Eighteen months after the nuclear accident in Fukushima, fishermen working mainly in Pacific coastal areas of northeastern Japan are catching more fish and shellfish off Fukushima Prefecture on a trial basis.

Marine experts are calling for detailed research of radioactive contamination of marine resources.

Following last year's nuclear accident in Fukushima, a fishing ban was imposed for safety reasons. But in June, commercial fishing restarted on an experimental basis off Fukushima for only of one type of shellfish and 2 kinds of octopuses.

On Monday, almost 18months after the nuclear accident, fishery cooperatives in the Tohoku region, as well as Ibaraki Prefecture, began fishing 10 types of marine resources, including crabs and squids.

They intend to take the products to market if sample tests show no radioactive contamination.

High levels of radiation have recently been detected in some fish types. A cod landed at a port in Aomori Prefecture in early August was found to be exposed to 132.7 becquerels of radioactive cesium per kilogram. That was 1.3 times the government safety limit.

Radiation 380 times the limit was detected in a rock-trout caught off Fukushima in early August. A black sea bream caught off Miyagi Prefecture, in July was 33 times over the limit.

The rock-trout and black sea bream had the highest levels of contamination for each of the fish species.

Radioactive cesium is hardly detected in seawater.

Experts say the levels may be concentrated in the particular kind of fish that eat sandworms.

This suggests that cesium accumulated on the seabed is now being taken up by such fish.