Huge Echizen jellyfish, which can weigh up to 200 kilograms and have an umbrella measuring two meters across, have been causing serious damage to the fishing industry off Japan's east coast.

Echizen jellyfish are the largest variety found in the Japan Sea, and their population has skyrocketed recently in the East China Sea. Also known as Nomura's jellyfish, they have poisonous tentacles.

Thousands of the jellyfish have damaged fixed fishing nets while also degrading the freshness of fish by flicking them with their tentacles. Fishermen who were gleefully awaiting the high season of winter fishing for fish such as yellowtails and salmon, are scratching their heads over how to deal with the problem.

Off the coast of Kurohime in Sado, Niigata Prefecture, a dozen fishermen recently pulled in their fixed shore nets to find their catch consisted mainly of Echizen jellyfish. Only a few yellowtails had been caught.

The fishermen kept the yellowtails and slashed the jellyfish with knives before throwing them back into the sea. They spent almost 2-1/2 hours disposing of the bothersome jellyfish.

Inakujira set-net fishery association in Sado saw its profits for October plunge to 2 million yen to 3 million yen, about half the average. In addition, it had to spend 4 million yen to repair fishing nets damaged or destroyed by the jellyfish.

Off Togawan in Oga, Akita Prefecture, which is famous for its sandfish, about 5,000 Echizen jellyfish were spotted in late October. According to a branch office of the prefectural fishery association, some fishing boat operators saw their profits fall below 1 million yen for the month, less than one-fifth of an average year.

The jellyfish drifted across the Tsugaru Strait and into the Pacific Ocean. Fishermen of the Fudaimura fishery association in Iwate Prefecture found holes in some fishing nets caused by the jellyfish on Oct. 24. Although the salmon season was entering its peak, the fishermen had to suspend operations for a week at a loss of 4 million yen compared with the same period last year.

Fishery associations in the prefecture decided to attempt to remove the jellyfish from the nets before pulling in their catches. In 2003, when a similar upsurge of jellyfish troubled the area, many salmon were crushed to death under the weight of the giant jellyfish as the nets were being pulled in.

According to the Fisheries Agency, the large-sized jellyfish were seen off 33 prefectures this year. Hundreds have been snared in fishing nets off the coasts of Aomori, Hokkaido, Iwate and Shimane prefectures.

As of Oct. 11, 396 complaints had been received by the agency, including reports of damaged fishing equipment, injured fish, and poor fish catches.

• The Yomiuri Shimbun