Shrimp seed recruitment in mixed shrimp and mangrove forestry farms in Ca Mau province, southern Vietnam.

摘要

The rapid expansion of shrimp aquaculture in Vietnam has contributed to considerable loss of mangrove forests and environmental degradation in the Mekong Delta. The reduction in forest area has led to declines in plankton and shrimp seed densities,and other environmental degradation. To ease the conflict between mangrove silviculture and shrimp aquaculture, State Forestry-Fisheries Enterprises were established for both activities within integrated farming systems. Despite this, shrimp yields havecontinued to decline. Densities of shrimp seed recruited into ponds at 2 mixed shrimp and mangrove forestry enterprises, covering 3300 and 6475 ha and each including several farms, in Ca Mau province, southern Vietnam, were monitored during 1996-98 to determine whether shrimp culture in the region is recruitment-limited. The numbers of shrimp seed lost during harvests were also monitored to assess whether current management strategies contribute to low stocking densities and pond production. Shrimp seedrecruitment densities were low and highly variable; the densities were higher at farms on rivers than at farms on small canals. Numbers of shrimp seed lost during harvests were also high, reducing net recruitment and stocking density to 0.15 postlarvae/m2 from a potential gross stocking density of 0.35 postlarvae/m2. It is concluded that shrimp yields on these farms will remain low and unsustainable with continued reliance on wild seed for stocking ponds. In the longer term, mangrove forest losses needto be minimized relative to rates of reforestation, and limits should be placed on fishing practices to maintain nursery grounds and improve wild stock numbers. Improvements in management strategies, particularly harvest techniques, would give shorter term increases in recruitment and production.