The present situation and problems of oyster culture in Hiroshima Bay [Japan]
2004
Hirata, Y. (Hiroshima-ken. Fisheries Experiment Station, Ondo (Japan)) | Akashige, S.
Abstract Hiroshima Bay including its adjacent area is one of the most important oysters farming areas in Japan. During 1980s, the oyster production in Hiroshima Bay was about 30,000 metric tons (t) scale by fresh meat weight (FMW) a year. In the early 1990s, the oyster production began to decrease and was about 20,000t in 2000. We analyzed the present situation and problems of oyster culture in Hiroshima Bay to show the problem solution. This decrease in oyster production in the 1990s was caused directly by typhoon damages; shellfish poisoning by Alexandrium spp.; and mortality by harmful dinoflagellate Heterocapsa circularisquama: and was caused by dense cultivation indirectly. The postponing of harvesting the oyster caused by shellfish poisoning prolonged the oyster culture period. The prolongation of the culture period in a limited culture ground caused eventually dense cultivation of oyster. Aged and large-sized oysters took much feed, therefore growth of all oysters in culture grounds were slowed down under low feed level. The low growth rate accelerated prolongation of a culture period. These vicious spirals promoted dense cultivation, and changed the environment of the culture ground into favorable environment for H. circularisquama. To analyze these situations, an oyster culture process model was built. This model showed that the reduction in oyster biomass in the culture grounds is needed to escape from the vicious spiral, and shortening of the culture period was the most effective method for this reduction without reducing harvest magnitude.
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