Vessel use and other activities

874             A detailed underwater noise modelling assessment has been carried out to investigate the potential for injurious and behavioural effects on marine mammals resulting from elevated underwater noise (non-impulsive sound), using the latest criteria (volume 3, appendix 10.1 of the Offshore EIA Report). A conservative assumption has been made that all individual marine mammals will respond aversively to increases in vessel noise (i.e. that there is no intra or inter-specific variation or context-dependent differences). The distance over which effects may occur will however, vary according to the species, the ambient noise levels, hearing ability, vertical space use and behavioural response differences. SELs have been estimated for each vessel type based on 24 hours continuous operation, although it is important to note that it is highly unlikely that any marine mammal would stay at a stationary location or within a fixed radius of a vessel for 24 hours. Therefore, subsea noise modelling has been undertaken based on an animal swimming away from the source (or the source moving away from an animal) as outlined in Table 13.8   Open ▸

875             The assessment of impacts from elevated underwater noise due to vessel use and other activities is based on vessel and/or activity basis, considering the maximum injury/disturbance range as assessed in volume 3, appendix 10.1 of the Offshore EIA Report. However, several activities could potentially occur concurrently therefore ranges of effects may extend from several vessels/locations where the activity is carried out and potentially overlap.

Construction phase

876             Construction phase impacts related to underwater noise include injury and disturbance during piling, injury and disturbance during site investigation surveys, injury and disturbance during UXO clearance and disturbance due to vessel use and other activities. Each of these potential effects are described below:

Decommissioning phase

877             During the decommissioning phase, there is potential for disturbance effects to Annex II marine mammal features due to vessel use and other activities:

  • Injury and disturbance due to vessel use and other activities – vessel movement during the decommissioning phase has the potential to result in a range of impacts on marine mammals. While the source activity is temporary, injury to Annex II marine mammals has the potential to be both permanent or temporary. Behavioural effects are considered temporary. An underwater noise modelling assessment has been carried out to investigate the potential for behavioural effects on marine mammals as a result of underwater noise from vessel use during decommissioning, using the latest criteria (volume 3, appendix 10.1 of the Offshore EIA Report), and is summarised in paragraph 988 et seq.

Maximum design scenario relevant to the assessment of adverse effects on integrity

878             The Maximum Design Scenario considered for the assessment of potential impacts on Annex II marine mammal features during construction and decommissioning from underwater noise are set out in Table 13.10   Open ▸ .

 

Table 13.10:
Maximum Design Scenarios Considered for the Assessment of Potential Impacts on Annex II Marine Mammal Features from Underwater Noise during Construction and Decommissioning

Table 13.10: Maximum Design Scenarios Considered for the Assessment of Potential Impacts on Annex II Marine Mammal Features from Underwater Noise during Construction and Decommissioning

 

Designed-in measures relevant to the assessment of adverse effects on integrity

879             Designed in measures (and the associated commitments) of relevance to the assessments of potential impacts on Annex II marine mammal features from underwater noise during construction and decommissioning are set out in Table 13.11   Open ▸ .

 

Table 13.11:
Designed in Measures Relevant to the Assessment of Adverse Effects on Integrity on European Sites Designated for Annex II Marine Mammal Features from Underwater Noise during Construction and Decommissioning

Table 13.11: Designed in Measures Relevant to the Assessment of Adverse Effects on Integrity on European Sites Designated for Annex II Marine Mammal Features from Underwater Noise during Construction and Decommissioning

 

Information to inform appropriate assessments

880             Results presented in this section refer to the assessment at species level for grey seal, harbour seal, harbour porpoise and bottlenose dolphin, as informed by volume 2, chapter 10 of the Offshore EIA Report. Assessment for these species as features of the designated sites is provided in section 13.6.

Injury and disturbance from elevated underwater noise during piling

Auditory injury

Grey seal and harbour seal

881             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 13.12   Open ▸ ; see volume 3, appendix 10.5 of the Offshore EIA Report for estimates using a range of conversion factors). The ranges are low due to the soft-start initiation of piling (see Table 13.11   Open ▸ ) 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 4,000kJ, there will be less than one animal (of each species) that could be potentially injured within the maximum range of 150 m.

882             To reduce the potential of injury, designed-in measures, involving visual and acoustic monitoring, will be adopted as part of a MMMP (see Table 13.11   Open ▸ ). Additionally, secondary mitigation will be applied in a form of ADDs to minimise residual risk of injury. Assuming conservative swim speeds, activation of an ADD for 30 minutes would deter grey seal and harbour seal beyond the maximum injury zone.

883             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 OSP/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 OSP/Offshore convertor station platforms). This will be intermittent over a 52-month piling phase within the total construction phase of 96 months (see Table 13.10   Open ▸ ).

884             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 the life cycle of harbour and grey seal is classified as medium term.

 

Table 13.12:
Summary of SPLpk and SELcum Injury Ranges and Areas of Potential Effect for Harbour Seal and Grey Seal Due to Impact Piling for Wind Turbine and OSP/Offshore Convertor Station Platform Jacket Foundations (Absolute Maximum Hammer Energy) Using 1% Constant Conversion Factor

Table 13.12: Summary of SPLpk and SELcum Injury Ranges and Areas of Potential Effect for Harbour Seal and Grey Seal Due to Impact Piling for Wind Turbine and OSP/Offshore Convertor Station Platform Jacket Foundations (Absolute Maximum Hammer Energy) Using 1% Constant Conversion Factor

 

885             With designed-in measures in place including soft start and an MMMP (see Table 13.11   Open ▸ ), 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.

886             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 assessment of the effect of injury from elevated underwater noise during piling on grey seal and harbour seal as features of respective designated sites is provided in section 13.6.

Harbour porpoise

887             The maximum range for injury to harbour porpoise was estimated as 449 m based on SPLpk and using the 1% constant conversion factor ( Table 13.13   Open ▸ ; see volume 3, appendix 10.5 of the Offshore EIA Report 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 4,000kJ, was estimated as less than one harbour porpoise.

888             To further reduce the potential for injury, designed-in measures will be adopted as part of a MMMP ( Table 13.11   Open ▸ ; see volume 4, appendix 23 of the Offshore EIA Report for more details). These measures will involve the use of visual and acoustic searches over a pre-defined mitigation zone. 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). Secondary mitigation in the form of ADDs will be applied to further minimise any residual risk of injury. Assuming conservative swim speeds, activation of an ADD for 30 minutes would deter harbour porpoises beyond the maximum injury zone.

889             The total duration of piling is presented in paragraph 883. 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 the 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 13.13:
Summary of SPLpk and SELcum Injury Ranges and Areas of Effect for Harbour Porpoise due to Impact Piling for Wind Turbine and OSP/Offshore Convertor Station Platform Jacket Foundations (Absolute Maximum Hammer Energy) Using 1% Constant Conversion Factor

Table 13.13: Summary of SPLpk and SELcum Injury Ranges and Areas of Effect for Harbour Porpoise due to Impact Piling for Wind Turbine and OSP/Offshore Convertor Station Platform Jacket Foundations (Absolute Maximum Hammer Energy) Using 1% Constant Conversion Factor

 

890             With designed-in measures in place, 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. Considering the duration of the impact the risk (albeit very low) could occur over the medium term.

891             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 assessment of the effect of injury from elevated underwater noise during piling on harbour porpoise as feature of designated site is provided in section 13.6.

Bottlenose dolphin

892             The maximum range for injury to bottlenose dolphin was estimated as 43 m based on SPLpk and using the 1% constant CF ( Table 13.14   Open ▸ see volume 3, appendix 10.5 of the Offshore EIA Report for estimates using a range of CFs). 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 of the Offshore EIA Report) and full hammer energy, there will be less than one animal that could be potentially injured within the maximum range of 43 m.

893             It is worth noting that this injury range will not overlap with the Forth of Tay and coastal areas (2-20 m depth) where the highest density of bottlenose dolphins is encountered. To further reduce the potential to experience injury, designed-in measures will be adopted as part of a MMMP (see volume 4, appendix 23 of the Offshore EIA Report). Additionally, secondary mitigation will be applied in the form of ADDs to minimise residual risk of injury. Assuming conservative swim speeds, activation of an ADD for 30 minutes would deter bottlenose dolphins beyond the maximum injury zone.

894             The total duration of piling is presented in paragraph 883. 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. However, it is worth noting that piling will be intermittent and will occur over small timespan (372 days) within the piling phase (52 months). Considering the above, the duration of the effect in the context of life cycle of bottlenose dolphin is classified as medium term.

 

Table 13.14:
Summary of SPLpk and SELcum Injury Ranges and Areas of Effect for Bottlenose Dolphin Due to Impact Piling for Wind Turbine and OSP/Offshore Convertor Station Platform Jacket Foundations (Absolute Maximum Hammer Energy) Using 1% Constant Conversion Factor

Table 13.14: Summary of SPLpk and SELcum Injury Ranges and Areas of Effect for Bottlenose Dolphin Due to Impact Piling for Wind Turbine and OSP/Offshore Convertor Station Platform Jacket Foundations (Absolute Maximum Hammer Energy) Using 1% Constant Conversion Factor

1 N/E = Threshold not exceeded

 

895             With designed-in measures in place including soft start and a MMMP (see volume 4, appendix 23 of the Offshore EIA Report) Table 13.11   Open ▸ , the magnitude of the impact would result in a negligible risk of injury to bottlenose 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.

896             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 assessment of the effect of injury from elevated underwater noise during piling on bottlenose dolphin as feature of designated site is provided in section 13.6.

Behavioural disturbance

897             The numbers of animals predicted to experience potential disturbance as a result of different piling scenarios is presented in this section ( Table 13.15   Open ▸ to Table 13.18   Open ▸ ). Predictions are based on the assumptions of the dose response relationship described in paragraphs 848 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).

898             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.

899             Assessment of magnitude for behavioural disturbance presented in this section is based on 1% constant conversion factor unless stated otherwise.

Grey seal

900             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 of the Offshore EIA Report 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 grey seal have been predicted (see Figure 10.21 in volume 2, chapter 10 of the Offshore EIA Report).

901             Both approaches were explored to determine which would lead to the most precautionary assessment in terms of number of individuals disturbed. Given that the outermost 135 dB behavioural disturbance contours do not overlap with areas of density hotspots for this species (see Figure 10.21 in volume 2, chapter 10 of the Offshore EIA Report), the most precautionary values were derived using the largest areas of effect for the single and concurrent scenarios (see Figure 10.19 and Figure 10.11 in volume 2, chapter 10 of the Offshore EIA Report) multiplied by the maximum density estimate from Table 13.4   Open ▸ . The application of this approach is considered to be precautionary, as realistically the density of grey seal will vary (as presented in Figure 10.21 to Figure 10.22 in volume 2, chapter 10 of the Offshore EIA Report, 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.

902             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 ( Table 13.15   Open ▸ ). For comparison, the number of animals that could be potentially disturbed during the same piling scenario but using 4% reducing to 0.5% CF has been conservatively assessed as up to 935 grey seals (see volume 3, appendix 10.5 of the Offshore EIA Report for estimates using various conversion factor).

903             The maximum numbers presented in Table 13.15   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 and 364 animals, respectively, compared to 1,358 animals 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 and 193 animals, respectively, compared to 720 animals using Carter et al. (2020) mean at-sea usage estimates.

904             Additionally, there is a number of conservative assumptions in the subsea noise model, as the maximum hammer energy of 4,000 kJ is unlikely to be reached at all piling locations (see paragraph 844 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 of the Offshore EIA Report), where up to 1,095 animals could potentially be disturbed during concurrent piling at wind turbine foundations.

905             Grey seal could also be potentially disturbed within the zone of possible disturbance during single piling at a wind turbine or an OSP/Offshore convertor station platform at a maximum hammer energy of 4,000 kJ, with up to 705 animals affected ( Table 13.15   Open ▸ ).

 

Table 13.15:
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

Table 13.15:  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

 

906             Two sites designated for grey seal are screened into the HRA Stage 2 Appropriate Assessment: the Berwickshire and North Northumberland Coast SAC and the Isle of May SAC. As water depth gets 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. 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. However, 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.

907             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 section 13.5 (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.

908             As previously described in paragraph 884, 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).

909             Given that grey seal individuals from the Berwickshire and North Northumberland Coast SAC are linked with the wider ES plus NE MUs population, 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 wider 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 (see volume 3, appendix 10.4 of the Offshore EIA Report). Therefore, it was considered that there is no potential for the long-term effects on this species within wider population as a result of underwater noise from piling (see volume 3, appendix 10.4 of the Offshore EIA Report for more details).

910             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 assessment of the effect of disturbance from elevated underwater noise during piling on grey seal as feature of designated sites is provided in section 13.6.

Harbour seal

911             As previously described in paragraph 900 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 grey seal, the approach using the uniformly distributed maximum density estimate ( Table 13.4   Open ▸ ) multiplied by the largest predicted areas of effect for single/concurrent piling (as presented in Figure 10.19 and Figure 10.11, volume 2, chapter 10 of the Offshore EIA Report) resulted in the most precautionary assessment. To reiterate, this is a precautionary approach, as realistically the density of harbour seal will vary (as presented in Figure 10.17 to Figure 10.18 of volume 2, chapter 10 of the Offshore EIA Report, showing harbour 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.

912             Up to three animals were predicted to experience potential disturbance from concurrent piling at a maximum hammer energy of 4,000 kJ ( Table 13.16   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 (volume 3, appendix 10.5 of the Offshore EIA Report for estimates using various conversion factor).

913             The maximum numbers of harbour seal individuals that could be potentially disturbed are considered to be 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 of the Offshore EIA Report, 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, compared to less than three based on maximum densities.

914             It is reasonable to consider that disturbance could be predicted by a realistic average maximum hammer energy of 3,000 kJ (see paragraph 904 for more details), where up to two animals could potentially be disturbed during concurrent piling at wind turbine foundations (volume 3, appendix 10.5 of the Offshore EIA Report).

915             Harbour seal could also be potentially disturbed within the zone of possible disturbance during single piling at a wind turbine or an OSP/Offshore convertor station platform at a maximum hammer energy of 4,000 kJ (see volume 2, chapter 10 of the Offshore EIA Report), with up to two animals affected ( Table 13.16   Open ▸ ).

 

Table 13.16:
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

Table 13.16: 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

 

916             A single site designated for harbour seal was screened into the Stage 2 Appropriate Assessment: the Firth of Tay and Eden Estuary SAC. 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 (see Figure 10.17 in volume 2, chapter 10 of the Offshore EIA Report). There will be no overlap of noise disturbance contours with Firth 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. However, given that the outer behavioural disturbance contours (135dB for seals) extend towards the coast, there is a potential that some of the animals within the impacted area may be associated with the Firth of Tay and Eden Estuary SAC (see volume 3, appendix 10.2 of the Offshore EIA Report for more details).

917             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 section 13.5 (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.

918             As previously described in paragraph 889, 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 over the medium term.

919             Given that harbour seal individuals from the Firth of Tay and Eden Estuary SAC are linked with the wider ES MU population, 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 wider 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 (see volume 3, appendix 10.4 of the Offshore EIA Report). Therefore, it was considered that there is no potential for the long-term effects on this species within wider population as a result of underwater noise from piling (see volume 3, appendix 10.4 of the Offshore EIA Report 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 Firth 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 MU counts appear to be relatively stable and that counts in the Northeast England have increased.

920             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 assessment of the effect of disturbance from elevated underwater noise during piling on harbour seal as feature of designated site is provided in section 13.6.

Harbour porpoise

921             Up to 2,822 harbour porpoise (based on seasonal peak density) are predicted to experience potential disturbance from concurrent piling at a maximum hammer energy of 4,000 kJ ( Table 13.17   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 (see volume 3, appendix 10.5 of the Offshore EIA Report for estimates using a range of conversion factors).

922             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 of the Offshore EIA Report 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 or 2,047 animals respectively compared to 2,822 animals using peak seasonal density.

923             It is reasonable to consider that disturbance could be predicted by a realistic average maximum hammer energy of 3,000 kJ (see paragraph 904 for more details), where up to 2,378 animals have the potential to experience disturbance.

924             Harbour porpoise could also be potentially disturbed within the zone of possible disturbance during single piling at a wind turbine or an OSP/Offshore convertor station platform at a maximum hammer energy of 4,000 kJ, with up to 1,754 animals affected based on the seasonal peak density (using 1% constant conversion factor, Table 13.17   Open ▸ ).

 

Table 13.17:
Number of Harbour Porpoises Predicted to be Disturbed Within Unweighted SELss Noise Contours as a Result of Different Piling Scenarios[11]

Table 13.17:  Number of Harbour Porpoises Predicted to be Disturbed Within Unweighted SELss Noise Contours as a Result of Different Piling Scenarios[11]

925             A single site designated for harbour porpoise was screened into the Stage 2 Appropriate Assessment: the Southern North Sea SAC. The Southern North Sea SAC is located 146 km from the Proposed Development array area. There is no potential for overlap of noise disturbance contours with this designated site. Given that harbour porpoise can travel over large distances, there is a possibility that a small number of individuals from the SAC population may be occasionally present within the disturbance contours. The population of the Southern North Sea SAC is estimated at between 20,237 and 41,538 individuals (see section 5.1.2 of appendix 10.2 of the Offshore EIA Report for more details).

926             As previously described in paragraph 889, 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 some individuals over the medium term.

927             Given that harbour porpoise individuals from the Southern North Sea SAC are linked with the wider North Sea MU population, 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 wider 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 (see volume 3, appendix 10.4 of the Offshore EIA Report). Therefore, it was considered that there is no potential for the long-term effects on this species (see volume 3, appendix 10.4 of the Offshore EIA Report for more details) within wider MU population. This was also the case when considered against the SCANS III Block R as a vulnerable subpopulation (see volume 3, appendix 10.4 of the Offshore EIA Report for more details).

928             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 assessment of the effect of disturbance from elevated underwater noise during piling on harbour porpoise as feature of designated site is provided in section 13.6.

Bottlenose dolphin

929             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 (see Figure 10.13 in volume 2, chapter 10 of the Offshore EIA Report). 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 13.3   Open ▸ ).

930             The outermost noise contours predicted from the maximum hammer energy of 4,000 kJ reach the coastal areas (see Figure 10.14 in volume 2, chapter 10 of the Offshore EIA Report) 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. 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 (volume 3, appendix 10.5 of the Offshore EIA Report for estimates using a range of conversion factors).

931             It is reasonable to consider that disturbance could be predicted by a realistic average maximum hammer energy of 3,000 kJ (see paragraph 904 for more details), where up to four animals could potentially be disturbed during concurrent piling at wind turbine foundations (volume 3, appendix 10.5 of the Offshore EIA Report).

932             Coastal bottlenose dolphin could also be potentially disturbed during single piling at a wind turbine or an OSP/Offshore convertor station platform, with up to four animals affected for the 4,000 kJ hammer energy ( Table 13.18   Open ▸ ).

933             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 National Marine Fisheries Service 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).

934             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 section 13.5 (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 13.18   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.

935             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 ( Table 13.18   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 of the Offshore EIA Report). 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 ( Table 13.18   Open ▸ ).

 

Table 13.18:
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

Table 13.18: 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

 

936             The maximum numbers presented in Table 13.18   Open ▸ are considered to be conservative as these are based on highly precautionary coastal and offshore density estimates ( Table 13.4   Open ▸ ). As described in more detail in volume 3, appendix 10.1 of the Offshore EIA Report, bottlenose dolphins were recorded in low numbers during the Proposed Development aerial digital surveys 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, especially in offshore waters, should be interpreted with caution as this is likely to be an overestimate.

937             The Moray Firth SAC designated for protection of bottlenose dolphin is located 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 of the Offshore EIA Report).

938             As previously described in paragraph 894, 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 over the medium term.

939             Given that bottlenose dolphin individuals from the Moray Firth SAC are functionally linked with the wider Coastal East Scotland population, 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 wider MU population showed that the median counterfactual of population size was 100% for all three scenarios (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 (see volume 3, appendix 10.4 of the Offshore EIA Report). Therefore, it was considered that there is no potential for the long-term effects on this species within the wider MU population (see volume 3, appendix 10.4 of the Offshore EIA Report for more details).

940             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 assessment of the effect of disturbance from elevated underwater noise during piling on bottlenose dolphin as feature of designated site is provided in section 13.6.