Active feeding of anadromous white-spotted charr Salvelinus leucomaenis at the southern latitudinal rivers

Although starvation poses a serious risk of death, it is a common phenomenon among anadromous salmonids that fast after returning to the river following oceanic feeding migration. We examined the river feeding patterns and condition factor of sea-run migrants of white-spotted charr (Salvelinus leucomaenis) in rivers with latitudinal variation from 37°N to 46°N along the Sea of Japan. The vacuity index showed a significant latitudinal trend: charr feed at lower latitudes and fast at higher latitudes. In contrast, their condition factor did not exhibit any latitudinal trends. Sea-run migrants at lower latitudes actively fed on terrestrial insects, as did freshwater residents. Based on the geographic trends in feeding and condition, the environmental conditions experienced by individuals before and after river entry would affect their river feeding. Active feeding by the southern sea-run migrant charr might be an adaptation to maintain their body condition. This study highlights the importance of rivers not only as spawning and growth habitats for juveniles, but also as feeding habitats for anadromous salmonids.