Native brook trout (Salvelinus fontinalis) populations typically persist in isolated headwater streams, particularly in their southern range. This distribution pattern is common in native salmonids globally. In this presentation, we studied demography and movement of two Japanese landlocked salmonids (white-spotted charr Salvelinus leucomanie japonicus and red-spotted masu salmon Oncorhynchus masou ishikawae) persisting for > 30 years in a headwater stream network that is highly fragmented due to low-head dams in the mainstem (six impassable infrastructures in a < 500 m segment). We marked individuals and tracked them annually for 9 years to investigate why these populations persisted despite habitat fragmentation. We found that tributaries supported higher survival rates and movement was asymmetrical from the tributaries to the mainstem. Accordingly, the tributaries rescued these populations from extirpation, although the tributaries (2 m wide) occupied only 12 or 18% of the study stream network by surface area. The tributaries harboured more physically and hydraulically complex instream habitats (i.e., higher wood density and flow refugia), indicating that habitat quality was more important than habitat size in generating the spatial population dynamics. Dr. Kanno will use these findings to discuss management implications and the importance of protecting small tributaries for native trout populations, including brook trout.