藉由耳石鍶鈣比探討義大利水域歐洲鰻之洄游生活史與棲地利用策略

Migratory history and habitat-use strategy of the European eel Anguilla anguilla in Italian waters as indicated by otolith Sr/Ca ratios

李玳瑜(Dai-Yu Li)

指導教授 ： 曾萬年

國立臺灣大學/生命科學院/漁業科學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.01503

摘要

耳石鍶鈣比能反應環境水體的鹽度變化，而被廣泛地應用於重建魚類在海水-淡水之間的洄游現象。本研究應用耳石鍶鈣比來探討地中海地區歐洲鰻(Anguilla anguilla)的棲地利用及其洄游環境史。使用的樣本分別採自義大利的Tevere River (TR，年平均鹽度為0.0 psu)、Lesina Lagoon (LL，年平均鹽度為16.0 ± 11.4 psu)、及Caprolace Lagoon (CL，年平均鹽度為38.1 ± 4.5 psu)等三個棲地。採樣數量總共180尾，全數進行生物學分析。並從中隨機挑選出56尾，利用電子微探分析儀 (EPMA) 測量其耳石邊緣以及從耳石原基至邊緣的鍶 (Sr)、鈣 (Ca) 濃度的時間序列變化，來重建每一尾鰻魚的洄游環境史。鰻魚在淡水的TR、半淡鹹水的LL 及海水的CL時的耳石邊緣鍶鈣比平均 (± SD) 值分別為2.8 ± 0.8×10-3、7.8 ± 1.9×10-3及 10.3 ± 1.7 ×10-3。非成對t值測驗結果顯示，耳石鍶鈣比比值在不同棲地之間具有極顯著的差異 (p < 0.01) ，且與水體環境的鹽度呈正相關關係 (R2 = 0.63, p < 0.01) 。此證明耳石鍶鈣比可以當作鰻魚洄游環境的指標。此外，也發現耳石鍶鈣比與水溫之間的關係，在TR於冬季所捕獲的鰻魚顯示為負相關，但在LL及CL的鰻魚不論捕獲於冬、夏季皆為無相關。這似乎暗示耳石鍶鈣比的溫度效應會受到鹽度的影響。根據鰻線階段以後耳石鍶鈣比的時序列變化，可將上述三種棲地的56尾鰻魚的洄游環境史分為淡水型 (FW)，半淡鹹水型 (BW) 和海水型 (SW)，以及棲地間洄游型(Inter-habitat shifter, IHS)。 IHS 在三個棲地的比例以貧營養鹽、高鹽度的CL為最高 (95%)，而在淡水的TR 和富營養鹽、半淡鹹水的LL則分別為40% 及35%，這表示歐洲鰻比較喜歡在具有豐富營養鹽及較低鹽度的環境下生長，且相較於棲息在高鹽度的鰻魚，棲息在較低鹽度的鰻魚有較高的成長率 ( p < 0.01) 。綜上所述，歐洲鰻在義大利水域的棲地利用非常多樣化且其棲地利用是屬於隨機性洄游 (Facultative catadromy)。此外，本研究的結果也符合前人所提出鰻魚的洄游行為主要是受到環境因子影響的觀點。

關鍵字

歐洲鰻 ； 洄游環境史 ； 棲地利用 ； 耳石鍶鈣比 ； 義大利水域

並列摘要

To understand the migratory behavior and habitat use of the European eel Anguilla anguilla in habitats with different salinities, a total of 180 eels were collected from Tevere River (TR, annual mean salinity = 0.0 psu), Lesina Lagoon (LL, annual mean salinity = 16.0 ± 11.4 psu), and Caprolace Lagoon (CL, annual mean salinity = 38.1 ± 4.5 psu), Central and Southern Italy. All of the 180 eels were conducted for biological estimation (e.g. age, total length, and weight) and 56 of them were randomly selected for otolith Sr/Ca ratios analysis. The analyzed path was separately from primordium to otolith edge and at the otolith edge by Electron Probe Micro-analyzer (EPMA).
The mean ( ± SD) Sr/Ca ratios at otolith edge are 2.8 ± 0.8×10-3, 7.8 ± 1.9×10-3, and 10.3 ± 1.7 ×10-3 for eels respectively collected from freshwater TR, brackish water LL, and seawater CL, significantly different among each other ( p < 0.01 ). The positive correlation between otolith Sr/Ca ratio and the ambient salinity (R2 = 0.63, p < 0.01) confirmed that Sr/Ca ratio is reliable in studying migratory history of the eel. Furthermore, the negative correlation between otolith Sr/Ca ratio and water temperature was only found in eels from TR, but not for eels from LL or CL, indicating that the effect of water temperature on otolith Sr/Ca ratio might be influenced by salinity.
Based on the temporal change in otolith Sr/Ca ratios, the migratory type and habitat use of 56 eels in the above three habitats were categorized into freshwater type (FW), brackish water type (BW), and seawater type (SW), as well as inter-habitat shifter type (IHS; eels migrated between habitats). The proportion of IHS is higher in the oligotrophic and highly saline CL (95%), followed by fresh TR (40%), and is lower in the eutrophic and brackish LL (35%). This suggests that eels preferred to settle in habitats with rich nutrient and lower salinity during the growth phase. To sum up, European eels in the Italian waters of Mediterranean area display high diversity of habitat use and their habitat use is facultative catadromy. In addition, our results are consistent with the hypothesis advanced in the previous studies that migratory behavior of the eel is mainly affected by environmental factors.

並列關鍵字

European eel Anguilla anguilla ； migratory history ； habitat use ； otolith Sr/Ca ratio ； Italian waters

參考文獻

林世寰 (2004) 鹽度與餌料對日本鰻鰻線體成長及耳石鍶鈣比的影響。國立台灣大學動物學研究所碩士論文，台北。

曾明彥 (2010) 台灣淡水河流域烏魚的生活史特徵及洄游行為。國立台灣大學漁業科學研究所碩士論文，台北。

林裕嘉 (2009) 高屏溪日本鰻族群動態及永續利用:YPR和SPR模式的應用。國立台灣大學漁業科學研究所博士論文，台北。

曲有為 (2005) 利用性比及耳石元素指紋圖辨識高屏溪野生與養殖日本鰻 (Anguilla japonica) 之研究。國立台灣大學漁業科學研究所碩士論文，台北。

References in English