Displacement/barrier effects – operation and maintenance
  1. As described in annex E of Offshore EIA Report, volume 3, appendix 11.6, estimates of breeding season displacement mortality which had been attributed to the Farne 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, 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 (annex D of Offshore EIA Report, volume 3, appendix 11.6), 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 according to both the Scoping Approach and Developer Approach (Table 5.111).

 

Table 5.111:
Estimated Annual Mortality of Farne 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 UK North Sea Wind Farms

Table 5.111: Estimated Annual Mortality of Farne 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 UK North Sea Wind Farms

 

  1. The potential mortality from the displacement effects associated with the other UK North Sea wind farms is limited to the passage periods, with none of these other wind farms identified as contributing to breeding season effects on this SPA population (see annex E of the Offshore EIA Report, volume 3, appendix 11.6). Thus, for the Developer Approach (for which the potential displacement mortality is limited to the breeding season), the in-combination effects from displacement are equivalent to those from the Proposed Development alone (Tables 5.108 and 5.111). For the Scoping Approach, the incorporation of the effects from the other UK North Sea wind farms leads to a near doubling in the mortality predicted from displacement compared to the Proposed Development alone, with less than 50% of the in-combination mortality attributed to the breeding season.
  2. For the Proposed Development in-combination with the other UK North Sea wind farms, the additional annual mortality of adult kittiwakes from the Farne Islands SPA population predicted due to displacement represents 0.05 – 0.16% of the current adult breeding population at this colony (i.e. 8,804 individuals – Table 3.3 in volume 3, appendix 11.5 of the Offshore EIA Report) 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 the Offshore EIA Report, volume 3, appendix 11.4 of the Offshore EIA Report), the estimates of adult displacement mortality equate to an increase of 0.4 – 1.1% for the lower and upper estimates from the Scoping Approach. For the Developer Approach, the equivalent percentages are as calculated above for the Proposed Development alone.
  3. The potential levels of impact on the Farne 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 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 Farne 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 the 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 D of the Offshore EIA Report, volume 3, appendix 11.46). The non-breeding season collision estimates were apportioned to the Farne 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 plans and projects were combined with those for the Proposed Development to give estimates for 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 5.112).

 

Table 5.112:
Predicted Collision Effects on the Farne Islands SPA Kittiwake 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 5.112: Predicted Collision Effects on the Farne Islands SPA Kittiwake 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

 

  1. As for the in-combination displacement effects on this SPA population (detailed above), the potential collision mortality associated with the other UK North Sea wind farms is limited to the passage periods, with none of these other wind farms identified as contributing to breeding season effects (see annex E of Offshore EIA Report, volume 3, appendix 11.6). The predicted collisions associated with other plans and projects increases that predicted for the Proposed Development alone by 53% for the Scoping Approach and 77% for the Developer Approach (Tables 5.109 and 5.112). In contrast to the effects associated with the Proposed Development alone, only 50 – 58% of the predicted collision mortality is attributed to the breeding season.
  2. For the Proposed Development in-combination with the other UK North Sea wind farms, the additional annual mortality of adult kittiwakes from the Farne Islands SPA population predicted due to collisions represents 0.32% of the current adult breeding population at this colony (i.e. 8,804 individuals – Table 3.3 in volume 3, appendix 11.5 of the Offshore EIA Report) as determined by the Developer Approach, and 0.41% 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 2.2% for the Developer Approach and of 2.9% for the Scoping Approach.
  3. The potential levels of impact on the Farne 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 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 5.111 and 5.112 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 5.113:
Projected 35 Year Population Sizes and Associated PVA Metrics for the Farne Islands SPA Kittiwake Population Under Different Impact Scenarios for the Proposed Development In-Combination with the other UK North Sea Wind Farms

Table 5.113: Projected 35 Year Population Sizes and Associated PVA Metrics for the Farne 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 the other UK North Sea wind farms suggest greater population-level impacts than as predicted for the Proposed Development alone (compare Table 5.113 with Table 5.110). Thus, the CPS value for the Developer Approach indicates that the SPA population size would be reduced by almost 11% relative to the predicted population size under baseline conditions after 35 years, whilst the equivalent reduction for the Scoping Approach is 13 – 16% (Table 5.113). Reductions in the annual population growth rate (relative to that predicted under baseline conditions) are estimated to be 0.3% for the Developer Approach and 0.4 – 0.5% for the Scoping Approach. The values for the centile metric are estimated as 39.2 after 35 years for the Developer Approach and as 34.3 – 37.2 for the Scoping Approach. For the Scoping Approach these suggest 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, whilst for the Developer Approach this likelihood is higher.
  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 the Developer Approach, the predicted levels of impact associated with the Proposed Development in-combination with the other UK North Sea wind farms remain relatively small, whilst the likelihood of the impacted population being similar in size to the un-impacted population after 35 years remains reasonably high. This is within the context of a population which (consistent with the documented long-term trend) is predicted to decline irrespective of the potential wind farm effects (which are likely to be of minor importance relative to other management and environmental factors in determining population status), and an assessment which incorporates high levels of precaution. Consequently, it is concluded that the effects from the Proposed Development in-combination with the other UK North Sea wind farms would not result in an adverse effect on this SPA population, as determined by the Developer Approach.
  2. For the Scoping Approach, the predicted levels of impact for the Proposed Development in-combination with the other UK North Sea wind farms are inevitably greater than as determined by the Developer Approach. It is considered that these may, potentially, be sufficient to result in an adverse effect on this SPA population. However, as has been detailed above (and in the Offshore EIA Report, volume 3, appendix 11.3), it is considered that the level of effects on kittiwakes assumed by the Scoping Approach are overly precautionary and without any reasonable basis or support from the available evidence. Given this, it is considered that greater weight should be given to the conclusions as determined by the Developer Approach.

Assessment for the herring gull population

  1. The Farne Islands SPA herring gull population is currently estimated to number 1,496 individuals, based upon the most recently available count data from 2019 (Offshore EIA Report, volume 3, appendix 11.5). The earliest counts of herring gull that are available on the SMP database (SMP 2022) for the SPA give an estimate of 1,148 individuals in 2000, with subsequent counts showing that the numbers of breeding individuals in the SPA population have fluctuated between a low of 1,048 in 2002 and a peak of 2,090 in 2006.
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 Farne Islands SPA, so that potential impacts on its herring gull population will only arise 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 of maintaining or restoring the populations of each qualifying feature, 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 Conservation Objective (as for maintaining or restoring the structure and function of the habitats of the qualifying features, because habitat structure and function would only be considered significant if it caused an adverse effect on the maintenance or restoration of the population of the qualifying features). In terms of the SACOs, this focus is most closely reflected in the attributes concerned with the abundance and diversity of the species assemblage which have the targets of maintaining; (i) the abundance of the breeding seabird assemblage qualifying feature at a level above 163,819 individuals, whilst avoiding deterioration from its current levels; and (ii) the species diversity of the breeding seabird assemblage qualifying feature.
  2. From published information on herring gull foraging ranges (Woodward et al. 2019), it is possible that during the breeding period herring gulls from the Farne 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 3% of the herring gulls occurring on the Proposed Development array area during the breeding season derive from this SPA colony (volume 3, appendix 11.5 of the Offshore EIA Report). 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, 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 Farne 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 Farne 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 Farne 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 Farne 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 Offshore EIA Report, volume 3, appendix 11.3 but, as a result of this overly precautionary approach (which does not follow previous precedent), the CRMs for herring gull were undertaken following:
  • The Scoping Approach of using the maximum monthly densities, and
  • The Developer Approach of using the mean monthly densities.
    1. In addition to the above, collision estimates for herring gulls were also calculated using options 2 and 3 of the stochastic version of the CRM (McGregor et al. 2018) with avoidance rates as derived from the bird collision-avoidance study undertaken at the Thanet offshore wind farm (Bowgen and Cook 2018). These additional collision estimates are not used as the basis of the assessments on the SPA herring gull populations but, instead, are used solely to illustrate the consequences of applying these alternative avoidance rates which have been derived from studies at an actual offshore wind farm. Details of these additional CRMs are provided in annex C of Offshore EIA Report, volume 3, appendix 11.3.
    2. Herring gull collision estimates are calculated for the breeding and non-breeding periods, with estimates apportioned to the Farne Islands SPA population according to the NatureScot (2018) approach but with allowance made for the influx of birds from other regions during the non-breeding period (Offshore EIA Report, volume 3, appendix 11.5). The resulting estimates were apportioned to age classes according to the plumage characteristics of herring gulls recorded during the baseline surveys (Offshore EIA Report, volume 3, appendix 11.1), whilst on the basis of advice provided by NatureScot and Marine Scotland Science following Roadmap Meeting 4 (G. Holland, email 26/01/2022), it was also assumed that 35% of the breeding adults in the SPA population miss breeding in any given year (i.e. sabbatical birds) so that the number of adult collisions estimated during the breeding season was adjusted accordingly.
    3. Based upon option 2 of the deterministic CRM with a 99.5% avoidance rate applied, and in conjunction with the estimates and assumptions detailed above, the annual collision mortality of herring gulls from the Farne Islands SPA is predicted to be a single individual (adults and immatures combined) as determined by the Scoping Approach, and less than a single individual as determined by the Developer Approach (Table 5.114). Almost all this mortality is predicted to occur during the breeding season. The collision estimates for option 3 of the deterministic CRM with a 99.0% avoidance rate applied (which was also recommended by the Scoping Opinion as a basis for the assessment) are not presented in Table 5.114but give outputs that are approximately 40% lower than the option 2 estimates for both the Scoping and Developer Approaches (Offshore EIA Report, volume 3, appendix 11.3). In addition, the collision estimates produced using options 2 and 3 of the stochastic CRM with the Bowgen and Cook (2018) avoidance rates applied were similar to those obtained from option 3 of the deterministic CRM with the SNCB recommended 99.0% avoidance rate, and hence also substantially lower than those presented in Table 5.114below (see annex C of the Offshore EIA Report, volume 3, appendix 11.3).

 

Table 5.114:
Predicted Collision Effects from the Proposed Development on the Farne 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 5.114: Predicted Collision Effects from the Proposed Development on the Farne 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 Farne Islands SPA population predicted due to collisions with wind turbines in the Proposed Development array represents approximately 0.04% of the number of adults currently estimated to breed at this colony (i.e. 1,496 individuals – Table 3.3 in volume 3, appendix 11.5 of the Offshore EIA Report) as determined by the Developer Approach and approximately 0.06% as determined by the Scoping Approach. In terms of percentage increases in the baseline annual adult mortality of the population (which is based on applying a mortality rate of 0.122 – see Table 2.11 in volume 3, appendix 11.6 of the Offshore EIA Report), the predicted adult collision mortality equates to increases of 0.3% and 0.5% for the Developer and Scoping Approaches, respectively.
  2. The potential levels of impact on the Farne Islands SPA herring gull population resulting from the predicted collision mortalities in Table 5.114 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 Farne 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 Farne 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 Farne 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 Farne 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 Tables 5.114 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 5.114 (noting that these are the more precautionary of the outputs from the different CRM approaches recommended by the Scoping Opinion - volume 3, appendix 6.2 of the Offshore EIA Report). 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 2019 count for the SPA, with the projected population trends considered over a 35 year timescale (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 (Offshore EIA Report, 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 5.115:
Projected 35 Year Population Sizes and Associated PVA Metrics for the Farne Islands SPA Herring Gull Population Under Different Impact Scenarios for the Proposed Development Alone

Table 5.115: Projected 35 Year Population Sizes and Associated PVA Metrics for the Farne Islands SPA Herring Gull Population Under Different Impact Scenarios for the Proposed Development Alone

 

  1. The PVA predicted that the Farne 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 more than 10 times larger than the current estimate of 1,496 adult birds under all scenarios, including the baseline which assumes no wind farm effects (Table 5.115). 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 relative stability (albeit with between-year fluctuations) in the size of this SPA population over the last 20 years or so (see above).
  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 less than 2% in the size of the SPA population after 35 years, relative to that in the absence of any wind farm effects (Table 5.115). The associated reduction in annual population growth rate (relative to that predicted under baseline conditions) is not detectable (at least when the CPGR value is expressed to three decimal places), whilst the centile value of 48.2 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 5.115). 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 Farne 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 Farne 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 Farne Islands SPA herring gull population in-combination with other plans and projects is limited to the collision risk effect pathway during operation and maintenance.
  3. As for other SPA populations, consideration was given to the potential collision mortality associated with the Proposed Development in-combination with the other UK North Sea wind farms. However, none of these other wind farms were identified as contributing to either the breeding or non-breeding season effects on the Farne Islands SPA herring gull population. This is unsurprising, given the considerable distance of this SPA to most other North Sea wind farms, together with the fact that during the non-breeding season the potential for effects was also assumed to be limited to those plans and projects which are within the breeding season foraging range of the herring gull SPA population (as advised by the Scoping Opinion – volume 3, appendix 6.2 of the Offshore EIA Report).
In-combination: conclusion
  1. Based on the above, the effects from the Proposed Development in-combination with the other UK North Sea wind farms are equivalent to those from the Proposed Development alone. Consequently, it is concluded that the effects from the Proposed Development in-combination with the other UK North Sea wind farms would not result in an adverse effect on the Farne Islands SPA herring gull population. This conclusion applies to both the Scoping and Developer Approaches.

Assessment for the lesser black-backed gull population

  1. The Farne Islands SPA lesser black-backed gull population is currently estimated to number 1,362 individuals, based upon the most recently available count data from 2019 (Offshore EIA Report, volume 3, appendix 11.5). The earliest counts of lesser black-backed gull that are available on the SMP database (SMP 2022) for the SPA give an estimate of 1,330 individuals in 2000, with subsequent counts showing that the numbers of breeding individuals in the SPA population have fluctuated between a low of 862 in 2005 and a peak of 1,598 in 2006.
The potential for impacts on the lesser black-backed gull population
  1. The Proposed Development and two kilometre buffer around the Proposed Development array area7 do not overlap with the Farne Islands SPA, so that potential impacts on its lesser black-backed gull population will only arise 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 of maintaining or restoring the populations of each qualifying feature, 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 Conservation Objective (as for maintaining or restoring the structure and function of the habitats of the qualifying features, because habitat structure and function would only be considered significant if it caused an adverse effect on the maintenance or restoration of the population of the qualifying features). In terms of the SACOs, this focus is most closely reflected in the attributes concerned with the abundance and diversity of the species assemblage which have the targets of maintaining; (i) the abundance of the breeding seabird assemblage qualifying feature at a level above 163,819 individuals, whilst avoiding deterioration from its current levels; and (ii) the species diversity of the breeding seabird assemblage qualifying feature.
  2. From published information on lesser black-backed gull foraging ranges (Woodward et al. 2019), it is likely that during the breeding period lesser black-backed gulls from the Farne Islands SPA occur within the area of the Proposed Development and of the two km buffer around the Proposed Development array area. This is supported by the findings of the apportioning exercise, which estimates that almost 14% of the lesser black-backed gulls occurring on the Proposed Development array area during the breeding season derive from this SPA colony (volume 3, appendix 11.5 of the Offshore EIA Report). The breeding period for lesser black-backed gull is defined as mid-March to August, following NatureScot (2020).
  3. In the non-breeding season lesser black-backed gulls from the Farne Islands SPA migrate south through the southern North Sea, undertaking the return journey in spring. It is likely that they winter predominantly in Iberia or on the coast of northwest Africa although a proportion may remain within the North Sea and Channel (Wernham et al. 2002, Furness 2015). Therefore, it is likely that there is the potential for birds from the Farne Islands SPA population to pass through offshore wind farms in the North Sea during the autumn and spring passage periods (defined as September to October and the first half of March, respectively, on the basis of applying the BDMPS defined periods within the context of the overall non-breeding period defined by NatureScot – Furness 2015, NatureScot 2020, Offshore EIA Report, volume 3, appendix 11.5), and to a lesser extent in winter as well (defined as November to February – Furness 2015). Given the above, the Proposed Development may have potential effects on the Farne Islands SPA lesser black-backed gull population during breeding and non-breeding periods.
Project alone: construction and decommissioning
Changes to prey availability
  1. Lesser black-backed gulls have a highly opportunistic diet (del Hoyo et al., 1996), utilising terrestrial, intertidal and marine habitats to forage for a wide variety of prey species including invertebrates, small fish and carrion (including fishery discards). Indirect effects on lesser black-backed gulls may arise as a result of changes in the availability, distribution, or abundance of these species during the construction and decommissioning phases of the Proposed Development. Reduction or disruption to prey availability may cause displacement from foraging grounds or reduced energy intake, affecting survival rates or productivity in the Farne Islands SPA lesser black-backed gull population in the short-term.
  2. During construction there are a number of ways in which effects on lesser black-backed 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. 1% of the total breeding season foraging area that is potentially available to the SPA lesser black-backed gull population, as defined by the species’ mean-maximum breeding season foraging range plus 1 SD (i.e. 127±109 km; Woodward et al., 2019) and assuming that this range is represented by a semicircle to the main seaward side of the colony. Furthermore, given their flexible foraging habits and the distance between the Proposed Development and the SPA, it is likely that the area of marine habitat encompassed by the Proposed Development is not of key importance for lesser black-backed gulls breeding at the Farne Islands SPA. Effects during the non-breeding season are considered to be lower than during the breeding season given that birds migrate south through UK waters to their wintering grounds (Wernham et al., 2002; Furness 2015).
  3. During decommissioning, the effects from changes in prey availability are considered to be the same (or less) as for construction. It is currently unclear as to how the presence, and subsequent removal of, subsea structures may affect the prey species of lesser black-backed gull (Birchenough and Degrae 2020; Scott, 2022). It is possible that prey abundance could decline from the levels present during the operation and maintenance period. This could occur if the sub-surface structures associated with the Proposed Development in the marine environment lead to an increase in key prey abundance within the Proposed Development array area and export cable corridor via the provision of artificial reef habitats. However, some infrastructure (such as scour and cable protection) is assumed to be left in situ with the impact of colonisation of infrastructure continuing in perpetuity following decommissioning. Thus, any reduction in prey abundance through removal of foundations is likely to be very small relative to the area over which lesser-black-backed gulls forage.
  4. Given their wide-ranging foraging behaviour and plasticity in foraging habitat and diet (del Hoyo et al., 1996), together with any effects being intermittent, spatially-restricted and temporary in nature, it is considered that there is no potential for construction or decommissioning related changes in prey availability to lead to an adverse effect on the Farne Islands SPA lesser-back-backed gull population. This conclusion is consistent with the outcome of the EIA which concluded that effects from changes in prey availability on lesser black-backed gulls during construction and decommissioning were not significant in EIA terms (volume 2, chapter 11 of the Offshore EIA Report).
Project alone: operation and maintenance
Collision risk
  1. Predictions of the number of lesser black-backed gulls at risk from collisions due to the Proposed Development were calculated using the deterministic version of the SOSS offshore collision risk model (Band 2012, Offshore EIA Report, volume 3, appendix 11.3). 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 98.9% were applied to the outputs from option 2 and option 3, respectively.
  2. As outlined for the St Abb’s Head to Fast Castle SPA kittiwake population above, guidance on the use of the CRM suggests that model predictions should be based upon the mean monthly densities of flying birds estimated within the array area (Band 2012)8 and, to the best of the Applicant’s knowledge, this approach has been applied in all recent UK offshore wind farm assessments. Despite this, the Scoping Opinion advised that the CRMs for the Proposed Development should use the maximum monthly densities of flying birds within the array area. Further details on this are provided above in the Project Alone: Operation and Maintenance - Collision Risk section for the St Abb’s Head to Fast Castle SPA kittiwakes population and in Offshore EIA Report, volume 3, appendix 11.3 but, as a result of this overly precautionary approach (which does not follow previous precedent), the CRMs for lesser black-backed gull were undertaken following:
  • The Scoping Approach of using the maximum monthly densities, and
  • The Developer Approach of using the mean monthly densities.
    1. In addition to the above, collision estimates for lesser black-backed gulls were also calculated using options 2 and 3 of the stochastic version of the CRM (McGregor et al. 2018) with avoidance rates as derived from the bird collision-avoidance study undertaken at the Thanet offshore wind farm (Bowgen and Cook 2018). These additional collision estimates are not used as the basis of the assessments on the SPA lesser black-backed gull populations but, instead, are used solely to illustrate the consequences of applying these alternative avoidance rates which have been derived from studies at an actual offshore wind farm. Details of these additional CRMs are provided in annex C of Offshore EIA Report, volume 3, appendix 11.3.
    2. Lesser black-backed gull collision estimates are calculated for the defined breeding period, with estimates apportioned to the Farne Islands SPA population according to the NatureScot (2018) approach (Offshore EIA Report, volume 3, appendix 11.5). The resulting estimates were apportioned to age classes according to the plumage characteristics of lesser black-backed gulls recorded during the baseline surveys (Offshore EIA Report, volume 3, appendix 11.1), whilst on the basis of advice provided by NatureScot and Marine Scotland Science following Roadmap Meeting 4 (G. Holland, email 26/01/2022), it was also assumed that 35% of the breeding adults in the SPA population miss breeding in any given year (i.e. sabbatical birds) so that the number of adult collisions estimated during the breeding season was adjusted accordingly.
    3. No lesser black-backed gull collisions were estimated for the non-breeding periods (Offshore EIA Report, volume 3, appendix 11.3).
    4. Based upon option 2 of the deterministic CRM with a 99.5% avoidance rate applied, and in conjunction with the estimates and assumptions detailed above, the annual collision mortality of lesser black-backed gulls from the Farne Islands SPA is predicted to be less than a single individual (adults and immatures combined) as determined by the Scoping Approach, and approximately one half of a bird as determined by the Developer Approach (Table 5.116). The collision estimates for option 3 of the deterministic CRM with a 98.9% avoidance rate applied (which was also recommended by the Scoping Opinion as a basis for the assessment) are not presented in Table 5.116 but give outputs that are 33 - 44% lower than the option 2 estimates for both the Scoping and Developer Approaches (Offshore EIA Report, volume 3, appendix 11.3). In addition, the collision estimates produced using options 2 and 3 of the stochastic CRM with the Bowgen and Cook (2018) avoidance rates applied were similar to those obtained from option 3 of the deterministic CRM with the SNCB recommended 98.9% avoidance rate, and hence also substantially lower than those presented in Table 5.116 below (see annex C of the Offshore EIA Report, volume 3, appendix 11.3).

 

Table 5.116:
Predicted Collision Effects from the Proposed Development on the Farne Islands SPA Lesser Black-Backed Gull Population, as Determined by the Scoping Approach and Developer Approach. Estimates are for the Maximum Design Scenario and are Based on Option 2 of the Deterministic CRM Using a 99.5% Avoidance Rate (see text)

Table 5.116: Predicted Collision Effects from the Proposed Development on the Farne Islands SPA Lesser Black-Backed Gull Population, as Determined by the Scoping Approach and Developer Approach. Estimates are for the Maximum Design Scenario and are Based on Option 2 of the Deterministic CRM Using a 99.5% Avoidance Rate (see text)

 

  1. Based upon the estimates from option 2 of the CRM, the additional annual mortality of adult lesser black-backed gulls from the Farne Islands SPA population predicted due to collisions with wind turbines in the Proposed Development array represents approximately 0.04% of the number of adults currently estimated to breed at this colony (i.e. 1,362 individuals – Table 3.3 in volume 3, appendix 11.5 of the Offshore EIA Report) as determined by the Developer Approach and approximately 0.05% as determined by the Scoping Approach. In terms of percentage increases in the baseline annual adult mortality of the population (which is based on applying a mortality rate of 0.087 – see Table 2.15 in volume 3, appendix 11.6 of the Offshore EIA Report), the predicted adult collision mortality equates to increases of 0.4% and 0.6% for the Developer and Scoping Approaches, respectively.
  2. The potential levels of impact on the Farne Islands SPA lesser black-backed gull population resulting from the predicted collision mortalities in Table 5.116 are considered in more detail below in the Project Alone: Population-Level Impacts section. This presents the outputs from PVAs of the potential effects of predicted collision mortality on the SPA population.
Changes to prey availability
  1. Potential impacts on key prey species for lesser black-backed gulls breeding at the Farne Islands SPA during the operation and maintenance phase have been assessed in volume 2, chapter 9 of the Offshore EIA Report using the appropriate maximum design scenarios for these receptors. Reduction or disruption to prey availability through temporary and long-term subtidal habitat loss/disturbance, increased SSC and deposition, EMF from subsea electrical cabling, and colonisation of subsea structures could affect lesser black-backed gull survival and productivity in the Farne 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 Farne Islands SPA lesser black-backed gull population. This conclusion is consistent with the outcome of the EIA which concluded that effects from changes in prey availability on lesser black-backed gulls during operation and maintenance were not significant in EIA terms (volume 2, chapter 11 of the Offshore EIA Report).
Project alone: population-level impacts
  1. As determined above, the effects from the Proposed Development alone which could lead to an adverse effect on the Farne Islands SPA lesser black-backed gull population are limited to collision mortality during the operation and maintenance phase. For other effect pathways, there is considered to be no potential for an adverse effect on this population as a result of the Proposed Development alone, with any such effects likely to be small and of little, or no, consequence in terms of impacts at the population level.
  2. Given this, PVA was undertaken on the mortality to the adult and immature age classes predicted due to the collisions associated with the Proposed Development, as determined by both the Scoping and Developer Approaches (see Table 5.116 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 5.116 (noting that these are the more precautionary of the outputs from the different CRM approaches recommended by the Scoping Opinion - volume 3, appendix 6.2 of the Offshore EIA Report). The population model for the SPA population was a stochastic, density independent, matrix model, based upon the demographic parameters specified in Table 2.15 of volume 3, appendix 11.6 of the Offshore EIA Report. The starting population size was the 2019 count for the SPA, with the projected population trends considered over a 35 year timescale (volume 3, appendix 11.5 of the Offshore EIA Report). The approach and methods to undertaking the PVA are as described for the St Abb’s Head to Fast Castle kittiwake above (with further details provided in volume 3, appendix 11.6 of the Offshore EIA Report).
  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 5.117:
Projected 35 Year Population Sizes and Associated PVA Metrics for the Farne Islands SPA Lesser Black-Backed Gull Population Under Different Impact Scenarios for the Proposed Development Alone

Table 5.117: Projected 35 Year Population Sizes and Associated PVA Metrics for the Farne Islands SPA Lesser Black-Backed Gull Population Under Different Impact Scenarios for the Proposed Development Alone

 

  1. The PVA predicted that the Farne Islands SPA lesser black-backed gull population would increase strongly over the 35 year projection period irrespective of the effects from the Proposed Development. Thus, the population is predicted to be approximately five times larger than the current estimate of 1,362 adult birds under all scenarios, including the baseline which assumes no wind farm effects (Table 5.117). 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 relative stability (albeit with between-year fluctuations) in the size of this SPA population over the last 20 years or so (see above).
  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 less than 2% in the size of the SPA population after 35 years, relative to that in the absence of any wind farm effects (Table 5.117). The associated reduction in annual population growth rate (relative to that predicted under baseline conditions) is not detectable (at least when the CPGR value is expressed to three decimal places), whilst the centile value of 47.3 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 5.117). In addition, it should be noted that these predicted levels of impact are derived from the more precautionary of the two CRM approaches recommended by the Scoping Opinion, with the alternative approach giving collision estimates that are 33 - 44% lower than those used for the PVA.
Project alone: conclusion
  1. For both the Developer and Scoping Approaches, the potential effects from the Proposed Development alone on the Farne Islands SPA lesser black-backed gull population are predicted to be small, with the resultant population-level impacts also predicted to be small. In addition, the PVA metrics indicate a high chance of the population being of a similar size to that which would occur in the absence of the Proposed Development after 35 years. Given this, it is concluded that the effects from the Proposed Development alone would not result in an adverse effect on this population.
Effects in-combination
Effects of relevance to the in-combination assessment
  1. As detailed above, any effects from the Proposed Development alone on the Farne Islands SPA lesser black-backed gull population during construction and decommissioning and resulting from changes to prey availability during operation and maintenance will be small and highly localised. As such, there is considered to be no potential for these effect pathways to add to impacts at the population-level that might result from other effects pathways associated with the Proposed Development or from the effects due to other plans and projects.
  2. Therefore, the potential for effects of the Proposed Development to act on the Farne Islands SPA lesser black-backed gull population in-combination with other plans and projects is limited to the collision risk effect pathway during operation and maintenance. The following sections consider this potential effect for the Proposed Development in-combination with the offshore wind farms in the UK North Sea.