‘Jellyfish typhoon’ bearing down on Japan

Koichi Yasuda / Yomiuri Shimbun Staff Writer

Swarms of giant Nomura’s jellyfish are expected in the coastal waters around Japan this year, a “jellyfish typhoon” that threatens to inflict massive damage to the fishing industry.

One of the biggest varieties of jellyfish in the world, Nomura’s jellyfish–also known as Echizen jellyfish–weigh as much as 200 kilograms and have heads reaching up to about 2 meters in diameter. The Fisheries Agency warned fishermen across the country about the arrival of the jellyfish after it received several reports of sightings in the sea around Japan this month.

Nomura’s jellyfish are a nightmare for fishermen–damaging fishing nets with their heavy weight and harming fish caught in the nets with their toxins. Fishermen also risk getting stung when removing the jellyfish from their nets.

They may even force fishermen to stop fishing.

In 2007, the last time hoards of Nomura’s jellyfish were seen in Japan’s coastal waters, the agency received about 15,500 complaints from fishermen concerning damage caused by the jellyfish.

According to experts, an unusually huge number of Nomura’s jellyfish are highly likely to come to Japan’s coastal waters this year. They usually propagate in the eastern part of the Yellow Sea, then some will drift toward Japan on the Tsushima Current.

Researchers with the Fisheries Research Agency surveyed the central waters of the East China Sea and coastal waters around Jeju Island, South Korea, in June and confirmed the presence of a few Nomura’s jellyfish within 10 meters of their vessel.

“The situation is quite similar to that when a large number of these jellyfish came to Japan’s coastal waters in the past,” said Hideki Akiyama, head of the agency’s East China Sea Fisheries Oceanography Division.

Based on the June survey, the Fisheries Agency warned the jellyfish would reach the sea off Tsushima island in Nagasaki Prefecture early this month. Since around July 4, the agency has received a number of reports that small Nomura’s jellyfish have been seen in the sea.

Prof. Shinichi Ue of Hiroshima University, a leading expert on Nomura’s jellyfish, said highly concentrated groups of the variety had been observed in the Yellow Sea as of Wednesday.

“The arrival [of a large number of the jellyfish] is inevitable. A huge ‘jellyfish typhoon’ will hit the country,” Ue said.

A fertilized egg of a Nomura’s jellyfish turns into a polyp that resembles a flower. As the polyp travels, it sheds parts of its body in the form of a cellular mass called a podocyst. The podocyst rests at the bottom of the sea and grows into a polyp that later turns into a jellyfish.

To complicate matters, podocysts maintain their form until the surrounding environment becomes optimal for their growth into a jellyfish.

Last year, there were few sightings of Nomura’s jellyfish and no complaints from fishermen were reported.

“I believe the environment in the East China Sea was bad, so the podocysts slept in that form last year,” Ue said. “However, they’ve all turned into polyps this year, resulting in a plague of jellyfish.”

The most recent massive infestation of Nomura’s jellyfish was observed in 2005. The year before that, only a few were reported.

Experts expect more jellyfish this year than in 2005. They are expected to drift north in the Sea of Japan to Aomori Prefecture, then into the Pacific Ocean through the Tsugaru Strait, then go south. They are expected to plague the coastal waters around Japan through February.

(Jul. 11, 2009) Yomiuri Shimbun


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