The potential for impacts on the lesser black-backed gull population
  1. The Proposed Development and two kilometre buffer around the Proposed Development array area7 do not overlap with the Forth Islands SPA, so that potential impacts on its lesser black-backed gull population will only occur as a result of individuals from the colony occurring in the area (or vicinity) of the Proposed Development. Consequently, the main focus of the assessment for this SPA is concerned with the Conservation Objective to maintain, in the long term, the population of the species as a viable component of the site because the other conservation objectives either apply to the site itself, and not to areas beyond the boundary, or are encompassed by the assessment of this first Conservation Objective (as for the maintain in the long term no significant disturbance of the species, because disturbance would only be considered significant if it caused an adverse effect on the population viability of the qualifying features).
  2. From published information on lesser black-backed gull foraging ranges (Woodward et al. 2019), it is likely that during the breeding period lesser black-backed gulls from the Forth Islands SPA occur within the area of the Proposed Development and of the two km buffer around the Proposed Development array area. This is supported by the findings of the apportioning exercise, which estimates that almost 53% of the lesser black-backed gulls occurring on the Proposed Development array area during the breeding season derive from this SPA colony (Offshore EIA Report, volume 3, appendix 11.5). The breeding period for lesser black-backed gull is defined as mid-March to August, following NatureScot (2020).
  3. In the non-breeding season lesser black-backed gulls from the Forth Islands SPA migrate south through the southern North Sea, undertaking the return journey in spring. It is likely that they winter predominantly in Iberia or on the coast of northwest Africa although a proportion may remain within the North Sea and Channel (Wernham et al. 2002, Furness 2015). Therefore, it is likely that there is the potential for birds from the Forth Islands SPA population to pass through offshore wind farms in the North Sea during the autumn and spring passage periods (defined as September to October and the first half of March, respectively, on the basis of applying the BDMPS defined periods within the context of the overall non-breeding period defined by NatureScot – Furness 2015, NatureScot 2020, Offshore EIA Report, volume 3, appendix 11.5), and to a lesser extent in winter as well (defined as November to February – Furness 2015). Given the above, the Proposed Development may have potential effects on the Forth Islands SPA lesser black-backed gull population during breeding and non-breeding periods.
Project alone: construction and decommissioning
Changes to prey availability
  1. Lesser black-backed gulls have a highly opportunistic diet (del Hoyo et al., 1996), utilising terrestrial, intertidal and marine habitats to forage for a wide variety of prey species including invertebrates, small fish and carrion (including fishery discards). Indirect effects on lesser black-backed gulls may arise as a result of changes in the availability, distribution, or abundance of these species during the construction and decommissioning phases of the Proposed Development. Reduction or disruption to prey availability may cause displacement from foraging grounds or reduced energy intake, affecting survival rates or productivity in the Forth Islands SPA lesser black-backed gull population in the short-term.
  2. During construction there are a number of ways in which effects on lesser black-backed prey species could occur, which are as outlined in the section on Project Alone: Construction and Decommissioning – Changes to prey availability for the St Abb’s Head to Fast Castle SPA kittiwake population. The Proposed Development array area encompasses 1,010 km2, whilst the Proposed Development export cable corrirdor encompasses 168 km2. Together these areas represent c. 1% of the total breeding season foraging area that is potentially available to the SPA lesser black-backed gull population, as defined by the species’ mean-maximum breeding season foraging range plus 1 SD (i.e. 127±109 km; Woodward et al., 2019) and assuming that this range is represented by a semicircle to the main seaward side of the colony. Furthermore, given their flexible foraging habits and the distance between the Proposed Development and the SPA, it is likely that the area of marine habitat encompassed by the Proposed Development is not of key importance for lesser black-backed gulls breeding at the Forth Islands SPA. Effects during the non-breeding season are considered to be lower than during the breeding season given that birds migrate south through UK waters to their wintering grounds (Wernham et al., 2002; Furness 2015).
  3. During decommissioning, the effects from changes in prey availability are considered to be the same (or less) as for construction. It is currently unclear as to how the presence, and subsequent removal of, subsea structures may affect the prey species of lesser black-backed gull (Birchenough and Degrae 2020; Scott, 2022). It is possible that prey abundance could decline from the levels present during the operation and maintenance period. This could occur if the sub-surface structures associated with the Proposed Development in the marine environment lead to an increase in key prey abundance within the Proposed Development array area and export cable corridor via the provision of artificial reef habitats. However, some infrastructure (such as scour and cable protection) is assumed to be left in situ with the impact of colonisation of infrastructure continuing in perpetuity following decommissioning. Thus, any reduction in prey abundance through removal of foundations is likely to be very small relative to the area over which lesser-black-backed gulls forage.
  4. Given their wide-ranging foraging behaviour and plasticity in foraging habitat and diet (del Hoyo et al., 1996), together with any effects being intermittent, spatially-restricted and temporary in nature, it is considered that there is no potential for construction or decommissioning related changes in prey availability to lead to an adverse effect on the Forth Islands SPA lesser-back-backed gull population. This conclusion is consistent with the outcome of the EIA which concluded that effects from changes in prey availability on lesser black-backed gulls during construction and decommissioning were not significant in EIA terms (volume 2, chapter 11 of the Offshore EIA Report).
Project alone: operation and maintenance
Collision risk
  1. Predictions of the number of lesser black-backed gulls at risk from collisions due to the Proposed Development were calculated using the deterministic version of the SOSS offshore collision risk model (Band 2012, Offshore EIA Report, volume 3, appendix 11.6). Following the Scoping Opinion (volume 3, appendix 6.2 of the Offshore EIA Report), the assessment is based on the outputs from both options 2 and 3 of the CRM, which use the generic flight height data and for which option 2 assumes a uniform distribution of flight heights across the rotor swept zone and option 3 assumes the modelled flight height distribution (Band 2012, Johnston et al. 2014a,b). In accordance with the recommendations of the SNCBs (2014), and as advised by the Scoping Opinion, avoidance rates of 99.5% and 98.9% were applied to the outputs from option 2 and option 3, respectively.
  2. As outlined for the St Abb’s Head to Fast Castle SPA kittiwake population above, guidance on the use of the CRM suggests that model predictions should be based upon the mean monthly densities of flying birds estimated within the array area (Band 2012)8 and, to the best of the Applicant’s knowledge, this approach has been applied in all recent UK offshore wind farm assessments. Despite this, the Scoping Opinion advised that the CRMs for the Proposed Development should use the maximum monthly densities of flying birds within the array area. Further details on this are provided above in the Project Alone: Operation and Maintenance - Collision Risk section for the St Abb’s Head to Fast Castle SPA kittiwakes population (and in volume 3, appendix 11.3 of the Offshore EIA Report) but, as a result of this overly precautionary approach (which does not follow previous precedent), the CRMs for lesser black-backed gull were undertaken following:
  • The Scoping Approach of using the maximum monthly densities, and
  • The Developer Approach of using the mean monthly densities.
    1. In addition to the above, collision estimates for lesser black-backed gulls were also calculated using options 2 and 3 of the stochastic version of the CRM (McGregor et al. 2018) with avoidance rates as derived from the bird collision-avoidance study undertaken at the Thanet offshore wind farm (Bowgen and Cook 2018). These additional collision estimates are not used as the basis of the assessments on the SPA lesser black-backed gull populations but, instead, are used solely to illustrate the consequences of applying these alternative avoidance rates which have been derived from studies at an actual offshore wind farm. Details of these additional CRMs are provided in annex C of Offshore EIA Report, volume 3, appendix 11.3.
    2. Lesser black-backed gull collision estimates are calculated for the defined breeding period, with estimates apportioned to the Forth Islands SPA population according to the NatureScot (2018) approach (Offshore EIA Report, volume 3, appendix 11.5). The resulting estimates were apportioned to age classes according to the plumage characteristics of lesser black-backed gulls recorded during the baseline surveys (Offshore EIA Report, volume 3, appendix 11.1), whilst on the basis of advice provided by NatureScot and Marine Scotland Science following Roadmap Meeting 4 (G. Holland, email 26/01/2022), it was also assumed that 35% of the breeding adults in the SPA population miss breeding in any given year (i.e. sabbatical birds) so that the number of adult collisions estimated during the breeding season was adjusted accordingly.
    3. No lesser black-backed gull collisions were estimated for the non-breeding periods (Offshore EIA Report, volume 3, appendix 11.3).
    4. Based upon option 2 of the deterministic CRM with a 99.5% avoidance rate applied, and in conjunction with the estimates and assumptions detailed above, the annual collision mortality of lesser black-backed gulls from the Forth Islands SPA is predicted to be three adults and 0.4 immatures as determined by the Scoping Approach, and two adults and 0.3 immatures as determined by the Developer Approach (Table 5.63). The collision estimates for option 3 of the deterministic CRM with a 98.9% avoidance rate applied (which was also recommended by the Scoping Opinion as a basis for the assessment) are not presented in Table 5.63 but give outputs that are 33 - 44% lower than the option 2 estimates for both the Scoping and Developer Approaches (Offshore EIA Report, volume 3, appendix 11.6). In addition, the collision estimates produced using options 2 and 3 of the stochastic CRM with the Bowgen and Cook (2018) avoidance rates applied were similar to those obtained from option 3 of the deterministic CRM with the SNCB recommended 98.9% avoidance rate, and hence also substantially lower than those presented in Table 5.63 below (see annex C of the Offshore EIA Report, volume 3, appendix 11.6).

 

Table 5.63:
Predicted Collision Effects from the Proposed Development on the Forth Islands SPA Lesser Black-Backed Gull Population, as Determined by the Scoping Approach and Developer Approach. Estimates are for the Maximum Design Scenario and are Based on Option 2 of the Deterministic CRM Using a 99.5% Avoidance Rate (see text)

Table 5.63: Predicted Collision Effects from the Proposed Development on the Forth Islands SPA Lesser Black-Backed Gull Population, as Determined by the Scoping Approach and Developer Approach. Estimates are for the Maximum Design Scenario and are Based on Option 2 of the Deterministic CRM Using a 99.5% Avoidance Rate (see text)

 

  1. Based upon the estimates from option 2 of the CRM, the additional annual mortality of adult lesser black-backed gulls from the Forth Islands SPA population predicted due to collisions with wind turbines in the Proposed Development Array represents approximately 0.05% of the number of adults currently estimated to breed at this colony (i.e. 4,006 individuals – Table 3.3 in volume 3, appendix 11.5 of the Offshore EIA Report) as determined by the Developer Approach and approximately 0.06% as determined by the Scoping Approach. In terms of percentage increases in the baseline annual adult mortality of the population (which is based on applying a mortality rate of 0.087 – see Table 2.15 in volume 3, appendix 11.6 of the Offshore EIA Report), the predicted adult collision mortality equates to increases of 0.6% and 0.8% for the Developer and Scoping Approaches, respectively.
  2. The potential levels of impact on the Forth Islands SPA lesser black-backed gull population resulting from the predicted collision mortalities in Table 5.63 are considered in more detail below in the Project Alone: Population-Level Impacts section. This presents the outputs from PVAs of the potential effects of predicted collision mortality on the SPA population.
Changes to prey availability
  1. Potential impacts on key prey species for lesser black-backed gulls breeding at Forth Islands SPA during the operation and maintenance phase have been assessed in volume 2, chapter 9 of the Offshore EIA Report using the appropriate maximum design scenarios for these receptors. Reduction or disruption to prey availability through temporary and long-term subtidal habitat loss/disturbance, increased SSC and deposition, EMF from subsea electrical cabling, and colonisation of subsea structures could affect lesser black-backed gull survival and productivity in the Forth Islands SPA population.
  2. Artificial structures introduced to the marine environment provide hard substrate for settlement of various organisms, which can increase local food availability for higher trophic levels. Whilst there is mounting evidence of potential benefits of artificial structures in marine environment (Birchenough and Degrae 2020), the statistical significance of such benefits and details about trophic interactions remain largely unknown (Scott, 2022).
  3. Given their wide-ranging foraging behaviour and plasticity in foraging habitat and diet (del Hoyo et al., 1996), together with any effects on prey during operation and maintenance being largely intermittent across a relatively small spatial extent, it is considered that there is no potential for operational or maintenance related changes in prey availability to lead to an adverse effect on the Forth Islands SPA lesser black-backed gull population. This conclusion is consistent with the outcome of the EIA which concluded that effects from changes in prey availability on lesser black-backed gulls during operation and maintenance were not significant in EIA terms (volume 2, chapter 11 of the Offshore EIA Report).
Project alone: population-level impacts
  1. As determined above, the effects from the Proposed Development alone which could lead to an adverse effect on the Forth Islands SPA lesser black-backed gull population are limited to collision mortality during the operation and maintenance phase. For other effect pathways, there is considered to be no potential for an adverse effect on this population as a result of the Proposed Development alone, with any such effects likely to be small and of little, or no, consequence in terms of impacts at the population level.
  2. Given this, PVA was undertaken on the mortality to the adult and immature age classes predicted due to the collisions associated with the Proposed Development, as determined by both the Scoping and Developer Approaches (see Table 5.63 above). This was undertaken using the outputs from option 2 of the deterministic CRM with a 99.5% avoidance rate applied, as presented in Table 5.63 (noting that these are the more precautionary of the outputs from the different CRM approaches recommended by the Scoping Opinion). The population model for the SPA population was a stochastic, density independent, matrix model, based upon the demographic parameters specified in Table 2.15 of volume 3, appendix 11.6 of the Offshore EIA Report. The starting population size was the 2018 – 2021 count for the SPA, with the projected population trends considered over a 35 year timescale (Offshore EIA Report, volume 3, appendix 11.5). The approach and methods to undertaking the PVA are as described for the St Abb’s Head to Fast Castle kittiwake above (with further details provided in the Offshore EIA Report, volume 3, appendix 11.6).
  3. Outputs from the PVA are summarised according to the median predicted population-sizes at the end of the projection period, and the three metrics which the Scoping Opinion (volume 3, appendix 6.2 of the Offshore EIA Report) advised should be used for the interpretation of outputs and which have been shown to have relatively low sensitivity to factors such as varying population status and the mis-specification of the demographic rates underpinning the population model (Cook and Robinson 2015, Jitlal et al., 2017). These metrics are:
  • The CPS – the median of the ratio of the end-point size of the impacted to un-impacted (or baseline) population, expressed as a proportion;
  • The CPGR - the median of the ratio of the annual growth rate of the impacted to un-impacted population, expressed as a proportion; and
  • The centile of the un-impacted population that matches the median (i.e. 50th centile) of the impacted population (based upon the distribution of the end-point population-sizes generated by the multiple replications of the model runs, the value should always be less than 50 because the median for the impacted population is not expected to exceed that for the un-impacted population).

 

Table 5.64:
Projected 35 Year Population Sizes and Associated PVA Metrics for the Forth Islands SPA Lesser Black-Backed Gull Population Under Different Impact Scenarios for the Proposed Development Alone

Table 5.64 Projected 35 Year Population Sizes and Associated PVA Metrics for the Forth Islands SPA Lesser Black-Backed Gull Population Under Different Impact Scenarios for the Proposed Development Alone

 

  1. The PVA predicted that the Forth Islands SPA lesser black-backed gull population would increase strongly over the 35 year projection period irrespective of the effects from the Proposed Development. Thus, the population is predicted to be almost five times larger than the current estimate of 4,006 adult birds under all scenarios, including the baseline which assumes no wind farm effects (Table 5.64). Although the predicted increases in population size are inevitably greatest for the baseline scenario (because the PVAs are based on density independent models, which assume all mortality from the wind farm effects is additive and that there are no compensatory mechanisms operating within the population), the differences with the two impact scenarios are small. The predicted levels of increase are unlikely to occur in reality (and are, in part, a consequence of the absence of any compensatory density dependence within the models – as discussed in the section on Project Alone: Population-level impacts for the St Abb’s Head to Fast Castle SPA kittiwake population), whilst it is also notable that the predicted increase differs from the documented long-term trend of relative stability for this SPA population (Figure 5.20).
  2. The predicted population-level impacts are small, irrespective of whether these are determined using the Developer or Scoping Approaches. Thus, for the Scoping Approach the CPS value indicates that the collision mortality associated with the Proposed Development alone would result in a reduction of approximately 2% in the size of the SPA population after 35 years, relative to that in the absence of any wind farm effects (Table 5.64). The associated reduction in annual population growth rate (relative to that predicted under baseline conditions) is estimated to be 0.1%, whilst the centile value of 46.7 indicates a considerable overlap in the distributions of the predicted impacted and un-impacted population sizes and, hence, a high likelihood of the impacted population being of a similar size to the un-impacted population after 35 years. As would be expected, the metrics for the Developer Approach suggest even smaller levels of impact (Table 5.64). In addition, it should be noted that these predicted levels of impact are derived from the more precautionary of the two CRM approaches recommended by the Scoping Opinion, with the alternative approach giving collision estimates that are 33 - 44% lower than those used for the PVA.
Project alone: conclusion
  1. For both the Developer and Scoping Approaches, the potential effects from the Proposed Development alone on the Forth Islands SPA lesser black-backed gull population are predicted to be small, with the resultant population-level impacts also predicted to be small. In addition, the PVA metrics indicate a high chance of the population being of a similar size to that which would occur in the absence of the Proposed Development after 35 years. Given this, it is concluded that the effects from the Proposed Development alone would not result in an adverse effect on this population.
Effects in-combination
Effects of relevance to the in-combination assessment
  1. As detailed above, any effects from the Proposed Development alone on the Forth Islands SPA lesser black-backed gull population during construction and decommissioning and resulting from changes to prey availability during operation and maintenance will be small and highly localised. As such, there is considered to be no potential for these effect pathways to add to impacts at the population-level that might result from other effects pathways associated with the Proposed Development or from the effects due to other plans and projects.
  2. Therefore, the potential for effects of the Proposed Development to act on the Forth Islands SPA lesser black-backed gull population in-combination with other plans and projects is limited to the collision risk effect pathway during operation and maintenance. Following advice from NatureScot provided through the Ornithology Roadmap process (at meeting 3, 8th December 2021), the following sections consider these potential effects for (i) the Proposed Development in-combination with the other Forth and Tay wind farms and (ii) the Proposed Development in-combination with the other UK North Sea wind farms (noting that scenario (ii) includes those plans and projects which comprise scenario (i)).
Collision risk - operation and maintenance
  1. Existing assessments for offshore wind farms that are in planning, consented, under construction or in operation were checked to determine the collision estimates to be attributed to the Forth Islands SPA lesser black-backed gull population during the breeding and non-breeding periods (annex E of Offshore EIA Report, volume 3, appendix 11.6).
  2. None of these assessments identified breeding season effects on the SPA population, noting that the Scoping Opinion for the revised designs of the three Forth and Tay projects (which are in closest proximity to the SPA) did not require this SPA population to be assessed (Marine Scotland 2017a,b,c). Additionally, the Appropriate Assessment for the original consents of the Forth and Tay projects predicted a reduction in adult survival rate of less than 0.1% as a result of the Neart na Gaoithe wind farm and concluded no adverse effect on the SPA population (Marine Scotland 2014).
  3. Cumulative collisions of lesser black-backed gulls for UK North Sea wind farms during the non-breeding periods have been estimated recently as approximately 365, of which nine are attributed to the Forth and Tay wind farms (MacArthur Green and Royal HaskoningDHV 2021). During the non-breeding periods, adult lesser black-backed gulls from the Forth Islands SPA are estimated to comprise approximately 1.5% of the autumn and spring passage populations in the North Sea and Channel BDMPS (each of which number approximately 200,000 birds) and approximately 4% of the smaller winter population in this BDMPS (which numbers approximately 39,000 birds) (Furness 2015). Given this, it is unlikely that more than 2% of the total collisions during the non-breeding periods (i.e. approximately 0.18 and 7 birds for the Forth and Tay in-combination scenario and UK North Sea in-combination scenario, respectively) would be adults from the Forth Islands SPA population. Immatures associated with the Forth Islands SPA population are estimated to represent approximately 0.8% of the passage populations and 0.3% of the winter population (Furness 2015), suggesting that approximately three of the total 365 non-breeding season collisions may be attributable to immatures from this SPA population.
  4. For the Proposed Development in-combination with the other Forth and Tay wind farms, the non-breeding season collisions would not add to the effects associated with the Proposed Development in any meaningful way. For the Proposed Development in-combination with the other UK North Sea wind farms, the addition of the non-breeding season collisions would give a total annual mortality of approximately nine adults and three immatures for the Developer Approach and 10 adults and three immatures for the Scoping Approach.
  5. The PVA undertaken for the Forth Islands SPA lesser black-backed gull population using incremental mortalities gives a CPS value of 0.901 and a CPGR value of 0.987 for a mortality of 10 adult birds per year (see Table 3.153 in volume 3, appendix 11.6 of the Offshore EIA Report). This suggests a reduction in the size of the SPA population after 35 years, relative to that in the absence of any wind farm effects, of approximately 10% as determined by the Scoping Approach (whilst the predicted impact would be slightly lower as determined by the Developer Approach – e.g. for an annual mortality of eight adult birds the reduction in population size after 35 years is 8%). The centile values associated with this level of mortality are 32.4 – 35.6, which suggest a reasonable likelihood that the impacted population will be similar in size to the un-impacted population after 35 years (see Table 3.153 in volume 3, appendix 11.6 of the Offshore EIA Report).
  6. However, the PVA for the incremental mortalities assumes that mortality across age classes occurs in proportion to the asymptotic age distribution (as calculated by the population model). Given that adults are estimated to comprise just 45% of the population, this means that the PVA grossly overestimates the level of immature mortality (relative to that estimated from the in-combination collision effects), meaning that the above metrics represent an overestimation of the population-level impacts.
In-combination: conclusion
  1. On the basis of the above considerations, it is concluded that the population-level impacts resulting from the Proposed Development in-combination with (i) the other Forth and Tay wind farms or (ii) the other UK North Sea wind farms would not produce an adverse effect on the Forth Islands SPA lesser black-backed gull population. This conclusion applies irrespective of whether effects are determined according to the Scoping Approach or the Developer Approach.

Assessment for the common tern population

  1. The Forth Islands SPA common tern population is largely restricted to the Isle of May, with few pairs occurring elsewhere in SPA and with the most recent count data available on the Seabird Monitoring Programme Database (Seabird Monitoring Programme | JNCC (bto.org)) giving an estimate of 30 Apparently Occupied Nests (AON) for 2017 - 2019. This represents a marked decline from the citation population size of 334 breeding pairs, which was determined for the period from 1997 – 2001. The SPA population is considered to be in ‘unfavourable declining’ condition.
The potential for impacts on the common tern population
  1. The Proposed Development and two kilometre buffer around the Proposed Development array area7 do not overlap with the Forth Islands SPA, so that potential impacts on its common tern population will only occur as a result of individuals from the colony occurring in the area (or vicinity) of the Proposed Development. Consequently, the main focus of the assessment for this SPA population is concerned with the Conservation Objective to maintain, in the long term, the population of the species as a viable component of the site because the other conservation objectives either apply to the site itself, and not to areas beyond the boundary, or are encompassed by the assessment of this first Conservation Objective (as for the maintain in the long term no significant disturbance of the species, because disturbance would only be considered significant if it caused an adverse effect on the population viability of the qualifying features.
  2. Based on the estimated foraging range, it is unlikely that common terns from the Forth Islands SPA will occur within the Proposed Development array to any extent during the breeding period. This is because the Proposed Development array is 41 km from the Isle of May (where almost all of the SPA common terns nest) at its closest point, which is considerably beyond the mean maximum breeding season foraging range plus 1 SD for the species (i.e. 26.9 km – Woodward et al. 2019). Thus, there is little, or no, potential for connectivity with the Proposed Development array (HRA Stage One Screening Report). The Proposed Development export cable corridor is 21.4 km from the Isle of May at its closest point, so this will transit waters on the periphery of the potential breeding season foraging range. The breeding period for common tern is defined as May to mid-September, following the NatureScot (2020) guidance.
  3. During the non-breeding season, the SPA common tern population contributes to the wider BDMPS spring and autumn passage populations in the UK North Sea and Channel waters (Furness 2015), so there is potential for birds from this SPA population to pass through offshore wind farms in the North Sea at these times (including the Proposed Development).
Project alone: construction and decommissioning
Disturbance
  1. Direct disturbance to common terns during the construction phase may arise as a result of increased vessel movements and helicopter activity, as well as from other activities associated with the installation of infrastructure associated with the Proposed Development. However, in large part, this will be limited to the increased vessel activity along the Proposed Development export cable corridor associated with the cable laying activities. This is because the Proposed Development array is beyond the likely foraging range of the SPA common terns during the breeding season. The levels of such activities that could arise are outlined in Table 4.1, with these activities occurring during construction campaigns within a construction period of at most eight years duration.
  2. A total of up to 11,482 vessel round trips may occur over the construction phase, whilst it is estimated that a maximum of 134 vessels could occur within the area of the Proposed Development at any one time (Table 4.1). However, this is within the context of high baseline levels of vessel traffic within this area (e.g. surveys recorded an average of 14 vessels per day within a 10 nm buffer around the Proposed Development over a 14-day period in August 2022, whilst also showing an average of three to four vessels intersecting the Proposed Development array area per day over summer - Offshore EIA Report, volume 2, chapter 13).
  3. When using the marine environment (and not at the breeding colony), common terns are considered to have a relatively low sensitivity to such sources of direct disturbance. Thus, reviews of the sensitivity of different seabird species to disturbance from vessels and helicopter traffic assign common tern as ‘2’ on a five-scale ranking system, where 1 indicates hardly any or limited escape/avoidance behaviour and very short flight distance when approached and 5 indicates strong escape/avoidance behaviour and a large response distance (Garthe and Hüppop 2004, Furness et al. 2013).
  4. The area of the potential breeding season foraging range (as defined by the mean maximum value plus 1SD) that would be affected by such disturbance is small because (as described above) the Proposed Development export cable corridor will only overlap with a small area near the limits of this range. Furthermore, it is likely that most of the ‘at-sea’ activity from the SPA common terns will occur within the mean maximum foraging range, which at 18.0 km (Woodward et al. 2019) does not encompass the Proposed Development export cable corridor (as measured from the Isle of May).
  5. During the non-breeding passage periods, common tern distribution is not constrained by the location of the breeding colonies and birds from the SPA population are unlikely to make extensive, or protracted, use of the waters encompassed by the Proposed Development given that they migrate from, or to, their breeding areas during these periods. The breeding adult birds from the Forth Islands SPA population comprise only 0.7% of the passage period BDMPS for the UK North Sea and Channel waters (Furness 2015).
  6. In addition, it is important to consider that the construction activities will not occur simultaneously across the entirety of the Proposed Development export cable corridor but, rather, will be carried out in different areas at different times. Thus, cable laying for the Proposed Development export cable will occur over a total of two years, whilst within the Proposed Development array area it is likely that construction activities would be confined largely to discrete areas at any one time.
  7. The potential for disturbance effects during decommissioning is assumed to be the same (or less) as for construction, noting that the duration of the decommissioning phase will not exceed that of construction, and may be shorter.
  8. Given the relatively low sensitivity of common tern to disturbance effects, the small area of their foraging range that is likely to be affected by activities with the potential to cause disturbance, the low levels of potential disturbance associated with the construction of the Proposed Development export cable corridor, and the fact that these potential effects will be temporary, it is considered that there is no potential for construction or decommissioning related disturbance to lead to an adverse effect on the Forth Islands SPA common tern population.
Displacement
  1. As detailed above, common tern is considered to have a relatively low sensitivity to disturbance, whilst potential effects of disturbance during the construction and decommissioning phases will only extend across a small part of the wider foraging areas used by the Forth Islands SPA population and be limited to the activities associated with the Proposed Development export cable corridor. Furthermore, as detailed above, potential effects of disturbance will not occur simultaneously across the entirety of the Proposed Development export cable corridor but, rather, will be carried out in different areas at different times. Thus, at any given time the potential for disturbance effects that could lead to displacement of common terns from this SPA will be limited to relatively small areas, with the potential effects also being of a temporary nature.
  2. Given the above, it is considered that there is little potential for the Forth Islands SPA common tern population to be affected by displacement during the construction or decommissioning phases, with any such effects only extending across small areas and being temporary in nature. Consequently, it is considered that there is no potential for construction or decommissioning related displacement to lead to an adverse effect on the Forth Islands SPA common tern population.
Changes to prey availability
  1. Key prey species for common terns include small forage fish such as sandeel (del Hoyo et al., 1996). Indirect effects on common terns may arise as a result of changes in the availability, distribution, or abundance of these species during the construction and decommissioning phases of the Proposed Development. Reduction or disruption to prey availability may cause displacement from foraging grounds or reduced energy intake, affecting survival rates or productivity in the Forth Islands SPA common tern population in the short-term.
  2. During construction there are a number of ways in which effects on common tern prey species could occur, which are as outlined in the section on Project Alone: Construction and Decommissioning – Changes to Prey Availability for the St Abb’s Head to Fast Castle SPA kittiwake population and in volume 2, chapter 9 of the Offshore EIA Report. However, as described above, it is unlikely that common terns from the Forth Islands SPA will occur within the Proposed Development array area to any extent during the breeding period given their foraging range (as defined by the mean maximum value plus 1 SD). Furthermore, it is likely that most of the ‘at-sea’ activity from the SPA common terns will occur within the mean maximum foraging range, which does not encompass the Proposed Development export cable corridor (as measured from the Isle of May; see above). Thus, there is no potential for connectivity with the Proposed Development array area during the breeding season, and very little with the Proposed Development export cable corridor. Effects during the non-breeding passage periods are considered to be further reduced given that breeding adults from the Forth Islands SPA comprise only 0.7% of the passage period BDMPS for the UK North Sea and Channel waters (Furness 2015).
  3. Given the limited potential for connectivity between the Proposed Development and the breeding common tern population of the Forth Islands SPA, together with any effects being intermittent, spatially-restricted and temporary in nature, it is considered that there is no potential for construction or decommissioning related changes in prey availability to lead to an adverse effect on the Forth Islands SPA common tern population. This conclusion is consistent with the outcome of the EIA which concluded that effects from changes in prey availability on common terns during construction and decommissioning were not significant in EIA terms (volume 2, chapter 11 of the Offshore EIA Report).
Project alone: operation and maintenance
Disturbance
  1. Vessel use within the Proposed Development array area and export cable corridor during the operation and maintenance phase may lead to direct disturbance of foraging common terns (see section on Project Alone: Construction and Decommissioning – Disturbance for the SPA population and Table 4.1).
  2. However, given the limited potential for connectivity between the Proposed Development and the breeding common tern population of the Forth Islands SPA (see section The Potential for Impacts on the Common Tern Population), the low sensitivity of common terns to disturbance effects at sea (Garthe and Hüppop 2004; Furness et al., 2013), and the fact that these potential effects will be reduced compared to the construction and decommissioning phases, it is considered that there is no potential for disturbance during operation and maintenance to lead to an adverse effect on the Forth Islands SPA common tern population. This conclusion is consistent with the outcome of the EIA which ‘screened’ out common tern as a species for which detailed consideration of the effects of construction disturbance was required (volume 2, chapter 11 of the Offshore EIA Report).
Displacement/barrier effects
  1. Given that the Proposed Development array is beyond the likely breeding season foraging range of the Forth Islands SPA common tern population, it is considered that there is little, or no, potential for effects of displacement or barrier effects to result. As such, it is considered that there is no potential for an adverse effect on this SPA population as a result of displacement/barrier effects.
Collision risk
  1. Given that the Proposed Development array is beyond the likely breeding season foraging range of the Forth Islands SPA common tern population, it is considered that there is little, or no, potential for effects of collision mortality to result.
  2. Collision estimates for common terns during the non-breeding period totalled just 0.50 birds (as determined by the Scoping Approach - Offshore EIA Report, volume 3, appendix 11.3), whilst the adult birds from the SPA population represent only 0.7% of the UK North Sea and Channel waters BDMPS (Furness 2015).
  3. As such, it is considered that there is no potential for an adverse effect on this SPA population as a result of collision mortality.
Changes to prey availability
  1. Potential impacts on key prey species for common terns breeding at Forth Islands SPA during the operation and maintenance phase have been assessed in volume 2, chapter 9 of the Offshore EIA Report using the appropriate maximum design scenarios for these receptors. Reduction or disruption to prey availability through temporary and long-term subtidal habitat loss/disturbance, increased SSC and deposition (which may also affect the ability of common terns to detect prey at the sea surface), EMF from subsea electrical cabling could affect common tern survival and productivity in the Forth Islands SPA population.
  2. Artificial structures introduced to the marine environment provide hard substrate for settlement of various organisms, which can increase local food availability for higher trophic levels. Whilst there is mounting evidence of potential benefits of artificial structures in marine environment (Birchenough and Degrae 2020), the statistical significance of such benefits and details about trophic interactions remain largely unknown (Scott, 2022).
  3. Given the limited potential for connectivity between the Proposed Development and the breeding common tern population of the Forth Islands SPA (see above), together with any effects being largely intermittent across a relatively small spatial extent, it is considered that there is no potential for operational or maintenance related changes in prey availability to lead to an adverse effect on the Forth Islands SPA common tern population. This conclusion is consistent with the outcome of the EIA which concluded that effects from changes in prey availability on common terns during operation and maintenance were not significant in EIA terms (volume 2, chapter 11 of the Offshore EIA Report).
Project alone: conclusion
  1. Based upon the above, it is concluded that the effects from the Proposed Development alone would not result in an adverse effect on the Forth Islands SPA common tern population.
Effects in-combination
  1. As detailed above, any effects from the Proposed Development alone on the Forth Islands SPA common tern population during construction and decommissioning and during operation and maintenance will be small and highly localised. As such, there is considered to be no potential for effects from the Proposed Development to add to impacts at the population-level from the effects due to other plans and projects and, therefore, no potential for the Proposed Development to contribute to the in-combination effects associated with other plans and projects.

Assessment for the arctic tern population

  1. The Forth Islands SPA Arctic tern population occurs on the Isle of May, with the most recent count data available on the Seabird Monitoring Programme Database (Seabird Monitoring Programme | JNCC (bto.org)) giving an estimate of 832 (AON) in 2017. This is higher than the citation population size of 540 breeding pairs but represents a decline from previous counts (e.g. 908 AON were estimated in 2000). The SPA population is considered to be in ‘favourable declining’ condition.
The potential for impacts on the arctic tern population
  1. The Proposed Development and two kilometre buffer around the Proposed Development array area7 do not overlap with the Forth Islands SPA, so that potential impacts on its Arctic tern population will only occur as a result of individuals from the colony occurring in the area (or vicinity) of the Proposed Development. Consequently, the main focus of the assessment for this SPA population is concerned with the Conservation Objective to maintain, in the long term, the population of the species as a viable component of the site because the other conservation objectives either apply to the site itself, and not to areas beyond the boundary, or are encompassed by the assessment of this first Conservation Objective (as for the maintain in the long term no significant disturbance of the species, because disturbance would only be considered significant if it caused an adverse effect on the population viability of the qualifying features).
  2. Based on the estimated foraging range, it is unlikely that Arctic terns from the Forth Islands SPA will occur within the Proposed Development array to any extent during the breeding period, although they are likely to occur in waters through which the Proposed Development export cable corridor transits. This is because the Proposed Development array is 41 km from the Isle of May (where the Arctic tern colony is located) at its closest point, which is just beyond the mean maximum breeding season foraging range plus 1 SD for Arctic tern (i.e. 40.5 km – Woodward et al. 2019). This would suggest that there is little, or no, potential for the connectivity with the Proposed Development array. The Proposed Development export cable corridor is 21.4 km from the Isle of May at its closest point. The breeding period for Arctic tern is defined as May to August, following the NatureScot (2020) guidance.
  3. During the non-breeding season, the SPA Arctic tern population contributes to the wider BDMPS spring and autumn passage populations in the UK North Sea and Channel waters (Furness 2015), so there is potential for birds from this SPA population to pass through offshore wind farms in the North Sea at these times (including the Proposed Development).
Project alone: construction and decommissioning
Disturbance
  1. Direct disturbance to Arctic terns during the construction phase may arise as a result of increased vessel movements and helicopter activity, as well as from other activities associated with the installation of infrastructure associated with the Proposed Development. However, in large part, this will be limited to the increased vessel activity along the Proposed Development export cable corridor associated with the cable laying activities. This is because the Proposed Development array is beyond the likely foraging range of the SPA Arctic terns during the breeding season. The levels of such activities that could arise are outlined in Table 4.1, with these activities occurring during construction campaigns within a construction period of at most eight years duration.
  2. A total of up to 11,482 vessel round trips may occur over the construction phase, whilst it is estimated that a maximum of 134 vessels could occur within the area of the Proposed Development at any one time (Table 4.1). However, this is within the context of high baseline levels of vessel traffic within this area (e.g. surveys recorded an average of 14 vessels per day within a 10 nm buffer around the Proposed Development over a 14-day period in August 2022, whilst also showing an average of three to four vessels intersecting the Proposed Development array area per day over summer - Offshore EIA Report, volume 2, chapter 13).
  3. When using the marine environment (and not at the breeding colony), Arctic terns are considered to have a relatively low sensitivity to such sources of direct disturbance. Thus, reviews of the sensitivity of different seabird species to disturbance from vessels and helicopter traffic assign Arctic tern as ‘2’ on a five-scale ranking system, where 1 indicates hardly any or limited escape/avoidance behaviour and very short flight distance when approached and 5 indicates strong escape/avoidance behaviour and a large response distance (Garthe and Hüppop 2004, Furness et al. 2013).
  4. The total area to be affected by such disturbance over the full eight years of the construction phase also represents a small proportion of the total area of marine habitat available to Arctic terns from the Forth Islands SPA. Given that the Proposed Development array is beyond the likely breeding season foraging range of the SPA population, it is only the Proposed Development export cable corridor which is relevant in this regard. The total area encompassed by the Proposed Development offshore export cable is 168 km2. This represents 6.5% of the total breeding season foraging area that is potentially available to the SPA Arctic tern population, as defined by the generic measure of the species’ mean maximum breeding season foraging range plus 1 SD (i.e. 25.7±14.8 km - Woodward et al. 2019) and assuming that this range is represented by a semicircle to the (main) seaward side of the colony. If the breeding season foraging range is defined as above but based on the mean maximum value instead, the Proposed Development export cable corridor only encroaches on the edge of this range (because it is 21.4 km from the Isle of May at its closest point).
  5. During the non-breeding passage periods, Arctic tern distribution is not constrained by the location of the breeding colonies and birds from the SPA population are unlikely to make extensive, or protracted, use of the waters encompassed by the Proposed Development given that they migrate from, or to, their breeding areas during these periods. The breeding adult birds from the Forth Islands SPA population comprise only 1% of the passage period BDMPS for the UK North Sea and Channel waters (Furness 2015).
  6. In addition, it is important to consider that the construction activities will not occur simultaneously across the entirety of the Proposed Development export cable corridor but, rather, will be carried out in different areas at different times. Thus, cable laying for the Proposed Development export cable will occur over a total of two years, whilst within the Proposed Development array area it is likely that construction activities would be confined largely to discrete areas at any one time.
  7. The potential for disturbance effects during decommissioning is assumed to be the same (or less) as for construction, noting that the duration of the decommissioning phase will not exceed that of construction, and may be shorter.
  8. Given the relatively low sensitivity of Arctic tern to disturbance effects, the low levels of potential disturbance associated with the construction of the Proposed Development export cable corridor and the small areas subject to such activities at any given time during the construction period, and the fact that these potential effects will be temporary, it is considered that there is no potential for construction or decommissioning related disturbance to lead to an adverse effect on the Forth Islands SPA Arctic tern population.
Displacement
  1. As detailed above, Arctic tern is considered to have a relatively low sensitivity to disturbance, whilst potential effects of disturbance during the construction and decommissioning phases will only extend across a small part of the wider foraging areas used by the Forth Islands SPA population and be limited to the activities associated with the Proposed Development export cable corridor. Furthermore, as detailed above, potential effects of disturbance will not occur simultaneously across the entirety of the Proposed Development export cable corridor but, rather, will be carried out in different areas at different times. Thus, at any given time the potential for disturbance effects that could lead to displacement of Arctic terns from this SPA will be limited to relatively small areas, with the potential effects also being of a temporary nature.
  2. Given the above, it is considered that there is little potential for the Forth Islands SPA Arctic tern population to be affected by displacement during the construction or decommissioning phases, with any such effects only extending across relatively small areas and being temporary in nature. Consequently, it is considered that there is no potential for construction or decommissioning related displacement to lead to an adverse effect on the Forth Islands SPA Arctic tern population.
Changes to prey availability
  1. Key prey species for Arctic terns include small forage fish such as sandeel (del Hoyo et al., 1996). Indirect effects on Arctic terns may arise as a result of changes in the availability, distribution, or abundance of these species during the construction and decommissioning phases of the Proposed Development. Reduction or disruption to prey availability may cause displacement from foraging grounds or reduced energy intake, affecting survival rates or productivity in the Forth Islands SPA Arctic tern population in the short-term.
  2. During construction there are a number of ways in which effects on Arctic tern prey species could occur, which are as outlined in the section on Project Alone: Construction and Decommissioning – Changes to Prey Availability for the St Abb’s Head to Fast Castle SPA kittiwake population and in volume 2, chapter 9 of the Offshore EIA Report. However, as described above, the Proposed Development array is beyond the likely breeding season foraging range of the SPA population. Therefore, it is only the Proposed Development export cable corridor which are relevant in relation to potential changes in prey availability. As described above, the Proposed Development export cable corridor represents 6.5% of the total foraging area (25.7±14.8 km - Woodward et al., 2019), assuming that this range is represented by a semicircle to the (main) seaward side of the colony, although it is likely that most of the ‘at-sea’ foraging activity will occur within the smaller mean maximum foraging range (25.7 km - Woodward et al., 2019) which reaches the very edges of the Proposed Development export cable corridor . Effects during the non-breeding passage periods are considered to be further reduced given that breeding adults from the Forth Islands SPA comprise only 1% of the passage period BDMPS for the UK North Sea and Channel waters (Furness 2015).
  3. Given the relatively small degree of overlap between the Proposed Development and the potential foraging range of breeding Arctic terns from the Forth Islands SPA, together with any effects being intermittent, spatially-restricted and temporary in nature, it is considered that there is no potential for construction or decommissioning related changes in prey availability to lead to an adverse effect on the Forth Islands SPA Arctic tern population. This conclusion is consistent with the outcome of the EIA which concluded that effects from changes in prey availability on Arctic terns during construction and decommissioning were not significant in EIA terms (volume 2, chapter 11 of the Offshore EIA Report).
Project alone: operation and maintenance
Disturbance
  1. Vessel use within the Proposed Development array area and export cable corridor during the operation and maintenance phase may lead to direct disturbance of foraging Arctic terns (see section on Project Alone: Construction and Decommissioning – Disturbance for the SPA population and Table 4.1).
  2. However, given the relatively small degree of overlap between the Proposed Development and the potential foraging range of breeding Arctic terns from the Forth Islands SPA (see section on The Potential for Impacts on the Arctic Tern Population), the low sensitivity of Arctic terns to disturbance effects at sea (Garthe and Hüppop 2004; Furness et al., 2013), and the fact that these potential effects will be reduced compared to the construction and decommissioning phases, it is considered that there is no potential for disturbance during operation and maintenance to lead to an adverse effect on the Forth Islands SPA Arctic tern population. This conclusion is consistent with the outcome of the EIA which ‘screened’ out Arctic tern as a species for which detailed consideration of the effects of construction disturbance was required (volume 2, chapter 11 of the Offshore EIA Report).
Displacement/barrier effects
  1. Given that the Proposed Development array is beyond the likely breeding season foraging range of the Forth Islands SPA Arctic tern population, it is considered that there is little, or no, potential for effects of displacement or barrier effects to result. As such, it is considered that there is no potential for an adverse effect on this SPA population as a result of displacement/barrier effects.
Collision Risk
  1. Given that the Proposed Development array is beyond the likely breeding season foraging range of the Forth Islands SPA Arctic tern population, it is considered that there is little, or no, potential for effects of collision mortality to result.
  2. Collision estimates for Arctic terns during the non-breeding period totalled just 0.13 birds (as determined by the Scoping Approach - Offshore EIA Report, volume 3, appendix 11.3), whilst the adult birds from the SPA population represent only 1% of the UK North Sea and Channel waters BDMPS (Furness 2015).
  3. As such, it is considered that there is no potential for an adverse effect on this SPA population as a result of collision mortality.
Changes to prey availability
  1. Potential impacts on key prey species for Arctic terns breeding at Forth Islands SPA during the operation and maintenance phase have been assessed in volume 2, chapter 9 of the Offshore EIA Report using the appropriate maximum design scenarios for these receptors. Reduction or disruption to prey availability through temporary and long-term subtidal habitat loss/disturbance, increased SSC and deposition (which may also affect the ability of Arctic terns to detect prey at the sea surface), EMF from subsea electrical cabling could affect Arctic tern survival and productivity in the Forth Islands SPA population.
  2. Artificial structures introduced to the marine environment provide hard substrate for settlement of various organisms, which can increase local food availability for higher trophic levels. Whilst there is mounting evidence of potential benefits of artificial structures in marine environment (Birchenough and Degrae 2020), the statistical significance of such benefits and details about trophic interactions remain largely unknown (Scott, 2022).
  3. Given the relatively small degree of overlap between the Proposed Development and the potential foraging range of breeding Arctic terns from the Forth Islands SPA (see above), together with any effects being largely intermittent across a relatively small spatial extent, it is considered that there is no potential for operational or maintenance related changes in prey availability to lead to an adverse effect on the Forth Islands SPA Arctic tern population. This conclusion is consistent with the outcome of the EIA which concluded that effects from changes in prey availability on Arctic terns during operation and maintenance were not significant in EIA terms (volume 2, chapter 11 of the Offshore EIA Report).
Project alone: conclusion
  1. Based upon the above, it is concluded that the effects from the Proposed Development alone would not result in an adverse effect on the Forth Islands SPA Arctic tern population.
Effects in-combination
  1. As detailed above, any effects from the Proposed Development alone on the Forth Islands SPA Arctic tern population during construction and decommissioning and during operation and maintenance will be small and highly localised. As such, there is considered to be no potential for effects from the Proposed Development to add to impacts at the population-level from the effects due to other plans and projects and, therefore, no potential for the Proposed Development to contribute to the in-combination effects associated with other plans and projects.

Assessment for the guillemot population

  1. The Forth Islands SPA guillemot population occurs on several islands in the Firth of Forth. The largest colony occurs on the Isle of May, with smaller colonies on Craigleith, Bass Rock, Fidra and The Lamb. The Isle of May colony represents approximately 68% of the SPA total. The guillemot population size in the SPA declined during the early to late 2000’s, but has shown limited signs of recovery in more recent years and remains close to the citation population size of 32,000 breeding adult birds (Figure 5.21).

Figure 521:
Guillemot Population Trend at the Forth Islands SPA Between 1996 and 2020 (Noting that the Latest SPA Count is shown for 2020 because it Spans the Period 2018 – 2021). The Red Line Shows the Citation Population Size for the SPA (32,000 Individuals)13. Data are from the Seabird Monitoring Programme Database (Seabird Monitoring Programme | JNCC (bto.org))

Figure 521: Guillemot Population Trend at the Forth Islands SPA Between 1996 and 2020 (Noting that the Latest SPA Count is shown for 2020 because it Spans the Period 2018 – 2021). The Red Line Shows the Citation Population Size for the SPA (32,000 Individuals)13. Data are from the Seabird Monitoring Programme Database (Seabird Monitoring Programme | JNCC (bto.org))