3.5. Gannet

  1. Apportioning values in the breeding season, for all colonies within foraging range of the Array, is presented in Table 3.7   Open ▸ , with SPA colonies shown in Figure 3.5   Open ▸ . Apportioning values for non-SPA colonies is presented in annex A. Apportioning values for use in the post-breeding and pre-breeding seasons are presented in Table 3.8   Open ▸ .

 

Table 3.7:
Apportioning Values for Gannet in the Breeding Season for SPAs Within Foraging Range of the Array

Table 3.7: Apportioning Values for Gannet in the Breeding Season for SPAs Within Foraging Range of the Array

Figure 3.5:
SPAs Included in the Apportioning Assessment for Gannet

Figure 3.5 SPAs Included in the Apportioning Assessment for Gannet

Table 3.8:
Post-breeding and Pre-breeding Season Apportioning Values for Gannet

Table 3.8: Post-breeding and Pre-breeding Season Apportioning Values for Gannet

4. Discussion

  1. This technical report uses NatureScot’s theoretical approach to apportioning impacts to breeding seabirds in SPAs and its consideration of immature birds.
  2. For kittiwake, in the breeding season, most birds are apportioned to Fowlsheugh SPA, Buchan Ness to Collieston Coast SPA or Flamborough and Filey Coast SPA. In the migratory seasons, Flamborough and Filey Coast SPA is again relatively important, and additionally East Caithness Cliffs SPA is relatively important – although it should also be noted that in the migratory seasons, birds come from a much wider range of SPAs and non-SPA colonies (including overseas colonies) and therefore the proportion attributed to SPAs with an LSE2 identified are small.
  3. For razorbill, only one SPA (Fowlsheugh SPA) has been identified as having potential LSE2.
  4. For puffin, in the breeding season most birds are apportioned to either the Farne Islands SPA or the Forth Islands SPA. In the non-breeding season, puffin are expected to disperse widely and apportionment is not carried out.
  5. For gannet, in the breeding season the majority of birds are apportioned to the Forth Islands SPA (which includes the UK’s largest breeding gannet colony at Bass Rock). In the non-breeding season, of the SPAs screened in, the Forth Islands SPA still has the highest apportionment value, although it should also be noted that in the migratory seasons, birds come from a much wider range of SPAs and non-SPA colonies (including overseas colonies) and therefore the proportion attributed to the Forth Islands SPA or any other SPAs with an LSE2 identified are small.
  6. For gannet, it should be noted that other projects (SSE Renewables, 2022; Seagreen Wind Energy Ltd, 2019; MacArthur Green, 2015) have considered an alternative approach to apportioning gannets in the migratory seasons to SPA populations. This alternative approach uses tracking data to infer the number of birds that may pass through a windfarm on migration, based on the location of the wind farm compared to all North Sea breeding colonies, and the typical direction of migration in the post-breeding and pre-breeding migration seasons. Whilst this approach has not been applied, it should be noted that this approach would be expected to result in fewer birds being apportioned to the Forth Islands SPA and the Flamborough and Filey Coast SPA, especially in the post-breeding season, due to the majority of birds migrating southwards towards the English Channel and therefore being less likely to interact with the Array (MacArthur Green, 2015).
  7. Using the approach recommended by NatureScot, no guillemot affected by the Array are expected to be birds associated with SPA colonies and therefore no apportionment is required in any season. However, following Natural England’s request, apportionment of guillemot to Flamborough and Filey Coast SPA during the non-breeding season has also been carried out using the method preferred by Natural England, and this is provided without prejudice for information only.  
  8. The results include several assumptions that may lead to an over-estimate of the proportion of breeding adult birds present in a given area. These assumptions are listed below.
  • breeding adult birds:

–           the assumption that birds are evenly distributed at sea, with this being extremely unlikely due to the known patchy distribution of prey species and information gained from tracking studies;

–           the assumption that seabird colonies are independent of one another;

–           the assumption that larger foraging ranges will occur at larger breeding colonies due to competition and prey depletion closer to the colony (Elliott et al., 2009); and

–           the use of mean-maximum plus one standard deviation foraging ranges.

  • immature birds:

–           limited information is available on the proportion of immature birds that return to natal waters and the distribution of immature birds within natal waters.

  1. Consideration has been given in the RIAA to these assumptions/limitations, including where available site-specific tracking studies, and what effect they may have on the overall magnitude of any impacts (Ossian OWFL, 2024). Further information on foraging range and immature proportions is provided in section 4.1 and 4.2 below.

4.1. Foraging Range

  1. NatureScot (2023b) typically recommends the use of the mean-maximum foraging range plus one standard deviation for each species considered.
  2. The use of a mean-maximum foraging range plus one standard deviation represents a highly precautionary approach regardless of its application as, although it ensures, from a HRA screening perspective, that no SPAs are erroneously omitted from the RIAA, the likelihood of an LSE2 occurring as a result of any project beyond mean-maximum foraging range is considered highly unlikely. A mean-maximum foraging range already represents the average of the maximum foraging ranges exhibited by birds across multiple studies. A standard deviation of a mean value represents the amount by which individual values differ from the mean value. It is an expression of confidence in the mean value and should not be applied as an absolute value as in the application of foraging ranges for screening. This is particularly so when the average value is already an average of maximum values from multiple studies which may not reflect the true foraging behaviour of all individuals from a colony.
  3.  It is considered that the application of a mean-maximum foraging range plus one SD for apportioning purposes is likely to be over precautionary in terms of including distant SPAs for assessment, for which the true impact is likely to be negligible or zero. It also leads to impacts being diluted across more SPAs and therefore potentially underestimates impacts on nearby colonies. However, this is the recommended approach and therefore has been applied in this apportioning assessment.

4.2. Immature proportions

  1. Although any population of breeding seabirds has an immature component associated with it, the spatial distribution of the immature component is often very different to the breeding adult component, especially in the breeding season. For many seabird species, immature birds gradually begin to return to natal waters in the breeding season as they get nearer to breeding age. The proportion of older immature age classes in natal waters is therefore higher than the proportion of younger immature age classes. In addition, the distribution of immature birds in natal waters may be dictated by proximity to breeding colonies either because birds are prospecting for breeding sites or due to competition with breeding adult birds. Where all immature classes of a species can be reliably identified during baseline surveys, this is less of an issue. However, for species for which only some age classes can be identified during baseline surveys (i.e. the birds obtain an adult type plumage before they are physically old enough to breed), resulting immature proportions represent an under-estimate.
  2. In the context of this apportioning appendix this is relevant to kittiwake. Whilst one year old kittiwakes can be easily identified due to differences in plumage, second and third year old birds, which have not yet reached the age of first breeding, cannot (Coulson, 2011; Olsen and Larsson, 2003). Therefore data on age class collected during surveys will potentially represent a considerable overestimate of the proportion of breeding adults present in a given sea area. As set out in section 2.3.2, the proportion of second and third year immatures (which show a much greater affinity for natal waters than first year birds) will be under-estimated.
  3. As detailed in section 2.3, an approach has been applied which aims to address the underestimation. Whilst maintaining the proportion represented of each year class of immatures at the Array, mortality reduces the absolute number of birds present from each successive year class of kittiwake. In calculating the number of two and three year old kittiwakes at the Array, the analysis uses survival rates of each immature age class of kittiwake that follows the rate provided in Horswill and Robinson (2015). This approach is considered precautionary for the following reasons:
  • it is known that older immature age classes that are not identifiable during baseline surveys will be present at the Array; and
  • a smaller proportion of one year old birds are likely to be present in natal waters with a much greater proportion of older age classes of immature birds showing affinity with natal waters and therefore the proportions of older age classes is likely underestimated when applying the approach.
  1. The identification of immature age classes of gannets during baseline surveys is far easier than for kittiwakes and the immature proportions calculated for these species are therefore considered to be more representative.
  2. The identification of immature age classes of auk species is not possible from baseline surveys (with the exception of juvenile birds in the post-breeding season) and, where necessary, other sources will be relied upon within the RIAA.