TOKYO – Radioactive cesium levels in most kinds of fish caught off the coast of Fukushima haven’t declined in the year since Japan’s nuclear disaster, a signal that the seafloor or leakage from the damaged reactors must be continuing to contaminate the waters – possibly threatening fisheries for decades, a researcher says.

Although the vast majority of fish tested off Japan’s northeast coast remain below recently tightened limits of cesium-134 and cesium-137 in food consumption, Japanese government data show that 40 percent of bottom-dwelling fish such as cod, flounder and halibut are above the limit, Ken Buesseler, a marine chemist at the Woods Hole Oceanographic Institution in Massachusetts, wrote in an article published Thursday in the journal Science.

In analyzing extensive data collected by Japan’s Ministry of Agriculture, Fisheries and Forestry, he found that the levels of contamination in almost all kinds of fish are not declining a year after the March 11, 2011 disaster. An earthquake and tsunami knocked out the Fukushima Dai-ichi plant’s vital cooling system, causing three reactor cores to melt and spew radiation onto the surrounding countryside and ocean.

“The (radioactivity) numbers aren’t going down. Oceans usually cause the concentrations to decrease if the spigot is turned off,” Buesseler said. “There has to be somewhere they’re picking up the cesium.”

“Option one is the seafloor is the source of the continued contamination. The other source could be the reactors themselves,” he said.

Most fish and seafood from along the Fukushima coast are barred from the domestic market and export.