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Jellyfish thrive as seas warm, threatening fishing industry worldwide

Japanese fishermen pulled in a net full of jellyfish. Once rare, jellyfish swarms are now an almost annual occurrence. Japanese fishermen pulled in a net full of jellyfish. Once rare, jellyfish swarms are now an almost annual occurrence. (Junji Kurokawa/Associated Press)
By Michael Casey
Associated Press / November 27, 2009

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KOKONOGI, Japan - A blood-orange blob the size of a small refrigerator emerged from the dark waters, its venomous tentacles trapped in a fishing net. Within minutes, hundreds more were being hauled up, a pulsating mass crowding out the catch of mackerel and sea bass.

The fishermen leaned into the nets, grunting and grumbling as they tossed the translucent jellyfish back into the bay, giants weighing up to 450 pounds, marine invaders that are putting the men’s livelihoods at risk.

The venom of the Nomura, the world’s largest jellyfish, a creature up to 6 feet in diameter, can ruin a whole day’s catch by tainting or killing fish stung when ensnared with them in the maze of nets here in Wakasa Bay in northwest Japan.

“Some fishermen have just stopped fishing,’’ said Taiichiro Hamano, 67. “When you pull in the nets and see jellyfish, you get depressed.’’

This year’s jellyfish swarm is one of the worst he has seen, Hamano said. Once considered a rarity, occurring every 40 years, they are now an almost annual occurrence along several thousand miles of Japanese coast and far beyond Japan.

Scientists believe that climate change, the warming of oceans, has allowed some of the almost 2,000 jellyfish species to expand their ranges, appear earlier in the year, and increase overall numbers.

The gelatinous seaborne creatures are blamed for decimating fishing industries in the Bering and Black seas; forcing the shutdown of seaside power and desalination plants in Japan, the Middle East, and Africa; and terrorizing beachgoers worldwide, the US National Science Foundation says.

A 2008 foundation study cited research estimating that people are stung 500,000 times every year, sometimes multiple times, in Chesapeake Bay on the US East Coast, and 20 to 40 die from jellyfish stings each year in the Philippines.

In 2007, a salmon farm in Northern Ireland lost its more than 100,000 fish to an attack by the mauve stinger, a jellyfish normally known for stinging bathers in warm Mediterranean waters. Scientists cite its migration to colder Irish seas as evidence of global warming.

Increasingly polluted waters - off China, for example - boost growth of the microscopic plankton that jellies feed on, while overfishing has eliminated many of the jellyfish’s predators and cut down on competitors for plankton feed.

“These increases in jellyfish should be a warning sign that our oceans are stressed and unhealthy,’’ said Lucas Brotz, a researcher at the University of British Columbia.

Here on the rocky Echizen coast, amid floodlights and the roar of generators, fishermen at Kokonogi’s bustling port made quick work of the day’s catch, packaging fish for shipment to market.

In rain jackets and hip waders, they crowded around a visitor to tell how jellyfish have upended a way of life in which men worked fishing trawlers on the high seas in their younger days and eased toward retirement by joining one of the cooperatives operating nets set in the bay.

It was a good living, they said, until the jellyfish began inundating the bay in 2002, sometimes numbering 500 million, reducing fish catches by 30 percent and slashing prices by half over concerns about quality.

Two nets in Echizen burst last month during a typhoon because of the sheer weight of the jellyfish, and jelly-filled nets capsized a 10-ton trawler off the east coast as its crew tried to pull them up. The three fishermen were rescued.

The invasions cost the industry up to $332 million a year, and tens of thousands of fishermen have sought government compensation, said scientist Shin-ichi Uye, Japan’s leading expert on the problem.

A US scientist, Jennifer Purcell of Western Washington University, has found a correlation between warming and jellyfish on a much larger scale, in at least 11 locations, including the Mediterranean and North seas and in Chesapeake and Narragansett bays.

“It’s hard to deny that there is an effect from warming,’’ Purcell said. “There keeps coming up again and again examples of jellyfish populations being high when it’s warmer.’’