Allometric Scaling in Environmental DNA Concentration of Japanese Eel <i>Anguilla japonica</i> Confirmed Under Laboratory and Natural Conditions

ABSTRACT Environmental DNA (eDNA) analysis offers a noninvasive, efficient, and sensitive approach for biomonitoring in aquatic ecosystems compared with traditional capture‐based methods. However, accurately estimating species abundance using eDNA analysis remains challenging due to uncertainty in the correlative relationship between eDNA concentration and organism abundance in natural environments. This uncertainty is partly attributed to variation in body mass distribution within and among populations, which may be addressed by integrating body size allometry into eDNA production models. In this study, we focused on the Japanese eel ( Anguilla japonica ), an endangered species of anguillid eel that is globally recognized as a significant food and cultural resource, to investigate whether eDNA production scales allometrically with body size. We reanalyzed existing datasets describing the relationships between A. japonica eDNA concentration and abundance under both laboratory and riverine conditions. Our results show that eDNA concentrations were scaled allometrically with body mass (0 &lt; b &lt; 1), with scaling coefficients closely matching those previously estimated for A. japonica oxygen consumption rate. The effect of allometric scaling, however, appeared weaker in riverine environments than under laboratory conditions, and integrating body size allometry did not substantially strengthen the relationship between eDNA concentration and abundance. These findings underscore the importance of body size structure in eDNA production for anguillid eels and highlight the potential of allometric scaling to refine eDNA‐based abundance estimates. Further studies on the mechanisms of eDNA production and the influence of environmental parameters are needed to enhance the accuracy and applicability of eDNA analytical procedures for population assessments in the wild.