Integrated study on the effect of environmental changes on the fisheries resources in Ariake Sound

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Integrating all of the results of this research, we have concluded as follows ; (1)It was revealed from numerical simulation of tidal currents that rapid extention of reclamation areas during late 1960s had accelerated eutrophication and subsequent environmental degradation of Ariake Sound. In addition, recent increase in transparency, which was probably caused by decrease in suspended sediment due to weakened tidal currents, apparently resulted in increase in red-tide frequency. (2)Fish catches have rapidly declined in 1990s, particularly in the latter half of 1990s, which might be resulted from environmental degradation in the bottom water like enlarged DO deficiency areas. On the other hand, rapid increase in the abundance of rays enhanced predatory pressure for shellfishes and competition for food among bottom dwelling species as well. (3)From the stable isotope analysis, it was revealed that benthic animals including some shellfishes on the estuarine sand-flat mainly eat phytoplankton originating from seawater, and that contribution of attached diatoms is not always large. (4)Further, several new findings were obtained on the implication of vertical stratification enhanced during the neap tide for primary production, utility of satellite remote sensing in monitoring red-tide outbreaks and suspended mud, and contamination of tidal flat fishes by endocrine disruptors. (5)As seen from a viewpoint of material budget, material balance between benthic tidal flat systems and pelagic plankton systems was maintained during 1960s, while decline in the tidal flat systems and subsequent deterioration of the pelagic systems symbolized by harmful red-tide outbreaks became prominent, resulting in losing the material balance in the ecosystem. The above results were presented at relevant academic meetings and symposiums, part of which will contribute to establishing the international framework for future collaborative research with Korean institutes and others.