以環境DNA技術評估臺灣河川中日本鰻資源現況

Abstract

日本鰻 (Anguilla japonica) 為臺灣重要的經濟性物種，然而近幾年來因過度捕撈、棲地破壞及氣候變遷等因素，使其野外族群數量大幅下降，面臨資源枯竭危機。為有效制定保育策略，本研究目標為評估環境DNA (environmental DNA, eDNA) 技術應用於日本鰻資源監測的可行性，結合即時定量聚合酶連鎖反應 (real-time qPCR) 與養殖槽實驗，建立eDNA濃度與生物量間的量化關係，並以此推估野外河川中日本鰻的相對生物量。本研究於2023年至2025年間，選取臺灣北、中、南部18條低污染河川作為調查目標河川，共設置91個樣點進行水樣採集與eDNA分析，利用本實驗室所設計針對日本鰻細胞色素B (Cytb) 基因的引子及探針進行即時定量聚合酶連鎖反應檢測，並利用養殖槽實驗所建立eDNA copy number與鰻魚生物量之間的換算公式，推估各樣點每公升水體中之日本鰻生物量。結果顯示，除雙溪外，其餘河川皆可檢測到日本鰻eDNA訊號，顯示日本鰻分布於多數臺灣河川中。然而，大多數樣點所推估之生物量皆偏低，並有多數需透過two-step PCR才能檢測到，暗示臺灣日本鰻族群數量已普遍處於低位階狀態。同時，也揭示出目前日本鰻資源急需保護的現況。另外，本研究亦指出，河川水量、底質型態、棲地結構及人為干擾 (如攔河堰與捕撈行為) 會可能會對日本鰻分布及其資源造成影響，各種環境參數亦會影響到eDNA檢測的結果。 簡而言之，本研究已成功地建立可用於評估日本鰻資源的eDNA技術，除了能夠調查出日本鰻存在與否，亦能夠推估其資源量，在未來可作為日本鰻資源評估與保育管理之重要工具。

Japanese eel (Anguilla japonica) is an important economic species in Taiwan. However, in recent years, due to overfishing, habitat degradation, and climate change, wild populations of this species have declined drastically, facing a severe risk of resource depletion. To establish effective conservation strategies, this study aimed to evaluate the feasibility of using environmental DNA (eDNA) techniques for monitoring Japanese eel resources. In combination with real-time quantitative polymerase chain reaction (real-time qPCR) and controlled tank experiments, this research established a quantitative relationship between eDNA concentration and eel biomass to estimate the relative biomass of Japanese eel in natural rivers. From 2023 to 2025, we selected 18 low-pollution rivers across northern, central, and southern Taiwan as target sites for investigation. A total of 91 sampling sites were set up for water sampling and eDNA analysis. Using primers and a TaqMan probe specifically designed by our laboratory targeting the cytochrome b (Cytb) gene of Japanese eel, we performed real-time qPCR to detect eDNA concentrations. The biomass of Japanese eel (per liter of water) at each site was estimated using a conversion formula established through tank experiments. The results showed that, except for the Shuang River, Japanese eel eDNA was detected in all surveyed rivers, indicating a widespread distribution across Taiwan. However, most sites showed relatively low estimated biomass, and many required two-step PCR to detect eDNA signals, revealing that Japanese eel populations in Taiwan rivers are generally at low density and in urgent need of conservation. In addition, this study also indicates that river discharge, substrate type, habitat structure, and human disturbances (such as weirs and fishing activities) may affect the distribution and resources of Japanese eel. Various environmental parameters could also influence the results of eDNA detection. This study successfully established an eDNA-based method for investigating Japanese eel resources. The technique not only enables detection of species presence but also allows for biomass estimation, offering a valuable tool for future resource assessment and conservation management of Japanese eel.