The interim Population Consequence of Disturbance (iPCoD) is a framework that allows individual-level effects from disturbance to be scaled to population-level impacts. This approach is parameterised by published figures for specific UK populations or derived from the literature for a given species. The original iPCoD model was developed in 2013, with subsequent reviews of the recommended demographic input parameters in 2014 and 2017. This current report by SMRU Consulting establishes the most up-to-date information on five key species of UK marine mammal (harbour porpoise, bottlenose dolphin, minke whale, harbour seal and grey seal) for use in the iPCoD model.
The report also examines the sensitivity of model output to potential misspecification in the various input parameters that are obtained via expert elicitation. Two approaches were used in the sensitivity testing: the effect of changing the value of a single parameter independently of the others and the effect of adjusting all the demographic parameters systematically to compare scenarios with the same population trajectory but different combinations of demographic parameters. The observed sensitivity to misspecification is complex, however, in general, the demographic parameter most sensitive to this issue was pup/calf survival. However, the sensitivities identified were only apparent at relatively high (and somewhat unrealistic) levels of impact, and therefore SMRU Consulting conclude that the metric of counterfactual of population size, which is presented in impact assessments, is robust to misspecification in demographic rates. Several criteria are still to be explored, such as the sensitivity of alternative output metrics, a wider range of impact scenarios and the effect of any density-dependence. Future directions and recommendations for the iPCoD approach are also suggested.
The updated demographic parameters will improve assessments, and will now be available in time for the upcoming ScotWind leasing round. Where the sensitivity analysis has identified sources of variability and uncertainty in outputs, this will aid interpretation of assessments by advisors and decision makers.
The project was undertaken by SMRU Consulting and funded by Scottish Government.