Potential of Stock Enhancement for Decapod Crustaceans

Abstract

To evaluate the potential of stock enhancement for decapod crustaceans, we analyzed stock enhancement programs for 4 species: the penaeid prawns (Penaeus japonicus) in Japan and (Penaeus chinensis) China, the European lobster (Homarus gammarus) in Norway, and the mud crab (Scylla paramamosain) in Japan, for which stocking effectiveness has been intensively examined. For each species, we summarized the life cycle, fishery, and stocking programs and then comparatively analyzed the recapture rates, the yield from the released individuals (YPR), and the economic efficiency. Scylla paramamosain had some advantages in stock enhancement, including restricted living areas such as bays and estuaries, a large body size, and high values of the ratio of price per landed individual to the cost per released juvenile. These characteristics promised higher values of YPR and economic efficiency, even at lower recapture rates. Therefore, hatchery releases affect areas with small stocks of S. paramamosain. This scenario might also be inferred for H. gammarus, which had the highest YPR and does not generally migrate from the release site, although the economic efficiency was low due to the high cost of juvenile production. On the other hand, fishery productions of the penaeid prawns, which had a lower YPR, could not be augmented without a huge number of released juveniles and the maintenance of nursery habitats. The restocking is a more cost-effective measure for sustainable fishery production than only a sea ranching (put and take) operation. Therefore, hatchery releases for decapod crustaceans should be applied to rebuild wild stocks (restocking) with appropriate fishing regulations and habitat restoration. In the future, selection of target species for stock enhancement programs should take into account the necessity for restocking and their life history characteristics.