Impact of the great tsunami in 2011 on the quality of nursery grounds for juvenile Japanese flounder Paralichthys olivaceus in Sendai Bay, Japan

The impact of the great tsunami, which was generated by the Great East Japan Earthquake on 11 March 2011, on the quality of a nursery ground for juvenile Japanese flounder Paralichthys olivaceus with a sandy bottom of <15m in depth in Sendai Bay, Japan, was evaluated. Growth rates of juveniles, as an index of the quality of the nursery ground, were compared between before and after the tsunami. Recent growth rates (RGR; mmday(-1)) between 1 and 6days before collection in 2011-2013, which were estimated from the width of otolith increments, ranged from 0.84 to 2.37mmday(-1) for juveniles of 24.8-146mm in total length (TL). These figures are comparable to the maximum RGR for juvenile Japanese flounder in the literature. A linear model for RGR selected TL and bottom temperature but rejected biomass of the mysid Orientomysis mitsukurii, the main prey item, as explanatory variables, indicating that the growth rates of juveniles after the tsunami were not controlled by food density, i.e., optimal food condition occurred in the nursery. A linear model for observed growth rate (mmday(-1)), which was calculated from the temporal changes in the juvenile size frequency distribution, suggested the growth rate did not change between before and after the tsunami. Additional information on prey abundance and sediment size distribution also support this conclusion. Therefore, we conclude that the quality of the nursery ground for juvenile Japanese flounder in the study site has not been damaged by the great tsunami.