Inshore boat-based cetacean Survey 2010

Concurrent visual and acoustic surveys for cetaceans were carried out within three survey blocks along the western seaboard of Ireland (Northwest – Block A, west – Block B and southwest – Block C) to investigate species distribution, relative abundance and absolute abundance where possible. Single platform line-transect surveys were carried out in each survey block between July and October 2010. Distance sampling was used to estimate the density and abundance of common dolphins (Delphinus delphis), within two survey blocks. A towed hydrophone was used to survey acoustically along the track-line. During the three surveys, 450 km of survey effort along 33 track-lines was carried out, of which around two-thirds was performed in sea-state ≤3. A total of 92 sightings comprising 528 individuals of at least six species were recorded. With 63 sightings of 458 individuals, common dolphins were by far the most abundant cetacean species recorded. There was a total of seven sightings of 12 harbour porpoise (Phocoena phocoena) recorded, 10 sightings of 12 grey seals (Halichoerus grypus), two sightings of single minke whales (Balaenoptera acutorostrata), one sighting of eight bottlenose dolphins (Tursiops truncatus) and one sighting of two killer whales (Orcinus orca). Six sightings with a total of 67 dolphins were not identified to species level.