A visual survey of harbour porpoises (Phocoena phocoena) was carried out in Roaringwater Bay and Islands SAC between June and September 2020 in order to derive local density and abundance estimates. Single platform line-transect surveys were carried out according to a standardised design across six days between June and September. Distance sampling was used to produce a detection function based on the observed distribution of harbour porpoise sightings. Abundance estimates were calculated using the survey day as the sample and sightings as the observation for 1) each survey day, 2) stratified by sea state and 3) for all surveys combined