以衛星遙測技術評估台灣主要河川日本鰻棲地品質現況

Abstract

日本鰻屬典型的降海產卵洄游魚種，分布於西太平洋地區，在東亞地區為高經濟價值魚種。但因完全養殖成本過高，目前養殖場的鰻苗來源仍完全仰賴天然資源。然而，隨著養殖產業的蓬勃發展，日本鰻的資源量自1970年代也開始急遽下降，直至目前，資源量已經不及1970年代的10%。棲地破壞、過漁、以及全球氣候變遷皆是潛在原因。為了評估鰻魚河川棲地品質，本實驗室於2013年使用了一種全新的評估指標－棲地品質指數 (HQI)，以衛星遙測技術評估日本鰻棲地的破壞程度，與過去的棲地調查方法相比，不但省下時間與成本，而且可頻繁的監控，配合水質汙染指標即可隨時做出適當的應變機制。在本篇研究中，我們利用國立中央大學太空及遙測研究中心提供的衛星影像，以及行政院環境保護署的河川汙染資料，評估2014 – 2017年全台灣共38條河川的最新棲地品質指數，每條河川在每個季節都有至少一筆的評估數據。評估結果顯示，台灣北部河川的棲地品質指數，在四個季節的變化上分別為：13.23、14.2、13.46、13.05，東部河川在四個季節的變化為：6、6.24、5.86、5.63，西南部河川在四個季節的變化為：22.87、28.08、27.03、21.63，北部與東部河川的棲地品質在四季變化間較為穩定，而西南部河川有較明顯的季節性變化，特別是在冬季與春季會有棲地品質下降的現象發生。本研究最後計算出2014 – 2017年全台灣共38條研究河川的棲地品質指數，總和為：44.97，扣除本次評估新增的12條中小規模河川所得的總和為：41.46，與本實驗室2016年的研究中所評估的2010年代全台灣共26條河川結果:38.14相比，有些微增加的趨勢，可能的原因為河川汙染程度降低，以及使用了更高解析度的衛星影像。本研究利用衛星遙測技術以及河川汙染資料，對全台共38條河川的日本鰻棲地進行棲地品質的評估，最後發現河川棲地品質會有季節性變化發生，因此各縣市政府在制訂日本鰻相關保護措施時，應該要優先選擇棲地品質指數較高且較穩定的河川以利於日本鰻的生存與保育，而本研究的評估結果可供各縣市政府做為參考依據。

The Japanese eel Anguilla japonica is a typical catadromous fish species that spawns in the sea and is distributed across the Western Pacific. Japanese eels are fish species of high economic value in East Asia. However, due to the high costs of complete aquaculture, currently the source of eel fry in farms still depends entirely on natural resources. Nevertheless, with the rapid development of aquaculture industry, the stock of Japanese eel has also sharply declined since 1970s, and to this day it is less than 10% of that observed in 1970. Habitat destruction, overfishing, and global climate change are all potential causes. In order to evaluate the habitat quality of the Japanese eel, our lab (2013) employed a new assessment indicator－Habitat Quality Index (HQI) that uses satellite remote sensing technology to assess the level of destruction of the Japanese eel habitats. Compared to past habitat survey methods, this method not only saves time and costs, but it also allows frequent monitoring and acts in concert with water quality indicators to implement appropriate response mechanism at any time. In this study, we use the satellite images provided by the Center for Space and Remote Sensing Research of the National Central University, as well as the information on river pollution from the Environmental Protection Administration, Executive Yuan of Taiwan, to evaluate the newest data of the HQI of a total of 38 rivers in Taiwan from 2014-2017. Every river has at least one assessment data for each season. The results showed that the HQI of rivers in the northern part of Taiwan across the four seasons were 13.23, 14.2, 13.46, 13.05; in the eastern part were 6, 6.24, 5.86, 5.63; and in southwestern rivers were 22.87, 28.08, 27.03, 21.63. The habitat quality of northern and eastern rivers is relatively stable across the four seasons, while there is noticeable seasonal variability in southwestern rivers in which the habitat quality declines especially during the winter and spring. Finally, this study calculated the HQIs of a total of 38 studied rivers in Taiwan from 2014-2017, and the sum was 44.97. After deducting the HQI of 12 small and medium sized rivers newly added to the assessment, the value obtained was 41.46. There is a trend of slight increase compared to our lab research (2016) of 38.14 obtained by evaluating a total of 26 rivers in Taiwan in the 2010s. Possible reasons for this trend may be a decrease of the levels of river pollution, and the use of higher-resolution satellite imagery. This study uses satellite imagery and river pollution data to assess the habitat quality of Japanese eel in a total of 38 rivers in Taiwan. The results said that the difference of HQI of rivers depended on the seasons in Taiwan. Therefore, in order to facilitate the conservation of Japanese eel, the governments should choose the rivers that have higher and more stable HQI as the priority selection of rivers to formulate the protective standard.The final assessment results can serve as a reference by county and city governments for developing Japanese eel protection measures.