應用克利金與逐步模擬分析魚類喜好流況之時空變異-以大屯溪日本禿頭鯊為例

Abstract

魚類在溪流生態中扮演舉足輕重的角色，其生活週期更與環境因子息息相關，其中以流況影響最為顯著。魚類會針對自身喜好，尋找適宜生長發育、遷徙、產卵、避難之流速/水深組合，因此進行魚類分布與流況分類的討論是有其必要性。本研究引用流速/水深分類法、福祿數法針對大屯溪河段內流況進行分類，然而許多文獻顯示上述兩種方法皆有其優、缺點。為確立何種流況分類法較為適宜大屯溪流域，採用大屯溪日本禿頭鯊為指標物種，探討其對於分類流況(深潭、淺瀨、深流、緩流)的選擇性，並輔以洄游文獻進行驗證。同時，結合克利金法推估河段內魚類出現機率、流速、水深值，量化日本禿頭鯊對於分類流況喜好程度，並利用地理資訊系統展示分類流況、魚類出現機率在空間、時間尺度上之變異。 研究結果顯示，利用克利金推估魚類出現機率、流速、水深，由流速/水深分類法、福祿數法進行流況分類後，其分類流況面積比例在不同調查河段各有差異。其後與魚類出現機率套疊，發現日本禿頭鯊在不同季節喜好不同分類流況，其中洄游季(春季)以出海口的深潭和淺瀨、下游的淺瀨、中上游的深流和淺瀨為主要訴求。此外，兩種流況分類法結果上相異，因此引用日本禿頭鯊洄游文獻驗證，建議流速/水深分類法應用於大屯溪日本禿頭鯊流況需求具有較高的適宜性。然而分類流況乃不同流速/水深組合結果，在溪流生態系統中存有空間不確定性，因此採用逐步指標模擬針對河段內流速、水深值進行各1000次模擬，並計算流速、水深的空間機率；再以流速/水深分類法針對逐步指標模擬結果進行流況分類，同時以地理資訊系統呈現並計算分類流況出現機率60%、80%以上之面積比例，與克利金推估之流況分類結果相互比對，提供大屯溪未來流況分類依據。

Fish communities play a important role in the freshwater ecosystem, and their life-cycles are obviously related to the environmental factors, especially flow conditions. Fish search for appropriate habitats for growing migrating, spawn, and refuge considering current velocity and depth. Therefore, it is necessary to delineate the correlation between the fish distributions and flow conditions. This main issue is to classify the flow conditions in the Datuan stream by the empirical rule and Froude number. However, various literatures showed that the two methods own the advantages but also drawbacks in the flow classifications. To determine whichever can describe better the flow conditions in the Datuan stream, we consider Sicyopterus japonicus as the indicator species for suiting flow conditions (Pool, Riffle, Run, and slack), and then compare the result to various of migration literatures. Meanwhile, using the Kriging to estimate the probability of occurrence of fish, velocity and depth value, and then qualify the preference of flow conditions of Sicyopterus japonicus. Lastly, display the variations in the flow conditions and the probability of fish in the spatial-temporal scale with geographic information system (GIS). The result showed that the flow conditions react differently among reaches. Then, the preferences of Sicyopterus japonicus in flow conditions change in the spatial and temporal scale by overlapping the flow conditions map and the contour of fish probability. In particular, the preference of Sicyopteru sjaponicus in the flow conditions is pool and riffle at estuary, riffle in the downstream, run and riffle in the middle and upstream during the migration season (spring). In addition, the outcome are significantly different between the two classifications methods. The empirical rule for flow conditions classification comes out to be more appropriate in the Datuan stream. Nevertheless, owing to the great variation of water depth and current velocity, the consideration of uncertainty is essential. Thus, Sequential indicator simulation (SIS) is applied with 1000 iterations to simulate the overall current velocity and water depth value. Eventually, this research provides the basis of the classifications of flow conditions in the Datuan stream by comparing the result in SIS and Kriging.