11.10. Measures Adopted as Part of the Array

62. As part of the Array design process, a number of designed in measures have been proposed to reduce the potential for impacts on offshore ornithology (refer to Table 11.18   Open ▸ ). They are considered inherently part of the design of the Array and, as there is a commitment to implementing these measures, these have been considered in the assessment presented in section 11.11 (i.e. the determination of magnitude and therefore significance assumes implementation of these measures). These designed in measures are considered standard industry practice for this type of development.

Table 11.18: Designed In Measures Adopted as Part of the Array

11.11. Assessment of Significance

63. The Maximum Design Scenarios (MDSs) identified in Table 11.11   Open ▸ are those expected to have the potential to result in the greatest effect on an identified VOR. These scenarios have been selected from the details provided in volume 1, chapter 3 of the Array EIA Report. Effects of greater adverse significance are not predicted to arise should any other development scenario, based on details within the Project Description (volume 1, chapter 3) (e.g. different infrastructure layout) be taken forward in the final design scheme.
64. Table 11.11   Open ▸ summarises the potential impacts arising from the construction, operation and maintenance and decommissioning phases of the Array, as well as the maximum design scenario against which each impact has been assessed. An assessment of the significance of the effects of the Array on the offshore ornithology VORs caused by each identified impact is given in sections 11.11 to 11.15.

Temporary habitat loss and disturbance

65. There is potential for temporary, direct benthic habitat loss as a result of activities during the construction and decommissioning phases (e.g. seabed preparation, UXO detonation, drilling, and inter-array and interconnector cables installation and removal). These activities have the potential to affect the foraging efficiency of diving birds.
66. In addition to this direct habitat loss, temporary disturbance as the result of activities during the construction and decommissioning phases of an offshore wind farm has the potential to displace seabirds from an area of sea in which the activity is occurring. In relation to offshore wind farm development, displacement is defined as a reduction in the number of seabirds occurring within or immediately adjacent to an offshore wind farm (Furness et al., 2013).
67. Displacement can be considered as indirect habitat loss, as it results in birds unable to utilise the habitat in the area from which they have been displaced. Therefore, the impacts from both direct habitat loss and disturbance have been considered together.
68. The loss of habitat means that displaced birds may move to areas already occupied by other birds and thus may face higher intra- or inter-specific competition due to a higher density of individuals competing for the same resources. Alternatively, displaced birds may be forced to move into areas of lower quality (e.g. areas of lower prey availability) or travel longer distances to reach habitat of a suitable quality. This could therefore affect their demographic fitness (i.e. survival rates and breeding productivity), as well as potentially impacting on other birds in areas that displaced birds move to (for example, by increasing competition for resources).
69. The MDS ( Table 11.11   Open ▸ ) gives the scenario that would lead to the greatest amount of temporary habitat loss and disturbance during the construction and decommissioning phases. The amount of direct habitat loss is small, with a maximum of 5.82% of the Array expected to be impacted. In addition, no significant adverse effects are expected on fish, shellfish or benthic invertebrate populations as a result of construction or decommissioning activities (see volume 2, chapters 8 and 9). Therefore, it is expected that disturbance and subsequent displacement would be the main impact pathway.
70. The displacement assessment for construction is based on a qualitative approach, considering the magnitude of impact and the sensitivity of the receptor. The species considered for temporary habitat and temporary disturbance during construction and decommissioning are kittiwake, guillemot, razorbill, puffin, fulmar and gannet. All other species were excluded on the basis there is no potential for a significant effect as a result of temporary habitat loss and disturbance (volume 3, appendix 11.3).
71. Few studies have directly considered displacement rates during the construction phase of an offshore wind farm. Most studies have compared pre-construction to post-construction. It is expected that the amount of displacement during the construction phase of the Array would be less than that during the operational phase due to there being a smaller footprint whilst the Array is being constructed.

                        Construction phase

                        Magnitude of impact

72. Disturbance and temporary loss of habitat (including habitat becoming temporarily unsuitable due to disturbance) will occur intermittently throughout the construction period. The construction period is expected to take up to eight years, with activities and locations varying within this time.
73. The impact is predicted to be of local spatial extent, intermittent and medium-term duration (although only a small proportion of the total area will be affected at any one time, with individual elements of construction having much shorter durations) and will affect any birds in the vicinity of these activities directly. The construction disturbance and temporary loss of habitat impacts will also be of high reversibility. The magnitude is therefore, considered to be negligible For all species being considered for disturbance and temporary loss of habitat impacts (kittiwake, guillemot, razorbill, puffin, fulmar and gannet).

Kittiwake

                        Sensitivity of receptor

74. In terms of behavioural response to offshore vessel traffic and helicopters, kittiwake are considered have a low vulnerability (Wade et al., 2016).
75. Kittiwake is a qualifying interest for several SPAs likely to be connected to the Array (within the mean-max + SD foraging range), with several non-SPA colonies also within range and so the species is considered to be of international value. Refer to Table 6.2 of volume 3, appendix 11.1 for details of SPAs with connectivity to the Array with regards to kittiwake.
76. Kittiwake lay two eggs and breed from the age of three onwards, typically living on average for 12 years (Burnell et al., 2023). Kittiwake have undergone decreases of approximately 57% in Scotland since the early 2000s. Surveys managed by the RSPB in 2023 have recorded indicative increases of 8% across a number of sites in Britain in 2023 when compared against a pre-HPAI baseline (Tremlett et al., 2024). Overall, kittiwake is deemed to have low recoverability.
77. Kittiwake is deemed to be of low vulnerability, low recoverability and international value. The sensitivity of the receptor is therefore, considered to be high.

                        Significance of the effect

78. Overall, the magnitude of the impact is deemed to be negligible and the sensitivity of the receptor is considered to be high. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Guillemot

                        Sensitivity of the receptor

79. Guillemot are considered to be moderately vulnerable to disturbance (Wade et al., 2016). Whilst there is evidence from studies that guillemot respond adversely to vessel traffic (Rojek et al., 2007), behavioural response to underwater and airborne sounds resulting from construction activities are unknown. Although guillemot are likely to respond to visual stimuli during the construction phase, the impacts of disturbance/displacement are short-term and guillemot have the ability to return to the baseline abundance and distribution after construction.
80. Guillemot raise a single chick per year and breed from the age of six onwards, typically living on average for 23 years (Burnell et al., 2023). Guillemot have undergone decreases of approximately 31% in Scotland since the early 2000s. Surveys managed by the RSPB in 2023 have recorded indicative decreases of 6% across a number of sites in Britain in 2023 when compared against a pre-HPAI baseline (Tremlett et al., 2024). Overall, Guillemot is deemed to have low recoverability.
81. Guillemot is a qualifying interest for three SPAs likely to be connected to the Array (within the mean-max + SD foraging range), with several non-SPA colonies also within range and so the species is considered to be of international value. The population recorded during baseline surveys of the Array was found to be of regional importance. Therefore, guillemot is considered to be of international value.
82. Guillemot is deemed to be of medium vulnerability, low recoverability and international value. The sensitivity of the receptor is therefore, considered to be high.

                        Significance of the effect

83. Overall, the magnitude of the impact is deemed to be negligible and the sensitivity of the receptor is considered to be high. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Razorbill

                        Sensitivity of the receptor

84. As with guillemot, razorbill are deemed to be moderately vulnerable to disturbance from vessels and helicopters at offshore wind farms (Wade et al., 2016). Although razorbill are likely to respond to visual stimuli during the construction phase, the impacts of disturbance/displacement are short-term and razorbill have the ability to return to the baseline conditions after construction.
85. Although the species has a low reproductive potential (only laying one egg) and does not breed until four years old (Robinson, 2005), razorbill are deemed to have a medium recoverability given their increasing trend in abundance in the UK (JNCC, 2020).
86. The Array is within the foraging range of razorbill from two SPAs at which the species is a qualifying feature (Fowlsheugh SPA and Troup, Pennan and Lion’s Heads SPA). In addition, there are a number of smaller colonies within foraging range. The numbers of razorbills recorded during baseline surveys of the Array are considered to be of national importance. Therefore, razorbill is considered to be of international conservation value.
87. Razorbill is deemed to be of medium vulnerability, medium recoverability and international value. The sensitivity of the receptor is therefore, considered to be high.

                        Significance of the effect

88. Overall, the magnitude of the impact is deemed to be negligible and the sensitivity of the receptor is considered to be high. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Puffin

                        Sensitivity of the receptor

89. Puffin are considered to be moderately vulnerable to disturbance (Wade et al., 2016). Behavioural responses to underwater and airborne sounds resulting from construction activities are unknown. Although puffin are likely to respond to visual stimuli during the construction phase, the impacts of disturbance/displacement are short-term and puffin have the ability to return to the baseline abundance and distribution after construction (MacArthur Green, 2023).
90. Puffin have a low reproductive potential (i.e. typically laying only one egg and not breeding until five years old) (Robinson, 2005). Given puffin nest in burrows, and often in inaccessible locations, abundance estimates are relatively infrequent. The long-term pattern indicates a population increase since the counts conducted for Operation Seafarer (1969/70) but small declines in recent years (JNCC, 2021; Burnell, 2023). Puffin is therefore assessed as having low recoverability.
91. Puffin is a qualifying interest for several SPAs likely to be connected to the Array (within the mean-max + SD foraging range), with several non-SPA colonies also within range and so the species is considered to be of international value. The population recorded during baseline surveys of the Array was found to be of regional importance. Therefore, puffin is considered to be of international value.
92. Puffin is deemed to be of medium vulnerability, limited potential recoverability and international value. The sensitivity of the receptor is therefore considered to be high.

                        Significance of the effect

93. Overall, the magnitude of the impact is deemed to be negligible and the sensitivity of the receptor is considered to be high. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Fulmar

                        Sensitivity of the receptor

94. In terms of behavioural response to vessel and helicopter traffic, fulmar are considered have a very low vulnerability (Wade et al., 2016).
95. Fulmar is a qualifying interest for several SPAs likely to be connected to the Array (within the mean-max + SD foraging range), with several non-SPA colonies also within range and so the species is considered to be of international value. Refer to Table 6.26 of volume 3, appendix 11.1 for details of SPAs with connectivity to the Array with regards to fulmar.
96. Fulmar are considered to have very low reproductive potential, due to an average age of recruitment of nine years old and typically laying only a single egg (Robinson, 2005; Horswill and Robinson, 2015). The fulmar population increased by 77% between the 1969 to 1970 and 1985 to 1988 censuses and remained relatively stable until the early 2000s. Numbers have since declined slightly since, but remain above the level in 1969 to 1970 (JNCC, 2022).
97. Fulmar is deemed to be of very low vulnerability, low recoverability and international value. The sensitivity of the receptor is therefore, considered to be high.

                        Significance of the effect

98. Overall, the magnitude of the impact is deemed to be negligible and the sensitivity of the receptor is considered to be high. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Gannet

                        Sensitivity of the receptor

99. Gannet are considered to have a very low vulnerability to other sources of disturbance such as vessel and helicopter traffic (Wade et al., 2016), and so gannet are considered to be of very low vulnerability.
100. Gannet have low reproductive potential given a typical age of first breeding of five years and typically laying only a single egg per breeding season. However, although gannet has a low reproductive potential, the species has demonstrated a consistent increasing trend in abundance since the 1990s (JNCC, 2020). It is of note that the species has suffered from the outbreak of HPAI during the 2022 breeding season (Pearce-Higgins et al., 2023), with declines of 25% recorded at certain sites in Britain in 2023 when compared against a pre-HPAI baseline (Tremlett et al., 2024). Therefore, whilst the overall population has shown steady growth, HPAI has led to some short-term declines. Therefore, overall gannet is deemed to have low recoverability.
101. Due to the large foraging range, gannet is a qualifying interest for several SPAs likely to be connected to the Array (within the mean-max + SD foraging range), including the UK’s largest gannet colony at Bass Rock. Bass Rock, which falls within the Outer Firth of Forth and St Andrews Bay Complex SPA, located 106.4 km south-west of the Array. The species is therefore considered to be of international value. Refer to volume 3, appendix 11.1 (Table 6.30) for details of SPAs with connectivity to the Array with regards to gannet.
102. Gannet is deemed to be of very low vulnerability, low recoverability and international value. The sensitivity of the receptor is therefore considered to be high.

                        Significance of the effect

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

                        Secondary mitigation and residual effect

104. No offshore ornithology secondary mitigation is considered necessary for any of the ornithological receptors, because the likely effect in the absence of mitigation is not significant in EIA terms.

                        Decommissioning phase

105. The MDS for the decommissioning phase is assumed to be equal or less than the construction phase ( Table 11.11   Open ▸ ). As such, the assessment of the impacts is the same and is not repeated here. Therefore, as concluded in the construction phase, the impact of temporary habitat loss and disturbance in the decommissioning phase is of minor adverse significance, which is not significant in EIA terms.

Indirect Impacts from Construction/Decommissioning Noise

106. Underwater sound produced during construction and decommissioning activities may impact upon the availability of prey items, for example by causing fish and mobile invertebrates to avoid the Array during construction and decommissioning. Underwater sound may also affect the physiology and behaviour of fish and mobile invertebrates. The reduction or disruption of prey availability due to underwater sound may cause reduced energy intake affecting productivity or survival of offshore ornithology receptors.
107. The potential effects on benthic invertebrates, fish and shellfish has been assessed in volume 2, chapters 8 and 9.

                        Construction phase

                        Magnitude of impact

108. A number of potential impacts on benthic subtidal ecology (including benthic invertebrates) associated with the Array were identified in volume 2, chapter 8, including disturbance during construction. The assessment identified an effect of minor adverse significance as a result of disturbance during construction, which is not significant in EIA terms.
109. With regards to fish and shellfish prey, volume 2, chapter 9 considered the potential impacts of disturbance during construction on marine species (including shellfish), sandeel, herring and diadromous fish. The assessment identified an effect of minor adverse significance on all fish and shellfish receptors as a result of disturbance during construction, which is not significant in EIA terms.
110. Based on the information presented in volume 2, chapters 8 and 9, the direct impact of construction noise on fish and mobile invertebrates is expected to be of minor adverse significance. The impact on ornithological receptors is predicted to be of local spatial extent, medium duration, intermittent and reversible. The magnitude is therefore considered to be of negligible significance.

                        Sensitivity of the receptor

111. None of the VORs considered in this assessment (as set out in Table 11.7   Open ▸ ) are highly specialist, with all VORs I a moderate degree of flexibility in their habitat preferences and prey items (Del Hoyo et al., 1992). As set out in volume 3, appendix 11.1, the VORs listed in Table 11.7   Open ▸ have a moderate or high habitat flexibility as assessed by Wade et al. (2016), with the exception of little tern, which has low flexibility. This moderate or high habitat flexibility equates to a medium or low vulnerability to changes in prey availability (low flexibility equates to high vulnerability).
112. The recoverability of kittiwake, guillemot, razorbill, puffin, fulmar and gannet is shown in Table 11.19   Open ▸ .
113. Herring gull lay up to three eggs and breed from the age of four onwards, typically living on average for 12 years (Burnell et al., 2023). Natural nesting colonies of herring gull have undergone decreases of approximately 44% in Scotland since the early 2000s, whereas urban-nesting populations have increased considerably. Given that the urban population is small compared to the natural population (Burnell et al., 2023), the overall trend is likely to be a decline. Surveys managed by the RSPB in 2023 have recorded indicative declines of 7% across a number of sites in Britain in 2023 when compared against a pre-HPAI baseline (Tremlett et al., 2024). Overall herring gull is considered to have low recoverability.
114. Lesser black-backed gull lay an average of three eggs and breed from the age of four onwards, typically living on average for 15 years (Burnell et al., 2023). Coastal colonies of lesser black-backed gull have undergone decreases of approximately 61% in Scotland since the early 2000s, whereas inland populations have increased by 145%, resulting in an overall decline of 48% (Burnell et al., 2023). Surveys managed by the RSPB in 2023 have recorded indicative declines of 25% across a number of sites in Britain in 2023 when compared against a pre-HPAI baseline (Tremlett et al., 2024). Overall lesser black-backed gull is considered to have low recoverability.
115. Sandwich tern typically lay two eggs and breed from the age of three onwards, typically living on average for 12 years (Burnell et al., 2023). Sandwich tern have undergone national decreases of approximately 54% since the early 2000s. Surveys managed by the RSPB in 2023 have recorded indicative decreases of 35% across a number of sites in Britain in 2023 when compared against a pre-HPAI baseline (Tremlett et al., 2024). Therefore, overall Sandwich tern is deemed to have low recoverability.
116. Little tern typically lay two to three eggs and breed from the age of three onwards, typically living on average for 12 years (Burnell et al., 2023). Little tern have undergone decreases of approximately 29% in Scotland since the early 2000s. Little tern is considered to have low recoverability.
117. Common tern typically lay two to three eggs and breed from the age of three onwards, typically living on average for 12 years (Burnell et al., 2023). Common tern have undergone a decline of 24% in Scotland since the early 2000s, but an overall increase of approximately 7% across Britain, Ireland, Isle of Man and Channel Islands (Burnell et al., 2023). Surveys managed by the RSPB in 2023 have recorded indicative decreases of 42% across a number of sites in Britain in 2023 when compared against a pre-HPAI baseline (Tremlett et al., 2024). Therefore, overall common tern is deemed to have low recoverability.
118. Arctic tern typically lay one to two eggs and breed from the age of four onwards. Although their average age is unknown, Arctic terns are long-lived and have been known to breed at 30-34 years of age (Burnell et al., 2023). Arctic tern have undergone a decrease of approximately 54% in Scotland since the early 2000s. Surveys managed by the RSPB in 2023 have recorded indicative decreases of 1% across a number of sites in Britain in 2023 when compared against a pre-HPAI baseline (Tremlett et al., 2024). Therefore, overall Arctic tern is considered to have low recoverability.
119. Great skua typically lay two eggs and breed from the age of four onwards. Although their average age is unknown, great skua are long-lived and have been known to reach 38 years of age (Burnell et al., 2023). Great skua have undergone an increase of approximately 14% in Scotland since the early 2000s. However, surveys managed by the RSPB have recorded indicative declines of 76% across a number of sites in Britain in 2023 when compared against a pre-HPAI baseline (Tremlett et al., 2024). Therefore, whilst the overall population has shown steady growth, HPAI has led to some significant short-term declines. Overall great skua is currently considered to have low recoverability.
120. European storm petrel lay one egg and breed from the age of four onwards, typically living on average for 12 years (Burnell et al., 2023). Storm petrel have undergone an increase of approximately 48% in Scotland since the early 2000s. Storm petrel is considered to have medium recoverability.
121. Leach’s storm petrel lay one egg and breed from the age of five onwards. Although their average age is unknown, Leach’s storm petrel are long-lived and have been known to reach 36 years of age (Burnell et al., 2023). Leach’s storm petrel have undergone declines of approximately 79% in Scotland since the early 2000s. Leach’s storm petrel is considered to have low recoverability.
122. Manx shearwater lay one egg and breed from the age of five onwards. Manx shearwater are long-lived and have been known to reach over 50 years of age (Burnell et al., 2023). Manx shearwater have undergone increases of approximately 133% in Scotland since the early 2000s. Manx shearwater is considered to have medium recoverability.
123. With the exception of little tern, the VORs are all deemed to be of low to medium vulnerability, low to medium recoverability and national to international value. The sensitivity of these receptors is therefore considered to range between medium to high sensitivity (refer to Table 11.19   Open ▸ ) .
124. Little tern has a high vulnerability to changes in prey availability, has a low recoverability and is of national conservation value. Therefore, little tern has a high sensitivity.

Table 11.19: Sensitivity of Receptors to Indirect Impacts from Construction/Decommissioning Noise

                        Significance of the effect

125. Given a magnitude of impact of negligible adverse significance, and a high sensitivity, the significance of the effect is concluded to be of minor adverse significance for all receptors, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

126. No offshore ornithology secondary mitigation is considered necessary because the likely effect in the absence of mitigation is not significant in EIA terms.

                        Decommissioning phase

127. The MDS for the decommissioning phase is assumed to be equal to the construction phase ( Table 11.11   Open ▸ ). As such, the assessment of the effects is the same and is not repeated here. Therefore, as concluded in the construction phase, the effect of indirect impacts from noise in the decommissioning phase is not significant in EIA terms.

Indirect impacts from UXO clearance

128. There is potential for disturbance, auditory injury and/or mortality for sensitive benthic invertebrates, fish and shellfish species as a result of UXO clearance during the construction phase. The reduction or disruption of prey availability due to UXO detonations may cause reduced energy intake affecting productivity or survival of offshore ornithology receptors.

                        Construction phase

                        Magnitude of impact

129. A number of potential impacts on benthic subtidal ecology (including benthic invertebrate prey) associated with the Array were identified in volume 2, chapter 8, including disturbance during construction. The assessment identified an effect of minor adverse significance as a result of disturbance during construction, which is not significant in EIA terms.
130. With regards to fish and shellfish prey, volume 2, chapter 9 considered the potential impacts of disturbance during construction on marine species (including shellfish), sandeel, herring and diadromous fish. The assessment identified an effect of minor adverse significance on all fish and shellfish receptors as a result of disturbance during construction, which is not significant in EIA terms.
131. Based on the information presented in volume 2, chapters 8 and 9, the direct impact of construction noise on fish and mobile invertebrates is expected to be of minor adverse significance. The impact on ornithological receptors is predicted to be of local spatial extent, medium duration, intermittent and reversible. The magnitude is therefore considered to be of negligible significance.

                        Sensitivity of the receptor

132. As with indirect impacts from construction/decommissioning noise, sensitivity is determined by vulnerability to changes in prey availability, recoverability of a species and its conservation value. Therefore, the sensitivity of the receptors is as set out in Table 11.19   Open ▸ , with all VORs having a high sensitivity to changes in prey availability.

                        Significance of the effect

133. Given a magnitude of impact of negligible adverse significance, and a high sensitivity, the significance of the effect is concluded to be of minor adverse significance for all receptors, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

134. No offshore ornithology secondary mitigation is considered necessary because the likely effect in the absence of mitigation is not significant in EIA terms.

Disturbance and displacement from the physical presence of wind turbines and maintenance activities

135. Disturbance as the result of the presence of wind turbines and operational activities during the operation and maintenance phase of an offshore wind farm has the potential to displace seabirds from the area of sea in which wind turbines are located or the activity is occurring. In relation to offshore wind farm development, displacement is defined as a reduction in the number of seabirds occurring within or immediately adjacent to an offshore wind farm (Furness et al., 2013).
136. Displacement can be considered indirect habitat loss, as the result is that that birds are unable to utilise the habitat in the area from which they have been displaced. The loss of habitat means birds may move to areas already occupied by other birds and thus face higher intra- or inter-specific competition due to a higher density of individuals competing for the same resource. Alternatively, displaced birds may be forced to move into areas of lower quality (e.g. areas of lower prey availability) or travel longer distances to reach habitat of a suitable quality. This could therefore affect their demographic fitness (i.e. survival rates and breeding productivity), as well as potentially impacting on other birds in areas that displaced birds move to (for example, by increasing competition for resources).
137. Table 11.11   Open ▸ gives the scenario that would lead to the greatest amount of disturbance and displacement during the operation and maintenance phase. This results from the largest Array and the greatest amount of vessel and helicopter activity.
138. The displacement assessment is based on the use of the matrix approach (JNCC et al., 2022), which was agreed as suitable in the post-Scoping consultation (see Table 11.3   Open ▸ ). As sensitivity to displacement differs considerably between seabird species, species were screened and progressed for the matrix approach using ‘Disturbance Sensitivity’ and ‘Habitat Specialisation’ scores from Bradbury et al. (2014) and Wade et al. (2016) as recommended by the Joint SNCB Interim Displacement Advice Note (JNCC et al., 2022). In addition to the species’ sensitivity rating, the importance of a species abundance as recorded during baseline surveys of the Array was considered as to whether species were progressed to the matrix stage (see volume 3, appendix 11.3). The species progressed to the matrix stage were kittiwake, guillemot, razorbill, puffin, fulmar and gannet, and these species are considered in detail in this section. All other species were excluded on the basis there was no potential for a significant effect (volume, 3, appendix 11.3).
139. For each of the species considered (kittiwake, guillemot, razorbill, puffin, fulmar and gannet: as identified in volume 3, appendix 11.3), displacement impacts were quantified for the population within the Array plus 2 km buffer. SNCBs recommend for most species a standard displacement buffer of 2 km with the exception of the species groups of divers as they can be affected at distances over 4 km (Natural England, 2022; JNCC, 2022).
140. Full displacement matrices showing the estimated mortality resulting from 0% to 100% displacement and 0% to 100% mortality of displaced individuals are provided in volume 3, appendix 11.3. Within the displacement matrices, the rates advocated for by NatureScot (2023h) have been utilised and presented alongside an Applicant’s Approach. These rates are discussed within volume 3, appendix 11.3 and within each species’ section below.
141. Where available, abundance estimates based on MRSea modelling have been used, with design-based abundance estimates used otherwise (see volume 3, appendix 11.1 for details on approaches to abundance estimation). Displacement matrices based solely on design-based abundance estimates are also presented in volume 3, appendix 11.3.

                        Evidence used to inform displacement and mortality rates used in Applicant’s Approach

142. There is limited empirical evidence on which mortality rate to use when assessing the impacts of displacement of offshore wind farms. However, the current NatureScot guidance, based on expert opinion, is to consider a mortality rate of up to 5% (NatureScot, 2023h). Van Kooten et al. (2019) studied the effects of displacement of seabirds using energy-budget models for two scenarios using habitat utilisation maps and a fixed 10% mortality rate. The evidence from this study suggests that a 1% mortality rate for displaced birds is more appropriate than the potentially over-precautionary 5% mortality rate.
143. APEM (2022a,b) also considered mortality rates, though fewer studies have attempted to quantify displacement-consequent mortality given the practical and theoretical limitations in doing so. The review 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 (2022a,b) suggest that a mortality rate of 1% or less would be more consistent with the available evidence and still precautionary. Therefore, the Applicant’s Approach applies a 1% mortality rate, based on this evidence. The mortality rate of 1% follows previous advice from the Marine Scotland on Forth & Tay projects (Marine Scotland, 2017).

                        Puffin, guillemot and razorbill

144. Evidence shows that auk species exhibit a medium level of sensitivity to vessel and helicopter traffic (Garthe and Hüppop, 2004; Furness and Wade, 2012; Bradbury et al., 2014). Furthermore, displacement impacts from post-consent monitoring studies (from 13 different European offshore windfarm sites) have been collated and reviewed by Dierschke et al., (2016), which found auk species to show ‘weak displacement’ overall, but results were highly variable. Similarly, a recent review submitted by Hornsea Four Offshore Wind Farm (APEM, 2022a) summarises all current post consent-monitoring studies undertaken to date within the North Sea and UK Western Waters and provides an extensive study and analysis of the empirical data from offshore wind farms. This review found that auk displacement varies considerably across different sites, with displacement rates ranging from +112% to -75%, with the most common finding being no significant effect.
145. Of projects that have quantified displacement post-construction, the closest to the Array is Beatrice Offshore Wind Farm (191.63 km from the Array), which has found low levels of guillemot displacement (MacArthur Green, 2023) with results suggesting that the area of decreased abundance which overlaps the wind farm is no more than partially related to the wind farm (and only in the pre-post-1 comparison), and is either linked to other changes in the area such as moving prey hotspots, or may simply be due to chance.
146. Furthermore, evidence suggests that although auk species are somewhat sensitive to displacement, the effects are short-term, and studies indicate auk habituation to offshore windfarms. For example, a study at Thanet Offshore Windfarm found auk species became habituated, and the displacement rate of between 75% and 85% in the first year of operations fell to between 31% and 41% within years two and three of operations (Royal Haskoning, 2013). Further evidence is emerging through additional post-construction monitoring of offshore windfarms; for instance, there are reports of auk numbers increasing and observations of foraging behaviour within the offshore wind farm itself (Leopold and Verdaat, 2018). This suggests the displacement rates of auk species within the Array will reduce over time.
147. Based on the review of the relevant literature, a displacement rate of 50% during the operations and maintenance phase of the Array has been deemed appropriate for the auk species (i.e. guillemot, razorbill and puffin) considered in this assessment. This rate is considered to be highly precautionary as a study of offshore wind farms in the German North Sea found reduced displacement rates (~20%) of guillemots during the breeding season compared to the non-breeding season (Peschko et al., 2020). This is of important consideration, as the mean displacement rates derived from the Dierschke et al. (2016) review was primarily from data collected in the non-breeding season. Therefore, by applying a single displacement rate of 50% across all bio-seasons within the Array, this ensures a precautionary rate is used for the assessment. Additionally, the recent study by MacArthur Green (2019 and 2023) highlighted that a displacement rate of 50% was also suitable for puffin and is therefore the displacement rate utilised within the Applicant’s Approach for all auk species.

                        Gannet

148. Evidence suggests that gannet show a low level of sensitivity to ship and helicopter traffic (Garthe and Hüppop, 2004; Furness and Wade, 2012). However, their avoidance rates to offshore wind farms can be high. Natural England recently reviewed nine studies that reported on northern gannet avoidance rates using a variation of survey methods (Pavat et al., 2023). The avoidance rates reported range from 61.7% to 100%. Another review by APEM (2022b) looked at studies across 25 offshore wind farms, over different seasons, and reported displacement rates of 40% to 60% during the breeding season, and 60% to 80% during the non-breeding season. In light of literature, and following guidance from NatureScot (2023h), using a displacement rate of 70% has been deemed appropriate for the Applicant’s Approach.

                        Kittiwake

149. Kittiwake are considered to have a low habitat specialisation score and low sensitivity to displacement (Bradbury et al., 2014; Furness and Wade, 2012; Nature Scot, 2023h).
150. Studies regarding the displacement at Egmond aan Zee Offshore Wind Farm (Leopold et al., 2011), Bligh Bank Offshore Wind Farm and Thorntonbank Offshore Wind Farm (Vanermen, 2013). Horns Rev Offshore Wind Farm, Princess Amalia Windpark (Furness, 2013) reported no significant displacement of kittiwake.
151. Nature Scot advise a 30% displacement for kittiwake in both the breeding and non-breeding season (Nature Scot, 2023h). In light of this guidance and additional evidence stated, for the purpose of this assessment, precautionary rates of 30% for displacement have been used for the operations and maintenance phase of the Array as part of the Applicant’s Approach.

                        Fulmar

152. Fulmar are considered to have a very low sensitivity to displacement (Bradbury et al. 2014). However Wade et al. (2016) states that the uncertainty surrounding this classification is very high, indicating that evidence around displacement impacts on fulmar are not well understood.
153. Dierschke et al. (2016) classified fulmars as weakly avoiding offshore wind farms, based on post-construction studies at 20 sites, however the authors note that data for this species are limited and fulmar may actually display stronger avoidance behaviour. It is possible that the lack of fishing vessels within wind farm areas makes them unattractive to fulmars (Neumann et al., 2013; Braasch et al., 2015). The study conducted at BARD Offshore Wind Farm showed that some displacement of fulmar occurred, with higher densities observed outside the wind farm area (Braasch et al., 2015), indicating that small scale displacement may be present. Vanermen et al. (2019) stated that no significant displacement results were found for fulmar at Thorntonbank Offshore Wind farm, with Furness (2013) indicating that it is very unlikely that fulmar would be affected by displacement.
154. NatureScot (2023h) do not provide recommended displacement rates for this species and so as a precaution, the Applicant utilised a wide range of displacement rates of 0 to 50% as part of their Applicant’s Approach. Fulmar was assessed as a precaution due to the large scale of uncertainty surrounding fulmar displacement. However, based on expert judgement and the fact that several post-construction monitoring studies have concluded little to no effect, focus has been placed on the 30% displacement rate. This rate was also utilised within the Pentland Floating Offshore Wind Farm Application (HiDef, 2022) as it was deemed the most appropriate rate for fulmar.

                        Operation and maintenance phase

Kittiwake

                        Magnitude of impact

155. The estimated mortality resulting from displacement during operation and maintenance was assessed for each season, and also on an annual basis by combining seasonal impacts and comparing them against the largest regional seasonal population (as set out in volume 3, appendix 11.3, and summarised in Table 11.20   Open ▸ ).
156. In all seasons and on an annual basis, even when using the NatureScot displacement and mortality rates, the predicted increase in the baseline mortality rate does not surpass the 1% threshold. The impact in each season using the NatureScot Approach is predicted to be below 0.07% increase in baseline mortality, and on an annual basis a maximum of 0.03% increase in baseline mortality ( Table 11.20   Open ▸ ).
157. Using the Applicant’s Approach rates, the increase in baseline mortality is expected to be well below a 0.1% increase in baseline mortality in each season. On an annual basis, an annual increase of 0.011% estimated ( Table 11.20   Open ▸ ).
158. The impact is predicted to be of local spatial extent. The impact is expected to occur for the lifespan of the project and therefore be long term, although it is reversible following decommissioning of the Array. It is predicted that the impact will affect the receptor directly. However, even considering the NatureScot Approach, the increase in baseline mortality is expected to be well below 1% and is unlikely to be detectable compared to natural variation in mortality rates. The magnitude is therefore considered to be negligible.

Table 11.20: Kittiwake Seasonal and Annual Displacement Estimates for the Array Plus 2 km Buffer During Operation and Maintenance

                        Sensitivity of the receptor

159. In terms of behavioural response to offshore wind farm structures, kittiwake are considered to be of low vulnerability, with a score of two (out of five) assigned by Wade et al. (2016).
160. Kittiwake is a qualifying interest for several SPAs likely to be connected to the Array (within the mean-max + SD foraging range), with several non-SPA colonies also within range and so the species is considered to be of international value. Refer to Table 6.2 of volume 3, appendix 11.1 for details of SPAs with connectivity to the Array with regards to kittiwake.
161. Kittiwake lay two eggs and breed from the age of three onwards, typically living on average for 12 years (Burnell et al., 2023). Kittiwake have undergone decreases of approximately 57% in Scotland since the early 2000s. Surveys managed by the RSPB in 2023 have recorded indicative increases of 8% across a number of sites in Britain in 2023 when compared against a pre-HPAI baseline (Tremlett et al., 2024). Overall, kittiwake is deemed to have low recoverability.
162. Kittiwake is deemed to be of low vulnerability, low recoverability and international value. The sensitivity of the receptor is therefore, considered to be high.

Significance of the effect

163. Overall, the magnitude of the impact is deemed to be negligible and the sensitivity of the receptor is considered to be high. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

164. No offshore ornithology secondary mitigation is considered necessary because the likely effect in the absence of mitigation is not significant in EIA terms.

Guillemot

                        Magnitude of impact

165. The estimated mortality resulting from displacement during operation and maintenance was assessed for each season, and also on an annual basis by combining seasonal impacts and comparing them against the largest regional seasonal population (as set out in volume 3, appendix 11.3, and summarised in Table 11.21   Open ▸ ).
166. When using the displacement and mortality rates recommended by NatureScot, (2023h) the predicted number of mortalities is 490 to 817 in the breeding season, and 290 to 870 in the non-breeding season. This is an increase in the baseline mortality rate of 0.40% to 0.67% in the breeding season, and 0.14% to 0.41% in the non-breeding season. On an annual basis, the number of mortalities is 780 to 1,687, which is an increase in baseline mortality rates of 0.36% to 0.79% ( Table 11.21   Open ▸ ).
167. Using the Applicant’s Approach of 50% displacement and 1% mortality (in all seasons) the number of mortalities is 136 in the breeding season and 242 in the non-breeding season. This is an increase in the baseline mortality rate of 0.11% in the breeding season, and 0.11% in the non-breeding season. On an annual basis, the number of mortalities is 378, which is an increase in baseline mortality rates of 0.18% ( Table 11.21   Open ▸ ).
168. It should be noted that recent work using time-depth-recorders to monitor auk diving activity indicates that there is significant variation in diving behaviour (Dunn et al., 2024). The results presented by Dunn et al. (2024) indicate that the correction factors applied to account for auk availability bias (see volume 3, appendix 11.1) are likely to lead to overestimates of the true abundance of auks within the Array Study Area. Therefore, the number of mortalities predicted, based on the abundance of birds present, is also likely to be an overestimate and the conclusions must be considered highly precautionary.
169. The impact is predicted to be of local spatial extent. The impact is expected to occur for the lifespan of the Array, although is reversible following decommissioning of the Array and is therefore considered to be of long-term duration. It is predicted that the impact will affect the receptor directly. However, even considering the NatureScot impact values, the increase in baseline mortality is expected to be below 1% and is unlikely to be detectable compared to natural variation in mortality rates. The magnitude of the impact is therefore deemed to be low.

Table 11.21: Guillemot Seasonal and Annual Displacement Estimates for the Array Plus 2 km Buffer During Operation

                        Sensitivity of the receptor

170. Guillemot is considered to have a high vulnerability to displacement from offshore wind farm structures, being assigned a score of 4 (out of 5) by Wade et al. (2016).
171. Guillemot raise a single chick per year and breed from the age of six onwards, typically living on average for 23 years (Burnell et al., 2023). Guillemot have undergone decreases of approximately 31% in Scotland since the early 2000s. Surveys managed by the RSPB in 2023 have recorded indicative decreases of 6% across a number of sites in Britain in 2023 when compared against a pre-HPAI baseline (Tremlett et al., 2024). Overall, guillemot is deemed to have low recoverability. The Array is not within the foraging range of guillemot from any SPAs at which the species is a qualifying feature. Based on the regional importance of the population recorded during baseline surveys of the Array guillemot is considered to be of international value.
172. Guillemot is deemed to be of high vulnerability, low recoverability and international value. The sensitivity of the receptor is therefore considered to be high.

                        Significance of the effect

173. Overall, the magnitude of the impact is deemed to be low and the sensitivity of the receptor is considered to be high. The effect will, therefore, be of minor to moderate adverse significance. However, as the predicted impact did not surpass 1% in increased mortality, the overall impact is categorised as having a minor adverse significance, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

174. No offshore ornithology secondary mitigation is considered necessary because the likely effect in the absence of mitigation is not significant in EIA terms.

Razorbill

                        Magnitude of impact

175. The estimated mortality resulting from displacement during operation and maintenance was assessed for each season, and also on an annual basis by combining seasonal impacts and comparing them against the largest regional seasonal population (as set out in volume 3, appendix 11.3, and summarised in Table 11.22   Open ▸ ).
176. When using the displacement and mortality rates recommended by NatureScot,(2023h) the predicted number of mortalities is one to four in the pre-breeding season, 47 to 78 in the breeding season, nine to 27 in the post-breeding season, and one to two in the non-breeding season. This is an increase in the baseline mortality rate of 0.001% to 0.004% in the pre-breeding season, 0.50% to 0.83% in the breeding season, 0.01% to 0.03% in the post-breeding season, and 0.003% to 0.01% in the non-breeding season. On an annual basis, the number of mortalities is 58 to 111, which is an increase in baseline mortality rates of 0.06% to 0.11% ( Table 11.22   Open ▸ ).
177. Using the Applicant’s Approach, the number of mortalities is one in the pre-breeding season, 13 in the breeding season, seven in the post-breeding season and one in the non-breeding season. This is an increase in the baseline mortality rate of 0.001% in the pre-breeding season, 0.14% in the breeding season, 0.01% in the post-breeding season, and 0.003% in the non-breeding season. On an annual basis, the number of mortalities is 22, which is an increase in baseline mortality rates of 0.02% ( Table 11.22   Open ▸ ).
178. It should be noted that recent work using time-depth-recorders to monitor auk diving activity indicates that there is significant variation in diving behaviour (Dunn et al., 2024). The results presented by Dunn et al. (2024) indicate that the correction factors applied to account for auk availability bias (see volume 3, appendix 11.1) are likely to lead to overestimates of the true abundance of auks within the Array Study Area. Therefore, the number of mortalities predicted, based on the abundance of birds present, is also likely to be an overestimate and the conclusions must be considered highly precautionary.
179. The impact is predicted to be of local spatial extent. The impact is expected to occur for the lifespan of the project, although is reversible following decommissioning of the project and is therefore considered to be of long-term duration. It is predicted that the impact will affect the receptor directly. Using both the Applicant's Approach rates and the rates recommended by NatureScot (2023h), the increase in mortality is below 1% of baseline mortality in each season and also on an annual basis. Therefore, the magnitude of impact is considered to be low.

Table 11.22: Razorbill Seasonal and Annual Displacement Estimates for the Array Plus 2 km Buffer During Operation and Maintenance

                        Sensitivity of the receptor

180. As with guillemot, razorbill are deemed to be highly vulnerable to displacement from offshore wind farms, being assigned a score of 4 (out of 5) by Wade et al. (2016). Although the species has a low reproductive potential (only laying one egg) and does not breed until four years old (Robinson, 2005), razorbill are deemed to have a medium recoverability given their increasing trend in abundance in the UK (JNCC, 2020).
181. The Array is within the foraging range of razorbill from two SPAs at which the species is a qualifying feature (Fowlsheugh SPA and Troup, Pennan and Lion’s Heads SPA). In addition, there are a number of smaller colonies within foraging range. The numbers of razorbills recorded during baseline surveys of the Array are considered to be of national importance. Therefore, razorbill is considered to be of international conservation value.
182. Razorbill is deemed to be of high vulnerability, medium recoverability and international value. The sensitivity of the receptor is therefore, considered to be high.

                        Significance of the effect

183. Overall, the magnitude of the impact is deemed to be low and the sensitivity of the receptor is considered to be high. The effect will, therefore, be of minor to moderate adverse significance. However, as the predicted impact did not surpass 1% in increased mortality, the overall impact is categorised as having a minor adverse significance, which is not significant in EIA terms.