Centuries ago, sailors feared the Kraken — legendary sea monsters so large, they were capable of bringing down ships. Now, modern Japanese fishermen have a new tale to tell of such gargantuan sea creatures — even if it wasn’t powerful tentacles that caused their ship to capsize.

The 10-ton Diasan Shinsho-maru went down in the waters off Japan while trying to haul a net containing dozens of gigantic gelatinous Nomura’s jellyfish, which can reach up to 6 feet 7 inches in diameter and weigh up to 440 pounds.

The load of jellyfish was so heavy that it caused the fishing trawler to sink, throwing the three-man crew into the sea despite clear skies and calm waters. Another trawler rescued the flailing crew.

The Sea of Japan is packed with these oversized creatures, which clog up and damage fishermen’s nets, rendering the fish caught alongside them inedible with their toxic stings. They even get sucked into pumps at nuclear power plants along the shore along with seawater used to cool the reactors.  

Scientists believe that some of the factors contributing to the ballooning Nomura’s jellyfish population may include warming seawaters and overfishing of other species.