Moray Firth SAC

Bottlenose dolphin

                        Injury

611. As presented in paragraph 566, the maximum injury (PTS) range estimated for bottlenose dolphin using the SPLpk metric was 840 m for the high order detonation of 698 kg NEQ. However, this was reduced to 577 m for the realistic maximum design scenario (227 kg NEQ) ( Table 6.21   Open ▸ ). Given relatively low densities of bottlenose dolphin within the Array marine mammal study area and small injury ranges, the high order detonation of 698 kg and 227 kg could result in injury for no more than one animal ( Table 6.23   Open ▸ ). With reference to the wider populations of the species, this equated to a small proportion of the Coastal East Scotland MU (less than 0.01%). For low order clearance donor charge (0.25 kg NEQ) and clearance shot (0.5 kg NEQ), the injury ranges were considerably lower with a maximum of 61 m and 77 m respectively ( Table 6.20   Open ▸ ), and there would be no more than one animal potentially injured within these ranges ( Table 6.22   Open ▸ ). The maximum auditory injury (PTS) range for bottlenose dolphin (840 m) does not overlap with the Moray Firth SAC, which is a minimum of 175.86 km north-west from the site boundary.
612. Based on the maximum injury (PTS) range (840 m; estimated using the SPLpk metric) this potential impact would be localised within one kilometre of the detonation. UXO clearance would occur intermittently throughout the construction phase of the Array and be very short term. Although the potential impact itself is reversible (i.e. the elevation in underwater noise only occurs during the detonation event), the effect of PTS on bottlenose dolphin is permanent. With tertiary mitigation applied ( Table 6.19   Open ▸ ), it is anticipated that bottlenose dolphin would be deterred from the injury zone and therefore the likelihood of PTS and population-level effects would be unlikely (paragraph 590).

                        Behavioural disturbance (TTS as a proxy)

613. As presented in paragraphs 574 to 579, the largest range of strong behavioural disturbance to bottlenose dolphin (using TTS as a proxy) was predicted for clearance of the 698 kg NEQ using the SPLpk metric: 1,550 m ( Table 6.25   Open ▸ ). The SELcum­ metric yielded slightly lower disturbance ranges during high order detonation than the SPLpk metric: 1,310 m ( Table 6.25   Open ▸ ). For bottlenose dolphin, the number of animals predicted to be disturbed was very small with no more than one animal within the predicted effect zones ( Table 6.26   Open ▸ , Table 6.27   Open ▸ ). It should be noted that impulsive noise thresholds (TTS onset) were used in the underwater noise modelling for strong behavioural disturbance as a result of UXO clearance. As previously described in paragraph 563, the noise is unlikely to be impulsive in character once it has propagated more than a few kilometres (Hastie et al., 2019) (see volume 3, appendix 10.1 of the Array EIA Report for more details). The strong behavioural disturbance ranges will not overlap with the Moray Firth SAC.
614. Finneran et al. (2000) investigated the behavioural and auditory responses of two captive bottlenose dolphin to noise that simulated distant underwater explosions. The animals were exposed to an intense noise once per day and no auditory shift (i.e. TTS) greater than 6 dB in response to levels up to 221 dB re 1 µPa peak-to-peak (p-p) was observed. Behavioural shifts, such as delaying approach to the test station and avoiding the ‘start’ station, were recorded at 196 dB re 1 µPa p-p and 209 dB re 1 µPa p-p for the two bottlenose dolphin and continued at higher levels. However, there are several caveats to this study as discussed in Nowacek et al. (2007), with the signals used in this study distant and the study measured masked-hearing signals. The animals used in the experiment were also trained and rewarded for tolerating high levels of noise and subsequently, it can be anticipated that behavioural disruption would likely be observed at lower levels in other contexts.
615. Whilst there are no available species-specific recovery rates for HF cetaceans to TTS, there is no evidence to suggest that recovery will be significantly different to harbour porpoise recovery rates (paragraphs 606 and 606), therefore animals can recover their hearing after they are no longer exposed to elevated noise levels. It can be anticipated that bottlenose dolphin would be able to tolerate the effect without any impact on reproduction or survival rates with the ability to return to previous behavioural states or activities once the impacts had ceased.

                        Conclusion

616. Adverse effects on the qualifying Annex II marine mammal features of the Moray Firth SAC which undermine the conservation objectives of the SAC will not occur as a result of underwater noise generated during UXO clearance in the construction phase. Potential effects from this activity on the relevant conservation objectives (as presented in section 6.2.3) are discussed in turn below in Table 6.31   Open ▸ .

Table 6.31: Conclusions Against the Conservation Objectives of the Moray Firth SAC from Underwater Noise Generated During UXO Clearance in the Construction Phase of the Array Alone

617. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the Moray Firth SAC as a result of underwater noise generated during UXO clearance in the construction phase of the Array alone.

6.3.3. Injury and Disturbance due to Site-Investigation Surveys (Including Geophysical Surveys)

618. The LSE2 assessment during the HRA Stage One process identified that during the construction and operation and maintenance phases, LSE2 could not be ruled out for injury and disturbance due to site-investigation surveys (including geophysical surveys). This relates to the following sites and relevant Annex II marine mammal features:

• Berwickshire and North Northumberland Coast SAC;

–           grey seal.

• Southern North Sea SAC; and

–           harbour porpoise.

• Moray Firth SAC;

–           bottlenose dolphin.

619. The MDS and designed in measures considered for the assessment of injury and disturbance due to site-investigation surveys (including geophysical surveys) are shown in Table 6.32   Open ▸ and Table 6.33   Open ▸ respectively.

Table 6.32: MDS Considered for the Assessment of Potential Impacts to Annex II Marine Mammals due to Injury and Disturbance due to Site-Investigation Surveys (Including Geophysical Surveys) during the Construction and Operation and Maintenance Phases

Table 6.33: Designed In Measures Considered for the Assessment of Potential Impacts to Annex II Marine Mammals to Injury and Disturbance due to Site-Investigation Surveys (Including Geophysical Surveys) during the Construction and Operation and Maintenance Phases

                        Information to support the assessment

                        Overview of underwater noise modelling conducted for the Array

620. Site-investigation surveys during the construction and operation and maintenance phases of the Array have the potential to cause direct or indirect effects (including injury or disturbance) on Annex II marine mammals.
621. A detailed underwater noise modelling assessment has been carried out to investigate the potential for injurious and behavioural effects on marine mammals as a result of geophysical and geotechnical surveys, using the latest noise criteria (see volume 3, appendix 10.1 of the Array EIA Report). Several sonar-like sources will potentially be used for the geophysical surveys, including MBES, SSS, SBP and UHRS. The equipment likely to be used can typically work at a range of signal frequencies, depending on the distance to the seabed and the required resolution. For sonar-like sources the signal is highly directional, acts like a beam and is emitted in pulses. Sonar-like sources are considered by the NMFS (2018) as continuous (non-impulsive) because they generally comprise a single (or multiple discrete) frequency. Unlike the sonar-like survey sources, the UHRS is likely to utilise a sparker, which produces an impulsive, broadband source signal. Additionally, MAG will be used to measure and detect anomalies within the existing magnetic field. The survey parameters, such as source SEL, used in the underwater noise modelling are presented in detail in volume 3, appendix 10.1 of the Array EIA Report. For geotechnical surveys, potential equipment to be used include CPT, vibrocore, piston core, box core and borehole ( Table 6.32   Open ▸ ).

                        Auditory injury (PTS)

622. As detailed in volume 3, appendix 10.1 of the Array EIA Report, Injury ranges for impulsive survey sources (UHRS, CPT) are based on a comparison to the Southall et al. (2019) thresholds for impulsive noise (with the distances presented in brackets for SPLpk thresholds) whereas non-impulsive survey sources (MBES, SSS, SBP, borehole, vibrocore) results are compared against the non-impulsive thresholds. It should be noted that for impulsive noise, the injury ranges were larger for the SELcum metric compared to SPLpk ( Table 6.34   Open ▸ , Table 6.35   Open ▸ ).
623. The maximum injury (PTS) range across all geophysical surveys was estimated as 310 m for harbour porpoise due to SBP activity ( Table 6.34   Open ▸ ). For bottlenose dolphin and grey seal the maximum PTS is expected to occur out to 75 m ( Table 6.34   Open ▸ ). However, it should be noted that as sonar-like sources have very strong directivity, there is only potential for injury when an animal is directly underneath the noise source. Once the animal moves outside of the main beam, there is no potential for injury.
624. With respect to the ranges within which there is a potential of PTS occurring to marine mammals because of geotechnical investigation activities, the PTS threshold was not exceeded for all species, except harbour porpoise ( Table 6.35   Open ▸ ). Harbour porpoise are at risk of potential injury within 45 m from the noise source during the CPT activity ( Table 6.35   Open ▸ ).
625. The number of marine mammals potentially injured within the modelled PTS ranges ( Table 6.34   Open ▸ , Table 6.35   Open ▸ ) were estimated using species-specific density estimates ( Table 6.36   Open ▸ ). Given that the potential PTS ranges are relatively low, no more than one animal of each species is at risk of experiencing PTS across all types of geophysical and geotechnical surveys ( Table 6.36   Open ▸ ).
626. The auditory injury (PTS) ranges will not overlap with the Berwickshire and North Northumberland Coast SAC, Southern North Sea SAC, or the Moray Firth SAC.

Table 6.34: Potential Injury (PTS) Impact Ranges (m) For Geophysical Site-Investigation Surveys
(N/E = Threshold Not Exceeded, Comparison to Ranges for SPLpk Where Threshold was Exceeded Shown in Brackets)

Table 6.35: Potential Injury (PTS) Impact Ranges (m) For Geotechnical Site-Investigation Surveys
(N/E = Threshold Not Exceeded, Comparison to Ranges for SPLpk Where Threshold was Exceeded Shown in Brackets)

Table 6.36: Estimated Number of Animals with the Potential To Experience Injury (PTS) During Geophysical and Geotechnical Site-Investigation Surveys (Number of Animals Based on SPLpk Where Threshold was Exceeded Shown in Brackets)

627. The site-investigation surveys are considered to be short term as they will take place over a period of up to five months as per the MDS ( Table 6.32   Open ▸ ). In line with best practice guidance, designed in measures during geophysical surveys will involve the use of MMO2 and PAM to ensure that the risk of injury over the defined mitigation zone is reduced (JNCC, 2017) ( Table 6.33   Open ▸ ). The largest PTS range was estimated as 310 m for harbour porpoise exposed to SBP and it is considered that standard industry measures will be effective at reducing the risk of injury over this distance (JNCC, 2017). Since the risk of injury is assumed to be fully mitigated via designed in measures there is considered to be no residual risk of injury and therefore no population-level effects for any species.

                        Behavioural disturbance

628. It is widely recognised that the transmission frequencies of commercial sonar systems (approximately 12 kHz to 1800 kHz) overlap with the hearing ranges of many marine mammal species (Richardson et al., 1995). Many frequencies associated with sonar systems are very high and have peak frequencies well above marine mammal hearing ranges, however it is possible that relatively high levels of sound are also produced as sidebands at lower frequencies (Hayes et al., 1992) and therefore may result in behavioural responses. Aside from displacement or avoidance, other behavioural responses have been demonstrated (Wright et al., 2015). Responses to seismic surveys have included cessation of singing (Melcón et al., 2012) and alteration of dive and respiration patterns which may lead to energetic burdens on the animals (Gordon et al., 2003). In some cases, behavioural responses may lead to greater effects, such as strandings (Cox et al., 2006, Tyack et al., 2006) or interruptions to migration (Heide-Jørgensen et al., 2013). However such responses are highly context-dependent and variable, contingent on factors such as the activity of the animal at the time (Robertson, 2014), prior experience to exposure (Andersen et al., 2012), extent or type of disturbance (Melcón et al., 2012), environment in which they inhabit (Heide-Jørgensen et al., 2013) and the type of survey.
629. For impulsive noise sources (UHRS, CPT) the underwater noise modelling adopted the NMFS (2005) thresholds of 140 dB re 1 µPa for mild disturbance and 160 dB re 1 µPa for strong disturbance. For non-impulsive noise sources (MBES, SSS, SBP, borehole, vibrocore) the underwater noise modelling used the NMFS (2005) threshold of 120 dB re 1 µPa for continuous noise. The underwater noise modelling predicted that behavioural disturbance due to non-impulsive site-investigation survey equipment could occur within a range of between 27 m (borehole drilling) and up to 9,101 m (vibrocoring) for all species ( Table 6.37   Open ▸ ). Potential disturbance ranges were 320 m, 375 m, and 1,340 m for SSS, MBES, and SBP, respectively ( Table 6.37   Open ▸ ).
630. For impulsive noise sources (UHRS, CPT) the strong behavioural disturbance ranges vary from 80 m during UHRS to 140 m during CPT ( Table 6.37   Open ▸ ). Qualitatively, no more than one animal of each species would be at risk of experiencing strong behavioural disturbance. Mild disturbance may occur within 565 m during UHRS to 1,330 m during CPT and for all species no more than one animal could be affected ( Table 6.38   Open ▸ ). Up to four harbour porpoise could experience mild behavioural disturbance during CPT ( Table 6.38   Open ▸ ), however, such low level disturbance could lead to mild disruptions of normal behaviours, but prolonged or sustained behavioural effects, including displacement are unlikely to occur.
631. For non-impulsive noise sources (MBES, SSS, SBP, borehole drilling, vibrocore), the maximum behavioural disturbance ranges vary from 27 m to the maximum 9,101 m for vibrocoring ( Table 6.37   Open ▸ ). Qualitatively, no more than one animal is predicted to be disturbed during MBES, SSS and borehole drilling. With the use of SBP, up to four harbour porpoise, two grey seal, and one bottlenose dolphin are at risk of experiencing disturbance. Due to relatively large disturbance ranges predicted for vibrocoring, based on conservative species-specific densities, up to 170 harbour porpoises could experience disturbance ( Table 6.38   Open ▸ ). Vibrocoring may also lead to disturbance of up to one bottlenose dolphin and 47 grey seal ( Table 6.38   Open ▸ ).
632. However, for those animals disturbed, there is likely to be a proportional response, e.g. not all animals will be disturbed to the same extent. There is no dose-response curve available to apply in the context of site-investigation surveys, however, Joy et al. (2019) derived a dose-response for killer whales and underwater noise from vessels, indicating that marine mammals display a proportional response to non-impulsive noise. It is important to note that the life history of an individual and the context will also influence the likelihood of an individual to exhibit an aversive response to noise. Furthermore, this threshold does not take into account of ambient sound levels in the area, which may be already be above the 120 dB re 1 μPa (Farcas et al., 2020). Considering that the underwater noise modelling used a single threshold that does not take into account the ambient noise, the numbers of animals potentially disturbed presented for vibrocore and other site-investigation surveys are likely to be an overestimate.
633. The behavioural disturbance ranges presented in Table 6.37   Open ▸ will not overlap with the Berwickshire and North Northumberland Coast SAC, Southern North Sea SAC, or the Moray Firth SAC.
634. The effect of behavioural disturbance is of high reversibility (with animals returning to baseline levels soon after surveys have ceased). Whilst there may be minor effects at an individual level, these are not predicted to be at a scale that would lead to any population-level effects for any species.

Table 6.37: Potential Disturbance Ranges For Geophysical and Geotechnical Site-Investigation Surveys

Table 6.38: Estimated Number of Animals With the Potential To Be Disturbed During Geophysical and Geotechnical Site-Investigation Surveys

                        Construction and operation and maintenance phases

635. The site-investigation surveys as listed in Table 6.32   Open ▸ for the construction phase will involve the use of up to four survey vessels with up to 50 vessel movements in total. The site-investigation surveys will be carried out over five months within a three year period.
636. In the operation and maintenance phase, the MDS comprises of routine geophysical surveys such as MBES and SBP ( Table 6.32   Open ▸ ). Routine geophysical surveys will take place once every 24 months for wind turbines and OSP foundations, as well as wind turbines interior and exterior and annually for the first 3 years, then every 24 months for inter-array cables and interconnector cables. The duration of each operation and maintenance geophysical survey campaign will be up to 3 months ( Table 6.32   Open ▸ ).
637. The modelling presented in paragraphs 620 et seq. is applicable to activities across both the construction and operation and maintenance phases, which have been combined here and to avoid repetition.

                        Berwickshire and North Northumberland Coast SAC

                        Grey seal

                        Injury

638. An overview of potential auditory injury due (PTS) to elevated underwater noise during site-investigation surveys is described in paragraph 620 et seq. and is applicable to construction and operation and maintenance phase activities. As detailed in Table 6.34   Open ▸ , the modelled PTS impact ranges were low for grey seal for geophysical site investigation techniques. The threshold was not exceeded for UHRS, and ranged from 5 m (MBES), 25 m (SSS), and 75 m (SBP) for the other geophysical survey techniques. Based on these modelled injury ranges, no more than one grey seal from the relevant SMUs would have the potential to experience PTS as a result of MBES, SSS, and SBP, and none for UHRS ( Table 6.36   Open ▸ ).
639. As detailed in Table 6.35   Open ▸ , the PTS impact range for grey seal will not be exceeded for any of the geotechnical site investigation survey techniques: borehole drilling, CPT, and vibrocoring, and therefore no animals will potentially be impacted as a result ( Table 6.36   Open ▸ ). The PTS ranges for any geophysical and geotechnical survey equipment will not overlap with the Berwickshire and North Northumberland Coast SAC, which is a minimum of 113.95 km south-west from the site boundary.
640. Overall, since the risk of injury is assumed to be fully mitigated via designed in measures ( Table 6.33   Open ▸ ) there is considered to be no residual risk of injury and therefore no population-level effects for grey seal.

                        Behavioural disturbance

641. An overview of potential behavioural disturbance due to elevated underwater noise during site-investigation surveys is described in paragraph 628 et seq. and is applicable to construction and operation and maintenance phase activities.
642. For impulsive noise sources (UHRS, CPT), as mentioned in paragraph 451, the underwater noise modelling adopted the NMFS (2005) thresholds of 140 dB re 1 µPa for mild disturbance and 160 dB re 1 µPa for strong disturbance. For non-impulsive noise sources (MBES, SSS, SBP, borehole, vibrocore) the underwater noise modelling used the NMFS (2005) threshold of 120 dB re 1 µPa for continuous noise.
643. For impulsive noise sources (UHRS and CPT) the strong behavioural disturbance ranges vary from 80 m during UHRS to 140 m during CPT for all species ( Table 6.37   Open ▸ ). Quantitively, no more than one grey seal would be at risk of experiencing strong behavioural disturbance as a result. Mild disturbance may occur within 565 m during UHRS to 1,330 m during CPT for all species, and no more than one grey seal could be affected as a result ( Table 6.38   Open ▸ ).
644. The underwater noise modelling predicted that behavioural disturbance due to non-impulsive site-investigation survey equipment could occur within a range of between 27 m (borehole drilling) and up to 9,101 m (vibrocoring) for all species ( Table 6.37   Open ▸ ). Potential disturbance ranges were 320 m, 375 m, and 1,340 m for SSS, MBES, and SBP, respectively ( Table 6.37   Open ▸ ). Quantitively, no more than one grey seal is predicted to be disturbed during MBES, SSS and borehole drilling ( Table 6.38   Open ▸ ). With the use of SBP, up to two grey seal are at risk of experiencing disturbance. Due to relatively large disturbance ranges predicted for vibrocoring, based on conservative species-specific densities, up to 47 grey seal could experience disturbance ( Table 6.38   Open ▸ ).
645. However, as described in paragraph 632, the numbers of animals potentially disturbed for vibrocore and other site-investigation surveys are likely to be an overestimate.
646. The behavioural disturbance ranges will not overlap with the Berwickshire and North Northumberland Coast SAC, which is 113.95 km south-west of the site boundary.
647. The effect of behavioural disturbance is of high reversibility (with animals returning to baseline levels soon after surveys have ceased). Whilst there may be minor effects at an individual level, these are not predicted to be at a scale that would lead to any population-level effects for the grey seal feature of the Berwickshire and North Northumberland Coast SAC.

                        Conclusion

648. Adverse effects on the qualifying Annex II marine mammal features of the Berwickshire and North Northumberland Coast SAC which undermine the conservation objectives of the SAC will not occur as a result of injury and disturbance due to site-investigation surveys during the construction and operation and maintenance phases. Potential effects from this activity on the relevant conservation objectives (as presented in section 6.2.1) are discussed in turn below in Table 6.39   Open ▸ .

Table 6.39: Conclusions Against the Conservation Objectives of the Berwickshire and North Northumberland Coast SAC from Injury and Disturbance due to Site-Investigation Surveys (Including Geophysical Surveys) during the Construction and Operation and Maintenance Phases of the Array Alone

649. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the Berwickshire and North Northumberland Coast SAC as a result of as a result of injury and disturbance due to site-investigation surveys during the construction and operation and maintenance phases of the Array alone.

                        Southern North Sea SAC

                        Harbour porpoise

                        Injury

650. An overview of potential auditory injury (PTS) due to elevated underwater noise during site-investigation surveys is described in paragraph 620 et seq. and is applicable to construction and operation and maintenance phase activities. As detailed in Table 6.34   Open ▸ , the modelled PTS impact ranges were low for harbour porpoise for geophysical site investigation techniques. These ranged from 10 m (UHRS), 75 m (MBES and SSS), and 310 m (SBP). Based on these modelled injury ranges, no more than one harbour porpoise from the North Sea MU population would have the potential to experience PTS as a result of geophysical site-investigation survey equipment ( Table 6.36   Open ▸ ).
651. As detailed in Table 6.35   Open ▸ , the PTS impact range for harbour porpoise will not be exceeded for borehole drilling and vibrocoring, and therefore no animals will potentially be impacted as a result ( Table 6.36   Open ▸ ). For CPT, potential PTS ranges were modelled out to a maximum of 45 m ( Table 6.35   Open ▸ ), with up to one harbour porpoise potentially impacted ( Table 6.36   Open ▸ ).  The PTS ranges for any geophysical and geotechnical survey equipment will not overlap with the Southern North Sea SAC, which is a minimum of 129.86 km south-east from the site boundary.
652. Overall, since the risk of injury is assumed to be fully mitigated via designed in measures ( Table 6.33   Open ▸ ) there is considered to be no residual risk of injury and therefore no population-level effects for harbour porpoise.

                        Behavioural disturbance

653. An overview of potential behavioural disturbance due to elevated underwater noise during site-investigation surveys is described in paragraph 628 et seq. and is applicable to construction and operation and maintenance phase activities.
654. For impulsive noise sources (UHRS, CPT) the underwater noise modelling adopted the NMFS (2005) thresholds of 140 dB re 1 µPa for mild disturbance and 160 dB re 1 µPa for strong disturbance. For non-impulsive noise sources (MBES, SSS, SBP, borehole, vibrocore) the underwater noise modelling used the NMFS (2005) threshold of 120 dB re 1 µPa.
655. For impulsive noise sources (UHRS and CPT) the strong behavioural disturbance ranges vary from 80 m during UHRS to 140 m during CPT for all species ( Table 6.37   Open ▸ ). Qualitatively, up to four harbour porpoise may experience strong behavioural disturbance as a result of CPT and up to one due to UHRS ( Table 6.38   Open ▸ ). Mild disturbance may occur within 565 m during UHRS to 1,330 m during CPT for all species. However, such low level disturbance could lead to mild disruptions of normal behaviours, but prolonged or sustained behavioural effects, including displacement are unlikely to occur.
656. The underwater noise modelling predicted that behavioural disturbance due to non-impulsive site-investigation survey equipment could occur within a range of between 27 m (borehole drilling) and up to 9,101 m (vibrocoring) for all species ( Table 6.37   Open ▸ ). Potential disturbance ranges were 320 m, 375 m, and 1,340 m for SSS, MBES, and SBP, respectively ( Table 6.37   Open ▸ ). Qualitatively, no more than one harbour porpoise is predicted to be disturbed during MBES, SSS and borehole drilling ( Table 6.38   Open ▸ ). With the use of SBP, up to four harbour porpoise are at risk of experiencing disturbance. Due to relatively large disturbance ranges predicted for vibrocoring, based on conservative species-specific densities, up to 170 harbour porpoise could experience disturbance ( Table 6.38   Open ▸ ). However, as described in paragraph 632, the numbers of animals potentially disturbed presented for vibrocore and other site-investigation surveys are likely to be an overestimate.
657. The behavioural disturbance ranges will not overlap with the Southern North Sea SAC, which lies 129.86 km south of the site boundary.
658. A study by van Beest et al. (2018) used fine-scale data from harbour porpoise equipped with high-resolution location and dive loggers when exposed to airgun pulses at ranges of 420 m to 690 m with sound level estimates of 135 dB re 1µPa2s to 147 dB re 1µPa2s (SEL). They showed different responses to sound exposure, with one individual displayed rapid and directed movements away from the exposure site whilst two individuals used shorter and shallower dives (compared to natural behaviour) immediately after exposure. This sound-induced movement typically lasted for eight hours or less, with an additional 24 hour recovery period until natural behaviour was resumed (van Beest et al. (2018)).
659. A recent study by Sarnocińska et al. (2020) indicated temporary displacement or change in harbour porpoise echolocation behaviour in response to a 3D seismic survey in the North Sea. No general displacement was detected from 15 km away from any seismic activity but decreases in echolocation signals were detected up to 8 to 12 km from the active airguns. Considering findings of other studies (Dyndo et al., 2015, Tougaard et al., 2015), harbour porpoise disturbance ranges due to airgun sound are predicted to be smaller than to piling sound at the same energy. The reason for this is that the perceived loudness of the airgun pulses is predicted to be lower than for piling due to less energy at the higher frequencies where porpoise hearing is better (Sarnocińska et al., 2020). Likewise, Thompson et al. (2013) used PAM and DAS to study changes in the occurrence of harbour porpoise across a 2,000 km2 study area during a commercial 2D seismic survey in the North Sea. The study found acoustic detections decreased significantly during the survey period in the impact area compared with a control area, but this effect was small in relation to natural variation. Animals were typically detected again at affected sites within a few hours, and the level of response declined through the survey period (ten days) suggesting exposure led to some tolerance of the activity (Thompson et al., 2013). Thompson et al. (2013) therefore suggested that prolonged seismic survey activity did not lead to broader-scale displacement into sub-optimal or higher risk habitat.
660. Overall, the effect of behavioural disturbance from site-investigation surveys is of high reversibility (with animals returning to baseline levels soon after surveys have ceased). Whilst there may be minor effects at an individual level, these are not predicted to be at a scale that would lead to any population-level effects for the harbour porpoise feature of the Southern North Sea SAC.

                        Conclusion

661. Adverse effects on the qualifying Annex II marine mammal features of the Southern North Sea SAC which undermine the conservation objectives of the SAC will not occur as a result of injury and disturbance due to site-investigation surveys during the construction and operation and maintenance phases. Potential effects from this activity on the relevant conservation objectives (as presented in section 6.2.2) are discussed in turn below in Table 6.40   Open ▸ .

Table 6.40: Conclusions Against the Conservation Objectives of the Southern North Sea SAC from Injury and Disturbance due to Site-Investigation Surveys (Including Geophysical Surveys) during the Construction and Operation and Maintenance Phases of the Array Alone

662. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the Southern North Sea SAC as a result of site-investigation surveys during the construction and operation and maintenance phases of the Array alone.

                        Moray Firth SAC

                        Bottlenose dolphin

                        Injury

663. An overview of potential auditory injury due (PTS) to elevated underwater noise during site-investigation surveys is described in paragraph 620 et seq. and is applicable to construction and operation and maintenance phase activities. As detailed in Table 6.34   Open ▸ , the modelled PTS impact ranges were low for bottlenose dolphin for geophysical site investigation techniques. These ranged between 65 m for MBES and 75 m for SSS and SBP. The threshold was not exceeded for UHRS. Based on these modelled injury ranges, no more than one bottlenose dolphin from the Coastal East Scotland MU population would have the potential to experience PTS as a result of geophysical site-investigation survey equipment ( Table 6.36   Open ▸ ).
664. As detailed in Table 6.35   Open ▸ , the PTS impact range for bottlenose dolphin will not be exceeded for any geotechnical site investigation survey techniques, and therefore no animals will potentially be impacted as a result ( Table 6.36   Open ▸ ). The PTS ranges for any geophysical and geotechnical survey equipment will not overlap with the Moray Firth SAC, which is a minimum of 175.86 km north-west from the site boundary.
665. Overall, since the risk of injury is assumed to be fully mitigated via designed in measures ( Table 6.33   Open ▸ ) there is considered to be no residual risk of injury and therefore no population-level effects for bottlenose dolphin.

                        Behavioural disturbance

666. An overview of potential behavioural disturbance due to elevated underwater noise during site-investigation surveys is described in paragraph 628 et seq. and is applicable to construction and operation and maintenance phase activities.
667. For impulsive noise sources (UHRS, CPT) the underwater noise modelling adopted the NMFS (2005) thresholds of 140 dB re 1 µPa for mild disturbance and 160 dB re 1 µPa for strong disturbance. For non-impulsive noise sources (MBES, SSS, SBP, borehole, vibrocore) the underwater noise modelling used the NMFS (2005) threshold of 120 dB re 1 µPa.
668. For impulsive noise sources (UHRS and CPT) the strong behavioural disturbance ranges vary from 80 m during UHRS to 140 m during CPT for all species ( Table 6.37   Open ▸ ). Qualitatively, up to one bottlenose dolphin may experience strong behavioural disturbance as a result of UHRS and none for CPT ( Table 6.38   Open ▸ ). Mild disturbance may occur up to 565 m during UHRS and up to 1,330 m during CPT for all species. Such low level disturbance could lead to mild disruptions of normal behaviours, but prolonged or sustained behavioural effects, including displacement are unlikely to occur.
669. The underwater noise modelling predicted that behavioural disturbance due to non-impulsive site-investigation survey equipment could occur within a range of between 27 m (borehole drilling) and up to 9,101 m (vibrocoring) for all species ( Table 6.37   Open ▸ ). Potential disturbance ranges were 320 m, 375 m, and 1,340 m for SSS, MBES, and SBP, respectively ( Table 6.37   Open ▸ ). Qualitatively, no more than one bottlenose dolphin is predicted to be disturbed during MBES, SBP, SSS and borehole drilling ( Table 6.38   Open ▸ ). Even given the relatively large disturbance ranges predicted for vibrocoring, based on conservative bottlenose dolphin densities, up to one bottlenose dolphin could experience disturbance ( Table 6.38   Open ▸ ). However, as described in paragraph 632, the numbers of animals potentially disturbed presented for vibrocore and other site-investigation surveys are likely to be an overestimate.
670. The behavioural disturbance ranges presented in Table 6.37   Open ▸ will not overlap with the Moray Firth SAC, which lies 175.86 km of the site boundary.

                        Conclusion

671. Adverse effects on the qualifying Annex II marine mammal features of the Moray Firth SAC which undermine the conservation objectives of the SAC will not occur as a result of site-investigation surveys during the construction and operation and maintenance phases. Potential effects from this activity on the relevant conservation objectives (as presented in section 6.2.3) are discussed in turn below in Table 6.41   Open ▸ .

Table 6.41: Conclusions Against the Conservation Objectives of the Moray Firth SAC from Injury and Disturbance due to Site-Investigation Surveys (Including Geophysical Surveys) during the Construction and Operation and Maintenance Phases of the Array Alone

672. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the Moray Firth SAC as a result of site-investigation surveys during the construction and operation and maintenance phases of the Array alone.

6.3.4. Changes in Prey Availability

673. The LSE2 assessment during the HRA Stage One process identified that LSE2 could not be ruled out for changes in prey availability due to underwater noise from piling and UXO clearance during the construction phase of the Array alone. This relates to the following sites and relevant Annex II marine mammal features:

• Berwickshire and North Northumberland Coast SAC;

–           grey seal.

• Southern North Sea SAC; and

–           harbour porpoise.

• Moray Firth SAC;

–           bottlenose dolphin.

674. The MDS and designed in measures considered for the assessment of changes in prey availability are shown in Table 6.42   Open ▸ and Table 6.43   Open ▸ respectively

Table 6.42: MDS Considered for the Assessment of Potential Impacts to Annex II Marine Mammals due to Changes in Prey Availability during the Construction Phase

Table 6.43: Designed In Measures Considered for the Assessment of Potential Impacts to Annex II Marine Mammals to Changes in Prey Availability during the Construction Phase