Environmental <scp>DNA</scp> analysis for estimating the abundance and biomass of stream fish

<jats:title>Summary</jats:title><jats:p> <jats:list> <jats:list-item><jats:p>Environmental <jats:styled-content style="fixed-case">DNA</jats:styled-content> (<jats:styled-content style="fixed-case">eDNA</jats:styled-content>) analysis for detecting the presence of aquatic and terrestrial organisms is an established method, and the <jats:styled-content style="fixed-case">eDNA</jats:styled-content> concentration of a species can reflect its abundance/biomass at a site. However, attempts to estimate the abundance/biomass of aquatic species using <jats:styled-content style="fixed-case">eDNA</jats:styled-content> concentrations in large stream and river ecosystems have received little attention.</jats:p></jats:list-item> <jats:list-item><jats:p>We determined the <jats:styled-content style="fixed-case">eDNA</jats:styled-content> concentration and abundance/biomass of a stream fish, <jats:italic>Plecoglossus altivelis</jats:italic>, by conducting a snorkelling survey in the Saba River, Japan. Furthermore, we evaluated the relationship between <jats:styled-content style="fixed-case">eDNA</jats:styled-content> concentrations and the estimated abundance/biomass of <jats:italic>P. altivelis</jats:italic>, and determined its spatial distribution within the river.</jats:p></jats:list-item> <jats:list-item><jats:p>Across the three seasons from spring to autumn, we found significant correlations between the <jats:styled-content style="fixed-case">eDNA</jats:styled-content> concentration of <jats:italic>P. altivelis</jats:italic> and its abundance/biomass at study sites within the river. We detected the <jats:styled-content style="fixed-case">eDNA</jats:styled-content> at the sites where we found only feeding traces on stones (where <jats:italic>P. altivelis</jats:italic> was not directly observed), but not at sites without feeding traces. Additionally, we tested the optimal number of <jats:styled-content style="fixed-case">qPCR</jats:styled-content> replicates needed for the <jats:styled-content style="fixed-case">eDNA</jats:styled-content> evaluation of <jats:italic>P. altivelis</jats:italic> abundance and biomass; only a small number of replicates was required when the <jats:styled-content style="fixed-case">eDNA</jats:styled-content> concentration was high.</jats:p></jats:list-item> <jats:list-item><jats:p>Our findings suggest that <jats:styled-content style="fixed-case">eDNA</jats:styled-content> analysis is a useful tool to estimate fish abundance/biomass as well as their spatial distribution in rivers.</jats:p></jats:list-item> </jats:list> </jats:p>