Abstract
Ten years have passed since the oligotrophication of the Seto Inland Sea was pointed out. This trend is ongoing, and the situation regarding fisheries in the western part is very serious. This paper summarizes the causes of this, as well as showing the trend and spatial differences in the conditions of basins and bays, alongside the supposed changes in the ecosystems, using the Lotka-Voltera model. These analyses will help to understand the processes of oligotrophication. It is clear that the oligotrophication in the Seto Inland Sea has been generated by human activities. Since we cannot expect recovery from the present oligotrophic state in the near future, the author recommends applying effective small-scale fertilization to enhance several important species in fisheries.
