Abstract
Natural materials are often used to construct low-water shore protection works. We investigated fish habitats at six types of low-water shore protection structures and one vegetated bank in May, July, and October, 2012. Fish abundance and species diversity were higher in shallow vegetated areas with low water velocity throughout the study period. Free-swimming fish increased at the vegetated bank in May. In July and October, fish moved to deeper waters. They were therefore distributed widely in habitats with various water velocities and depths, particularly in October. Juvenile free-swimming fish were distributed only at the vegetated bank. Results suggest that the life history of juvenile free-swimming fish requires emergent plant banks for nursery and overwintering habitats. Adults need a bank habitat with various water velocities and depths. For benthic fishes dominated by Cottus pollux, the riverbed structure （i.e., loose stone） was apparently more important than the shore protection structure. These results indicate that straightening of rivers degrades the habitats of free-swimming fish and benthic fish troughs by decreasing the heterogeneity of water flow and benthic environments, even in rivers with low-water shore protection produced using natural materials.
