Summary of Interim Population Consequences of Disturbance (iPCoD) modelling

110. There is limited understanding of how behavioural disturbance and auditory injury affect survival and reproduction in individual marine mammals and consequently how this translates into effects at the population level. The iPCoD model was developed using a process of expert elicitation to determine how physiological and behavioural changes affect individual vital rates (i.e. the components of individual fitness that affect the probability of survival, production of offspring, growth rate and offspring survival).
111. Expert elicitation is a widely accepted process in conservation science whereby the opinions of many experts are combined when there is an urgent need for decisions to be made but a lack of empirical data with which to inform them. In the case of iPCoD, the marine mammal experts were asked for their opinion on how changes in hearing resulting from PTS and behavioural disturbance (equivalent to a score of 5* or higher on the ‘behavioural severity scale’ described by Southall et al. (2007)) associated with offshore renewable energy developments affect calf and juvenile survival and the probability of giving birth (Harwood et al., 2014). Experts were asked to estimate values for two parameters which determine the shape of the relationships between the number of days of disturbance experienced by an individual and its vital rates, thus providing parameter values for functions that form part of the iPCoD model (Harwood et al., 2014).
112. The iPCoD model simulates the mean population difference over time for an impacted versus and unimpacted population to provide comparison of the type of changes that could occur resulting from natural environmental variation, demographic stochasticity[6] and human-induced disturbance. The results are summarised in relation to the forecasted population size over time with forecasts made at certain timepoints (e.g. two, seven, 13, 19 and 25 years) after piling commences. In addition, the model calculates the ratio of the unimpacted to the impacted population size at these timepoints. A caveat of this model, however, is that the model does not account for density dependence and therefore the forecasts may be unrealistic as they assume that vital rates in the population will not alter as a result of density dependent factors (e.g. competition).
113. Whilst there are many limitations to this process, iPCoD modelling was requested by statutory consultees as part of the offshore EIA Scoping process as it represents the best available approach for the species considered in this assessment ( Table 10.9   Open ▸ ). In addition, any uncertainties have been offset as far as possible by adopting a precautionary approach at all stages of the assessment from the maximum design parameters in the project envelope, conservatism in the subsea noise model and adoption of precautionary estimates to represent the densities of key species. Thus, the result from the iPCoD modelling undertaken for the Proposed Development is considered to be inherently cautious and should be interpreted as such.
114. Population modelling using iPCoD was carried out for the following species (agree through with marine mammal Road Map process) due to the potential number of animals affected relative to the relevant MU populations (and SCANS III abundances for harbour porpoise and minke whale):

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

Construction Phase

Magnitude of Impact

115. The assessment of magnitude with respect to auditory injury is presented paragraph 117 et seq. based on a species-specific basis, where the maximum adverse scenario is identified for each species (i.e. based on the dual metrics (SPLpk and SELcum) and whichever of the two conversion factors (1% constant and 4% reducing to 0.5%) results in the largest effect range). The effect ranges for injury presented in the quantitative assessment considered designed-in measures in the form of low hammer initiation and soft start ramp up. The assessment of magnitude for behavioural disturbance presented in paragraph 138 et seq. is based on the 1% constant conversion factor.

Auditory injury

Harbour porpoise

116. The maximum range for injury to harbour porpoise was estimated as 449 m based on SPLpk and using the 1% constant conversion factor ( Table 10.26   Open ▸ ; see volume 3, appendix 10.5 for estimates using a range of conversion factors). The effect range is based on SPLpk for the maximum hammer energy but noting that during soft start initiation this range will be considerably smaller. The most conservative number of individuals that could be potentially injured within the maximum range of 449 m, based on the peak seasonal densities from site-specific survey data and concurrent piling of wind turbines at 4,000 kJ, was estimated as less than one harbour porpoise.
117. To further reduce the potential for injury, designed-in measures will be adopted as part of a MMMP ( Table 10.21   Open ▸ ). These measures will involve the use of visual and acoustic searches over a pre-defined mitigation zone (see volume 4, appendix 23).  The 449 m falls within the standard JNCC mitigation zone of 500 m (JNCC, 2010a). There are, however, often difficulties in detecting marine mammals (particularly harbour porpoise) over large ranges (McGarry et al., 2017). Visual surveys note that there is often a significant decline in detection rate with increasing sea state (Embling et al., 2010; Leaper et al., 2015).Additional mitigation applied in the form of ADDs will be applied as secondary mitigation further minimise any residual risk of injury subject to the limitations highlighted above (see paragraph 244 et seq. for further details).
118. The total duration of piling is estimated at over 16,368 hours (wind turbines and OSPs/Offshore convertor station platforms) for the absolute maximum temporal scenario. Up to five piles per 24-hour period will be installed at wind turbine foundations (assuming concurrent piling with two vessels) and up to three piles will be installed per 24 hours at OSPs/Offshore convertor station platforms/ Offshore convertor station platform foundations (assuming a single piling vessel). It is anticipated that piling could occur for up to 372 days during construction of foundations (wind turbines and OSPs/Offshore convertor station platform). This will be intermittent over a 52-month piling phase within the total construction period of 96 months.
119. Harbour porpoise typically live between 12 and 24 years and give birth once a year (Fisher and Harrison, 1970). The duration of piling could potentially overlap with a maximum of five breeding cycles. However, it is worth noting that piling will be intermittent and will occur over small timespan (372 days) within piling phase (52 months). The duration of the effect in the context of the life cycle of harbour porpoise is classified as medium term, as the risk could occur over a meaningful proportion of the lifespan of these species.

Table 10.26: Summary of SPLpk and SELcum Injury Ranges and Areas of Effect for Harbour Porpoise due to Impact Piling for Wind Turbine and OSPs/Offshore Convertor Station Platform Jacket Foundations (Absolute Maximum Hammer Energy) Using 1% Constant Conversion Factor

120. With designed-in measures in place including soft start and an MMMP, the magnitude of the impact would result in a low risk of injury as the scale of effects (range and number of animals potentially injured) is small (paragraph 117). Considering the duration of the impact the risk (albeit very low) could occur over the medium term. The magnitude of the assessment has been, conservatively, concluded considering the limitations in the efficacy of the pre-start visual and acoustic monitoring within respect to the potential variability of the sea conditions (sea state and visibility) at the time of piling.
121. The impact (elevated underwater noise from piling) is predicted to be of local spatial extent, medium term duration, intermittent and low reversibility (PTS). It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Bottlenose dolphin and white-beaked dolphin

122. The maximum range for injury to bottlenose and white-beaked dolphin was estimated as 43 m based on SPLpk and using the 1% constant conversion factor ( Table 10.27   Open ▸ ; see volume 3, appendix 10.5 for estimates using a range of conversion factors). Therefore, the spatial extent of PTS will be localised for all piling scenarios. Considering the most conservative scenario, which is the highest coastal bottlenose dolphin density (for outer Firth of Tay region, see volume 3, appendix 10.2) and full hammer energy, there will be less than one animal that could be potentially injured within the maximum range of 43 m. The same applies to white-beaked dolphins, as considering the most conservative scenario (concurrent piling of wind turbines at 4,000 kJ), less than one animal could be potentially injured.
123. It is worth noting that this injury range will not overlap with the coastal areas where the highest density of bottlenose dolphins is encountered. To further reduce the potential to experience injury, designed-in measures, involving visual and acoustic monitoring, will be adopted as part of a MMMP ( Table 10.21   Open ▸ ). For all marine mammals, secondary mitigation will be applied in a form of ADDs to minimise residual risk of injury (see paragraph 244 seq. for further details).
124. The total duration of piling is presented in paragraph 119. Bottlenose dolphin typically live between 20 and 30 years, females reproduce every three to six years. Given that gestation takes 12 months followed by calves suckling of 18 to 24 months, the duration of piling could potentially overlap with a maximum of two breeding cycles. Less is known about reproductive behaviour of white-beaked dolphins; however, it has been reported that females are pregnant for about 11 months and give birth to a single calf (Reid et al., 2003). Therefore, the duration of piling could potentially overlap with approximately five breeding cycles of white-beaked dolphin. However, it is worth noting that piling will be intermittent and will occur over small timespan (372 days) within piling phase (52 months). Considering the above, the duration of the effect in the context of life cycle of bottlenose dolphin and white-beaked dolphin is classified as medium term.

Table 10.27: Summary of SPLpk and SELcum Injury Ranges and Areas of Effect for Bottlenose Dolphin and White-Beaked Dolphin due to Impact Piling for Wind Turbine and OSPs/Offshore Convertor Station Platform Jacket Foundations (Absolute Maximum Hammer Energy) Using 1% Constant Conversion Factor

1 N/E = Threshold not exceeded

125. With designed-in measures in place including soft start and an MMMP, the magnitude of the impact would result in a negligible risk of injury to bottlenose dolphin and white-beaked dolphin as the scale of effects (range and number of animals potentially injured) is very small. Considering the duration of the impact, the risk (albeit negligible) could occur over a meaningful proportion of the lifespan of these species and therefore is classed as medium term.
126. The impact (elevated underwater noise from piling) is predicted to be of local spatial extent, medium term duration, intermittent and low reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Minke whale

127. The maximum range for injury to minke whale was estimated as 2,319 m based on SELcum and using the 4% reducing to 0.5% conversion factor ( Table 10.28   Open ▸ ; see volume 3, appendix 10.5 for estimates using a range of conversion factors). Injury ranges predicted using SELcum are considered very precautionary for reasons described in paragraph 95 and therefore may be an overestimate of the effect range. The most conservative number of individuals that could be potentially injured within the maximum range of 2,319 was estimated as less than one minke whale. In comparison, maximum instantaneous injury ranges predicted using different conversion at the maximum 4,000 kJ hammer energy were: 83 m for 4% reducing to 0.5%, 109 m for 1% constant and 359 m for 10% constant (as requested by consultees during Road Map Meeting #4, see Table 10.9   Open ▸ ). In addition, the 2,319 m range is based on a concurrent scenario of two adjacent piling vessels; for single piling the injury range would be reduced to a maximum of 1,030 m ( Table 10.28   Open ▸ ). Taking into account the most conservative scenario (concurrent piling of wind turbines at 4,000 kJ), it is estimated there will be less than one animal that could be potentially injured within the maximum range of 2,319 m.
128. To reduce the potential to experience injury, designed-in measures will be adopted as part of a MMMP (see Table 10.21   Open ▸ ). These measures will involve the use of visual and acoustic searches over a pre-defined mitigation zone (see volume 4, appendix 23). Given that injury could occur over ranges greater than the standard 500 m mitigation zone (JNCC, 2010a) and subject to the limitations of standard approaches (paragraph 118), secondary mitigation will be applied in a form of ADDs to minimise residual risk of injury (see paragraph 244 et seq. for further details).
129. The total duration of piling is presented in paragraph 119. Minke whale typically lives up to 60 years and the gestation period is believed to be around ten months. As females give birth to a calf every 12 to 14 months, the duration of piling could potentially overlap with a maximum of five breeding cycles. However, it is worth noting that piling will be intermittent and will occur over small timespan (372 days) within piling phase (52 months). Considering the above, the duration of the effect in the context of life cycle of minke whale is classified as medium term, as the risk could occur over a meaningful proportion of the lifespan of this species.

Table 10.28: Summary of SPLpk and SELcum Injury Ranges and Areas of Effect for Minke Whale due to Impact Piling for Wind Turbine and OSPs/Offshore Convertor Station Platform Jacket Foundations (Absolute Maximum Hammer Energy) Using 4% Reducing to 0.5% Conversion Factor

130. With designed-in measures in place including soft start and an MMMP, the magnitude of the impact would result in a low risk of injury to minke whale as the scale of effects (range and number of animals potentially injured) is small. There may, however, be a residual risk of injury to some individuals of this species as the radius of effect for PTS (up to 2,319 m) is likely to exceed the range over which effective visual and acoustic monitoring of minke whale can occur.
131. The impact (elevated underwater noise from piling) is predicted to be of local spatial extent, medium term duration, intermittent and low reversibility. It is predicted that the impact will affect the receptor directly. Given that the maximum injury range may not be fully mitigatable by designed-in measures only (see Table 10.21   Open ▸ ), the magnitude is considered to be medium.

Harbour seal and grey seal

132. The maximum range for injury to harbour and grey seal was estimated as 118 m based on SPLpk and using the 1% constant conversion factor ( Table 10.29   Open ▸ ; see volume 3, appendix 10.5 for estimates using a range of conversion factors). The ranges are low due to the soft-start initiation of piling which is likely to reduce the probability of marine mammals being in proximity to piling activities on full power. Therefore, the spatial extent of PTS will be localised for all piling scenarios. Taking into account the most conservative scenario, maximum density for both species (based on mean at-sea seal usage from Carter et al. 2020) as well as concurrent piling of wind turbines at 4,000 kJ, there will be less than one animal (of each species) that could be potentially injured within the maximum range of 118 m.
133. To reduce the potential to experience injury, designed-in measures, involving visual and acoustic monitoring, will be adopted as part of a MMMP (see Table 10.21   Open ▸ ). For all marine mammals, secondary mitigation will be applied in a form of ADDs to minimise residual risk of injury (see paragraph 244 et seq. for further details).
134. The total duration of piling is presented in paragraph 119. Both species of seal typically live between 20 to 30 years with gestation lasting between ten to 11 months (SCOS, 2015; SCOS, 2018), thus the duration of piling could potentially overlap with a maximum of five breeding cycles. However, it is worth noting that piling will be intermittent and will occur over small timespan (372 days) within piling phase (52 months). Considering the above, the duration of the effect in the context of life cycle of harbour and grey seal is classified as medium term.

Table 10.29: Summary of SPLpk and SELcum Injury Ranges and Areas of Effect for Harbour Seal and Grey Seal due to Impact Piling for Wind Turbine and OSPs/Offshore Convertor Station Platform Jacket Foundations (Absolute Maximum Hammer Energy) Using 1% Constant Conversion Factor

1 N/E = Threshold not exceeded

135. With designed-in measures in place including soft start and an MMMP, the magnitude of the impact would result in a negligible risk of injury to harbour and grey seal as the scale of effects (range and number of animals potentially injured) is very small. Considering the duration of the impact, the risks (albeit negligible) could occur over a meaningful proportion of the lifespan of these species.
136. The impact (elevated underwater noise from piling) is predicted to be of local spatial extent, medium term duration, intermittent and low reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Behavioural disturbance

137. The numbers of animals predicted to experience potential disturbance as a result of different piling scenarios is presented in this section ( Table 10.30   Open ▸ to Table 10.35   Open ▸ ). Predictions are based on the assumptions of the dose response relationship described in paragraphs 97 et seq. using the SELss metric. The estimated numbers of animals potentially disturbed are based on the maximum adverse piling scenario which describe the maximum potential impact for each species. This has been defined with reference to either the extent of the effect, or spatial overlap with abundance hotspots (e.g. areas near the coast).
138. Scientific literature suggests that inshore and offshore populations of bottlenose dolphins are often ecologically and genetically discrete (Hoelzel et al., 1998). Therefore, this assessment considered two separate populations of bottlenose dolphin; those distributed in coastal waters as well as offshore.
139. Assessment of magnitude for behavioural disturbance presented in this section is based on 1% constant conversion factor unless stated otherwise.

Harbour porpoise

140. Up to 2,822 animals (based on seasonal peak density) are predicted to experience potential disturbance from concurrent piling at a maximum hammer energy of 4,000 kJ ( Figure 10.10   Open ▸ ). This equates to 0.81% of the NS MU population and 7.3% of SCANS III Block R estimated abundance ( Table 10.30   Open ▸ ). For comparison, the number of animals that could be potentially disturbed during the same piling scenario but using a 4% reducing to 0.5% conversion factor has been conservatively assessed as up to 2,090 harbour porpoises. This equates to 0.60% of the NS MU population and 5.41% of SCANS III Block R estimated abundance (see volume 3, appendix 10.5 for estimates using a range of conversion factors).
141. The estimated numbers of individuals potentially impacted are based on conservative densities. Although the distribution of harbour porpoise across the Proposed Development marine mammal study area was found to be uneven (see volume 3, appendix 10.2 for more details), it was assumed that the peak seasonal density of 0.826 animals per km2 is uniformly distributed within all noise contours to provide a precautionary assessment. Comparison of the estimated number of harbour porpoise potentially disturbed using the mean monthly density derived from the Proposed Development aerial digital survey data (0.299 animals per km2) or using the modelled density estimate for SCANS III for this area (0.599 animals per km2) demonstrates that the peak seasonal density estimates generate highly precautionary results. For example, based on the mean monthly density from aerial data or SCANS III data, the number of harbour porpoise affected by possible disturbance for the maximum adverse scenario (concurrent piling at 4,000 kJ) would be 1,021 animals (0.29% of the NS MU) or 2,047 animals (0.59% of the NS MU) respectively compared to 2,822 animals (0.81% of the NS MU) using peak seasonal density.  
142. Additionally, there is a number of conservative assumptions in subsea noise model, as the maximum hammer energy of 4,000 kJ is unlikely to be reached at all piling locations (see paragraph 95 for more details). It is therefore reasonable to consider the number of animals potentially disturbed could be based on estimates for a realistic average maximum hammer energy of 3,000 kJ (using 1% constant conversion factor) (volume 3, appendix 10.5), where up to 2,378 animals have the potential to experience disturbance, which represents 0.69% of the NS MU population 6.15% of SCANS III Block R estimated abundance ( Table 10.30   Open ▸ ).
143. Harbour porpoise could also be potentially disturbed within the zone of possible disturbance during single piling at a wind turbine or an OSPs/Offshore convertor station platform at a maximum hammer energy of 4,000 kJ ( Figure 10.11   Open ▸ ), with up to 1,754 (0.51% of the NS MU population and 4.54% of SCANS III Block R estimated abundance) animals affected based on the seasonal peak density (using 1% constant conversion factor, Table 10.30   Open ▸ ).

Figure 10.10: Unweighted SELss Contours Due to Concurrent Impact Piling of Wind Turbine Piles at Maximum Hammer Energy (4,000 kJ) Using 1% Constant Conversion Factor

Figure 10.11: Unweighted SELss Contours Due to Single Piling at Maximum Hammer Energy (4,000 kJ) Using 1% Constant Conversion Factor

Table 10.30: Number of Harbour Porpoises Predicted to be Disturbed within Unweighted SELss Noise Contours as a Result of Different Piling Scenarios. Average Number is Based on the Monthly Average Density whilst Maximum is Based on the Seasonal Peak Density Using 1% Constant Conversion Factor

144. As identified in appendix 10.2, four European marine sites designated for protection of harbour porpoise are located within the regional marine mammal study area. The Southern North Sea is located in the closest proximity to the Proposed Development array area (i.e. 146 km as crow flies). Doggersbank SAC, Doggerbank SCI and Klaverbank SAC are located 295 km, 314 km and 332 km from the Proposed Development array area, respectively. There is no potential for overlap of noise disturbance contours with any of these designated sites. Given that harbour porpoise can travel over large distances, there is a possibility that a small number of individuals from these SACs/SCI populations may be occasionally present within the disturbance contours. For the closest European marine site (the Southern North Sea SA), the population is estimated at between 20,237 and 41,538 individuals (see volume 2, appendix 10.2). Full consideration of potential for AeoI is also given in RIAA (SSER, 2022d).
145. As previously described in paragraph 120 et seq., the duration of piling could potentially affect harbour porpoise over a maximum of five breeding cycles. The magnitude of the impact could also result in a small but measurable alteration to the distribution of marine mammals during piling only (372 days over 52 months) and may affect the fecundity of small proportion of the population (up to 0.81% of the NS MU at any one time) over the medium term.
146. As agreed with consultees ( Table 10.9   Open ▸ ) population modelling was carried out to explore the potential of disturbance during piling to affect the population trajectory over time and provide additional certainty in the predictions of the assessment of effects. Results of the iPCoD modelling for harbour porpoise against the MU population showed that the median of the ratio of the impacted population to the unimpacted population was 99.9% at 25 years regardless of the conversion factor scenario assessed (1% constant, 4% reducing to 0.5% or 10% reducing to 1% conversion factors). Small differences in population size over time between the impacted and unimpacted population falls within the natural variance of the population as can be seen in Figure 10.12   Open ▸ , where results of simulated population number (y axis) are similar on either side of the median line for both, impacted and unimpacted population. Therefore, it was considered that there is no potential for a long-term effect on this species (see volume 3, appendix 10.4 for more details). This was also the case when considered against the SCANS III Block R as a vulnerable subpopulation ( Figure 10.12   Open ▸ ).

Figure 10.12: Simulated Harbour Porpoise Population Sizes for Both the Baseline and the Impacted Populations Under the Maximum Adverse Scenario Using 1% Conversion Factor and 11.1% Vulnerable Subpopulation.

147. The impact (elevated underwater noise from piling) is predicted to be of regional spatial extent, medium term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptor directly. The results suggest that in short to medium term the magnitude would be low. Recovery is considered likely to occur soon after cessation of piling and there were predicted to be no long-term population-level effects on harbour porpoise as corroborated by the population modelling. The magnitude is therefore considered to be low.

Bottlenose dolphin

148. Given that bottlenose dolphin distribution may be coastal or offshore, a dual approach has been taken to estimate the number of animals potentially disturbed. The noise contours predicted to result from piling were overlaid with 2 m to 20 m depth contours and the number of animals potentially disturbed within those areas was calculated. Estimates were based on the area of overlap and an average density of 0.197 animals per km2 from Peterhead to Farne Islands. This is with the exception of the outer Firth of Tay, where the density is higher with 0.294 animals per km2 ( Figure 10.13   Open ▸ ). For the purpose of this assessment it has been assumed that density of 0.294 animals per km2 is uniformly distributed within the 2 m to 20 m depth contour of outer Firth of Tay. This approach is based on the assumption that half of the CES MU population is present within the Firth of Tay and adjacent waters and therefore this approach is highly precautionary. Given that both densities, 0.197 and 0.294 animals per km2, were obtained from coastal distribution studies, the number of bottlenose dolphins potentially disturbed during piling in offshore areas was calculated using densities from SCANS III Block R data with 0.0298 animals per km2 ( Table 10.31   Open ▸ ).

Figure 10.13: Proposed Development and Bottlenose Dolphin Coastal Densities Overlaid with Unweighted SELss Contours Due to Concurrent Impact Piling of Wind Turbine Piles at Maximum Hammer Energy (4,000 kJ) Using 1% Constant Conversion Factor

Figure 10.14: Proposed Development and Bottlenose Dolphin Coastal Densities Overlaid with Unweighted SELss Noise Contours Due to Single Piling at Maximum Hammer Energy (4,000 kJ) Using 1% Constant Conversion Factor

149. As seen in Figure 10.13   Open ▸ , the outermost noise contours predicted from the maximum hammer energy of 4,000 kJ reach the coastal areas and therefore overlap with the key distribution of bottlenose dolphin. Up to five animals are predicted to have the potential to experience disturbance from concurrent piling in coastal waters, which equates to 2.25% of the CES MU population ( Table 10.31   Open ▸ ). For comparison, the number of animals that could potentially be disturbed during the same piling scenario but using 4% reducing to 0.5% conversion factor has been conservatively assessed as up to four bottlenose dolphins, which equates to 1.38% of the CES MU population (volume 3, appendix 10.5 for estimates using a range of conversion factors).
150. It is reasonable to consider that disturbance could be predicted by a realistic average maximum hammer energy of 3,000 kJ (see paragraph 143), where up to four animals could potentially be disturbed during concurrent piling at wind turbine foundations, representing 1.71% of the CES MU population (volume 3, appendix 10.5).
151. Coastal bottlenose dolphin could also be potentially disturbed during single piling at a wind turbine or an OSPs/Offshore convertor station platform, with up to four (1.49% of the CES MU population) animals affected for the 4,000 kJ hammer energy ( Figure 10.14   Open ▸ , Table 10.31   Open ▸ ).
152. Since the outer contours reach areas occupied by the coastal bottlenose dolphin population, the potential for barrier effects (e.g. restricting animals from moving along the coast) must also be considered for both concurrent and single piling scenarios. Received noise levels within the 2 m to 20 m depth contour are predicted to reach maximum SELss levels of 130 dB. This is equivalent to the outer limit of the US NMFS threshold (140 dBrms) for mild disturbance (NMFS, 2005) and therefore likely to elicit less severe disturbance reactions compared to higher received levels of 150 dB SELss (=160 dBrms for strong disturbance).
153. According to the behavioural response severity matrix suggested by Southall et al. (2021) low level disturbance (scoring between 0 to 3 on 0 to 9 scale) could lead to mild disruptions of normal behaviours but prolonged or sustained behavioural effects, including displacement are unlikely to occur. Further discussion on the sensitivity of bottlenose dolphin is provided in paragraph 219 et seq. (with respect to survival, feeding and reproductive behaviours) but for the purposes of assessing magnitude, it is considered that up to four or five animals from the coastal population (depending on the scenario, Table 10.31   Open ▸ ) could experience mild disturbance but that this is unlikely to lead to barrier effects as animals are unlikely to be excluded from the coastal areas.
154. Potential effects on the offshore bottlenose dolphin population were also assessed. During concurrent piling at maximum 4,000 kJ hammer energy, up to 102 individuals occurring in offshore waters have the potential to experience disturbance ( Figure 10.13   Open ▸ ). This equates to 5.29% of the SCANS III Block R estimated abundance. Estimates for 4,000 kJ hammer energy are shown to be precautionary if compared with estimates based on concurrent piling at a realistic average maximum hammer energy of 3,000 kJ, where up to 86 animals could potentially be disturbed (4.46% of the SCANS III Block R estimated abundance; volume 3, appendix 10.5). For the single piling scenario with a hammer energy of 4,000 kJ, up to 64 individuals have the potential to experience disturbance offshore, which equates to 3.29% of the SCANS III Block R estimated abundance ( Figure 10.14   Open ▸ ).

Table 10.31: Number of Bottlenose Dolphins Predicted to be Disturbed within Unweighted SELss Noise Contours as a Result of Different Piling Scenarios Using 1% Constant conversion factor

1 CES MU population was used as a reference population for individuals disturbed in coastal areas.

2 SCANS III bottlenose dolphin estimated abundance was used as a reference population individuals disturbed in coastal areas.

155. The maximum numbers presented in Table 10.31   Open ▸ are considered to be conservative as these are based on highly precautionary coastal and offshore density estimates (SCANS III Block R density of 0.0298 individuals per km2). As described in more detail in volume 3, appendix 10.2, bottlenose dolphins were recorded in low numbers during the DAS and only on two occasions within the 24-month survey period (encounter rate varied between 0.0005 individuals per km in October 2019 and 0.0024 individuals per km in April 2021). Considering the above, the estimated number of bottlenose dolphins with the potential to be disturbed in offshore waters, should be interpreted with caution as this is likely to be an overestimate.
156. As identified in volume 3, appendix 10.2, the Moray Firth SAC designated for protection of bottlenose dolphin is located within the regional marine mammal study area, approximately 167 km from the Proposed Development array area. There is no potential for overlap of noise disturbance contours with this designated site, however, noise contours have the potential to overlap with the main distributional range of its population. It is important to note that recent studies have shown that although the numbers of bottlenose dolphin using the Moray Firth SAC appear to be stable, the proportion of the population using these waters has declined due to overall increase in population size and expansion of range along the eastern coast (in southern direction, for more details see volume 3, appendix 10.2). Full consideration of potential for AeoI is given in RIAA (SSER, 2022d).
157. As previously described in paragraph 125 et seq., the duration of piling could potentially affect bottlenose dolphin over a maximum of three breeding cycles. The magnitude of the impact could also result in a small but measurable alteration to the distribution of marine mammals during piling only (372 days over 52 months) and may affect the fecundity of some individuals (up to 2.25% of the CES MU population at any one time) over the medium term.
158. As agreed with consultees ( Table 10.9   Open ▸ ) population modelling was carried out to explore the potential of disturbance during piling to affect the population trajectory over time and provide additional certainty in the predictions of the assessment of effects. Results of the iPCoD modelling for bottlenose dolphin against the MU population showed that the median of the ratio of the impacted population to the unimpacted population was between 100% at 25 years for all conversion factor scenarios assessed (1% constant, 4% reducing to 0.5% or 10% reducing to 1% conversion factors). Very small differences in population size over time between the impacted and unimpacted population fall within the natural variance of the population as can be seen in Figure 10.15   Open ▸ , where results of simulated population number (y axis) are similar on either side of the median line for both, impacted and unimpacted population. Therefore, it was considered that there is no potential for a long-term effect on this species ( Figure 10.15   Open ▸ , see volume 3, appendix 10.4 for more details).

Figure 10.15: Simulated Bottlenose Dolphin Population Sizes for Both the Baseline and the Impacted Populations Under the Maximum Adverse Scenario Using 1% Conversion Factor and no Vulnerable Subpopulation.

159. The impact is predicted to be of regional spatial extent, medium term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude in short to medium term could be considered as medium, however because population modelling results shown that piling activities will not have adverse effect on the bottlenose dolphin population in the long term, the magnitude is therefore considered to be low.

White-beaked dolphin

160. Based on SCANS III block R white-beaked dolphin density estimates, up to 830 animals have the potential to experience disturbance during concurrent piling at a maximum hammer energy of 4,000 kJ. This equates to 1.89% of the CGNS MU population and 5.0% of the SCANS III block R estimated population abundance ( Table 10.32   Open ▸ ). The noise contours associated with maximum adverse piling scenarios (i.e. those at a maximum hammer energy of 4,000 kJ) are the same as those assessed for harbour porpoise (i.e. based on the piled location that could lead to the largest propagation ranges, Figure 10.10   Open ▸ ). For comparison, the number of animals that could be potentially disturbed during the same piling scenario as above but using 4% reducing to 0.5% conversion factor has been conservatively assessed as up to 615 white-beaked dolphins, which equates to 1.40% of the CGNS MU population (volume 3, appendix 10.5 for estimates using a range of conversion factors).
161. It is reasonable to consider that disturbance could be predicted by a realistic average maximum hammer energy of 3,000 kJ (see paragraph 143), where up to 700 animals could potentially be disturbed during concurrent piling at wind turbine foundations, representing 1.59% of the CGNS MU population and 4.3% of the SCANS III block R estimated abundance (volume 3, appendix 10.5).
162. White-beaked dolphin could also be potentially disturbed within the zone of possible disturbance during single piling at a wind turbine or OSPs/Offshore convertor station platform foundation at a maximum hammer energy of 4,000 kJ ( Figure 10.11   Open ▸ ), with up to 516 (1.17% of the CGNS MU population and 3.1% of the SCANS III block R estimated abundance) animals affected ( Table 10.32   Open ▸ ).

Table 10.32: Number of White-Beaked Dolphins Predicted to be Disturbed in the Vicinity of the Proposed Development as a Result of Different Piling Scenarios Using 1% Constant Conversion Factor

163. The maximum numbers presented in Table 10.32   Open ▸ are considered to be conservative as these are based on the SCANS III block R densities (0.243 animals per km2) and assume uniform distribution. As described in more detail in volume 3, appendix 10.2, the mean monthly density of white-beaked dolphin (corrected for availability bias) estimated from the Proposed Development aerial digital data was 0.05 individuals per km2. These results are in line with findings of Grellier and Lacey (2011) aerial survey analysis, where minimum density estimates for Firths of Forth and Tay waters during summer (peak) were assessed as 0.052 individuals per km2. If maximum numbers were compared with estimates based on the latter density, the number of white-beaked dolphin potentially disturbed for the maximum adverse scenario (concurrent piling at 4,000 kJ) would be 177 animals (0.40% of the CGNS MU), compared to 828 animals (1.88% of the CGNS MU) based on SCANS III Block R density estimates. Therefore, the number of white-beaked dolphins that may be disturbed as a result of all piling scenarios should be interpreted with caution as these animals are likely to be present in lower densities.
164. As previously described in paragraph 125 et seq., the duration of piling could potentially affect white-beaked dolphin over a maximum of five breeding cycles. The magnitude of the impact could also result in a small but measurable alteration to the distribution of marine mammals during piling only (372 days over 52 months) and may affect fecundity of some individuals (up to 1.89% of the CGNS MU population) over the medium term. The area of effect is however small in relation to the extensive distribution of the population for this species (Celtic and Greater North Seas).
165. Since iPCoD did not facilitate modelling for white-beaked dolphin, as agreed with consultees ( Table 10.9   Open ▸ ) no population modelling was carried out for this species.
166. The impact is predicted to be of regional spatial extent, medium term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Minke whale

167. Based on SCANS III block R minke whale density estimates, up to 132 animals have the potential to be disturbed as a result of concurrent piling at a maximum hammer energy of 4,000 kJ, which equates to 0.66% of the CGNS MU and 5.3% of the SCANS III block R estimated abundance ( Table 10.33   Open ▸ ). The noise contours associated with maximum adverse piling scenarios (i.e. those at a maximum hammer energy of 4,000 kJ) are the same as those assessed for harbour porpoise ( Figure 10.10   Open ▸ ). For comparison, the number of animals that could be potentially disturbed during the same piling scenario but using 4% reducing to 0.5% conversion factor has been conservatively assessed as up to 97 minke whales, which equates to 0.49% of the CES MU population (volume 3, appendix 10.5 for estimates using a range of conversion factors).
168. The maximum numbers presented in Table 10.33   Open ▸ are considered to be conservative as these are based on the SCANS III Block R densities and assume uniform distribution. Minke whale exhibit a temporal distribution, with most sightings in continental shelf waters occurring between May and September. SCANS III surveys were carried out during summer months, and therefore density values, and subsequently predicted numbers to be disturbed for minke whale will be overly conservative for piling activities occurring during winter months. As described in more detail in volume 3, appendix 10.2, mean monthly density of minke whale (corrected for availability bias) estimated from the Proposed Development aerial digital data was 0.016 individuals per km2. If maximum numbers were compared with estimates based on this density, the number of minke whale potentially disturbed using the maximum adverse scenario (concurrent piling at 4,000 kJ) would be 55 animals (0.27% of the CGNS MU), compared to 132 animals (0.66% of the CGNS MU) based on SCANS III Block R density estimates. Therefore, the number of minke whales disturbed as a result of all piling scenarios should be interpreted with caution as these animals are likely to be present in lower densities.
169. It is reasonable to consider that disturbance could be predicted by a realistic average maximum hammer energy of 3,000 kJ (see paragraph 143) where up to 112 animals could potentially be disturbed during concurrent piling at wind turbine foundations, representing 0.55% of the CGNS MU population and 4.5% of the SCANS III Block R estimated abundance (volume 3, appendix 10.5).
170. Minke whale could also be potentially disturbed within the zone of possible disturbance during single piling at a wind turbine or an OSPs/Offshore convertor station platform at a maximum hammer energy of 4,000 kJ (noise contours presented in Figure 10.11   Open ▸ ), with up to 82 (0.41% of the CGNS MU population and 3.2% of the SCANS III Block R estimated abundance) animals affected ( Table 10.33   Open ▸ ).

Table 10.33: Number of Minke Whales Predicted to be Disturbed within Unweighted SELss Noise Contours as a Result of Different Piling Scenarios Using 1% Constant Conversion Factor

171. As previously described in paragraph 130 et seq., the duration of piling could potentially affect minke whale over a maximum of five breeding cycles. The magnitude of the impact could result in a small but measurable alteration to the distribution of marine mammals during piling only (372 days over 52 months) and may affect the fecundity of some individuals (up to 0.66% of the GCNS MU population at any one time) over the medium term. The area of effect is however small in relation to the extensive distribution of the population for this species (Celtic and Greater North Seas).
172. As agreed with consultees ( Table 10.9   Open ▸ ) population modelling was carried out to explore the potential of disturbance during piling to affect the population trajectory over time and provide additional certainty in the predictions of the assessment of effects. Results of the iPCoD modelling for minke whale against the MU population showed that the median of the ratio of the impacted population to the unimpacted population was 98.9% at 25 years regardless of the conversion factor scenario assessed (1% constant, 4% reducing to 0.5% or 10% reducing to 1% conversion factors). Small differences in population size over time between the impacted and unimpacted population fall within the natural variance of the population as can be seen in Figure 10.16   Open ▸ , where results of simulated population number (y axis) are similar on either side of the median line for both, impacted and unimpacted population. Therefore, it was considered that there is no potential for a long-term effect on this species (see volume 3, appendix 10.4 for more details). This was also the case when considered against the SCANS III Block R as a vulnerable subpopulation ( Figure 10.16   Open ▸ ).

Figure 10.16: Simulated Minke Whale Population Sizes for Both the Baseline and the Impacted Populations Under the Maximum Adverse Scenario Using 1% Conversion Factor and 11.1% Vulnerable Subpopulation.

173. The impact is predicted to be of regional spatial extent, medium term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude in short to medium term is predicted to be low. Recovery is considered likely to occur soon after cessation of piling and there were predicted to be no long-term population-level effects on minke whale as corroborated by the population modelling. The magnitude is therefore considered to be low.

Harbour seal

174. The magnitude of effects with respect to disturbance was initially estimated using two approaches. The first used the representative maximum species density value, derived from Carter et al. (2020) across Proposed Development array area and Proposed Development export cable corridor (see volume 3, appendix 10.2 for more details) and, assuming uniform densities across the site, multiplied this value by the area of effect. The second estimate was achieved by overlaying the noise contours on the spatial at-sea density map provided by Carter et al. (2020) and summing the values for all cells where more than 50% of the cell lay within a contour. For the first approach the most precautionary estimate was derived from the largest area of effect (i.e. whichever location and scenario leads to the maximum area disturbed at any one time). For the second approach, the modelled location was more important as, where piling occurs closer to the coast, the areas of disturbance are more likely to overlap with hotspots where higher densities of harbour seal have been predicted (i.e. inner Firth of Forth and Firth of Tay; Figure 10.17   Open ▸ ).
175. Both approaches were explored to determine which would lead to the most precautionary assessment in terms of number of individuals disturbed. Figure 10.17   Open ▸ to Figure 10.18   Open ▸ illustrates the piling locations considered in the assessment and shows that in both cases the outermost 135 dB behavioural disturbance contours do not overlap with areas of density hotspots for this species. Therefore, the most precautionary values were derived using the largest areas of effect for the single and concurrent scenarios (as presented in Figure 10.19   Open ▸ and Figure 10.11   Open ▸ ) multiplied by the maximum density estimate from Table 10.13   Open ▸ and have been presented in paragraph 177 et seq. The application of this approach is considered to be precautionary, as realistically the density of harbour seal will vary and therefore will not reach a maximum value across all parts of the Proposed Development marine mammal study area
176. Up to three animals were predicted to experience potential disturbance from concurrent piling at a maximum hammer energy of 4,000 kJ ( Figure 10.10   Open ▸ ). This equates to 0.39% of the ES plus North-east England (NE) Mus population ( Table 10.34   Open ▸ ). For comparison, the number of animals that could be potentially disturbed during the same piling scenario but using 4% reducing to 0.5% conversion factor has been conservatively assessed as up to two harbour seals, which equates to 0.27% of the ES plus NE MU population (volume 3, appendix 10.5 for estimates using various conversion factor).
177. The maximum numbers of harbour seal individuals that could be potentially disturbed are considered conservative as they are based on the most precautionary density values (0.002 animals per km2) taken from Carter et al. (2020). As described in more detail in volume 3, appendix 10.2, the average density of harbour seal within the Proposed Development array area based on Carter et al. (2020) is 0.0001 individuals per km2. If maximum numbers were compared with estimates based on this average density, the number of harbour seal affected by possible disturbance during concurrent piling at 4,000 kJ) would be less than one animal (0.02% of the ES plus NE Mus population), compared to less than three animals (0.41% of the ES plus NE Mus population) based on maximum densities.
178. It is reasonable to consider that disturbance could be predicted by a realistic average maximum hammer energy of 3,000 kJ (see paragraph 143), where up to two animals could potentially be disturbed during concurrent piling at wind turbine foundations, representing 0.31% of the ES plus NE Mus population (volume 3, appendix 10.5).
179. Harbour seal could also be potentially disturbed within the zone of possible disturbance during single piling at a wind turbine or an OSPs/Offshore convertor station platform at a maximum hammer energy of 4,000 kJ ( Figure 10.11   Open ▸ ), with up to two (0.20% of the ES plus NE Mus population) animals affected ( Table 10.34   Open ▸ ).

Figure 10.17: Proposed Development and Harbour Seal Mean At-Sea Usage (Carter et al., 2020) Overlaid with Unweighted SELss Contours Due to Concurrent Impact Piling of Wind Turbine Piles at Maximum Hammer Energy (4,000 kJ) Using 1% Constant Conversion Factor

Figure 10.18: Proposed Development and Harbour Seal Mean At-Sea Usage (Carter et al., 2020) Overlaid with Unweighted SELss Noise Contours Due to Single Piling at Maximum Hammer Energy (4,000 kJ)

Figure 10.19: Unweighted SELss Noise Contours Due to Single Piling at Maximum Hammer Energy (4,000 kJ)

Table 10.34: Number of Harbour Seals Predicted to be Disturbed within Unweighted SELss Noise Contours as a Result of Different Piling Scenarios Using 1% Constant Conversion Factor

< = less than

180. As identified in volume 3, appendix 10.2, two sites designated for protection of harbour seal are located within the regional marine mammal study area. There is no potential for overlap of noise contours with the Dornoch Firth and Morrich More SAC, as it is located approximately 195 km from the Proposed Development array area. Given that harbour seal forage mostly within approximately 50 km from the haul out site, it is also very unlikely that individuals from this population will travel as far south. The behavioural disturbance contours during piling at location closest to the shore do not reach the coastal areas where the highest density of harbour seal is encountered ( Figure 10.17   Open ▸ ). There will be no overlap of noise disturbance contours with Forth of Tay and Eden Estuary SAC (located approximately 47 km from the Proposed Development array area) or any of the haul-out sites designated for harbour seals ( Figure 10.17   Open ▸ ). However, given that the outer behavioural disturbance contours (135 dB for seals) extend towards the coast, there is a potential that some of the animals within the impacted area may be associated with the Forth of Tay and Eden Estuary SAC, which has a breeding colony of approximately 41 individuals (SCOS, 2020). Full consideration of potential for AeoI is given in RIAA (SSER, 2022d).
181. The potential for barrier effects (i.e. the ability to move between key areas such as haul-out sites and foraging areas offshore) is considered for both concurrent and single piling scenarios. The level at which a measurable response is predicted to occur in seal species is at a maximum received noise level of SELss 135 dB (= 145 dBrms) which was predicted over a shorter range compared to the NMFS (2005) threshold for mild disturbance (140 dBrms = 130 dBss). Animals exposed to lower noise levels in the outer disturbance contours are likely to experience mild disruptions of normal behaviours but prolonged or sustained behavioural effects, including displacement, are unlikely to occur (Southall et al., (2021). Further discussion on the sensitivity of harbour seal is provided in paragraph 227 et seq. (with respect to survival, feeding and reproductive behaviours) but for the purposes of assessment, it is considered that harbour seal close to the coast could experience mild disturbance but that this is unlikely to lead to barrier effects, (i.e. preventing animals from using the foraging grounds in waters along the coast) as animals are unlikely to be excluded from the coastal areas. However, when piling occurs, these is a potential for some animals to be temporarily deterred from the offshore areas. Animals would therefore need to find alternative foraging grounds and there may be an energetic cost associated with longer foraging trips.
182. As previously described in paragraph 135 et seq., the duration of piling could potentially affect harbour seal over a maximum of five breeding cycles. The magnitude of the impact could also result in a small but measurable alteration to the distribution of marine mammals during piling only (372 days over 52 month piling phase) and may affect the fecundity of some individuals (up to 0.39% of the ES plus NE MU population at any one time) over the medium term.
183. As agreed with consultees ( Table 10.9   Open ▸ ) population modelling was carried out to explore the potential of disturbance during piling to affect the population trajectory over time and provide additional certainty in the predictions of the assessment of effects. Results of the iPCoD modelling for harbour seal against the MU population showed that the median of the ratio of the impacted population to the unimpacted population was 100% at 25 years regardless of the conversion factor scenario assessed (1% constant, 4% reducing to 0.5% or 10% reducing to 1% conversion factors). Very small differences in population size over time between the impacted and unimpacted population fall within the natural variance of the population as can be seen in Figure 10.20   Open ▸ , where results of simulated population number (y axis) are similar on either side of the median line for both, impacted and unimpacted population. Therefore, it was considered that there is no potential for a long-term effects on this species ( Figure 10.20   Open ▸ , see volume 3, appendix 10.4 for more details). These results are not in agreement with findings of Hanson et al. (2017), who suggested that the continuation of current decline trend in the Forth of Tay and Eden Estuary SAC could result in the species disappearing from this area within next 20 years. The reason for this discrepancy is that the revised demographic parameters to inform iPCoD models (Sinclair et al., 2020) indicate that with inclusion of the Firth of Forth counts, the total East Scotland (ES) MU counts appear to be relatively stable. Additionally, sporadic counts in the area indicate that the decline is localised within the SAC and may not represent the trends in the overall MU population (SCOS, 2020; Sinclair et al., 2020). 

Figure 10.20: Simulated Harbour Seal Population Sizes for Both the Baseline and the Impacted Populations Under the Maximum Adverse Scenario Using 1% Conversion Factor and no Vulnerable Subpopulation.

184. The impact is predicted to be of regional spatial extent, medium term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptor directly. The results suggest that in short to medium term the magnitude would be low. Recovery is considered likely to occur soon after cessation of piling and there were predicted to be no long-term population-level effects on harbour seal as corroborated by the population modelling. The magnitude is therefore considered to be low.

Grey seal

185. As previously described in paragraph 175 et seq., there were two main approaches used to calculate the magnitude of effects with the potential to cause disturbance to marine mammals. As with harbour seal the approach using the uniformly distributed maximum density estimate ( Table 10.13   Open ▸ ) multiplied by the largest predicted areas of effect for single/concurrent piling (as presented in Figure 10.19   Open ▸ and Figure 10.11   Open ▸ ) resulted in the most precautionary assessment. To reiterate, this is a precautionary approach, as realistically the density of grey seal will vary (as presented in Figure 10.21   Open ▸ to Figure 10.22   Open ▸ showing grey seal at-sea usage based on Carter et al. (2020) study), and therefore will not represent a mean value across the Proposed Development marine mammal study area.
186. Using the most precautionary approach up to 1,358 animals were predicted to have the potential to be disturbed from concurrent piling at a maximum hammer energy of 4,000 kJ ( Figure 10.10   Open ▸ ). This equates to 3.19% of the ES plus NE Mus population ( Table 10.35   Open ▸ ). For comparison, the number of animals that could be potentially disturbed during the same piling scenario but using 4% reducing to 0.5% conversion factor has been conservatively assessed as up to 935 grey seals, which equates to 2.19% of the ES plus NE MU population (see volume 3, appendix 10.5 for estimates using various conversion factor).
187. Grey seal could also be potentially disturbed within the zone of possible disturbance during single piling at a wind turbine or an OSPs/Offshore convertor station platform at a maximum hammer energy of 4,000 kJ ( Figure 10.11   Open ▸ ), with up to 705 (1.66% of the ES plus NE Mus population) animals affected ( Table 10.35   Open ▸ ).
188. The maximum numbers presented in Table 10.35   Open ▸ are considered conservative as these are based on the mean at-sea usage estimates (1.2 animals per km2) from Carter et al. (2020). If maximum numbers were compared with estimates of the number of potentially disturbed grey seals using the mean monthly (0.276 animals per km2) or even the peak seasonal densities (0.321 animals per km2), derived from the Proposed Development aerial digital survey data, these estimates would be shown to be highly precautionary. For example, based on the mean and peak densities from aerial data, the number of grey seals affected by possible disturbance for the maximum adverse scenario (concurrent piling at 4,000 kJ) would be 312 animals (0.73% of the ES plus NE Mus population) and 364 animals (0.85% of the ES plus NE Mus population), respectively, compared to 1,358 animals (3.19% of the ES plus NE Mus population) estimated for mean at sea usage from Carter et al. (2020). Similarly, for the single piling at 4,000 kJ scenario, the estimates using the mean and peak densities from aerial data, would be 166 animals (0.39% of the ES plus NE Mus population and 193 animals (0.45% of the ES plus NE Mus population), respectively, compared to 720 animals (1.69% of the ES plus NE Mus population) using Carter et al. (2020) mean at-sea usage estimates.
189. It is reasonable to consider that disturbance could be predicted by a realistic average maximum hammer energy of 3,000 kJ (see paragraph 143), where up to 1,095 animals could potentially be disturbed during concurrent piling at wind turbine foundations, representing 2.57% of the ES plus NE Mus population (volume 3, appendix 10.5).

Figure 10.21: Proposed Development and Grey Seal At-Sea Usage (Mean) Overlaid with Unweighted SELss Contours Due to Concurrent Impact Piling of Wind Turbine Piles at Maximum Hammer Energy (4,000 kJ) Using 1% Constant Conversion Factor

Figure 10.22: Proposed Development and Grey Seal At-Sea Usage (Mean) Overlaid with Unweighted SELss Noise Contours Due to Single Piling at Maximum Hammer Energy (4,000 kJ) Using 1% Constant Conversion Factor

Table 10.35: Number of Grey Seals Predicted to be Disturbed within Unweighted SELss Noise Contours as a Result of Different Piling Scenarios Using 1% Constant Conversion Factor

190. As identified in volume 3, appendix 10.2, two sites designated for protection of grey seal are located within the regional marine mammal study area, the Berwickshire and North Northumberland Coast SAC and the Isle of May SAC. As water depth is getting shallower closer to land, the outer behavioural disturbance contours (135 dB) overlap only slightly with coastal areas south of the Proposed Development and therefore there is a small overlap with northern part of the Berwickshire and North Northumberland Coast SAC ( Figure 10.21   Open ▸ ). However, although there is a potential for overlap of disturbance contours with northern section of the SAC, it is the southern half of the SAC which is an important breeding site for grey seals (SCOS, 2020; see Figure 6.21 in volume 3, appendix 10.2, where grey seal telemetry tracks are concentrated in waters around Farne Islands). There is no direct overlap of the outer behavioural noise contours with Isle of May SAC, located approximately 40 km from the Proposed Development array area ( Figure 10.24   Open ▸ ). As the outer behavioural disturbance contours extend towards Fife and Berwickshire coasts, it is assumed that some of the animals in the impacted area could be associated with both, Isle of May SAC and Berwickshire and North Northumberland Coast SAC. These sites support breeding populations of 5,900 and 1,000 individuals, respectively. As these SACs represent areas of higher density for grey seal (and near to coastal haul-outs), the potential for barrier effects (i.e. the ability to move between key areas such as haul-out sites and foraging areas offshore) has also been considered in paragraph 192. As advised by consultees for the HRA purposes (SSER, 2022d), grey seal foraging trips extend out to 20 km from the haul-out site during breeding season. Based on Carter et al. (2020) seal at-sea density grids and the area of overlap between the maximum foraging range and the outer disturbance contour, a maximum of 532 individuals within the foraging range from Berwickshire and North Northumberland Coast SAC ( Figure 10.23   Open ▸ ) and 18 individuals within the foraging range from Isle of May ( Figure 10.24   Open ▸ ) could potentially experience mild disturbance (i.e. received levels of no greater than 135 dB SELss). It must be noted that behavioural disturbance contours presented in Figure 10.23   Open ▸ and Figure 10.24   Open ▸ represent the maximum adverse scenario for concurrent piling at the closest wind turbine locations to the designated sites. Therefore, it is likely that for most wind turbine/OSPs/Offshore convertor station platform locations the disturbance contours will not reach as far towards the SACs during the piling and thus smaller numbers of animals would be disturbed. Full consideration of potential adverse effects on the integrity on European Sites (AeoI) is also given in RIAA (SSER, 2022d).
191. The level at which a measurable response is predicted to occur in seal species is at a maximum received noise level of SELss 135 dB (≡ 145 dBrms) which was predicted over a shorter range compared to the NMFS (2005) threshold for mild disturbance (140 dBrms ≡ 130 dB SELss). Animals exposed to lower noise levels in the outer disturbance contours are likely to experience mild disruptions of normal behaviours but prolonged or sustained behavioural effects, including displacement are unlikely to occur (Southall et al., 2021). Further discussion on the sensitivity of grey seal is provided in paragraph 227 et seq. (with respect to survival, feeding and reproductive behaviours). For the purposes of assessment, it is considered that grey seal close to the coast could experience mild disturbance but that this is unlikely to lead to barrier effects (i.e. prevent animals from using the foraging grounds in waters along the coast), as animals are unlikely to be excluded from the area. However, when piling occurs, there is the potential for some animals to be temporarily deterred from the offshore areas. Animals would therefore need to find alternative foraging grounds and there may be an energetic cost associated with longer foraging trips.

Figure 10.23: Unweighted SELss Contours Due to Concurrent Piling Overlaid with 20 km Buffer from the Coast Along the Berwickshire and North Northumberland Coast SAC

Figure 10.24: Unweighted SELss Contours Due to Concurrent Piling Overlaid with 20 km Buffer from the Isle of May SAC

192. As previously described in paragraph 135 et seq., the duration of piling could potentially affect grey seal over a maximum of five breeding cycles. The magnitude of the impact could also result in a small but measurable alteration to the distribution of marine mammals during piling only (372 days over 52 months) and may affect the fecundity of relatively large numbers in the context of the reference population (up to 3.19% of the ES plus NE MU population at any one time) over the medium term.
193. As agreed with consultees ( Table 10.9   Open ▸ ) population modelling was carried out to explore the potential of disturbance during piling to affect the population trajectory over time and provide additional certainty in the predictions of the assessment of effects. Results of the iPCoD modelling for grey seal against the MU population showed that the median of the ratio of the impacted population to the unimpacted population was 100% at 25 years regardless of the conversion factor scenario assessed (1% constant, 4% reducing to 0.5% or 10% reducing to 1% conversion factors). Very small differences in population size over time between the impacted and unimpacted population fall within the natural variance of the population as can be seen in Figure 10.25   Open ▸ , where results of simulated population number (y axis) are similar on either side of the median line for both, impacted and unimpacted population. Therefore, it was considered that there is no potential for a long-term effect on this species. ( Figure 10.25   Open ▸ , see volume 3, appendix 10.4 for more details).

Figure 10.25: Simulated Grey Seal Population Sizes for Both the Baseline and the Impacted Populations Under the Maximum Adverse Scenario Using 1% Conversion Factor and no Vulnerable Subpopulation.

195. The impact is predicted to be of regional spatial extent, medium term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude in short to medium term could be considered as medium,  however, behavioural effects are likely to be short-lived with recovery occurring soon after cessation of piling and because population modelling results shown that piling activities will not have adverse effect on grey seal population in the long term, the magnitude is therefore considered to be low.