Assessment of the effects of damming and channelization on freshwater fish habitats

我根据过去50年在北海道进行的水坝和鱼类调查数据库，使用地理信息系统评估了筑坝造成的栖息地碎片化对物种丰富度和个体物种发生的影响。研究发现，在海岛海拔较低的溪流和河流河段，鱼类物种丰富度和因筑坝造成的物种丰富度损失都较大。受筑坝影响最大的物种属于所谓的在淡水和咸水之间迁徙的泛水物种，例如鲑鱼和许多虾虎鱼物种。研究表明，为便于鱼类和其他水生生物绕过堤坝而设计的鱼类方式，对于有足够游泳能力的鱼类，如鲑鱼和鲑鱼，功能较好，但对于没有游泳能力的鱼类，如戈比目鱼和其他小型底栖鱼类，功能较差。此外，我还开发了一个指数来衡量由于河道化或河道拉直而导致的栖息地简化程度，并将该指数应用于北海道的溪流。基于熵概念的指数被应用于久路河支流，并在这些支流之间进行了比较，这些支流是从20世纪20年代、50年代、70年代和90年代四个时代出版的1：50,000张拓扑图中进行数字追踪的。结果，随着时间的推移，特别是自20世纪70年代以来，由于通道化，河道的复杂性已经明显降低。此外，我开始利用全国可用的地理信息开发各种数据库的基础设施，以扩大研究的空间范围，并研究人类活动对全国生态系统的影响。作为基础设施发展的一步，我创建了日本大型水坝的地理信息系统数据，并开发了一种算法，利用地理信息系统识别和直观地掌握水坝分散的流域和年份。我还根据在日本进行的两次全国调查开发了一个鱼类数据库。

I assessed using GIS the effects of habitat fragmentation caused by damming on species richness and individual species occurrence based on the databases of dams and fish surveys conducted during the past 50 years in Hokkaido. It was found that both fish species richness and the loss of the species richness due to damming are greater in reaches of streams and rivers with lower elevations in the island. Species that were most significantly impacted by damming belonged to the so-called diadromous species which migrate between freshwater and salt water, for instance salmon and many gobiids species. It was suggested that fish ways that are designed to facilitate fish and other aquatic creatures to pass around dams function effectively for fishes with sufficient swimming ability, such as salmon and trout, but function poorly for fishes without the ability, such as gobiids and other small benthic fishes.In addition, I developed an index to measure the degree of habitat simplification due to channelization or channel straightening and applied this index to streams in Hokkaido. The index which is based on the concept of entropy was applied to and compared among the tributaries of the Kushiro River which were digitally traced from 1:50,000 topological maps published in four eras of 1920s, 1950s, 1970s, and 1990s. As a result, it became obvious that channel complexity has been reduced over periods, especially since 1970s, due to channelization.Furthermore, I started developing infrastructure of various databases with geographical information that are available nationwide in order to expand the spatial scale of the study and to examine anthropogenic impacts on ecosystems in the whole nation. As a step toward this infrastructure development, I created GIS data of large dams in Japan and developed an algorithm to identify and visually grasp using GIS the watersheds and years fragmented by the dams. I also developed a fish database based on two national surveys conducted in Japan.