Density estimates of harbour porpoises Phocoena phocoena at eight coastal sites in Ireland

Single platform line-transect surveys with distance sampling were carried out at eight sites between July and September 2008 to derive density and abundance estimates of harbour porpoises. Over 37 days at sea, a total of 475 track-lines were surveyed for a total distance of 20,623km. From the 332 sightings, a total of 618 individual harbour porpoise were recorded. Overall density estimates ranged from 0.53 to 2.03 porpoises km^-2 (without correction for g(0)). Mean group size varied from 1.41 to 2.67. These data provide baseline information to help identify important habitats for harbour porpoise and reference values for monitoring future changes in harbour porpoise distribution and densities in Ireland.