オホーック海沿岸域における貝毒発生予測研究

摘要

The coastal area of Hokkaido in the Okhotsk Sea is one of the major scallop (Mizuhopecten yessoensis (Jay)) aquaculture areas in the world. Paralytic shellfish poisoning (PSP) caused by the toxic dinoflagellate Atexandrann tamarense (Lebour) Balech has led to extensive economic damage to the fishery and the scallop aquac-ulture industry in summer along the Okhotsk Sea coast of Hokkaido once every few years. The ability to predict PSP occurrence would have important advantages for fishing and the shipping plans for scallops. We examined the relationship between the distribution of the toxic dinoflagellate, Alexandrium tamarense and the dynamics of the Soya Warm Current (SWC) in the Okhotsk Sea off Hokkaido, to design a method for predicting outbreaks of PSP in scallop fishing grounds. Surveys were conducted from May to June in 2004, 2007 and 2008 to clarify the transpor-tation mechanism of A. tamarense from the oceanic area to the coastal area. Water samples for cell counts of A. tamarense were collected and the water temperature and salinity were measured at each station. The sea-level differ-ence (SLD) between Wakkanai and Abashiri was monitored as an index of the strength of the SWC southeastward flow in an alongshore belt to examine the possible occurrence of A. tamarense in the coast during temporal weaken-ing of the SWC. A bottom-mounted ADCP was used for direct observations of the SWC. The results indicated that PSP occurred when the low salinity water contaminated with A. tamarense extended to the coast during the temporal weakening of the SWC due to a decrease of the SLD. A retrospective analysis of the relationship between PSP occurrences and changes of SLD showed that PSP occurred within a few weeks after the decrease of SLD. These results strongly indicate that we can predict PSP occurrence by monitoring the decrease of SLD as an index of the temporal weakening of the SWC after surveys of the distribution of A. tamarense in the oceanic area before the period of NP occurrence.