ObSERVE Phase II Aerial Project recorded 39,400 sightings of 24 seabird species and 2,200 sightings of 17 cetacean species. Common seabirds included northern gannets, black-legged kittiwakes, northern fulmars, and common guillemots. Cetaceans sighted included common dolphins, bottlenose dolphins, harbour porpoise, and minke whales, with rare sightings of killer whales and beaked whales. The project highlighted seabird hotspots in the Irish Sea and southwest coastal waters, and cetacean hotspots in the Celtic Sea and west coast. Avian flu caused mortality of up to 3,000 northern gannets. The findings will inform future regulation and sustainable management of Ireland’s maritime area.