LAUSR

A dendritic or web-like network is a unique property of inland freshwater systems. The dispersal and movement of freshwater fish are restricted to a network of such waterways. Therefore, during dispersal or movement, fish have to select their way at each junction (i.e. the confluence of two channels) in the network, and their channel selection (route selection) would be reflected in the spatial variations in fish assemblage composition. In this study, we surveyed the channel selection of three fish species during their movement in a braided river. We also analysed correlative patterns among local abundances of fish assemblage members and local habitat variables in study sites established in the channel network, to examine whether fish assemblage composition reflected their channel selection. The channel-selection survey showed that the channels selected by two species, fat minnow and spined loach, were characterised by lower flow volume. These two species tended to avoid stronger currents at the confluence. The analysis of correlative patterns showed that no species were affected by local habitat variables, while the clearest pattern was strong positive correlations between the densities of fat minnow and spined loach, which were found to have similar channel preferences. These results suggest that the fish assemblage composition of local habitats in our braided river reflected channel selection by fish during their movement. Route selection by fish during dispersal or movement can be a notable factor determining the assemblage composition of freshwater fish, especially in habitats where regional processes, rather than local processes, have overriding effects.