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

Abstract

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 <15 m 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; mm day−1) between 1 and 6 days before collection in 2011–2013, which were estimated from the width of otolith increments, ranged from 0.84 to 2.37 mm day−1 for juveniles of 24.8–146 mm 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 (mm day−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.

Limited effect of the massive tsunami caused by the 2011 Great East Japan Earthquake on the shallow sandy shore demersal fish assemblages in Sendai Bay

“…The sandy shore did not change markedly after the tsunami based on aerial photos (http://mapps.gsi.go.jp/maplibSearch.do#1, Geospatial Information Authority of Japan) and the sediment particle size distribution (Kurita et al ., in press). Therefore, the shallow sandy habitat was almost similar after the tsunami, despite substantial disturbances to the shallow areas of Sendai Bay.…”

“…In contrast, the reduction in O. iburia abundance after the tsunami (2012 and 2013) could not be explained by the local environmental conditions or sampling constraints. Moreover, an abundance of P. olivaceus has increased since 2010, and recruitment of P. olivaceus after 2010 has remained relatively high in Sendai Bay and its adjacent waters (Kurita et al ., in press). Furthermore, adult P. olivaceus are distributed in deeper offshore areas where less physical effects of the tsunami occurred during early spring (Sato, ; Kurita et al ., ); thus, the surviving adult population may have spawned in the summer of 2011 as in normal years.…”

“…In fact, new recruitment of P. olivaceus was observed in August 2011 (Fig. ), and the growth rates of P. olivaceus juveniles did not change before and after the tsunami event (Kurita et al ., in press). As a result, P. olivaceus abundance did not decrease after the tsunami.…”

Consequences of “natural” disasters on aquatic life and habitats

“…In other locations, the abundance, diversity, and species composition of shallow demersal fish assemblages did not appear to change significantly, which may be explained by the translocation or movements of more mobile fishes, enabling high survival rates (Okazaki et al 2017). Juvenile growth rates of a regional flounder species off Japan showed no change up to two years after the event (Kurita et al 2017). Populations of Pacific cod (Gadus macrocephalus) off northeastern Japan showed a remarkable four-fold increase in the three years after the tsunami, which was suggested to be linked to lower mortality resulting from a marked decrease in fishing mortality arising from damage to the fishing fleet (Narimatsu et al 2017).…”

Estimating the maximum sustainable yield of snow crab (Chionoecetes opilio) off Tohoku, Japan via a state‐space stock assessment model with time‐varying natural mortality

“…This is not the special case. For example, the abundance of Japanese flounder ( Paralichthys olivaceus ) had increased rapidly after 2011 because the decreased fishing effort caused the number of juveniles to increase (Kidokoro, Togashi, Narimatsu, & Shibata, 2019) where their growth rate (mm/day) did not change before and after 2011 (Kurita et al, 2017). In addition, their abundance after 2011 was predicted where observed fishing effort was given and the predicted values well matched to observed values obtained from other surveys, although biological parameters such as M and migration parameters were the same through simulation periods (Shibata et al, 2017).…”