Since the beginning of the 21st century, the Naru eagle ray, Aetobatus narutobiei, has distributed in the Ariake Sound and the western Seto Inland Sea. Bivalve populations in both sea areas have decreased sharply as a result of predation by the eagle ray. We conducted ecological study on this eagle ray in the western Seto Inland Sea from 2004 to 2013. In this paper age and growth of the Naru eagle ray in the western Seto Inland Sea was reported. Comparing our results with data on the growth patterns in the Ariake population, it seems that both eagle ray subpopulations of the Ariake Sound and the western Seto Inland Sea are separating biologically together.