Updated

Pink, slimy and repellent, the Nomura’s jellyfish is an authentic horror of the deep that's been assaulting Japan. Now the creatures have sunk a 10-ton fishing trawler.

The boat was capsized off Chiba in Japan, as its three-man crew was trying to haul in a net containing dozens of huge Nomura's jellyfish. Four years after they last reared their slimy heads, and for reasons that remain mysterious, an armada of the gelatinous giants has gathered in the Yellow Sea off China and the Korean peninsula.

Now it has drifted into the Sea of Japan, and brought down the Diasan Shinsho-maru. One of the largest jellyfish in the world, the Nomura's jellyfish can grow up to 6 feet in diameter and weigh as much as 400 pounds.

The Telegraph reports that the boat's crew was thrown into the sea, but the three men were rescued by another trawler. The local Coast Guard office reported that the weather was clear and the sea was calm at the time of the accident.

Experts believe weather and water conditions in the breeding grounds, off the coast of China, have been ideal for the jellyfish in recent months.

"The arrival is inevitable," Professor Shinichi Ue at Hiroshima University, told the Yomiuri newspaper. "A huge jellyfish typhoon will hit the country."

In 2005, fishermen looking for anchovies, salmon and yellowtail began finding huge numbers of the jellyfish in their nets. When the Nomuras grow larger than a metre in diameter, half a dozen of them can destroy a fishing net. The fish caught alongside them are poisoned and covered in slime and rendered unsaleable.

So serious was the situation that salmon boats in northern Japan stopped going out, and in some places fishermen lost 80 per cent of their income. Even staff at some of the nuclear power plants along the Japan Sea coast found that the jellyfish got sucked into the pumps which take in sea water to cool the reactors.

No one is sure about the reasons for the slimy plague. One theory is that climate change is heating up the sea water and encouraging them to breed. Another blames effluent from rivers in China, which carries nutrients on which the jellyfish feed. Another blames over-fishing of other species, leaving a surfeit of plankton for the Echizen kurage to feed on.

The Times of London contributed to this story.