Abstract
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。The project investigated the water temperature of streams ofthe Chichiawan Stream basin, including Chichiawan Stream, WulingStream, and Taoshan Nothern Stream. The basin is the lasthabitat of the endangered Formosan landlocked salmon(Oncorhynchus masou formosanus). The water temperature data wascollected with optical dataloggers from January, 1996 to May,1997 to understand (1) the characters of watertemperature variation and (2) the relation between watertemperature and the salmon population variation.Annual water temperature variation can be divided into risingstage(from February to July)and falling stage(from August tonext January). The maximum raise and daily difference inwater temperature occured early in June. The most crucialand significant falling stage occured early in November, at thebeginning of breeding season of the salmon. The watertemperature rises as the water flows downstream. Thephenomenon is prominent in winter, especially December toFebruary at the middle and lower reaches, which are also themajor habitats of salmon. The low percentage of stream surfaceshading and the gentle slope of river caused by check damsmay significantly to elevate water temperature.Adult salmon ( >20cm ) aggregates to reproduce at the upperreaches with the properly low water temperature. Highmortality occurred when the mean water temperature exceeds12℃ at the early embryo ( before optic vesicledifferentiation stage ) of salmon eggs in the wild. The 12℃isothermal line is nearby the reaches of check dam number 2now. It has back upstream 1.56 km since 1985.In conclusion, high water temperature has markedly negativeinfluence on the reproduction of adult salmon and hatch ofeggs. High water temperature cause high mortality of salmoneggs to reduce the salmon population.