The aim of this project is to investigate the influence of environmental and observational effects on Harbour Porpoise survey counts from the NPWS monitoring programme conducted across three spatial areas of conservation in 2007, 2008, 2013-2016 and 2018. First, the detection probability function will be estimated using distant sampling methods extended with covariates in order to understand their effect on the function. Then, the probability of detection will be incorporated into spatial model (density surface model). Finally, using the estimated density surface model, the power to detect changes at given sampling intensities (survey intervals, number of surveys) will be calculated on a site-by-site basis. The project team consist of 2 modellers and 3 marine mammal experts.