Protesters took to the sky in Whitianga to protest the Billfish Classic.

A group of people pooled money and rented an aeroplane, flying over the start line of the fishing competition, marine scientist and protest spokesman Thomas Everth said.

The competition, which ran for three days from March 12 to March 15, sold out, with 470 boats registered, according to Allaboutwhitanga.co.nz

Some of the 470 boats lining up at Buffalo Beach in Whitianga for the competition start.

The tournament features over $1.7 million in prizes, including $400,000 for the heaviest billfish, a $125,000 gate prize, jackpot options up to $1,575,000 and various category awards for tuna, mahimahi and kingfish, and for women and junior anglers.

Marlin generally migrate through New Zealand waters and do not spend their lifetimes here, Everth said.

“The greatest abundance is between December, January, February, and March. That’s when the peak of marlin visits happen here.”

Because of increasing water temperatures due to climate change, marlin numbers have increased around Aotearoa, New Zealand, Everth said.

“However, on a global scale, marlins are part of a species that is going down and down and down,” he said.

There has been a commercial moratorium on game fishing since 1987 because of concerns initiated by the bill fishing clubs about the dwindling numbers of marlins, Everth said.

Few of the marlin caught are killed, and many are tagged and put back into the water, he said.

The deaths occur due to exhaustion and the aneurysms that happen in their hearts and so forth, he said.

While NZ Sports Fishing spokesman Mike Plant is sympathetic to the protesters' cause, he said in an email that the well-intentioned actions are directed in the wrong place.

Led by the New Zealand Sport Fishing Council (NZSFC), this was a hard-fought victory to prioritise the environment and rebuild the country’s billfish populations, Plant said.

“Arguably, New Zealand is a global leader in billfish conservation. In 1987, the Billfish Moratorium was agreed upon,” he said.

The key pillars are commercial fishing of striped, black and blue marlin, which has been banned within New Zealand’s Exclusive Economic Zone, and tagging and releasing a minimum of 50% of all billfish caught nationwide.

“These days, roughly 70% of all recreationally caught marlin are tagged and released,” Plant said.

The NZSFC echoes the protesters' worries about overfishing, he said.

Billfish are highly migratory and travel through the South Pacific, only spending a few months in New Zealand’s subtropical waters, he said.

“Management of the marlin fishery is conducted jointly by neighbouring nations including Australia, Fiji, Tonga and New Zealand, among others.”

Plants said that less than 40 tonnes of marlin are estimated to be landed within New Zealand waters yearly, and all are shared with the community.

“Yet commercially in the wider South Pacific fisheries area, over 2400 tonnes are harvested by industrial surface longliners and commercial vessels yearly.”

The NZSFC is not associated with the Billfish Classic, but Plant said the event needs to be put into context.

“The event happens once a year. Last year, they only landed eight fish. Of course, all of the fish were shared with the community.

“This includes the heads and frames and offal. After all, maximum utilisation is another form of conservation.”

The Billfish Classic had received plenty of support from the local community, tournament director Tom Maxwell said.

“We have had about 5000 people on the beach supporting us,” he said.