Impacts of the 2011 Mega-earthquake and Tsunami on Ezo Abalone Haliotis discus hannai at Iwaisaki, Miyagi, Japan

Abstract

On 11 March 2011, a massive tsunami generated by a mega-earthquake hit a wide area of the Pacific coast of northeast Japan. We have analysed the effects of the tsunami on Ezo abalone Haliotis discus hannai population at Iwaisaki in Miyagi, Japan. Ezo abalone is among the most economically valuable fisheries resources, so assessments are needed to evaluate the effects of the disaster on this important species. Before the tsunami, algal forests dominated by the brown macroalga Eisenia bicyclis had developed in the survey area, where large juvenile and adult abalone >30 mm in shell length (SL) inhabited. Juvenile abalone <30 mm SL inhabited the area dominated by crustose coralline algae (CCA). After the tsunami, no apparent decrease was observed in the density of large juvenile and adult abalone inhabited in the algal forests. The impact of the tsunami was more profound in the CCA area than in the algal forests. Just before the tsunami, the intensive recruitment of zero-year-old juveniles was observed, but individuals of this year class were not detected after the event. The distribution pattern of juveniles could be a cause of the marked decrease, because most of them inhabited the CCA area where the disturbance by the massive water movement was not reduced by the effects of the macro algal forest. Since the age at first capture of abalone is at 4–5 years old, the future commercial catch may considerably decrease for at least 4–5 years after the tsunami.