Changes to prey availability

935. Potential impacts on key prey species for gannets 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 gannet survival and productivity in the Forth Islands SPA population.
936. 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).
937. Given their wide-ranging foraging behaviour and degree of plasticity in diet (del Hoyo et al., 1996), 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 gannet population. This conclusion is consistent with the outcome of the EIA which concluded that effects from changes in prey availability on gannets during operation and maintenance were not significant in EIA terms (volume 2, chapter 11 of the Offshore EIA Report).

Project alone: population-level impacts

938. As determined above, the effects from the Proposed Development alone which could lead to an adverse effect on the Forth Islands SPA gannet population are displacement (inclusive of barrier effects) and 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.
939. Given this, PVA was undertaken on the mortality to the adult and immature age classes predicted due to the combined displacement and collision effects associated with the Proposed Development, as determined by both the Scoping and Developer Approaches (see Tables 5.44 and 5.45 above). The population model for the SPA population was a stochastic, density independent, matrix model, based upon the demographic parameters specified in Table 2.7 of volume 3, appendix 11.6 of the Offshore EIA Report. The starting population size was the 2014 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 in the section on Project Alone: Population-Level Impacts for the St Abb’s Head to Fast Castle SPA kittiwake above (with further details provided in the the Offshore EIA Report, volume 3, appendix 11.6).
940. 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 5.46: Projected 35 Year Population Sizes and Associated PVA Metrics for the Forth Islands Gannet Population Under Different Impact Scenarios for the Proposed Development Alone

941. The PVA predicted that the Forth Islands SPA gannet 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 seven times larger than the current estimate of 150,518 adult birds under all scenarios, including baseline conditions which assume no wind farm effects (Table 5.46). 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 various impact scenarios are small.
942. The levels of increase in population size predicted by the PVA are highly unlikely to occur in reality and are, in part, a consequence of the absence of any compensatory density dependence within the population model (as discussed in the section on Project Alone: Population-level impacts for the St Abb’s Head to Fast Castle SPA kittiwake population). The prediction of a strongly increasing trend is consistent with the documented long-term trend for this SPA population (Figure 5.17) and, more widely, for breeding gannet populations across Scotland and the rest of the UK (Mitchell et al. 2004, Murray et al. 2015). However, it is likely that the availability of resources (possibly nesting sites on the Bass Rock – Murray et al. 2015) will limit further growth of the SPA population at some point within the next few years (and almost certainly within the 35 year timescale of the PVA projections). If this occurs, it is likely that there would remain considerable capacity for population regulation via the operation of compensatory density dependence, making it likely that the SPA population would remain stable despite increased levels of mortality.
943. The predicted population-level impacts are small, irrespective of whether these are determined using the Developer or Scoping Approaches. Thus, for the upper range of the Scoping Approach the CPS value indicates that the combined collision and displacement mortality associated with the Proposed Development alone would result in a reduction of approximately 4% in the size of the SPA population after 35 years, relative to that in the absence of any wind farm effects (Table 5.46). 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 44.0 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 lower range of the Scoping Approach and the Developer Approach suggest even smaller levels of impact (Table 5.46).

Project alone: conclusion

944. For both the Developer and Scoping Approaches, the potential effects from the Proposed Development alone on the Forth Islands SPA gannet 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

945. As detailed above, any effects from the Proposed Development alone on the Forth Islands SPA gannet population during construction and decommissioning and resulting from disturbance and 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.
946. Therefore, the potential for effects of the Proposed Development to act on the Forth Islands SPA gannet population in-combination with other plans and projects is limited to the displacement (inclusive of barrier effects) and collision risk effect pathways 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 the (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 in (noting that scenario (i) represents a ‘regional’ subset of (ii)).

Displacement/barrier effects – operation and maintenance

947. As described in volume 3, appendix 11.6, annex E of the Offshore EIA Report estimates of displacement mortality were not available for gannet from other Scottish offshore wind farm projects because displacement has not been considered to be an important source of potential mortality in the assessments for the more recent submissions of Scottish projects (e.g. Marine Scotland 2017a,b,c). Thus, to obtain breeding season estimates for projects in Scottish waters, the mean peak breeding season population sizes were extracted for the array areas plus 2 km buffers of the offshore wind farms in the Forth and Tay and Moray Firth development zones which were identified in the relevant assessments as having connectivity with the Forth Islands SPA population (as agreed through the Ornithology Roadmap process at meeting 6, 18th May 2022). Gannets from the Forth Islands SPA may also use the waters in and around the Dogger Bank wind farms during the breeding season (Wakefield et al. 2013, Lane et al. 2020), with the breeding season numbers for those sites extracted from MacArthur Green and Royal HaskoningDHV (2021) and an assumption made that 10% of these birds derive from the Forth Islands SPA population. Displacement mortality estimates for the breeding season were then calculated for each of these projects using the displacement and mortality rates appropriate to the Scoping and Developer Approaches (Table 5.44).
948. For the non-breeding periods, gannet numbers associated with other offshore wind farms that are in planning, consented, under construction or in operation were extracted for each of the relevant seasonal periods from the cumulative totals collated for the East Anglia TWO and East Anglia ONE North submissions (MacArthur Green and Royal HaskoningDHV 2021, see volume 3, appendix 11.6, annex E of the Offshore EIA Report for more details). The cumulative numbers for each of the autumn and spring passage periods were apportioned to the Forth Islands SPA gannet population according to the BDMPS approach as detailed in the assessment for the East Anglia THREE wind farm (MacArthur Green 2015, Royal HaskoningDHV et al. 2015). The subsequent displacement mortality was calculated according to the displacement and mortality rates appropriate to each of the Scoping and Developer Approaches (Table 5.44). This was done separately for all of the other UK North Sea wind farms and for the subset represented by the other Forth and Tay wind farms.

Table 5.47: Estimated Annual Mortality of Forth Islands SPA Gannets as a Result of Displacement from the Proposed Development Array Area and 2 km Buffer as Determined by the Scoping Approach and Developer Approach, In-Combination With Other Forth and Tay Wind Farms and UK North Sea Wind Farms

949. The incorporation of the potential mortality associated with the other plans and projects results in substantive increases in the mortality predicted due to displacement effects relative to that from the Proposed Development alone. Thus, the potential mortality of adult birds from the Proposed Development in-combination with the other Forth and Tay wind farms is more than three times greater than for the Proposed Development alone, whilst that from the in-combination with the other UK North Sea wind farms is approximately four and a half times greater than for the Proposed Development alone (Tables 5.44 and 5.47). Increases in the potential mortality amongst the immature age class (relative to that from the Proposed Development alone) for the in-combination with the Forth and Tay wind farms are of similar magnitude to that of the adults but are approximately 15 times greater for the in-combination with the other UK North Sea wind farms (although predicted mortality of immature birds remains low compared to that of adults). These levels of increase apply equally to the Scoping and Developer Approaches.
950. For the Proposed Development in-combination with the other Forth and Tay wind farms, the additional annual mortality of adult gannets from the Forth Islands SPA population predicted due to displacement represents 0.07% of the current adult breeding population at this colony (i.e. 150,518 individuals – Table 3.3 in volume 3, appendix 11.5 of the Offshore EIA Report) as determined by the Developer Approach, and between approximately 0.07 – 0.21% of this population as determined by the lower and upper estimates from 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 0.046 – see Table 2.7 in volume 3, appendix 11.6 of the Offshore EIA Report), the estimates of adult displacement mortality equate to an increase of 1.5% for the Developer Approach and of 1.5 – 4.6% for the lower and upper estimates from the Scoping Approach.
951. For the Proposed Development in-combination with the other UK North Sea wind farms, the additional annual mortality of adult gannets from the Forth Islands SPA population predicted due to displacement represents 0.09% of the current adult breeding population at this colony as determined by the Developer Approach, and between approximately 0.09 – 0.29% of this population as determined by the lower and upper estimates from the Scoping Approach. In terms of percentage increases in the baseline annual adult mortality of the population, the estimates of adult displacement mortality equate to an increase of 2.1% for the Developer Approach and of 2.1 – 6.2% for the lower and upper estimates from the Scoping Approach.
952. The potential levels of impact on the Forth Islands SPA gannet population resulting from the mortality predicted from displacement and barrier effects associated with the Proposed Development in-combination with either the other Forth and Tay wind farms or the other UK North Sea wind farms during the operation and maintenance phase are considered in more detail below in the In-combination: Population-Level Impacts section. This presents the outputs from PVAs of the combined effects of predicted displacement and collision mortality on the SPA population.

Collision risk - operation and maintenance

953. Breeding season collision estimates attributed to the Forth Islands SPA gannet population were extracted from existing assessments for offshore wind farms that are in planning, consented, under construction or in operation (volume 3, appendix 11.6, annex E of the Offshore EIA Report). As stated above, gannets from the Forth Islands SPA may also use the waters in and around the Dogger Bank wind farms during the breeding season (Wakefield et al. 2013, Lane et al. 2020), with the breeding season numbers for those sites extracted from MacArthur Green and Royal HaskoningDHV (2021) and an assumption made that 10% of these birds derive from the Forth Islands SPA population.
954. For the non-breeding periods, collision estimates for other offshore wind farms that are in planning, consented, under construction or in operation were derived from the information collated in the East Anglia TWO and East Anglia ONE North submissions (MacArthur Green and Royal HaskoningDHV 2021), with the collision numbers for some projects updated using more recent design information where required (volume 3, appendix 11.6, annex E of the Offshore EIA Report). These collision estimates were apportioned to the SPA population according to the BDMPS approach as detailed in the assessment for the East Anglia THREE wind farm (MacArthur Green 2015, Royal HaskoningDHV et al. 2015).
955. Collision estimates based on consented and ‘as-built’11 designs were also considered but for the current SPA population this did not affect the collision estimates for the other Forth and Tay wind farms and had minimal effects on those for the other UK North Sea wind farms (with the respective totals differing by approximately four adult birds, representing less than 1% of the in-combination totals). Therefore, only the estimates for the consented designs are considered in this case.
956. In contrast to the displacement estimates derived for the other plans and projects, existing collision estimates for these plans and projects were not adjusted to align with the Scoping Approach of using the maximum (rather than the mean) monthly estimate of the density of birds in flight (with all of the other projects likely to have followed the ‘standard’ approach of using the mean density). Such an adjustment would require the re-calculation of the CRMs for each project, which would not be feasible in many cases because of the difficulty in accessing the appropriate baseline data.
957. As for displacement, the potential mortality estimates derived for the other projects were combined with those for the Proposed Development to give estimates 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 according to both the Scoping Approach and Developer Approach (noting that for the Scoping Approach it is only the estimates for the Proposed Development that are calculated according to this approach) (Table 5.48).

Table 5.48 Predicted Collision Effects on the Forth Islands SPA Gannet Population due to the Proposed Development In-Combination with Other Wind Farms in the Forth and Tay and in UK North Sea Waters. Estimates are Presented for both the Scoping Approach and Developer Approach

958. As with the displacement effects, the incorporation of the potential collisions associated with the other plans and projects results in substantive increases in the predicted collision mortality relative to that from the Proposed Development alone. Thus, the potential mortality of adult birds from the Proposed Development in-combination with the other Forth and Tay wind farms is three to four times greater than for the Proposed Development alone (depending on whether the Scoping or Developer Approaches are considered), whilst that from the in-combination with the other UK North Sea wind farms is approximately five times greater than for the Proposed Development alone for both the Scoping and Developer Approaches (Tables 5.45 and 5.48). The predicted mortality amongst the immature age class also increases markedly compared to that for the Proposed Development alone (for both the Scoping and Developer Approaches), with this increase particularly marked for the UK North Sea in-combination scenario (due to the higher levels of mortality apportioned to this age class during the passage periods).
959. For the Proposed Development in-combination with the other Forth and Tay wind farms, the additional annual mortality of adult gannets from the Forth Islands SPA population predicted due to collisions represents 0.32% of the current adult breeding population at this colony (i.e. 150,518 individuals – Table 3.3 in volume 3, appendix 11.5 of the Offshore EIA Report) as determined by the Developer Approach, and between approximately 0.34% of this population 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 0.046 – see Table 2.7 in the Offshore EIA Report, volume 3, appendix 11.6), the estimates of adult collision mortality equate to an increase of 6.9% for the Developer Approach and of 7.3% for the estimates from the Scoping Approach.
960. For the Proposed Development in-combination with the other UK North Sea wind farms, the additional annual mortality of adult gannets from the Forth Islands SPA population predicted due to collisions represents 0.43% of the current adult breeding population at this colony (i.e. 150,518 individuals – Table 3.3 in volume 3, appendix 11.5 of the Offshore EIA Report) as determined by the Developer Approach, and between approximately 0.46% of this population 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 0.046 – see Table 2.7 in the Offshore EIA Report, volume 3, appendix 11.6), the estimates of adult collision mortality equate to an increase of 9.5% for the Developer Approach and of 9.9% for the estimates from the Scoping Approach.
961. The potential levels of impact on the Forth Islands SPA gannet population resulting from the predicted collision mortality associated with the Proposed Development in-combination with either the other Forth and Tay wind farms or the other UK North Sea wind farms during the operation and maintenance phase are considered in more detail below in the In- combination: Population-Level Impacts section. This presents the outputs from PVAs of the combined effects of predicted displacement and collision mortality on the SPA population.

In-combination: population-level impacts

962. As for the Proposed Development alone, PVA was undertaken on the mortality to the adult and immature age classes predicted due to the combined displacement and collision effects associated with the Proposed Development in-combination with the other Forth and Tay wind farms and the Proposed Development in-combination with the other North Sea wind farms. This was on the basis of the potential mortality as determined by both the Scoping and Developer Approaches (see Tables 5.47 and 5.48 above).
963. The approach to the PVA and the metrics used to summarise the PVA outputs are as described for the Proposed Development alone (see Project Alone: Population-Level Impacts section above).

Table 5.49: Projected 35 Year Population Sizes and Associated PVA Metrics for the Forth Islands SPA Gannet Population Under Different Impact Scenarios for the Proposed Development In-Combination with the Other Forth and Tay Wind Farms

Table 5.50: Projected 35 Year Population Sizes and Associated PVA Metrics for the Forth Islands SPA Gannet Population Under Different Impact Scenarios for the Proposed Development In-Combination with the Other UK North Sea Wind Farms

964. Given the increase in the scale of the effects (from both displacement and collisions) for the in-combination scenarios compared to the Proposed Development alone, the PVA metrics for the Proposed Development in-combination with either the other Forth and Tay wind farms or the other UK North Sea wind farms suggest substantially greater population-level impacts than as predicted for the Proposed Development alone (compare Table 5.46 with Tables 5.49 and 5.50). However, the PVAs continue to predict a strongly increasing population trend, despite this substantive increase in the scale of the effects.
965. For the Proposed Development in-combination with the other Forth and Tay wind farms, the CPS value for the upper range of the Scoping Approach (i.e. B) indicates that the SPA population size would be reduced by almost 14% relative to that in the absence of any wind farm effects (Table 5.49). The reduction in annual population growth rate (relative to that predicted under baseline conditions) remains small (at 0.4%), whilst the centile value of 30.6 suggests a moderate degree of overlap in the distributions of the predicted impacted and un-impacted population sizes and, hence, a reasonable likelihood of the impacted population being of a similar size to the un-impacted population after 35 years. The levels of impact on the population predicted by the Developer Approach (and also the lower range of the Scoping Approach) are smaller than this.
966. For the Proposed Development in-combination with the other UK North Sea wind farms, the PVA metrics associated with the Developer Approach are similar in value to those described above for the upper range of the Scoping Approach as derived from the Forth and Tay in-combination scenario (Table 5.50). The values for the metrics obtained on the basis of the Scoping Approach indicate reductions of 15 – 20% in population size after 35 years relative to that in the absence of any wind farm effects, with slightly greater reductions in the annual population growth rates (relative to the baseline situation) than predicted for the Forth and Tay in-combination scenario. The centile values (21.9 – 28.5) suggest low to moderate overlap in the distributions of the predicted impacted and un-impacted population sizes and, hence, a reasonably high chance of the impacted population being smaller than the un-impacted population after 35 years.
967. As detailed above, the Forth Islands SPA gannet population has shown a marked, and consistent, long-term increase in size (Figure 5.17). This reflects the wider trend in gannet populations across Scotland and the rest of the UK, whilst earlier count data indicate that the period of rapid increase in the Forth Islands SPA population extends back to the 1950s or 1960s (Mitchell et al. 2004, Murray et al. 2015, Natural England 2020). Based on the data in Figure 5.17, the annual growth rate of the Forth Islands SPA population averaged approximately 4.4% between 1985 and 2014. If this growth rate was to be maintained over the 35 year operation and maintenance period for the Proposed Development, the Forth Islands SPA population would still be more than three and half times larger than currently even when accounting for the 0.6% reduction in annual growth rate, as predicted by the upper range of the Scoping Approach for the Proposed Development in-combination with the other UK North Sea wind farms (Table 5.50). The mean annual growth rate for the SPA population under baseline conditions (i.e without any wind farm effects) would have to decrease to below 0.6% for this predicted impact to result in the population declining below its current level over the 35 year operation and maintenance period.
968. As already discussed in the section on Project Alone: Population-Level Impacts for this SPA population, it seems likely that the availability of resources will limit further growth of this SPA population at some point within the 35 year operation and maintenance period for the Proposed Development. If this occurs, it is likely that there would remain a considerable capacity for population regulation via the operation of compensatory density dependence, particularly given the evidence for environmental conditions remaining highly suitable for the SPA (and other gannet) population(s) over the long term. Thus, it is likely that the SPA population would remain stable despite increased levels of mortality (at least of a scale which could potentially occur as a result of the effects from the Proposed Development in-combination with the other UK North Sea wind farms).
969. As for the assessments of the St Abb’s Head to Fast Castle SPA populations presented above, the assessment of the Forth Islands SPA gannet population incorporates high levels of precaution, which extend beyond the differences between the Developer and Scoping Approaches that are outlined above (and detailed in the Offshore EIA Report, volume 3, appendices 11.3 and 11.4). This includes the reliance on PVAs which are based on density independent population models, as already considered in relation to the expectation that compensatory density dependence would offset increased mortality resulting from the predicted effects. In addition, and of particular relevance to the gannet assessment, the avoidance rate used with the CRM relates to behaviour within the wind farm array only and excludes consideration of macro-avoidance, which is likely to be high for gannet (Cook et al. 2014, Cook 2021, Peschko et al. 2021). This issue is now recognised in recent advice from Natural England, which recommends the application of a macro-avoidance correction for gannet (ranging from 65 – 85%) to reduce the estimated density of birds in flight within the array area (Natural England 2022b)[14]. This would (obviously) substantially reduce the collision estimates and, hence, the scale of the predicted population-level impacts. In relation to the estimation of displacement effects, as for other species, these are based upon the seasonal mean peak abundance estimates (which are substantially higher than the seasonal mean values).

In-combination: conclusion

970. On the basis of the Developer Approach, the potential effects from the Proposed Development in-combination with the other Forth and Tay wind farms or the other UK North Sea wind farms on the Forth Islands SPA gannet population are predicted to be relatively small, with the resultant population-level impacts also predicted to be relatively small. In addition, the PVA metrics indicate that it is at least reasonably likely that the population would be of a similar size to that which would occur in the absence of the Proposed Development after 35 years. Considering this within the context of a highly precautionary assessment and a population that has shown a strongly increasing trend over the long term, it is concluded that these in-combination scenarios would not result in adverse effect on the Forth Islands gannet population.
971. The above conclusion is also considered to apply to the levels of impact as determined by the Scoping Approach. For the Scoping Approach, the predicted reductions in population size are greater, whilst it is also likely that the impacted population will be smaller than the un-impacted population after 35 years (for the UK North Sea in-combination scenario). However, when these predicted levels of impacts are considered within the context of the precaution incorporated within the assessment and the status and long-term, strongly increasing, trend of the SPA population, as well as the consequences in terms of population growth rates, it is concluded that they would not lead to an adverse effect.

Assessment for the kittiwake population

972. The Forth Islands SPA kittiwake population is distributed across 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 holds approximately 75% of the total SPA population. The kittiwake population has declined in number since the SPA was designated (Figure 5.18), with the SPA counts being below the citation population size in all but two years since the mid-1980s. Counts from 2013 provide a tentative indication of some stabilisation in the SPA population size, albeit at a level well below the citation size.

Figure 518: Kittiwake Population Trend at the Forth Islands SPA Between 1986 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 (6,600 pairs). Data are from the Seabird Monitoring Programme Database (Seabird Monitoring Programme | JNCC (bto.org))

The potential for impacts on the kittiwake population

973. 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 kittiwake 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).
974. From published information on kittiwake foraging ranges generally (Woodward et al. 2019) and tracking from the SPA specifically (Wakefield et al. 2017, Bogdanova et al. 2022), it is apparent that during the breeding period kittiwakes from the Forth Islands SPA occur within the area of the Proposed Development and of the two km buffer around the Proposed Development array. This is reflected in the findings of the apportioning exercise, which estimates that approximately 6% of the kittiwakes 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 kittiwake is defined as mid-April to August, following the NatureScot (2020) guidance.
975. For the reasons described for the St Abb’s Head to Fast Castle SPA kittiwake population, during the non-breeding season there is likely to be the potential for kittiwake from the Forth Islands SPA to pass through offshore wind farms in the North Sea during the autumn and spring passage periods (defined as September to December and January to mid-April, 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). Given the above, the Proposed Development may have potential effects on the Forth Islands SPA kittiwake population during breeding and non-breeding periods.

Project alone: construction and decommissioning

Disturbance

976. Direct disturbance to kittiwakes during the construction phase may arise within the Proposed Development array area (and its immediate vicinity) as a result of increased vessel movements and helicopter activity, as well as from other activities directly associated with the installation of the wind turbine foundations and other infrastructure, whilst there will also be increased vessel activity along the Proposed Development export cable corridor due to the cable laying activities. 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.
977. 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).
978. When using the marine environment (and not at the breeding colony), kittiwakes 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 kittiwake 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).
979. 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 kittiwakes from the Forth Islands SPA. Thus, the Proposed Development array area encompasses 1,010 km2, whilst the Proposed Development export cable corridor encompasses 168 km2. Together these areas represent less than 1% of the total breeding season foraging area that is potentially available to the SPA kittiwake population, as defined by the generic measure of the species’ mean maximum breeding season foraging range plus 1 SD (i.e.156.1±144.5 km - Woodward et al. 2019) and assuming that this range is represented by a semicircle to the (main) seaward side of the colony. Similarly, the Proposed Development array and export cable corridor represent approximately 3% of the breeding season foraging area if considering the mean maximum foraging range only.
980. Tracking data (and associated modelling of foraging distributions) for kittiwake show that the Proposed Development array area and Proposed Development export cable corridor overlap with, or occur close to, waters that are heavily used by birds from the Forth Islands SPA during the breeding season (Cleasby et al. 2018, Bogdanova et al. 2022). However, the degree of overlap is limited and excludes those areas of heaviest usage. For example, based on the data from 50 birds tracked from this SPA population during the 2021 breeding season, the Proposed Development array area does not overlap with the core foraging area of the tracked birds (as defined by the 50% utilisation distribution), and overlaps with only 0.4% of the core ‘resting at sea’ area (Bogdanova et al. 2022). The overlaps between the Proposed Development array area and the wider foraging and ‘resting at sea’ areas of these tracked birds (as defined by the respective 90% utilisation distributions) represented 13% and 17% of these wider areas, respectively. Although a high proportion of these 50 birds (i.e. 72%) were recorded in flight through the Proposed Development array area at some point during the tracking period, only 8% of the 2,271 fight tracks were recorded doing so (Bogdanova et al. 2022).
981. During the non-breeding periods, kittiwake distribution is not constrained by the location of the breeding colonies and birds from the SPA population are likely to occur across large expanses of oceanic and maritime waters (Frederiksen et al. 2012, Furness 2015) and the potential for effects of construction-related disturbance is lower than during the breeding season.
982. In addition, it is important to consider that the construction activities will not occur simultaneously across the entirety of the Proposed Development array area or the Proposed Development export cable corridor but, rather, will be carried out in different areas at different times. Thus, the activities will be concentrated within discrete (often small) parts of these wider areas, and within such areas they will not extend over the full duration of the construction phase, so further reducing the potential to which birds may be subject to disturbance effects. For example, 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.
983. 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.
984. Given the low sensitivity of kittiwake to disturbance effects, the relatively small areas that will be subject to activities with the potential to result in disturbance 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 kittiwake population. This conclusion is consistent with the outcome of the EIA which ‘screened’ out kittiwake 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

985. As detailed above, kittiwake is considered to have a 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 kittiwake population and be limited to, at most, an eight year period during construction (and a likely similar or shorter period during decommissioning). Furthermore, as detailed above, potential effects of disturbance will not occur simultaneously across the entirety of the Proposed Development array area or 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 kittiwakes from this SPA will be limited to relatively small areas, with the potential effects also being of a temporary nature.
986. Therefore, based upon the above, it is considered that there is relatively little potential for the Forth Islands SPA kittiwake population to be affected by displacement during the construction or decommissioning phases, with any such effects only extending across relatively small areas and tending to be 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 kittiwake population. This conclusion is consistent with the outcome of the EIA which ‘screened’ out kittiwake as a species for which detailed consideration of the effects of construction-related displacement was required (volume 2, chapter 11 of the Offshore EIA Report).

Changes to prey availability

987. Key prey species for kittiwakes include sandeel and sprat (del Hoyo et al., 1996). Indirect effects on kittiwakes 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 kittiwake population in the short-term.
988. During construction and decommissioning there are a number of ways in which effects on key prey species of seabirds may occur, which are 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 same evidence basis and context applies to the Forth Islands SPA kittiwake population as to the St Abb’s Head to Fast Castle SPA population in relation to the potential for such effects to lead to impacts on the population.
989. Given this, it is considered that there is relatively little potential for the Forth Islands SPA kittiwake population to be affected by changes to prey availability during the construction and decommissioning phases, with any such effects being largely intermittent across a relatively small spatial extent, with most effects temporary in nature. Consequently, 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 kittiwake population.

Project alone: operation and maintenance

Disturbance

990. Vessel use and associated activities within the Proposed Development array area and export cable corridor during the operation and maintenance phase may lead to direct disturbance of kittiwakes from Forth Islands SPA. As described in the section on Project Alone: Construction and Decommissioning – Disturbance for the SPA population, kittiwakes are considered to have a relatively low sensitivity to such sources of direct disturbance at sea (Garthe and Hüppop 2004, Furness et al., 2013).
991. The maximum design scenario is for up to 3,393 vessel round trips per year over the operational lifetime of the project. Vessel types which will be required during the operation and maintenance phase include those used during routine inspections, repairs and replacement of equipment, major component replacement, painting or other coatings, removal of marine growth, replacement of access ladders, and geophysical surveys (Table 4.1).
992. Based on information presented in the Project Alone: Operation and Maintenance – Disturbance for the St Abb’s Head to Fast Castle SPA kittiwake population and in the Offshore EIA Report, volume 2, chapter 13, baseline levels of vessel traffic in the Offshore Ornithology study area are relatively high. In the context of the baseline levels of vessel traffic across the Offshore Ornithology study area, the increase during the operation and maintenance phase is considered to be relatively small. Vessel movements will be within the Proposed Development array area and export cable corridor and will follow existing shipping routes to/from ports. In addition, Project Codes of Conduct included as a part of the NSVMP (Offshore EIA Report, volume 4, appendix 25) will be issued to all project vessel operators to avoid sudden changes in course or speed which will minimise the potential for disturbance. Within the Proposed Development array area, movements and associated maintenance activities will be restricted to individual wind turbines over a period of days to weeks.
993. The size and noise outputs from vessels during the operation and maintenance phase will be similar to those used in the construction phase. However, the number of vessel return trips per year and their frequency will be much lower for the operation and maintenance phase compared to the construction phase. In addition, activities during the operation and maintenance phase will not occur simultaneously across the entirety of the Proposed Development array area and export cable corridor but intermittently within discrete (often very small) parts of these wider areas.
994. Given the discrete areas relative to the species’ foraging range that will be subject intermittently to potential disturbance from vessel use and maintenance activities (Woodward et al., 2019), 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 kittiwake population.

Displacement/barrier effects

995. As outlined above, the SNCB matrix approach provides the basis for estimating displacement effects on seabird species in this assessment, with this approach assumed to also incorporate the impact of barrier effects within the estimates that are derived (SNCBs 2022, Offshore EIA Report, volume 3, appendix 11.4). Thus, throughout this section, mortality from displacement is assumed to refer to that which results from both displacement and barrier effects. The approach used to derive predicted levels of mortality is as described in the section on Project Alone: Operation and Maintenance – Displacement/Barrier Effects for the St Abb’s Head to Fast Castle SPA kittiwake population above (and in the Offshore EIA Report, volume 3, appendix 11.4).
996. On the basis of the advice provided in the Scoping Opinion (volume 3, appendix 6.2 of the Offshore EIA Report), displacement effects on kittiwake are estimated for the breeding and non-breeding periods, with the latter separated into autumn and spring passage periods (Offshore EIA Report, volume 3, appendix 11.5). The displacement and associated mortality rates advised in the Scoping Opinion (subsequently termed the Scoping Approach) for kittiwake are:

• Breeding period: 30% displacement with lower and upper mortality rates of 1% and 3%.
• Non-breeding periods: 30% displacement with lower and upper mortality rates of 1% and 3%.
  997. However, the approach to estimating kittiwake displacement effects advocated by the Scoping Opinion was considered overly precautionary in relation to the upper mortality rate used and the incorporation of mortality effects in the non-breeding periods, as detailed in volume 3, appendix 11.4, annex G of the Offshore EIA Report. In particular, it represented a marked change from the assumptions applied in assessments for other recent Scottish offshore wind farms (Marine Scotland 2017a,b,c) with no clear evidence apparently being available to justify such a change. Thus, based on a consideration of the available evidence for kittiwake displacement, the extent of the species’ ranging behaviour (particularly in the non-breeding periods), previous precedent and a need to incorporate precaution within the assessment, an alternative Developer Approach to estimating displacement effects was determined (volume 3, appendix 11.4, annex G of the Offshore EIA Report). The rates adopted by the Developer Approach are:
• Breeding period: 30% displacement with a mortality rate of 2%.
• Non-breeding periods: No measurable effects of displacement on mortality.
  998. Estimates of kittiwake mortality were produced using the SNCB matrix on the basis of both the Scoping Approach and the Developer Approach (Offshore EIA Report, volume 3, appendix 11.4), with these estimates then apportioned to the Forth Islands SPA kittiwake population during the breeding and non-breeding periods according to the MS Apportioning Tool (Butler et al. 2020) and the BDMPS approach (Furness 2015), respectively (Offshore EIA Report, volume 3, appendix 11.5, Table 5.51). The resulting mortality estimates for the breeding period were apportioned to age classes on the basis of the plumage characteristics of kittiwakes recorded during the breeding period in the baseline surveys (Offshore EIA Report, volume 3, appendix 11.1), whilst for the non-breeding periods age classes were apportioned according to the stable age distributions of the population model used in Furness (2015). Based on advice provided by NatureScot and Marine Scotland Science following Roadmap Meeting 4 (G. Holland, email 26/01/2022), it was also assumed that 10% of the breeding adults in the SPA population miss breeding in any given year (i.e. sabbatical birds) so that the number of estimated adult deaths during the breeding season was adjusted accordingly.

Table 5.51: The Mean Peak Abundance Estimates Of Kittiwake in the Proposed Development Array Area and 2 km Buffer for Each Seasonal Period, Together with the Proportion of Birds Estimated to Belong to the Breeding Adult Age Class and to be from the Forth Islands SPA Population in Each Period. The Proportion of Adults Assumed to be Sabbaticals During the Breeding Season is also Presented

999. Based upon the estimates and assumptions detailed above, the potential annual mortality amongst the SPA kittiwake population as a result of displacement is estimated as four adult and 0.3 immature birds based on the lower mortality rates for the Scoping Approach (i.e. Scoping Approach A) and as 11 adult and one immature birds based upon the higher mortality rates for the Scoping Approach (i.e. Scoping Approach B) (Table 5.52). As expected on the basis that kittiwakes from this breeding colony SPA use the waters within the vicinity of the Proposed Development array area during the breeding season (and as reflected by the seasonally-specific apportioning rates), the displacement effects predicted by the Scoping Approach are largely attributable to the breeding season (with the potential breeding season mortality accounting for almost 85% of the overall annual mortality – Table 5.52).
1000. The annual mortality from displacement as determined using the Developer Approach is predicted to be approximately six adult and 0.2 immature birds, so lies midway between the mortality predictions from the Scoping Approach and is entirely attributable to breeding season effects (on the basis that displacement effects on kittiwake during the non-breeding periods are considered unlikely to result in detectable impacts on the population – volume 3, appendix 11.4, annex G of the Offshore EIA Report).

Table 5.52: Estimated Potential Annual Mortality of Forth Islands SPA Kittiwakes as a Result of Displacement from the Proposed Development Array Area and 2 km Buffer as Determined by the Scoping Approach and Developer Approach

1001. The additional annual mortality of adult kittiwakes from the Forth Islands SPA population predicted due to displacement from the Proposed Development array represents 0.07% of the current adult breeding population at this colony (i.e. 9,034 individuals – Table 3.3 in volume 3, appendix 11.5 of the Offshore EIA Report) as determined by the Developer Approach, and between approximately 0.04 – 0.12% of this population as determined by the lower and upper estimates from 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 0.145 – see Table 2.13 in volume 3, appendix 11.6 of the Offshore EIA Report), the estimates of adult mortality equate to an increase of 0.5% for the Developer Approach and of 0.27 – 0.82% for the lower and upper estimates from the Scoping Approach.
1002. The potential levels of impact on the Forth Islands SPA kittiwake population resulting from the mortality predicted from displacement and barrier effects associated with the Proposed Development array during the operation and maintenance phase are considered in more detail below in the Project Alone: Population-Level Impacts section. This presents the outputs from PVAs of the combined effects of predicted displacement and collision mortality on the SPA population.

Collision risk

1003. Predictions of the number of kittiwakes 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 11.3). Following the Scoping Opinion (volume 3, appendix 6.2 of the Offshore EIA Report), the assessment is based on option 2 of the CRM, which uses the generic flight height data from Johnston et al. (2014a,b) and assumes a uniform distribution of flight heights across the rotor swept zone (as opposed to using the modelled flight height distribution) (Band 2012). An avoidance rate of 98.9% was applied to these CRM outputs, as recommended for kittiwake (SNCBs 2014) and as advised by the Scoping Opinion.
1004. As detailed for the St Abb’s Head to Fast Castle SPA kittiwake population, 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 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 Forth Islands SPA kittiwakes were undertaken following:

• The Scoping Approach of using the maximum monthly densities, and
• The Developer Approach of using the mean monthly densities.
  1005. As for the St Abb’s Head to Fast Castle SPA kittiwake population, collision estimates were also calculated:
• Using option 2 of the deterministic version of the CRM but with site-specific flight height data from boat-based surveys of the Proposed Development array area10 (as opposed to the generic flight height data of Johnston et al. 2014a,b).
• 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), noting that option 3 of the CRM uses the modelled flight height distributions from Johnston et al. (2014a,b).
  1006. These additional collision estimates are not used as the basis of the assessments on the SPA kittiwake populations but, instead, are used in a comparative way to illustrate the extent to which some estimates may vary according to certain of the key assumptions on which they are based. Details of these additional CRMs are provided in annex B and annex C of the Offshore EIA Report, volume 3, appendix 11.3.
  1007. As for the predicted displacement effects, kittiwake collision estimates are calculated for the breeding and non-breeding periods, with the latter separated into autumn and spring passage periods (Offshore EIA Report, volume 3, appendix 11.5). Estimates were apportioned to the Forth Islands SPA population during the breeding and non-breeding periods according to the MS Apportioning Tool (Butler et al. 2020) and the BDMPS approach (Furness 2015), respectively (Offshore EIA Report, volume 3, appendix 11.5, Table 5.51). The age class proportions and assumptions on sabbatical rates are also as detailed above in relation to displacement effects (Table 5.51).
  1008. Based upon option 2 of the deterministic CRM with a 98.9% avoidance rate applied, and in conjunction with the estimates and assumptions detailed above, the annual collision mortality of kittiwakes from the Forth Islands SPA is predicted to be approximately 33 adults and two immatures as determined by the Scoping Approach, and approximately 23 adults and two immatures as determined by the Developer Approach (Table 5.53). As for displacement, the vast majority of this mortality (i.e. over 90%) is predicted to occur during the breeding season.

Table 5.53: Predicted Collision Effects from the Proposed Development on the Forth Islands SPA Kittiwake 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 98.9% Avoidance Rate (see text)

1009. The additional annual mortality of adult kittiwakes from the Forth Islands SPA population predicted due to collisions with wind turbines in the Proposed Development array represents approximately 0.25% of the number of adults currently estimated to breed at this colony (i.e. 9,034 individuals – Table 3.3 in volume 3, appendix 11.5 of the Offshore EIA Report) as determined by the Developer Approach and approximately 0.36% 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 0.145 – see Table 2.13 in volume 3, appendix 11.6 of the Offshore EIA Report), the predicted adult collision mortality equates to increases of 1.7% and 2.5% for the Developer and Scoping Approaches, respectively.
1010. As outlined in the Project Alone: Operation and Maintenance - Collision Risk section for the St Abb’s Head to Fast Castle SPA kittiwake population, using the collision estimates derived from the site-specific flight height data or from the stochastic CRM with avoidance rates as calculated for the bird collision-avoidance study (Bowgen and Cook 2018) would result in predicted collision mortalities on the Forth Islands SPA kittiwake population that are at least 50% lower than those presented in Table 5.53 above (and on which the assessment is based).
1011. More detailed consideration of the potential population-level impacts associated with the predicted collision mortalities in Table 5.53 is undertaken below in the Project Alone: Population-Level Impacts section, which presents the outputs from PVAs of the combined effects of predicted displacement and collision mortality on the SPA population.