Effects of constructing concrete revetments on fish assemblages in small to medium streams

Marginal areas in small to medium streams are important as spawning and nursery habitat for freshwater fish, and then there have been concerns about negative effects of covering stream banks with concrete revetments on freshwater fish. It has been reported that water-column fish were negatively influenced by the covering, but little reported for benthic fish. Streamside vegetation can alter substrates, likely relating to benthic fish, from those that prefer sand or mud to those that prefer gravel. Thus, the effects of the covering may differ depending on the life type and species composition of freshwater fish. We examined fish assemblages in reaches with three types of both stream edges: stream water ran along concrete revetments (CC), a concrete revetment and a sand bank (CS), and sand banks (SS). The study reaches were located in small to medium streams which join to the midstream and downstream of the Ibi and Nagara Rivers, and species composition may differ depending on longitudinal positions. Species richness and individuals of the water-column fish were lower in CC than in SS, whereas individuals of the benthic fish preferring gravel were highest in CC. Species composition in CC differed from that in CS and SS in the streams joining to downstream but not in those to midstream. Thus, effects of the covering depended on the life type of freshwater fish and the longitudinal position. The community structures, represented by the species richness, individuals and species composition, in the reaches along a concrete revetment and a sand bank (CS) tended to be similar to those in the reaches along sand banks (SS), suggesting that installation of concrete revetments limited to one-sided bank may mitigate the impact on fish assemblages in small to medium streams.