水溫對櫻花鉤吻鮭族群的影響

外文標題: 
The Effect of the Water Temperature on Taiwan Landlocked Salmon (Oncorhynchus masou formosanus) in Chichiawan Stream Basin
校院系所: 
國立清華大學 生命科學系
指導教授: 
曾晴賢
出版年份: 
1997年
主題類別: 
摘要: 

本研究監測櫻花鉤吻鮭(Oncorhynchus masou formosanus)的最後 棲息地-七家灣溪流域的全年水溫變化。探討水溫變化的特性與影響櫻花 鉤吻鮭各時期的程度,以瞭解天然 族群量變化與水溫之間的關係。 自1996年元月至1997年五月間,以自動記錄的光學型溫度記錄器放置於七 家灣溪上中 下游各河段讀取水溫資料,分析可知七家灣溪流域水溫的變 化具有空間上與時間上的特色 。 在時間上,全年水溫變化可分為升溫時期(二月至七月)與降溫時期(八 月至隔年元 月)。最大的升溫幅度在六月初,並造成最大的日溫差變化 。最大的降溫幅度是在十一月 末至十二月初,此時期也是櫻花鉤吻鮭受 精卵孵化的重要時期。在空間上,自三號壩以下 至二號壩間河段的升溫 速率(定義為℃/㎞)由於河川罩蓋度改變而較二號壩至一號壩間 河段 高出許多,最高差異達94倍(1996年十二月)。兩河段間升溫速率差異程 度與河川流 量與日照輻射周期變化有關,冬季(十一月至二月)最為顯 著。研究中發現防砂壩的淤滿 使河床坡度減緩,會造成七家灣溪中下游 水溫升高與升溫速率增加。 在二號壩以下水溫 過高的河段,櫻花鉤吻鮭受精卵的野外死亡率在65﹪至100﹪間,發育初 期的死亡率為40﹪至100﹪間。過高水溫與日溫差對櫻花鉤吻鮭族群天然 更新有不利的影響。孵化前期的平均水溫12℃可視為孵化期的上限致死溫 度。估計十二年間(1985年至 1996年),12℃等溫線往上游退縮約1.56 ㎞。二齡以上成鮭在繁殖期的分布與水溫的相對 高低有關,性成熟的成 鮭有聚集河川封閉區間的低溫區以尋求有利於孵化的水溫環境。水 溫對 亞成鮭與幼鮭的影響則不顯著。 七家灣溪流域櫻花鉤吻鮭孵化前期(十一月)平均溫度12℃等溫線在三號 壩附近河段 ;臺灣鏟頷魚生殖末期(六月)17℃等溫線在觀魚臺附近河 段。三號壩以上河段與武陵溪 一號壩站河段全年水溫可視為低於17℃; 觀魚臺站與一號壩站河段則在夏季六月中旬至七 月中旬水溫有超過17℃ 的現象。 總結可知,七家灣溪低罩蓋度與防砂壩造成的水溫升高現象,引起櫻花鉤 吻鮭繁殖期 的孵化卵高死亡率,而影響族群更新,將造成七家灣溪中下 游河段(二號壩以下)櫻花鉤 吻鮭族群量縮減。

外文摘要: 

The project investigated the water temperature of streams of the Chichiawan Stream basin, including Chichiawan Stream, Wuling Stream, and Taoshan Nothern Stream. The basin is the last habitat of the endangered Formosan landlocked salmon (Oncorhynchus masou formosanus). The water temperature data was collected with optical dataloggers from January, 1996 to May, 1997 to understand (1) the characters of water temperature variation and (2) the relation between water temperature and the salmon population variation. Annual water temperature variation can be divided into rising stage(from February to July)and falling stage(from August to next January). The maximum raise and daily difference in water temperature occured early in June. The most crucial and significant falling stage occured early in November, at the beginning of breeding season of the salmon. The water temperature rises as the water flows downstream. The phenomenon is prominent in winter, especially December to February at the middle and lower reaches, which are also the major habitats of salmon. The low percentage of stream surface shading and the gentle slope of river caused by check dams may significantly to elevate water temperature. Adult salmon ( >20cm ) aggregates to reproduce at the upper reaches with the properly low water temperature. High mortality occurred when the mean water temperature exceeds 12℃ at the early embryo ( before optic vesicle differentiation stage ) of salmon eggs in the wild. The 12℃ isothermal line is nearby the reaches of check dam number 2 now. It has back upstream 1.56 km since 1985. In conclusion, high water temperature has markedly negative influence on the reproduction of adult salmon and hatch of eggs. High water temperature cause high mortality of salmon eggs to reduce the salmon population.