Reproductive homing and fine?scaled genetic structuring of anadromous Baltic Sea perch ( <i>Perca fluviatilis</i> )

To investigate the population dynamics of anadromous Baltic Sea perch Perca fluviatilis (Linnaeus), we studied migratory behaviour (arrival to spawning location) and structure (genetic differentiation) three closely located (<50 km) populations. Spawning migration lasted for 32–80 days, passive integrated transponder tag (PIT-tag) data indicated that displayed reproductive homing. Populations were differentiated, despite low levels gene flow (3%–5%), differentiation increased with increasing geographic distance. This fine-scaled spatial structuring was likely, at least partly, explained by homing behaviour. Analyses temporal within-stream substructuring yielded inconclusive results, so further studies are required evaluate this. Taken together, our findings highlight potential genetic in indicate multiple mechanisms, such as isolation distance, homing, timing could contribute this pattern. illustrates importance considering cryptic barriers accurately identify units, points need local management perch.