A Northland commercial fisherman has caused an uproar by the way he celebrates killing a mako shark.

The Whangarei man calling himself the "Original Fishkiller" posted a video of himself with a just-caught 2-metre shark on the boat's deck.

Then aiming his remarks at television fishing celebrity Matt Watson of the ITM Fishing Show, the man says: "Tranquillise them? This is how we roll on the Starglazer Matt Watson, there is no letting them go brother…"

He then bashes the shark with a large piece of wood and watches as it thrashes around, before dying.

The video was posted on The ITM Fishing Show's Facebook page yesterday, with the administrator commenting: "Check out this guy…Yes fish are killed for consumption, but hopefully this wasn't just killed to mock our conservation efforts. Not a good look."

It has had more than 39,000 views so far with hundreds of comments.

Damian Callesen Mitchell posted: "In my 20 years of commercial fishing i was glad to release alive and unharmed the 2 mako sharks that came up in the trawl… There was no benefit in killing and landing them that i could perceive either then or now."

Richard John Deeble also commented: "The guy's page is called original fishkiller - at best its really not a good look. At worst it indicates the guy takes pleasure in killing stuff. Fishing and hunting for sport and food is one thing. Its a whole other ballgame implying you are motivated by killing."

Watson questioned why the man had filmed and posted the killing, saying he took it as an attack on the way his Fishing Show championed shark conservation.

"I have no problem with any one killing any fish for food, so long as it isn't endangered, and the whole fish is used," he said.

"Not all commercial fishermen are like that. There are idiots like that in every sector. It wasn't a cool thing to do. I think it a poke at me for my conservation efforts."

Watson said fish caught in bottom-trawling probably had a much longer death than the filmed shark did.

"It is a respect thing," he said.

He said if a shark needed to be killed, for food and not just the fins, there was a proper way to do it.

"You cut down through the back of the head, the top of the spine," he said.

Other Facebook users have tried identifying Original Fishkiller without success.

According to Forest & Bird, mako sharks, like most shark species, are slow-growing and highly vulnerable to overfishing.

They are known to be taken in large numbers in New Zealand's tuna longline fisheries.

The practice of shark finning continues to be legal in New Zealand, however it is illegal for a commercial fisher to remove the fins from any shark and discard the body of the shark at sea.