Poisonous hyomon-dako or blue-ringed octopuses, which inhabit mainly tropical and semitropical zones in the Western Pacific, have been recently found in increasing numbers in the Kumano-nada area off the coast of southern Mie Prefecture.
It is rare for blue-ringed octopuses, which carry tetrodotoxin, the same deadly poison present in fugu blowfish, to be found in the area during February and March when the weather is cold.
An expert said, "Their habitat might have expanded north due to the rise in sea temperatures caused by global warming."
An official of the Mie Prefecture Fisheries Research Institute in Shima found a blue-ringed octopus on the seafloor at a depth of 10 meters off the coast of Taiki, Mie Prefecture, on Feb. 16.
Another was caught after being found on rocks about seven meters under water off Shima on March 7. Both octopuses were adults about 10 centimeters in length, the institute said.
The octopuses' saliva contains tetrodotoxin, and anyone who is bitten will experience symptoms such as vomiting, paralysis and spasms.