Ecological and genetic effects on diadromous fishes according to the artificial enviromental changes in rivers

本研究通过研究河道筑坝、筑坝后二恶鱼的生活史特征和发生频率的变化，作为一种模型研究，根据河道环境的人为变化估计对二恶鱼的损害程度。详细地说，我们选择了建堰的河流作为研究对象。在河流中，将居住在河堰上游的白斑棘鱼（Salvelinus leucomaenis）和三刺棘鱼（Gasterosteus aculeatus）的内陆种群与下游溯河种群进行生活史特征、基因频率和遗传变异的比较，以评估其对种群的生物学效应。首先，河流种群主要分布在河堰上游，表明人工形成了内陆种群。西北塔浦河河流棘鱼种群遗传效度低、寿命延长、性成熟体型小、繁殖季节宽、卵数少。热本岛河流中的白斑鲑也得到了类似的结果。由于在两种雌雄同体的内陆种群中发现了许多生物洼地，这些洼地是在修建堰后形成的，因此有必要从保护生物多样性的角度重新考虑天然河流修建堰的利弊。

In the present study, the changes of life-history characteristics and genefrequency in anadromous after construction of dams or weirs in the course of rivers were investigated as a model study to estimate the degree of damage to diadromous fishes according to the artificial changes of environments in rivers. In detail, the rivers where weir was constructed were selected for this research. In the rivers, the land-locked populations of white-spotted charr (Salvelinus leucomaenis) and threespine stickleback (Gasterosteus aculeatus) inhabited upstream form the weir were compared with the downstream anadromous populations of each species for life-history characters, gene frequency and genetic variability, in order to estimate the biological effects on the populations.Firstly, the fluvial populations were found to be distributed in the upstream reaches from the weir, suggesting the artificial formation of land-locked populations. The fluvial stickleback population from the NIshikitappu River showen low genetic valiability, prolongation of longevity, small body size at sexual maturity, wide reproductive season and small clutch size, compared with those of anadromous population. Similar results were obtained for white-spotted charrs in the rivers of Rebun Island.As many biological depressions were detected in the land-locked populations of two anadromous species which had been already formed after construction of weirs, it is necessary to reconsider the merits and demerits of weir construction in natural rivers from the view points of conservation of biodiversity.