Population dynamics and reproductive biology of the mysid Orientomysis japonica in Tango Bay, Japan

The mysids, Orientomysis spp., are common in shallow coastal waters and estuaries in Japan, and are reported to be one of the main prey items for juveniles of many commercially important fish species. Some studies have suggested that the seasonal dynamics of mysids are an important factor determining the biomass and production structure of demersal fish communities. In this study, seasonal variation in the population structure and reproductive traits of Orientomysis japonica Marukawa, 1928 were investigated in Tango Bay, the western part of Wakasa Bay, Japan, from April 2007 to April 2009. Mean densities at depths of 5 and 10 m were highest in spring (ca. 100 ind. m−2), decreasing drastically in early summer to nearly 0 ind. m−2. Juveniles and immature individuals dominated the population (>80%) in spring and decreased in summer (