TOKYO, July 20 (UPI) -- Giant jellyfish, which wreak havoc in its wake, are again threatening Japan's coastal areas and its fishermen this year.
The Nomura jellyfish, as they are called in Japan, can measure up to 6 feet in diameter and weigh more than 450 pounds, CNN reported.
They grow as they are transported into the Sea of Japan by ocean currents from their origins, believed to be in China's Yellow Sea. Japan has been tormented by Nomura jellyfish since 2005, the report said.
Monty Williams, a U.S. marine biologist at Alabama's Dauphin Island Sea Lab, told CNN the jellyfish stay in packs and get caught in fishing nets as they drift northward.
Villagers along the Japanese coast say the jellyfish ruin catches and destroy expensive nets.
"Communities of fishermen and these fishing villages own these nets," Williams said. "When these nets get wiped out, it actually has this economic devastation for an entire community."
Japanese authorities have placed a warning system this year so fishermen may save their nets.
The reason for the current migration is unclear. Some speculate it could be overfishing, pollution or rising ocean temperatures, which may have destroyed the fish that prey on Nomura's jellyfish in the polyp stage.
