利用棲地品質指數 (HQI) 評估中國長江日本鰻棲地品質的長期變遷

Abstract

日本鰻為東亞地區的養殖魚種，具極高經濟價值，但因過高的種苗人工繁殖成本，至今仍需透過在河口進行人工捕撈鰻苗的方式獲得。因棲息地破壞、水質汙染、過度捕撈等因素，日本鰻資源量快速下降，對比於1970年代，現今已不及當時候的10%。日本鰻主要棲息於中國、日本、韓國、台灣，其中中國約佔總資源量的60%，而1980年代中國經濟快速發展，除修築水泥化河道外，大量興建攔沙壩及水閘門等水利設施，嚴重破壞日本鰻棲息地。本研究聚焦在日本鰻於中國最大的日本鰻棲息地－長江流域，使用陳等人(2013)所發展的評估方法，即棲地品質指數 (HQI) ，分析長期以來的棲息地變化。棲地品質指數使用衛星遙測技術中常態化差異水指標 (NDWI) 得出評估日本鰻棲地面積削減程度，再配合水質汙染程度及河道水泥化程度來計算，和傳統的棲地調查方法相比，可節省大量的時間及調查成本，且能作為長期監控日本鰻棲地品質之指標。 結果顯示，長江之日本鰻棲地品質指數自1970年代至2020年代下降了92%，而有效棲地面積下降86%。長江地區興建攔沙壩及水閘門對於棲地面積影響甚鉅，應儘快制定河川管理，考慮興建魚梯及日本鰻洄游時期水閘門適度開放等生態系統管理思維，修復日本鰻於長江流域之棲地環境。

The Japanese eel is a high-value aquaculture species in East Asia. However, due to the high cost of artificial propagation, seeds for aquaculture still need to be caught at the estuaries. The Japanese eel population has declined quickly because of habitat destruction, climate change, water pollution, and overfishing. Today, the population is less than 10% of what it was in the 1970s. The Japanese eel is mainly found in China, Japan, Korea, and Taiwan, with China accounting for 60% of the total resource. In the 1980s, China's rapid economic development led to the construction of numerous hydraulic structures, such as sand dams and water gates, which severely damaged the Japanese eel's habitat. This study focused on the largest habitat of Japanese eel in China, the Yangtze River basin, with assessing the long-term habitat change by the Habitat Quality Index (HQI) developed by Chen (2013). HQI was calculated from the degree of destruction of the Japanese eel’s habitat assessed by the Normalized Difference Water Index (NDWI) in remote sensing technology, the degree of water pollution, and the degree of river cementation. Compared with traditional habitat survey methods, the method of HQI can save a lot of time and survey costs. In addition, it also can be used as an indicator for the long-term monitoring of the habitat quality of the Japanese eel. The results showed that the HQI and effective habitat area of the Japanese eel in the Yangtze River had decreased by 92% and 86%, respectively, from the 1970s to the 2020s. The construction of sand dams and water gates in the Yangtze River region has significantly impacted the habitat area. Therefore, it is necessary to develop river management measures and consider ecological management strategies, such as the construction of fish ladders on sand dams and opening water gates during the Japanese eel's migration period, to restore the habitat environment of the Japanese eel in the Yangtze River.