Abstract
The aim of this study was to describe the population characteristics of Monetaria annulus (Linnaeus, 1758), including the density, abundance of different developmental stages, sex ratio, and size dimorphism between sexes, which are significant factors for resource management. We surveyed populations in the Philippines (tropical area) for comparison with populations in Japan (subtropical and temperate areas). The population density in the tropical area was intermediate between that in the sub-tropical and temperate areas, although density varied among stations in the same geographical area. There was a low proportion or absence of immature cowries in the habitat shared with adults, except for Nogas Island in the Philippines. Because marine protected areas (MPAs) include a nursery area, which is a protective area for immature cowries, further study was required to determine where juveniles are recruited and grow. We detected the sex of adult cowries by histological analysis and measured the length of each shell to distinguish sexual dimorphism. Females were larger than males in some sampling sites. When formulating fisheries guidelines, including controlling the collection of larger individuals, we should investigate the sex ratio and size dimorphism in each resource population to avoid a sex ratio that is biased toward males.
