Habitat use by white-spotted charr in a stream reach with sequential low-head dams in the Daiya River, central Japan

In recent years, the population of white-spotted charr (Salvelinus leucomaenis) has been declining in the upper reaches of the Daiya River, Nikko City, Tochigi Prefecture. One of the causes is the deterioration of the river environment due to an influx of sediment and construction work. Among the studies investigating the habitat preferences of charr, there are few examples of habitat assessment of stream channels severely altered by artificial structures, such as dams, revetments and concrete riverbeds. For this reason, this study investigated the presence/absence of charr in a reach with sequential low-head dams in the Daiya River that has all those structures. The results indicate that the presence of charr in the altered reach was associated with the abundance of rocks or greater water depth (>20 cm). Based on these results, we conclude that when trying to create a habitat for charr in a stream reach with sequential low-head dams, one should consider adding complexity in terms of rocks and water depth.