||Japanese eel is an important aquaculture species in Taiwan with very high economic benefit. Because the commercial scale of artificial propagation of the glass eel has not been established yet, the needed fries are all caught from the wild. This results in a serious bottleneck for the aquaculture industry. It is estimated that the current eel resource in Taiwan also suffers the same impact. The Japanese eel is mainly cultured in Taiwan, China, Korea, and Japan, with mean elver demands about 100 metric tons annually. Taiwan needs about 20 tons for aquaculture but only catches less than 5tons in recent years. Thus, to manage and recover the valuable eel resource is a key for the sustainability of eel aquaculture industry.
An efficient Japanese eel releasing method is one of the methods to increase migratory eels. The Fengshan River, Touchan River, Yilan River and Kaoping River of Taiwan will be selected for eel mark-releasing location. In addition, the radio-tagged silver eels were performed in Yilan River. Their life history dynamics and downstream migration will be traced to evaluate a better stock releasing strategy. The five results of the project are:
1. The re-catch of the eel: till Nov. of 2013, a total of 253 wild and 36 released (Female: 23, male: 13) eels were caught. 24 eels were caught from Yilan River (re-catch rate 2.8%, 9 eels with chips). 3 eels were caught from Fengshan and Touchan Rivers (re-catch rate 0.36%). 9 eels were caught from Kaoping River (re-catch rate 1.9%). The average re-catch rates were lower than they were before.
2. Growth and maturation of the re-catch eels: The re-catch eels from Yilan River were mainly concentrated around Dec. 2013, thus there were no significant change on total length and only slightly decrease on body weight. The mean GSI was 0.62, which covered both yellow and silver eels.
3. Tracing of the radio-tagged eels: till Nov. 2013, 15 tagged eels were detected. Their migratory routes were identified by GPS. The overall movement was toward the lower reach, similar to those of the wild eels.
4. Promotion of eel conservation: We had designed the Eel Expo in LanYang Museum between 2012/11/27 – 2013/05/05 and help the related promotion and education activities.
5. Collection of eel resource information: During years 2010、2011、2012、2013,The total annual catch of the Japanese glass eel in East Asia were 41、35、26、19 tons, respectively. The catches in Taiwan were 4.2、4.2、1.9、1.5 tons, respectively. The eel resource seems to become lower and lower.