The clupeid fishes, Konosirus punctatus and Sardinella zunasi, are dominant in the larval ichthyofauna of Ariake Sound, Shimabara Bay, where they spawn in spring and spring to summer, respectively. The distribution of two species larvae partly overlapped in the inner estuaries in spring. To clarify the early life histories of both species, the pelagic, demersal and immigrated stages were collected with larva nets, a beam trawl and a seine net, respectively, in Ariake Sound in May 2006 and 2019. While egg and larva distribution of both species spatially fluctuated between two years, both larvae were fundamentally observed to aggregate in the inner parts of the sound. K. punctatus and S. zunasi used the littoral zone and the inner estuaries as their nursery grounds, respectively, but they overlapped to inhabit some estuaries. Then, the vertical distributions of larvae in the estuary showed that K. punctatus was aggregated in the surface layer, and S. zunasi was dispersed during all tidal phases. Thus, there is likely less serious competition of larval niche during early larval period between two species in the estuaries.
