We’re delighted to announce the release of a new report,  where we used the Interim Population Consequences of Disturbance (iPCoD) model to investigate the potential ‘aggregate effects’ that could arise from the currently planned 12 years of English wind farm construction on the North Sea harbour porpoise population.

The effects of pile-driving noise has been established to have the potential to impact harbour porpoises from a number of studies. The objective of the study, funded by Natural England and the Joint Nature Conservation Committee, was to explore the forecasts of aggregate impact based on the planned construction activities from 10 wind farms off the east coast of England. With a lot of uncertainty about the harbour porpoise population and the effects of pile driving on individuals it was essential to model a suite of different scenarios to provide a range of plausible outcomes of the likelihood that pile driving might affect the North Sea harbour porpoise population. The report is available here.

As highlighted by Natural England:

There are limitations with such predictive models and also uncertainties in our knowledge of harbour porpoise ecology, movements, and in particular how disturbance affects vital rates. These are clearly stated within the report. Population modelling exercises such as this one help to identify which elements of the interaction between noise and species might be the most important in influencing population outcomes. This in turn informs which key areas of uncertainty should be the focus of further work.

To deliver this project, we collated information from 10 wind farms on the planned construction schedules, estimated disturbance impact ranges (i.e. how far the sound from pile-driving might impact animals) and numbers of porpoise predicted to be affected. Initially the information presented in the licensing documents (e.g. environmental statements (ESs)) was used for each site and simulations run exploring how the disturbance associated with construction of these sites could impact the porpoise population. However, as licensing documents are prepared years in advance of construction and due to uncertainties in final wind farm design, they tend to represent the worst case (i.e. longest construction period and largest estimates of disturbance). Therefore a second set of up-to-date scenarios was built by liaising directly with the relevant offshore wind farm developers. We’re grateful to developers for contributing to this project allowing realistic construction schedules to be modelled.

Using the worst case from the ESs, the predictions of a risk – of a population annual decline equal or greater than 1% occurred in between approximately 1 in 5 and 1 in 8 of scenarios when assessed 12 years after the start of construction. However, the updated, more realistic simulations resulted in a dramatic lowering of this risk, with the chance of such declines being between approximately 1 in 16 and 1 in 333 . In general, the observed variation in predicted risk in different scenarios depended on the impact density estimates, predicted noise impact ranges and dose response functions used. Crucially, they also varied depending on the assumptions made about how porpoises use their environment and the longevity of disturbance effects on porpoises.

The Interim PCOD model was specifically built to assess the impacts of offshore renewable energy development on UK marine mammals. It has been designed to use the kinds of information that are likely to be provided by developers in their Environmental Statements and Habitats Regulations Assessments. The model is freely available and allows the user to predict the population consequences of disturbance and injury on five key priority species of marine mammal found in the UK – bottlenose dolphins, harbour porpoise, minke whale, harbour and grey seals.

You can learn more about PCoD here.