Other marine reserves, such as Leigh's Goat Island, had led to a ten-fold increase in fish numbers. Despite being a "very ordinary bit of coastline" compared to the Bay of Islands, it attracted 300,000 visitors and $28 million in direct spending a year.
Once marine reserves were established, their opponents often became their biggest supporters because they could see the benefits as fish numbers increased outside the protected areas as well as inside.
Bay of Islands Swordfish Club president Bruce Smith, however, said he used to be a fan of marine reserves but had changed his mind after researching their claimed benefits. In particular the fishing charter operator did not believe fish spread beyond their boundaries.
"The Poor Knights reserve is chocka with fish, but they don't spread out. All marine reserves do is put pressure on other areas," he said.
Mr Smith said reserves would be worthwhile if, once numbers built up, fish could be caught and released elsewhere to boost stocks over a wider area, but that was not allowed.
Former MP Dover Samuels, who was at the launch, commended the group for their bravery.
"Any time you mention marine reserves, you generate a lot of heat. There's a lot of competing interests, and many of them don't understand the benefits."
Mr Samuels said he supported the proposal but urged the group to get fishers and iwi around a table to explain what it would achieve.
"If you don't, you will have problems, especially with my whanaunga (relatives). Once you have the people on board, this kaupapa will succeed."
Forest and Bird has welcomed the proposal, saying protection for one of the country's most popular marine areas is long overdue.
Fish Forever also wants some estuaries made into scientific reserves, bringing the total area protected to 10 per cent of the Bay. The proposal includes a review after 25 years. Go to www.fishforever.org.nz for more information.