TDA-IME Project Final Report June, 2013 FIGURE 2: Life cycle of the mud crab Scylla olivacea in Ranong, Thailand (from Moser, 2001). The life histories of the four Scylla species are believed to be similar (Overton and Macintosh, 2002), indicating that there is considerable natural movement of mud crabs across boundaries due to their adult spawning and larval recruitment migrations. They are also traded extensively across boundaries as they are easy to transport alive. Adult crabs are sold as high value seafood, while there is also significant movement of juveniles for stocking in aquaculture ponds. Mud crabs from Myanmar and Cambodia are imported into Thailand, for example, while “jumbo” crabs from Sri Lanka are advertised in restaurants in Malaysia and Singapore. The abundance of mud crabs can be used as an indicator of mangrove ecosystem health, while their size (carapace width) can provide a very reliable indicator of fishing pressure. It is easy to measure the size of crabs caught by fisher folk at the point of sale to crab dealers (“middlemen”) and the crabs’ sex and maturity (immature, mature, gravid) can also be readily determined and recorded (Overton and Macintosh, 2002). Overfishing quickly translates into a decrease in the average size of mud crabs in the fishery, plus an increase in the relative number of immature crabs caught. These same indicators can be used to monitor the effectiveness of introducing fishery regulations, such as a minimum size rule, or a ban on removing female crabs during the breeding season. Socio-economic and Development Aspects The countries of Indochina are very diverse in area and coastal geography, population size, and GDP (see Table 1). Poverty is still prevalent in Cambodia, Philippines and Viet Nam, where per capita GDP is still only USD 2,400 to USD 4,300. This largely explains why coastal communities in these countries still have a high dependency on mangrove and other 44
Transboundary Diagnostic Analysis of Indochina Mangrove Ecosystems
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