With its rich fishing grounds, the far northern and mostly rural prefecture of Aomori is reeling from a ban on shipments of Pacific cod after two instances of fish were found with exceptionally high readings of radioactive cesium.
The ban, imposed by the central government on Aug. 27, comes at a bad time as local fishermen had anticipated good hauls of the fish in the weeks ahead.
Pacific cod features in traditional "nabe" hot pot dishes that grace Japanese dinner tables during autumn and the gloomy winter months.
Hauls of Pacific cod in Aomori Prefecture totaled 1.4 billion yen ($18 million) last year.
Local officials are puzzled by the fact that the two contaminated fish were caught in waters far from the stricken Fukushima No. 1 nuclear power plant.
The latest case was identified Aug. 9, following one in June. Most cod caught in fishing grounds 400 kilometers north of the devastated nuclear plant have shown only slight readings of contamination.
The fish was found to have a cesium concentration of 133 becquerels per kilogram, far above the government's safety standard of 100 becquerels per kilogram.
The inspections were undertaken voluntarily by the Morioka City Central Wholesale Market in adjacent Iwate Prefecture.
The fish was caught off Hachinohe, Aomori Prefecture, and landed at Hachinohe Port two days earlier. Slices of the meat had already been sold to consumers.
"It would be a disaster if we were not allowed to catch them," said one senior official of the Hachinohe Port fishermen's association.
In Tokyo, the Fisheries Agency is trying to determine why only sporadic cases of cesium have been detected in the species.
It was the second time that cesium concentrations in cod caught off Aomori Prefecture had exceeded the safety standard. The first instance turned up a cesium reading of 116 becquerels per kilogram.
The central government on Aug. 27 ordered Aomori Prefecture to suspend shipments of cod from the area where the suspect fish were caught. It was the first time the government has slapped a ban on shipments of products from Aomori Prefecture, which is famed for its seafood.
Except for the two cases, however, cesium readings have remained largely low. In 23 of 26 cases where cod caught off Aomori Prefecture was inspected following reactor meltdowns at the Fukushima nuclear power plant in March 2011, the readings were less than 50 becquerels per kilogram.
Port authorities took it upon themselves to suspend shipments following the first instance two months ago of a highly contaminated fish. They lifted the self-imposed ban a month later because inspections were consistently turning out low readings.
The fishing grounds in question lie far to the north of the disabled nuclear plant. Cesium concentrations have remained mostly below the detection limit, and exceeded 10 becquerels per kilogram only in two cases, in inspections of fish other than the Pacific cod in Aomori Prefecture in April this year and later.
So why Pacific cod, one might ask.
According to the Fisheries Research Agency, a research institution affiliated with the Fisheries Agency, Pacific cod live at depths of hundreds of meters and feed on the seabed. They swim to coastal areas to spawn in January through spring.
One of the major cod spawning areas along the Pacific coast of the Tohoku region is Sendai Bay. Cod are also believed to spawn off northern Fukushima Prefecture.
While little is known about their ecology, cod are known to swim long distances. One survey found that an individual fish had traveled 400 km.
"Some fish that ate highly radioactive offerings off Fukushima Prefecture probably traveled north (and produced the high cesium readings in Aomori)," said one FRA official who is knowledgable about Pacific cod.
In an effort to better understand cod behavior, the FRA has tagged and released 130 cod that were caught off Fukushima and Miyagi prefectures between February and April this year.
The FRA also plans a follow-up tagging survey this winter with the aim of tracking individual fish.
Pacific cod is a major target species of trawling operations that will resume in September.
"I am worried about how the publicity will have a negative effect on other fish species," said one official at the Aomori prefectural government's Fisheries Promotion Division. "I hope the authorities can clarify the reason (for the isolated cases of contamination), so that we can declare with pride that the waters around Aomori are clean."
In the case of fish that travel long distances, "it is not rational to believe that all fish in coastal waters are dangerous just because one caught there happened to be highly radioactive," said Hiroyuki Matsuda, a professor of environmental risk management at Yokohama National University's Graduate School of Environment and Information Science. "The impact on fisheries will be huge unless we think about limiting the extent of shipment bans, be they voluntary or compulsory."
Matsuda continued: "The current regulations are aimed at containing the annual internal radiation dose to 1 millisievert or less. Studies have found that actual doses are much lower."
Pacific cod is not the only species that interests the FRA. It is keen to understand isolated high radioactivity readings of other fish that travel great distances from the stricken Fukushima nuclear plant.
In July, a black sea bream caught in Sendai Bay off Higashi-Matsushima, Miyagi Prefecture, showed an alarming cesium reading of 3,300 becquerels per kilogram.
Black sea bream live in brackish water, which is midway between seawater and freshwater. Researchers believe they are prone to accumulate cesium in the same way that freshwater fish do.
Japanese flounder, like Pacific cod, also travel long distances.
Many experts believe flounder that have shown isolated, high radioactive readings simply migrated from contaminated marine areas.
Fish with high radioactive readings continue to be found off Fukushima Prefecture. This month, Tokyo Electric Power Co., operator of the Fukushima nuclear plant, detected an all-time record of 25,800 becquerels per kilogram in two greenling caught within a 20-km radius of the stricken nuclear plant.
"There may be radiation hot spots on the seabed," a TEPCO official said.
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