Key Points:

An exhausted 18-year-old spearfisherman is admiring what could be a record-setting marlin caught after a 150-minute battle off Great Barrier Island.

Nick Dobbyn speared the 213kg blue marlin after he spotted it "tailing along" on the surface of the water last Saturday afternoon.

"I got ready and we got close to it, about 50-60 metres away. I jumped into the water and swam closer to it when I pulled the trigger. That's when the war started," Mr Dobbyn said.

He had been in the water for about 20 seconds and was about five metres from the fish when the spear struck.

It took off with the most "explosive power" he had ever seen, dragging the spear, which had been clipped on to a buoy. "I had to swim to catch [the buoy]. That's what I was most sore from afterwards, was that swim."

Exhausted but happy to see the buoy bobbing in the water, Mr Dobbyn tried to get more shots off - but the Marlin had other ideas and fought him for nearly two-and-a-half hours.

He stayed above the water for most of the battle, during which he was dragged about 3km. His friend, Mark Colville, followed on their boat, encouraging him and making sure he didn't get tangled in the line.

"I was just dehydrated and hot. My arms weren't that sore but my legs were. I couldn't walk once I got on to the boat, my legs were like jelly."

Mr Dobbyn said he never thought of abandoning the fight: "If you're an idiot for pulling the trigger, then you have to stay with it."

After about two hours he fired his fourth and final shot at the marlin when it rounded on the boat.

"It was thrashing its bill and wanted a piece of us, too. That's when it started to get a little bit out of control. The bill would slice you up, too."

The thought of injury never crossed Mr Dobbyn's mind.

"The adrenaline was going though. It was better than some go-kart ride that's for sure."

Speaking to the Herald from his Warkworth home yesterday, Mr Dobbyn said everyone he told about the "war" thought he was mad.

"People have said good on you, because there are fishermen who have seen 100 marlin but never pulled the trigger once."

It was only when he, Mr Colville and two others managed to haul it on to their boat Assassin that they realised it's size.

"I knew it was a record because I knew there had never been a blue marlin speared in New Zealand before."

He wouldn't tell the Herald how he celebrated the catch, other than to admit there were "a few sore heads the next day". But he said he would have the marlin's head mounted and the rest of it chopped up ready to be smoked.

Darren Shields, of Open Oceans spearfishing club, said whether or not Mr Dobbyn had the New Zealand record would depend on how he landed it.

"It's still got to go through the process ... but it's a great feat," he said.

A spearfisherman spoken to by the Herald yesterday said it was a "great catch for a young fella. 213kg is a medium size - but it's big on a spear".