Conservation objectives
1543 The conservation objectives for the Southern North Sea SAC have been developed jointly by JNCC and Natural England (JNCC, 2019b) and are as follows:
- To ensure that the integrity of the site in maintained and that it makes the best possible contribution to maintaining Favourable Conservation Status (FCS) for harbour porpoise in UK waters. In the context of natural change, this will be achieved by ensuring that:
– harbour porpoise is a viable component of the site;
– there is no significant disturbance of the species; and
– the condition of supporting habitats and processes, and the availability of prey is maintained.
1545 It is noted that the advice on operations (JNCC, 2019b) state that, with regard to assessing impacts to Conservation Objective 1 (harbour porpoise is a viable component of the site), ‘the reference population for assessments against this objective is the Management Unit (MU) population in which the SAC is situated (IAMMWG, 2015).’ As agreed through the Road Map process (volume 3, appendix 10.3 of the Offshore EIA Report), IAMMWG (2021) abundance data are used as the reference population for harbour porpoise. The IAMMWG (2021) estimated abundance for the North Sea Management Unit (NS MU) is 346,601 individuals.
1546 Further information on the conservation objectives for the Southern North Sea SAC is provided in the document ‘conservation objectives and Advice on Operations’ (JNCC, 2019b). This further advice is outlined in appendix A.
Features and effects for assessment
1547 The potential for adverse effects has been identified for the following Annex II marine mammal features of this site:
- Harbour porpoise
1548 The following impacts associated with the construction and decommissioning of the Proposed Development have been identified as having the potential for adverse effects on harbour porpoise at this site:
- Injury and disturbance from underwater noise generated by following activities:
– piling of fixed foundations;
– clearance of UXO; and
– site investigation surveys.
- Changes in fish and shellfish communities affecting prey availability causing potential shifts in distribution, abundance and migration patterns, community structure, susceptibility to disease due to changes in prey availability.
1549 The following impacts associated with the operation and maintenance of the Proposed Development have been identified as having the potential for adverse effects on harbour porpoise at this site:
- Injury and disturbance from underwater noise generated by site investigation surveys; and
- Changes in fish and shellfish communities affecting prey availability causing potential shifts in distribution, abundance and migration patterns, community structure, susceptibility to disease due to changes in prey availability.
1550 The following assessment is structured to first assess whether the construction and decommissioning impacts will have an adverse effect on the integrity of the harbour porpoise feature of the site, and then the impacts associated with operation and maintenance will be assessed. For the purposes of these assessments, the potential effects are considered in relation to the site’s conservation objectives.
Construction and decommissioning
Injury and disturbance from elevated underwater noise during piling
1551 Underwater noise could affect the population and distribution of the qualifying species. Underwater noise modelling has been undertaken to estimate the maximum potential injury ranges for underwater noise that could arise during construction and decommissioning in relation to harbour porpoise. The modelling was based on the maximum design scenario (as outlined in Table 13.10 Open ▸ ) with summary of noise modelling provided in paragraph 834 et seq.
1552 The maximum range for injury to harbour porpoise was estimated as 449 m based on SPLpk and using the 4% reducing to 0.5% conversion factor (see paragraph 887 et seq). Taking into account the most conservative scenario, less than one harbour porpoise was predicted to be potentially injured, which accounts for <0.005% of the Southern North Sea SAC population. Additionally, with designed-in measures in place ( Table 13.11 Open ▸ ) which are in line with recommended best practice guidelines, the magnitude of the impact would result in a negligible risk of injury to harbour porpoise.
1553 In terms of behavioural disturbance, up to 2,822 animals were predicted to be potentially disturbed from concurrent piling at a maximum hammer energy of 4,000 kJ ( Table 13.17 Open ▸ ). These results are considered highly precautionary as there is a number of conservative assumptions in subsea noise model (i.e. the maximum hammer energy of 4,000 kJ is unlikely to be reached at all piling locations (see paragraph 844 for more details)).
1554 It should be noted that because harbour porpoise are highly mobile, the numbers utilising UK waters will vary both seasonally and annually (Teilmann et al., 2008; Sveegaard et al., 2011). Therefore, although there is no potential for overlap of noise disturbance contours with this designated site, there is a potential for individuals from this SAC to be present within noise disturbance contours. The maximum disturbance scenario suggests that a maximum of 14% of the harbour porpoise population from Southern North Sea SAC (based on a minimum SAC population size of 20,237 animals) have the potential to be disturbed as a result of piling. This maximum disturbance scenario suggests that a relatively large proportion of the Southern North Sea SAC have the potential to be disturbed as a result of piling. However, considering the distance from the Proposed Development to the SAC, it is a highly precautionary assumption that 100% of disturbed animals will come from this SAC. Therefore, this number is likely to be an over-estimation of the proportion of harbour porpoises from the Southern North Sea SAC affected.
1555 Findings presented in paragraph 793 suggest that the Firth of Forth and Tay area is unlikely to represent important breeding or foraging habitat for harbour porpoise that would not be available elsewhere within the species’ home range over the North Sea. If individuals are deterred from the foraging grounds in the vicinity of the Proposed Development, it can be anticipated that harbour porpoise can compensate for any resulting loss in energy intake by increasing foraging activities beyond impact zone (Benhemma-Le Gall et al., 2021).
1556 Piling activities will not take place within or nearby to the SAC and therefore will not exclude harbour porpoise from the relevant area of the site up to the threshold limit (20% in any given day or 10% over a season)[20], behavioural disturbance as a result of piling is unlikely to be significant. It will not alter the distribution of harbour porpoise such that recovery cannot be expected or effects on Southern North Sea SAC population can be considered long term.
1557 Additionally, since there is no potential for injury ranges or disturbance contours to reach the SAC, it will not affect foraging habitats and areas important for breeding and calving within the designated site. Therefore, there is no potential for piling activities to restrict the survivability and reproductive potential of harbour porpoises using the site. As such harbour porpoise will remain a viable component of the site.
1558 As previously described for harbour porpoise in paragraph 889, the duration of piling could potentially overlap with a maximum of five breeding cycles. However, it is worth noting that piling will be intermittent and will occur over small timespan (372 days) within piling phase (52 months). Considering the above, the duration of the effect in the context of life cycle of harbour porpoise is classified as medium term.
1559 Significant adverse effects on the qualifying Annex II marine mammal feature, harbour porpoise of the Southern North Sea SAC, are not predicted to occur as a result of underwater noise during piling during the construction phase (i.e. in relation to maintaining the population, distribution of species within the site, connectivity and disturbance to species).
Conclusion
1560 The assessment has concluded that piling activities will not take place within or nearby to the Southern North Sea SAC and will not exclude harbour porpoise from the relevant area of the site up to the threshold limit. Therefore, underwater noise from piling will not result in significant disturbance of the species. Piling will not affect areas important for breeding and calving within the site and therefore harbour porpoise will remain a viable component of the site. Piling activities will not affect the condition of supporting habitats and processes. As such, the conservation objectives for Annex II species, harbour porpoise, will not be undermined.
1561 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity of the Southern North Sea SAC from injury and disturbance due to underwater noise during piling with respect to the construction of the Proposed Development acting alone.
Injury and disturbance from elevated underwater noise during site investigation surveys
1562 The noise modelling demonstrated that ranges within which there is a risk of PTS to harbour porpoise as a result of geophysical surveys are relatively low with a maximum impact range of 360 m (due to operation of SBP; Table 13.20 Open ▸ and Table 13.21 Open ▸ ). PTS ranges for harbour porpoise as a result of cone penetration test and vibro-coring are 60 m and 5 m, respectively ( Table 13.21 Open ▸ ). There is potential for less than one animal to experience PTS as a result of geophysical and geotechnical site investigation surveys (<0.005% of the Southern North Sea SAC population). It should be noted that since sonar-based systems have strong directivity, there is only potential for injury when marine mammals are directly underneath the sound source. The site-investigation surveys are considered to be short term as they will take place over up to a period of up to three months. With designed-in measures in place, which are in line with recommended best practice guidelines (see Table 13.11 Open ▸ ), due to the low risk of PTS occurring and the short-term duration of the geophysical surveys, no adverse effects associated with auditory injury and disturbance to harbour porpoise were predicted as a result of site investigations surveys.
1563 In terms of behavioural disturbance, the largest distance over which disturbance could occur potentially affecting harbour porpoise is out to approximately 7.5 km during vibro-coring with up to 144 harbour porpoises predicted to be potentially disturbed ( Table 13.23 Open ▸ ). The maximum disturbance scenario suggests that a maximum of 0.7% of the harbour porpoise population from Southern North Sea SAC (based on a minimum SAC population size of 20,237 animals) have the potential to be disturbed as a result of vibro-coring piling. However, considering the distance from the Proposed Development to the SAC, it is a highly precautionary assumption that 100% of disturbed animals will come from this SAC. Therefore, this number is likely to be an over-estimation of the proportion of harbour porpoises from the Southern North Sea SAC affected.
1564 Site investigation surveys are expected to be very short in duration with animals returning to baseline levels soon after surveys have ceased. Site investigation activities will not take place within or nearby to the SAC and therefore will not exclude harbour porpoise from relevant proportion from the site22, behavioural disturbance is unlikely to be significant. It will not alter the distribution of harbour porpoise such that recovery cannot be expected or effects on Southern North Sea SAC population can be considered long term.
1565 Additionally, since there is no potential for injury ranges or disturbance contours to reach the SAC, it will not affect foraging habitats and areas important for breeding and calving within the designated site. Therefore, there is no potential for site investigation surveys to restrict the survivability and reproductive potential of harbour porpoise using the site. As such harbour porpoise will remain a viable component of the site.
1566 Significant adverse effects on the qualifying Annex II marine mammal feature, harbour porpoise of the Southern North Sea SAC, are not predicted to occur as a result of underwater noise during site investigation surveys during the construction phase (i.e. in relation to maintaining the population, distribution of species within the site, connectivity and disturbance to species).
Conclusion
1567 The assessment has concluded that site investigation surveys will not take place within or nearby to the Southern North Sea SAC and will not exclude harbour porpoise from the relevant area of the site up to the threshold limit. Therefore, underwater noise from site investigation surveys will not result in significant disturbance of the species. Site investigation surveys will not affect areas important for breeding and calving within the site and therefore harbour porpoise will remain a viable component of the site. Site investigation surveys will not affect the condition of supporting habitats and processes. As such, the conservation objectives for Annex II species, harbour porpoise, will not be undermined.
1568 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Southern North Sea SAC from injury and disturbance due to underwater noise during site investigation surveys with respect to the construction of the Proposed Development acting alone.
Injury and disturbance from elevated underwater noise during UXO clearance
1569 Harbour porpoise is sensitive to potential injury from high order UXO clearance. Based on the maximum design scenario of high order detonation, the underwater noise modelling results show that harbour porpoise could be potentially affected by PTS at the maximum range of 10,630 m due to detonation of charge size of 300 kg ( Table 13.24 Open ▸ ). There is potential for up to 293 animals to experience PTS as a result of UXO clearance using high order detonation (<1.5% of the Southern North Sea SAC population). It is however anticipated that only 10% of all UXO clearance events will result in high order detonation as low order techniques will be applied as the intended methodology for clearance of UXO. The underwater noise modelling results show that harbour porpoise can be potentially affected by PTS at the maximum range of 1,265 m due to detonation of 0.5 kg clearance shot ( Table 13.25 Open ▸ ).
1570 To reduce the potential of harbour porpoise experiencing injury, designed-in measures, which are in line with recommended best practice guidelines, will be adopted as part of a MMMP (see Table 13.11 Open ▸ ). Given that there is a potential to experience auditory injury by harbour at a greater range than can be mitigated by monitoring of the 1 km mitigation zone alone, an ADD and soft-start charges will be deployed to deter marine mammals to a greater distance prior to any detonation. However, the maximum deterrence zone has been assessed as 7,200 m and PTS range for this species has been modelled as 10,630 m, and so there is a risk that animals could potentially experience an auditory injury at distances that cannot be fully mitigated by application of ADD and soft-start charges. Post application submission, when details about UXO sizes and specific clearance techniques to be used become available, a more detailed assessment will be produced as a part of the EPS licence supporting information for the UXO clearance works. Appropriate mitigation measures will be agreed with stakeholders as a part of a UXO specific MMMP. Therefore following the application of mitigation measures, the risk of injury will be reduced to low.
1571 As described in paragraph 971, the threshold for potential temporary loss of hearing (TTS) was also assessed. Based on the maximum design scenario of high order detonation, the underwater noise modelling results show that harbour porpoise can be potentially affected by TTS at the maximum range of 19 km due to detonation of charge size of 300 kg ( Table 13.32 Open ▸ ) with up to 995 animals impacted. TTS is a temporary hearing impairment and therefore animals are likely to fully recover from the effect. Effects caused by UXO clearance are considered unlikely to cause a change in reproduction and survival rates or alteration in the distribution of the population from the Southern North Sea SAC.
1572 UXO clearance activities will not take place within or nearby to the Southern North Sea SAC and therefore will not exclude harbour porpoise from the relevant area of the site up to the threshold limit (20% in any given day or 10% over a season)[21], behavioural disturbance as a result of UXO clearance is unlikely to be significant. It will not alter the distribution of harbour porpoise such that recovery cannot be expected or effects on Southern North Sea SAC population can be considered long term.
1573 Additionally, since there is no potential for injury ranges or disturbance contours to reach the SAC, it will not affect foraging habitats and areas important for breeding and calving within the designated site. Therefore, there is no potential for UXO clearance activities to restrict the survivability and reproductive potential of harbour porpoises using the site. As such harbour porpoise will remain as a viable component of the site.
1574 Significant adverse effects on the qualifying Annex II marine mammal feature, harbour porpoise of the Southern North Sea SAC, are not predicted to occur as a result of underwater noise during UXO clearance during the construction phase (i.e. in relation to maintaining the population, distribution of species within the site, connectivity and disturbance to species).
Conclusion
1575 The assessment has concluded that UXO clearance will not take place within or nearby to the Southern North Sea SAC and will not exclude harbour porpoise from the relevant area of the site up to the threshold limit. Therefore, injury and disturbance due to underwater noise during UXO clearance will not result in significant disturbance of the species. UXO clearance will not affect areas important for breeding and calving within the site and therefore harbour porpoise will remain a viable component of the site. UXO clearance activities will not affect the condition of supporting habitats and processes. As such, the conservation objectives for Annex II species, harbour porpoise, will not be undermined.
1576 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Southern North Sea SAC from injury and disturbance due to underwater noise during UXO clearance with respect to the construction of the Proposed Development acting alone.
Changes in fish and shellfish communities affecting prey availability
1577 As outlined in paragraph 1010 et seq., there is potential for changes to prey availability for harbour porpoise during construction and decommissioning of the Proposed Development. These impacts include temporary and long-term habitat loss/disturbance, increased SSC and associated sediment deposition, injury and/or disturbance from underwater noise and vibration.
1578 There is potential for temporary habitat loss/disturbance to affect up to 113,974,700 m2 of seabed during the construction phase, which equates to 9.7% of the fish and shellfish ecology study area. Only a small proportion of the maximum footprint of habitat loss/disturbance may be affected at any one time during the construction phase, with areas starting to recover immediately after cessation of construction activities in the vicinity. Additionally, habitat disturbance during the construction phase will also expose benthic infaunal species from the sediment, potentially offering foraging opportunities to some fish and shellfish species (e.g. opportunistic scavenging species) immediately after completion of works. The presence of infrastructure within the Proposed Development, including foundations and associated scour protection, cable protection, OSP/Offshore convertor station platform interconnector and offshore export cables will result in long term habitat loss of up to 7,798,856 m2 (0.7% of the Proposed Development fish and shellfish ecology study area; volume 2, chapter 9 of the Offshore EIA Report. The areas within Southern North Sea SAC provide good foraging habitat for harbour porpoise. Given that all construction and decommissioning activities will take place outside the SAC, the condition of supporting habitats and processes within site will not be impaired and the availability of prey will be maintained.
1579 In terms of indirect effects on marine mammals as a result of underwater noise, it is assumed that marine mammals would be disturbed from the area in vicinity of the noise source, and so any changes to the distribution of prey resources would not affect marine mammals as they would already be disturbed from the same (or larger) area.
1581 The impacts of construction and decommissioning will be highly localised and largely restricted to the boundaries of the Proposed Development, only a small area will be affected when compared to available foraging habitat in the North Sea and impacts will take place outside of the Southern North Sea SAC. Harbour porpoise eat a variety of prey including gobies, sandeel, whiting, herring and sprat. Findings presented in paragraph 793 suggest that for this species Firth of Forth and Tay area is unlikely to represent important breeding or foraging habitat that would not be available elsewhere within the species home range over the North Sea. There may be, however, an energetic cost associated with increased travelling and due to harbour porpoise high metabolic rate (see paragraph 1028), this species may be particularly vulnerable to this effect. However, 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) or moving relatively large distances on a daily basis (Nielsen et al., 2013). Based on findings of Benhemma-Le Gall et al. (2021) it can be anticipated that harbour porpoise can compensate for any resulting loss in energy intake by increasing foraging activities beyond impact zone. Therefore, individuals may move to alternative foraging grounds without affecting animals health.
1582 The magnitude of the indirect impact on marine mammals as a result of changes in fish and shellfish communities during the decommissioning phase is not expected to differ or be greater than that assessed for the construction phase.
1583 Considering the above, it is anticipated that the availability of suitable foraging grounds for harbour porpoise will not be impaired and availability of prey will be maintained within the wider distributional range.
1584 Significant adverse effects on the qualifying Annex II marine mammal feature, harbour porpoise of the Southern North Sea SAC, are not predicted to occur as a result of changes in fish and shellfish communities affecting prey availability during construction and decommissioning phases (i.e. in relation to maintaining the cover and abundance of preferred food items required by the species).
Conclusion
1585 The assessment has concluded that the impacts of construction and decommissioning will be highly localised and largely restricted to the boundaries of the Proposed Development, only a small area will be affected when compared to available foraging habitat in the North Sea and impacts will take place outside of the Southern North Sea SAC. Therefore, the condition of supporting habitats and processes will not be affected. Given that individuals may move to alternative foraging grounds without affecting animals’ health, availability of prey within the wider distributional range will not be affected. As such, the conservation objectives for Annex II species, harbour porpoise, will not be undermined.
1586 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Southern North Sea SAC from changes in fish and shellfish communities affecting prey availability with respect to the construction and decommissioning of the Proposed Development acting alone.
Operation and maintenance
Injury and disturbance from elevated underwater noise during site investigation surveys
1587 As discussed in paragraph 1562 et seq., the maximum range at which there is a risk of PTS to harbour porpoise as a result of site investigation surveys is 360 m. With designed in measures ( Table 13.11 Open ▸ ), which are in line with recommended best practice guidelines, implemented for the geophysical surveys, the risk of PTS occurring to harbour porpoise will be low. With regard to behavioural disturbance, a maximum potential disturbance range across all survey types is approximately 7.5 km during vibro-coring. The assessment based on a maximum disturbance scenario suggests that a maximum of 0.7% of the harbour porpoise population from Southern North Sea SAC (based on a minimum SAC population size of 20,237 animals) have the potential to be disturbed as a result of vibro-coring piling. Considering the distance from the Proposed Development to the Southern North Sea SAC, it is a highly precautionary assumption that 100% of the disturbed animals will come from this SAC. Therefore, this number is likely to be an over-estimation of the proportion of harbour porpoises from the Southern North Sea SAC affected.
1588 The maximum design scenario for routine geophysical surveys is estimated as a survey every six months for the first two years and annually thereafter. This equates to 37 surveys over the 35-year life cycle of the Proposed Development ( Table 13.10 Open ▸ ).
1589 Site investigation surveys are expected to be very short in duration with animals returning to baseline levels soon after surveys have ceased. Site investigation activities will not take place within or nearby to the SAC and therefore will not exclude harbour porpoise from the relevant area of the site up to the threshold limit (20% in any given day or 10% over a season)[22], behavioural disturbance is therefore unlikely to be significant. It will not alter the distribution of harbour porpoise such that recovery cannot be expected or effects on Southern Nort Sea SAC population can be considered long term.
1590 Additionally, since there is no potential for injury ranges or disturbance contours to reach the SAC, it will not affect foraging habitats and areas important for breeding and calving within the designated site. Therefore, there is no potential for site investigation surveys to restrict the survivability and reproductive potential of harbour porpoises using the site. As such harbour porpoise will remain a viable component of the site.
1591 Significant adverse effects on the qualifying Annex II marine mammal feature, harbour porpoise of the Southern North Sea SAC, are not predicted to occur as a result of underwater noise during site investigation surveys during the operation and maintenance phase (i.e. in relation to maintaining the population, distribution of species within the site, connectivity and disturbance to species).
Conclusion
1592 The assessment has concluded that site investigation surveys will not take place within or nearby to the Southern North Sea SAC and will not exclude harbour porpoise from the relevant area of the site up to the threshold limit. Therefore, underwater noise during site investigation surveys will not result in significant disturbance of the species. Site investigation surveys will not affect areas important for breeding and calving within the site and therefore harbour porpoise will remain a viable component of the site. Site investigation surveys will not affect the condition of supporting habitats and processes. As such, the conservation objectives for Annex II species, harbour porpoise, will not be undermined.
1593 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Southern North Sea SAC from injury and disturbance due to underwater noise during site investigation surveys with respect to the operation of the Proposed Development acting alone.
Changes in fish and shellfish communities affecting prey availability
1594 As outlined in paragraph 1048 et seq., there is potential for changes to prey availability for harbour porpoise due to potential impacts on prey species during operation and maintenance of the Proposed Development. These impacts include temporary subtidal habitat loss/disturbance, long-term subtidal habitat loss, increased SSC and associated sediment deposition, EMF from subsea electrical cabling and colonisation of foundations, scour protection and cable protection.
1595 Potential temporary habitat loss/disturbance during operation and maintenance equates to a smaller area than that affected during construction (up to 989,000 m2 which equates to 0.08% of the fish and shellfish ecology area, compared with 9.7% during the construction phase). Operation and maintenance activities will occur periodically over the full lifetime of the project (estimated to be 35 years) and therefore only a small proportion of the maximum footprint of habitat loss/disturbance may occur at any one time (e.g. during offshore export cable repair/reburial or wind turbine replacement events). Affected areas are expected to start recovering immediately after cessation of maintenance activities. The areas within Southern North Sea SAC provide good foraging habitat for harbour porpoise. Given that all operation and maintenance activities will take place outside the SAC, the condition of supporting habitats and processes within site will not be impaired and the availability of prey will be maintained.
1596 Increased SSC could occur as a result of repair or remedial burial activities during the operation and maintenance phase. The maintenance activities will be undertaken at intervals over the 35 years operation and maintenance phase. The assessment presented in volume 2, chapter 9 of the Offshore EIA Report considered that any suspended sediments and associated deposition will be of the same magnitude, or lower as for construction. Therefore, the availability of suitable food supply for harbour porpoise is not expected to be impaired as a result of increase in SSC and associated deposition.
1597 The presence and operation of inter-array, interconnector and offshore export cables will result in emissions of localised electrical and magnetic fields, which could potentially affect the sensory mechanisms of some species of fish and shellfish. The range over which species can detect EMF will be very localised to within a few centimetres of the buried cable, with rapid decay of the EMF with increasing distance. Considering the above, adverse effects on harbour porpoise as a result of changes in prey availability due to EMF are unlikely.
1598 The impacts of activities undertaken as a part of the operation and maintenance phase of the Proposed Development will be highly localised and largely restricted to the boundaries of the Proposed Development, with only a small area affected when compared to available foraging habitat in the North Sea. Harbour porpoise eat a variety of prey including gobies, sandeel, whiting, herring and sprat. Findings presented in paragraph 793 suggest that Firth of Forth and Tay area for this species is unlikely to represent important breeding or foraging habitat that would not be available elsewhere within the species home range over the North Sea. There may be, however, an energetic cost associated with increased travelling and due to harbour porpoise high metabolic rate (see paragraph 1028), this species may be particularly vulnerable to this effect. However, 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) or moving relatively large distances on a daily basis (Nielsen et al., 2013). Based on findings of Benhemma-Le Gall et al. (2021) it can be anticipated that harbour porpoise can compensate for any resulting loss in energy intake by increasing foraging activities beyond impact zone. The availability of wider suitable habitat suggest that individuals may move to alternative foraging grounds without affecting animals health.
1599 Although there will be long term loss of habitat due to the presence of infrastructure associated with the Proposed Development, it is also anticipated that artificial structures will provide hard settlement opportunities and provide a valuable food source for fish. As discussed in paragraph 1021 et seq, evidence increasingly suggests that foraging opportunities for marine mammals are increased around offshore wind farm structures. Acoustic results from a T-POD measurement within a Dutch wind farm found that relatively more harbour porpoises are found in the wind farm area compared to the two reference areas, likely due to increased food availability as well as the exclusion of fisheries and reduced vessel traffic in the wind farm (shelter effect, see paragraph 1022). Therefore, presence of artificial structures may benefit harbour porpoise population in the long-term.
1600 Considering the above, it is anticipated that the availability of suitable foraging grounds for harbour porpoise will not be impaired and availability of prey will be maintained within the wider distributional range.
1601 Significant adverse effects on the qualifying Annex II marine mammal feature, harbour porpoise of the Southern North Sea SAC, are not predicted to occur as a result of changes in fish and shellfish communities affecting prey availability during operation and maintenance phase (i.e. in relation to maintaining the cover and abundance of preferred food items required by the species).
Conclusion
1602 The assessment has concluded that the impacts of construction and decommissioning will be highly localised and largely restricted to the boundaries of the Proposed Development, only a small area will be affected when compared to available foraging habitat in the North Sea and impacts will take place outside of the Southern North Sea SAC. Therefore, the condition of supporting habitats and processes will not be affected. Given that individuals may move to alternative foraging grounds without affecting animals’ health, availability of prey within the wider distributional range will not be affected. As such, the conservation objectives for Annex II species, harbour porpoise, will not be undermined.
1603 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Southern North Sea SAC from changes in fish and shellfish communities affecting prey availability with respect to the operation of the Proposed Development acting alone.
Effects in-combination
1604 An assessment of in-combination effects upon the qualifying Annex II marine mammal species of the Southern North Sea SAC arising from each identified impact is provided below.
1605 The potential to experience injury in terms of PTS by marine mammal receptors as a result of underwater noise due to piling be expected to be largely localised within the boundaries of the respective projects (assuming similar ranges of effect as presented for the Proposed Development). It is also anticipated that standard offshore wind industry construction methods (which include soft starts and visual and acoustic monitoring of marine mammals as standard) will be applied, thereby reducing the magnitude of the impact with respect to auditory injury occurring in marine mammals. Therefore, there is no potential for significant cumulative impacts for injury from elevated underwater noise during pilling and the cumulative assessment focuses on disturbance only.
Assessment of in-combination effects during construction and decommissioning
Injury and disturbance from elevated underwater noise during piling
Tier 2
1607 Behavioural disturbance is expected to occur during piling at all offshore wind farms. Of all projects listed in paragraph 1606, only construction of Dogger Bank Teesside A, Sofia Offshore Wind Farm, Hornsea Project Three and Hornsea Project Four will overlap with the piling phase for Proposed Development. Although there is an overlap of construction of Inch Cape and Seagreen 1A Project and construction of Proposed Development, the construction of both projects will be completed prior to commencement of piling at the Proposed Development and therefore could lead to a longer duration of piling operations (i.e. sequential rather than concurrent piling). The construction phases of Moray West, Blyth Demo 2, Dogger Bank Creyke Beck A and Dogger Back Creyke Beck B finish in the year following commencement of construction works at Proposed Development (i.e. two years before the commencement of the piling phase at Proposed Development). However, these projects are included in the assessment to consider temporal scenario to take account for potential disturbance to harbour porpoise caused by subsequent piling at Proposed Development. Where project piling phases overlap, the assessment is, conservatively, based on a maximum design scenario of all projects potentially piling at exactly the same time, however, in practice this is considered to be unlikely. For example, in order to reduce impacts on harbour porpoise within the Southern North Sea SAC, as a part of Site Integrity Plan, Hornsea Project Three and Hornsea Project Four have committed to schedule piling having regard to previous, ongoing and future piling associated with other offshore developments and other activities likely to act in-combination (GoBe, 2018b; GoBe, 2021).
1608 Seagreen 1A Project predicted that up to 1,882 animals could be exposed to noise levels that could result in behavioural disturbance at any one time during piling at Seagreen 1A Project (Seagreen Wind Energy Ltd, 2020). The original EIA (Seagreen Wind Energy Ltd, 2012) indicated that there is no evidence to show that the impacted area for this species represents important breeding or foraging habitat that would not be available elsewhere within the species home range over the North Sea793). The revised EIA for Inch Cape predicted that up to 302 harbour porpoises could be disturbed as a result of piling (Inch Cape Offshore Limited, 2018). The EIA for Moray West assessed potential numbers of harbour porpoises potentially affected by behavioural disturbance during piling as 1,609 individuals (Moray West, 2018).
1610 It should be noted that there is no potential for overlap of piling phases for projects considered in paragraphs 1608 and 1609 and piling at Proposed Development, therefore if animals would be impacted by behavioural disturbance that would happen sequentially, rather than concurrently.
1611 Piling at projects considered in this paragraph have a potential to occur simultaneously with piling phase at Proposed Development. The Dogger Bank Teesside A EIA predicted that harbour porpoise is expected to be disturbed within approximately 34 km from the source with up to 2,148 animals potentially affected (Royal Haskoning DHV, 2020). The assessment for Sofia Offshore Wind farm demonstrated that potential numbers of harbour porpoises potentially affected by behavioural disturbance during piling is up to 2,263 individuals (Innogy, 2020). The assessment for Hornsea Project Three predicted 7,330 porpoises to be exposed to behavioural disturbance during concurrent piling events (GoBe, 2018a). Hornsea Project Four predicted that up to 9,686 harbour porpoises could be disturbed during piling and the residual effect of behavioural disturbance on harbour porpoise from piling was predicted to be slight.
1612 Most projects and respective EIAs refer to the North Sea reference population, which, as presented in original Seagreen EIA (Seagreen Wind Energy Ltd, 2012), stretches across an area of 750,000 km2. The number of harbour porpoise potentially disturbed has been considered for projects located more than 300 km from the Proposed Development array area. Delineating the spatial extent of cumulative effects is commonly acknowledged as a challenge and although harbour porpoise is generally rare in waters >200 m depth, the fact that this species utilises such a vast area further complicates a choice of appropriate spatial scale (Murray et al., 2014). Population modelling was carried out to explore the potential of cumulative effects as a result of disturbance during piling to affect the wider population trajectory over time. Population modelling considered all projects listed in paragraph 1606 and respective numbers of animals potentially impacted against the MU population (see volume 3, appendix 10.4 for methods applied in the model). Results of the cumulative iPCoD modelling for harbour porpoise showed that the difference in population trajectory between the impacted and unimpacted population fall within the natural variance of the population (see paragraph 927 et seq.). Therefore, it was considered that there is no potential for the long-term effects on this species within wider population as a result of cumulative piling at proposed Development and respective projects (see volume 3, appendix 10.4 for more details).
1613 As previously described in paragraph 1544, noise disturbance from a project individually or in-combination is regarded as significant if it excludes harbour porpoises from more than 20% of the relevant area in any given day, and an average of 10% of the relevant area of the site over a specific season (JNCC, 2019c). Although there is a potential for harbour porpoises to be present within behavioural disturbance footprint of Proposed Development and that is the primary reason why the SAC has been screened in for the in-combination assessment, the advice on operations suggest that HRA should be considered for projects using pile driving within the SAC or within 26 km of site boundaries (JNCC, 2019c). Given the distance from the Southern North Sea SAC, the behavioural disturbance footprint of the Proposed Development will not contribute to total of 20% of the relevant area disturbed in any given day or 10% of the relevant area of the site over season with projects located in closer vicinity to the SAC and therefore behavioural disturbance as a result of piling in-combination with other projects is unlikely to be significant. It will not alter the distribution of harbour porpoise such that recovery cannot be expected or effects on SAC population can be considered long term.
1614 As presented by Benhemma Le Gall et al. (2021) during extended periods of disturbance, porpoises must make trade-offs between fleeing or remaining in areas that have a higher risk of disturbance. The study found that individual responsiveness to anthropogenic disturbances is therefore to be context dependent (i.e. whether the animal decides to flee high-quality feeding habitat or not and related to animal fitness). As presented in more details in paragraph 793, the Firth of Forth and Tay are not expected to represent important foraging grounds for harbour porpoise. If disturbed from the area by sequential piling at Inch Cape, Seagreen 1A Project and the Proposed Development, animals may leave the foraging grounds, however even with incurred energetic cost, it is likely that they will move to areas with the same or better quality of foraging habitat. Based on findings of the same study it can be anticipated that harbour porpoise can compensate for any resulting loss in energy intake by increasing foraging activities beyond impact zone (Benhemma-Le Gall et al., 2021). Therefore, it is anticipated that the availability of suitable foraging grounds for harbour porpoise will not be impaired and availability of prey will be maintained within the wider distributional range.
1615 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Southern North Sea SAC as a result of underwater noise during piling during construction with respect to the Proposed Development acting in-combination with Tier 2 projects.
Injury and disturbance from elevated underwater noise during UXO clearance
Tier 2
1617 For the Proposed Development alone, the maximum range across which harbour porpoise have the potential to experience PTS due to high order detonation of 300 kg charge was assessed as approximately 10,630 m. To reduce the potential of experiencing injury, designed-in measures, which are in line with recommended best practice guidelines, will be adopted as part of a MMMP (see Table 13.11 Open ▸ ). As described in paragraph 1570, there is a risk that harbour porpoise could potentially experience an auditory injury at distances that cannot be fully mitigated by application of ADD and soft-start charges (the maximum deterrence zone has been assessed as 7,200 m and PTS range for this species has been modelled as 10,630 m). Given that details about UXO clearance technique to be used and charge sizes will not be available until after the consent is granted (pre-construction phase, following UXO survey), it is not possible to quantify the effects of UXO detonations and therefore the residual number of animals affected is not presented within this document. 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 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 for the UXO clearance works. Appropriate mitigation measures will be agreed with stakeholders as a part of a UXO specific MMMP. It is therefore anticipated that following the application of mitigation measures following receipt of more detail regarding size and number of UXO, the risk of injury will be reduced to low.
1618 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. During the low order clearance, harbour porpoise can be potentially affected by PTS at the maximum range of 1,265 m due to detonation of 0.5 kg clearance shot. 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.
1619 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 works. 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. PTS onset ranges for Inch Cape Offshore Wind Farm, 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 not greater than assessed for the Proposed Development alone. 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.
1620 For Hornsea Project Three there was no site-specific modelling undertaken, however as a part of the EIA, the assessment of potential impacts in terms of injury (PTS) on marine mammals as a result of underwater noise during UXO clearance was based on the NOAA modelling for Hornsea Project One (GoBe, 2018a). The assessment predicted that up to 200 animals could experience injury, however, 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 (GoBe, 2018a). Due to lack of project specific UXO noise modelling, in the EIA for Hornsea Project Four, the assessment of potential impacts used estimates of the source level and predicted PTS-onset impact ranges based on Hornsea Project Two, estimating that up to 630 animals could be potentially injured (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 (example here is based on 800kg UXO size). The assessment concluded that with secondary 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.
1621 As such, with appropriate designed-in and secondary mitigation measures, only small proportion of the SAC population could be potentially affected and considering the size of the harbour porpoise population within Southern North Sea SAC, it is highly unlikely that the reproductive and recruitment capability of the species will be affected. Therefore, harbour porpoise will remain a viable component of the site.
1622 In terms of TTS, for the Proposed Development alone, the range across which harbour porpoise have the potential to experience TTS due to high order detonation of a 300 kg charge was assessed as approximately 19 km (see paragraph 971 et seq.). TTS onset ranges for Inch Cape Offshore Wind Farm, 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. Hornsea Project Three assessed potential impacts from TTS on marine mammals using two approaches, however one of them is more precautionary and therefore will be discussed further. The buffer of 26 km around the source location was applied to determine behavioural impact area and the assessment estimated that up to 1,869 harbour porpoises could potentially experience disturbance (GoBe, 2018a). Hornsea Project Four presented the predicted ranges for the onset of TTS from UXO clearance, but since no assessment of the number of animals was given, TTS with respect to this project could not be quantitatively assessed (SMRU Consulting, 2021).
1623 A spatial maximum adverse 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 listed in paragraph 1616 start their construction activities at least a year 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.
1624 As previously described in paragraph 1544, noise disturbance from a plan individually or in-combination is regarded as significant if it excludes harbour porpoises from more than 20% of the relevant area in any given day, and an average of 10% of the relevant area of the site over specific season (JNCC, 2019c). Given the distance from the Southern North Sea SAC, the PTS and/or TTS footprint of the Proposed Development will not contribute to total of 20% of relevant area disturbed in any given day or 10% of the relevant area of the site over a season with projects located in closer vicinity to the SAC and therefore disturbance as a result of UXO clearance in-combination with other projects is unlikely to be significant. It will not alter the distribution of harbour porpoise such that recovery cannot be expected or effects on SAC population can be considered long term. Therefore, harbour porpoise will remain a viable component of the site.
1625 Additionally, as presented in more detail in paragraph 1614, if the animal flees the ensonified area, it can be anticipated that harbour porpoise can compensate for any resulting loss in energy intake by increasing foraging activities beyond impact zone (Benhemma-Le Gall et al., 2021). Given that Firth of Forth and Tay are not expected to represent important foraging grounds for harbour porpoise (see paragraph 793), it is anticipated that the availability of suitable foraging grounds for harbour porpoise will not be impaired and availability of prey will be maintained within the wider distributional range.
1626 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Southern North Sea SAC as a result of site investigation surveys during the construction phase with respect to the Proposed Development acting in-combination with Tier 2 projects.