Benthic ecology
  1. A review by Degraer et al. (2020) explained the process by which rapid colonisation can occur on all submerged parts of wind turbine components. Vertical zonation of species is usually observed with different species colonising the splash, inter-tidal, shallow and deeper subtidal zones (Degraer et al., 2020). Colonising communities on offshore installations are typically dominated by mussels, macroalgae and barnacles near the water surface, which essentially creates a new intertidal zone, while the community is dominated by filter feeding arthropods at intermediate depths, and by anemones at deeper locations (De Mesel et al., 2015; Karlsson et al., 2022). Colonisation of the hard substrates associated with the Array is therefore likely to result in an increase in biodiversity and a change compared to the baseline if no hard substrates were present (Lindeboom et al., 2011). In addition, the structural complexity of artificial substrates such as Offshore Substation Platform (OSP) foundations and floating wind turbine foundations may provide refuge as well as increasing feeding opportunities for larger and more mobile species. For example, Mavraki et al. (2020), demonstrated higher food web complexity associated with zones which had high accumulation of organic material (such as soft substrate or scour protection), suggesting potential reef effect benefits from the presence of artificial hard structures.
  2. Colonisation of hard structures may have indirect effects on the baseline communities and habitats identified within the Site boundary due to increased predation on and competition for the existing soft sediment species. These effects are difficult to predict, especially as monitoring to date has focused on the colonisation and aggregation of species close to the wind turbine foundations rather than broad scale studies.
  3. Some studies have also shown that the installation and operation of offshore wind farms has a negligible impact on the soft sediment environments. De Backer et al. (2020) found that the soft sediment benthic community underwent no drastic changes eight to nine years after the installation of C-power and Belwind Offshore Wind Farms in Belgium and that the species originally inhabiting the sandy substrate were still present and remained dominant in the offshore wind farms. Hutchinson et al. (2020) found that, during post-construction monitoring at the Block Island Wind Farm in the USA, no strong gradients of change in sediment grain size, enrichment or benthic macrofauna within 30 m to 90 m distance of the wind turbines was found. APEM (2022) found that at the Beatrice Offshore Wind Farm in the Moray Firth, colonisation of wind turbines resulted in zonation of the foundation itself and had little influence on the sedimentary habitat below. Across all wind turbines, plumose anemones Metridium senile and tube worms Spirobranchus sp. were the most abundant species, with the highest biomass at 40 m depth. Similarly, at the Hywind Scotland Pilot Park off the coast of Aberdeenshire, plumrose anemones and tube worms. dominated the bottom and mid-section of wind turbines, and a general increase of epifouling growth between 2018 and 2020 was recorded, indicating a source of food was present (Karlsson et al., 2022).
  4. The MDS assumes that up to 19.27 km2 of artificial hard substrate will be installed on the seabed within the Array benthic subtidal ecology study area (2.25% of the entire area). This comprises mooring lines and anchors on the seabed, OSP foundations, inter-array and interconnector cable protection and cable crossing protection, subsea junction boxes, and scour protection for mooring lines, anchors, OSP foundations, and subsea junction boxes. The floating wind turbine foundations represent up to 3.79 km2 of hard substrate which may be colonised within the water column. It is expected that these artificial hard structures will be colonised by epifaunal species local to the site boundary (volume 2, chapter 8).
  5. The ocean quahog IEF and phosphorescent sea pen IEF require a soft sedimentary habitat, and physical change to hard artificial or rock substratum would represent habitat loss for these species, which are highly vulnerable to this impact (Hill and Tyler-Walters, 2018).
  6. In contrast however, the dead man’s fingers IEF and the sea tamarisk IEF naturally live on hard substrates, including bedrock, rocks, boulders, shells, and man-made artificial hard structures (Budd, 2008, Wilson, 2002). Therefore, this impact does not represent a change from a preferred habitat to an unsuitable one for these IEFs, in comparison to the other IEFs. In addition, hydroids (such as sea tamarisk) are typically one of the first taxa to colonise new substrates (Boero, 1984). For example, a study on marine growth on the North Sea oil platform Montrose Alpha recorded eight species of hydroid (although none were sea tamarisk), present on the hard structures associated with the platform (Forteath et al., 1982).
Fish and shellfish ecology
  1. As discussed in volume 2, chapter 9, the introduction of hard substrates can have indirect and direct effects on fish as follows:
  • indirect effects on fish through the potential of the reef effect to bring about changes to food resources; and
  • direct effect on fish through the potential to act as fish aggregation devices.
  1. The colonisation of epifaunal species on to the artificial hard structures of the Array may result in increased availability of prey species, which in turn may lead to increased numbers of fish and shellfish species utilising the hard substrate habitats.
  2. The introduction of hard structures such as foundations will likely lead to the colonisation of this substrate by fish and shellfish species. Primary colonisation may occur within hours or days by demersal and semi-pelagic species (Andersson, 2011). Colonisation has been seen to occur for a number of years following the initial construction, until a structured recolonised population is formed (Krone et al., 2013). The colonisation of these structures hence may attract fish from the surrounding areas to occupy the habitat with increased complexity, which will then increase the carrying capacity of the area (Andersson and Öhman, 2010; Bohnsack, 1989). The extent and nature of the colonisation of the new species will be determined by the dominant natural substrate character of the fish and shellfish ecology study area (largely muddy sand, sand, and slightly gravelly sand). For example::
  • hard structures on an area of seabed are already characterised by rocky substrates, resulting in few new species but the ability to sustain a higher abundance (Andersson and Öhman, 2010); and
  • hard structures on a soft seabed, may result in increased diversity of fish normally associated with rocky (or other hard bottom) habitats (Andersson et al., 2009). A new baseline species assemblage will be formed via recolonisation, and the original soft-bottom population will be displaced (Desprez, 2000).
  1. However, it was noted in volume 2, chapter 9, that the longest monitoring programme conducted to date at the Lillgrund Offshore Wind Farm in the Öresund Strait in southern Sweden, showed no overall decrease in fish numbers although redistribution towards the foundations within the offshore wind farm area was noticed for some species (i.e. cod, eel and eelpout) (Andersson, 2011). More species were recorded after construction than before, which is consistent with the hypothesis that localised increases in biodiversity may occur following the introduction of hard substrates in a soft sediment environment. However, there is uncertainty as to whether:
  • artificial reefs facilitate recruitment in the local population; or
  • the effects are simply a result of concentrating biomass from surrounding areas (Inger et al., 2009).
  1. Overall, results from earlier studies reported in the scientific literature did not provide robust data (e.g. some were visual observations with no quantitative data) that could be generalised to the effects of the addition of hard infrastructure on fish abundance in offshore wind farm areas (Wilhelmsson et al., 2010). More recent papers are, however, beginning to assess population changes and observations of recolonisation in a more quantitative manner (Bouma and Lengkeek, 2012; Krone et al., 2013), with hard structures consistently increasing species richness in the long term, but changing species composition towards a shellfish-dominated hard structures community, thus having an impact of local ecological function (Coolen, et al., 2020).
  2. Post construction fisheries surveys conducted in line with the Food and Environmental Protection Act licence requirements for the Barrow and North Hoyle offshore wind farms, found no evidence of fish abundance across these sites being affected, either beneficially or adversely, by the presence of the offshore wind farms (Centre for Environment, Fisheries and Aquaculture (Cefas), 2009; BOWind, 2008). These suggested that any effects, if seen, are likely to be highly localised, site dependent and while of uncertain duration, the evidence suggests effects are not necessarily adverse, although uncertainty does exist surrounding this issue (volume 2, chapter 9). Monitoring of fish populations in the vicinity of an offshore wind farm off the coast of the Netherlands indicated that the offshore wind farms acted as a refuge for at least part of the cod population (Lindeboom et al., 2011; Winter et al., 2010). Similarly, horse mackerel, mackerel, herring, and sprat have been found to utilise the new hard structures for spawning, or predation on the newly developed community (Glarou et al., 2020).
  3. The greatest potential benefit from the introduction of hard structures is likely to exist for crustacean species, such as crab and lobster. Evidence has been found that foundations can provide new potential sources of food, new potential habitat range and refuge areas and even successful hatchery and nursery grounds for several crab species (Linley et al., 2007; Hooper et al., 2014; BioConsult, 2006).
  4. Other shellfish species have the potential for great expansion of their normal habitats due to increased hard structures in areas of sandy habitat, as found in the fish and shellfish ecology study area. Krone et al. (2013) found that over a three-year period, almost the entire vertical surface of area of the platform piles had been colonised by three key species blue mussel, the amphipod Jassa spp. and anthozoans (mainly Metridium senile).
  5. In most cases, it is expected that diadromous fish are unlikely to utilise the increase in hard structures within the fish and shellfish ecology study area for feeding or shelter opportunities as they are only likely to be in the vicinity when passing through during migration to and from rivers located on the east coast of Scotland. Therefore, the reef effect is not anticipated to effect diadromous fish species numbers or behaviour. There is potential for impacts upon diadromous fish species resulting from increased predation by marine mammal species within offshore wind farms. Tagging of harbour seal and grey seal Dutch and UK wind farms provided significant evidence that the seal species were utilising wind farm sites as foraging habitats (Russel et al., 2014), specifically targeting introduced structures such as foundations. However, a further study using similar methods concluded that there was no change in seal behaviour within the offshore wind farm (McConnell et al., 2012), so it is not certain exactly to what extent seals utilise offshore wind developments and effects may be site-specific. Effects on marine mammals as a result of the colonisation of hard structures is discussed further in section 20.9.10.
  6. Research has shown that Atlantic salmon smolts spend little time in the coastal waters, and instead are very active swimmers in coastal waters, making their way to feeding grounds in the north soon after maturation (Gardiner et al., 2018; Newton et al., 2017; Newton et al., 2019; Newton et al., 2021) (see volume 3, appendix 9.1 for further detail on Atlantic salmon migration). Due to the evidence that Atlantic salmon tend not to forage in the coastal waters of Scotland, they are therefore at low risk of impact from increased predation from seals and other predators in the fish and shellfish ecology study area.
  7. Sea trout may be at higher risk of increased predation from seals than Atlantic salmon due to their higher usage of coastal environments. Given that sea trout are typically more coastal than Atlantic salmon, greater abundance would be expected further inshore than compared with the offshore waters of the site boundary (approximately 80 km offshore). Sea trout are generalist, opportunistic feeders with their diet comprising mainly of fish, crustaceans, polychaetes and surface insects with proportion of each of these prey categories varying dependent on season (Rikardsen et al., 2006; Knutsen et al., 2001). Due to the potential for increase in juvenile crustacean species and other shellfish species, which are possible prey items from sea trout, it is possible that foraging sea trout may be attracted to the hard structures introduced by installation of the Array. This attraction could in turn lead to increased predation of seal species upon sea trout species. However, there is little evidence at present documenting an increased abundance of sea trout around foundations (increases in fish abundance tend to be hard bottom dwelling fish species), therefore the above effect of increased prey items attracting sea trout is yet to be recorded. As sea trout abundance is typically greater inshore, it is unlikely that sea trout will spend time foraging around the foundations, and therefore there is a low risk of impact from increased predation from marine predators in the fish and shellfish ecology study area (volume 2, chapter 9).
                        Underwater noise impacting fish and shellfish receptors
  1. As discussed in volume 2, chapter 9, underwater noise may arise due to UXO clearance and piling for the installation of wind turbines and OSPs. This may cause direct and indirect impacts fish and shellfish receptors. However, this is unlikely to result in significant mortality due to the designed mitigation measures adopted as part of the Array (e.g. implementation of piling soft start and ramp up measures which will allow individuals to flee the area before noise levels reach a level at which injury may occur).
  2. Behavioural effects are expected over larger ranges. Some fish species (e.g. prat and herring) have special structures mechanically linking the swim bladder to the ear. Herring in particular are known to be particularly sensitive to underwater noise and have specific habitat requirements for spawning which makes them particularly vulnerable to impacts associated with construction related increases in underwater noise. However, due to the small proportion of undetermined intensity spawning grounds for herring within range of underwater sound levels, the effects are unlikely to result in a measurable impact on fish and shellfish receptors.
                        Underwater noise from the operation of floating wind turbines and anchor mooring lines impacting fish and shellfish receptors
  1. As discussed in volume 2, chapter 9 and volume 3, appendix 10.1, underwater noise has the potential to arise from wind turbine operation and movement of anchor mooring lines. This impact is relevant to the operation and maintenance phase and has the potential to cause direct and indirect impacts on fish and shellfish receptors.
  2. Studies have demonstrated that underwater noise from operational fixed wind turbines is only high enough to possibly cause a behavioural reaction in fish and shellfish species within metres from a wind turbine. In addition, noise generated by operational fixed wind turbines is of a low frequency and low sound pressure level (Andersson et al., 2011). Therefore, noise levels from operational wind turbines at a level where there is a potential effect on fish and shellfish receptors are considered highly unlikely to occur (Sigray and Andersson, 2011). These observations from earlier fixed offshore wind farms (with smaller wind turbines) are supported by modelling of the noise emissions from larger fixed offshore wind turbines, which demonstrate that the risk of injury or behavioural effects on fish and shellfish populations is negligible (SSER, 2022a). Putland (2022) and Risch et al. (2023) found that the operational noise of floating offshore wind is comparable to that of fixed bottom wind turbines, generating low level noise which is unlikely to cause significant disturbance effects to fish. Further details of these studies can be found in volume 2, chapter 9.
  3. It is acknowledged in volume 3 appendix 10.1 that underwater noise may occur due to mooring line slackening and tensioning which has the potential to produce transient ‘pinging’ or ‘snapping’ noises during the operation and maintenance phase of the Array (Liu, 1973). With specific reference to operational turbines, the distances and exposures of fish reported by various studies (as set out in volume 3, appendix 10.1) conclude that while sound levels would likely be audible, these would not be at a level sufficient to cause injury or behavioural changes to fish. This is due to the slight increase in SPL compared to the ambient noise measured before the construction of the wind farms and even when the highest increases in SPL was assumed (i.e. 20 to 25 dB re 1 μ Pa), these are unlikely to result in a measurable impact on fish and shellfish receptors.
                        Increased SSCs and associated deposition
  1. As stated in volume 2, chapter 9, the prey fish species most likely to be affected by sediment deposition are sandeel and herring because they spawn on the seabed. Sandeel have low intensity spawning and nursery grounds within the fish and shellfish ecology study area however sandeel eggs are likely to be tolerant to some level of sediment deposition due to the nature of the re-suspension and deposition within their natural high energy environment (Ellis et al., 2012). Therefore, effects on sandeel spawning populations are predicted to be limited. Sandeel populations are also sensitive to sediment type within their habitat, preferring coarse to medium sands and showing reduced selection or avoidance of gravel and fine sediments (Holland et al., 2005). This is as identified by the Feature Activity Sensitivity Tool (FeAST) tool as the pressure ‘siltation changes’ (low) which has identified that sandeel have medium sensitivity to this impact (Wright et al., 2000). Therefore, any increase in the fine sediment fraction of their habitat may cause avoidance behaviour until such time that currents remove fine sediments from the seabed, although modelled sediment deposition levels are expected to be highly localised and at very low levels.
  2. Herring occur mostly in pelagic habitats, but utilise benthic environments for spawning, and are known to prefer gravelly and coarse sand environments for this purpose, with low intensity nursery grounds present within the site boundary and low intensity spawning grounds nearby (Coull et al., 1998). With respect to the effects of sediment deposition on herring spawning activity, it has been shown that herring eggs may be tolerant of very high levels of SSC (Messieh et al., 1981; Kiorbe et al., 1981). However, detrimental effects may be seen if smothering occurs and the deposited sediment is not removed by the currents (Birklund and Wijsmam, 2005).
  3. The potential of an increase in SSCs may arise as a result of mooring lines or cables making contact with and moving on the seabed, disturbing seabed materials and causing scouring and increased SSCs within the water column. Any increase in SSCs and associated deposition will include native material only, and although comprises predominantly mobile sand material, the low rates of sediment transport, will ensure it is redeposited close by after a short period of suspension, thus not impacting significantly on seabed morphology. Any significant changes to the seabed morphology will not recover immediately, due to the low rates of sediment transport, however the evidence of mobile sediments implies any impacts will be fully recoverable after some time (volume 2, chapter 7).
                        Effects to fish and shellfish receptors due to EMFs from subsea electrical cabling
  1. As discussed in volume 2, chapter 9, the presence and operation of inter-array and interconnector cables within the fish and shellfish ecology study area may result in emission of localised EMFs which may affect some fish species. It is common practice to block the direct electrical field using conductive sheathing, meaning that the only EMFs that are emitted into the marine environment are the magnetic field and the resultant induced electrical field. Fish (particularly elasmobranchs) and shellfish species are able to detect applied or modified magnetic fields. However, the rapid decay of the EMF with horizontal and vertical distance (Bochert and Zettler, 2006) (i.e. within metres) minimises the extent of potential impacts. A study investigating the effect of EMFs on sandeel larvae spatial distribution found that there was no effect on the larvae (Cresci et al., 2022), and a prior study concluded the same for herring (Cresci et al., 2020).

                        Conclusions

  1. This section summaries the assessments from the topic specific chapters to inform the ecosystem effects assessment of the Array on prey species, to determine whether there will be any increases or decreases in predation and prey distribution and availability as a result of the Array.
  2. The impacts resulting from the lifetime of the Array (construction, operation and maintenance and decommissioning) which are relevant to prey species include temporary habitat loss and disturbance; long-term habitat loss and disturbance; colonisation of hard structures; underwater noise impacting fish and shellfish receptors; underwater noise from the operation of floating wind turbines and anchor mooring lines impacting fish and shellfish receptors; increased SSCs and associated deposition; and effects to fish and shellfish receptors due to EMFs from subsea electrical cables.
  3. The colonisation of hard structures has the potential to lead to increases in fish species through potential reef effect and fish aggregation. It is uncertain to what degree this may occur, however, any beneficial effects are predicted to be highly localised and not significant.

20.9.10. Effects of the Array on Predator Species

  1. Section 20.9.9 examined the impacts as a result of the Array which could have either positive or negative effects on the distribution of key prey species. This section assesses the sensitivity of fish, seabird and marine mammal predator species to prey availability and draws on the conclusions of section 20.9.9 to determine if there are any potentially significant effects on predators as a consequence of changes in prey availability. The likelihood of increased predation of key prey species as a result of the Array is considered highly unlikely due to the mobile nature of both prey and predator species and therefore has not been assessed further.

                        Piscivorous fish

  1. The typical prey species of the key predators (piscivorous fish) are listed in section 20.9.5 which shows these fish species have broad diets comprising not only of small fish but also benthic species including invertebrates, molluscs and crustaceans. This suggests, the fish predator species are likely to be less sensitive to the availability of the key prey species of sandeel, herring, mackerel and sprat.
  2. As discussed in section 20.9.9, adverse effects on prey species as a result of the Array were assessed to have adverse effects on marine fish (including prey species), which would not result in a significant change to prey species populations. The colonisation of hard structures has the potential to lead to localised increases in fish species through potential reef effect and fish aggregation. However, the assessments of effects concluded any increases would be localised and did not conclude that the Array would lead to a significant increase in prey species.

                        Marine mammals

  1. As discussed in volume 2, chapter 10, marine mammals are likely to profit from locally increased food availability and/or shelter and therefore have the potential to be attracted to forage within an offshore wind farm. While species such as harbour porpoise, minke whale, white-beaked dolphin, harbour porpoise and grey seal have been frequently recorded around offshore oil and gas structures, little is known about the how their distribution is linked to the reef effect or sheltering effect (Todd et al., 2016; Delefosse et al., 2018; Lindeboom et al., 2011). Acoustic results from a Towed Passive Acoustic Monitoring Device (T- POD) measurement within a Dutch wind farm found that relatively more harbour porpoises were found in the wind farm area compared to the two reference areas (Lindeboom et al., 2011, Scheidat et al., 2011). This study concluded that the presence within the wind farm area was due to increased food availability as well as the exclusion of fisheries and reduced vessel traffic in the wind farm (shelter effect). Further evidence suggesting that wind farms are used for foraging includes a study by Russell et al. (2014) where the movements of tagged harbour seals commonly exhibited grid-like movement patterns within two active wind farms in the North Sea. However, other studies have detected no statistical differences in the presence of harbour porpoises inside and outside a Danish wind farm (Brandt et al., 2009). Brandt et al. (2009) suggested, however, that a small increase in detections during the night at hydrophones deployed in close proximity to single wind turbines may indicate increased foraging behaviour near the monopiles. Whilst there is some mounting evidence of potential benefits of man-made structures in marine environment (Coolen et al., 2017), the statistical significance of such benefits and details about trophic interactions in the vicinity of artificial structures and their influence on ecological connectivity remain largely unknown (Elliott and Birchenough, 2022; Inger et al., 2009; McLean et al., 2022; Rouse et al., 2020).
  2. In terms of the reef effect, the assessment of effects concluded any increases would be localised and would not lead to a significant increase in prey species. For example, sandeel, a popular prey species for harbour porpoise, require specific sediment habitat conditions and are therefore unlikely to be attracted to the hard structures of offshore wind farm infrastructure.
  3. Marine mammals exploit a range of different prey items and can forage widely, sometimes covering extensive distances. As the potential impacts of construction on prey resources will be localised and largely restricted to the site boundary, only a small area will be affected when compared to the available foraging habitat in the North Sea. The fish and shellfish communities found within the fish and shellfish ecology study area (see volume 2, chapter 9) are characteristic of fish and shellfish assemblages in the northern North Sea. It is therefore reasonably to assume that, due to the highly mobile nature of marine mammals, there will be similar prey resources available in the wider area surrounding the site boundary.
  4. Despite this, foraging over greater distances could result in an energetic cost with the associated increased travel with this effect being particularly pertinent for harbour porpoise. Harbour porpoise has a high metabolic rate and only a limited energy storage capacity, which limits their ability to buffer against diminished food. Despite this, if animals do have to travel further to alternative foraging grounds, the impacts are expected to be largely short term in nature and reversible (i.e. elevated underwater noise would occur during site investigation surveys, geophysical surveys, vessel activity, UXO clearance, piling and other noise producing activities) and are likely to return to the area after the noise activity has ceased. Whilst the impact of elevated underwater noise from the operation of floating wind turbines and anchor mooring lines is long-term it is of highly local spatial extent and therefore of minor adverse significance. Injury or disturbance is discussed further in paragraphs 50 to 57.
  5. In volume 2, chapter 10 it was identified that minke whale have the potential to be particularly vulnerable to potential effects on sandeel, particularly if there is potential for reduced abundance. Studies analysing the stomach contents of minke whale found that in the North Sea this species is their key food resource, followed by clupeids Clupeidae and to a lesser extent mackerel (Robinson and Tetley, 2005; Tetley et al., 2008), see volume 3, appendix 10.2 for more details. However, as presented in volume 2, chapter 10, modelling by Langton et al. (2021) shows that the marine mammal study area has extremely low probability of sandeel presence, with areas where predicted density is high closer to the coasts or towards the Firth of Forth.

                        Seabirds

  1. Prey availability is one of the most important controls of species abundance and distribution in the higher trophic levels, including birds (Lynam et al., 2017; Mitchell et al., 2020). Reduced availability or shifts in the distribution of prey species means seabirds are having to travel further distances to forage for food. Fayet et al. (2021) conducted a study comparing the foraging behaviour of puffin populations across the north-east Atlantic and found that puffins from declining populations had to cover greater distances for foraging and had less energy-dense diets. Low prey availability close to the colonies, potentially resulting from climate or commercial fisheries effects, is also amplified by increased intra-specific and inter-specific competition which forces birds to forage further from their colonies.
  2. The extent to which seabirds respond to changes in prey availability is dependent on species. Generalist species, such as gulls, feed on a range of prey types and are therefore more resilient to these changes whereas specialist species, such as kittiwake, predominantly prey on small fish and struggle to adapt to changes in prey availability as easily (Furness and Tasker, 2000).
  3. Changes to prey distribution within the water column resulting from changes to stratification or temperature, will affect surface feeding species (e.g. kittiwake and terns) differently to water column feeding species (e.g. auks). Typically, water column feeding species can adapt better to changes in prey availability as they are not restricted to prey available in the upper 1 m to 2 m of the sea surface, as is the case for surface feeding species. The primary feeding strategies for key seabird species that have the potential to be impacted by the Array are detailed in Table 20.18   Open ▸ .
  4. The presence of sandeel has been linked to the reproductive success and survival of kittiwakes (Frederiksen et al., 2004, 2008; Carroll et al., 2017). During April and May, adult kittiwakes predominantly consume older sandeel (1+ year group), transitioning to juvenile (0 year group) sandeel in June and July while rearing chicks (Lewis et al., 2001). This dietary pattern aligns with the annual cycle of sandeel as 1+ sandeel group are active in the water column during spring and 0 year group, having newly metamorphosed from larvae to juveniles, are available from June. Both year groups then bury themselves over winter, surviving on the lipids they have accumulated during the spring months (Wright and Bailey, 1996). Sandeel stock levels have seen significant reductions as a result of climate change and commercial fisheries (as detailed in section 20.9.8) which may contribute to kittiwake declines (Caroll et al., 2017).
  5. In the Firth of Forth region, a decline in the average length-at-age of both the 0 year group and 1+ year group sandeel brought to puffin chicks on the Isle of May indicated a considerable decline in prey quality between 1973 and 2015. This trend is associated with reductions in kittiwake populations. It is estimated that the energy content of sandeel decreased by around 70% and 40% for 0 and 1+ sandeel groups, respectively, potentially leading to a significant change in the diet or behaviour of seabirds that rely on sandeel species (Wanless et al., 2018). The diet of chick-rearing kittiwakes, puffins, razorbills and shags was predominantly sandeel between 1973 and 2015 in the North Sea. More recently, a shift to sprat and herring has been observed in guillemots, razorbills and kittiwakes (Walness et al., 2018). Sprat feed and spawn repeatedly throughout spring and summer in coastal and offshore waters are therefore more readily available, which could account for this shift. As plunge divers, gannet predominantly feed on pelagic fish such as mackerel and sandeel or fisheries discards (Le Bot et al., 2019).
  6. Overall, the construction and operation of wind turbines may lead to changes in the behaviour, availability or distribution of prey species for seabirds. However, the majority of seabird species have large foraging ranges and a variety of target species (with the exception of little terns) ( Table 20.18   Open ▸ ) meaning they are able to adapt to short temporal changes in prey availability due to construction activities. This impact is further discussed in volume 2, chapter 11.
  7. The majority of marine fish species are expected to avoid habitat loss effects due to their greater mobility and recoverability post-construction. As discussed in section 20.9.9, sandeel are particularly vulnerable to long-term habitat and disturbance. However, the effects are unlikely to result in a measurable impact on fish and shellfish receptors.
  8. During the construction phase, as per volume 2, chapter 9, the impact to all fish and shellfish species is considered to be of negligible. Construction works will be spatially and temporally restricted, covering only a small portion of the site at any given time. Construction impacts are restricted to the duration of the construction phase, and once construction has finished, the adverse impacts will cease and any change on prey species will likely be reversed.
  9. During the operation and maintenance phase, as per volume 2, chapter 9, the impact to all fish and shellfish species is considered to be of negligible to minor adverse significance. Temporary habitat loss will occur as a result of the use of jack-up usage for operation and maintenance activities (10,500 m2 per year over the 35-year lifecycle), and also due to disturbance caused by reburial of inter-array and interconnector cables (1,222,400 m2 and 236,000 m2 per year, respectively). The maximum design scenario is for up to 51,411,500 m2 of temporary habitat loss/disturbance during the operation and maintenance phase. This equates to 5.99% of the total site boundary and therefore this represents a relatively small proportion of the fish and shellfish ecology study area. It should also be noted that only a small proportion of the total habitat loss/disturbance is likely to be occurring at any one time over the 35-year operation phase of the Array. During the operation and maintenance phase, changes to prey availability are expected to be minimal although as requested by NatureScot, this effect has been considered for this phase (volume 2, chapter 11). With the exception of little tern, the sensitivity of the VORs is considered to range between low to medium ( Table 20.19   Open ▸ ).

 

Table 20.19:
Sensitivity of Receptors to Indirect Impacts from Construction/Decommissioning Noise

Table 20.19: Sensitivity of Receptors to Indirect Impacts from Construction/Decommissioning Noise

 

  1. It is challenging to separate the effects of different pressures, due to the complexity of how they interact and the combined impact they have on seabird populations, their environment and their prey at all scales. Although offshore wind farms can impact local seabird populations directly through displacement and collision, there may also be beneficial indirect impacts, such as the creation of artificial reefs and the resulting potential of an increase in prey availability (Coolen, 2017).
  2. Overall, gannet, herring gull and lesser black-backed gull are thought to be buffered from the impacts of climate change, mostly relating to their ability to access a wider variety of prey, but they may be sensitive to controls on fisheries discards (Johnston et al., 2021). Guillemot, kittiwake, puffin and razorbill abundances have been more closely linked to the success of their prey, which may make them more vulnerable to bottom-up climate change impacts (Burthe et al., 2014; Johnston et al., 2021). A reduction in prey quality and availability may also reduce the resilience of these species against storm events, which could lead to an increase in large-scale wrecks as climate change leads to an increase in extreme weather (Anker-Nilssen et al., 2017; Camphuysen et al., 1999; Heubeck et al., 2011; Morley et al., 2016). Cliff nesting species, such as kittiwake and razorbill, may also be sensitive to nest failure in high winds and storm surges (Newell et al., 2015).
  3. Climate change is considered to be the likely primary cause of decline in seabird populations in the future. It is believed that the absence of the Array would further delay the transition of the UK from reliance on fossil fuels and therefore further contribute towards climate change impacts and declining seabird populations.

                        Conclusions

  1. This section assessed whether there will be any changes to the key predator species as a result of the Array. This was achieved by assessing the sensitivity of the predator species to changes in prey availability and drawing on the conclusions of section 20.9.9 along with the findings of the relevant Array EIA Report chapters to determine if any changes to predator species are predicted. The following conclusions were made:

–           broad range of prey species making them less sensitive to the availability of the key forage prey species (sandeel, herring, sprat and mackerel);

  • marine mammals

–           harbour porpoise

  • may be more sensitive to disturbance due to the energetic cost associated with increased travelling, however, the impacts are expected to be short-term in nature and reversible;

–           minke whale

  • may be more sensitive to the any potential changes in the abundance or distribution of sandeel; and
  • seabirds

–           kittiwake are identified as being particularly sensitive to changes in prey availability of their favoured prey species, sandeel. Significant changes to prey species as a result of the Array are however not predicted due to the non-favourable habitats for sandeel within the fish and shellfish ecology study area.