Efficacy of environmental DNA to detect and quantify stream tadpoles of Odorrana splendida

Environmental DNA (eDNA) can be used to detect and estimate the density of rare or secretive species, especially in aquatic systems. However, the efficacy of eDNA method has not been validated in lotic systems. We examined the efficacy of the eDNA method to detect and estimate abundance and biomass of a stream-dwelling frog species, Odorrana splendida. We conducted eight field surveys over 2 years and obtained 53 water samples from 10 streams with known distribution of O. splendida tadpoles. The eDNA method accurately detected the presence of O. splendida in 79.2% of survey samples. The amount of O. splendida eDNA (copies s(−1)) in the water samples fluctuated seasonally and each site showed different peaks during different seasons. The relationship between the abundance or biomass of tadpoles and the amount of eDNA was significantly positive, but was not strong, probably because of a large difference in the relationship patterns among streams. In lotic systems, water flow might prevent even distribution of eDNA and thus make it difficult to obtain eDNA reflecting its total amount in the water. Sampling a larger amount of water or higher number of subsamples might more accurately reflect the presence and absolute amount of eDNA in water.