Reliability of Unmanned Aerial Vehicles for the groups size estimation of Grampus griseus (Cuvier, 1812) in the Gulf of Taranto (Northern Ionian Sea, Central-eastern Mediterranean Sea)

In the last decade, Unmanned Aerial Vehicles (UAVs) were applied in monitoring studies addressing to marine and terrestrial wildlife for their multiple advantages. Due to their operational flexibility and low cost, UAVs have been applied in studies aimed at studying behavior, estimating group size and abundance of species as well as at measuring the individuals through photogrammetry methods. In this work, numerical estimates of group size of Risso's dolphin sighted in the Gulf of Taranto from UAVs video-analysis were compared from those recorded by MMO on board of a research vessel. Data were collected from April 2018 to September 2020 for a total of 109:58 minutes of recording. Aerial shots together traditional survey methods allowed a more thorough analysis of the number of individuals observed, offering a better estimates overview, with the possibility of viewing videos several times and taking screenshots. Using UAVs could provide more accurate estimates on Risso's dolphin population. In conclusion, given the efficiency such systems found in this work, the use of UAV could be instrumental in broadening perspectives on marine mammal studies.