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SHANGHAI, Dec. 15 Kyodo

Japanese government-backed scholars said Thursday an unusually large drift of jellyfish that has hurt Japan's ocean fishing industry this year may come from the mouth of the Yangtze River and other Chinese waters.

Jellyfish up to a meter in diameter that are clogging fishing nets in Japanese waters, mainly in the Tsushima Strait between Kyushu Island and South Korea, appear to come from the Yangtze River Delta and the river-fed Yellow Sea, the Japanese scholars said at a two-day, information exchange conference that began Thursday in Shanghai with colleagues from China and South Korea.

They are thought to drift toward Japan on relatively cold water with relatively low salt content.

The jellyfish species Nemopilema nomurai could have drifted on windblown currents from Chinese waters to the Tsushima Strait, said Koh Nishiuchi and Takeshi Taneda, both scholars of the Nagasaki-based Seikai National Fisheries Research Institute, which is under the Japanese government's Fisheries Research Agency.

Jellyfish clog fishing nets, reduce finfish catches and require extra and sometimes dangerous human labor to remove. Between January and mid-October this year, Japan nationally logged about 400 fishing net upsets caused by jellyfish.

''The origin of nomurai may be the Yangtze estuary and the coastal region of the southern part of the Yellow Sea, and nomurai is thought to be transported to the coastal region of Japan through the northern East China Sea,'' the two researchers say in a report. ''However, little is known about mechanisms of the transportation of nomurai to the coastal region of Japan.''

Ten Japanese institutions began studying jellyfish drift in April 2004 after unusually large drifts in 2002 and 2003. The jellyfish drift this year may be the worst since 1920, causing hundreds of millions of dollars in damage to the Japanese fishing industry, scholars expect.

A decrease in the population size of a nomurai jellyfish's food competitor, such as a plankton-eating fish, or a reproductive increase in jellyfish caused by global warming might explain the spike this year, said Shinichi Uye and Masato Kawahara, scholars at the graduate school of Hiroshima University, in their report to the conference.

Chinese scholars have not reacted formally to the suspicion that Japan's jellyfish problem started in the ocean near China.

The conference brings together about 50 people and papers from 16 Chinese, Japanese and South Korean researchers. It follows an international jellyfish bloom workshop last year in Yokohama.

Conference participant Hitoshi Iizumi of the Seikai National Fisheries Research Institute proposed on Thursday an international ocean cruise next year to understand the jellyfish drift.

China, Japan and South Korea should arrange the cruise, Iizumi said.