Vessel-based surveys as a tool to fill critical knowledge gap on Grampus griseus in the northeastern Aegean Sea

Data on Risso’s dolphin are very scarce, possibly due to its wide-ranging movements in the Mediterranean basin. Available data suggest the presence of this species in deep waters, shelf-break areas where the slope is steepest, around offshore islands and archipelagos. A total of eight sightings were recorded during vessel-based surveys carried out along opportunistic line transects from March 2017 to October 2019. The results of the monitoring activity showed that the occurrence of this species in the water surrounding Samos Island is unpredictable and that the characteristics of the environment of each sighting are various, as already shown by previous Mediterranean studies. Nonetheless, the results of this study are promising concerning Risso’s dolphin presence and conservation in the waters surrounding Samos Island.