New directions for research in prawn (shrimp) stock enhancement and the use of models in providing directions for research

Despite attempts in many countries, large-scale prawn (shrimp) stock enhancement programmes have only been implemented and continue to operate in Japan (Penaeus japonicus) and China (Penaeus chinensis). In these countries, prawn stock enhancement has been possible because of the capacity to produce large numbers of small individuals for release as a result of aquaculture. While exploring the feasibility and bio-economics of tiger prawn (Penaeus esculentus) stock enhancement in Exmouth Gulf, Australia, a broad framework for stock enhancement research was developed. This framework included developing a bio-economic model and risk assessment for all components of a stock enhancement operation, i.e., hatchery, grow-out, harvest–transport–release, population dynamics of released and wild prawns, and monitoring the fishery. However, predictions from the bio-economic model were made with great uncertainty about the values for post-release mortality of prawns because there were no data from experiments on optimal release strategies. Consequently, data from field studies of growth, and laboratory studies of predation, were used to set values for growth and mortality in Monte-Carlo simulations of the potential success of P. esculentus releases in different habitats. The survival of 2 mm carapace length (CL) prawns to the size at emigration from the nursery habitat was ∼1.9 times higher for individuals associated with seagrass of high (∼100 g m−2) than for those in low (∼10 g m−2) plant biomass. Survival was 19 times higher for prawns in high biomass seagrass than for those on bare substratum. The differences in survival between habitats were reduced greatly when the releases of much larger prawns (10 mm CL) were simulated. These findings highlight the importance of research on developing optimal release strategies for prawns in stock enhancement programmes. In particular, the size, habitat, time and density at release needs to be identified to provide more reliable information for the bio-economic assessments of releasing hatchery-reared juveniles to augment production in stock enhancement programmes.