"It's a terrible problem. They're like aliens," Noriyuki Kani of the fisheries federation in Toyama, northwest of Tokyo, told Reuters ahead of the conference.Wikipedia has an entry on the giant jellyfish. From Wikipedia:
There are no official figures on the size of the problem, but Kani says the financial losses are obvious.
"If your nets are full of jellyfish, of course there is no space for fish," he said.
Nomura's jellyfish (Stomolophus nomurai) is a very large Japanese jellyfish. Known in Japanese as echizen kurage, it is one of the largest species of jellyfish.
Growing up to 2m wide and weighing up to 200kg, with countless poisonous tentacles, they drift across the waters between China and Japan, causing problems for the local residents. Previously found mainly in the Yellow Sea, the Echizen's sting can be fatal, causing a build-up of fluid in the lungs. Victims can take up to a day to die.