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

根据5年环境变化监测资料，对长原河口拦河坝4条鱼道的实际效果进行了考察。应该指出的是，在Seseragi（溪型）鱼道中，每小时和每天都观察到上游迁移的时间浓度。鱼类向上游迁移的高峰与小潮期相对应。在自然条件下，随着涨潮，咸水的范围向上游延伸得更远。调查了日本绒螯蟹（Eriocheir japonica）在塞塞拉吉-鱼道的定居情况。大鳞鱼幼虫在鱼道上潮区定居并蜕变为蟹期。最年轻的螃蟹的甲壳宽度接近两毫米。大鳞蝇幼虫主要在夏初（6月）和冬初（12月）定居。由于水温过低，大部分在冬季定居的幼虫无法存活并蜕变成蟹。由此可见，河口水温对中华绒螯蟹的生长和洄游具有强烈的影响。小潮时，大鳞蝇幼虫的适宜沉降位置与盐水入侵的尖端相对应。本研究阐明了Seseragi-fishway对河口带减少具有完全的缓解作用，使水生生物的相由淡水变为海水。在均匀基质条件下，研究了咸水入侵特征对长原河口拦河坝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3个部分；淡水，咸水和过渡段。底栖动物群落和藻类主要栖息于该剖面，与海水入侵特征有关。日本绒螯蟹（Eriocheir japonica）的大鳞幼虫在鱼道的上潮区定居并蜕变为蟹期。大鳞蝇幼虫主要在夏初（6月）和冬初（12月）定居。由于水温过低，大部分在冬季定居的幼虫无法存活并蜕变成蟹。由此可见，河口水温对日本绒螯蟹的生长和上游洄游具有强烈的影响。小潮时，大鳞蝇幼虫的适宜沉降位置与盐水入侵的尖端相对应。本研究阐明了seseragi -鱼道对河口带减少具有充分的缓解作用，使水生昆虫和生物的相由淡水变为海水。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