Examination of factors causing the depletion of Manila clams (Ruditapes philippinarum) on the eastern coast of Ise Bay, central Japan, using a growth model
2020
Shiba, S. (Chateau Marine Survey Co., Ltd., Osaka (Japan)) | Himeno, T. | Yoshida, T. | Kamohara, S. | Tanaka, Y. | Suzuki, T.
Total nitrogen, total phosphorus and chlorophyll a concentrations have decreased markedly, and water temperature has shown a tendency to rise in Ise Bay, central Japan in recent years. On the other hand, decrease of the standing stock of Manila clams (Ruditapes philippinarum) occurred suddenly in spring of 2014 at the Kosugaya tidal flat, one of the main fisheries areas on the eastern coast of Ise Bay, thereafter the decline of standing stock has continued. To clarify the relationship between environmental conditions and the standing stock of Manila clams, we added a term of the energy distribution to gonad to a conventional clam growth model that assumes water temperature and the quantity of phytoplankton as variables, and created a model that is capable of estimating growth and judging physiological death. Calculated growth of clams using time series data in 2014 suggested that the sudden decrease of standing stock in the Kosugaya tidal flat was likely due to physiological death caused by a drop in the quantity of phytoplankton. Moreover, based on the calculated growth of clams using the past trophic condition estimated from Aichi Prefecture environmental data, it is suggested that physiological death did not occur before 2008.
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