Broodstock management and the potential to improve the exploitation of mangrove crabs, Scylla serrata (Forskål), through pond fattening in Ranong, Thailand

Abstract Mangrove crabs, Scylla serrata (Forskål), represent one of the main economic resources in the Ranong mangrove ecosystem on the Andaman Sea cost of southern Thailand. However, there is a serious problem of overfishing which has caused fishermen increasingly to sell undersized crabs to meet market demand and maintain their income levels. The crab population and fishing activities were studied to assess the scope for better management of the fishery, especially protection of female broodstock, and the feasibility of using young crabs for aquaculture. Berried crabs examined were always larger than 10·0cm (carapace width), with the great majority of females maturing in the size range 10·0–11·5cm. Gonosomatic index values peak in September, within a main egg carrying and spawning period from July to December. Protecting female crabs from fishing pressure during this season, plus limits on the harvesting of crabs less than 10cm, or using them for fattening in ponds, could lead to better utilization of this resource. Crab farming in Ranong is constrained by climatic factors, the presence of acid-sulphate soils and lack of technical knowledge among the local fishermen. An attempt initially to culture crabs from Ranong under more favourable conditions at Surat Thani showed limited success. Nonetheless, there is a considerable price differential between wild and pond-fattened crabs to encourage further interest in crab farming in Ranong.