河川與農田水路共構對日本絨螯蟹棲地利用之關係

Abstract

日本絨螯蟹(Eriocheir japonica)是台灣少數具有洄游行為的生物種類之一。若是有日本絨螯蟹活動的水域，則代表水流有連續性，因此日本絨螯蟹為水域生態復育成功的生物指標。 室外實驗探討日本絨螯蟹在溪口下圳三種魚道的遷移以及利用Forage ratio指數來做日本絨螯蟹在農田水路與河川中的棲地選擇依據。研究結果顯示：日本絨螯蟹在大屯溪下游的遷移主要是以階段式魚道為主。日本絨螯蟹在農田水路或河川之中皆偏好棲息於福祿數小於0.18之處，代表日本絨螯蟹適合潭型(pool)棲地。日本絨螯蟹在農田水路中對底質的選擇以砂土為主；在河川中則是偏愛粒徑較大的石頭作為棲地。此外，日本絨螯蟹在農田水路中會棲息在周圍作物為水耕作物之處。 室內實驗利用混凝土表面渠道與牡蠣殼表面渠道，調整不同的坡度，來比較日本絨螯蟹的爬行狀況。研究結果顯示：日本絨螯蟹在混凝土渠道上無法在坡度超過45度的情況下爬完渠道。日本絨螯蟹的第三步足移動距離與爬行速率會因為渠道表面材質以及坡度而有顯著差異，兩者皆會因為坡度的增加而減少，但是在牡蠣殼表面渠道上減少的幅度會比在混凝土表面渠道小。此外，日本絨螯蟹在牡蠣殼表面渠道的停留時間會比在混凝土表面渠道長。此結果說明牡蠣殼的表面材質對於日本絨螯蟹的遷移有正面影響。

Eriocheir japonica is one of the minor migratory species in Taiwan. If there is Eriocheir japonica in aquatic environment, it indicates the flow is continuous. Therefore, Eriocheir japonica is a biological indicator, showing that the ecological restoration is performed well in this aquatic environment. In the field, the study is to investigate the migration of Eriocheir japonica in three different fishways in Xi-Kou-Xia Channel and to evaluate the habitat selection of Eriocheir japonica in channels and rivers by applying Forage ratio. The results show that Eriocheir japonica prefer to live in agricultural waterways and rivers where Froude number is lower than 0.18. It represents that Eriocheir japonica like to dwell in the pool habitat. Eriocheir japonica selected the substrate which is sand in channels, and the stone with bigger coarse length in rivers. In additional, Eriocheir japonica would inhabit around hydroponic crops in agricultural waterways. In the laboratory, the experiment applies the two different channels with different slope to compare the climbing behavior of Eriocheir japonica. The surfaces of the two different channels are spread with concretes and oyster shells. The results show that Eriocheir japonica can’t climb all the concrete channel with the slope more than 45 degrees. Besides, Eriocheir japonica’s moving distance of the third walking legs and the rate of the climbing would reduce by changing the material of the channel surface from oyster shells to concrete and the increase of slope. In addition, the resident time of Eriocheir japonica in oyster shells channel is longer than concrete channel. The result suggests the effect of the surface with oyster shells to the migration of Eriocheir japonica is positive.