A Study on Evaluation of Fishways of the Nagara Estuary Barrage based on Habitat and Upstream Migration for Japanese Mitten Crab

根据五年的环境变化监测数据，调查了长加拉口围堰四条鱼道的实际成效。应当指出，在Seseragi(溪流型)渔道，每小时和每天都可以观察到上游迁徙的时间集中。鱼类上游迁徙的高峰期对应于小潮期。在自然条件下，随着潮汐的推进，咸水的范围向上游延伸得更远。对日本绒螯蟹(Eriocheir Japan Onica)在Seseragi渔道的定居进行了调查。大眼幼虫在鱼道上潮带定居并蜕变为蟹状阶段。最小的螃蟹有近两毫米的甲壳宽。巨眼幼虫的定居主要发生在初夏(6月)和初冬(12月)。大多数越冬的幼虫由于水温较低而不能存活并蜕变到蟹期。因此，Growth…河口水温似乎对日本绒螯蟹的上游迁徙有很大影响。大眼鱼幼虫的适宜定居位置对应于小潮时咸水入侵的尖端。在本研究中，阐明了Seseragi渔道对减少河口地带由淡水向海水转变水生生物阶段具有一定的缓解作用。此外，在均匀底质下，研究了咸水入侵特征对长加拉口拦河口鱼道底栖动物群落和藻类的影响。通过对底栖动物群落的聚类分析，将鱼道区划分为淡水区、咸水区和过渡区。底栖动物群落和藻类群落主要栖息于该地段，与咸水入侵特征有关。日本绒螯蟹(Eriocheir Japan Onica)的大眼幼体在鱼道上潮带定居并蜕变为蟹期。巨眼幼虫的定居主要发生在初夏(6月)和初冬(12月)。大多数越冬的幼虫由于水温较低而不能存活并蜕变到蟹期。因此，日本绒螯蟹的生长和上游迁徙似乎受到河口水温的强烈影响。大眼鱼幼虫的适宜定居位置对应于小潮时咸水入侵的尖端。在本研究中，阐明了Seseragi渔道对减少河口地带由淡水向海水转变水生昆虫和生物阶段具有一定的缓解作用。较少

Actual achievements of the four fishways of the Nagara estuary barrage for fishes were investigated based on the data of five-years monitoring on environmental changes. It should be noted that temporal concentration of upstream migration was observed both hourly and daily in the Seseragi (brook-type) fishway. The peak of the upstream migration of fishes corresponded to the neap tide period. Under natural condition, the range of salt water extends upstream farther as the tide advances. Settlement of the Japanese mitten crab (Eriocheir japonica) was investigated in the Seseragi-fishway. The megalopa larvae settled and metamorphosed to crab stage in the upper tidal zone in the fishway. The youngest crabs were nearly two millimeters in carapace width. Settlement of megalopa larvae occurred mainly in early summer (June) and early winter (December). The majority of larvae that settled in winter did not survive and metamorphose to the crab stage due to low water temperatures. Thus, the growth … More and upstream migration of the Japanese mitten crab seemed to be strongly influenced by water temperature in the estuary. The suitable settlement position of megalopa larvae corresponded to the tip of salt water intrusion at neap tide. In this study, it is clarified that the Seseragi-fishway have a fulfill function to mitigate for decreased estuary zone that change aquatic organism phase from freshwater to seawater. Furthermore, the effects of saltwater intrusion characteristics on benthic animal communities and algae were investigated in the fishways of the Nagara estuary barrage under uniform substrate. As a result of the cluster analysis of the benthic animal communities, the fishway zone was divided into three parts ; the freshwater, the saltwater and the transitional section. The benthic animal communities and algae inhabited mainly in these section related to saltwater intrusion characteristics. The megalopa larvae of the Japanese mitten crab (Eriocheir japonica) settled and metamorphosed to crab stage in the upper tidal zone in the fishway. Settlement of megalopa larvae occurred mainly in early summer (June) and early winter (December). The majority of larvae that settled in winter did not survive and metamorphose to the crab stage due to low water temperatures. Thus, the growth and upstream migration of the Japanese mitten crab seemed to be strongly influenced by water temperature in the estuary. The suitable settlement position of megalopa larvae corresponded to the tip of salt water intrusion at neap tide. In this study, it is clarified that the Seseragi-fishway have a fulfill function to mitigate for decreased estuary zone that change aquatic insect and organism phase from freshwater to seawater. Less