5. Assessment of Potential Adverse Effects on Integrity

5.1. Introduction

  1. This section provides background information and explanation for the approach taken to assess the potential impacts of the Array on SPAs designated for marine ornithological features, and presents the Stage Two assessments for the site features for which LSE2 was identified (section 3.1). These features and sites are listed in Table 5.1   Open ▸ and shown in Figure 5.1   Open ▸ .

 

Table 5.1:
European Sites Designated for Marine Ornithological Features for Which an Appropriate Assessment is Required

Table 5.1: European Sites Designated for Marine Ornithological Features for Which an Appropriate Assessment is Required

Figure 5.1:
Location of European Sites Designated for Marine Ornithological Features for Which an Appropriate Assessment is Required

Figure 5.1: Location of European Sites Designated for Marine Ornithological Features for Which an Appropriate Assessment is Required

  1. LSE2s on the SPAs presented in Table 5.1   Open ▸ were identified for construction, operation and maintenance, and decommissioning phases of the Array. The potential impacts are outlined below in Table 5.2   Open ▸ .

 

Table 5.2:
Potential Impacts to Marine Ornithological Features of the European Sites Identified for Appropriate Assessment

Table 5.2: Potential Impacts to Marine Ornithological Features of the European Sites Identified for Appropriate Assessment

 

5.2. Potential Impacts and Method of Assessment

5.2.1. Introduction to the Applicant’s Approach

  1. As described in sections 1 and 2, the assessments within this RIAA have been carried out with regards to NatureScot’s Guidance Notes (NatureScot, 2023a-k) along with advice received through the consultation process. However, the Habitats Regulations requires HRA to be based on the best available scientific information and, in some instances, the Applicant considers the advice and guidance provided to be overly precautionary based on a review of the available scientific literature. Therefore, for some assessments, this RIAA presents a separate NatureScot Approach and Applicant’s Approach. The NatureScot approach follows NatureScot’s guidance and advice received from NatureScot through the consultation process. The Applicant’s Approach follows the Applicant’s interpretation of the best available scientific information to present an approach that the Applicant feels better reflects the best available evidence, whilst still being sufficiently precautionary to account for the uncertainty in the scientific information available.

5.2.2. Disturbance and displacement

  1. This pressure relates to the physical disturbance of birds and the displacement that could occur if birds avoid the area occupied by the Array during operation and/or the vessels and activities involved during construction, operation and maintenance, and/or decommissioning.
  2. It should be noted that for breeding seabirds, it can be difficult to distinguish between displacement and barrier effects for breeding seabirds (JNCC et al., 2022). JNCC et al. (2022) defines barrier effects as “a physical factor that limits the migration, or free movement of individuals or populations, thus requiring them to divert from their intended path in order to reach their original destination”. For any individual seabird, whether the Array creates a displacement effect, a barrier effect, both, or neither would depend on where that individual would have foraged in the absence of the Array, where it chooses to forage instead, and the route it takes to get there.
  3. The current guidance from NatureScot (2023h) therefore recommends treating both displacement and barrier effects together as “distributional responses” and, for breeding seabirds, recommends assessing these distributional responses together. Therefore, for breeding seabirds, the approach to “disturbance and displacement” assessment covers both disturbance and barrier effects, whilst the assessment of “barrier to movement” (see below) only considers the barrier effect to migratory birds.
  4. Disturbance and displacement has been screened in for a number of sites and species, including within the Array during construction and decommissioning, from activities such as vessel movements, seabed preparation and cable laying. Disturbance and displacement has also been screened in for a number of sites and species during operation and maintenance, as a result of a direct response to operational wind turbines, as well as maintenance activities, such as vessel movements.
  5. Disturbance and displacement as a result of vessel movements has also been screened in for a number of qualifying species at Outer Firth of Forth and St Andrews Bay Complex SPA, as requested by NatureScot and MD-LOT (refer to Table 2.1   Open ▸ ),
  6. Disturbance and displacement can be temporary and short term (for example relating to construction activities or vessel movements associated with maintenance) or for the duration of the Array (for example the physical presence of the wind turbines).
  7. A distributional response may impact bird populations by affecting site usage which may be for foraging, resting or moulting purposes. As a result of a disturbance and displacement, an individual bird may experience a decrease in fitness, due to the effect of re-locating to alternative foraging grounds and or changes to energy budgets due to the increased energy expenditure when avoiding a wind farm. These impacts, in turn, may have indirect effects on birds in areas that may be some distance from the wind farm, including reduced energy acquisition as a result of increased competition at other foraging sites which can result in further reductions in fitness affecting reproductive success.
  8. Vulnerability to these pressures is species-specific; pressure vulnerability has been determined using the evidence provided in the relevant literature including Wade et al. (2016) and Bradbury et al. (2014).
  9. The assessment has drawn on the conclusions of the relevant Technical Reports in the Array EIA Report, specifically the following:
  • volume 3, appendix 11.1: Offshore Ornithology Baseline Characterisation Technical Report; and
  • volume 3, appendix 11.3: Offshore Ornithology Displacement Technical Report.
  1. The impact of disturbance and displacement has been assessed qualitatively in the construction and decommissioning phases. Construction activity is expected to be intermittent and spatially limited at any given time, and therefore a qualitative assessment is considered to be proportional to the magnitude of the anticipated impacts.
  2. The impact of disturbance and displacement during the operation and maintenance phase has been assessed quantitatively. This quantitative assessment relies on the “matrix approach”, as described in SNCBs (2022) and volume 3, appendix 11.3 of the Array EIA Report. The SeabORD tool (Searle et al., 2018) was not available to use for this project and has not been run, in agreement with NatureScot ( Table 2.1   Open ▸ ).
  3. Note that, as detailed in volume 3, appendix 11.3 of the Array EIA Report, abundance estimates derived from MRSea modelling were used where available, and supplemented with design-based abundance estimates for months when MRSea estimates were unavailable.
  4. It should be noted that a recent study (Dunn et al., 2024) indicates there is significant temporal and spatial variation in the diving behaviour of auks, with generally a much smaller proportion of time spent diving during the non-breeding season. The correction factors applied (based on studies carried out during the breeding season) are therefore likely to lead to overestimates of the total abundance of auks, especially in the non-breeding season.
  5. Seabirds may not be displaced solely from the Array itself, but also a Zone of Influence (ZoI) around the array. This ZoI is defined as the Array plus a 2km buffer in all directions, in line with the recommended approach (NatureScot 2023h; SNCBs 2022). Therefore, all species, seasonal mean peak abundances used for displacement analysis are based on the abundance within the Array plus 2 km buffer.
  6. The effect of distributional responses on puffin during the non-breeding season are not included. Puffin are known to disperse rapidly and widely post-breeding and are therefore considered unlikely to be affected by the presence of the Array outside the breeding season.
  7. The consequences of a distributional response can include displacement and potentially mortality, with percentage values applied for these. These are presented in Table 5.3   Open ▸ in terms of the values defined in NatureScot (2023h) alongside values that represent the Applicant’s approach. Note that the non-breeding season rate presented in Table 5.3   Open ▸ applies to all seasons other than the breeding season, such as post-breeding and pre-breeding seasons, where relevant. Both sets of values are provided to enable a comparison to be made.

 

Table 5.3:
Displacement and Mortality Rates Included for Consideration in Assessment

Table 5.3: Displacement and Mortality Rates Included for Consideration in Assessment

 

  1. The displacement report (volume 3, appendix 11.3 of the Array EIA Report) provides information on total impacts for the Array, for all birds regardless of their age or origin. For a HRA, it is necessary to ‘apportion’ the total impact to estimate the impact on breeding adults from specific SPAs. Full details of the approach to apportionment are presented in appendix 3A. The approach taken follows NatureScot’s guidance (NatureScot 2023c-d). During the breeding season, a theoretical approach (developed by NatureScot (NatureScot, 2018)) has been applied to determine the proportion of birds from SPA sites which use proposed development areas in the breeding season. In the non-breeding period, the “BDMPS approach” to apportioning that utilises the information presented in Furness (2015), is adopted for most species. For guillemot, NatureScot (2023d) recommend an approach based on evidence that they largely remain in the broad vicinity of their breeding colonies, and this approach has been adopted. In addition, apportionment of guillemot to Flamborough and Filey Coast SPA has been carried out using the BDMPS approach, as requested by Natural England and the Scottish Ministers (see Table 2.1   Open ▸ ).
  2. It is noted that in the breeding season an alternative apportioning tool can be applied for kittiwake, guillemot, razorbill and shag, referred to as the Butler Tool (Butler et al. 2020). However, the Butler Tool requires an update (which is understood to be pending at the time of writing this RIAA) before it can be applied with the recently updated colony count data (Seabirds Count; Burnell et al., 2023) which itself is an update on the Seabird 2000 data. Utilizing outdated population information such as Seabird 2000 data (which is based on data from 1998 to 2002) not only inaccurately represents todays populations (as data is at least 22 years old) but due to the counts age, there is a lack of compatibility with the baseline characterisation surveys undertaken for the Array. Therefore, the incompatibility between the two datasets suggests that using them simultaneously would not be appropriate. The apportioning undertaken here therefore applies the theoretical approach excluding the Butler Tool but inclusive of the updated colony count data and therefore provides the most up to date apportioning results for the Array.
  3. Following apportioning, there is the potential requirement to undertake PVA. This requirement follows where the potential for impact could exceed a 0.02 percentage point increase to the baseline mortality (following NatureScot 2023k). That guidance states that the use of the Natural England PVA tool (Searle et al., 2019) is required over three time periods (25 years, anticipated operational period of 35 years and 50 years) (NatureScot, 2023k). Given the anticipated operational period of 35 years, the conclusions after 35 years are used as the basis for this assessment, but the 25 year and 50 year results are presented in full in appendix 3B.
  4. If the increase in baseline mortality is below the threshold of 0.02 percentage points, then it can be concluded that there is no possibility for the additional mortality caused by disturbance and displacement to have any discernible impact on the relevant population. Seabird survival and productivity is influenced by environmental stochasticity, leading to natural variation in survival and productivity rates. This natural variation far exceeds a 0.02 percentage point increase in mortality (Horswill & Robinson, 2015) and therefore it can be concluded that the additional mortality would not have an impact on the population size that is detectable within the operational lifespan of the Array. 

                        Auks

  1. A 50% displacement and 1% mortality has been applied for auks in the Applicant’s approach. The Applicant’s approach is in line with that advocated by the developer in many previous offshore wind farm applications as the approach supported by the best available science (e.g. the recent Green Volt Offshore Wind Farm project). The values are considered precautionary, especially in light of the recent publication of the Beatrice Year Two monitoring (Macarthur Green, 2023; Trinder et al., 2024). Since the UK SNCBs published guidance on defining displacement and mortality rates for auks in 2017 (SNCBs, 2022), a number of studies have been undertaken.
  2. For displacement rates, NatureScot recommends that a 60% displacement rate is applied to auks in both the breeding and non-breeding season (NatureScot, 2023h). Real-world displacement rates are variable (APEM, 2022), for example, 44% to 63% was recorded at sites in the German North Sea (Peschko et al., 2020). Following review of data collected from 21 developments, APEM (2022) suggest that a 50% displacement rate is more appropriate for auks. Although greater than 50% displacement was observed at five developments in the APEM (2022) study, all had very low abundance of auks within the study area. Where auk abundance was greater, <50% displacement was recorded. Therefore, considering the abundance of auks within the Array plus 2 km buffer, a 50% displacement rate is considered appropriate (and given the findings at Beatrice noted above) precautionary for the Array.
  3. For mortality rates of displaced birds, work by van Kooten et al. (2019) and APEM (2022) suggest that the recommended mortality rates are overly precautionary. Van Kooten et al. (2019) used individual based models and prey distributions to assess the effects of displacement on auks. The results indicate that breeding season mortality rates in displaced birds are likely to be in the region of 1.0% (van Kooten et al., 2019). APEM (2022) reviewed available literature and concluded that the available evidence is “incompatible” with a 10% mortality rate and the most likely mortality rate is considered to be “negligible or undetectable”. APEM (2022) therefore suggest that a mortality rate of 1% would be more consistent with the available evidence, whilst still being precautionary. Outside the breeding season, auks are typically more widely dispersed and are not tied to a specific coastal site or colony (Camphuysen, 2002; Christie, 2021). With wider dispersal, pressure on individuals to forage in specific areas is lower, and thus displacement is likely to result in lesser effects. This is particularly relevant in the post breeding period, when peaks in auk density were observed at the Array footprint, and when parents with chicks are moving rapidly offshore. A 1% mortality rate for guillemot and razorbill is also in line with advice from the Scottish Ministers to other projects (e.g. Marine Scotland, 2017a,b). Therefore, a 1% mortality rate is applied for the assessment.

                        Gannet

  1. A 70% displacement and 1% mortality has been applied for gannets in the Applicant’s approach, a change in mortality rate only compared to NatureScot (2023h). Masden et al. (2010) assessed the energetic costs of displacement in seabirds. Results suggest that increasing gannet flight distance by 2 km increases energetic cost by 1.25%. A 10 km increase may result in a 4.50% increase in energy expenditure. However, this is based on a foraging range of 160 km, where 10 km represents a 6.25% increase in distance flown. Scaling this to the mean maximum plus 1 SD foraging range of 509 km (Woodward et al., 2019), an additional flight distance of 10 km represents a scaled 1.02% increase in expenditure. This minimal increase in energy expenditure is unlikely to result in notable mortalities. Therefore, also considering the small spatial extent of The Array, the lower end of the recommended mortality rate (1%) is considered appropriate. It has also previously been advised by NatureScot (and Marine Scotland Science) that the assessment of displacement impacts on gannet is not required based on work undertaken by Searle et al. (2014) that although showing gannet were displaced by offshore wind farms this did not lead to population-level effects.

                        Kittiwake

  1. A 30% displacement and 1% mortality has been applied for kittiwake in the Applicant’s approach, a change in mortality rate only compared to NatureScot (2023h). Prior to the current ScotWind Licensing Round, Scottish Minister advice on EIA ornithological assessments for kittiwake displacement (e.g. Marine Scotland, 2017a) was for a displacement rate of 30%, a mortality rate of 2% in the breeding season and a qualitative assessment only in the non-breeding season (in contrast to the advice in the same document from NatureScot (at that time Scottish Natural Heritage (SNH)), which for kittiwake displacement was ‘that there was no need to include kittiwake, the data available from post construction monitoring indicates no significant avoidance behaviour by this species’). In the joint SNCBs (2022) updated and interim advice note on displacement, kittiwake is not included in the ‘more sensitive’ category, scoring too low. In recent consented offshore wind farm projects in England, kittiwake are not typically included within an assessment of displacement as a result of the low sensitivity of the species to the pressure (e.g. for Hornsea Four, kittiwake at Flamborough and Filey Coast SPA was assessed for collision only and not displacement (DESNZ, 2023)).
  2. The low sensitivity of kittiwake to displacement is supported by a number of post-construction studies of seabirds at offshore wind farms, which have concluded that kittiwake was one of the species hardly affected by displacement (Dierschke et al., 2016). Most recently, the Beatrice Year Two monitoring report found there was an overall increase in kittiwake abundance between 2015 and 2021, although this was not significant, with some areas of increase and some of decrease (MacArthur Green, 2023). In relation to wind turbine locations, kittiwake densities were variable in both survey years and overall slightly higher in 2021, but there was no indication of any significant responses, either avoidance or attraction in either year. For kittiwake, the report concluded ‘neither of the pre vs post comparisons indicated any decreases across the wind farm’. A 30% displacement is therefore considered highly precautionary.
  3. Ruffino et al. (2023) reviewed information available on kittiwake foraging behaviour, and from that study it is apparent that kittiwake forage widely across the region, with the Array itself representing a fraction of the total available foraging habitat. Therefore, any kittiwakes that are displaced from the Array will have access to an extensive alternative foraging area. The potential for a displacement mortality to result in the non-breeding season, when kittiwake are not associated with a breeding colony, is even less. A mortality rate of 1% is therefore considered precautionary.

5.2.3. Changes to prey availability

  1. Changes to prey availability may occur as a result of construction and decommissioning activities, especially those that disturb the seabed. During the operational phase, changes to prey availability are expected to be minimal and therefore this impact has been screened out during the operational phase. The ZoI has been defined as 100km, as considered in the Array EIA Report volume 2, chapter 9 for potential noise impacts on fish.
  2. Changes to prey availability in the construction and decommissioning phases are assessed using a qualitative approach, considering the expected impacts on potential prey species (i.e. fish and benthic invertebrates) and the potential for those to lead to indirect impacts on seabirds that may feed on them.

5.2.4. Artificial light

  1. This pressure relates to the potential for light pollution to affect the behaviour of birds. Lighting will be used on the Array infrastructure and on vessels throughout all phases. Several types of lighting may be used, including navigational lights, safety lighting, and for illumination if works are conducted between dusk and dawn. The ZoI for artificial light is defined as the zone in which lights may be visible and sufficiently bright to be stimulate a biological response This zone is therefore not a static distance but will vary depending on weather conditions and other factors, along with the species being considered.
  2. The response of birds to nocturnal lighting is complex and the disturbance effects of lighting may derive from changes in disorientation and attraction (phototaxis) or repulsion from the altered light environment, which in turn may affect foraging, migration and communication (Longcore and Rich, 2004). Birds may collide with each other or a structure, or become exhausted as a result. Conversely, for unlit structures at night or during foggy conditions, it is possible that the risk of collision may be greater because moving rotors may not be detectable (Trapp, 1998). Migrating birds are likely to be particularly susceptible to any adverse effects of lighting. Around two thirds of all bird species migrate during darkness, when collision risk is expected to be higher than during daylight (Hüppop et al., 2006). The evidence for this impact mixed. International Council for the Exploration of the Sea (ICES) (2011) state that birds are somewhat less inclined to avoid wind turbines at night, but in contrast, extended periods of infra-red monitoring at night using a Thermal Animal Detection System (TADS) at Nysted provided unexpected evidence that no movements of birds were detected below 120 m during the hours of darkness, even during periods of heavy seabird migration (Desholm, 2005). Welcker et al. (2017) found nocturnal migrants do not have a higher risk of collision with wind energy facilities than diurnally active species, but rather appear to circumvent collision more effectively.
  3. Lights on wind turbines would need to meet the minimum regulatory requirements as set out in the International Association of Marine Aids to Navigation and Lighthouse (IALA) Recommendation O117 on ‘The Marking of Offshore Wind Farms’ for navigation lighting and by the Civil Aviation Authority in the Air Navigation Orders (Civil Aviation Publication (CAP) 393 and guidance in CAP 764). Whilst subject to these minimum requirements, the Array will not have any additional or unnecessary lighting, which will minimise the risks of migrating birds becoming attracted to, or disorientated by, wind turbines at night or in poor weather.
  4. The recently published review by Deakin et al. (2022) highlighted that likely seabird species susceptible to disorientation and attraction are Manx shearwater, Leach’s petrel and storm petrel. As discussed within volume 3, appendix 11.11 of the Array EIA Report, Leach’s petrel and storm petrel were not recorded during the aerial surveys. Only Manx shearwater was recorded therefore it has been screened in and assessed for lighting impacts. This species is active nocturnally, and there is evidence to suggest they are sensitive to light attraction which could render them especially vulnerable to adverse impacts from offshore wind farms, for example, if attracted to the rotor-swept area by lights on the wind turbines that are required for navigation purposes. The review however identifies critical knowledge gaps relating to light attraction and disorientation. Specific aspects include: the range over which light attraction of nocturnal species may occur (and therefore the size of the light catch basin for wind farms and related activities or infrastructure); the extent to which light attraction is exacerbated by particular meteorological conditions (e.g. fog, rain); the influence of wavelength and pattern of illumination (flashing/steady); the extent to which light attraction differentially affects adults and juveniles, and for how long after fledging juveniles may remain particularly susceptible to light attraction.
  5. Given the current uncertainties surrounding light impacts on Manx shearwater, this species and impact has been screened in for further assessment in the RIAA on a precautionary basis. This is assessed using a qualitative approach.

5.2.5. Collision risk

  1. This pressure relates to the potential for mortality arising from birds colliding with turbine structures, which will only occur within the Array once operational. Therefore, the ZoI defined for collision risk is the Array only.
  2. Operational wind turbines and associated infrastructure present a collision risk for seabirds flying within the Array. This includes birds commuting between breeding and foraging sites, migrating birds, and those foraging for food within the Array. Direct collision with infrastructure may result in injury or death, however, it is assumed that all collisions with operational wind turbines result in mortality.
  3. For regularly occurring seabirds, CRM was undertaken to produce mathematical based quantitative estimates of the number of collisions per species per season for each year of operation. The input parameters are presented in full in volume 3, appendix 11.2 of the Array EIA Report, with the analysis performed using the StochLab R package (v0.1.1) produced by Caneco et al. (2022), with stochastic and deterministic results presented, as per NatureScot advice on the Array EIA Scoping Report and requested by MD-LOT in the Ossian Array Scoping Opinion (MD-LOT, 2023).
  4. Collision estimates are based on seabird flight heights, with generic Flight Height Distribution (FHD) data (Johnston et al., 2014) used to determine the proportion of flights at Collision Risk Height (CRH) per species. Density estimates are also incorporated into the model, used to determine flux, or the rate at which each species is likely to fly through the wind farm.
  5. Flight height and density information, along with the wind turbine specifications, number of wind turbines, and other seabird parameters (e.g. size, flight type and nocturnal activity), are used to estimate the number of collisions. Initially, the model assumes that birds within the wind farm do not avoid individual wind turbines, swept areas, or blades, nor do they avoid the whole wind farm (macro-avoidance). Avoidance rates are then applied to adjust collision estimates. It is noted that advice in the Ossian Array Scoping Opinion (MD-LOT, 2023) referred to the SNCB (2014) rates (as provided in JNCC et al., 2014); revised avoidance rates are now available (Ozsanlav-Harris et al., 2023) which are now recommended by NatureScot (2023g).
  6. For HRA purposes, as for the displacement assessment (section 5.4.1), it is then necessary to ‘apportion’ the impact to multiple SPAs. For the Array, the apportioning values applied are presented in appendix 3A. During the breeding season, a theoretical approach (developed by NatureScot (NatureScot, 2018)) has been applied to determine the proportion of birds from SPA sites which use proposed development areas in the breeding season. In the non-breeding period, the standard approach to apportioning that utilises the information presented in Furness (2015), is adopted. As outlined in the displacement section above (section 5.4.1), an alternative apportioning tool could be applied for certain species (Butler et al. 2020), however due to the reasons provided the tool was not used for collision risk apportionment with the NatureScot method again used.
  7. Following apportioning, there is the potential requirement to undertake PVA. This requirement follows where the potential for impact could exceed a 0.02 percentage point increase to the baseline mortality (following NatureScot 2023k). That guidance states that the use of the Natural England PVA tool (Searle et al., 2019) is required over three time periods (25 years, 35 years (the lease period) and 50 years) (NatureScot (2023k). Given that the lease period is 35 years, the conclusions after 35 years are used as the basis for this assessment, but the 25 year and 50 year results are presented in full in appendix 3B.
  8. If the increase in baseline mortality is below the threshold of 0.02 percentage points, then it can be concluded that there is no possibility for the additional mortality caused by collision to have any discernible impact on the relevant population. Seabird survival and productivity is influenced by environmental stochasticity, leading to natural variation in survival and productivity rates. This natural variation far exceeds a 0.02 percentage point increase in mortality (Horswill and Robinson, 2015) and therefore it can be concluded that the additional mortality would not have an impact on the population size that is detectable within the operational lifespan of the Array.  
  9. Note that the potential for impact made here then differs from the Array EIA Report, for which the impact is determined at population level. At population level, the significance of impact resulting from collision risk was determined to be negligible for all species.
  10. It is recognised that the approach to assessing collision risk for regularly occurring seabirds may not adequately capture the risk to migratory birds. Therefore, a different approach is used for migratory birds that aims to overcome that limitation. For migratory birds, the assessment has been carried out qualitatively by reviewing available information, most significantly Woodward et al. (2023). This has been supplemented by a quantitative estimate of collision risk using the SOSSMAT (Wright et al., 2012). It is noted that a revised mCRM tool is currently being developed; however, at the time of writing this mCRM tool was still undergoing testing and not approved for use in assessment (as agreed with NatureScot, refer to Table 2.1   Open ▸ ). Therefore, the approach used for migratory birds is considered to represent the best currently available scientific approach.

5.2.6. Barrier to movement

  1. As discussed in section 5.2.1, JNCC et al. (2022) defines barrier effects as “a physical factor that limits the migration, or free movement of individuals or populations, thus requiring them to divert from their intended path in order to reach their original destination. This effect is expected to increase the energy expenditure of birds if they have to fly around the area in question in order to reach their goal”.
  2. Once the Array is operational, the presence of wind turbines could create a barrier to the movements of flying birds. This could lead to permanent changes in the flight routes of birds, which in turn would lead to an increase in energy demands, and could result in reduced breeding success and/or reduced survival rates. The ZoI for barrier to movement is defined as the Array only, as there is no impact on birds which would not fly through the Array anyway.
  3. Barriers to movement could affect birds that would pass through the Array on their annual migrations, and also birds that would pass through the Array during their daily movements between their roosting/breeding area and foraging sites. The latter of these scenarios may impose an additional energetic cost to movements at a key period in the annual cycle when seabirds are making daily commutes between foraging grounds at sea and breeding sites. Additional energetic costs could have long term implications for individuals, impacting bird fitness (breeding productivity and survival) and for populations. Barrier effects are considered to be less impactful when affecting migratory flights as avoidance of a single wind farm may be trivial relative to the total length and cost of the journey (Masden et al., 2010; 2012).
  4. As discussed in section 5.2.1, for breeding seabirds, NatureScot (2023h) consider barrier effects alongside displacement as “distributional responses”. This is because it can be difficult to distinguish barrier effects from the effects of displacement, for breeding seabirds foraging in the region. NatureScot (2023h) advise that distributional responses are assessed using the displacement matrix approach, and therefore for breeding seabirds, no separate assessment of barrier to movement is carried out, with impacts considered to be included in the assessments carried out under Disturbance and Displacement (section 5.4.1).

5.2.7. Entanglement

  1. This pressure relates to the potential for diving seabirds to become entangled as a consequence of the Array. The pressure is screened in for the Array during the operation and maintenance phase only. The ZoI for entanglement is defined as the Array only.
  2. There is a potential risk that diving seabirds could become entangled in mooring lines associated with wind turbine infrastructure (primary entanglement) or in marine debris that itself becomes entangled in mooring lines (secondary entanglement). Primary entanglement is considered unlikely due to mooring lines consisting of thick components meaning small animals, such as birds, cannot physically become entangled (Benjamins et al., 2014). Natural Resources Wales (NRW) have also previously stated that interactions between seabirds and the cables and mooring lines associated with floating offshore wind farms are of negligible importance (Aquaterra and MarineSpace, 2022). There is a greater risk of secondary entanglement with marine debris (such as netting or free-floating fishing line).
  3. There is currently no clear guidance on how to assess the risk of seabird entanglement or how to monitor for an occurrence with respect to floating offshore wind. Due to the physical characteristics of the cables and mooring lines, in the context of the size of diving birds and the lack of evidence for any such entanglement elsewhere, it is considered extremely unlikely that direct entanglement of seabirds will occur with respect to the Array.
  4. Therefore, entanglement, with reference to seabirds, refers solely to secondary entanglement. Depending on the number of new mooring lines and the length of dynamic cable present in the water column, the risks of derelict fishing gear being caught within marine renewable energy structures can increase. Derelict fishing gear is a well-known cause of mortality in marine life, including in seabirds (e.g. Hyrenbach et al., 2020; Berón and Seco Pon, 2021); however, the degree of impact is dependent on the size and location of the gear. As the location of lost gear and the likelihood of it entering the Array at any point in time is difficult to determine, a worst-case scenario for this impact is difficult to establish. Mooring lines and dynamic inter-array cables in the water column will undergo regular inspections during the operation and maintenance phase with inspection frequency more frequent initially for the first two years and then decreasing to an annual schedule. The removal of marine debris from mooring lines and inter-array cables will be undertaken as necessary following monitoring and further relevant action taken if required, based on findings from the inspections. The removal of debris from mooring lines and cables further reduces the likelihood of secondary entanglement.
  5. The Array EIA Report concluded the magnitude of secondary entanglement for seabirds to be negligible, with a sensitivity of low to medium (medium related to diving seabirds, such as auks, which spend the greatest amount of time underwater), with an overall significance of negligible to minor adverse significance.
  6. For this RIAA, the Stage One Screening Report (Ossian OWFL, 2023) identified a potential LSE2 from entanglement to four diving seabirds: guillemot, razorbill, puffin and gannet, based on vulnerability and connectivity to the Array. This list has been refined for this RIAA (see section 3.1 and Table 3.1   Open ▸ ) and a potential LSE2 has been identified only for razorbill, puffin and gannet (including where those species are named components of a seabird assemblage). The impact on these species is assessed using a qualitative approach.