Stock enhancement and translocation of the shrimp Penaeus chinensis in China

Hatchery releases of the prawn (shrimp), Penaeus chinensis, have been made in China for 20 years, both within and outside the natural distribution of the species. The number of released prawns reached a peak of 5.213 billion in 1991 and currently remains at ∼600 million p.a., providing annual landings of around 720 t. Catches of released prawns have contributed >90% to total landings in one region, the Haiyangdao Fishing Ground in the north Yellow Sea. Although recapture rates of hatchery released juveniles varied greatly between release sites, they reached an average of 9.2% at the Haiyangdao Fishing Ground from 1985 to 1992, and 9% in Xiangshan Bay from 1984 to 1995 and 5.4% in Dongwuyang Bay from 1986 to 1995, two bays in the East China Sea. The ratio of production costs to revenue from the catches of released prawns reached 1:8.5 for the stock enhancement programmes in the Yellow Sea, and averaged 1:5.6 in the translocation of prawns outside their natural range in the East China Sea. Although releases of hatchery-reared prawns in China have succeeded in augmenting production of commercial prawn fisheries, they have not increased the size of the wild prawn populations in the Yellow-Bohai Sea region due to over-fishing of pre-spawning animals. Similarly, they have not succeeded in establishing self-replenishing populations in areas when P. chinensis was translocated outside its natural distribution. Instead, the various prawn stock enhancement initiatives have led to successful sea ranching operations, i.e., releasing juveniles and harvesting them when they reach market size but before they reach sexual maturity. However, rebuilding the wild prawn stock through management regulations promises to be a more cost-effective approach to increasing prawn production than the current sea ranching operations. ‘Put and take’ releases are an inappropriate substitute for more urgently needed fisheries management actions, such as habitat restoration and reduction in fishing effort, and management to allow releases of hatchery-reared prawns to contribute to spawning biomass.