an increase in numbers of bottlenose dolphins present in the area.
801 Bottlenose dolphins were also positively identified in historic inshore (inside 12 nm) and offshore (outside 12 nm) aerial surveys between May 2009 and March 2010 (Grellier and Lacey, 2011). During summer there was just one encounter of one individual outside 12 nm and during winter two sightings of three individuals were recorded inside 12 nm. The average encounter rate of bottlenose dolphin during aerial surveys was 0.0002 individuals per km (Grellier and Lacey, 2011). Some unidentified cetacean and dolphin species were also recorded, in each case with an encounter rate of 0.0012 individuals per km, although no distinction was made between species for these sightings. No bottlenose dolphins were encountered during Seagreen Firth of Forth Round 3 boat-based surveys between 2010 and 2011 (Sparling, 2012).
802 Bottlenose dolphins were recorded in low numbers during the Proposed Development aerial digital surveys, with one and six individuals encountered in October 2019 and April 2021 respectively. The encounter rate varied between 0.0005 individuals per km in October 2019 and 0.0024 individuals per km in April 2021 (see volume 3, appendix 10.2 of the Offshore EIA Report).
804 It is noted 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; whilst the Moray Firth is clearly an important area for this population, they are not restricted to either the Moray Firth SAC or the wider Moray Firth (Cheney et al., 2018).
805 Based on historical photo ID data collected from 1997 to 2010 and 2012 to 2013 in the Tayside and Fife area (including Firth of Forth), Quick et al. (2014) reported that the majority of dolphin encounters were recorded within the Tay estuary (see volume 3, appendix 10.2 of the Offshore EIA Report). Between 71 and 91 bottlenose dolphins (35 to 46% of the total Scottish east coast population) were estimated to be using the Tay area during 2009 – 2013 (Quick et al., 2014). Arso Civil et al. (2019) analysed and compared photoidentification data collected during consistent dedicated surveys from 2009 and 2015 in similar study areas to Quick et al. (2014), St Andrews Bay and the Tay estuary as well as the Moray Firth SAC. Over the study period, 35.2% of the marked animals were seen only in St Andrews Bay and the Tay estuary, 35.9% were seen only in the Moray Firth SAC, and 28.9% were seen in both areas. The study reported that the number of dolphins using the Tay estuary and adjacent waters increased and ranged from a minimum of 85 (95% CI = 77 to 93) animals in 2011 to a maximum of 121 (95% CI = 84 to 173) in 2014 which represented 52.5% of the estimated total east coast population (i.e. using the population's main range). The most recent study in the Tay estuary and adjacent waters integrated data collected during boat-based surveys in summers 2017 to 2019 (May to September) and data collected under the Moray Firth Marine Mammal Monitoring Programme (Arso Civil et al., 2021; Graham et al., 2017). This study corroborated previous findings and reported that this area continues to be used by more than half of the total estimated east coast population every summer; 53.8% between 2009 and 2019 (Arso-Civil et al. 2021). Studies suggest that inshore and offshore populations are often ecologically and genetically discrete (Cheney et al., 2013).
806 To estimate the density of bottlenose dolphin in coastal areas, it was important to understand both the abundance and distribution of the east coast population. A five-year weighted average of the east coast bottlenose dolphin population provided an estimated population of 224 individuals (95% CI = 214 to 234) (Arso Civil et al., 2021). The main distributional range of this population is Moray Firth to the Firth of Forth (Cheney et al., 2013), however, as mentioned (see paragraph 805), approximately 53.8% of the east coast population (=120 individuals) use the Tay area and adjacent waters (Arso Civil et al., 2021). Therefore, it was assumed that the same proportion is likely to be present anywhere between Peterhead and further south as far as the Farne Islands (as recent studies reported that the east coast population is extending their range south). Previous studies reported that bottlenose dolphins are likely to be recorded within 5 km from the shore (Arso Civil et al., 2014; Palmer et al., 2019; Oudejans et al., 2015). Quick et al. (2014) provided that in the Tayside and Fife area as well as between Montrose and Aberdeen, dolphins were encountered usually in waters 2 m to 20 m deep. Therefore, the 2 m to 20 m depth contour polygon was identified as the key habitat preference of bottlenose dolphin along the east coast, between Peterhead and Farne Islands.
807 ECOMMAS data suggested that there was a patchiness in distribution along the east coast with occupancy of bottlenose dolphin (dolphin positive minutes) different across the five monitored locations (Palmer et al., 2019). Recent literature (Arso Civil et al., 2019, Arso Civil et al., 2021) and feedback from consultees during the Proposed Development Road Map meetings indicated that, in particular, the Firth of Tay is an important area for the east coast bottlenose dolphin population. There were, however, no C-POD arrays located in the Firth of Tay and therefore the occupancy of this area could not be compared with the other five areas monitored using ECOMMAS datasets. To capture the patchiness in coastal distribution of bottlenose dolphins and estimated density, a dual approach was applied. First, for all areas except the outer Firth of Tay, the east coast proportion of the population (120 animals), was assumed to be evenly distributed across the area between the 2 m to 20 m bathymetric contours, between Peterhead and the Farne Islands, giving a density of 0.197 animals per km2. Second, 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. The map of habitat preference was analysed using the most precautionary scenario when current direction was between 300 to 010 degrees and associated bottlenose dolphin presence was recorded during the corresponding tidal condition. Four distinct segments were identified on the habitat preference maps: Fife Ness to St Andrews, Outer Firth of Tay, Arbroath and Montrose. A probability of occurrence value was assigned to each segment based on the value with widest spread across the segment and subsequently these values were used to weight each segment (as a percentage) in relation to other segments. The outer Firth of Tay had the highest weighting with a probability of occurrence of 0.8 ( Table 13.2 Open ▸ ). As per the advice received from the Scoping Representation provided by MSS on 9 December 2021, it was conservatively assumed that 53.8% of the east coast proportion of the population (120 individuals) may be present within the Firth of Tay and adjacent waters and, using the weightings, the number of bottlenose dolphins was estimated for each of the segments ( Table 13.2 Open ▸ ). Subsequently, to estimate density of bottlenose dolphins specifically within the outer Firth of Tay segment the number of dolphins (53.3 individuals) was divided by the area within that segment to give 0.294 animals per km2 ( Table 13.3 Open ▸ ).
Table 13.2: Approach to Estimating Abundance in Different Sectors for the Firth of Tay and Adjacent Areas Based on Arso Civil et al. (2019) Habitat Preference Map
808 Within the Proposed Development array area (offshore), the density of bottlenose dolphin was taken as 0.0298 from SCANS-III (Hammond et al., 2021) as described in paragraph 805 ( Table 13.3 Open ▸ ).
Table 13.3: Summary of Bottlenose Dolphin Densities for Different Sections Within the Regional Marine Mammal Study Area
Summary of Annex II densities and population estimates
809 Table 13.4 Open ▸ presents density estimates for Annex II marine mammals in the Proposed Development marine mammal study area for use in quantifying the scale of effects as part of the appropriate assessments.
Table 13.4: Density Estimates and Population Assessments for Annex II Marine Mammals in the Proposed Development Marine Mammal Study Area
1 Site-specific densities (mean and seasonal peak) estimated from Proposed Development aerial digital survey data (2019 to 2021)
2 Average coastal density derived from five-year average from Arso Civil et al. (2021) with proportion at the outer Firth of Tay assigned using habitat preference modelling data from Arso Civil et al. (2019)
3 SCANS-III (Hammond et al., 2021)
4 Mean and maximum across the Proposed Development marine mammal study area based on at-sea mean density maps (Carter et al., 2020)
5 Mean monthly density based on site-specific Proposed Development aerial digital survey data (2019 to 2021) and density based on at-sea mean usage maps (Carter et al., 2020) across the Proposed Development marine mammal study area.
13.2.5 Approach to the In-combination Assessments
810 The in-combination assessment takes into account the impact associated with the Proposed Development together with other relevant plans, projects and activities. In-combination effects are therefore the combined effect of the Proposed Development in combination with the effects from a number of different projects, on the same receptor or resource. This is informed by the findings of the cumulative effects assessment presented in volume 2, chapter 10 of the Offshore EIA Report.
811 The projects and plans selected as relevant to the in-combination assessment presented within this section are based upon the results the assessment presented in volume 2, chapter 10 of the Offshore EIA Report. Each project or plan has been considered on a case by case basis for screening in or out of this assessment based upon data confidence, effect-receptor pathways and the spatial/temporal scales involved. The projects included in this in-combination assessment are detailed in Table 13.5 Open ▸ and volume 2, chapter 10 of the Offshore EIA Report.
812 The in-combination effects presented and assessed in this section have been selected from the details provided in volume 1, chapter 10 of the Offshore EIA Report as well as the information available on other projects and plans, to inform a maximum design scenario. Effects of greater adverse effects are not predicted to arise should any other development scenario, based on details within the Project Design Envelope (e.g. different wind turbine layout), to that assessed here, be taken forward in the final design scheme.
813 Where there is no spatial or temporal overlap with the activities during construction, operation or decommissioning of the Proposed Development, impacts associated with other projects listed in Table 13.5 Open ▸ may be excluded from further consideration. For the purposes of the assessment of impact on conservation objectives, in-combination effects have been screened in/out on the following basis:
- Injury/disturbance to marine mammals from elevated underwater noise during pile driving (construction phase) – the ZoI for pile driving can extend beyond the boundaries of proposed offshore wind farms and therefore, adopting a precautionary approach, the assessment has screened in projects within the regional marine mammal study area (harbour porpoise from the Southern North Sea SAC) and within the north-east of Scotland (bottlenose dolphin from Moray Firth SAC, grey seal from Berwickshire and North Northumberland Coast SAC and Isle of May SAC and harbour seal from the Firth of Tay and Eden Estuary SAC) whose construction phases overlap with the construction phase for the Proposed Development. Projects whose construction phase finishes in a year preceding the commencement of construction phase at the Proposed Development (2024) were screened in as the sequential piling at respective projects could lead to a longer duration of effect.
- Injury/disturbance to marine mammals from elevated underwater noise during site investigation surveys (pre-construction phase, operation and maintenance phase) – it is anticipated that the magnitude of the impacts will be of a similar scale to that described for the Proposed Development with the potential to experience disturbance by marine mammal receptors expected to be localised to within the boundaries of the respective projects. Therefore, the in-combination assessment has focussed only on site investigation surveys for those projects within the Firth of Forth and Tay region. Of these, very few projects have considered site-investigation surveys within the EIA. For pre-construction phase, where surveys are known to have been completed, this impact has been screened out of the in-combination assessment.
- Injury/disturbance to marine mammals from elevated underwater noise during UXO clearance (pre-construction phase) - the ZoI for UXO clearance can extend beyond the boundaries of other proposed offshore wind farms. Therefore, adopting a precautionary approach, the assessment has screened in projects within the regional marine mammal study area (harbour porpoise from the Southern North Sea SAC) and within the north-east of Scotland (bottlenose dolphin from Moray Firth SAC, grey seal from Berwickshire and North Northumberland Coast SAC and Isle of May SAC and harbour seal from the Firth of Tay and Eden Estuary SAC) whose construction phases (which would include pre-construction UXO clearance) overlap with the construction phase for the Proposed Development. Note, projects with completed UXO clearance campaigns are screened out of the assessment (e.g. Seagreen 1A Project). Projects whose construction phase finishes in a year preceding the commencement of construction phase at the Proposed Development (2024) were screened in as the sequential UXO clearance at respective projects could lead to a longer duration of effect.
- Injury and disturbance to marine mammals from elevated underwater noise due to vessel use and other activities (all phases) – it is expected that each project will contribute to the increase of vessel traffic and hence to the amount of vessel noise in the environment during the construction, operation and maintenance and decommissioning phases. However, the potential for marine mammal receptors to experience disturbance would be expected to be localised to within the close vicinity of the respective projects and as such the assessment has focussed only on projects within the Firth of Forth and Tay region. However, where there is no effect-receptor pathway, projects have been screened out from in-combination assessment.
- Changes in fish and shellfish communities affecting prey availability (all phases) – potential in-combination effects on fish and shellfish assemblages, as identified in volume 2, chapter 9 of the Offshore EIA Report, may have indirect effects on marine mammals. For the purposes of the fish and shellfish ecology assessment of effects, in-combination effects have been assessed within a representative 20 km buffer of the Proposed Development fish and shellfish ecology study area. This 25 km buffer applies to all impacts considered in the assessment, except underwater noise, where a larger buffer of 100 km has been used to account for the larger ZoI of impacts. Therefore, only the projects considered in volume 2, chapter 9 of the Offshore EIA Report are considered in the assessment of in-combination indirect impacts due to changes in fish and shellfish communities affecting prey availability.
814 The assessment of in-combination effects with relevant projects has focussed on information available in the public domain (e.g. where the impact has been identified in the scoping study (Tier 3 projects) or the environmental statement (Tier 2 projects)). In this regard, where an impact has been identified and screened in, there is considered to be a potential for in-combination effects. Therefore, the impact will be considered further. Impacts scoped out from individual assessments of respective projects are not considered further.