A monster bluefin tuna - weighing in at 415kg - is on ice and heading to Japan for auction where it could earn the man that caught it tens of thousands of dollars.

Wayne MacFarlane and his crew in his ship the Karina B were fishing off the East Coast south of the Ranfurly Banks on Tuesday afternoon when they used a winch to drag up the North Pacific bluefin tuna that had been caught on one of the 20-metre commercial boat's longline hooks.

The crew of three processed it and put it on ice immediately.

It was sent via air freight to Japan this morning where it will be auctioned to the highest bidder at a fish market.


Mr MacFarlane's father, Dougle, said his son and his crew had left Whitianga about two weeks ago to target bluefin but probably weren't expecting a haul like this one.

"He's caught other really big fish before - he's been commercial fishing for 20 years - but nothing ever as big as this."

He said the season for catching bluefin tuna was a relatively short one and the only decent ones were generally around the East Cape at this time of year.

"You get other ones around the West Coast that hang around the hoki boats but they are actually worth nothing commercially," he said.

"If you send them to Japan they are worth nothing because they have no oil content and the cost of packaging and freighting them there is more than you could sell them for.

"But the one that they caught is the type that are on the move that are eating and feeding and building the oil content. Later on the southern blue fin will come through."

Mr MacFarlane was loath to say how much the fish could fetch at market in Japan but his son was hoping to get about $40,000 - after processing costs - for it.