In June 2008 Gaia Research Institute Onlus started a systematic survey of mega-fauna in the Northern Eastern Ionian Sea, in cooperation with the researchers of the Life and System Biology Department of the University of Turin (Italy). GAIA_IONIAN_2008-2018 dataset includes ten years of effort (survey track) and sightings data of marine mammals and marine reptiles collected by experienced marine mammal observers (MMOs) on board of a 12m sailing vessel. MMOs visually inspected both sides (130° angle) of the research vessel, while navigating along random transects. Distance and angle from the track line of each sighting were always recorded.