Sediment Size Composition as an Important Factor in the Selection of Spawning Site by the Japanese Surf Smelt Hypomesus japonicus

We examined the relationship between egg distribution of Japanese surf smelt, Hypomesus japonicus and characteristics of the five beaches in Otsuchi Bay. It was elucidated that sediment size composition was important for spawning site selection by the fish among characteristics of the beaches. They spawned in beaches where bottom sediment contained both gravels and an amount of fine sand, but they did not use beaches composed entirely of gravels or fine sands for spawning site. It is thought that gravels were efficient in oxygen supply for eggs in sediments and fine sediments in the interstices of the gravel matrix would play an important role in moisture retention.