Small rivers, great importance: refuge and growth sites of juvenile migratory fishes in the upper Sao Francisco basin, Brazil

Abstract

Studies of migratory fish species in Neotropical Basins have generally focused on adult fishes, especially on their reproductive migration, whereas sites of growth and refuge of juveniles remain poorly investigated. We aimed to evaluate if smaller rivers play a role in the life cycle of these species. We used 13 rivers of different sizes in the upper São Francisco Basin, Brazil. We found that smaller rivers, especially when draining regions close to floodplains, were the first places where juveniles moved after leaving floodplain lakes. We also found that individuals moved downstream as they grew, and were found in increasingly larger rivers that were more distant from floodplains. Currently, the best-known strategy for conservation of neotropical migratory fishes is the maintenance of free-flowing stretches encompassing necessary habitats for life cycle completion. We conclude that small tributaries near floodplain regions are also needed in these protected free-flowing river systems.