Fisherman and TV host Matt Watson has developed a new device to make the most selective form of fishing even more sustainable.
The gadget allows spear fishers the option of tagging fish rather than killing them and it's gaining international interest.
"The tagger allows them to shoot to their hearts content. They can hit the fish and get the same thrill, and you do get the same thrill, but they're just helping research," Mr Watson said.
A typically Kiwi invention, the earliest prototype was a rough-cut piece of broomstick in black insulation tape - first trialled in 2008.
That device delivered a satellite tag on impact.
"That worked but it was a big, expensive operation," Mr Watson said.
Since then, Mr Watson has been refining and rummaging in his shed at home in Kerikeri.
He's developed a $26 dollar easily-detachable, non-transmitting tag, similar to that used by sports fishers.
"How can anyone that wants to go in the water spearfishing have the same option for release that rod and reel fishermen do," Mr Watson said.
Spearfishing is a selective method of fishing, but Watson says some end up killing too much.
"You don't have to go far on social media to find pictures of boats full of kingfish, where guys have got excited and they've just shot way more than they can eat," Mr Watson said.
"I like anything that's going to save multitudes of fish getting killed but at the end of the day, we're all hunter gatherers and we all want to catch a feed of fish," said Spearfishing New Zealand President Darren Shields
Mr Shields says most spearfishers only take enough for a feed.
He likes the tagging innovation, but thinks the tagger could actually end up killing fish anyway.
"Now if a guy doesn't depower his gun and he gets up close to a small fish to put a tag in it, the spear could end up penetrating right through the fish," he said.
But Mr Watson says the mechanism can be adjusted to lessen the impact and depth of the tag.
"I've literally shot everything from wee snapper inshore to huge marlin," he said.
Mr Watson thinks the product can be cheaply mass produced.
He's had interest from companies in France and the US, but says it's not about making money - he wants any royalties to go to conservation groups.
If you’d like learn more about spear tagging, visit www.ultimatefishing.tv