Harbour porpoise surveys in the Blasket Islands SAC, 2014

A visual and acoustic survey of harbour porpoises (Phocoena phocoena) in the Blasket Islands SAC was carried out in 2014 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 between June and September 2014, 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 (i) day for three of the survey days as not enough sightings were achieved on the remaining days and (ii) using pooled survey effort and sightings information for those three surveys. The effect of seas-state on density estimates was also investigated. A combined total of 592km of track-line effort was surveyed over the six surveys throughout the survey area. Sightings per survey ranged from 6 to 18 and from 6 to 57 individuals with a total of 68 sightings of 134 individual porpoises overall. Other species recorded included minke whale (43 sightings, 33% of total sightings) and common dolphin (18 sightings, 14% of total sightings). Harbour porpoise density estimates ranged from 0.59 animals per km2 to 2.20 per km2. Surveys took place on: 17th, 18th, 24th June, 23rd August, and 8th and 9th September.