Growing up to 2 meters (6 feet 7 inches) in diameter and weighing up to 220 kilograms (ca. 450 pounds), Nomura's Jellyfish reside primarily in the waters between China and Japan, primarily centralized in the Yellow Sea and East China Sea .
The most recent problems first became obvious in late August 2005 when Japanese fishermen fishing for squid, anchovies, salmon and Japanese amberjack began finding huge numbers of the jellyfish in their nets. The areas that were hardest hit were the Sea of Japan coasts of Fukui and Shimane prefectures in western Japan.
Often, the weight of the echizen kurage broke the nets or crushed fish in the net. In the worst cases, as many as 1000 Nomura's jellyfish have been trapped in one net. Many fish trapped within the net with the jellyfish that survived were too poisoned and slimed by the tentacles to be of commercial value.
In some places, jellyfish density is reported to be "one hundred times higher" than normal, without explanation. There was a previous spike in the population recorded in 1958 and in 1995. There have been widely disseminated theories as to the cause of the population increase, but no definite explanation. One such theory is that development of ports and harbors along the Chinese coast have provided an increase in structures for the Nomura larvae to attach themselves to. Another is that the seas off of China have been inundated with nutrient-rich run-off from farms and industry. Yet another is that China has over-fished their waters and reduced the populations of the jellyfish's natural predators, which fed on the larvae while they are still zooplankton. Yet another cause may be China's new dam, the Three Gorges Dam. On the Yangtze River, the Three Gorges Dam, the world's largest hydroelectric project, has increased the amount of phosphorus and nitrogen in the waters off China, creating an ideal breeding ground for Nomura's jellyfish. A final possibility is global warming which would cause the heating up of the seawater and encourage jellyfish breeding. The water could become more acidic, making it it a more suitable environment for jellyfish survival. Jellyfish also have the ability to take in oxygen directly from their skin. This allows the jellyfish thrive in the oceans growing dead zones.
The problem with combating the jellyfish is that when they are under attack or killed, they release billions of sperm or eggs which connect in the water and attach to rocks or coral formations. when the conditions are favorable, the creatures detach from their home millions at a time and grow into more jellyfish.
In an attempt to utilize the jellyfish in a productive manner, coastal communities in Japan are doing their best to promote jellyfish as a novelty food, sold dried and salted; students in Obama, Fukui (Japan) have managed to turn them into tofu, and jellyfish collagen is also reported to be beneficial to the skin.
The jellyfish population has become such a substantial problem for Japan that it has led the government to form a committee to combat the problem. They have been creating kill-nets to catch and destroy the jellyfish before they can do any more harm, yet this typically only results in the aforementioned survival tactic of releasing their sperm and eggs.