Spatial and temporal variations of sediment quality in and around fish cage farms: A case study of aquaculture in the Seto Inland Sea, Japan

Fish cage farming generates large amounts of organic waste in the form of u nconsumed feed and fecal matter, resulting in sediment deterioration and a threat to its own sustainability. Field studies analysed the scale of the i mpact of fish cage farming on sediment quality, variability of impact and s pread of sediment enrichment in the vicinity of a fish farm. Two fish cultu re sites near the Fukuyama area of the Seto Inland Sea of Japan were chosen for the study. There was a significant difference between the quality of t he sediment in aquaculture and non-aquaculture areas. The sediment underlyi ng the fish cage farms was found to be extremely reducing, acidic and sulfi dic. Sediment ignition loss did not vary markedly with the season. However, the redox potential and acid volatile sulfide content of aquaculture areas did show some seasonal variation. Sediment encircling a 165 m radius from the center of a farm in Yokota was judged as organically enriched by fish f arming. A variation in sediment quality within the two sites and also withi n the stations was observed. Based on sediment quality, the stations could be categorized as less affected, highly affected or moderately affected.