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研究報告

更新日期: 2015-02-09
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日本鰻人工放流效益及策略評估之研究

年度 2014
計劃名稱 日本鰻人工放流效益及策略評估之研究
中文摘要 一、日本鰻是水產養殖的重要魚種之一,然而目前養殖所需的大量鰻苗仍然依賴天然捕撈,成為養殖產業的重大瓶頸,而人工增殖放流,為增加降海種鰻的手段之一,進而可以增加天然鰻線的數量。有鑑於此本計劃與水產試驗所合作,選定臺灣宜蘭縣宜蘭河、新竹縣鳳山溪,以及南部高屏溪,進行日本鰻的標識放流,並追蹤野放後之鰻魚之生活史動態與降海洄游情形,評估較佳之放流策略,以作為後續辦理鰻魚放流工作之依據。執行方式分為兩部分,第一部分水產試驗所配合執行,從去年底至今協助完成兩次辦理鰻魚標識放流,第一次於2013年11月21日進行標識,放流鰻體型約1.5尾/公斤,共放流約800公斤 (約1200尾),放流前以剪尾鰭、注射耳石螢光劑 (OTC 100 ppm)、以及植入微晶片進行三重標識處理,並於隔日放流500公斤於宜蘭縣宜蘭河,以及300公斤於新竹縣鳳山溪。第二次於2014年6月3日放流約1100公斤,捨去剪尾鰭之體外標識,放流前僅進行注射耳石螢光劑 (OTC 100 ppm)以及植入微晶片等雙重標識處理,隔日放流550公斤於宜蘭縣宜蘭河、250公斤於新竹縣鳳山溪,以及300公斤於南部高屏溪。鰻魚放流後的回收,則分別利用蛇籠、垂釣以及電捕法三種方法同時進行,以進行後續追蹤調查。迄今年10月底為止,鰻魚放流後回收情形,共採集野生鰻 198 尾,放流鰻 20 尾 (雌 13 隻、雄 7 隻),宜蘭河回收到的成鰻共 85 尾,其中有晶片的18尾,鳳山所回收到的鰻魚總共有90尾,其中有晶片的鰻魚總共有2尾,今年度各溪流鰻魚的回收率較低。因放流鰻為養殖鰻魚且環境尚未有大規模的變動,大部分的鰻魚會待在原處,放流後初期的回收率會如此高,推估原因為放流初期鰻魚尚未適應環境,因此較易遭捕獲。而鳳山溪放流初期回收率不如宜蘭河,因漁法為垂釣的關係,鰻魚大多還在適應環境不攝餌,故回收率不佳。放流回收鰻魚體長平均為730  64 mm,最小體長為655 mm,最大為930 mm;體重平均為597  178 g,最小體長為419 g,最大為1053 g。計算所得的肥滿度介於1.3 - 1.8之間,顯示放流鰻在自然環境中適應良好。消化道指數為0.9  0.3 % (0.6 -1.4 %),略低於野生鰻表示放流初期之養殖鰻尚屬適應階段。眼徑指數為5.0  0.9 %,生殖腺指數(GSI)為.0.6  0.5,表示大部分放流鰻尚未銀化,皆屬黃鰻階段。成長部分以耳石來估計正確成長率,評估放流後之體長增加比例,結果發現魚體平均成長4.41.0 cm,最少也有2.3 cm的成長,最多有5.8 cm之成長,表示放流鰻在自然環境中有持續成長。而放流點與回收地點在鳳山溪部分相距不遠,僅有小距離移動,推測鰻魚放流後移動至適當棲地便定棲於定點,或是小範圍往河口移動,無放流鰻上溯之情形被發現。此外本研究評估出宜蘭河流域鰻魚族群數為3675尾,新竹鳳山溪的鰻魚族群數為8550尾,而高屏溪由於沒有回收到任何標識的個體,故無法進行估算。第二部分將利用無線電標識設備,標識30尾鰻魚個體。以GPS全球定位系統定點收發器偵測分別放流於宜興橋下方,在四次偵測中,上段鰻魚總共16隻,都無大量移動,多停留在原處,中段的鰻魚總共10隻及下段的鰻魚總共3隻,發現大部分的魚體順流向下游移動,只有兩隻溯河向上,其推測原因為下游餌料生物選擇性較上游高且棲地環境更適。這些遷移現象與野生鰻銀鰻之降海洄游習性相符,證明鰻魚人工放流有助於資源量的恢復。然持續放流鰻魚於同一河川中須考慮其食餌數量是否足夠,並調查河川之承載量,以做為未來放流河川選擇及放流數量之參考。
英文摘要 一、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 high-cost can not fully support aquaculture needed. Thus, the needed fries are all caught from the wild till now, resulting in a serious bottleneck for the eel aquaculture industry. Thus, to manage and recover the valuable natural eel resource is a key for the sustainability of eel aquaculture industry. This project aims to identify an efficient Japanese eel releasing method by studying the growth, maturation and migration of the released eels in the river. This year we will cooperate with Fisheries Research Institute for eel stock releasing work on Ilan River and Fongshan River. The eels will be marked before releasing. After re-capture, the dynamics of its life history and downstream migration will be evaluated. First part of the project is to cooperate with Fisheries Research Institute to complete the marking procedures. Two release activities were carried out and first time was done in 21th November, 2013. Total of 800 kg of eels at size of 1.5 individual/kg (1200 eels) were undergoing triple marking procedure, including cutting caudal fin, injection of 100 ppm oxyteracycline solution (OTC) and a chip with scanable number into abdominal cavity. Three fishing methods including net, fishing rod and electron fishing were used for recapture. By the end of October 2014, a total of 198 Japanese eel were caught in both rivers, and 20 of them were marked eels, including 13 females and 7 males. In ILan River, 85 wild eels has been recapture (18 marked eels), and 90 individuals were recapture in Fongshan River, including 2 marked individuals. The recapture rates were slightly lower than previous year, and we hypothesis that released eels not get used to the new environment so stop feeding in the beginning so the fishing is not efficient to catch eel. Total length of the recapture eels averaged at 730 ± 64 mm (range 655-930 mm), and average weight is 597 ± 178 g (range 419-1053 g). The condition factor (CF) ranged at 1.3 -1.8, which is similar to wild eel. The digestosomatic index was 0.9 ± 0.3 % which is slight lower indicating the releasing eels stops feeding in the nature environment for the time being. Ocular index is 5.0 ± 0.9 % and GSI is 0.6 ± 0.5 % indicating the releasing eels are still at yellow eel stage but not start silvering yet. We used otolith flurorescent OTC mark to back-calculate the growth after eel release. The eel grew 4.4±1.0 cm (range 2.3-5.8 cm) after released showing the eels continuous grow after been release into nature rivers. The recapture site is closed to the released site showing the eels settle in the nature river once they found suitable habitat, and some individuals migrated downstream for higher productivity. None upstream migration individuals were discovered. The calculated eel population size in Ilan River is 3675 individuals, and in Fongshan River is 8550 individuals. None tagged individuals were recaptured so the population size in Kaoping River can not be calculated. Second part of the project is to use radiometry tags to mark 30 eel individuals and to use receptor together with a GPS system to trace the eel movement in the river. After 4 scanning in every week after releasing, about half of the eels (16 individuals) remain in the location close to the releasing site without any movement. Among them, 10 eels downstream migrated to middle stream and 3 eels migrated even down to estuary, while only 2 eels moved slightly upstream. Those migration direction is close to the eel catadromous nature, and showing the eel releasing can benefit to the spawning eel population. However, the future releasing activities show put other factors, such as the food abundance and carry capacity of the river ecology system, into consideration before determine future site and amount to release.
計畫編號 103農科-11.3.4-漁-F1(2)
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