(CBS) - Huge swarms of giant jellyfish are seriously threatening Japan's fishing industry as schools of the slimy creatures, some as big as a sumo wrestler, are ruining fishermen's nets and catches.
And some scientists believe global warming might be a factor.
Vast numbers of Echizen jellyfish have appeared on Japan's Pacific coast apparently after drifting from Chinese and Korean waters where they reproduce every year.
One Echizen jellyfish can be up to 2.2 metres (7.2ft) in diameter and weigh up to 300 kg (661lbs).
The non-edible creature has the local fishing industry in the grip of its poisonous tentacles as the invertebrates clog fishing nets, poisoning and crushing the catch.
Some experts estimate that the outbreak of jellyfish has brought Japan's fishing industry financial losses amounting to at least 1 billion yen (110 million dollars).
"I had never seen anything like this big before," said one local fisherman in the port of Akiya on Japan's Pacific coast.
One Japanese fishing boat in the Pacific capsized by the weight of the heavy jellyfish that got stuck in its fishing net.
Still, much about the jellyfish remains a mystery.
"Since 2002, we've seen huge numbers of giant jellyfish around the coast of Japan every year. In recent years, 2005 was the year when they particularly appeared en masse," said Kiyoshi Kawasaki, assistant director of Japan Fisheries Research Agency.
"The rising sea temperatures could be a factor behind this phenomenon as they foster the growth of these jellyfish," Kawasaki said.
Pollution in the waters off China is also believed to making it easier for jellyfish to breed.
Japan's Meteorological Agency says the waters of the Sea of Japan - an area surrounded by Japan, China and South Korea - are warming at a speed three times faster than that of the global average.