Asia Dive News : China blamed for Japan's giant jellyfish invasion

SHANGHAI (Kyodo) Japanese government-backed scholars have said 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 1 meter in diameter are clogging fishing nets in Japanese waters, mainly in the Tsushima Strait between Kyushu and South Korea. They may come from the Yangtze River Delta and the river-fed Yellow Sea, the Japanese scholars said at a two-day, information exchange conference last week in Shanghai with colleagues from China and South Korea.

They are thought to drift toward Japan in relatively cold water with 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 at the Nagasaki-based Seikai National Fisheries Research Institute, which is under the 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, 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 said in a report.

Ten Japanese institutions began studying drift jellyfish 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 say.

A decrease in the population size of a nomurai jellyfish's food competitor, including 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.

Source: Japan Times