Japanese eel is an important aquaculture species in East Asia with high economic value. Although artificial propagation of the glass eel has been successful, the commercial scale of production still cannot been established yet due to high cost. Thus, the needed fries are all caught from the wild till now, resulting in a serious bottleneck for the eel aquaculture industry. It is estimated that the current eel resource in East Asia is less than 5-10% in comparing to that in year 1970s. Taiwan also suffers the same impact. The Japanese eel is mainly cultured in Taiwan, China, Korea, and Japan, with mean elvers demand about 80-100 metric tons annually. However, the amounts of glass eel catch in recent years decline rapidly, with one piece of glass eel even charging more than 200 NTD. This seriously bugs the eel aquaculture in East Asia. Thus, to manage and recover the valuable natural eel resource is a key for the sustainability of eel aquaculture industry.
The Council of Agriculture announces the regulation of glass eel catching in year 2013. The glass eel are only allowed to be caught during Nov. 1st through Feb. 28th of the next year. Besides, all counties of Taiwan should choose at least one river as the eel protection river. Eel larger than 8 cm are not allowed to be caught in order to protect the seawater migration of the wild and released eels. Besides, Fisheries Research Institute performs eel stock releasing every year to hope that the released eels could go seawater migration and spawning. Thus, the aims of this project are: (1) To investigate resource status and distribution of the glass eel in Taiwan; (2) To investigate the eel resource and catch status of rivers around Taiwan; (3) To investigate the eel resource status of Lanyang Rivers, Kaoping Rivers and Toucian Rivers; (4) To investigate the long-term change of the eel habitat quality of eel protection rivers.
The present results include:
1. There are a total of 6 eel species found in Taiwan, including the very rare A. interioris. The mean CPUE (individuals/hr/net) of the Japanese eel between Nov.-Feb. of this year in Yilan River eatuary is higher than that of the last year (30.8 vs. 10.4), suggesting good correlation to the total catch of the Japanese glass eels in Taiwan. The peak CPUE of A. marmorata occurs around Jun.-Jul. in this year, different to the usual two peaks occurring around Apr. and Sep., respectively.
2. The eel habitat quality of rivers is bad in Taiwan due to pollution, river bank cement and re-directing of river water. The wild eel resource is scare now. The professional eel catchers are almost disappear nowadays; eels are by catch by only some fishing people and fisherman. The Yilan County has most abundant Japanese eel resource in Taiwan. 30 years before the Japanese eel is far more abundant than that of the A. marmorata, now the ratio reversed due to rapid loss of the Japanese eel. In Hualiang and Taidong Counties, A. marmorata is more abundant, but also suffer resource decline. Overall, the resource of A. marmorata is more than that of the Japanese eel, with annual catch in Taiwan below 5 and 1 tons, respectively. They are bought by some local restaurants or eaten by the catchers, and very few wild eels are sold in the market.
3. The eel resource status of Lanyang Rivers, Kaoping Rivers and Toucian Rivers are investigated by electric fishing in the up-stream and by net trap in the estuary. From Nov. 21, 2013 through middle Nov., 2014, Fengshan Rivers have most abundant Japanese eel resource. The catch data by net trap mostly reflect the Japanese eel and thus have some bias.
4. By using Arc GIS to analyze the long-term changes (between 1970-2010) of river habitat quality, the HQI (habitat quality index), the HQI of Lanyang Rivers decrease 72%, the Toucian Rivers decrease 56%, and the Kaoping Rivers decrease 85%. The quality of eel river habitat decreases significantly in the past 4 decades.