IWAKI, Fukushima -- As radioactive cesium levels in fish caught off the Fukushima Prefecture coast show lower levels that fall within safety limits set by the government, the Mainichi Shimbun recently accompanied a volunteer group that continues to measure these fish on one of its outings.
The group, called "Iwaki Kaiyo Shirabetai Umi Labo" (Iwaki marine investigative squad ocean lab), began its activities three years ago. Rather than relying on the national government, Fukushima nuclear plant operator Tokyo Electric Power Co. or others for data on radioactive pollution in the ocean off Fukushima Prefecture, the group aims to obtain this information itself and share it across the country.
On Nov. 13, a Mainichi Shimbun reporter boarded one of the group's fishing ships, which set out from Hisanohama Port in Iwaki, Fukushima Prefecture. Two kilometers from the disaster-stricken plant, the group pulled up a large, 90-centimeter, 7.7-kilogram olive flounder. This fish was caught by Eriko Kawanishi, a civil servant who came from Tokyo to participate in the outing and said it was her first time ever to hold a fishing rod. A 90-centimeter fish would be a rare catch even for a veteran fisherman.
The olive flounder was refrigerated and taken back to veterinarian Seiichi Tomihara at the Aquamarine Fukushima aquarium in Iwaki for dissection. Based on the growth rings on its "otoliths," a structure located near the brain, Tomihara estimated the fish's age at 11 years. He said there is research estimating the life expectancy of olive flounders at around 12 years, adding, "This looks like one of the oldest (one can find)."
A 1-kilogram slice of the fish put in a detector showed 14.6 becquerels of radioactive cesium -- below the 100 becquerels-per-kilogram national safety limit for regular food products. Lately the research group has found no fish, including bottom-dwelling fish like olive flounder, that exceed this limit. In addition, radiation checks done by the prefectural government find hardly any cases of fish that top the safety limit.
Riken Komatsu, 37, joint-representative for the group, says, "This is the first time for us to check such an old olive flounder, and I thought there would be dozens of becquerels detected. The result was lower than I had imagined and I feel relieved."
Fish that were already adult at the time of the disaster, with a slowed metabolism and a narrow range of habitat, tend to show high radiation levels, Komatsu says. With time having passed since the disaster, the generational replacement of the fish in the area has moved forward. The group says the highest radiation level it has detected so far was 138 becquerels from a 56-centimeter olive flounder in July 2014.
Olive flounder caught off of Iwaki are known as "Joban-mono" and have a good reputation. There is hope among locals that the fish will regain their pre-disaster popularity.
Komatsu says, "The prefectural government and fishing cooperatives are also releasing radiation readings from fish taken off Fukushima Prefecture, but I feel there are few taken from waters near the nuclear plant. Stronger data showing the fish's safety (like data from fish near the plant) should raise the value of Fukushima olive flounder."