Behavioural disturbance
  1. Disturbance during piling was predicted to have far-reaching potential impacts across the northern North Sea. It should be noted that the extent of the contours is likely to be an overestimate as it assumes that the sound from piling maintains its impulsive characteristics at large distances, which is considered unlikely to be the case. Since there is no agreed approach to modelling the cross-over point from impulsive to continuous sound and this is an ongoing active area of research (see volume 3, appendix 10.1 for more details), it was not possible to account for it in the underwater noise modelling for the Array. Applying associated impulsive sound thresholds for the whole contour range is likely to overestimate predicted impact distances and therefore leads to a potentially over-precautionary assessment. Considering this, as well as caveats highlighted by Southall et al. (2021) (see paragraph 108 et seq. for more details), quantitative assessment of disturbance based on SELss metric should be interpreted with caution.
  2. The application of the harbour porpoise dose-response curve ( Figure 10.4   Open ▸ ) (in the absence of species-specific data for other cetacean species) represents a precautionary approach to assessment of HF and LF cetaceans, as other cetacean species are likely to be less sensitive than harbour porpoise to behavioural disturbance as noted in the literature (Tougaard, 2021). For minke whale, some limited evidence available from studies investigating the effects of sound from naval sonar devices, indicates that they are less sensitive than harbour porpoise by about 40 dB to 50 dB (Kvadsheim et al., 2017, Sivle et al., 2015). However, sound energy of piling is highest in the low frequency range and overlaps more with the hearing range of minke whale for example, than harbour porpoise.
  3. Considering the caveats discussed below in paragraph 176, the estimated numbers of animals predicted to experience potential disturbance as a result of different piling scenarios are presented in Table 10.32   Open ▸ . To provide additional context and allow an area-based assessment (for HRA purposes) the quantitative impact on marine mammal species has also been presented for relevant fixed thresholds (as described in paragraph 102 et seq.).
  4. 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).
  5. For harbour porpoise, white-beaked dolphin and minke whale, a quantitative assessment of the number of animals predicted to experience disturbance was undertaken by multiplying the density values ( Table 10.16   Open ▸ ) with the areas within each 5 dB isopleth for the piling location that would result in the highest number of animals potentially disturbed. This value was then corrected using the relevant proportional response from Graham et al. (2019) for the unweighted SELss level ( Figure 10.4   Open ▸ ).
  6. For the bottlenose dolphin CES2 MU population, given its coastal distribution, a piling location taken forward to the assessment was chosen based on the highest overlap of noise disturbance contours with CES2 MU boundaries. The calculations of the number of animals predicted to experience disturbance were undertaken by multiplying the density values from Lacey et al. (2022) with the areas within each 5 dB isopleth that overlap with CES2 MU boundaries and correcting the value using the relevant proportional response from Graham et al. (2019) for the unweighted SELss level ( Figure 10.4   Open ▸ ).
  7. For grey seal the quantitative assessment was undertaken by overlaying the unweighted SELss contours for the piling location that would result in the highest overlap with the density hotspots based on at-sea density maps produced by Carter et al. (2022). The number of animals in each 5 km x 5 km grid cell was summed for each isopleth and corrected using the proportional response as per Whyte et al. (2020) ( Figure 10.5   Open ▸ ).
Table 10.32:
Potential Number of Animals Predicted to be Disturbed Within Weighted SELss Sound Contours Based on Relevant Dose-Responses (Graham et al., 2019, Whyte et al., 2020) for the Array Piling Scenarios. Numbers in Bold Represent the Modelling Location Scenarios with the Highest Number of Animals Potentially Impacted

Table 10.32: Potential Number of Animals Predicted to be Disturbed Within Weighted SELss Sound Contours Based on Relevant Dose-Responses (Graham et al., 2019, Whyte et al., 2020) for the Array Piling Scenarios. Numbers in Bold Represent the Modelling Location Scenarios with the Highest Number of Animals Potentially Impacted

Harbour porpoise

  1. Based on the most conservative scenario for concurrent piling of the wind turbine (3,000 kJ) in the centre and OSPs (4,400 kJ) at the northern limit of the site boundary, up to 8,309 harbour porpoises are predicted to experience potential disturbance ( Table 10.32   Open ▸ , Figure 10.9   Open ▸ ) (based upon maximum numbers derived from dose-response). This equates to 2.4% of the North Sea MU population. The estimated number of individuals potentially impacted is based on conservative densities and the assumption that the peak seasonal site-specific density of 0.651 animals per km2 is uniformly distributed within all noise contours. Additionally, the underwater noise modelling assumed that the maximum hammer energies are reached and maintained at all piling locations (see volume 3, appendix 10.1 for more details).
  2. The Southern North Sea SAC is the only site designated for protection of harbour porpoise within the regional marine mammal study area. The SAC is located approximately 130.7 km to the south-east of the Array marine mammal study area. Given the far-reaching extent of the outer noise contours, there is potential for overlap with the Southern North Sea SAC. Based on the dose-response curve presented in Graham et al. (2019), from 1% to 4% of animals are likely to respond within noise contours that overlap with this SAC (120 to 130 dB SELss) which is also below the NMFS (2005) threshold for strong disturbance (=160 dB rms) ( Figure 10.10   Open ▸ ). Moreover, there is a possibility that a small number of individuals from these SAC populations may be occasionally present within the mapped disturbance contours outside the site. Therefore, using the area-based approach (see paragraph 105) for the unweighted noise threshold of 143 dB re 1µPa2s disturbance contours were presented for the maximum design case concurrent piling at wind turbines (3,000 kJ) in the centre and OSPs (4,400 kJ) at the southern limit of the site boundary (i.e. the closest to the SAC) ( Figure 10.10   Open ▸ ). This approach, which focuses on a threshold associated with the onset of avoidance behaviour, showed that the 143 dB contour does not extend to the Southern North Sea SAC and therefore animals are unlikely to experience significant disturbance within the SAC. Additionally, at these distances it is unlikely that noise contours would result in barrier effects restricting harbour porpoise from reaching key habitats within the SAC.
  3. The different approaches described above suggest that close to the piling the disturbance response is likely to be measurable and the probability of such a response is high such that individuals could change their baseline behaviour or in some cases actively avoid disturbed areas. Moving further away from the piling source, behavioural responses are likely to decrease with some individuals (proportional to the distance from the source) tolerating the increase in elevated underwater sound ( Figure 10.4   Open ▸ ). At ranges beyond the received level of 143 dB re 1 µPa2s (SELss) the disturbance is unlikely to be significant with less likelihood of active avoidance (Brandt et al., 2018, NRW, 2023b).
  4. Intermittent piling within an eight-year construction phase could coincide with key breeding periods of harbour porpoise and is considered to be notable in the context of the lifespan of this species (see paragraph 154). In line with the Marine Mammal Methodology Note 1 ( Table 10.10   Open ▸ ; volume 3, appendix 5.1, annex B), 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. Detailed modelling is presented in volume 3, appendix 10.3.
  5. Simulated harbour porpoise population trajectories for both the baseline (unimpacted) and the impacted populations (based on the North Sea (NS) MU) are presented in Figure 10.7   Open ▸ for the maximum temporal scenario and Figure 10.8   Open ▸ for the maximum spatial scenario. Results of iPCoD modelling of the maximum temporal scenario for harbour porpoise showed that the median ratio of the impacted population to the unimpacted population at six years was 0.9986 and at 25 years was 0.9985. For the maximum spatial scenario these ratios were 0.9995 at six years and 0.9994 at 25 years. For both scenarios, results indicate no significant difference between the population trajectories for an unimpacted population and the impacted population.
  6. The impact (elevated underwater noise arising during piling) is predicted to be of regional spatial extent in the context of the geographic frame of reference, medium term duration, intermittent and the effect of behavioural disturbance is reversible (as receptors are expected to recover within hours/days). It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.
  7. At 25 years after the start of piling, the simulated impacted population was estimated to be 1,878 animals smaller than the unimpacted population for the maximum temporal scenario, equating to 0.005% of the NS MU. For the maximum spatial scenario, there were estimated to be 1,302 fewer animals in the impacted versus unimpacted population, equating to 0.004% of the MU. Given these results, it is expected that there would be no potential long term effects on the NS MU harbour porpoise population resulting from elevated underwater noise arising during piling for the Array.

Figure 10.7:
Simulated Harbour Porpoise Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Temporal Scenario

Figure 10.7: Simulated Harbour Porpoise Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Temporal Scenario

Figure 10.8:
Simulated Harbour Porpoise Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Spatial Scenario

Figure 10.8: Simulated Harbour Porpoise Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Spatial Scenario

 


.

Figure 10.9:
Unweighted SELss Contours as a Result of Concurrent Piling at Wind Turbine (3,000 kJ) at the Centre and OSP (4,400 kJ) at the Northern Limit of the Site Boundary

Figure 10.9: Unweighted SELss Contours as a Result of Concurrent Piling at Wind Turbine (3,000 kJ) at the Centre and OSP (4,400 kJ) at the Northern Limit of the Site Boundary


Figure 10.10:
Unweighted SELss Contours as a Result of Concurrent Piling at Wind Turbine (3,000 kJ) at the Centre and OSP (4,400 kJ) at the Southern Limit of the Site Boundary and Southern North Sea SAC

Figure 10.10: Unweighted SELss Contours as a Result of Concurrent Piling at Wind Turbine (3,000 kJ) at the Centre and OSP (4,400 kJ) at the Southern Limit of the Site Boundary and Southern North Sea SAC


Bottlenose dolphin

  1. Based on the most conservative scenario for concurrent piling of the wind turbine (3,000 kJ) in the centre and OSPs (4,400 kJ) at the northern limit of the site boundary, up to five bottlenose dolphins are predicted to experience potential disturbance ( Table 10.32   Open ▸ , Figure 10.11   Open ▸ ). This equates to 2.23% of the CES2 MU population.
  2. The assessment assumed precautionarily that bottlenose dolphins from the CES2 MU can be present within the whole extent of the MU ( Figure 10.11   Open ▸ ), although it should be noted that empirical evidence from studies on this population suggest that they are mostly encountered 2 km to 5 km from the shore (Palmer et al., 2019, Paxton et al., 2016, Quick et al., 2014, Thompson et al., 2015b). Animals from the CES2 MU are unlikely to be present in the offshore areas that may be exposed to high levels of noise from piling at the Array. However, bottlenose dolphins from the offshore populations may experience behavioural disturbance outside the CES2 MU. Given that there is an estimate of 2,022 animals for the entire Greater North Sea MU, which extends across to Europe (IAMMWG, 2022) and no further information on offshore populations, the impact has not been quantified for behavioural disturbance during piling outside the CES2 MU.
  3. The CES2 MU lies approximately 56 km from the site boundary and at this distance the received level from piling will have lost much of the impulsive characteristics ( Figure 10.11   Open ▸ ). The outermost noise contours reach the coastal areas and therefore may overlap with the key inshore distribution of bottlenose dolphin in the CES2 MU ( Figure 10.11   Open ▸ ), potentially resulting in barrier effects, e.g. restricting animals from moving along the coast. Received sound levels within the CES2 MU are predicted to reach maximum SELss levels of 135 dB ( Figure 10.11   Open ▸ ), which is below the NMFS (2005) threshold for strong disturbance (=160 dB rms) and therefore likely to elicit less severe disturbance reactions. However, the modelled noise contours that overlap with the CES2 MU are above the threshold for mild disturbance (=140 dB rms). According to the behavioural response severity matrix suggested by Southall et al. (2021) such low level disturbance (scoring between 0 to 3 on a 0 to 9 scale) could lead to mild disruptions of normal behaviours, but prolonged or sustained behavioural effects, including displacement are unlikely to occur. Based on the dose-response presented in Graham et al. (2019) ( Figure 10.4   Open ▸ ), from 1% to 10% of animals are likely to respond within noise contours (120 to 135 dB SELss) that overlap with the CES2 MU ( Figure 10.11   Open ▸ ).
  4. The Moray Firth SAC is the only site designated for protection of bottlenose dolphin within the regional marine mammal study area. The SAC located approximately 176.5 km north-west from the Array marine mammal study area. There is no potential for overlap of the noise contours with the SAC ( Figure 10.11   Open ▸ ). However, as noted in paragraph 188, there is a possibility that a small number of individuals from this SAC population may be occasionally present within the mapped disturbance contours outside the site (though it is not possible to apportion numbers of animals disturbed to the Moray Firth SAC).
  5. Intermittent piling within an eight-year construction phase could coincide with key breeding periods of bottlenose dolphin and is considered to be notable in the context of the lifespan of this species (see paragraph 158). In line with the Marine Mammal Methodology Note ( Table 10.10   Open ▸ ; volume 3, appendix 5.1, annex B), 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.
  6. Simulated bottlenose dolphin population trajectories for both the baseline (unimpacted) and the impacted populations (using the CES2 MU) are presented in Figure 10.12   Open ▸ for the maximum temporal scenario, and Figure 10.13   Open ▸ for the maximum spatial scenario. Results of iPCoD modelling for the CES2 MU bottlenose dolphin population indicated that the median ratio of the impacted population to the unimpacted population was 1.000 at six years and at 25 years, for both the maximum temporal scenario and the maximum spatial scenario. A ratio of 1 corresponds to no significant difference between the population trajectories for an unimpacted population and the impacted population. At 25 years after the start of piling, for the maximum temporal scenario the impacted population was predicted to be seven animals smaller than the unimpacted population, equating to 0.031% of the CES2 MU. For the maximum spatial scenario, the impacted population was predicted to be four animals smaller than the unimpacted population, equating to 0.018% of the CES2 MU. It is therefore considered that there would be no potential long term effects upon the coastal bottlenose dolphin population resulting from elevated underwater noise arising during piling.
  7. The impact (elevated underwater noise arising during piling) is predicted to be of regional spatial extent in the context of the geographic frame of reference, medium term duration, intermittent and the effect of behavioural disturbance is reversible (as receptors are expected to recover within hours/days). It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

White-beaked dolphin

  1. Based on the most conservative scenario for concurrent piling of the wind turbine (3,000 kJ) in the centre and OSPs (4,400 kJ) at the northern limit of the site boundary, up to 1,531 white-beaked dolphins are predicted to experience potential disturbance ( Table 10.32   Open ▸ ). This equates to 3.48% of the CGNS MU population. The estimated number of individuals potentially impacted is based on the assumption that the density of 0.120 animals per km2 is uniformly distributed within all noise contours. Additionally, in the underwater noise modelling it was assumed that the maximum hammer energies are reached at all piling locations (see volume 3, appendix 10.1 for more details). Using the dose-response approach, up to 153 white-beaked dolphins are predicted to experience strong disturbance (160 dB rms), with up to 1,013 experiencing mild disturbance (140 dB rms).
  2. There are no designated sites for white-beaked dolphin within the regional marine mammal study area ( Table 10.16   Open ▸ ).
  3. Intermittent piling within an eight-year construction phase could coincide with key breeding periods of white-beaked dolphin and is considered to be notable in the context of the lifespan of this species (see paragraph 158). Population modelling for iPCoD does not facilitate white-beaked dolphin, therefore no population modelling was carried out for this species.
  4. The impact (elevated underwater noise arising during piling) is predicted to be of regional spatial extent in the context of the geographic frame of reference, medium term duration, intermittent and the effect of behavioural disturbance is reversible (as receptors are expected to recover within hours/days). It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Minke whale and humpback whale

  1. Based on the most conservative scenario for concurrent piling of the wind turbine (3,000 kJ) in the centre and OSPs (4,400 kJ) at the northern limit of the site boundary, up to 362 minke whale are predicted to experience potential disturbance ( Table 10.32   Open ▸ , Figure 10.9   Open ▸ ). This equates to 1.80% of the CGNS MU population. The estimated number of individuals potentially impacted is based on the assumption that the density of 0.0284 animals per km2 is uniformly distributed within all noise contours. Additionally, in the underwater noise modelling it was assumed that the maximum hammer energies are reached and maintained at all piling locations (see volume 3, appendix 10.1 for more details).
  2. Given that no species-specific densities are available for humpback whale, the numbers of animals potentially impacted could not be estimated. However, it can be anticipated that humpback whale may be at risk of experiencing strong disturbance within noise contours above 150 dB (SELss).According to the behavioural response severity matrix suggested by Southall et al. (2021), beyond this range low level disturbance (scoring between 0 to 3 on a 0 to 9 scale) could lead to mild disruptions of normal behaviours, but prolonged or sustained behavioural effects, including displacement are unlikely to occur.
  3. Intermittent piling within an eight-year construction phase could coincide with key breeding periods of minke whale and humpback whale and is considered to be notable in the context of the lifespan of this species. For minke whale, in line with the Marine Mammal Methodology Note ( Table 10.10   Open ▸ ; volume 3, appendix 5.1, annex B), 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.
  4. Simulated unimpacted and impacted population trajectories for the CGNS minke whale MU are presented in Figure 10.15   Open ▸ for the maximum temporal scenario and in Figure 10.16   Open ▸ for the maximum spatial scenario. Results of iPCoD modelling based on the SPLpk metric (from which no animals were predicted to experience PTS) showed that the median ratio of the impacted population to the unimpacted population was 1.000 at six years and 25 years, for both the maximum temporal scenario and the maximum spatial scenario. This indicates that there would be no significant difference between population trajectories for an unimpacted population or for an impacted population.
  5. At 25 years after piling, for both the maximum temporal scenario and the maximum spatial scenario, there was one less animal in the impacted population compared to the unimpacted population, equating to 0.00005% of the CGNS MU. Therefore, it is considered that there would be no potential long term effects on the minke whale population resulting from elevated underwater noise arising during piling.
  6. Underwater noise modelling based upon the SELcum metric predicted that, under the maximum spatial scenario, up the three animals could experience PTS due to concurrent piling at wind turbine anchors and OSP foundations, with one animal predicted to experience PTS due to single piling at OSP foundations. For the maximum temporal scenario this was one animal only, due to single piling at OSP foundations. Simulated unimpacted and impacted population trajectories for the CGNS minke whale MU, with numbers of affected animals based upon the SELcum metric, are presented in Figure 10.17   Open ▸ for the maximum temporal scenario and in Figure 10.18   Open ▸ for the maximum spatial scenario.
  7. Results of iPCoD modelling showed that for the maximum spatial scenario, based on the SELcum metric, the median ratio of the impacted population to the unimpacted population was 0.998 at six years and 0.992 at 25 years. For the maximum temporal scenario, based on the SELcum metric, the median ratio of the impacted population to the unimpacted population was 1.000 at six years and 0.998 at 25 years. The small deviation from a ratio of 1.000 for both scenarios, when based on the SELcum metric, indicates that there would be no significant difference between population trajectories for an unimpacted population or for an impacted population.
  8. At 25 years after piling, for the maximum spatial scenario there was 173 fewer animals in the impacted population compared to the unimpacted population, equating to 0.86% of the CGNS MU. For the maximum temporal scenario this reduced to 55 fewer animals in the impacted population compared to the unimpacted population, equating to 0.27% of the CGNS MU. Therefore, it is considered that there would be no potential long term effects on the minke whale population resulting from elevated underwater noise arising during piling.


Figure 10.11:
Unweighted SELss Contours as a Result of Concurrent Piling at Wind Turbine (3,000 kJ) at the Centre and OSP (4,400 kJ) at the Northern Limit of the Site Boundary, CES2 MU and Moray Firth SAC

Figure 10.11: Unweighted SELss Contours as a Result of Concurrent Piling at Wind Turbine (3,000 kJ) at the Centre and OSP (4,400 kJ) at the Northern Limit of the Site Boundary, CES2 MU and Moray Firth SAC


Figure 10.12:
Simulated Bottlenose Dolphin Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Temporal Scenario

Figure 10.12: Simulated Bottlenose Dolphin Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Temporal Scenario

Figure 10.13:
Simulated Bottlenose Dolphin Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Spatial Scenario

Figure 10.13: Simulated Bottlenose Dolphin Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Spatial Scenario


Figure 10.14:
Unweighted SELss Contours as a Result of Concurrent Piling at Wind Turbine (3,000 kJ) at the Centre and OSP (4,400 kJ) at the Northern Limit of the Site Boundary and the Southern Trench ncMPA

Figure 10.14: Unweighted SELss Contours as a Result of Concurrent Piling at Wind Turbine (3,000 kJ) at the Centre and OSP (4,400 kJ) at the Northern Limit of the Site Boundary and the Southern Trench ncMPA


Figure 10.15:
Simulated Minke Whale Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Temporal Scenario, Based on the SPLpk Metric

Figure 10.15: Simulated Minke Whale Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Temporal Scenario, Based on the SPLpk Metric

Figure 10.16:
Simulated Minke Whale Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Spatial Scenario, Based on the SPLpk Metric

Figure 10.16: Simulated Minke Whale Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Spatial Scenario, Based on the SPLpk Metric

Figure 10.17:
Simulated Minke Whale Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Spatial Scenario, Based on the SELcum Metric

Figure 10.17: Simulated Minke Whale Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Spatial Scenario, Based on the SELcum Metric

Figure 10.18:
Simulated Minke Whale Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Temporal Scenario, Based on the SELcum Metric

Figure 10.18: Simulated Minke Whale Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Temporal Scenario, Based on the SELcum Metric

 

  1. As reported by Ryan et al. (2022), humpback whales in Scottish waters have been matched with both recovering (Guadeloupe) and non-recovering (Cape Verde) populations in the western North Atlantic. The photographs of humpback whale matched to Guadeloupe were made only around Shetland (Scottish Humpback, 2023). The photographs of individuals matched with records from Cape Verde as well as Arctic feeding grounds were taken from various locations in Aberdeenshire (including Aberdeen beach) and Fife (Kinghorn) (Scottish Humpback, 2023) on the eastern coast of Scotland. Leaper et al. (2022) suggested that adverse effects on humpback whales occurring in Scottish waters could potentially impact populations in Cape Verde and Wenzel et al. (2020) estimated the total number of individual whales that occurred in the Cape Verde between 2010 and 2018 as 272 animals. Sighting records suggest that humpback whale individuals are recorded off east Scotland in consecutive years and identified sighting records suggest that there is only one individual present at any given time (Scottish Humpback, 2023). However, a substantial number of unidentified sightings is based on heavily cropped photos or the shape of the blow seen at distance and, therefore, it is not feasible to assess how many individuals were present off eastern Scotland in total over recent years. Although it has been suggested that the Firth of Forth may represent a migratory stopover, or a feeding or recovery opportunity (O’Neil et al., 2019) for humpback whales, there is no evidence that the waters in the vicinity of the Array marine mammals study area represent an important feeding ground during their migration for a notable proportion of the population. Considering the above, alongside the seasonality of humpback whale encounters (see paragraph 163) as well as piling activities at the Array concentrated in periods of suitable weather (i.e. piling is less likely during winter due to inclement weather), it is unlikely that potential disturbance of humpback whales during piling could result in measurable long term population consequences.
  2. The areas of importance off eastern Scotland were not yet specified for humpback whale. As such, potential for barrier effects is challenging to assess. However, considering that animals may be displaced from the areas only in the vicinity of the noise source during the duration of piling, it can be anticipated that individuals will temporarily shift their foraging efforts to other areas within the regional marine mammal study area.
  3. The Southern Trench ncMPA is the only site designated for protection of minke whale within the regional marine mammal study area. The ncMPA is located approximately 66.9 km north of the Array marine mammal study area. Given the far-reaching extent of the noise contours, there is potential for overlap of the outer noise contours with the Southern Trench ncMPA. Received sound levels within the CES2 MU are predicted to reach maximum SELss levels of 135 dB ( Figure 10.14   Open ▸ ) and this is below the NMFS (2005) threshold for strong disturbance (=160 dB rms). However, the modelled noise contours that overlap with the CES2 MU are above the threshold for mild disturbance (=140 dB rms). According to the behavioural response severity matrix suggested by Southall et al. (2021) such low level disturbance (scoring between 0 to 3 on a 0 to 9 scale) could lead to mild disruption of normal behaviours, but prolonged or sustained behavioural effects, including displacement are unlikely to occur. Based on minke whale densities within the ncMPA presented in NatureScot (2020), minke whales prefer the areas in the Outer Moray Firth along the northern Aberdeenshire coast, whilst the overlap of the noise contours with the MPA will be mostly along the eastern Aberdeenshire coast, where minke whale densities are expected to be low. It should also be noted, that as described in paragraph 173, the extent of the SELss contours is likely to be an overestimate as it assumes that the sound from piling maintains its impulsive characteristics at large distances, which is considered unlikely to be the case. As such, given the considerable distance to the Southern Trench ncMPA, the received level from piling is expected to have lost much of the impulsive characteristics and therefore the overlap shown in Figure 10.14   Open ▸ should be interpreted with caution.
  4. For minke whale and humpback whale, the impact (elevated underwater noise arising during piling) is predicted to be of regional spatial extent in the context of the geographic frame of reference, medium term duration, intermittent and the effect of behavioural disturbance is reversible (as receptors are expected to recover within hours/days). It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Grey seal

  1. Based on the most conservative scenario for concurrent piling of the wind turbine (3,000 kJ) in the centre and OSPs (4,400 kJ) at the northern limit of the site boundary, up to 436 grey seals are predicted to experience potential disturbance ( Table 10.32   Open ▸ , Figure 10.17   Open ▸ ). This equates to 1.19% of the East Scotland MU plus North-east England seal MU population. The estimated number of individuals potentially impacted is based on overlap of noise contours with spatial at-sea density map provided by Carter et al. (2022) and the assumption that the maximum hammer energies are reached at all piling locations (see volume 3, appendix 10.1 for more details). Findings presented by Whyte et al. (2020) indicate that there will be no measurable response in seal species at sound levels below 145 dB re 1 µPa2 SELss ( Figure 10.5   Open ▸ ). As such, for all piling locations, the outermost noise contours will not reach the coastal areas where grey seal densities are the highest (). Due to relatively low grey seal densities in the offshore waters, barrier effects (i.e. the ability to move between key areas such as haul-out sites and foraging areas offshore) will be unlikely to affect a notable proportion of the population.


Figure 10.19:
Unweighted SELss Contours as a Result of Concurrent Piling at Wind Turbine (3,000 kJ) at the Centre and OSP (4,400 kJ) at the Northern Limit of the Site Boundary overlaid with Carter et al. (2022) At-sea Density Maps

Figure 10.19: Unweighted SELss Contours as a Result of Concurrent Piling at Wind Turbine (3,000 kJ) at the Centre and OSP (4,400 kJ) at the Northern Limit of the Site Boundary overlaid with Carter et al. (2022) At-sea Density Maps


Figure 10.20:
 Unweighted SELss Contours as a Result of Concurrent Piling at Wind Turbine (3,000 kJ) at the Centre and OSP (4,400 kJ) at the Southern Limit of the Site Boundary Overlaid with Carter et al. (2022) At-sea Density Maps and Berwickshire and North Northumberland SAC

Figure 10.20:  Unweighted SELss Contours as a Result of Concurrent Piling at Wind Turbine (3,000 kJ) at the Centre and OSP (4,400 kJ) at the Southern Limit of the Site Boundary Overlaid with Carter et al. (2022) At-sea Density Maps and Berwickshire and North Northumberland SAC


  1. Following a comprehensive assessment of potential connectivity (see volume 3, appendix 10.2) and consideration of feedback received from stakeholders ( Table 10.10   Open ▸ ), the Berwickshire and North Northumberland Coast SAC is the only site designated for protection of grey seal taken forward to the assessment in the EIA. The SAC located approximately 114 km south-west from the Array marine mammal study area. In line with findings presented in Whyte et al. (2020), noise contours within which there could be a measurable grey seal response will not overlap with the SAC ( Figure 10.20   Open ▸ ).
  2. Although there is a possibility that a small number of individuals from these SAC populations may be occasionally present within the mapped disturbance contours outside the site, grey seals usually forage within 20 km from the haul-out side during their breeding season and therefore it is unlikely that individuals will travel as far offshore ( Figure 10.20   Open ▸ ). Given that the closest designated haul-out site is located approximately 157 km south-west from the Array marine mammal study area (Kinghorn Rocks, see volume 3, appendix 10.2 for more details), grey seals present within this site and in the vicinity of it are unlikely to be affected by behavioural disturbance during piling.
  3. Intermittent piling within an eight-year construction phase could coincide with key breeding periods of grey seal and is considered to be notable in the context of the lifespan of this species (see paragraph 171). In line with the Marine Mammal Methodology Note ( Table 10.10   Open ▸ ; volume 3, appendix 5.1, annex B), 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.
  4. Simulated trajectories for both the unimpacted and the impacted grey seal populations (using the total population estimate for the East Scotland seal MU (10,783) and North-east England seal MU (25,913)) are presented in Figure 10.21   Open ▸ for the maximum temporal scenario and Figure 10.22   Open ▸ for the maximum spatial scenario. Results of iPCoD modelling for grey seal against the combined seal MU populations showed that the median ratio of the impacted population to the unimpacted population was 1.000 at six years and 25 years, for both the maximum temporal scenario and the maximum spatial scenario. This indicates that there would be no significant difference between the population trajectories for the unimpacted (baseline) population and the impacted population.
  5. At 25 years after the start of piling there was no difference in the number of animals in the impacted population when compared to the unimpacted population, for both the maximum temporal and maximum spatial scenario. It is therefore considered that there would be no potential long term effects on the grey seal population resulting from elevated underwater noise arising during piling.


Figure 10.21:
Simulated Grey Seal Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Temporal Scenario

Figure 10.21: Simulated Grey Seal Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Temporal Scenario

Figure 10.22:
Simulated Grey Seal Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Spatial Scenario

Figure 10.22: Simulated Grey Seal Population Sizes for Both the Baseline (un-impacted) and the Impacted Populations Under the Maximum Spatial Scenario

 

  1. The impact (elevated underwater noise arising during piling) is predicted to be of regional spatial extent, medium term duration, intermittent and high reversibility (the impact itself occurs only during piling). Similarly, the effect of behavioural disturbance is reversible as receptors are expected to recover within hours/days. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be negligible.

 

Sensitivity of the receptor
Auditory injury (PTS)

Harbour porpoise

  1. Scientific understanding of the biological effects of threshold shifts is limited to the results of controlled exposure studies on small numbers of captive animals (reviewed in Finneran (2015)) where TTS are experimentally induced (given it is unethical to induce PTS in animals) and thresholds for PTS extrapolated using TTS growth rates. Kastelein et al. (2013) demonstrated that hearing impairment as a result of exposure to piling sound is likely to occur where the source frequencies overlap the range of peak sensitivity for the receptor species, rather than across the whole frequency hearing spectrum. The study demonstrated that for simulated piling sound (broadband spectrum), harbour porpoise hearing around 125 kHz (the key frequency for echolocation) was not affected. Rather, a measurable threshold shift in hearing was induced at frequencies of 4 kHz to 8 kHz, noting the magnitude of the hearing shift was relatively small (2.3 dB to 3.6 dB at 4 kHz to 8 kHz) due to the lower received SELs at these frequencies. This was due to most of the energy from the simulated piling occurring in lower frequencies (Kastelein et al., 2013). Kastelein et al. (2017) confirmed sensitivity declined sharply above 125 kHz in a following study.
  2. The duty cycle (the time period in which a signal or system is active) of fatiguing sounds is also likely to affect the magnitude of a hearing shift, e.g. hearing may recover to some extent during inter-pulse intervals (Kastelein et al., 2014). Other studies reported that whilst a threshold shift can accumulate across multiple exposures, the resulting shift will be less than the shift from a single, continuous exposure with the same total SEL (Finneran, 2015).
  3. In order to minimise exposure to sound, cetaceans are able to undertake some self-mitigation measures e.g. the animal can change the orientation of its head so that sound levels reaching the ears are reduced, or it can suppress hearing sensitivity by one or more neurophysiological auditory response control mechanisms in the middle ear, inner ear, and/or central nervous system. Kastelein et al. (2020) highlighted the lack of reproducibility of TTS in a harbour porpoise after it was exposed to repeated airgun sounds, and suggested self-mitigation may lead to the discrepancies.
  4. It is important to highlight that extrapolating the results from captive bred studies to how animals may respond in the natural environment should be treated with caution as there are discrepancies between experimental and natural environmental conditions. In addition, the small number of test subjects does not account for intraspecific differences (i.e. differences between individuals) or interspecific differences (i.e. extrapolating to other species) in response. However, based on the latest scientific evidence, PTS is a permanent and irreversible hearing impairment. It is therefore anticipated that harbour porpoise is sensitive to this effect as the loss of hearing would affect key life functions (such as mating and maternal fitness, communication, foraging, predator detection) and could lead to a change in an animal’s health (chronic) or vital rates (acute) (Erbe et al., 2018). In addition to studies conducted in controlled environments, there is also evidence on sound-induced hearing loss, based on inner ear analysis in a free-ranging harbour porpoise (Morell et al., 2021). Considering the above, a potential consequence of a disruption in key life functions is that the health of impacted animals would deteriorate and potentially lead to reduced birth rate in females and mortality of individuals (Costa, 2012).
  5. The assessment of sensitivity provided below takes into account the uncertainty surrounding the effects of PTS on survival and reproduction and the importance of sound for echolocation, foraging and communication in all cetaceans. Although a threshold shift may occur outside of the most sensitive hearing range, the occurrence of PTS in harbour porpoise, due to the species reliance on hearing, could be detrimental to an individual’s capacity for survival and reproduction.
  6. Therefore, harbour porpoise is deemed to have limited resilience to PTS, low recoverability or adaptability, and high international value. The sensitivity of the receptor is therefore, considered to be high.

Bottlenose dolphin and white-beaked dolphin

  1. Individual dolphins experiencing PTS would suffer a biological effect that could impact the animal’s health and vital rates (Erbe et al., 2018). Bottlenose and white-beaked dolphin are both classed as HF cetaceans (Southall et al., 2019). As described for harbour porpoise in paragraph 217 et seq. there are frequency-specific differences in the onset and growth of a noise-induced threshold shift in relation to the characteristics of the noise source and hearing sensitivity of the receiving species. For example, exposure of two captive bottlenose dolphins to an impulsive noise source between 3 kHz and 80 kHz found that there was increased susceptibility to auditory fatigue between frequencies of 10 kHz to 30 kHz (Finneran and Schlundt, 2013). The SELcum threshold incorporates hearing sensitivities of marine mammals and the magnitude of effects were considerably smaller compared to the VHF (e.g. harbour porpoise) and LF (e.g. minke whale) species, highlighting that HF species are less sensitive to the frequency components of the piling noise signal. The assessment considered the irreversibility of the effects (i.e. as noted for harbour porpoise) and importance of sound for echolocation, foraging and communication in small, toothed cetaceans.
  2. Therefore, bottlenose dolphin and white-beaked dolphin is deemed to have limited resilience to PTS, low recoverability or adaptability, and high international value. The sensitivity of both receptors is therefore, considered to be high.

Minke whale and humpback whale

  1. Empirical evidence of hearing sensitivities for minke whale is limited, although studies suggest that their vocalisation frequencies are likely to overlap with anthropogenic sounds. Minke whale do not echolocate but likely use sound for communication and, like other mysticete whales, are able to detect sound via a skull vibration enabled bone conduction mechanism (Cranford and Krysl, 2015). Mysticetes have an estimated functional hearing range between 17 Hz and 35 kHz and it is likely that they rely on low frequency hearing (Ketten and Mountain, 2009). A strong reaction to a 15 kHz ADD has been recorded in controlled exposure study on free-ranging minke whale in Iceland, suggesting that this frequency is at the likely upper limit of their hearing sensitivity (Boisseau et al., 2021). As described for harbour porpoise in paragraph 217, there are likely to be frequency-specific differences in the onset and growth of a sound-induced threshold shift in relation to the characteristics of the sound source and hearing sensitivity of the receiving species. The assessment considered the irreversibility of the effects (i.e. as noted for harbour porpoise) and importance of sound for echolocation, foraging and communication in baleen cetaceans.
  2. Therefore, minke whale is deemed to have limited resilience to PTS, low recoverability or adaptability, and high international value. The sensitivity of both receptors is therefore, considered to be high.

Grey seal

  1. In comparison to cetaceans, seals are less dependent on hearing for foraging, but may rely on sound for communication and predator avoidance (e.g. Deecke et al., 2002). Seals can detect swimming fish with their vibrissae (Schulte-Pelkum et al., 2007) but, in certain conditions, they may also listen to sounds produced by vocalising fish in order to hunt for prey. Consequently, the ecological consequences of a noise-induced threshold shift in seals may be a reduction in fitness, reproductive output and longevity (Kastelein et al., 2018). A study by Hastie et al. (2015a) reported that, based on calculations of SEL of tagged harbour seals during the construction of the Lincs Offshore Wind Farm (Greater Wash, UK), at least half of the tagged seals would have received sound levels from pile driving that exceeded auditory injury thresholds for pinnipeds (PTS). Nevertheless, population estimates indicated that the relevant population trend was increasing and therefore (whilst there are many other ecological factors that will influence the population health) this indicated that predicted levels of PTS did not affect a sufficient numbers of individuals to cause a decrease in the population trajectory (Hastie et al., 2015b). Hastie et al. (2015a) did note that the paucity of data on effects of sound on seal hearing means the exposure criteria used are intentionally conservative and therefore predicted numbers of individuals likely to be affected by PTS would also have been highly conservative.
  2. Reichmuth et al. (2019) reported the first confirmed case of PTS following a known acoustic exposure event in a seal. The study evaluated the underwater hearing sensitivity of a trained harbour seal before and immediately following exposure to 4.1 kHz tonal fatiguing stimulus (SPLrms was increased from 117 dB re 1 μPa to 182 dB re 1 μPa). Rather than the expected pattern of TTS onset and growth, an abrupt threshold shift of >47 dB (i.e. the difference between the pre-exposure and post-exposure hearing thresholds in dB) was observed half an octave above the exposure frequency. Hearing at 4.1 kHz recovered within 48 hours, however, there was a PTS of at least 8 dB at 5.8 kHz, and hearing loss was evident for more than ten years.
  3. Despite the uncertainty in the ecological effects of PTS on seals, seals rely on hearing much less than cetaceans and therefore would exhibit some tolerance (i.e. the effect is unlikely to cause a change in either reproduction or survival rates). In addition, it has been proposed that seals may be able to self-mitigate (i.e. reduce their hearing sensitivity in the presence of loud sounds in order to reduce their perceived SPL) (Kastelein et al., 2018). Although this evidence suggests a lower sensitivity of pinnipeds to PTS, based on uncertainties, a precautionary approach has been taken.
  4. The telemetry data in of volume 3, appendix 10.2, annex B confirmed some connectivity between the Isle of May SAC (2% of tagged adult grey seals, 13% of tagged juvenile/pups) and Berwickshire and North Northumberland Coast SAC (12% of tagged seals, 20% of tagged juvenile/pups), designated for grey seal within the regional marine mammal study area, and the Array marine mammal study area. No connectivity was observed between these grey seal pups and any SAC outside the East Scotland MU and North-east England seal MU.
  5. Grey seal pup production at the Isle of May SAC increased at a rate of 9.9% per year since surveys began (1979), before reaching a peak of approximately 2,000 pups in the late 1990s (SCOS, 2022). However pup production is now considered to be stable or potentially declining (SCOS, 2023, Stevens, 2023). The Berwickshire and North Northumberland Coast SAC contains two large, discrete Annex II grey seal breeding populations at the Farne Islands and Fast Castle, with grey seal pup production at these breeding sites showing a recent, rapid increase (Stevens, 2023). From 2014 to 2019, the mean estimated increase in grey seal pup production at Farne Islands was 53% (SCOS, 2022).
  6. Therefore, grey seal is deemed to have limited resilience to PTS, low recoverability or adaptability and high international value. The sensitivity of the receptor is therefore, considered to be high.