Massive Jellyfish Threaten Japanese Waters

Many Nomura's jellyfish grow to be as large as a sumo wrestler. At that size, it only takes between about 5 to 10 of them to destroy a commercial fishing net.

Marine researchers in Japan say they are alarmed by unusually large swarms of Nomura’s jellyfish now swimming in the Yellow Sea and East China Sea.

Once fully mature, the jellyfish is one of the largest cnidarians in the world, reaching the size of an adult human.

The scientists warn that ocean currents could bring the huge jellies toward the coast of Japan this summer.

Spikes in the Nomura’s population during 1958 and 1995 dealt a huge blow to Japan’s fishing fleets. In addition to damaging nets, Nomura’s are blamed for killing fish with their venom and for stinging fishermen.

During the peak of the massive 2005 invasion, an estimated 300 to 500 million of the monster jellyfish passed through the Tsushima Strait between South Korea and Japan each day.

Combating the jellyfish is made extremely difficult because when they are attacked or killed, they release billions of offspring into the water.

The young attach to rocks or coral formations until favorable conditions allow them to grow.

Theories for why population spikes have occurred range from agricultural runoff in East China to overfishing, which reduced the populations of the young jellyfish’s natural predators.

Photo: Sankei