The Effect of the Water Temperature on Taiwan Landlocked Salmon (Oncorhynchus masou formosanus) in Chichiawan Stream Basin

• Main Authors: Yang, Cheng-hsiung, 楊正雄
• Other Authors: Tzeng C.S.
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/10939280488755502353

碩士 === 國立清華大學 === 生命科學系 === 85 === 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.