Using unoccupied aerial systems (UASs) to reveal sex-specific strategies of sea turtles for informed conservation action

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Liam C Dickson and Gail Schofield, School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom

Background/Question/Methods
Current advances in understanding the ecology of large-marine vertebrates are driven by technological advances, with unoccupied aerial systems (UASs) providing a novel perspective facilitating population level studies. Resource requirements often vary among individuals in a population, such as males versus females, leading to sex-specific requirements, which might not be encompassed in conservation efforts. Here, we used UASs to evaluate sex-specific differences in the distribution and orientation of male and female loggerhead sea turtles during the breeding period and the potential implications on conservation action. Two sites (Zakynthos and Kyparissia; >100 to 480 individuals/year frequenting ̴10 km coastline/site) in western Greece (Mediterranean) were uniformly surveyed at 1-2 week intervals during the breeding period (May to July) over three years (2017 to 2019). The number, geographical position, behaviour, sex, orientation and geographic position of all turtles detected on UAS footage were documented.
Results/Conclusions
At both sites, around four times more females were present, indicating the need to ensure sufficient protection for males. Males were more widely distributed across the breeding area and were primarily orientated parallel to shore and typically swimming. These strategies likely maximise search effort for females, with parallel movement to shore enhancing encounter rates with females and, hence, chances for mating. In comparison, females were predominantly stationary (resting or basking), and were primarily orientated parallel to shore during the mating period, and perpendicular to shore afterwards (nesting period). This is likely associated to mate detection and maintaining position, respectively. Through maintaining position, females optimise nearshore habitat use (access to warm water) for developing eggs before egg laying, minimising energy expenditure, which is vital as this site is on the edge of the breeding range (i.e. thermally suboptimal). Thus, males and females utilise different strategies at breeding aggregations to meet sex-specific resource requirements and enhance reproductive fitness, resulting in differences in spatial habitat use. In conclusion, UAS surveys provide the opportunity to elucidate relative numbers and varying resource needs of different components of populations for integration in conservation planning.