Tier 3

Construction phase
  1. The only Tier 3 project which has been identified in the CEA with the potential to result in cumulative effects as a result of injury and disturbance from elevated underwater noise during piling within the regional marine mammal study area is Green Volt Floating Offshore Wind Farm.

Magnitude of impact

  1. The Green Volt scoping report has identified potential for auditory injury and disturbance as a result of underwater noise during piling as potential impacts during construction of the project (Royal Haskoning DHV, 2021). Floating wind turbine and OSPs/Offshore convertor station platform structures offer benefits over conventional fixed foundations in terms of reduced underwater noise as extensive piling operations are not required. Floating wind therefore also minimises potential noise impacts upon sea mammals during the construction phase of the project. If the floating structures for OSPs/Offshore convertor station platforms are not opted for, limited piling activities (installation of four substation foundations over an estimated period of 36 hours) may take place in offshore waters (approximately 75 km from the coast; Royal Haskoning DHV, 2021). However,
  2. Given the distance from the Proposed Development, the overlap of disturbance range as a result of underwater noise due to piling is highly unlikely. No site-specific underwater noise modelling or assessment of impacts on marine mammals is currently available for the Green Volt Floating offshore Wind Farm, however, if required, piling at this project will be of short duration (36 hours) and negligible in comparison to piling periods at offshore wind farms listed in Tier 2 (see paragraph 478 et seq.).
  3. The cumulative impact of behavioural disturbance with respect to marine mammal IEFs is predicted to be of regional spatial extent, medium term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Sensitivity of receptor

  1. The sensitivity of marine mammals to cumulative disturbance from elevated underwater noise due to piling is as described in paragraph 538 et seq. for the Tier 2 project.
  2. All marine mammals, which are IEFs of international value, are deemed to be of medium vulnerability and high recoverability. The sensitivity of the receptors to behavioural disturbance is therefore considered to be medium.

 

Significance of effect

  1. Overall, the magnitude of the cumulative effect is deemed to be low and the sensitivity of the receptor is considered to be medium. The cumulative effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Further mitigation and residual effect

  1. No secondary marine mammal mitigation, other than that proposed for the Proposed Development alone (described in detail in paragraph 244 et seq.) is considered necessary because the predicted effect in the absence of mitigation is not significant in EIA terms. Therefore, the residual effect is considered to be of minor adverse significnce which is not significant in EIA terms.

Injury and disturbance to marine mammals from elevated underwater noise during site investigation surveys

  1. The risk of injury in terms of PTS to marine mammal receptors as a result of underwater due to site investigation surveys would be expected to be localised to within the boundaries of the respective projects. The assessment for the Proposed Development found that the numbers of animals impacted will be extremely low and the magnitude of the impact with respect to auditory injury occurring in marine mammals has been assessed as minor. Therefore, there is no potential for cumulative impacts for injury from elevated underwater noise due to site investigation surveys and the cumulative assessment provided in paragraph 551 et seq. focuses on disturbance only.

Tier 2

Construction phase

Magnitude of impact

  1. The construction of the Proposed Development, together with Tier 2 projects identified in Table 10.55   Open ▸ may lead to disturbance to marine mammals site investigation surveys. Projects screened into this assessment include the construction and operation and maintenance Eastern Link 1 and Eastern Link 2.
  2. The construction as well as operation and maintenance phases of Eastern Link 1 and Eastern Link 2, located respectively 14 km and 28 km from the Proposed Development array area, will overlap with the construction phase of the Proposed Development. Based on the Environmental Appraisals for both projects, the only underwater sound noise sources that are within hearing range of marine mammals and have potential to have an effect, are the operation of the Ultra-short Baseline (USBL) and the SBP (AECOM, 2022a; 2022b). The disturbance ranges for marine mammals were estimated as 63 m for USBL and 4,642 m for SBP. The detailed assessment of underwater noise impacts for both projects was presented only for installation phase. However, the significance of the effect resulting from increased underwater noise due site investigation surveys was assessed for both phases – installation as well as operation and maintenance – as minor and therefore not significant[13]. There are no disturbance ranges presented for the USBL for the Proposed Development alone but the disturbance range for SBP has been assessed as 2,045 m. Nevertheless, the assessment presented in paragraph 257 et seq. is based on the maximum disturbance range estimated as 7,459 m for vibro-coring. Based on the distance from the Proposed Development to both projects, the overlap of disturbance ranges is highly unlikely. The potential for an overlap exists only for site-investigation surveys taking place in the northern part of the Eastern Link 1, close to the Proposed Development export cable corridor and landfall. However, it needs to be noted that site investigation survey equipment will not be operating continuously, it will be used when required for investigations of particular areas of the seabed where additional information is required to inform the construction. Surveys are anticipated to be short-term in nature (weeks to a few months) and occur intermittently over the construction phase.
  3. The impact of site investigation surveys leading to behavioural effects is predicted to be of local spatial extent, short term duration, intermittent and the effect of behavioural disturbance is of high reversibility (with animals returning to baseline levels soon after surveys have ceased). It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Sensitivity of receptor

  1. The sensitivity of marine mammals to elevated underwater noise due to site investigation surveys is as described in section 10.11, paragraph 273 et seq.
  2. Berwickshire and North Northumberland Coast SAC is designated for grey seal and located on the east coast of Scotland, within the close vicinity of the projects screened into this assessment. With foraging ranges of up to 100 km this species may be sensitive to a behavioural disturbance during the site-investigation surveys as they move between haul-outs and key foraging areas. As advised by NatureScot for HRA purposes (see SSER, 2022d), grey seal in Scotland tend to stay within 20 km of the breeding colony during the breeding season, therefore that further restrict the foraging grounds in the vicinity of haul outs. During the breeding or moulting season many seals tend to spend more time on land, unaffected by underwater sound. Nevertheless, males and females have different requirements and fattening patterns throughout the year and they rely heavily on fat as a metabolic fuel and for insulation (Bennett et al., 2017). Females accumulate fat stores during seven months of foraging at sea between the moulting and breeding period, and the amount stored is roughly equivalent to the amount lost during breeding (Sparling et al., 2006), therefore the availability of food is vital to offspring survival and female fitness. Animals may be deterred from foraging grounds during the operation of the survey equipment, however, given that alternative areas for foraging are widely available, the disturbance to seals foraging offshore is not considered likely to have a significant impact on food availability (see paragraph 430 et seq. for the cumulative assessment of impacts as a result of changes in prey availability) and therefore on fitness and survival of the grey seal population.
  3. It is expected that, to some extent, marine mammals will be able to adapt their behaviour to reduce impacts on survival and reproduction rates and tolerate elevated levels of underwater noise during site investigation surveys. Marine mammals, which are IEFs of international value, are deemed to be of medium vulnerability and high recoverability. The sensitivity of the receptor to PTS and disturbance from elevated underwater noise during site investigation surveys is therefore considered to be medium.

Significance of effect

  1. Overall, the magnitude of the cumulative impact is deemed to be low and the sensitivity of the receptor is considered to be medium. Cumulatively, the effect will therefore be of minor adverse significance, which is not significant in EIA terms.

Further mitigation and residual effect

  1. No secondary marine mammal mitigation is considered necessary as the predicted effect in the absence of further mitigation (beyond the designed in measures outlined in section 10.10) is not significant in EIA terms. Therefore, the residual effect is considered to be of minor adverse significance which is not significant in EIA terms.
Operation and maintenance phase

Magnitude of impact

  1. The operation and maintenance activities of the Proposed Development will overlap with Tier 2 projects identified in Table 10.55   Open ▸ and may lead to disturbance to marine mammals from site investigation surveys. Projects screened into this assessment include disposal activities at the Eyemouth disposal site, the operation and maintenance of Eastern Link 1 and Eastern Link 2.
  2. The maximum design scenario for Proposed Development alone comprises routine geophysical surveys estimated to occur every six months for first two years and annually thereafter. This equates to up to 37 surveys over the 35-year life cycle of Proposed Development ( Table 10.16   Open ▸ ).
  3. As presented in paragraph 552, the detailed assessment of impacts on marine mammals as a result of underwater noise during the maintenance and operation and maintenance phase of the Eastern Link 1 and Eastern Link 2 is unavailable. However, the significance of the effect for the operation and maintenance phase has been estimated as minor based on the assessment presented for the cable installation phase (AECOM, 2022a; 2022b).
  4. An overview of potential impacts resulting from behavioural disturbance due to elevated underwater noise during geophysical site investigation surveys is described in paragraph 552 et seq. for the construction phase and has not been reiterated here for the operation and maintenance phase. The magnitude of the impact of underwater noise from geophysical surveys during operation and maintenance phase in combination with other projects considered in this cumulative assessment could result in a negligible alteration to the distribution of marine mammals and overlap of disturbance ranges is unlikely to occur. Surveys are anticipated to be short-term in nature (weeks to a few months) and occur intermittently over the operation and maintenance phase.
  5. With designed-in measures implemented for the geophysical surveys, the impact is predicted to be of local to regional spatial extent, short-term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Sensitivity of receptor

  1. The sensitivity of marine mammals to cumulative disturbance from elevated underwater noise due to vessel use and other activities is as described in paragraph 554 et seq. for the construction phase.
  2. All marine mammals, which are IEFs of international value, are deemed to be of medium vulnerability and high recoverability. The sensitivity of the receptor is therefore considered to be medium.

Significance of effect

  1. Overall, the magnitude of the cumulative impact is deemed to be low and the sensitivity of the receptor is considered to be medium. Cumulatively, the effect will therefore be of minor adverse significance, which is not significant in EIA terms.

Further mitigation and residual effect

  1. No secondary marine mammal mitigation is considered necessary as the predicted effect in the absence of further mitigation (beyond the designed in measures outlined in section 10.10) is not significant in EIA terms. Therefore, the residual effect is considered to be minor which is not significant in EIA terms.

Injury and disturbance to marine mammals from elevated underwater noise during UXO clearance

Tier 2

Construction phase
  1. The construction of the Proposed Development, together with construction of Tier 2 projects identified in Table 10.55   Open ▸ , may lead to injury and/or disturbance to marine mammals from underwater noise during UXO clearance. Other projects screened into the assessment within the regional marine mammal study area include construction of Inch Cape Offshore Wind Farm, Moray West, Blyth Demo 2 for bottlenose dolphin, grey seal and harbour seal and additional following projects Dogger Bank Creyke Beck A, Dogger Bank Creyke Beck B, Dogger Bank Teesside A, Sofia Offshore Wind Farm, Hornsea Project Three and Hornsea Project Four for harbour porpoise, white-beaked dolphin and minke whale.
  2. Potential effects of underwater noise from UXO detonations on marine mammals include mortality, physical injury or auditory injury. The risk of injury in terms of PTS to marine mammal receptors as a result of underwater noise during UXO clearance would be expected to be localised to the vicinity around the boundaries of the respective projects. It is anticipated that standard offshore wind industry mitigation methods (which include visual and acoustic monitoring of marine mammals as standard and additional mitigation in form of ADDs and/or soft start charges) will be applied based on UXO specific risk assessment, thereby reducing the magnitude of the impact with respect to auditory injury occurring in marine mammals. However, the potential for a residual risk of injury was investigated based on the UXO clearance technique and mitigation proposed. As previously presented for the Proposed Development alone in paragraph 295 et seq., the duration of effect for each UXO detonation is less than one second and behavioural effects are therefore considered to be negligible in this context. Potential cumulative effects from TTS are also investigated.

Magnitude of impact

  1. Projects screened in for this cumulative assessment are expected to involve similar construction activities to those described for the Proposed Development alone, including UXO clearance activities. It is anticipated that, for all projects, impacts associated with these activities will require additional assessment under EPS licensing, however such applications are not yet available in the public domain. Hornsea Project Three provides a high-level assessment of the impacts of potential UXO clearance as a part of the EIA Report (GoBe, 2018a) with the maximum design scenario for the assessment based on the number of UXO cleared for Hornsea Project One. Similarly, for Hornsea Project Four separate Marine Licence application will be submitted pre-construction for the detonation of any UXO. However, since detonation of UXO is a source of underwater noise the assessment has been also provided as a part of the EIA chapter (SMRU Consulting, 2021). For all other projects, due to the lack of project information at this stage, it is not possible to undertake a full, quantitative assessment for this impact therefore a qualitative assessment has been provided.
  2. For Hornsea Project Three, there was no site-specific modelling undertaken and therefore the assessment of potential impacts on marine mammals as a result of underwater noise during UXO clearance was based on noise modelling for Hornsea Project One (PTS ranges) and 26 km buffer (disturbance range; Table 10.62   Open ▸ ) (GoBe, 2018a). In addition, no noise modelling was conducted for UXO clearance for Hornsea Project Four (SMRU Consulting, 2021).

 

Table 10.62:
UXO Clearance Parameters for Proposed Development and Hornsea Project Three

Table 10.62: UXO Clearance Parameters for Proposed Development and Hornsea Project Three

 

Permanent threshold shift

  1. For a given marine mammal hearing group, exceedance of the threshold for the onset of PTS may result in a permanent hearing loss which in turn could inhibit ecological functioning, such as communication, foraging, navigation and predator avoidance. The inability to continue with these important activities could eventually lead to a decline in vital rates of an individual, including growth, reproduction and subsequently survival.
  2. For the Proposed Development alone, the maximum range across which animals have the potential to experience PTS due to high order detonation of 300 kg charge was assessed for harbour porpoise as approximately 10,630 m (see paragraph 300 et seq.). Minke whale could potentially experience PTS within a maximum of approximately 4 km from the source. The PTS ranges for HF cetaceans (bottlenose dolphin and white-beaked dolphin) as well as seals are relatively smaller with a maximum range of approximately 615 m and 2,085 m, respectively. PTS onset ranges for Inch Cape Offshore Wind Farm, Moray West, Blyth Demo 2, Dogger Bank Creyke Beck A, Dogger Bank Creyke Beck B, Dogger Bank Teesside A and Sofia Offshore Wind Farm are unknown, but for the purpose of this assessment we can assume that the maximum adverse scenario is no greater than assessed for the Proposed Development alone (since 300 kg represents a typical large munition size for the northern North Sea; Seagreen Wind Energy, 2021). Depending on the type of detonation and size of UXO, UXO clearance activities may have residual effects in respect to marine mammals and PTS injury. In November 2021, the UK government published a joint interim statement advising to use low noise alternatives to high order detonations where possible and it is anticipated that future developments will follow this guidance. However, due to a small inherent risk with these clearance methods that the UXO will detonate or deflagrate violently, accidental high order detonation can be expected as a maximum adverse scenario. Taking into account high order detonation of 300 kg charge and secondary mitigation measures, only small proportion of the respective species MU population would be affected (for more details on the number of animals potentially injured and percentage of respective populations for Proposed Development see paragraph 305 et seq.).
  3. For the Proposed Development alone, with secondary mitigation applied (described in detail in paragraph 338 et seq.), there was predicted to be a small residual effect of PTS based on accidental high order detonation of UXOs. The residual magnitude for all species, except for harbour porpoise, was determined to be negligible. For harbour porpoise, it is expected that small, nominal number of animals could be exposed to PTS threshold. Given that details about UXO clearance technique to be used and charge sizes will not be available until after the consent is granted, it is not possible to quantify the effects of UXO detonations and therefore the residual number of animals is not presented within this chapter. At a later stage, when details about UXO sizes and specific clearance techniques to be used become available, it will be possible to provide detailed assessment and tailor the secondary mitigation to specific UXO sizes and species in order to reduce the risk of injury. Therefore, prior to the commencement of UXO clearance works, a more detailed assessment will be produced as a part of the EPS licence supporting information. Additionally, appropriate secondary mitigation measures will be agreed as a part of a UXO specific MMMP. It is therefore anticipated that following the application of secondary mitigation measures, agreed as a part of the UXO specific MMMP, the residual magnitude of this effect will be reduced to low.
  4. As previously stated, for Hornsea Project Three there was no site-specific modelling undertaken and therefore the assessment of potential impacts in terms of injury (PTS) on marine mammals as a result of underwater noise during UXO clearance used the NOAA modelling for Hornsea Project One (GoBe, 2018a). The PTS ranges were presented for harbour porpoise based on the 260 kg charge. The remainder of the Hornsea Project One noise modelling predicted impact ranges for white-beaked dolphin and minke whale based on 227 kg charge ( Table 10.63   Open ▸ ). The sensitivity of cetaceans and seals was assessed as high and medium, respectively. Following the application of appropriate secondary mitigation measures (to be agreed as a part of a UXO specific MMMP) the residual risk of injury was expected to be negligible for all marine mammal species (GoBe, 2018a).
  5. Due to lack of project specific UXO noise modelling, Hornsea Project Four used estimates of the source level and predicted PTS-onset impact ranges based on Hornsea Project Two, calculated for a range of expected UXO sizes (up to 800 kg; SMRU Consulting, 2021). It was highlighted in the assessment that PTS-onset impact ranges, and number of animals affected, are likely to be overestimated, especially for large charge sizes ( Table 10.63   Open ▸ ). The assessment concluded that with mitigation measures, which will be agreed as a part of the UXO MMMP, the impact of the UXO clearance on marine mammals will not be significant.

 

Table 10.63:
Number of Animals with the Potential to Experience PTS During UXO Clearance at Hornsea Project Three and Hornsea Project Four

Table 10.63: Number of Animals with the Potential to Experience PTS During UXO Clearance at Hornsea Project Three and Hornsea Project Four

 

  1. The cumulative impact of PTS from elevated subsea noise during UXO clearance is predicted to be of local to regional spatial extent, very short-term duration, intermittent and the effect of injury is of low reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Temporary threshold shift

  1. The resulting effect of TTS onset would be a potential temporary loss in hearing. Whilst some ecological functions could be inhibited in the short-term due to TTS, these are reversible on recovery of the animal’s hearing and therefore not considered likely to lead to any long-term effects on the individual.
  2. For the Proposed Development alone, the maximum range across which animals have the potential to experience TTS due to high order detonation of a 300 kg charge (maximum adverse scenario) was assessed for minke whale as approximately 54 km (see paragraph 310 et seq.). Harbour porpoise could potentially experience TTS within a maximum of 19 km from the source. The TTS ranges for HF cetaceans (bottlenose dolphin and white-beaked dolphin) as well as seals are relatively smaller with a maximum of approximately 1 km and 6 km, respectively. TTS onset ranges for Inch Cape Offshore Wind Farm, Moray West, Blyth Demo 2, Dogger Bank Creyke Beck A, Dogger Bank Creyke Beck B, Dogger Bank Teesside A and Sofia Offshore Wind Farm are unknown, but for the purpose of this assessment we can assume that the maximum adverse scenario is no greater than assessed for the Proposed Development alone (since 300 kg represents a typical large munition size for the northern North Sea; Seagreen Wind Energy Ltd, 2021). A spatial maximum design scenario would occur where UXO clearance activities occur concurrently at the respective projects considered in the cumulative assessment. This is however highly unlikely, as due to safety reasons the UXO clearance activities takes place before other construction activities commence, and all projects considered in the CEA start their construction activities between three to one year/s before commencement of construction at Proposed Development. Temporally however, sequential UXO clearance at respective projects could lead to a longer duration of effect. Since each clearance event results in no more than a one second ensonification event and since TTS is a recoverable injury, the potential for cumulative effects with respect to TTS is considered to be very limited, even for projects within Firth of Forth and Tay (i.e. Inch Cape).
  3. For the Proposed Development alone, harbour porpoise, minke whale and grey seal have the potential to be affected by TTS in relatively high numbers although these numbers will be reduced with additional secondary mitigation proposed (see paragraph 338; Table 10.49   Open ▸ ). As previously stated, for Hornsea Project Three there was no site-specific modelling undertaken and therefore the assessment of potential impacts on marine mammals as a result of underwater noise during UXO clearance compared results from two approaches: 1) using a buffer of 26 km around the source location to determine the behavioural impact area, and 2) TTS onset ranges modelled by the Beatrice Offshore Wind Farm from a 50 kg charge mass (GoBe, 2018a). Given that the former option is more precautionary, it has been carried forward to the assessment with disturbance area and number of animals presented in Table 10.64   Open ▸ . For Hornsea Three the magnitude was assessed as low and sensitivity of marine mammal receptors as medium. Therefore, the overall significance of this effect for Hornsea Project Three was assessed as negligible to minor.
  4. Hornsea Project Four presented the predicted ranges for the onset of TTS from UXO clearance, but since no assessment of the number of animals, magnitude, sensitivity or significance of effect was given, TTS with respect to this project could not be quantitatively assessed.

 

Table 10.64:
Number of Animals with the Potential to Experience TTS Onset During UXO Clearance at Hornsea Project Three

Table 10.64: Number of Animals with the Potential to Experience TTS Onset During UXO Clearance at Hornsea Project Three

 

  1. Production of underwater sound during detonation of UXOs as a part of the cumulative projects as well as the Proposed Development have the potential to cause TTS (disturbance) in marine mammal receptors, however, this effect will be very short-lived (during detonation only) and reversible.
  2. The cumulative impact of TTS from elevated subsea noise during UXO clearance is predicted to be of regional spatial extent, very short-term duration, intermittent and the effect is of high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore, considered to be low to medium.

Sensitivity of receptor

  1. The sensitivity of marine mammals to disturbance from elevated underwater noise during UXO clearance is as described in section 10.11, paragraph 327 et seq.

Permanent threshold shift

  1. Various studies proven that harbour porpoise is at risk of permanent hearing loss at distances of several kilometres (up to 6 km for 325 charge mass) (Von Benda-Beckmann et al., 2015; Salomons et al., 2021). There is much less known about the sensitivity of other species to PTS, however studies reported that even when dolphins experience inner ear damage as a result of explosives, their surface behaviour near blast areas is not altered (Ketten, 1993).
  2. Cumulatively, harbour porpoise and grey seal are animals likely to be impacted in highest numbers. Harbour porpoises are widely distributed throughout the North Sea and throughout the regional marine mammal study area. Based on historic records, as well as DAS , harbour porpoise have been recorded in the Firth of Forth most often during summer months, however, the reasons for higher abundance during that period are unknown. Grey seals, which are designated feature of Isle of May SAC, may be more sensitive to PTS during their breeding period (September to December).
  3. All marine mammals, which are IEFs of international value, are deemed to be of high vulnerability and low recoverability. The sensitivity of the receptor to PTS is therefore considered to be high.

Temporary threshold shift

  1. The degree and speed of hearing recovery after experiencing TTS by an animal will depend on the characteristics of the sound the animal is exposed to, and on the degree of shift in hearing experienced. A study measuring recovery rates of harbour porpoise following exposure to sound source of 75 db re 1 μPa (SEL) over 120 minutes found that recovery to the pre-exposure threshold was estimated to be complete within 48 minutes following exposure (SEAMARCO, 2011) suggesting that recovery may be rapid. Whilst there are no available species-specific recovery rates for bottlenose dolphin, white-beaked dolphin and minke whale to TTS, there is no evidence to suggest that recovery will be significantly different to harbour porpoise recovery rates. Various studies measures recovery rates of harbour seal following exposure to a sound sources and found that recovery from TTS to the pre-exposure baseline was estimated to be complete within 30 to 72 minutes following exposure (Kastelein et al., 2018a; SEAMARCO, 2011).
  2. Whilst TTS could affect many tens of animals (depending on the densities within the respective project areas) recovery to baseline conditions would be anticipated to occur within a short timeframe (hours) following cessation of the detonation. If UXO clearance activities were to occur over similar time periods, this could lead to a larger area of effect and larger cumulative number of animals that could experience TTS (noting that this is considered to be unlikely; paragraph 579). However, given the short-lived nature of the ensonification during UXO detonation and the reversibility of TTS animals are expected to recover quickly. The majority of the marine mammal receptors identified as IEFs in this assessment are wide ranging species and therefore there is a potential that some individuals may be repeatedly exposed to TTS at different times regardless of the distance from the Proposed Development.
  3. Based on historic records, as well as Proposed Development DAS, harbour porpoise and minke whale have been recorded in the Firth of Forth most often during summer months (Sparling, 2012; Grellier and Lacey, 2011; Seagreen Technical Report, 2018; Paxton et al., 2016). Minke whales are moving to inshore waters during summer due to increased abundance of sandeel (Robinson et al., 2009). Minke whale and harbour porpoises have a widespread distribution and individuals have been documented either switching to different prey species depending on the prey availability (Santos and Pierce, 2003; Haug et al., 2002) or moving relatively large distances on a daily basis (Nielsen et al., 2013). The availability of wider suitable habitat across the MU, feeding patterns of respective species and their mobility, suggest that individuals may move to alternative foraging grounds. However, as access to feeding grounds in the area may be restricted and individuals need to venture further in order to find appropriate feeding grounds, the displacement may result in a reduction in health and vital rates. Given that offshore wind farm developers are expected to follow the JNCC guidance to minimise the risk of disturbance (JNCC, 2010b) and that the temporal overlap of UXO detonation events at respective projects is unlikely, the UXO clearance events are not expected to result in a cumulative impact that would affect vital rates (e.g. reproduction) at a population level.
  4. Based on the most conservative approach of high order detonation of 300 kg mass charge, there will be no spatial overlap of the predicted TTS range as a result of UXO detonation at Proposed Development with the Forth of Tay area, where the density of bottlenose dolphins is the highest. Inch Cape Offshore Wind Farm is located slightly closer to the Forth of Tay area, however it is anticipated that the UXO clearance works will be carried out before the UXO clearance at the Proposed Development (construction of Inch Cape commences in 2023). Additionally, because the number and size of the UXOs is unknown for this project, it is not possible to assess the impact quantitatively. If there is a requirement to detonate an explosive within the offshore cable route, some individuals within the coastal range, south from Firth of Forth, may be affected by TTS. As described in more detail in volume 3, appendix 10.2, C-PODs deployed at St Abbs as a part of the ECOMMAS study recorded very low occupancy rates in comparison to other sites (5%) and therefore even if some individuals have the potential to be affected by TTS, the numbers of animals affected will represent small percentage of the east coast population.
  5. Seasonal sensitivities are difficult to determine. Grey seals, which are designated features of the Isle of May SAC and Berwickshire and North Northumberland Coast SAC, may be sensitive to TTS during their breeding period (September to December). In addition, as capital breeders, female grey seals spend more time during summer months foraging at-sea to build energy reserves prior to lactation when they may also be vulnerable to disturbance. Seals could experience TTS across relatively large ranges of up to 6,430 m as a result of a high order detonation of a charge size of 300 kg., The closest distance to Isle of May SAC (when measured from the Proposed Development cable corridor) equates to approximately 21 km. Therefore, direct overlap of noise impacts from the Proposed Development with areas in vicinity of this SAC is not expected.
  6. Subsea noise leading to TTS onset could affect seals foraging in the vicinity or within the Proposed Development marine mammal study area, as the telemetry study demonstrated connectivity between Isle of May SAC and Proposed Development marine mammal study area (volume 3, appendix 10.2, Annex B). An even higher proportion of tagged individuals were tracked between the Proposed Development marine mammal study area and the Berwickshire and North Northumberland Coast SAC, which is located only 4.1 km from the Proposed Development export cable corridor. The expert elicitation carried out to inform the iPCoD modelling of population consequences found that experts considered that disturbance to grey seals could result in reduced foraging efficiency, which could in turn affect fertility and interfere with mating opportunities due to habitat displacement (Harwood et al., 2014). However, Russell et al. (2013) have shown that individual grey seals tagged at different Mus on the east coast may utilise different haul-outs around the UK. There are three grey seal breeding colonies in the vicinity of the Proposed Development, it is therefore anticipated that if individuals are deterred from one breeding site, they could move to alternative breeding grounds. Even if individual seals leave the MU to reach an alternative breeding site, as they can travel large distances, it is likely that changes in the size of the populations in affected Mus will have a negligible effect on the density of adult females on individual breeding colonies, and therefore negligible effect on the survival of pups born to females from those MU.
  7. All marine mammals, which are IEFs of international value, are deemed to be of medium vulnerability and high recoverability. The sensitivity of the receptor is therefore, considered to be low.

Significance of effect

Permanent threshold shift

  1. Overall, the magnitude of the cumulative impact is deemed to be negligible to low and the sensitivity of the receptor is considered to be high. Given that the risk of injury will be reduced by appropriate measures (including visual and acoustic monitoring) at respective projects and only a small proportion of respective populations could be potentially injured (PTS), the effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Temporary threshold shift

  1. Overall, the magnitude of the cumulative impact is deemed to be low to medium and the sensitivity of the receptor is considered to be low. Given that the effect is reversible and will affect small proportion of populations only during the UXO clearance, which is unlikely to occur simultaneously at all sites, cumulatively, the effect will be of minor adverse significance, which is not significant in EIA terms.

Further mitigation and residual effect

  1. Each project is expected to reduce the risk of injury (PTS and TTS) by project specific designed-in measures as well as secondary mitigation. Therefore, no secondary marine mammal mitigation, other than that proposed for Proposed Development alone (described in detail in paragraph 338 et seq.) is considered necessary. The residual effect is considered to be of minor adverse significance, which is not significant in EIA terms.

Tier 3

Construction phase
  1. The only Tier 3 project which has been identified in the CEA with the potential to result in cumulative effects as a result of injury and disturbance from elevated underwater noise during UXO clearance within the regional marine mammal study area is Green Volt Floating Offshore Wind Farm.

Magnitude of impact

Permanent threshold shift and temporary threshold shift

  1. The scoping report has identified potential for auditory injury and disturbance as a result of underwater noise during UXO clearance as potential impacts during construction of the project (Royal Haskoning DHV, 2021). As per the scoping report, the potential for UXO within the Green Volt site and the offshore export cable routes is limited due the significant amount of previous collected survey data over both the development site and export cable corridors (Royal Haskoning DHV, 2021). Since no UXO survey has as yet been undertaken to determine possible risk, the impacts on marine mammals were screened out from the considerations in the Green Volt EIA and will most likely be considered at a later stage.
  2. Given the distance from the Proposed Development, the overlap of PTS/TTS ranges as a result of underwater noise due to UXO clearance is highly unlikely. As described above, the potential for UXO within Green Volt site is limited and it is anticipated that the magnitude of impact will be negligible in comparison to numbers of UXOs requiring clearance at offshore wind farms listed in Tier 2 (see paragraph 568 et seq.).

Permanent threshold shift

  1. The cumulative impact of PTS from elevated subsea noise during UXO clearance is predicted to be of local to regional spatial extent, very short-term duration, intermittent and the effect of injury is of low reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Temporary threshold shift

  1. The cumulative impact of TTS from elevated subsea noise during UXO clearance is predicted to be of regional spatial extent, very short-term duration, intermittent and the effect is of high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore, considered to be low to medium.

Sensitivity of receptor

  1. The sensitivity of marine mammals to disturbance from elevated underwater noise during UXO clearance is as described in paragraph 584 et seq. for Tier 2 projects.

Permanent threshold shift

  1. All marine mammals, which are IEFs of international value, are deemed to be of high vulnerability and low recoverability. The sensitivity of the receptor to PTS is therefore considered to be high.

Temporary threshold shift

  1. All marine mammals, which are IEFs of international value, are deemed to be of medium vulnerability and high recoverability. The sensitivity of the receptor is therefore, considered to be low.

Significance of effect

Permanent threshold shift

  1. Overall, the magnitude of the cumulative impact is deemed to be negligible to low and the sensitivity of the receptor is considered to be high. Given that the potential risk of injury at respective projects is reduced by appropriate designed-in measures, cumulatively, the effect will therefore be of minor adverse significance, which is not significant in EIA terms.

Temporary threshold shift

  1. Overall, the magnitude of the cumulative impact is deemed to be low to medium and the sensitivity of the receptor is considered to be low. Given that the effect is reversible and will affect small proportion of populations only during the UXO clearance, which is unlikely to occur simultaneously at all sites, cumulatively, the effect will be of minor adverse significance, which is not significant in EIA terms.

Further mitigation and residual effect

  1. Each project is expected to reduce the risk of injury (PTS and TTS) by project specific designed-in measures as well as secondary mitigation. Therefore, no secondary marine mammal mitigation, other than that proposed for Proposed Development alone (described in detail in paragraph 335 et seq.) is considered necessary. The residual effect is considered to be of minor adverse significance, which is not significant in EIA terms.

Injury and Disturbance to Marine Mammals from Elevated Underwater Noise Due to Vessel Use and Other Activities

  1. The risk of injury in terms of PTS to marine mammal receptors as a result of underwater due to vessel use and other activities would be expected to be localised to within the boundaries of the respective projects. The assessment for the Proposed found that the numbers of animals impacted will be extremely low and the magnitude of the impact with respect to auditory injury occurring in marine mammals has been assessed as negligible. Therefore, there is no potential for cumulative impacts for injury from elevated underwater noise due to vessel use and the cumulative assessment provided in paragraph 610 et seq. focuses on disturbance only.

Tier 2

Construction phase

Magnitude of impact

  1. The construction of the Proposed Development, together with Tier 2 projects identified in Table 10.55   Open ▸ may lead to disturbance to marine mammals from vessel use and other activities. Projects screened into this assessment include disposal activities at the Eyemouth disposal site, the construction and operation and maintenance of Inch Cape Offshore Wind Farm, Seagreen 1A Project, Eastern Link 1 and Eastern Link 2 and operation and maintenance of Neart na Gaoithe Offshore Wind Farm, Seagreen 1 and Blyth Demo 2.
  2. The construction as well as operation and maintenance phases of Inch Cape Offshore Wind Farm, located 15 km from the Proposed Development array area, will overlap with the construction phase of the Proposed Development. Based on the revised design, the maximum design scenario for vessel movements predicted approximately 1,500 vessel movements over total construction period (2023 to 2025) and scheduled maintenance and inspection of each wind turbine is likely to occur every six to twelve months during the operation and maintenance phase (Inch Cape Offshore Ltd Scoping Report, 2017). Vessels involved in the construction phase are jack-up platforms, barges, dredgers, cable laying vessels and tugs. The impacts from increased underwater noise due to vessel traffic were assessed as minor (not significant) for the Original Development (Inch Cape Offshore Ltd, 2014). As the revised design includes a reduction in vessel movements during the construction phase (from 3,5000 vessel round trips in the Original Inch Cape EIA Report to 1,500 vessel round trips in the revised version), the Revised Inch Cape Offshore Wind Farm project was anticipated to have less of an impact compared to the original Inch Cape Offshore Wind Farm and therefore the impacts from increased underwater noise due to vessel traffic were scoped out of the revised EIA (Inch Cape Offshore Ltd, 2018). None of the assessments, either original (Inch Cape Offshore Ltd, 2014) nor the revised version (Inch Cape Offshore Ltd, 2018), assessed the impacts associated with disturbance of marine mammals from elevated underwater noise due to vessel use and other activities during the operation and maintenance phase.
  3. The construction and operation and maintenance phases of Seagreen 1A Project as well as operation and maintenance of Seagreen 1, located 5 km from the Proposed Development array area, will overlap with the construction phase of the Proposed Development. The construction activities within Seagreen 1A Project will involve up to eight large installation vessels on site as well as a cable laying vessel, piling vessel, structure installation vessel and a rock dispoal vessel, however the approximate number of round trips was not specified (Seagreen Wind Energy Ltd, 2012). Operation and maintenance activities within both offshore wind farms will include biannual visits per wind turbine with two vessels on site at any one time (Seagreen Wind Energy, 2012). The significance of the effect resulting from increased underwater noise due to vessel traffic for both phases was assessed as negligible.
  4. The operation and maintenance phase of Neart na Gaoithe Offshore Wind Farm, located 16 km from the Proposed Development array area, will overlap with the construction phase of the Proposed Development. It is predicted that during the operation and maintenance phase, vessels such as SOV (20 to 30 round trips annually), maintenance (10 to 20 two week campaigns annually), jack-up barge (average two events annually) and SOV or catamaran for visual inspections (400 to 600 events annually) will be used (Mainstream Renewable Power, 2019). The effects resulting from increased vessel traffic during operation and maintenance phase, such as masking, displacement or behavioural changes, have been assessed as not significant in the original EIA Report (Mainstream Renewable Power, 2012) and were scoped out from the further assessment in the revised EIA Report (Mainstream Renewable Power, 2019).
  5. The operation and maintenance phase of Blyth Demo Phase 2, located 102 km from the Proposed Development array area, will overlap with the construction phase of the Proposed Development. The original Blyth Offshore Demonstration Project EIA Report assessed impacts such as lethality, physical injury and behavioural avoidance, due to increased anthropogenic noise from vessel use and other activities such as cable burying and/or trenching (NAREC, 2012). The potential magnitude of the impact of anthropogenic noise was concluded as low (NAREC, 2012). A review of the assessment of effects for marine mammals was undertaken as part of the 2013 SEI but it did not lead to any change in the conclusions of the original EIA Report (NAREC, 2013). The exact number of round vessel trips for operation and maintenance phase was not provided in the original EIA Report (NAREC, 2012), however, the potential for impacts as a result of increased anthropogenic noise from vessel traffic and other activities during operation of the Blyth Demo 2 are considered to be less or equivalent when compared to original consent where the magnitude was assessed as low (EDF, 2020).
  6. The construction as well as operation and maintenance phases of Eastern Link 1 and Eastern Link 2 located 28 km and 14 km from the Proposed Development array area, will overlap with construction phase of the Proposed Development. Sound as a result of vessel movements, including cable lay vessels with dynamic positioning has been listed as potential impact on marine mammal during construction as well as operation and maintenance phases of both projects. The Environmental Appraisals for the Eastern Link 1 (AECOM, 2022a) and the Eastern Link 2 (AECOM, 2022b) predicted that the underwater sound from vessels involved in installation is not considered to be at a level that would have a significant impact on the ambient underwater soundscape. The initial assessment of underwater noise impacts for both projects was presented only for installation phase. This impact has been scoped out, based on the assumption that there is no evidence of injury caused by a constantly moving vessel. Subsequently, the disturbance effects as a result of vessel movements during construction as well as operation were not determined. For construction activities such as rock placement or ploughing, jet trenching and mechanical trenching during cable installation, it was assessed that underwater sounds will not be generated at a level where injury or disturbance could be expected.
  7. The operation of Eyemouth disposal site located 35 km from the Proposed Development array area, will overlap with the construction phase of the Proposed Development. A proposed dredging programme assumed use of a hopper barge that may require approximately 30 vessel round trips over a period of approximately 16 days between 2020 to 2023 (Eyemouth Harbour Trust, 2020). There was no information about the duration and/or number of vessel round tips after that date. Only one vessel will be involved in disposal activities at the Eyemouth disposal site and therefore, even if temporal overlap with the construction phase of the Proposed Development will take place, the increase in traffic is negligible when compared to vessel movements at offshore wind farms considered above and therefore is not anticipated to lead to cumulative disturbance to marine mammals.
  8. The maximum scenario for the construction phase of the Proposed Development is presented in Table 10.16   Open ▸ with up to 9,806 vessel round trips over the period of 6 years. Vessel use during the construction phase of the Proposed Development is described in more detail in paragraph 353 et seq. The impacts due to disturbance to marine mammals from vessel use and other activities for the Proposed Development alone during the construction phase were assessed as minor.
  9. Whilst there is no quantitative information available for noise disturbance ranges for offshore wind farms included in this CEA, it is anticipated that there will be a similar scale of effects with respect to noise effects as those described for Proposed Development alone (paragraph 351 et seq.). Therefore, the risk of injury in terms of PTS to marine mammal receptors would be expected to be localised to within the boundaries of the respective projects. It is expected that all projects will adhere to project specific mitigation plans to reduce the potential risk of auditory injury. Disturbance could occur over larger ranges compared to PTS, subsea noise modelling predicted a range of 4 km disturbance range for construction activities such as cable laying as well as activity of rock placement vessels (described in detail in volume 3, appendix 10.1) and therefore, only disturbance effects (not PTS) are likely to occur cumulatively. Given that construction activities for the other offshore wind projects have commenced in 2020 and that this is an area of high vessel traffic (see paragraph 354 et seq. for more details), it can be anticipated that marine mammals present in the vicinity of Firth of Forth demonstrate some degree of habituation to ship noises.
  10. The highest number of vessels movements was predicted during the construction phase of each offshore wind farm. There would potentially be a relatively small temporal overlap of the construction phases, with only one year of overlap with Inch Cape as well as Seagreen 1A Project and the Proposed Development. Therefore, the potential cumulative effect during construction phases of the respective projects and the proposed Development will be short-term (no more than one year).
  11. Vessel movements will be confined to the array areas and/or offshore export cable corridor routes and will follow existing shipping routes to/from port. As presented in volume 2, chapter 13, the commercial vessel numbers in the vicinity of the Proposed Development are expected to remain reasonably consistent in the future. In the longer term, there may be increases in wind farm related traffic associated with the ScotWind developments north and east of the Proposed Development. However, given the low data confidence associated with these developments it was not possible to make any quantitative assumptions. It has been assumed that future case traffic growth is likely to fluctuate depending on seasonality and cargo and industry trends.
  12. As described in more detail in volume 2, chapter 13, commercial vessels do not transit through arrays, which has been corroborated during consultation for the Proposed Development. Two areas of sea room (gaps) between the Proposed Development array area and other future offshore wind farm developments were established, namely between Seagreen 1 and Inch Cape. The cumulative effect is predicted to be of local spatial extent, medium term duration, intermittent and the effects of behavioural disturbance are of high reversibility. It is predicted that the impact will affect the receptor directly. Given the minor temporal overlap in construction activities and that the operation and maintenance activities associated with the relevant projects will not add substantially to the total number of vessel round trips associated with the Proposed Development, with only a proportion of the operation and maintenance operations occurring during the construction phase of the Proposed Development, the magnitude of the impact will not be greater than that assumed for the project alone. The magnitude is therefore, considered to be low.

Sensitivity of receptor

  1. The sensitivity of marine mammals to elevated underwater noise due to vessel use and other activities is as described in section 10.11, paragraph 369 et seq.
  2. There are interspecific differences in the potential sensitivity of cetaceans to vessel noise with some species actively avoiding vessels, whilst other are attracted towards them. Harbour porpoise was highlighted as being particularly sensitive to vessel noise and avoidance is likely (Heinänen and Skov, 2015). Similarly, bottlenose dolphins reduce their activity in response to the noise arising from vessel movements (Pirotta et al., 2015). However, the link between vessel noise and reduced marine mammal activity is not straightforward to establish due to intrinsic factors that may also contribute to a variance in distribution and abundance (e.g. changes in prey distribution and natural seasonal fluctuations). Despite the known sensitivity of harbour porpoise to vessel noise (i.e. active avoidance of vessels; Hermannsen and Bedholm, 2014, Dyndo et al. 2015), there was no detectable decrease in the numbers of harbour porpoise associated with an increase in vessel activity during pipeline construction (Culloch et al., 2016).
  3. The sensitivity of seals to vessel noise was described previously in paragraph 377 et seq and highlighted that the presence of boats near seal haul-outs could lead to disruption of foraging and potentially reduced pupping success. Key harbour and grey seal haul-outs nearest the Proposed Development were identified as Kinghorn Rocks and Inchmickery and Cow and Calves. There are also three grey seal breeding colony sites (Fast Castle, Inchkeith and Craigleith). Harbour and grey seals at sea within the vicinity of the haul-outs in the inner Firth of Forth are likely to be exposed to existing high levels of vessel activity to/from busy ports and harbours in the area (e.g. Rosyth, Braefoot Bay, Methill and North Berwick). Therefore, seals in the vicinity of haul-out sites are anticipated to demonstrate some degree of habituation to ship noises.
  4. On the east coast of Scotland, and within the vicinity of the other projects screened into this assessment, there are two SACs designated to support breeding colonies of harbour seals, namely Firth of Tay and Eden Estuary SAC and Dornoch Firth and Morrich More SAC. With small foraging ranges, harbour seal may be sensitive to a cumulative increase in vessel activity near key haul-outs. The closest point of the Proposed Development is located approximately 4 km from Berwickshire and North Northumberland Coast SAC and 21 km from Isle of May SAC, designated for grey seals. Therefore, grey seals from these SACs may occur in the vicinity of the Proposed Development, which has been confirmed by the telemetry data (see more details in volume 3, appendix 10.2, Annex B), with individuals also likely to move within project areas. With greater foraging ranges, grey seal, in particular, may be sensitive to an uplift in vessel activity as they move between haul-outs and key foraging areas. As described previously, however, seals in these areas (near busy ports) are already exposed to existing levels of baseline vessel activity and therefore are likely to be tolerant to intermittent uplifts in vessel traffic and associated noise. Due to the small and localised nature of the uplift in vessel activity and associated noise compared to baseline levels, it is considered unlikely that marine mammals will be more sensitive to the cumulative effects of disturbance compared to the Proposed Development alone.
  5. Bottlenose dolphin occurring in the main distributional range of the population (Moray Firth to Firth of Forth) and south to Farne Islands are also expected to demonstrate a degree of habituation to ship noise. It is because this range overlaps with majority of the largest and busiest Scottish ports, namely Cromarty, Peterhead, Aberdeen, Dundee and ports within Firth of Forth. Furthermore, ports in Dundee support large numbers of cargo vessels and offshore support vessels (described in more detail in volume 2, chapter 13) that pass through the Firth of Tay, the area supporting approximately 50% of east coast bottlenose dolphin population. Cromarty port is known as leading hub for offshore renewable energy projects, and a primary location for oil rig inspection, repair and maintenance as well as subsea work. It is located in the Cromarty Firth, which as an arm of the Moray Firth and overlaps with Moray Firth SAC, which supports the only known resident population of bottlenose dolphin in the North Sea. Given that bottlenose dolphins aggregate in areas characterised by high vessel activity, the uplift in vessel traffic associated with Proposed Development and projects screened in for cumulative assessment is unlikely to affect survival or reproduction rate of individuals.
  6. All marine mammals, which are IEFs of international value, are deemed to be of low vulnerability and high recoverability. The sensitivity of the receptor is therefore considered to be medium.

Significance of effect

  1. Overall, the magnitude of the cumulative impact is deemed to be low and the sensitivity of the receptor is considered to be medium. Cumulatively, the effect will therefore be of minor adverse significance, which is not significant in EIA terms.

Further mitigation and residual effect

  1. No secondary additional marine mammal mitigation is considered necessary as the predicted effect in the absence of further mitigation (beyond the designed-in measures outlined in section 10.10) is not significant in EIA terms. Therefore, the residual effect is considered to be of minor adverse significance, which is not significant in EIA terms.