In order to contribute to the Department Housing, Local Government & Heritage (DHLGH) site management and surveillance, visual monitoring of harbour porpoises was carried out in Rockabill to Dalkey Island SAC during the summer of 2021. This was the third dedicated line transect survey of harbour porpoises within this SAC which enabled ongoing trends in summer density estimates to be explored. The objectives of the survey in 2021 were to:

i) derive updated summer density and population estimates for harbour porpoises within the Rockabill to Dalkey Island SAC using robust sampling methods for small cetacean density/population estimation;

ii) estimate associated Coefficients of Variation and 95% Confidence Intervals