Successful stock enhancement of a lagoon prawn fishery at Rekawa, Sri Lanka using cultured post-larvae of penaeid shrimp

Abstract

Rekawa Lagoon, Sri Lanka (area 250 ha) has an artisanal fishery for penaeid shrimp, predominantly Penaeus indicus (93.6% of catch), but with small numbers (0.8%) of Penaeus monodon. Neither species breeds in the lagoon; larvae and post-larvae enter the lagoon: during brief periods in July and November (P. indicus) or just November (Pen. monodon) when a sand bar blocking the lagoon entrance is breached. Detailed information on fishery characteristics was collected during the fishing season of 1995-1996. The P. indicus fishery began in October, peaked in February and was over by late April/early May; while Pen. monodon was only caught from March to early May. The fishery was extremely intensive, removing virtually all shrimp by early May. In the light of these data, two stock enhancement exercises were carried out with Pen. monodon post-larvae in July 1996 (55,000 post-larvae) and July 1997 (70,000 post-larvae). These led subsequently to commercial catches of Pen. monodon from September to January (roughly 6 months out of phase with the natural fishery) in both years. Total catch in 1996-1997 represented 3.5% of the number of post-larvae released. In 1996-1997, the total shrimp catch was worth 33% more than in 1995-1996, while the annual Pen. monodon catch was enhanced by 1400%. Economic analysis and scenario modelling were used to evaluate the biological and economic feasibility of more intensive stock enhancement. This study represents an ecologically and economically sustainable penaeid stock enhancement approach by which shrimp aquaculture and artisanal fishing can co-exist.