To the great relief and puzzlement of fishermen and researchers, the Sea of Japan this year has seen a drastic decline in the huge, toxic jellyfish that have damaged the nation’s seafood haul in recent years.
Known either as Nomura’s jellyfish or Echizen “kurage” (jellyfish), the bottom creatures can reach 1 to 2 meters in diameter and weigh 100 to 200 kg.
Thousands can attach themselves to a single fixed fishing net, poisoning the fish inside and often breaking the net itself.
According to the Japan Fisheries Information Service Center, fishermen had reported about 6,300 sightings of Nomura’s jellyfish as of Nov. 20 last year, compared with only 128 this year.
“This is a dramatic fall in numbers,” said Katsuya Saito, an official at the Tokyo-based nonprofit research center.
“Up to last year, 3,000 to 5,000 of the jellyfish would get tangled up in a single fixed net in some cases. But this year, only one or two were reported to have been caught,” Saito said.
Saito said that until 2001, a heavy presence of the jellyfish occurred only once every several decades.
But from 2002 to 2007, thousands were seen in fall and winter in the Sea of Japan and parts of the East China Sea, Saito said.
The giant creatures have wreaked havoc with fishermen, not only because of the labor entailed in ridding their nets of them, but also the damage they cause to catches.
At one point the crisis prompted fishermen to come up with cooking recipes, although the jellyfish are rarely eaten in Japan.
Hitoshi Iizumi, an official at Japan Sea National Fisheries Research Institute, a government-affiliated agency, said scientists have not determined the cause of the sudden disappearance.
According to Iizumi, the jellyfish are believed grow big when they are along the coast of China and then drift toward Japan.
Researchers believe three factors near China may have been behind the surge in jellyfish until last year: eutrophic water coming to the sea from modern Chinese cities, global warming that has increased the sea temperatures, and increased fish catches resulting in more zooplankton.
But researchers are not sure if those factors changed this year, Iizumi said.