This report describes an approach for assessing the collision risk of diving birds with marine renewable energy devices, known as the exposure time population model (ETPM). The approach explores the collision rate required to achieve a critical level of additional mortality by estimating (i) thresholds of additional mortality for the population at risk of collision and (ii) the potential time that each individual within the population is at risk of collision. A judgement is then made as to whether the maximum acceptable collision rate is likely to occur or not.
The ETPM approach provides a broad based assessment of the potential impact of collisions with tidal turbines on populations of diving birds. Given the limited knowledge base and poor understanding of the underwater movements of diving birds and their behavioural responses to underwater devices, this approach is considered an appropriate and useful method for assessing collision risk of diving birds.
Apart from the ETPM, there are a number of other models used to assess collision risk of marine wildlife, namely the adapted Band / SNH collision risk model and the SRSL encounter rate model. We currently do not favour any one model when undertaking a collision risk assessment. All of the available models are likely to have imperfections, and the accuracy of the model predictions is dependent on the quality of the input data. In particular scenarios, the preferred model choice may differ, for which an appreciation of the model parameters and mathematical functions is required. Ultimately, however, the results of any assessment of overall risk are likely to be determined by the assumptions made about the animals’ ability to avoid collisions. At this early stage of our understanding it may be necessary to take a relatively precautious approach in collision risk assessment, including model design and choice, with a view to improving these options as real-life observations improve our understanding of how animals behave in the water and around these developments.
We advise that developers establish early contact with Marine Scotland and SNH to discuss options for undertaking collision risk assessment in connection with any planned marine renewable energy development. Further guidance on underwater collision risk assessments for marine wildlife is currently in development by SNH.