A Sino-Japanese Enviro-Economic Jellyfish Quarrel

♠ Posted by Emmanuel in , at 11/28/2007 01:58:00 AM

As a SpongeBob SquarePants fan, I find jellyfish rather charming. Japanese fishermen, however, do not. Regions which have traditionally been fishing grounds in Japan have been inundated by jellyfish which are making it difficult to catch fish. They destroy fishing nets, poison fish, and generally make life hard for anglers. Who's to blame? Why, of course, that universal bogeyman for what ails the world, China. From a 2005 Economist article:
The jellyfish spawn along the coasts of the East China Sea and the Yellow Sea and some drift towards Japan. It usually takes two months or more for the first to reach the Japanese island of Tsushima, in the middle of the strait between South Korea and Kyushu. This year, however, the jellyfish arrived a month earlier than usual, in August, and in big numbers. In May and June, heavy rains in the basin of the Yangtze river had created an enormous flow of fresh water, and this jet had sluiced the jellyfish towards Japan...

No one knows the exact reason for the rise in the jellyfish population, but there are suspicions. One is the development of ports and harbours along the Chinese coast, which has created many more structures to which echizen larvae can attach themselves. Another is that the seas off China are choked with nutrient-rich run-off from farms and industry. A third is Chinese overfishing in local waters: with fewer fish, there are more of the kinds of plankton on which the jellyfish feed.
[UPDATE: You must see these photos to appreciate the size of these jellyfish.] See? Even Japanese fishermen are going China bashing; it's the global sport of choice. Unfortunately, things have not gotten any better since 2005. Here is more from the accompanying Wall Street Journal article to the clip above. Interestingly, the mega-disastrous Three Gorges Dam even figures its way into the story:

Fisherman Ryoichi Yoshida pulled in his nets before dawn one morning, hoping for lots of yellowtail and mackerel. But the fish were overwhelmed by a heaving mass of living pink slime. The creatures, called Nomura jellyfish, can measure six feet across and weigh up to about 450 pounds. They have been drifting en masse to places like Oki, a small island 40 miles off the coast, bobbing beneath the surface of the water like pink mines. They rip holes in fishermen's nets, and they poison fish.

"Normally, we just bring up the nets and it takes about an hour," said the weather-beaten Mr. Yoshida, 61 years old, after his crew had cleared the jellyfish out of the nets using long poles and hooks. "Now it takes two or three hours. And some of the fish escape."

Until 2002, these giant creatures were seen only occasionally in Japanese waters. But for the past five years, they have been swarming every year into the Sea of Japan, the water that separates Japan from mainland Asia. During the biggest invasion so far, in 2005, an estimated 500 million jellyfish -- not yet mature -- drifted in each day.

It's hard to calculate financial damage to fishermen, but the Japanese government last year counted about 50,000 incidents of jellyfish trouble. Fish poisoned by jellyfish tentacles die with their mouths agape. That mars their appearance and reduces their value by as much as 20%. "When their mouths are wide open, it means they've died going, 'I'm in pain! I'm in pain!' " explains Mr. Yoshida.

Scientists have various ideas about what causes the outbreak. One has devised a computer model of ocean currents that suggests the jellyfish are breeding off the Chinese coast near the mouth of the Yangtze River. One theory is that pollution, perhaps linked to industrialization in China, is helping create more algae in the sea. The algae are food for plankton, which is food for jellyfish.

Then, too, there is speculation about a link to the Three Gorges Dam, the world's largest hydroelectric-power project under construction in the Yangtze, which could be changing water flows to the sea. A dam in a section of the Danube that runs between Serbia and Romania completed in 1972 changed the river flow, after which the jellyfish population of the Black Sea exploded.

Chinese officials and scientists deny that Chinese pollution has caused the outbreaks [would they say otherwise?] "No research evidence in China supports a connection between pollution and jellyfish," says Li Qi, a dean of the Ocean University of China. "Floating jellyfish are mostly in the Sea of Japan....That's Japan and Korea's problem."

Eager for a solution, slasher squads of fishermen went out last year armed with barbed poles to attack jellyfish that were jamming up nets. If the jellyfish are cut into three or more bits, they usually die and get eaten by other sea creatures. Fishermen have also taken a trawl net and added a wire grill like a large potato masher at the trailing end: When the net is pulled through a swarm of jellyfish, they float through and are sliced up. [So violent...]

The Japanese government is doing what it can. It tracks the progress of jellyfish as they swarm through the Sea of Japan, urging trawlers to steer clear of them. The Japanese harvest some jellyfish to eat. Jellyfish can be boiled and added to salads -- though smaller varieties are said to be more tender and tasty. Trying to win converts, the fisheries ministry has drawn up a manual with tips on cooking with giant jellyfish. Menus include jellyfish-flavored biscuits, jellyfish soaked in rum and a dessert of jellyfish chunks in coconut milk...

One fear among scientists is that the creatures are multiplying in a "jellyfish spiral." Shinichi Uye, a leading jellyfish researcher at Hiroshima University in western Japan, thinks overfishing off China has led to fewer plankton-eating fish, leaving more plankton for the jellyfish to suck up. This growing army of jellyfish then also eats fish eggs, resulting in even fewer fish. Whatever the details, says Prof. Uye, the problem seems to be industrial development. "It's like a harmless living thing has been angered," he says. "The reason for its anger might lie with human activity."

Trying to understand why the jellyfish have started appearing in such numbers, marine biologist Kohzoh Ohtsu studies their reproductive cycle on another part of Oki. One afternoon he and a colleague -- dressed in rubber clothing to protect against the poison -- cut lumps of tentacle from a 200-pound jellyfish with a knife to make it light enough to bring aboard. One cause of the mass invasions, he says, "could be rising sea temperatures" making it easier for the jellyfish to breed and feed near China. Though he doesn't know details of the sea temperatures there, the peak water temperature in the Sea of Japan has been four or five degrees Fahrenheit higher than normal in a couple of recent years, indicating warmer seas in the region. One fear is that higher temperatures or other environmental changes might one day even allow the giant jellyfish to breed around Japan, adding further to their numbers.