淀川の流量が天然海産アユ個体群に及ぼす影響

抄録

We conducted field survey on larval drift of Ayu-fish, Plecoglossus altivelis altivelis, in the lower Yodo River. Most of the larvae flowed down through the Kema-suimon Floodgates to the Kyu-Yodogawa River (the Okawa River), and the rest of them through the Yodogawa-ozeki Wier to the Shin-Yodogawa River accounting for only a small proportion of the whole population. We also found some Ayu-fish of landlocked type in the backwater area of the Yodogawa-Ozeki Weir. Correlation analyses between a set of flow parameters and the annual total number of upstream migration of Ayu-fish at the Yodogawa-Ozeki Weir resulted in a positive correlation with time duration the Regulating gate discharge in December of the previous year. This indicates that the total number of upstream migration of Ayu-fish is determined by the total the number of drifting larvae to the Shin-Yodogawa River in the previous year. Therefore, it can be concluded that increasing the discharge of the Yodogawa-Ozeki Weir in December is necessary for increasing the population of Ayu-fish in the Yodogwa River.