Massive Schools Of Nomura Jellyfish - Which Grow Up To 450 Lbs - Now Appear Every Year Off Japan

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OKI, Japan -- Fisherman Ryoichi Yoshida pulled in his nets before dawn one morning, hoping for lots of yellowtail and mackerel. But the fish were overwhelmed by a heaving mass of living pink slime.

The creatures, called Nomura jellyfish, can measure six feet across and weigh up to about 450 pounds. They have been drifting en masse to places like Oki, a small island 40 miles off the coast, bobbing beneath the surface of the water like pink mines. They rip holes in fishermen's nets, and they poison fish. "Normally, we just bring up the nets and it takes about an hour," said the weather-beaten Mr. Yoshida, 61 years old, after his crew had cleared the jellyfish out of the nets using long poles and hooks. "Now it takes two or three hours. And some of the fish escape."

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Scientists have various ideas about what causes the outbreak. One has devised a computer model of ocean currents that suggests the jellyfish are breeding off the Chinese coast near the mouth of the Yangtze River. One theory is that pollution, perhaps linked to industrialization in China, is helping create more algae in the sea. The algae are food for plankton, which is food for jellyfish.

Then, too, there is speculation about a link to the Three Gorges Dam, the world's largest hydroelectric-power project under construction in the Yangtze, which could be changing water flows to the sea. A dam in a section of the Danube that runs between Serbia and Romania completed in 1972 changed the river flow, after which the jellyfish population of the Black Sea exploded.

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http://online.wsj.com/article/SB119612452419404666.html