4. Summary

  1. This report presents the results of the iPCoD population modelling undertaken for key marine mammal species with the potential to be affected by the Proposed Development and for cumulative projects within relevant study areas. Overall, the iPCoD modelling results demonstrate that there is negligible significant effect to any species under any scenario assessed.
  2. The population models were run to predict potential changes in population size as a result of piling at the wind turbine locations and offshore substation platforms associated with the Proposed Development. Reference populations were based on the latest estimates of population size for the relevant species’ Management Units. The numbers of animals disturbed were based on the maximum design scenario of a 4,000 kJ hammer energy only on the assumption that any population changes would be smaller considering the realistic hammer energy of 3,000 kJ which would affect smaller numbers of animals.
  3. The modelling demonstrated that for all species there was predicted to be no long-term decline in the population with negligible to very small differences between the unimpacted to impacted population size. Even where there were notable differences in the number of animals within the undisturbed compared to the disturbed population (i.e. for minke whale using the 10% reducing to 1% conversion factor) it is considered likely that this variation will fall within the natural stochasticity of the population and therefore would not represent a measurable (and significant) difference.
  4. Results were similar regardless of the conversion factor used to predict numbers of animals disturbed or assessed against a vulnerable subpopulation (harbour porpoise and minke whale). This suggests that even using the most conservative conversion factor of 10% reducing to 1%, the populations of all species are not predicted to be adversely affected by piling at the Proposed Development in the long term and are therefore likely to recover following cessation of piling. Furthermore, a precautionary assumption has been made for this study that animals are disturbed both on the day of piling and for 24 hours the following day leading to additional conservatism in the model.
  5. Similarly, for cumulative projects where piling could occur sequentially and concurrently with the Proposed Development, there were no long-term population level effects predicted for any of the species. The assessment was based on the maximum design scenario for each respective cumulative project (i.e. largest number of animals potentially disturbed at any one time) and therefore represents a conservative approach to the cumulative assessment. Results should, however, be interpreted with caution as there were no details on the actual piling schedules for cumulative projects and it is likely that such activity would be phased due to global availability of piling vessels.  
  6. Though the iPCoD model attempts to model major sources of uncertainty, results will always vary greatly due to environmental and demographic stochasticity in the model (evidenced in the 95% confidence limits in population size; Table 3.1   Open ▸ to Table 3.5   Open ▸ ). Whilst the model shows no evidence of population change from the Proposed Development, there are sources of uncertainty. Variation in demographic rates among years may exist as a result of changes in environmental conditions, or as a result of random processes or chance events which impact vital rates (e.g. survival, fertility, etc.). In two, otherwise identical populations that experience exactly the same sequence of environmental conditions, demographic stochasticity will mean populations will follow slightly different trajectories over time. The model assumes that the effects of environmental variation on survival and fertility are adequately reflected by the range of values obtained from the expert elicitation (and shown in the spread of data around the mean trajectories Figure 3.1   Open ▸ to Figure 3.28:). In addition, the model assumes that survival and fertility rates are not affected by population size (i.e. that there is no density dependent response).
  7. In summary, whilst it is understood that iPCoD is a relatively simple population model (which links days of disturbance to changes in individual vital rates), the most obvious sources of uncertainty have been captured in the model development. In addition, the marine mammal assessment has adopted a precautionary approach in recognition of the uncertainties in how animals respond to repeated piling over time.

5. References

Booth, C.G. and Heinis, F. (2018). Updating the Interim PCoD Model: Workshop Report - New transfer functions for the effects of permanent threshold shifts on vital rates in marine mammal species. Report Code SMRUC-UOA-2018-006, submitted to the University of Aberdeen and Department for Business, Energy and Industrial Strategy (BEIS), June 2018 (unpublished).

Booth, C.G, Heinis, F. and Harwood J. (2019). Updating the Interim PCoD Model: Workshop Report - New transfer functions for the effects of disturbance on vital rates in marine mammal species. Report Code SMRUC-BEI-2018-011, submitted to the Department for Business, Energy and Industrial Strategy (BEIS), February 2019 (unpublished).

Brandt, M. J., Diederichs, A., Betke, K. and Nehls, G. (2011). Responses of harbour porpoises to pile driving at the Horns Rev II offshore wind farm in the Danish North Sea. Marine Ecology Progress Series, 421, 205-216.

Carter, M. I. D., Boehme, L., Duck, C. D., Grecian, W. J., Hastie, G. D., McConnell, B. J., Miller, D. L., Morris, C. D., Moss, S. E. W., Thompson, D., Thompson, P. M. and Russell, D. J. F. (2020). Habitat-based predictions of at-sea distribution for grey and harbour seals in the British Isles. Sea Mammal Research Unit, University of St Andrews, Report to BEIS, OESEA-16-76/OESEA-17-78.

Czapanskiy, M. F., Savoca, M. S., Gough, W. T., Segre, P. S., Wisniewska, D. M., Cade, D. E. and Goldbogen, J. A. (2021). Modelling short‐term energetic costs of sonar disturbance to cetaceans using high‐resolution foraging data. Journal of Applied Ecology, 58(8), 1643-1657.

Donovan, C., Harwood J., King S., Booth C., Caneco B. and Walker C. (2016). Expert elicitation methods in quantifying the consequences of acoustic disturbance from offshore renewable energy developments. Pages 231-237. The Effects of Noise on Aquatic Life II. Springer.

Graham, I. M., Cheney, B., Hewitt, R., Cordes, L., Hastie, G. and Thompson, P.M. (2017). Strategic Regional Pre-Construction Marine Mammal Monitoring Programme 2017. Annual Report for the Moray Firth Regional Advisory Group.

Graham, I.M., Merchant, N.D., Farcas, A., Barton, T.R., Cheney, B., Bono, S. and Thompson, P.M (2019). Harbour porpoise responses to pile-driving diminish over time. Royal Society open science, 6(6), 190335.

Harwood, J., King, S., Schick, R., Donovan, C. and Booth, C. (2014). A protocol for implementing the interim population consequences of disturbance (PCoD) approach: quantifying and assessing the effects of UK offshore renewable energy developments on marine mammal populations. Report number SMRUL-TCE-2013-014. Scottish Marine and Freshwater Science, 5(2).

King, S. L., Schick R. S., Donovan C., Booth C. G., Burgman M., Thomas L., and Harwood J. (2015). An interim framework for assessing the population consequences of disturbance. Methods in Ecology and Evolution, 6, 1150-1158.

Sinclair, R.R., Sparling, C.E., and Harwood, J. (2020) Review of Demographic Parameters and Sensitivity Analysis to Inform Inputs and Outputs of Population Consequences of Disturbance Assessments for Marine Mammals. Scottish and Freshwater Science Vol 11 No 14. 78pp.

Sinclair, R., Booth, C., Harwood, J. and Sparling, C. (2019). Helpfile for the Interim PCoD v5 Model. March 2019.

Southall, B.L., Bowles, A.E., Ellison, W.T., Finneran, J.J., Gentry, R.L., Greene Jr, C.R., Kastak, D Miller, J.H., Nachtigall, P.E. and Richardson, W.J. (2007). Marine Mammal Noise-Exposure Criteria: Initial Scientific Recommendations. Aquatic Mammals 33 (4): 411–521.

Southall, B.L., Finneran, J.J., Reichmuth, C., Nachtigall, P.E., Ketten, D.R., Bowles, A.E. Ellison, W.T., Nowacek, D.P. and Tyack, P.L. (2019). Marine Mammal Noise Exposure Criteria: Updated Scientific Recommendations for Residual Hearing Effects. Aquatic Mammals 45 (2): 125–232.

Taylor, B.L. and DeMaster, D.P. (1993). Implications of non-linear density dependence. Marine Mammal Science, 9(4): 360 – 371.

 

[1] https://smruconsulting.com/?page_id=12050

[2] https://smruconsulting.com/?page_id=13194

[3] Note: Year 4 = Start of 2028 (After Completion of First Two Piling Campaigns) and Year 8 = Start of 2032 (After Completion of Third and Final Piling Campaign).