Conservation objectives
1402 The conservation objectives for harbour seal at Firth of Tay and Eden Estuary SAC have been developed by NatureScot[19] as follows:
- To avoid the deterioration of the habitat of the qualifying species or significant disturbance to the qualifying species, thus ensuring that the integrity of the site is maintained and the site makes an appropriate contribution to achieving favourable conservation status for each of the qualifying features; and
- To ensure for the qualifying species that the following are maintained in the long term:
– Population of the species as a viable component of the site;
– Distribution of the species within site;
– Distribution and extent of habitats supporting the species;
– Structure, function and supporting processes of habitats supporting the species; and
– No significant disturbance of the species.
1403 No supplementary advice on the conservation objectives, or Conservation Advice Packages (CAP) are available for the Firth of Tay and Eden Estuary SAC.
Features and effects for assessment
1404 The potential for adverse effects has been identified for the following Annex II marine mammal features of this site:
- Harbour seal
1405 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 seal at this site:
- Injury and disturbance from underwater noise generated by following activities:
– piling of fixed foundations;
– clearance of UXO;
– site investigation surveys; and
– vessel use and other activities.
- 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.
1406 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 seal at this site:
- Injury and disturbance from underwater noise generated by site investigation surveys as well as vessel use and other activities;
- 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.
1407 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 seal 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
1408 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 seal. 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.
1409 The maximum range for injury to harbour seal was estimated as 118 m based on SPLpk and using the 1% constant conversion factor (see paragraph 881 et seq). Taking into account the most conservative scenario and maximum harbour seal densities ( Table 13.4 Open ▸ ), less than one individual was predicted to be potentially injured, which accounts for 2.4% of the Firth of Tay and Eden Estuary SAC population. As outlined in paragraph 785, of the 46 adult harbour seals tagged in East Scotland between 2001 and 2017, 25 had telemetry track data recorded within the Proposed Development Marine Mammal study area and all 25 of these harbour seals also showed connectivity with the Firth of Tay and Eden Estuary SAC ( Figure 13.6 Open ▸ ). 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 seal.
1410 In terms of behavioural disturbance, up to three animals were predicted to be potentially disturbed from concurrent piling at a maximum hammer energy of 4,000 kJ ( Table 13.16 Open ▸ ; Figure 13.6 Open ▸ ). On the basis of the assumption that the three animals potentially disturbed originate from the SAC, this represents 7.3% of the Firth of Tay and Eden Estuary SAC population. These results are, however, 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 et seq. for more details)). Additionally, although the population of harbour seals withing the East Scotland MU is mainly concentrated in the Firth of Tay and Eden Estuary SAC, additional groups are also present in the Firth of Forth, Montrose Basin and at coastal sites in Aberdeenshire (SCOS, 2021). Therefore it is highly unlikely that all seals potentially present within the noise disturbance contours will originate from this SAC.
1411 The outer behavioural disturbance contours do not overlap with Firth of Tay and Eden Estuary SAC ( Figure 13.6 Open ▸ ). Harbour seals present in the vicinity of the habitats which they utilise throughout their life cycle (sandbanks and estuaries), are therefore unlikely to experience disturbance as these areas lie outside of the noise disturbance contours. As such, piling activities are highly unlikely to disrupt normal behaviours of harbour seals or adversely affect maintaining supporting habitats.
1412 Harbour seal in inshore waters could experience mild disturbance where these areas overlap with 135 dB disturbance contour, but prolonged or sustained behavioural effects, including displacement, are unlikely to occur (Southall et al., 2021). As outlined in paragraph 1085 et seq, barrier effects and altered behaviour could affect reproduction and lactation, however, harbour seal foraging is restricted during this period (see paragraph 1086 et seq). Considering that barrier effects are unlikely, disturbance caused by piling is not anticipated to result in reduced reproductive success and will not affect the status of this population as a viable component of the site (noting that the population of this SAC is in decline due to factors not associated with the Proposed Development, see paragraph 1415).
1413 Harbour seals tend to stay within 50 km of the coast, although most foraging trips are over shorter ranges (see paragraph 1025). Telemetry tracks show that few animals may venture further from the coast and therefore during piling, there is the potential for some animals to be temporarily deterred from the offshore areas ( Figure 13.6 Open ▸ ). It should be noted that behavioural disturbance contours presented in Figure 13.6 Open ▸ represent the maximum adverse scenario for concurrent piling at wind turbine locations where noise contours propagate in the direction of the Firth of Tay and Eden Estuary SAC. Therefore, the disturbance contours will not reach that far towards the SAC during the piling at remaining wind turbine/OSP-Offshore convertor station platform locations. As described in paragraph 1478, harbour seals although initially displaced due to pile-driving, are likely to return to the same area within two hours following cessation of piling. Therefore, it is anticipated that piling will not result in any long-lasting changes in the distribution of seals from this SAC and the connectivity with areas of high importance outside the site is not expected to be impaired.
1414 As outlined in paragraph 884, the total duration of piling could potentially affect a maximum of five breeding cycles for harbour seals. Piling activities will be intermittent and will occur over small timespan (372 days) within piling phase (52 months) and therefore can affect harbour seals over the medium term.
Figure 13.6: Unweighted SELss Contours Due to Concurrent Impact Piling of Wind Turbine Piles at Maximum Hammer Energy (4,000 kJ) Overlaid With Adult Harbour Seal Telemetry Tracks
1415 The population of harbour seals in Firth of Tay and Eden Estuary SAC is known to be in decline since the early 2000s after the phocine distemper virus (PDV) epidemic (see volume 3, appendix 10.2, annex B of the Offshore EIA Report). Population modelling work conducted for the Firth of Tay and Eden Estuary SAC population has concluded that if this declining trend continues, the population may become extinct within the next 20 years (Hanson et al., 2017). The same study concluded that although the cause of this decline is unknown, it must be reducing adult survival because the high rate of decline cannot be wholly accounted for by changes in other demographic parameters. There are a few theories about potential links to population decline, including harmful algal toxins (Hall and Frame, 2010; Jensen et al., 2015) or competition between grey seals and harbour seals (see Figure 13.1 Open ▸ where the density of adult grey seal telemetry tracks with connectivity to the Firth of Tay and Eden Estuary SAC is high; Wilson and Hammond, 2016). This population is deemed sensitive to any additional anthropogenic disturbance, especially during the breeding season (spring and summer), however, based on findings of Hanson et al. (2017) the population will not recover if sources of increased mortality is not identified and measures to manage these are not put in place. Therefore, although potential anthropogenic disturbance may be intolerable for this species, it will also not influence the population trajectory, which is in decline.
1416 No population trajectory is available for Firth of Forth, although sporadic counts in the area indicate that the decline is localised within the SAC and may not represent the trends in the overall MU population (SCOS, 2020; Sinclair et al., 2020). The results of the iPCoD modelling for harbour seal against the wider ES MU population showed that the difference in population trajectory between the impacted and unimpacted population fall within the natural variance of the population (see paragraph 919 et seq.). Therefore, it was considered that there is no potential for long-term effects on this species within the wider population as a result of piling during construction phase of the Proposed Development (see volume 2, chapter 10 of the Offshore EIA Report).
1417 Significant adverse effects on the qualifying Annex II marine mammal feature, harbour seal of the Firth of Tay and Eden Estuary 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
1418 The assessment has concluded that piling activities are highly unlikely to disrupt normal behaviours of harbour seal because the behavioural disturbance contours do not reach the coast and hence do not overlap with the site. Therefore the distribution of the species within the site will not be affected and neither will be the distribution and extent of habitats supporting the species. Animals would be potentially exposed only to low noise levels along the coast and these are unlikely to lead to barrier effects or strong behavioural response. Therefore, disturbance caused by piling is considered unlikely to cause a change in reproduction and survival rates and will not influence the population of the species as a viable component of the site (noting that the population of this SAC is in decline due to factors not associated with the Proposed Development). As such, the conservation objectives for Annex II species, harbour seal, will not be undermined.
1419 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Firth of Tay and Eden Estuary 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
1420 The noise modelling showed that ranges within which there is a risk of PTS to harbour seal as a result of geophysical surveys are relatively low with a maximum impact range of 65 m (due to operation of SSS, SBES and SBP; see paragraph 945 et seq.). For geotechnical survey activities, PTS impact thresholds for harbour seal are not exceeded ( Table 13.21 Open ▸ ).
1421 There is potential for less than one animal to experience PTS as a result of geophysical and geotechnical site investigation surveys (2.4% of the Firth of Tay and Eden Estuary SAC population). The surveys are considered to be short-term as they will take place over a period of up to three months. 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. With designed-in measures in place ( 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 to harbour seals are predicted as a result of site investigations surveys. It is anticipated that as a result of site investigation surveys there will be no introduction of barriers to wider movement or impact to connectivity between different important habitats for harbour seals at the SAC.
1422 In terms of behavioural disturbance, estimated maximum ranges for onset of disturbance are based on exceeding the 120 dB re 1 μPa (rms) threshold applicable for all marine mammals, noting that this threshold is for ‘mild disturbance’ and therefore is not likely to result in displacement of animals. Additionally, Russell et al. (2017) study reported the highest received level at which a response was detected by seals at 135 dB SELss with a zero probability of response measured at 130 dB SELss. The largest distance over which disturbance could occur potentially affecting harbour seal is out to approximately 7.5 km during vibro-coring. The assessment predicted that a maximum of one individual could be disturbed as a result of vibro-coring (2.4% of the Firth of Tay and Eden Estuary SAC population). Since the adult harbour seal telemetry tracks are mostly confined to the northern part of the Proposed Development array area, only surveys taking place in close vicinity to this area could result in a potential disturbance. Although there is a potential for behavioural disturbance during vibro-core survey, this survey is expected to be very short in duration with animals returning to baseline levels soon after surveys have ceased. Therefore, the underwater noise during site-investigation surveys is unlikely to result in reduced reproductive success and will not affect the status of this population as a viable component of the site (noting that the population of this SAC is in decline due to factors not associated with the Proposed Development, see paragraph 1415).
1423 It is anticipated that there will be no introduction of barriers to wider movement or impact to connectivity between different important habitats for harbour seals at the SAC as a result of site investigation surveys. Therefore, it is highly unlikely that site investigation surveys will influence distribution of the species within and outside the site.
1424 Significant adverse effects on the qualifying Annex II marine mammal feature, harbour seal of the Firth of Tay and Eden Estuary 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
1425 The assessment has concluded that there will be no introduction of barriers to wider movement for harbour seal as a result of elevated sound from site investigation surveys. Therefore the distribution of the species within the site will not be affected and neither will be the distribution and extent of habitats supporting the species. Underwater noise during site-investigation surveys is unlikely to affect harbour seal at a level that would substantially affect their behaviour and cause change in reproduction and survival rates and therefore will not influence the population of the species as a viable component of the site (noting that the population of this SAC is in decline due to factors not associated with the Proposed Development). As such, the conservation objectives for Annex II species, harbour seal, will not be undermined.
1426 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Firth of Tay and Eden Estuary 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
1427 Based on the maximum design scenario of high order detonation, the underwater noise modelling results show that harbour seal can be potentially affected by PTS at the maximum range of 2,085 m due to detonation of charge size of 300 kg ( Table 13.24 Open ▸ ). Conservatively, the number of harbour seals that could be potentially injured by the high order UXO clearance event has been assessed as up to one animal (Table 13.27). This represents a possible 2.4% of the Firth of Tay and Eden Estuary SAC population.
1428 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 ▸ ). Given that there is a potential to experience auditory injury by harbour seal at a greater range than can be mitigated by monitoring of the 1 km mitigation zone alone ( Table 13.24 Open ▸ ), an ADD will be deployed for a pre-determined length of time to deter marine mammals to a greater distance prior to any detonation. Activation of ADD for 22 minutes is considered sufficient to deter harbour seal from the potential injury zone as a result of high order detonation of 300 kg UXO ( Table 13.24 Open ▸ ). A MMMP will be developed for the purpose of mitigating the risk of auditory injury (PTS) to marine mammals from the proposed UXO clearance activities at the Proposed Development based on an assessment which will be provided as a part of the EPS licence supporting information.
1429 Moreover, it is 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 seal can be potentially affected by PTS at the maximum range of 250 m due to detonation of 0.5 kg clearance shot ( Table 13.24 Open ▸ ), with one animal potentially affected ( Table 13.25 Open ▸ , 2.4% of the Firth of Tay and Eden Estuary SAC population).
1430 As described in paragraph 971, the threshold for potential temporary loss of hearing (TTS) was also assessed. The onset of TTS also corresponds to a ‘fleeing response’ as this is the threshold at which animals are likely to flee from the ensonified area. Thus, the onset of TTS reflects the threshold at which behavioural displacement could occur. It is important to note that the sound is unlikely to be impulsive in character once it has propagated more than a few kilometres. It is particularly important when interpreting results for TTS with impact ranges of several kilometres as these are likely to be significantly lower than predicted.
1431 Based on the maximum design scenario of high order detonation, the underwater noise modelling results show that harbour seal can be potentially affected by TTS at the maximum range of 6,430 m due to detonation of charge size of 300 kg ( Table 13.32 Open ▸ ) with up to 156 harbour seal individuals affected ( Table 13.33 Open ▸ ). As low order techniques are preferred option for UXO clearance, the underwater noise modelling results show that harbour seal can potentially experience TTS at the maximum range of 455 m due to detonation of 0.5 kg clearance shot ( Table 13.30 Open ▸ ) with less than one animal potentially affected ( Table 13.31 Open ▸ ). This accounts for 2.4% of the Firth of Tay and Eden Estuary SAC population.
1432 TTS is a temporary hearing impairment and therefore animals are likely to fully recover from the effect. Therefore, effects caused by UXO clearance are considered is unlikely to result in reduced reproductive success and will not affect the status of this population as a viable component of the site (noting that the population of this SAC is in decline due to factors not associated with the Proposed Development, see paragraph 1415).
1433 Considering the number of animals potentially affected by the PTS and TTS, respective proportions of the SAC population potentially affected and designed-in measures reducing the risk of adverse effects, an alteration in the distribution of the population from Firth of Tay and Eden Estuary SAC is considered highly unlikely.
1434 Significant adverse effects on the qualifying Annex II marine mammal feature, harbour seal of the Firth of Tay and Eden Estuary 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
1435 The assessment has concluded that UXO clearance activities are highly unlikely to disrupt normal behaviours of harbour seal. Since TTS is a temporary hearing impairment, it is unlikely to cause a change in reproduction and survival rates and will not influence the population of qualifying species (noting that the population of this SAC is in decline due to factors not associated with the Proposed Development). Changes in distribution of qualifying species within the site are highly unlikely. As such, the conservation objectives for Annex II species, harbour seal, will not be undermined.
1436 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Firth of Tay and Eden Estuary SAC from injury and disturbance due to underwater noise during UXO clearance with respect to the construction of the Proposed Development acting alone.
Injury and disturbance from elevated underwater noise during vessel use and other activities
1437 With regards to PTS, the modelling shows that for harbour seal, the threshold for PTS is not exceeded by any vessel with the exception of rock placement vessels, for which an injury range of 5 m from the source was reported ( Table 13.35 Open ▸ ). PTS ranges for seal were not exceeded for any other activities except for cable laying, where an injury range of 5 m from the source was reported. The number of harbour seals potentially affected within the modelled ranges for PTS from vessels and other activities were found to be less than one individual. For Firth of Tay and Eden Estuary SAC, this equates to 2.4% of harbour seal population. Given that vessels will follow a Code of Conduct (including advice to operators to not deliberately approach marine mammals) and NSPVMP, the risk of potential auditory injury will be low.
1438 With regard to behavioural disturbance to harbour seal, cable laying activities result in the greatest modelled disturbance ranges out to 4,389 m. Similar ranges for behavioural effects are predicted to occur due to underwater noise from installation and construction vessels as well as rock placement vessels with disturbance ranges of 4,389 m. In comparison, vessels such as excavator, backhoe dredger, pipe laying, geophysical survey vessel and jack up vessel as well as jack-up rig were predicted to result in disturbance ranges out to 300 m.
1439 As discussed in paragraph 874, there is likely to be a proportionate response of animals within the modelled contours (i.e. not all animals will be disturbed to the same extent). Most of the vessel traffic associated with construction within the Proposed Development array area will take place at distances >45 km from the Firth of Tay and Eden Estuary SAC. Vessel movements will also increase over construction phase along the Proposed Development export cable corridor. Although there is some connectivity of individual harbour seal telemetry tracks between the SAC and Proposed Development export cable corridor, majority of harbour seal movements are confined within the outer Firth of Tay and north-west to the Proposed Development array area ( Figure 13.6 Open ▸ ).
1440 Additionally, vessels will be moving to and from ports and harbours and this traffic is likely to intersect with the areas characterised by high density of harbour seal telemetry tracks ( Figure 13.6 Open ▸ ). As previously discussed in paragraph 1109, seals exhibit avoidance behaviour or alert reactions when disturbed, as hauled out seals typically flush into the water which may be detrimental during pupping season. The presence of vessels in foraging grounds could result in reduced foraging success, particularly in harbour seals given reduced foraging ranges out to 50 km. Study commissioned by the FTOWDG presented analysis of telemetry data available from harbour seals tagged by SMRU in the East Scotland SMA between 2001 and 2008 and the analysis demonstrated that harbour seal movements are mostly coastal (Sparling et al., 2012). The NSPVMP will be produced and will include agreed routes and potential speed restrictions in order to reduce the disturbance. Given the existing levels of vessel activity within the Firths of Tay and Forth, it is expected that harbour seals could tolerate the effects of vessel presence to some extent. Even if individuals are temporarily deterred from offshore foraging grounds, given that the impacts of construction will be highly localised, largely restricted to the boundaries of the Proposed Development (vessel movements intersecting the areas potentially important for harbour seal closer to the coast will be intermittent), only a small area will be affected when compared to available foraging habitat for harbour seals. Therefore, it is anticipated that the connectivity with suitable foraging grounds and supporting habitats will not be impaired. As such, impacts associated with vessel use are considered is unlikely to result in reduced reproductive success and will not affect the status of this population as a viable component of the site (noting that the population of this SAC is in decline due to factors not associated with the Proposed Development, see paragraph 1415).
1441 Significant adverse effects on the qualifying Annex II marine mammal feature, harbour seal of the Firth of Tay and Eden Estuary SAC, are not predicted to occur as a result of underwater noise during vessel use and other activities during the construction phase (i.e. in relation to maintaining the population, distribution of species within the site, connectivity and disturbance to species).
Conclusion
1442 The assessment has concluded that vessel use and other activities are highly unlikely to affect reproductive and recruitment capability of the species because the behavioural disturbance ranges do not reach the coast and hence do not overlap with the site. Therefore, it will not influence the population of the species as a viable component of the site (noting that the population of this SAC is in decline due to factors not associated with the Proposed Development). The availability of foraging grounds for harbour seal will not be impacted and the distribution of the species within the site will not be affected and neither will be the distribution and extent of habitats supporting the species. As such, the conservation objectives for Annex II species, harbour seal, will not be undermined.
1443 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Firth of Tay and Eden Estuary SAC from injury and disturbance due to underwater noise during vessel use and other activities with respect to the construction and decommissioning of the Proposed Development acting alone.
Changes in fish and shellfish communities affecting prey availability
1444 As outlined in paragraph 1001 et seq., there is potential for changes to prey availability for harbour seal during construction and decommissioning of the Proposed Development. These impacts include temporary and long-term habitat loss/disturbance, increased SSC and associated sediment deposition, and injury and/or disturbance from underwater noise and vibration.
1445 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 (see volume 3, chapter 9 of the Offshore EIA Report). 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 impacts will be highly localised. As presented in Figure 13.6 Open ▸ , areas within the Proposed Development array area and Proposed Development export cable corridor are not characterised by high densities of harbour seal telemetry tracks and therefore these areas are highly unlikely to represent important foraging grounds for this species. However, for these individuals visiting Proposed Development to find prey, it is expected that harbour seal could come back to forage within areas previously disturbed after cessation of works and therefore their distribution and connectivity with important habitats within and outside the site is unlikely to be impaired in long term.
1446 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.
1448 As outlined in paragraph 1026 et seq., harbour seals are generalist feeders and can forage on variety of species, usually within 50 km from the coast. Given that the impacts of construction 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 within the outer Firth of Tay. Based on the telemetry data ( Figure 13.6 Open ▸ ), harbour seal presence is confined mostly within approximately 30 km from the SAC limits and the overlap with Proposed Development is limited. Due to the presence of alternative prey resources and foraging grounds available in the wider area, harbour seals are not expected to be constrained by the temporary and reversable nature of impacts associated with construction. It is expected that harbour seal population would be able to tolerate the effect without any impact on reproduction and survival rates.
1449 Significant adverse effects on the qualifying Annex II marine mammal feature, harbour seal of the Firth of Tay and Eden Estuary 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
1450 The assessment has concluded that distribution of the species within the site and the distribution and extent of habitats supporting the species is unlikely to be impaired in long term. It is expected that harbour seal population would be able to tolerate the effect of changes in fish and shellfish communities without any impact on reproduction and survival rates and it will not influence the population of the species as a viable component of the site (noting that the population of this SAC is in decline due to factors not associated with the Proposed Development). As such, the conservation objectives for Annex II species, harbour seal, will not be undermined.
1451 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Firth of Tay and Eden Estuary 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
1452 As discussed in paragraph 945 et seq., the maximum range at which there is a risk of PTS to harbour seal as a result of site investigation surveys is 65 m. With designed in measures ( Table 13.40 Open ▸ ) implemented for the geophysical surveys, the risk of PTS occurring to harbour seals will be low. With regard to behavioural disturbance, although a maximum potential disturbance range across all survey types is 7.5 km during vibro-coring, this survey is expected to be very short in duration with animals returning to baseline levels soon after surveys have ceased.
1453 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 ▸ ). Surveys are anticipated to be short-term in nature (weeks to a few months) and occur intermittently over the operation and maintenance phase. Given that the surveys will be confined within limits of the Proposed Development, it is anticipated that there will be no introduction of barriers to wider movement or impact to connectivity between different important habitats for harbour seals. Therefore, it is highly unlikely that they will influence distribution of harbour seal within and outside the SAC.
1454 Significant adverse effects on the qualifying Annex II marine mammal feature, harbour seal of the Firth of Tay and Eden Estuary 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
1455 The assessment has concluded that there will be no introduction of barriers to wider movement for harbour seal as a result of elevated sound from site investigation surveys. Therefore the distribution of the species within the site will not be affected and neither will be the distribution and extent of habitats supporting the species. Underwater noise during site-investigation surveys is unlikely to affect harbour seal at a level that would substantially affect their behaviour and cause change in reproduction and survival rates and therefore will not influence the population of the species as a viable component of the site (noting that the population of this SAC is in decline due to factors not associated with the Proposed Development). As such, the conservation objectives for Annex II species, harbour seal, will not be undermined.
1456 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Firth of Tay and Eden Estuary SAC from injury and disturbance due to underwater noise during site investigation surveys with respect to the operation of the Proposed Development acting alone.
Injury and disturbance from elevated underwater noise during vessel use and other activities
1457 As described in paragraphs 989 et seq., vessel use during the operation and maintenance phase of the Proposed Development is considered a relatively small increase in the context of baseline traffic and the size and noise outputs from vessels will be similar to those used in the construction phase. The number of vessel round trips and their frequency will be much lower compared to the construction phase.
1458 Most of the vessel traffic associated with operation and maintenance within the Proposed Development array area will take place at distances >45 km from the Firth of Tay and Eden Estuary SAC. Vessel movements may occasionally increase along the Proposed Development export cable corridor. Although there is some connectivity of individual harbour seal telemetry tracks between the SAC and Proposed Development export cable corridor, majority of harbour seal movements are confined within the outer Firth of Tay and north-west to the Proposed Development array area ( Figure 13.6 Open ▸ ).
1459 Additionally, vessels will be moving to and from ports and harbours and this traffic is likely to intersect with the areas characterised by high density of harbour seal telemetry tracks ( Figure 13.6 Open ▸ ). Richardson et al. (2005) reported avoidance behaviour or alert reactions in harbour seal when vessels approach within 100 m of a haul-out site and when disturbed, seals that are hauled-out typically flush into the water which could be detrimental during pupping season (see paragraph 1109 et seq.). As previously described for the construction phase, the presence of vessels in foraging grounds could result in reduced foraging success (paragraph 1440). Impacts associated with vessel use are considered is unlikely to result in reduced reproductive success and will not affect the status of this population as a viable component of the site (noting that the population of this SAC is in decline due to factors not associated with the Proposed Development, see paragraph 1415).
1460 Effects on harbour seal at this SAC are therefore considered to be the same or less than the effects of vessel use and other activities during the construction and decommissioning phases. It should be noted that operation and maintenance activities will occur over the full lifetime of the project (estimated to be 35 years) and therefore only a small proportion of vessel use and other activities will occur at any one time.
1461 Significant adverse effects on the qualifying Annex II marine mammal feature, harbour seal of the Firth of Tay and Eden Estuary SAC, are not predicted to occur as a result of underwater noise during vessel use and other activities 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
1462 The assessment has concluded that vessel use and other activities are highly unlikely to affect reproductive and recruitment capability of the species because the behavioural disturbance ranges do not reach the coast and hence do not overlap with the site. Therefore, it will not influence the population of the species as a viable component of the site (noting that the population of this SAC is in decline due to factors not associated with the Proposed Development). The availability of foraging grounds for harbour seal will not be impacted and the distribution of the species within the site will not be affected and neither will be the distribution and extent of habitats supporting the species. As such, the conservation objectives for Annex II species, harbour seal, will not be undermined.
1463 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Firth of Tay and Eden Estuary SAC from injury and disturbance due to underwater noise during vessel use and other activities with respect to the operation of the Proposed Development acting alone.
Changes in fish and shellfish communities affecting prey availability
1464 As outlined in paragraph 1051 et seq., there is potential for changes to prey availability for harbour seal 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.
1465 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; see volume 2, chapter 9 of the Offshore EIA Report). Operation and maintenance activities will occur periodically over the full lifetime of the project (estimated to be 35 years) and only a small proportion of the maximum footprint of habitat loss/disturbance may occur at any one time, with areas starting to recover immediately after cessation of maintenance activities. As presented in Figure 13.6 Open ▸ , areas within the Proposed Development array area and Proposed Development export cable corridor are not characterised by high densities of harbour seal telemetry tracks and therefore these areas are highly unlikely to represent important foraging grounds for this species. However, for these individuals visiting Proposed Development to find prey, it is expected that harbour seal could come back to forage within areas previously disturbed after cessation of works. Therefore, the distribution and extent of habitats supporting the species outside of the SAC is unlikely to be impaired.
1466 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. Given the small and localised extent of these effects, the availability of suitable foraging grounds for harbour seal is not expected to be impaired.
1467 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 seal as a result of changes in prey availability due to EMF are highly unlikely.
1468 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. Individual harbour seals demonstrate high levels of site-fidelity and foraging ranges may be constrained around these favoured breeding and haul-out sites (Thompson et al., 2013). Additionally, because displacement could potentially lead to increased competition for food between competing species (grey seal and harbour seal; Wilson and Hammond, 2016), presence of artificial structures in offshore waters is unlikely to benefit harbour seal population.
1469 As outlined in paragraph 1026 et seq., harbour seals are generalist feeders and can forage on variety of species, usually within 50 km from the coast. Given that the impacts of construction 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 within the outer Firth of Tay. Based on the telemetry data ( Figure 13.6 Open ▸ ), harbour seal presence is confined mostly within approximately 30 km from the SAC limits and the overlap with Proposed Development is limited. Due to the presence of alternative prey resources and foraging grounds available in the wider area, harbour seals are not expected to be constrained by the temporary and reversable nature of impacts associated with operation and maintenance phase. It is expected that harbour seal population would be able to tolerate the effect without any impact on reproduction and survival rates.
1470 Significant adverse effects on the qualifying Annex II marine mammal feature, harbour seal of the Firth of Tay and Eden Estuary 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
1471 The assessment has concluded that distribution of the species within the site and the distribution and extent of habitats supporting the species is unlikely to be impaired in long term. It is expected that harbour seal population would be able to tolerate the effect of changes in fish and shellfish communities without any impact on reproduction and survival rates and it will not influence the population of the species as a viable component of the site (noting that the population of this SAC is in decline due to factors not associated with the Proposed Development). As such, the conservation objectives for Annex II species, harbour seal, will not be undermined.
1472 Therefore, it can be concluded that there is no risk of an Adverse Effect on Integrity on the Firth of Tay and Eden Estuary SAC from changes in fish and shellfish communities affecting prey availability with respect to the operation of the Proposed Development acting alone.