A visual and Passive Acoustic Monitoring (PAM) survey of harbour porpoises (Phocoena phocoena) was carried out in 2013 at two Special Areas of Conservation (Rockabill to Dalkey Island SAC, Co Dublin and Roaringwater Bay and Islands SAC, Co Cork) in order to derive local density and abundance estimates. Single platform line-transect surveys were carried out according to a standardised design on six days at each site between July and October 2013, and a towed hydrophone array was deployed during all surveys to collect ancillary passive acoustic data. Distance sampling was used to produce a detection function based on the observed distribution of harbour porpoise sightings. Abundance estimates were calculated using the day as the sample and the sighting as the observation (i) for all survey days with sufficient sightings and (ii) for each site overall using pooled survey effort and sightings information