Drone aerial survey: a new method for monitoring sea turtles in offshore areas

The study of the distribution at sea is of major importance for conservation of big marine vertebrates - such as sea turtles - which spend almost their life in marine environments, facing relevant threats as fishery bycatch. A plethora of methods have been used traditionally on a coarse scale, while fine scale distribution studies only recently started taking advantage of new technologies. In the present thesis I describe a new method of drone aerial survey for data collection about fine scale distribution, providing first information about offshore turtle density within the Tunisian continental shelf. The fieldwork took place during summer 2017 and 2018: I surveyed two marine areas of 1 km2, by means of a quadcopter remotely controlled from a boat, producing high resolution videos which I analysed a posteriori by means of a protocol, aimed to maximize the control of false negatives and false positives. I provide turtle surface density estimates for my surveyed areas and investigate differences in density, by means of generalized linear mixed models; sample size estimate is provided, needed to reach 80% power for significative difference in mean density between areas. This method can be easily reproduced, in space and time, within my study area or elsewhere. The surface density data I provide are the first fundamental information about distribution in an important foraging ground for loggerheads and can be improved by future external studies about behaviour and environment