Using traps and passive integrated transponder (PIT) telemetry, we investigated the effectiveness of the nature-like fishway installed at Sangju Weir on the Nakdong River, Korea. In 11 regular checks over the study period, 1474 individuals classified into 19 species belonging to 5 families were collected by the traps, representing 66% of the species inhabiting the main channel of the Nakdong River. PIT tags were applied to 1615 individuals belonging to 22 species, revealing fishway attraction and passing rates of 20.7% and 14.5%, respectively. Interspecific differences were also shown. For 63.2% of fishes, it took more than a day to pass through the fishway. Some individuals spent a longer time (>28 days) inside the fishway, suggesting the fishway was also being used for purposes other than passage. In this study, we verified species diversity of fish using a nature-like fishway installed in a large river in Korea. The results of this study provide a useful contribution to the development of fishways suitable for fish species endemic to Korea and for non-salmonid fish species worldwide.

In this study, the relationship between hydrological characteristics and phytoplankton biomass (chlorophyll a concentration) was explored using long-term hydrological and limnological data (1994–2007) in a flow-regulated river system (the lower Nakdong River, South Korea). This river has four multi-purpose dams and an estuarine barrage, and river flow is extensively controlled. Dynamics of chlorophyll a concentration responded well to changes in hydrology, such as rainfall, dam discharge and river flow. The hydrological characteristics strongly affected the decrease of chlorophyll a concentration in summer to winter but not in spring (p<0.05; n=42). An application of Self-Organizing Map (SOM) model to the database returned three clusters, and strong seasonality in water quality as well as hydrological characteristics was identified. Long-term rainfall data exhibited no statistical tendencies of increase or decrease, with respect to total annual rainfall. In comparison, summer rainfall increased while that of winter (December to the following February) decreased. Summer rainfall affected total dam discharges in all seasons in a positive manner (p<0.05; n=14), corresponding to winter water quality of the lower Nakdong River likely to be dependent largely upon changes in summer rainfall. Therefore, the development of an effective management strategy for summer rainfall and dam discharge control is strongly required.