The mass mortality of Manila clam, Ruditapes philippinarum, caused by Heterocapsa circularisquama red tides in the recesses of Lake Hamana [Japan]
2009
Suzuki, K., Shizuoka-ken. Research Inst. of Fishery, Hamamatsu (Japan). Hamanako Branch | Matsuura, R. | Koizumi, K. | Wakuda, M.
We investigated the distributions of Heterocapsa circularisquama red tides that appeared at the recesses of Lake Hamana and the mass mortality of the Manila Clam, Ruditapes philippinarum, in 2007. We were able to identify a method to reduce damage caused to clam fisheries by H. circularisquama red tides. H. circularisquama formed red tides from the middle till the end of September, extending rapidly from Lake Hosoe to the recesses of Lake Hamana, with the concentration of cells reaching 22,530 cells/ml. The mortality rates of the clams were especially high at 2 places located in the recesses of Lake Hamana, which corresponded to high densities of H. circularisquama. The mortality rate of 20mmSL clam was 56%, and that of 25mmSL, 30mmSL, and 35mmSL clams were 78%, 95%, and 100% respectively, which means that the larger the clam scale, the higher the mortality rate. The damage to clams in the propagation ground at Osaki (2 ha) was estimated to be 37 tons, which translates into a financial loss of 12.71 million yen. These results indicate that to prevent such extensive damage, large-scale clams should be caught before the outbreak of the red tide in mid-September, and the clams of 20-28mmSL should be transferred to the front of Lake Hamana.
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