By Haruka Saijo

TOKYO (Reuters) - As they hauled in their net on the frigid seas of northern Japan, Shigenori Goto and the crew of his boat were hoping for a good catch of yellowtail. Instead, what slowly appeared was a mammoth squid, still alive.

Giant squid, mysterious creatures thought to have inspired the myth of the monstrous "kraken", make occasional appearances near the Japanese archipelago. Last year, a Japanese-led team made history when it released the first live images taken of one, nearly 1 km (3,280 feet) beneath the surface.

"We were about 30 minutes into our day when this large, reddish-brown thing came swimming up from the depths," Goto, 44, told Reuters about the fishing expedition off the coast of Niigata, northwest of Tokyo.

"I was surprised - there's no other word for it. We all started shouting 'giant squid, giant squid' all at once."

The squid, a male weighing 163 kg (360 pounds), died shortly after being pulled to the surface last Wednesday and was trucked to a research institute.

Experts said the squid, which lost its super-long tentacles during the capture, was likely to have been around 8 meters (26 feet) in total, since the tentacles usually equal the rest of the body in length.

Still, it was relatively small by giant squid standards. The largest ever caught measured some 18 meters from tail to tentacle tip.

Goto, who has been besieged by calls from the media since word of his unusual haul became public, said he regretted the roughing up the squid had suffered.

"I wish we'd been able to make it more presentable," he said. "If I'd known it was going to be such a big deal, I'd have treated it with more respect."

Squid, both raw and cooked, is a popular food in Japan but Goto said the thought of eating the catch never crossed his mind.

"If it had been smaller, we might have," he said. "But something that big really isn't all that edible."

(Writing by Elaine Lies; Editing by John O'Callaghan)