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Water sampling for environmental DNA surveys by using an unmanned aerial vehicle

Environmental DNA (eDNA) techniques utilizing DNA fragments from water have recently been developed to investigate the distribution and abundance/biomass of aquatic organisms. The eDNA technique is based on the analysis of DNA fragments in sampled water; thus, an unmanned aerial vehicle (UAV; drone) would be a useful way of collecting water for eDNA sampling, and may consequently allow us to extend eDNA surveys both spatially and temporally. Here, we developed a new method of water collection by using UAV with bleachable equipment, to avoid DNA contamination. To test the performance and contamination risk of UAV water sampling in eDNA surveys, we sampled water from a dam reservoir, detected eDNA from two fish species, and compared the water samples obtained by UAV with those obtained by boat. Additionally, we investigated contamination using blank samples. The results revealed that our UAV water sampling method performed similar to the boat sampling method. No positive signals were detected in the blank samples, including those used for UAV sampling, transportation, filtering, and PCR blanks. Our UAV method can be used to investigate species distributions using eDNA. Combinations of UAV technologies, including remote and thermal sensing, will enable efficient environmental monitoring in various waterbodies.