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標題: | 臺灣櫻花?吻鮭之族群生態學研究 Population Ecology of Formosan Landlocked Salmon Oncorhynchus masou formosanus |
作者: | 戴永禔 |
出版年 : | 1992 |
學位: | 碩士 |
摘要: | 至西元1916年,櫻花?吻鮭(Oncorhynchus masou formosanus)才在臺灣地區發現,目前本地族群已經面臨瀕臨絕種的危機;於西元1984年文化資產保存法訂定後,各界才開始進行保育的工作。中華民國行政院農業委員會資助保育及進行其生物、物理、化學環境研究所需之經費,除了基本研究之外,放流及保護措施也同時進行中,而且農委會亦推動有關櫻花?吻鮭的大眾教育。本文目的在藉由族群生態學之研究,來釐清何者為阻止櫻花?吻鮭族群成長的限制因數,及其作用的機制為何,進一步描述不同體型大小櫻花?吻鮭對棲地的需求(包括稚魚的微棲地):並且利用鱗相與體長頻度法來瞭解櫻花?吻鮭的成長模式,以做為其生活史的基本資料。另外就每年調查櫻花?吻鮭族群動態之際,同時記錄放流魚群的位置與數量,以期了解放流魚群的動態與初步評估人工飼養放流的成效。 自1987至1991年以浮潛觀察法進行族群數量估算調查,發現於七家灣溪的櫻花?吻鮭最近仍然在減少中,1987年10月的琳恩颱風使該年出生的同齡群受到嚴重的破壞;於攔砂壩上游,愈靠近壩的溪段中之櫻花?吻鮭數量愈少,其年間變異則愈大,可見較差的溪段都集中在攔砂壩之上。一般而言,成魚(體長>20cm)的聚集強度比幼魚(體長<20cm)為大;但是在1989年9月發生莎拉颱風之後,幼魚於1990年1月則表現出特別高的聚集強度,最大聚集塊中心溪段的位置於1990年1月有向下遊移動的現象,而且在貳號壩上游沒有任何聚集塊,顯示颱風確實會將鮭魚向下游沖刷。由於洪水作用與泥砂堆積,七家灣溪在過去四年期間變得較寬、較淺以及流速較緩,其中深度減少是降低成魚棲地品質的主要原因。自然災害(颱風與洪水)與人為幹擾(農業活動與水力工程)影響了櫻花?吻鮭在空間分佈與隨時間的變異,並經由棲地惡化使得其數量減少。 不同體型大小櫻花?吻鮭在不同季節內對溪流棲地物理性因數的需求不同;小型魚夏天偏好較寬、較多遮蔽以及具有階瀨與側刷潭較多的溪段;冬天則喜歡平瀨階瀨與側刷潭較多的溪段。對成魚而言,於夏季,距攔砂壩上游越遠、棲地類型歧異度越大以及有下蝕潭的溪段較佳;冬季時成魚則多出現在有側刷潭的溪段。分析櫻花?吻鮭稚魚的微棲地因數,可作為未來放流稚魚的基本依據;結果顯示稚魚全都分佈在溪流兩側靠近岸邊而水面會晃動的靜水區中;稚魚棲地的主要底質組成則以小碟石、大礫石最多;而大巨石在水下所形成的遮蔽所對櫻花?吻鮭稚魚有利;生物因數中,梭德氏赤蛙蝌蚪與落葉枯木的存在與否,對稚魚的分佈沒有影響,而盤古蟾蜍蝌蚪則可能會妨礙櫻花?吻鮭稚魚的生存。櫻花?吻鮭的鱗輪數與尾差長有顯著的線性關係(Circuli=0.033FKL+13.9),然而櫻花?吻鮭的鱗片並不是年齡鑑定的好材料,所能獲取的成長資料有限。自1988年7月至1989年6月間,在一個長100公尺溪段中,以浮潛觀察法所得之櫻花?吻鮭體長頻度資料,利用Pauly估算程式求得von Bertalanffy成長曲線如下: Lt=57.5{1-exp[-0.38(t-0.3628) (0.6)(0.38) - ——————(sin2π(t-1.4)-sin2π(0.3628-1.4))]} (2π) ,其最佳的參數值之成長係數(k)=0.38;由極限體長(L∞)=57.5cm可算出櫻花?吻鮭的壽命為4.1年;波動強度因數(C)=0.6應證環境溫差為攝氏6度;冬季點(WP)=0.9,表示10月下旬是成長最慢的時期而正逢櫻花?吻鮭的生殖季。 放流的魚群在七家灣溪散佈的範圍乃不超過下游兩公里;1989年7月以前,帶黃標的鮭魚全都分佈在釋放點下游200公尺的範圍內,而帶藍標的鮭魚則全都分佈在釋放點上游400公尺的範圍內。在放流的4個月後,櫻花?吻鮭至少有16%存活,10個月後則至少存活5.5%;而其「相對年存活率」則在9%與20%之間。 為了保護櫻花?吻鮭免幼絕滅,應該考慮放流零齡幼魚或直接於適當的棲地放置受精卵,以加強放流魚群的適應能力,並減少養殖與孵化所需的巨額花費;由於當族群減少時會產生近親交配而使得族群基因庫縮減,應藉由雜交的方法來增加族群的遺傳歧異性,以增加櫻花?吻鮭受精、存活與成長的能力。為了免除砂石繼續在攔砂壩上堆積,至少應拆除一個或所有在七家灣溪的攔砂壩,即可能清除堆積於此的砂石而達到長期地改善棲地品質之目地。將攔砂壩上游溪段堆積的巨量砂石以人工移除,或以定錨法、卵石池法等棲地改良技術,以達短期改善棲地品質的目的並可延長攔砂壩的使用年限。 A local population of Formosan landlocked salmon Oncorhynchus masou formosunus was first discovered in Taiwan in 1916. It is considered an endangered species locally now. After the enaction of the Cultural Heritage Preservation Act in 1984, conservation actions were taken to save the salmon population. The budget for conservation and research related to biological, chemical, and physical aspects of this species were sponsored by the Council of Agriculture, Republic of China. Besides the fundamental research, a restoration program and protection measures were also undertaken. In addition, efforts were put into public education. The objectives of this study were to find out the limiting factors and their mechanism to the salmon population, and to determine the habitat preference of the fry, juveniles, and adults. The growth, the basic information of life history, was revealed by analysing scale pattern and length frequency data. Furthermore, the status and movement of restored hatchery stocks were monitored. Population abundance of Formosan landlocked salmon was estimated visually by snorkeling in Chichiawan Stream from September 1987 to January 1991. The salmon population decreased, and the stream habitat was deteriorated. Yearly fluctuation in salmon abundance was larger in the young (TL<20cm) than that in the adult (TL<20). The young abundance in summer was greater than that in winter. In the area close to the sand-retention dam, salmon abundance decreased downstream, while the temporal variability of abundance increased. The distribution of the juvenile and the adult were similar in July 1989, but were different in January and July 1990, and January 1991. The distribution of the salmon along the stream were similar between the two summers, but not the two winters. In general, the intensity of aggregation of the adult was greater than that of the juvenile, except the juvenile exhibited high aggregation in January 1990. The typhoon occurred in September 1989 increased the variability of the average width and the relative composition of habitat types of the stream. Furthermore, the typhoon might directly cause mortality and downstream shift of the salmon, and increased the intensity of aggregation for the juvenile indirectly through habitat deterioration. The stream became wider, shallower, and slower during the study period. The decrease of stream depth was the major factor affecting the adult salmon in term of habitat quality, while it was not significant for the young. Type I sections with good habitat quality had greater tendency of the salmon reduction. Typhoon Lynn, occurred in the breeding season of the salmon, destroyed the cohort born in 1987. Natural disturbance interacting with anthropogenic factors controlled the spatial and temporal variability of salmon, and decreased its abundance with habitat degradation. The salmon selected different stream structures in different seasons at different sizes. The juvenile preferred stream sections with greater width, heavier cover, cascade, and lateral scour pool in summer; glide, cascade, and lateral scour pool in winter. In summer, stream sections with plunge pool, more diverse structure, and farther to sand-retention dam upstream supported more adults; in winter, the adult preferred sections with lateral scour pool. The microhabitat study indicated that masu fry occurred in edge water with waving surface. The main substracts were cobble and pebble, and the shelter provided by large boulder was aslo important to the fry. Among the biotic factors, present of sticks, leaves, and tadpoles of Rans sauteri were not important to the occurence of the fry, while the present of tadpoles of Bufo bufo may prevent the occurence of the fry. The number of circuli and fork length of the salmon had linear relationship (Circuli=0.033FKL+13.9); however, scale pattern was poor to provide solid information on the growth of the salmon. Monthly length frequency data of the salmon were observed in a 100m section in the Chichiawan Stream between July 1988 and June 1989, and a von Bertalanffy growth equation was calculated using Pauly’s algorithm. The optimal equation was Lt=57.5{1-exp[-0.38(t-0.3628) (0.6)(0.38) - ——————(sin2π(t-1.4)-sin2π(0.3628-1.4))]} (2π) where the growth coeffecient (K) was 0.38, the asymptotic length (L∞) was 57.5 cm. Parameter C indicated the water temperature of environment were 6 degrees Celsus. Winter point (WP) was 0.9 indicated the growth was the slowest in late October during a year, while it happened to be the breeding season of the salmon. The hachery stocks released in March 1988 dispersed downstream less than 2 km in distance in general. Yellow-tagged individuals were occurred within 200m downstrem to the released location before July 1989, while blue- tagged individuals were with 400 m upstream. Four months after release, at least 16% of restored stocks survived, and at least 5.5% suvived for 10 months in the wild. The relative year suvival rate was between 9 to 20%. On the conservation for the salmon, following measures should be considered: (1) The effect of inbreeding depression caused by reduced population size may occur in Taiwanese salmon; heterosis to increase its fertility, survival, growth should be conducted (Allendorf and Leary, 1986). (2) Artificially fertilized eggs may be restored directly to the stream in the year with severe flood. (3) All or at least some sand-retention dams in Chichiawan Stream should be demolished (Chang, 1989). (4) Relocation of sand and stones depositing above the sand-retention dams could improve habitat quality and extend the longevity of the dams (Hansen et al., 1983). (5) Techniques such as anchoring system (Fontaine and Merritt, 1988), gravel pit ponds (Bryant, 1988), and so forth, might be temporary solutions to improve the habitat quality. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/75855 |
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