There are around 380 sperm whales off the west coast of Ireland, according to research conducted by Galway-Mayo Institute of Technology.
The whales were counted over the course of six dedicated surveys between May and October during 2015 and 2016.
During a single dive, sperm whales can spend nearly an hour at depths in excess of 300m, with only short periods at the surface.
The Principal Investigator at the GMIT of the ObSERVE_Acoustic said the significance of the discovery is "fundamental to try and understand better Ireland's marine biodiversity in offshore waters".
Speaking to RTÉ's Morning Ireland, Dr Simon Berrow Berrow explained that because sperm whales live far off shore and stay in deep water, the survey team used underwater microphones called hydrophones to record sperm whale sounds or "clicks".
The distinctive echolocation clicks of sperm whales are thought to be the most powerful vocalisations produced by any animal and can be heard over tens of kilometres.
Dr Berrow said the study relied solely on being able to detect the distinctive powerful click trains of sperm whales using the hydrophones.
He said each whale was pinpointed by comparing the exact time that each click arrived at each hydrophone and then triangulating bearings from sequential clicks over extended encounters.
Dr Berrow said this research will help understand the status and habitat of the species so that decisions can be made on how they can be protected.