The impact of the Goesan dam on fish communities up- and downstream

Dams can cause fragmentation of the natural structure and function of fish communities up-and downstream of the dam. In this study, we examined the effects of the Goesan Dam on the longitudinal distribution of fish in the Dal stream, using two computational methods: a self-organizing map (SOM) and spatial autocorrelation. Fish were collected at 16 different study sites in two seasons (spring and autumn). SOM classified the study sites into four clusters (1-4), reflecting differences in the longitudinal distribution patterns of fish, and the effects of the dam on fish community composition. Samples in clusters 1 and 2 mostly originated from tributaries and the upstream section of the dam, whereas samples in cluster 4 originated from downstream study sites of the dam. Cluster 3 included study sites originating directly from up-and downstream of the dam. Species turnover and spatial autocorrelation results confirmed the fish community alteration near the dam. Species turnover was the highest between study sites directly up-and downstream of the dam. The Mantel correlogram was positive when applied to short distances between the study sites. However, it was negative for the farthest distance, including sites near the dam, indicating that the dam caused significant alterations to the fish community. Overall, our results suggest that the habitat alterations (e.g., fragmentation of longitudinal gradients and disruption of flow regimes) due to dam construction have caused fragmentation of fish communities.