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

本研究以河道修建水坝或堰后溯河产卵鱼类生活史特征和基因频率的变化为模型研究，根据河流环境的人为变化来估计对产卵鱼类的损害程度。具体来说，本研究选择了修建堰的河流。在河流中，将堰上游的内陆种群白点红点鲑（Salvelinus leucomaenis）和三棘刺鱼（Gasterosteus aculeatus）与下游溯河产卵种群的生活史特征、基因频率和遗传变异性进行比较，以估计其对种群的生物学影响。堰，表明内陆人口是人工形成的。与溯河产卵种群相比，西北多浦河流域棘鱼种群遗传有效性低、寿命延长、性成熟体型小、繁殖季节宽、窝产数小。礼文岛河流中的白点红点鲑也得到了类似的结果。由于在建堰后已形成的两种溯河产卵物种的内陆种群中发现了许多生物洼地，因此有必要从生物多样性保护的角度重新考虑在天然河流中建堰的利弊。

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.