Differences in Habitat Utilization Pattern of Eriocheir japonica (Decapoda: Grapsidae) in Natural Rivers and Agricultural Waterways

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.