Assessing Japanese eel (Anguilla japonice) resource in Taiwan by using Habitat Quality Index (HQI)

日本鰻為日本、韓國、台灣與中國等國家的重要養殖魚種。由於日本鰻的完全養殖成本過高，目前人工養殖的魚苗來源仍須仰賴漁民於河口所捕撈的天然鰻苗。然而，自1970年代起日本鰻的資源量就嚴重下降。為了制定出良好且有效的日本鰻管理計畫，評估日本鰻棲地的破壞程度與計算河川中的鰻魚資源量是極為重要的。為此，邵等(2015)發展出一種全新的指標名為棲地品質指數(HQI)，並表示此指標能夠間接並迅速的估算日本鰻的資源量。在本篇研究中，我們試著強化棲地品質指數與台灣河川中日本鰻資源量之間的相關性，並利用這項指標評估台灣26條主要河川中日本鰻資源量自1970年代至2010年代之間的變遷。實驗結果根據皮爾森相關係數分析發現，強化後的棲地品質指數與台灣河川中的日本鰻資源量有極顯著的正相關，因此能被用來估算河川中的日本鰻資源量。而結果也顯示，本篇研究中的26條河川的棲地品質指數總和在1970年代、1980年代、1990年代、2000年代與2010年代中分別為106.9、40.7、31.1、28.7與38.1，從1970年代到2010年代之間，棲地品質指數共下降了64.3個百分比。在台灣這26條河川中，推估現今的日本鰻資源量大約是44601尾。本研究所使用之日本鰻棲地品質指數較其他資源量評估方式節省成本，未來可應用在其他國家估算日本鰻資源量。The Japanese eel Anguilla japonica is an important aquaculture species in Japan, Korea, Taiwan and China. Eel fry used in aquaculture can only be obtained via the field capture of glass eels in estuaries due to the high cost of artificial propagation. However, eel stock has been in rapid decline since 1970s. Assessing continent habitat degradation and estimate natural eel resource in river thus become important for establishing eel management plans. Shao et al. (2015) developed a novel index called habitat quality index (HQI) and suggested that HQI could be used for indirect, fast and large-scale eel abundance evaluation. In present study, we tried to strengthen the relationship between HQI and eel abundance in the rivers of Taiwan, then using HQI to estimate the overall eel resource in Taiwan, and to assess the long-term eel resource variation (between1970s-2010s). According to the result of Pearson’s correlation analysis, the correlation between HQI and eel resource was significant, thence could be used for estimating eel abundance in rivers. The total HQI from twenty six rivers in 1970s, 1980s, 1990s, 2000s and 2010s is 106.9, 40.7, 31.1, 28.7 and 38.1. The total HQI between 1970s-2010s in twenty six rivers of Taiwan decreased 64.3%. The proximate Japanese eel resource in 26 rivers of Taiwan in current status is 44601 fish. This Japanese eel resource assessment method could also be used to assess the eel resource in other country