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

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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.