Swarms of giant jellyfish threaten fisheries along the Sea of Japan coast
Off the coast of Fukui Prefecture, dozens to hundreds of Nomura’s jellyfish have been observed since mid-August, mainly in Wakasa Bay where about 800 jellyfish were caught in fixed nets on Sept. 7
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Swarms of giant jellyfish are floating along the coastline of the Sea of Japan, and the damage they may cause to fisheries is feared to be the worst in more than a decade.
Nomura’s jellyfish is one of the world’s largest jellyfish, with a bell of up to 2 meters in diameter and weighing up to 200 kilograms.
The jellyfish destroy fishing nets and damage freshly caught fish after being caught in the nets. In 2009, the last time a jellyfish bloom occurred, it caused an estimated 10 billion yen in damages to the fisheries industry nationwide.
Nomura’s jellyfish are usually found off the coast of China in the spring. These cnidarians are pushed by ocean currents and arrive in the waters near Japan in summer.
Only about 10 Nomura’s jellyfish have been caught in fishing nets in Japan in recent years, according to the Japan Fisheries Information Service Center, an organization that disseminates fisheries-related information.
However, this year, about 1,000 of these jellyfish were caught in fixed nets near the Oki Islands in Shimane Prefecture in late August. Not only does each jellyfish appear to be larger, but their range has increased as well. They have been spotted from Nagasaki Prefecture to Aomori Prefecture.
Off the coast of Fukui Prefecture, dozens to hundreds of Nomura’s jellyfish have been observed since mid-August, mainly in Wakasa Bay where about 800 jellyfish were caught in fixed nets on Sept. 7. The Koshino fisheries cooperative in Fukui City suffered losses because the jellyfish damaged its catch of Spanish mackerel and horse mackerel.
“It takes a lot of work to remove the jellyfish from the nets,” said Motoaki Kawabata, the head of the cooperative. “Also, if the jellyfish’s tentacles touch the fish, they become discolored and damaged, making them unsellable.”
When the jellyfish bloom appeared in 2009, thousands to tens of thousands were caught in fixed nets in Fukui Prefecture. As a result, most fishermen had to end their fixed-net fishing season half a month earlier than usual. Normally, the season lasts until December. It has also affected crab fisheries in the prefecture.
Although there has been no damage to nets this year, the Fukui prefectural government held a liaison meeting on Sept. 8 with those involved in the fisheries industry.
In Ishikawa Prefecture, about 400 large jellyfish were caught in fixed nets on Sept. 5.
Nomura’s jellyfish tend to appear in large numbers in Japan when the water temperature along the coast of China is quite warm in February, according to Shinichi Ue, a special appointment professor at Hiroshima University who specializes in marine ecology.
“These jellyfish have been seen less and less since mid-September, but we need to keep an eye on them because the life cycle of Nomura’s jellyfish is not well understood,” said Ue.