Resident fisherman Shigenori Goto claimed he discovered the 13ft long squid splashing in one of his installed fishing nets near the island in Niigata Prefecture as he taken it in the morning.
The squid, afterwards discovered to be male, supposedly died after being taken to the surface.
As reported by Mr Goto, the fishing net, fixed to capture Japanese amberjack, was positioned at a depth of around 70m deep about a mile near the coast.
“This is the very first time I’ve observed such a huge squid,” he shared with regional press in Japan.
The squid was brought to a local authorities marine analysis institute in Niigata for investigation.
Giant squid is among the biggest invertebrates, and most strange animals, on the planet – the biggest ever documented by researchers was nearly 43 feet (13m) long.