An eight day cruise led by Galway Mayo Institute of Technology (Ireland) on board the RV Celtic Voyager in the North East Atlantic Ocean in April 2021. Extensive visual surveys and Passive Acoustic Monitoring (PAM) for marine mammals was carried. Additionally, 22 CTD deployments were conducted. Visual monitoring: Single platform line-transect survey mode was conducted following track lines. The visual survey was carried out by a team of 2 Marine Mammal Observers (MMOs) and 1 data logger. Watches were conducted during daylight hours. Observers and data logger were rotating positions every hour in order to avoid fatigue and optimize data collection. The MMOs scanned the area from the platforms located on the bridge wings of the R.V. Celtic Voyager, 5.5m above the waterline, provided that environmental conditions allow. The area was scanned within an arc from 10° starboard to 90° port and from 10° port to 90° starboard to a distance of 1km. Watches were conducted by naked eye and the help of high quality 8 x 42 binoculars. Binoculars and digital cameras with telescopic lenses were used to confirm species identification and group size. Vessel position, sightings (species, group size, behaviour, distance, bearing and heading) and environmental data were recorded using the software IFAW Logger 2000 TM, which logged the data into a Microsoft Access database. GPS position of the vessel was also recorded into the database. Passive Acoustic Monitoring: Passive Acoustic Monitoring was conducted simultaneously with visual monitoring. The acoustic equipment consisted on a 200 m hydrophone array that allowed the detection of low and high frequency sounds. This was connected to an interface unit, in turn connected to external soundcards, all of which was fed into the detection software PAMGuard. An external GPS unit provided data to the setup. Real-time acoustic monitoring was carried out by the data logger. The vessel was in operation 12 hours per day, following transects along the shelf edge during the 3rd and 4rd of April. Due to adverse weather conditions, effort was maintained but in different areas: from the 5th to the 9th of April, areas along the west coast of Ireland, from the Aran Islands to Loop Head and Galway Bay were surveyed. Collect information about the distribution and abundance of marine mammal species inhabiting offshore Irish waters specially of deep-diving cetaceans (sperm, beaked and pilot whales) taking into account oceanographic parameters. Carry out real-time passive acoustic monitoring in offshore Irish waters along the shelf edge covering areas of the Porcupine Bank, Porcupine Sea Bight, slopes and submarine canyons systems, key-habitats for deep-divers and other species present in the area and monitor the soundscape and the potential presence of anthropogenic noise in the surveyed areas. Carry out single-platform visual surveys to complement passive acoustic monitoring and provide absolute abundance estimates for marine mammals in the surveyed areas. Conduct CTD sampling at different stations in order to obtain oceanographic parameters that could be included in modelling approaches, helping to identify environmental drivers of cetaceans’ distribution and abundance along the surveyed areas. Update existing time-series data allowing to identify temporal trends and areas of conservation concern.