Detecting Japanese Eels (Anguilla japonica) and Revealing Their Distribution in Taiwanese Rivers by Environmental DNA Analysis

The Japanese eel (Anguilla japonica) is the most prevalent freshwater eel species in Taiwan. However, its population has undergone a significant decline in recent decades due to factors such as overfishing, habitat destruction, and the effects of climate change. Urgent action is needed to conserve this species. Before implementing conservation measures, it is imperative to ascertain the distribution of Japanese eels in Taiwan’s rivers. This study’s primary objective was to assess the effectiveness of eDNA analysis as a method for detecting Japanese eels. To achieve this goal, we compared eDNA analysis data with results obtained from electrofishing, with the Fengshan and Shimen Rivers serving as our designated test sites. Additionally, we collected water samples from 34 other rivers across Taiwan to comprehensively assess the species’ wider distribution using eDNA analysis. Our findings demonstrated eDNA analysis’s viability for detecting Japanese eels. Of the 36 rivers tested, Japanese eel DNA was detected in samples from 21 rivers, scattered across northern, eastern, southern, and western Taiwan, with no specific concentration in any region. We also noted reduced detectability of Japanese eel DNA in highly polluted rivers, indicating that river pollution may have a potential impact on their population. In the future, expanding eDNA analysis to more rivers could identify additional rivers that Japanese eels inhabit. Subsequently, resource management and conservation efforts can be focused on these identified habitats. Furthermore, developing advanced eDNA-based methods for estimating the abundance or biomass of Japanese eels could enhance the flexibility of management and conservation measures.