Environmental DNA concentrations of Japanese eels in relation to habitat characteristics

Abstract

The Japanese eel (Anguilla japonica), is listed as 'Endangered' by the IUCN. Understanding eel riverine habitat is useful in considering conservation strategies. This study sought to determine the relationship between environmental DNA (eDNA) concentrations derived from Japanese eels, water quality, and river structure in three small rivers in Nagasaki, Japan. eDNA was detected at 14 of 15 sites (93%). The concentration of eDNA in brackish water was significantly higher than that in freshwater and was correlated with water depth. Eel occurrence throughout the river suggests a need to conserve a diversity of habitats.

Environmental DNA Reveals the Geographic Distributions of Two Eel Species,Anguilla japonicaandA. marmorata, in Western Kyushu, Japan

“…Japanese eel eDNA was detected in rivers across the country, with the exception of the northern part of the Sea of Japan, in an extensive eDNA survey by Kasai et al (2021). Ono et al (2023) also reported detection in three small rivers in northwest Kyushu, consistent with this study’s high detection rates in all regions (Figs. 1 and 2).…”

“…No correlation was found between eDNA concentrations of the two species at these sites, suggesting that their habitat preferences differ. The wide distribution of Japanese eels from freshwater to brackish water was also reported by Ono et al (2023). In contrast, giant mottled eels were detected at shallower depths, around larger rocks in streams surrounded by thick woodlands.…”

“…Japanese eel and giant mottled eel eDNA concentrations were also reported to be correlated with distances from river mouths (Itakura et al, 2019). Ono et al (2023) also recently reported that eDNA concentrations of Japanese eel were higher at downstream than upstream sites. eDNA surveys of eels on the west coast of Kyushu, Japan may provide insights into dispersal and settlement mechanisms of eels.…”

“…eDNA extraction employed the methods of Itakura et al (2019) and Ono et al (2023). Briefly, eDNA was extracted from the filter using a DNeasy Blood and Tissue Kit (Qiagen, Hilden, Germany) and recovery was performed using a spin column method.…”

“…qPCR assays were performed according to the protocols of Itakura et al (2019, 2020) and Ono et al (2023). Species-specific primers for Japanese eel and giant mottled eel amplify 16SrRNA (Itakura et al, 2019; 2020, Ono et al, 2023).…”