2.4. Demographic Parameters

  1. Demographic parameters for the key species that have been used in the population models are presented in Table 2.4   Open ▸ . These were selected from Sinclair et al. (2020), and agreed with NatureScot via consultation on the Marine Mammal Methodology Note in September 2023 (volume 3, appendix 5.3, annex B) and the Marine Mammal Consultation Note 2 in January 2024 (volume 3, appendix 5.3, annex E).

 

Table 2.4:
Marine Mammal Vital Rates Used to Parameterise iPCoD Models, from Sinclair et al. (2020)

Table 2.4: Marine Mammal Vital Rates Used to Parameterise iPCoD Models, from Sinclair et al. (2020)

 

2.5. Residual Days Disturbance

  1. Empirical evidence from the constructed Beatrice and Horns Rev 2 offshore wind farms (Graham et al., 2019, Brandt et al., 2011) suggests that the detection of animals returns to baseline levels in the hours following disturbance from piling and therefore, for the most part, it can be assumed that the disturbance occurs only on the day (24 hours) that piling takes place.
  2. Due to the potential duration of piling occurring at the Array (e.g. up to eight hours maximum piling per pile, therefore three piles installed per day, associated with wind turbine anchors), in a 24 hour period. Therefore, the number of residual days of disturbance has, conservatively, been selected as one, meaning that the model assumes that disturbance occurs on the day of piling and persists for a period of 24 hours after piling has ceased.

2.6. Number of Animals Experiencing Injury and Disturbance

  1. The number of animals predicted to experience disturbance or PTS as a result of piling at the Array was based on the density values provided as part of the individual species baseline assessments in volume 3, appendix 10.2.
  2. For the assessment of PTS an average density value was applied to the potential area of effect; calculated from the range out to which the injury threshold was modelled to be exceeded for each marine mammal hearing group. For harbour porpoise the maximum density is based upon 24 months of site-specific DAS data, aggregated over the months of April to September (see volume 3, appendix 10.2, annex A for full details of DAS campaign and analysis methods). For bottlenose dolphin and minke whale density estimates were derived from Lacey et al. (2022), and for grey seal density estimates were obtained from Carter et al. (2022).

 

Table 2.5:
Summary of Species Densities Used in Calculating Numbers of Animals Potentially Disturbed

Table 2.5: Summary of Species Densities Used in Calculating Numbers of Animals Potentially Disturbed

 

  1. To estimate the number of animals potentially disturbed during piling at the Array, the sound contours were mapped, and a dose response approach applied to calculate the number of animals within each 5 dB isopleth using the density values as described in Table 2.5   Open ▸ . For grey seal, however, the quantitative assessment was undertaken by overlaying the unweighted SELssn contours on at-sea density maps ( Figure 2.5   Open ▸ ) produced by Carter et al. (2022). The number of animals in each 5x5 km grid cell was summed for each isopleth and corrected using the proportional response as per Whyte et al. (2020).


Figure 2.5:
Mean Density of Grey Seal per 5 km x 5 km Grid Square (Carter et al., 2022)

Figure 2.5: Mean Density of Grey Seal per 5 km x 5 km Grid Square (Carter et al., 2022)


  1. For all scenarios, designed in measures were applied (see volume 2, chapter 10). Relevant primary mitigation included as designed in measures for the Array are:
  • implementation of soft-start and ramp-up measures or piling and UXO clearance
  1. With these designed in mitigation measures in place, the residual number of individuals potentially affected by PTS was taken forward for the iPCoD model. This is a conservative approach since mitigation measures (i.e. application of an outline Marine Mammal Mitigation Plan (MMMP)) will reduce the risk of PTS further. However, the large injury ranges predicted for some species (volume 2, chapter 10) requires that a conservative approach is taken in parameterising iPCoD models.
  2. Currently the underwater noise models for the Array, assume one minke whale experiencing PTS for the maximum temporal scenario based on the SELcum metric, and up to three minke whale (SELcum) for concurrent piling of wind turbine anchors and OSP foundations under the maximum spatial scenario No other species were predicted to experience PTS based on the SELcum metric, and models based on the SPLpk metric predicted no individuals experiencing PTS for any species. Maximum potential numbers of animals disturbed and injured (PTS) for the maximum temporal scenario is presented in Table 2.6   Open ▸ and maximum numbers of animals disturbed and injured (PTS) for the maximum spatial scenario is presented in Table 2.7   Open ▸ .
  3. To provide context between species, iPCoD models for all species incorporate the number of animals predicted to be affected, based on modelling of the SPLpk metric. Since minke whale is the only species with the potential to experience PTS (when the SELcum metric is considered) additional iPCoD models have also been run for this species to incorporate the potential for PTS. A summary of all models for each species is presented in section 2.9.
  4. For the maximum spatial scenario, modelling locations are detailed in volume 3, appendix 10.1. For disturbance, modelling has been undertaken for piling at the northern location concurrently with the central location, and the southern location concurrently with the central location and is representative of the largest separation of the piling vessels, as detailed within volume 1, chapter 3. Modelling of injury ranges has been undertaken for two adjacent piles at the northern and southern locations.

 

Table 2.6:
Maximum Temporal Scenario: Estimated Number of Animals Predicted to be Disturbed or Injured (PTS) at Any One Time During Piling

Table 2.6: Maximum Temporal Scenario: Estimated Number of Animals Predicted to be Disturbed or Injured (PTS) at Any One Time During Piling

 

Table 2.7:
Maximum Spatial Scenario: Estimated Number of Animals Predicted to be Disturbed or Injured (PTS)[1] at Any One Time During Piling

Table 2.7: Maximum Spatial Scenario: Estimated Number of Animals Predicted to be Disturbed or Injured (PTS)[1] at Any One Time During Piling

 

2.7. Indicative Piling Schedule

  1. The piling schedule used in the iPCoD modelling was developed from the Project Description (volume 1, chapter 3). This provides an estimate of the maximum number of days of piling required for installation of the wind turbine anchors and OSP jacket foundations, within a defined piling window.
  2. The piling phase for the Array is expected to occur across 63 months within the eight-year offshore construction phase (i.e. between 2031 and 2038), with piling for wind turbine anchors expected to be completed in year seven (i.e. 2037). Offshore construction activities are anticipated to reduce during the winter months due to greater risk of adverse weather restricting operations. The iPCoD models are not able to accommodate  fine scale changes in piling intensity over the year, so the estimated piling schedules used for iPCoD modelling assume that no piling will occur in the months of January, February or March.
  3. For the purposes of developing the piling schedule for iPCoD (a required input for all models) indicative programmes were specifically developed for the maximum temporal scenario, maximum spatial scenario, and cumulative scenarios, tailored to each species and based on a realistic installation approach, with piling spread across the eight years. It is important to note, however, that while indicative piling schedules are intended to provide a realistic basis on which iPCoD models are run, these schedules are not intended to reflect the actual final piling operations for an individual project. Fine-scale variability such as seabed composition, environmental factors (such as weather conditions) and transit time between piling locations would be too complex to predict at this stage in the project development process, and the iPCoD framework does not facilitate such nuance.
  4. For the maximum temporal scenario, piling was assumed to occur over the greatest time frame. The 602 piling days ( Table 2.1   Open ▸ ) have therefore been spread as evenly as practicable across the eight-year construction phase, with an interval of two to three days between piling for wind turbine anchors (530 piling days) and approximately 30 days between piling for OSP jacket foundations (72 piling days).
  5. For the maximum spatial scenario, piling was assumed to generate greater levels of underwater noise, but to occur over a shorter time frame than for the maximum temporal scenario. Concurrent piling has been assumed at the wind turbine anchors and the majority of OSP jacket foundations, and all piling at these locations has subsequently been assumed to occur across 306 piling days ( Table 2.2   Open ▸ ).
  6. A summary of the piling schedules for the maximum temporal scenario and maximum spatial scenario used in the iPCoD models is presented in Table 2.8   Open ▸ , and the time points selected from the iPCoD model outputs are summarised in Table 2.9   Open ▸ .
  7. Time points have been selected to coincide with key periods in the piling schedule, and with the six-year duration of statutory reporting periods for SACs. Although no SACs are expected to be directly affected by piling for the Array, and the six-year reporting period may not align precisely with key points in the indicative piling schedule, this interval provides a useful periodicity for reporting of population trajectories, and is close to the generation times for the modelled species (i.e. five to nine years: see Table 2.4   Open ▸ ). Similarly, it is the approach taken for the reporting of offshore piling in Welsh and English waters for the Mona and Morgan Offshore Wind Projects (Mona Offshore Wind Ltd, 2024, Morgan Offshore Wind Ltd, 2023).
Table 2.8:
Indicative Piling Programme for Each Piling Scenario for the Array Within the Eight-Year Offshore Construction Phase

Table 2.8: Indicative Piling Programme for Each Piling Scenario for the Array Within the Eight-Year Offshore Construction Phase

 

Table 2.9:
Selected Time Points from iPCoD Simulation Output and Corresponding Events

Table 2.9: Selected Time Points from iPCoD Simulation Output and Corresponding Events