Marine aquaculture has enormous potential in providing humans with food and high-quality protein. However, with the rapid development and expansion of marine aquaculture, excessive nutrient loading from the farm causes the deterioration of the water environment, resulting in eutrophication and red tide. Therefore, a suitable cultural density within the ecological carrying capacity should be understood for the sustainable development of marine aquaculture. The present study was conducted to propose an index to assess the sustainability for fish culture within semi-closed bays in Japan.
The target area of ??this study are semi-closed bays in Japan where fish farming is currently carried out. Waste nutrient loading from fish farms was calculated based on the average annual biomass of farmed fish. Fish biomass was calculated based on the number and size of fish cages detected from satellite imagery. The nutrient load released from watershed of bays was also calculated. Based on analysis of factors affecting water quality within the bay, an evaluation index is proposed that integrates the water depth of the bays, area, closure degree, fish farm location, nutrient loading from fish farms and watersheds.
The results of factor analysis show that the nutrient loading, topography, closure degree and the allocation of fish farms are important factors affecting the water environment within the bay. The result of the correlation analysis between the proposed index and the frequency of red tides (Fig. 1) shows that the greater the index value, the higher the probability of red tides and the lower the sustainability for fish aquaculture.