Immediate impact of the tsunami associated with the 2011 Great East Japan Earthquake on the Plecoglossus altivelis altivelis population from the Sanriku coast of northern Japan

Abstract

The huge tsunami associated with the 2011 Great East Japan Earthquake severely impacted the ecosystems on the Sanriku coast of Japan. The life history traits of ayu, Plecoglossus altivelis altivelis, which have a one-year amphidromous life history, were investigated by otolith analyses in two rivers of the Sanriku coast just after the tsunami compared with results before the tsunami to reveal the immediate impact of the tsunami. Hatching date compositions differed between the upstream migrants before and after the tsunami. The migrants after the tsunami were solely composed of fish hatched during October and November, whereas the migrants before the tsunami were mostly composed of fish hatched in September. Discrepancies between the hatching dates of the migrants and drifting larvae (hatched larvae) indicate that selective mortality of early-hatched fish occurred during the tsunami. Differences in otolith Sr:Ca ratios between upstream migrants before and after the tsunami suggest that fish surviving the tsunami inhabited saline water and early-hatched fish that inhabited the estuary decreased selectively in number because of the severe erosion around the river mouth. The oceanic growth period shortened in accordance with the change in hatching date. These results show that the tsunami drastically altered the ecology of P. altivelis altivelis on the Sanriku coast.