Minamata Bay (Fig. 6). The dividing nets were removed in 1997 on the grounds that the mercury levels for seven species of fish were below the provisional control values (the average total mercury and average methylmercury levels for fish are 0.4 ppm and 0.3 ppm respectively) for three consecutive years.
(2) Restrictions on Fishing
In the area around Minamata Bay, reasonable suspicion began to occur around 1956 that the eating of local fish and shellfish was the cause of Minamata Disease. Based on this, the Kumamoto Prefectural Government issued guidance to voluntarily restrain from eating fish and shellfish caught in Minamata Bay and also advised the Minamata City Fishermen's Cooperative to voluntarily refrain from fishing inside Minamata Bay. This voluntary restraint from fishing, i.e. self-imposed restraint, prohibition of fishing based on the fisheries compensation agreement and compulsory purchase of locally caught fish and shellfish intermittently continued until October 1997 when the dividing nets in Minamata Bay was completely removed. During this period, Chisso and others paid fisheries compensation from time to time.
In regard to Agano River, the Niigata Prefectural Government regulated the fishing activities of the relevant fishermen's cooperatives and provided guidance for local people to refrain from eating locally caught fish and shellfish. Meanwhile, Showa Denko paid fisheries compensation.
Changing State of Pollution Situation
In Minamata Bay and the Agano River, water quality, sediments, and fish have been monitored continuously on a regular basis.
A mercury survey conducted by the Kumamoto Prefectural Government in FY 2009 found that the sea environment was favourable, as was the case in the previous year. To be more precise, the water quality met the environmental standard values (total mercury of 0.0005mg/l or less and zero detection of alkylmercuric compound); the bottom sediment cleared the provisional reference value for removal, and fish also cleared the provisional control value. A similar survey conducted by the Niigata Prefectural Govenrment found that the water quality standard was achieved along with clearance of the provisional reference value for sediment removal and of the provisional control value for fish, indicating a favourable river environment as was the case in the previous year.
It is important to continue regular monitoring of water quality, sediments, and fish in these locations. With regard to Minamata Bay, it is also important to conduct appropriate safety control measures, such as inspection of reclaimed land.