Changes to prey availability
  1. Potential impacts on key prey species for kittiwakes breeding at the 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 kittiwake survival and productivity in the Forth Islands SPA kittiwake population.
  2. The same evidence basis and context in relation to this effect pathway for the operation and maintenance phase applies to the Forth Islands SPA kittiwake population as to the St Abb’s Head to Fast Castle SPA kittiwake population. This is detailed in the section on Project Alone: Operation and Maintenance – Changes to Prey Availability for the St Abb’s Head to Fast Castle SPA population.
  3. 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 operation and maintenance phase, with any such effects being largely intermittent across a relatively small spatial extent. Consequently, 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 kittiwake population.
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 kittiwake 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.
  2. 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 5.52 and 5.53 above). The population model for the SPA population was a stochastic, density independent, matrix model, based upon the demographic parameters specified in Table 2.13 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 in the section on Project Alone: Population-Level Impacts for St Abb’s Head to Fast Castle SPA kittiwake population 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 5.54:
Projected 35 Year Population Sizes and Associated PVA Metrics for the Forth Islands SPA Kittiwake Population Under Different Impact Scenarios for the Proposed Development Alone

Table 5.54: Projected 35 Year Population Sizes and Associated PVA Metrics for the Forth Islands SPA Kittiwake Population Under Different Impact Scenarios for the Proposed Development Alone

 

  1. The PVA predicted a continuing population decline for the Forth Islands SPA kittiwake population, irrespective of the effects from the Proposed Development. Thus, under baseline conditions (i.e. no wind farm effects), the population is predicted to decline by 73% after 35 years from the current estimate of 9,034 adult birds (Table 5.54). Given that 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 predicted declines are inevitably greater for those scenarios incorporating the effects from the Proposed Development.
  2. Considering the PVA metrics, the CPS values indicate that the SPA population size would be reduced by approximately 9% and 11 – 13%, relative to the predicted population size under baseline conditions, after 35 years for the Developer Approach and Scoping Approach, respectively (Table 5.54). Reductions in the annual population growth rate (relative to that predicted under baseline conditions) are estimated to be approximately 0.3% on the basis of the Developer Approach and 0.3 – 0.4% on the basis of the Scoping Approach (Table 5.54). On the basis of the Developer Approach, the centile value is estimated to be almost 43 after 35 years, whilst for the Scoping Approach the equivalent values are 39.0 – 40.7 (Table 5.54). Thus, overall, the centile metric indicates considerable overlap in the distribution of the predicted impacted and un-impacted population sizes, suggesting a high likelihood of the impacted population being of similar size to the un-impacted population after 35 years, irrespective of whether the effects are estimated using the Developer or Scoping Approaches.
  3. The PVA outputs described above, and detailed in Table 5.54, need to be considered within the context of the fact that the SPA population is predicted to decline irrespective of the wind farm effects and that such a trend is broadly consistent with the documented long-term trend for this population, albeit that there is some suggestion of a levelling off in this decline over the past decade (Figure 5.18). As described in the Project Alone: Population-Level Impacts section for the St Abb’s Head to Fast Castle SPA kittiwake population, the available evidence suggests that the long-term decline of kittiwake populations in the North Sea and the Forth and Tay region (including the Forth Islands SPA) is associated with fisheries management and climate change (Frederiksen et al. 2004). Therefore, without appropriate management to mitigate these effects, it is likely that the Forth Islands SPA population will remain in unfavourable condition and that the predicted effects from the Proposed Development may be unimportant in this regard. Furthermore, it is also relevant to consider the high levels of precaution incorporated within the assessment, particularly as determined by the Scoping Approach (with this also detailed in the Project Alone: Population-Level Impacts section for the St Abb’s Head to Fast Castle SPA kittiwake population).
Project alone: conclusion
  1. Overall, it is considered that the predicted levels of impact from the Proposed Development alone on the Forth Islands SPA kittiwake population are of a small (for the Developer Approach) to, at most, moderate scale (for the upper range of the Scoping Approach). For both the Developer and Scoping Approaches it is also the case that the centile metric indicates a high likelihood of the impacted population being of similar size to the un-impacted population after 35 years. Given this is within the context of a population which (consistent with the documented long-term trend) is predicted to decline irrespective of the effects from the Proposed Development, and for which the assessment incorporates high levels of precaution (particularly as determined by the Scoping Approach), it is concluded that the effects from the Proposed Development alone would not result in an adverse effect on this SPA 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 kittiwake 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.
  2. Therefore, the potential for effects of the Proposed Development to act on the Forth Islands SPA kittiwake 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 two in-combination scenarios, i.e. (i) the Proposed Development in-combination with the other Forth and Tay offshore wind farms and (ii) the Proposed Development in-combination with the offshore wind farms in the UK North Sea (noting that scenario (ii) includes those plans and projects which comprise scenario (i)).
Displacement/barrier effects – operation and maintenance
  1. As described in annex D of Offshore EIA Report, volume 3, appendix 11.6, estimates of breeding season displacement mortality which had been attributed to the Forth Islands SPA kittiwake population were extracted from the existing assessments for offshore wind farms that are in planning, consented, under construction or in operation. As for the potential displacement mortality estimated for the Proposed Development (Table 5.52), the mortality attributed to the SPA population from other offshore wind farms was estimated using the SNCB matrix approach, with details on the displacement and mortality rates that had been applied being available in each case. Thus, it was possible to adjust the estimated mortalities from each of the other projects to align with the displacement and mortality rates on which the Scoping and Developer Approaches are based.
  2. Few estimates of displacement mortality are available from other projects for kittiwake (for any SPA population) during the non-breeding periods because such effects have not been considered important in most previous assessments for offshore wind farms in Scotland or England. Therefore, relevant seasonal mean peak abundance estimates of kittiwake were extracted from the baseline data from the assessments for other projects in the UK North Sea waters (Offshore EIA Report, volume 3, appendix 11.6, annex E), with the in-combination estimates derived according to the Scoping and Developer approaches as detailed above in the section on the in-combination Displacement/Barrier Effects – Operation and Maintenance for the St Abb’s Head to Fast Castle SPA kittiwake population.
  3. The potential mortality estimates derived for the other projects were combined with those for the Proposed Development to give in-combination estimates for both the Forth and Tay wind farm scenario and the UK North Sea wind farm scenario, according to both the Scoping Approach and Developer Approach (Table 5.55).

 

Table 5.55:
Estimated 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, In-Combination with other Forth and Tay Wind Farms and UK North Sea Wind Farms.

Table 5.55: Estimated 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, In-Combination with other Forth and Tay Wind Farms and UK North Sea Wind Farms.

 

  1. The potential mortality resulting from the predicted displacement effects associated with other plans and projects increases the levels predicted for the Proposed Development alone by factors of two and half to three (Tables 5.52 and 5.55). For the Scoping Approach, these increases are slightly greater for the other UK North Sea wind farms in-combination scenario than for the other Forth and Tay wind farms scenario (due to the incorporation of effects from a greater number of wind farms during the passage periods in the former scenario). However, for the Developer Approach, the increases are the same for both scenarios (because no mortality is attributed to displacement during the non-breeding periods, whilst displacement effects during the breeding season on the SPA population are limited to the Proposed Development and the other Forth and Tay wind farms – see Offshore EIA Report, volume 3, appendix 11.6, annex D). As for the Proposed Development alone, the vast majority (i.e. 75 – 100%) of the predicted mortality from displacement is attributed to effects during the breeding season (Table 5.55).
  2. For the Proposed Development in-combination with the other Forth and Tay wind farms, the additional annual mortality of adult kittiwakes from the Forth Islands SPA population predicted due to displacement represents 0.20% 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 0.11 – 0.32% 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 the Offshore EIA Report, volume 3, appendix 11.6), the estimates of adult displacement mortality equate to an increase of 1.4% for the Developer Approach and of 0.7 – 2.2% for the lower and upper estimates from the Scoping Approach.
  3. For the Proposed Development in-combination with the other UK North Sea wind farms, the additional annual mortality of adult kittiwakes from the Forth Islands SPA population predicted due to displacement represents between approximately 0.12 – 0.36% of the current adult breeding population at this colony 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 0.8 – 2.5% for the lower and upper estimates from the Scoping Approach. The equivalent figures for the predicted additional mortality as determined by the Developer Approach are as for the Proposed Development in-combination with the other Forth and Tay wind farms.
  4. 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 in-combination with other wind farms in the Forth and Tay or in-combination with other wind farms in the UK North Sea during the operation and maintenance phase are considered in more detail below in the Effects 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
  1. As for displacement, breeding season collision estimates attributed to the Forth Islands SPA kittiwake population were extracted from the existing assessments for offshore wind farms that are in planning, consented, under construction or in operation (annex D of Offshore EIA Report, volume 3, appendix 11.6). Kittiwake collision estimates for the non-breeding periods 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 (annex E of Offshore EIA Report, volume 3, appendix 11.6). The non-breeding season collision estimates were apportioned to the Forth Islands SPA population according to the BDMPS approach (Furness 2015).
  2. 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 one adult bird). Therefore, only the estimates for the consented designs are considered in this case.
  3. In contrast to the displacement estimates derived for the other projects, existing collision estimates for these 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.
  4. 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 5.56).
Table 5.56:
Predicted Collision Effects on the Forth Islands SPA Kittiwake Population Due to the Proposed Development In-Combination with Other Projects in the Forth and Tay and in UK North Sea Waters. Estimates are Presented for both the Scoping Approach and Developer Approach

Table 5.56 Predicted Collision Effects on the Forth Islands SPA Kittiwake Population Due to the Proposed Development In-Combination with Other Projects in the Forth and Tay and in UK North Sea Waters. Estimates are Presented for both the Scoping Approach and Developer Approach

 

  1. The potential mortality resulting from the predicted collision effects associated with other plans and projects increases that predicted for the Proposed Development alone by approximately 50 – 75% for the other Forth and Tay wind farms in-combination scenario and by approximately 75 – 125% for the other UK North Sea wind farms in-combination scenario (with the greater increases associated with the Developer Approach in each case - Tables 5.53 and 5.56). The vast majority of the collision mortality predicted on the SPA population (i.e. approximately 70 – 90%) is again attributable to the breeding season effects (Table 5.56), with the breeding season effects essentially limited to the Proposed Development and the other Forth and Tay wind farms (see annex D to the Offshore EIA Report, volume 3, appendix 11.6).
  2. For the Proposed Development in-combination with the other Forth and Tay wind farms, the additional annual mortality of adult kittiwakes from the Forth Islands SPA population predicted due to collisions represents 0.43% 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 0.54% 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 0.145 – see Table 2.13 in volume 3, appendix 11.6 of the Offshore EIA Report), the estimates of adult collision mortality equate to an increase of 2.9% for the Developer Approach and of 3.7% for the Scoping Approach.
  3. For the Proposed Development in-combination with the other UK North Sea wind farms, the additional annual mortality of adult kittiwakes from the Forth Islands SPA population predicted due to collisions represents 0.52% 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 0.63% 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 0.145 – see Table 2.13 in volume 3, appendix 11.6 of the Offshore EIA Report), the estimates of adult collision mortality equate to an increase of 3.6% for the Developer Approach and of 4.4% for the Scoping Approach.
  4. The potential levels of impact on the Forth Islands SPA kittiwake population resulting from the mortality predicted from collisions associated with the Proposed Development in-combination with other wind farms in the Forth and Tay or in-combination with other wind farms in the UK North Sea during the operation and maintenance phase are considered in more detail below in the Effects 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
  1. 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 UK North Sea wind farms. This was on the basis of the potential mortality as determined by both the Scoping and Developer Approaches (see Tables 5.55 and 5.56 above).
  2. 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 5.57:
Projected 35 Year Population Sizes And Associated PVA metrics for the Forth Islands SPA Kittiwake Population Under Different Impact Scenarios for the Proposed Development in-Combination with the Other Forth and Tay Wind Farms

Table 5.57: Projected 35 Year Population Sizes And Associated PVA metrics for the Forth Islands SPA Kittiwake Population Under Different Impact Scenarios for the Proposed Development in-Combination with the Other Forth and Tay Wind Farms

Table 5.58:
Projected 35 Year Population Sizes and Associated PVA Metrics for the Forth Islands SPA Kittiwake Population Under Different Impact Scenarios for the Proposed Development in-Combination with the other UK North Sea Wind Farms

Table 5.58 Projected 35 Year Population Sizes and Associated PVA Metrics for the Forth Islands SPA Kittiwake Population Under Different Impact Scenarios for the Proposed Development in-Combination with the other UK North Sea Wind Farms

 

  1. Given that the in-combination effects are inevitably greater than those for 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 greater population-level impacts than as predicted for the Proposed Development alone (compare Tables 5.57 and 5.58 with Table 5.54). Focussing on the outputs for the Proposed Development in-combination with the other UK North Sea wind farms, the CPS value for the Developer Approach indicates that the SPA population size would be reduced by almost 20% relative to the predicted population size under baseline conditions after 35 years, whilst the equivalent reduction for the Scoping Approach is 21 – 26% (Table 5.58). Reductions in the annual population growth rate (relative to that predicted under baseline conditions) are estimated to be 0.6% for the Developer Approach and 0.6 – 0.8% for the Scoping Approach. The values for the centile metric are estimated as 33.7 after 35 years for the Developer Approach and as 27.5 – 32.8 for the Scoping Approach, suggesting moderate levels of overlap in the distribution of the predicted impacted and un-impacted population sizes and, hence, a reasonable likelihood of the impacted population being similar in size to the un-impacted population after 35 years. The PVA metrics for the Proposed Development in-combination with the other Forth and Tay wind farms indicate slightly lower levels of impact, being closer to those for the UK North Sea in-combination scenario than to those for the Proposed Development alone.
  2. The context within which the PVA metrics from these in-combination scenarios should be considered is outlined above in the Project Alone: Population-Level Impacts section for this SPA population.
In-combination: conclusion
  1. For both the Scoping and Developer Approaches, the predicted levels of impact associated with the two in-combination scenarios represent a marked increase compared to those associated with the Proposed Development alone. These levels of impact suggest the potential for the in-combination effects to lead to a marked reduction in the size of the Forth Islands SPA population after 35 years relative to that which would occur in the absence of these effects. The predicted levels of impact are such that for the Developer Approach (which predicts lower levels of impact than the Scoping Approach), this potential reduction in population size is almost 20% for the Proposed Development in-combination with the other UK North Sea wind farms.
  2. The centile values continue to indicate a reasonable likelihood of the impacted population being similar in size to the un-impacted population after 35 years, whilst the context that has been outlined above (in relation to (i) the high levels of precaution incorporated in the assessment and (ii) the likelihood that the effects from wind farm developments will be of minor importance relative to other management and environmental factors in determining the future status of the SPA kittiwake population) remains highly relevant. However, despite this, it is considered that the scale of the potential reduction in the size of the SPA population associated with the in-combination effects means that the possibility of an adverse effect on the SPA population cannot be excluded.
  3. Consequently, it is concluded that there is the potential for an adverse effect on the Forth Islands kittiwake population as a result of the predicted effects from (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. This conclusion applies to the assessments undertaken according to both the Developer Approach and the Scoping Approach.

Assessment for the herring gull population

 

  1. The Forth Islands SPA herring gull population is currently estimated to number 5,934 breeding pairs, which is slightly below the citation population of 6,600 pairs (Figure 5.19). The available count data for the population suggest that it has remained relatively stable and close to the citation size since the late 1980s at least.
Figure 519:
Herring Gull Population Trend at the Forth Islands SPA Between 1987 and 2020 (Noting That The Latest SPA Count is Shown for 2020 because it Spans the period 2019 – 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)).

Figure 519   Open ▸ : Herring Gull Population Trend at the Forth Islands SPA Between 1987 and 2020 (Noting That The Latest SPA Count is Shown for 2020 because it Spans the period 2019 – 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 herring 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 herring 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 herring gull foraging ranges (Woodward et al. 2019), it is likely that during the breeding period herring 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. This is supported by the findings of the apportioning exercise, which estimates that almost 60% of the herring 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 herring gull is defined as April to August, following NatureScot (2020).
  3. In the non-breeding season, herring gulls in Great Britain are largely sedentary with relatively short local movements only (Wernham et al. 2002). However, there is an influx of breeding birds of Scandinavian breeding subspecies, L. argentatus argentatus (Coulson et al., 1984). On this basis, and following the scoping advice from NatureScot (volume 3, appendix 6.2 of the Offshore EIA Report), it is assumed that during the non-breeding period herring gulls remain largely within the waters in the region of the breeding colony, as defined by the mean maximum foraging range plus 1 SD (Woodward et al. 2019, Offshore EIA Report, volume 3, appendix 11.5). To account for the influx of birds from other regions to this regional population during the non-breeding period, the regional non-breeding population is assumed to increase (relative to the size of the breeding population) in accordance with the proportion of continental and western UK birds estimated to be present in the UK North Sea and Channel BDMPS (Furness 2015, volume 3, appendix 11.5 of the Offshore EIA Report).
  4. Given the above, there is potential for the Proposed Development to have effects on the Forth Islands SPA herring gull population during both the breeding and non-breeding periods.
Project alone: construction and decommissioning
Changes to prey availability
  1. Herring 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 herring 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 herring gull population in the short-term.
  2. During construction there are a number of ways in which effects on herring gull 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 corridor encompasses 168 km2. Together these areas represent c. 10% of the total breeding season foraging area that is potentially available to the SPA herring gull population, as defined by the species’ mean-maximum breeding season foraging range plus 1 SD (i.e. 58.8±26.8 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 herring gulls breeding at the Forth Islands SPA. Non-breeding season effects are expected to similar since herring gulls in Great Britain do not disperse widely during winter (Wernham et al. 2002).
  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 herring gull prey species (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 breeding and non-breeding herring 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 herring population. This conclusion is consistent with the outcome of the EIA which concluded that effects from changes in prey availability on herring 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 herring 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 11.3). 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 99.0% 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 herring gull were undertaken following:

 

Table 5.59:
Predicted Collision Effects from the Proposed Development on the Forth Islands SPA Herring 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 5.59: Predicted Collision Effects from the Proposed Development on the Forth Islands SPA Herring 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 herring gulls from the Forth Islands SPA population predicted due to collisions with wind turbines in the Proposed Development array represents approximately 0.09% of the number of adults currently estimated to breed at this colony (i.e. 11,868 individuals – Table 3.3 in volume 3, appendix 11.5 of the Offshore EIA Report) as determined by the Developer Approach and approximately 0.14% 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 0.122 – see Table 2.11 in volume 3, appendix 11.6 of the Offshore EIA Report), the predicted adult collision mortality equates to increases of 0.7% and 1.2% for the Developer and Scoping Approaches, respectively.
  2. The potential levels of impact on the Forth Islands SPA herring gull population resulting from the predicted collision mortalities in Table 5.59 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 herring gulls breeding at the 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 herring 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 herring gull population. This conclusion is consistent with the outcome of the EIA which concluded that effects from changes in prey availability on herring 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 herring 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 5.59 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 5.59 (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 2.11 of volume 3, appendix 11.6 of the Offshore EIA Report. The starting population size was the 2016 – 2020 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 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 5.60:
Projected 35 Year Population Sizes and Associated PVA Metrics for the Forth Islands SPA Herring Gull Population Under Different Impact Scenarios for the Proposed Development alone

Table 5.60: Projected 35 Year Population Sizes and Associated PVA Metrics for the Forth Islands SPA Herring Gull Population Under Different Impact Scenarios for the Proposed Development alone

 

  1. The PVA predicted that the Forth Islands SPA herring 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 10 times larger than the current estimate of 11,868 adult birds under all scenarios, including the baseline which assumes no wind farm effects (Table 5.60). 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 5.19).
  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 3% in the size of the SPA population after 35 years, relative to that in the absence of any wind farm effects (Table 5.60). 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 45.6 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 5.60). 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 40% 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 herring 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 herring 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 herring 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. Breeding and non-breeding season collision estimates attributed to the Forth Islands SPA herring gull population were extracted from the existing assessments for offshore wind farms that are in planning, consented, under construction or in operation (annex E of Offshore EIA Report, volume 3, appendix 11.6). As for the Proposed Development, the non-breeding season collision estimates for the other plans and projects were adjusted to account for the influx of birds from other regions to this regional population during the non-breeding period, in accordance with the estimates used for the UK North Sea and Channel BDMPS (see above, Offshore EIA Report, volume 3, appendix 11.5, Furness 2015).
  2. The collision estimates derived for the other plans and projects were combined with those for the Proposed Development to give in-combination estimates for both the Forth and Tay wind farms and the UK North Sea wind farms according to both the Scoping Approach and Developer Approach. However, the potential effects on the SPA population were limited to the other Forth and Tay wind farms, noting that apportioning of the non-breeding season effects for herring gull assumed that birds remain within the waters in the region of the breeding colony (as described above, see also the Offshore EIA Report, volume 3, appendix 11.5). Given that these two different in-combination scenarios are equivalent, the predicted effects are reported solely for the UK North Sea wind farms in the tables below (Table 5.61). Options based on consented and ‘as-built’12 designs did not affect the collision estimates from the other plans and projects, so that estimates are reported for the consented designs only. The collision estimates used for the Proposed Development are those presented in Table 5.59, which derived from the more precautionary of the two different CRM approaches recommended by the Scoping Opinion (see above).
  3. The existing collision estimates for the other 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 included with the in-combination scenario having followed the ‘standard’ approach of using the mean density). As explained for St Abb’s Head to Fast Castle SPA kittiwake above, 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. Thus, it is only the estimates for the Proposed Development which differentiate the Developer and Scoping Approaches for the in-combination scenarios that are presented below.

 

Table 5.61:
Predicted Collision Effects on the Forth Islands SPA Herring Gull Population Due to the Proposed Development in-combination with Other Projects in the UK North Sea Waters. Estimates are Presented for both the Scoping Approach and Developer Approach

Table 5.61: Predicted Collision Effects on the Forth Islands SPA Herring Gull Population Due to the Proposed Development in-combination with Other Projects in the UK North Sea Waters. Estimates are Presented for both the Scoping Approach and Developer Approach

1The Forth and Tay and UK North Sea in-combination effects for the SPA population are equivalent (so that they are reported for the latter scenario only).

 

  1. Incorporating the potential mortality resulting from the predicted collision effects associated with other plans and projects increases the predicted annual collision mortality of adult birds by approximately 50% and 30% compared to the Proposed Development alone for the Developer and Scoping Approaches, respectively (Tables 5.59 and 5.61). The increase in the predicted collision mortality amongst the immature age class when compared to the Proposed Development alone is of a similar or greater extent (depending on whether the Developer or Scoping Approaches are considered), although the level of mortality predicted amongst this age class remains small relative to the predicted adult mortality. As noted above, the predicted collision effects to the SPA population are limited to the Proposed Development and the other Forth and Tay wind farms (see annex D of the Offshore EIA Report, volume 3, appendix 11.6).
  2. For the Proposed Development in-combination with these other wind farms, the additional annual mortality of adult herring gull from the Forth Islands SPA population predicted due to collisions represents 0.13% of the current adult breeding population at this colony (i.e. 11,868 individuals – Table 3.3 in volume 3, appendix 11.5 of the Offshore EIA Repor) as determined by the Developer Approach, and 0.19% 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 0.122 – see Table 2.11 in volume 3, appendix 11.6 of the Offshore EIA Report), the estimates of adult collision mortality equate to an increase of 1.0% for the Developer Approach and of 1.5% for the Scoping Approach.
  3. The potential levels of impact on the Forth Islands SPA herring gull population resulting from the predicted collision mortalities in Table 5.61 are considered in more detail below in the In-Combination: Population-Level Impacts section. This presents the outputs from PVAs of the potential effects of predicted collision mortality on the SPA population.
In-combination: population-level impacts
  1. As for the Proposed Development alone, PVA was undertaken on the mortality to the adult and immature age classes predicted due to the collision effects associated with the Proposed Development in-combination with the other UK North Sea wind farms. This was on the basis of the potential mortality as determined by both the Scoping and Developer Approaches (see Table 5.61 above).
  2. 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 5.62:
Projected 35 Year Population Sizes and Associated PVA Metrics for the Forth Islands SPA Herring Gull Population Under Different Impact Scenarios for the Proposed Development in-Combination with the Other UK North Sea Wind Farms

Table 5.62: Projected 35 Year Population Sizes and Associated PVA Metrics for the Forth Islands SPA Herring Gull Population Under Different Impact Scenarios for the Proposed Development in-Combination with the Other UK North Sea Wind Farms

 

  1. Given that the in-combination effects are inevitably greater than those for the Proposed Development alone, the PVA metrics for the Proposed Development in-combination with the other UK North Sea wind farms suggest greater population-level impacts than as predicted for the Proposed Development alone (compare Table 5.62 with Table 5.60). However, the changes in the values of the PVA metrics are small, with the reduction in the size of the SPA population after 35 years relative to that in the absence of any wind farm effects predicted to be approximately 5% for the Scoping Approach (compared to 3% for the Proposed Development alone). The equivalent reduction is smaller for the metrics associated with the Developer Approach. For both the Developer and Scoping Approaches, the centile metric continues to indicate a high likelihood of the impacted population being of a similar size to the un-impacted population after 35 years (Table 5.62).
  2. It is also the case that these predicted levels of impact are derived using the more precautionary of the two CRM approaches recommended by the Scoping Opinion for the Proposed Development. Reliance on the alternative approach would likely reduce the predicted levels of impact considerably, given that it reduces the collision estimates for the Proposed Development by approximately 40% and that the collision effects for the Proposed Development comprise a substantial part of the overall in-combination effects.
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 the other UK North Sea wind farms would not result in an adverse effect on the Forth Islands SPA herring gull population. This conclusion applies irrespective of whether effects are determined according to the Scoping Approach or the Developer Approach.

Assessment for the Lesser Black-Backed Gull Population

  1. The Forth Islands SPA lesser black-backed gull population is currently estimated to number 2,003 breeding pairs, which is above the citation population of 1,500 pairs (Figure 5.20). Based on those years for which full count data are available for the SPA, numbers have remained above the citation level since designation and appear relatively stable (albeit with indications of some fluctuations).

Figure 520:
Lesser Black-Backed Gull Population Trend at the Forth Islands SPA Between 1987 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 (1,500 pairs). Data are from the Seabird Monitoring Programme Database (Seabird Monitoring Programme | JNCC (bto.org))

Figure 520: Lesser Black-Backed Gull Population Trend at the Forth Islands SPA Between 1987 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 (1,500 pairs). Data are from the Seabird Monitoring Programme Database (Seabird Monitoring Programme | JNCC (bto.org))