James Shaw says a marine sanctuary off coast of Whanganui and South Taranaki could create an eco-tourism industry.
The Green Party leader was in the region on Tuesday to announce his party's proposed marine mammal sanctuary which would be the largest in the country.
It would be a more economically and environmentally sustainable alternative to seabed mining and would protect what is a blue whale feeding area, he said.
The policy is a direct response to Trans-Tasman Resources' application to mine off the coast of Patea which was granted by the Environmental Protection Agency this month.
"Rather than just opposing seabed mining, what are we actually opposing it for?" Mr Shaw told the Chronicle.
"And the reason we oppose seabed mining is because it is an area where blue whales come to feed and other mammals as well.
"Why don't we actually flip it on it's head and declare this whole area a marine mammal sanctuary with a particular focus on blue whales."
Mr Shaw believed the business case for TTR's application was weak.
"You talking about literally only ten of millions of dollars so it's not a terribly significant economic activity," he said.
"It's fly in, fly out. There aren't a lot of jobs locally created.
"In our view if you had a sanctuary, and the area became known for that, that would spur an eco-tourism industry which would employ local people and the money would stay locally.
"That's a far more economically sustainable activity."
He said the sanctuary would not affect the fishing industry and existing oil and gas activity would continue until the permits ran out.
Given TTR have already been given the go-ahead the proposal might be relying on the outcome of appeals which several groups have indicated they will lodge.
"If the appeals fail and it goes through then we'll have to look at what the options are," Mr Shaw said.
And it would likely need support from Labour, too, if it made it into Government.
"My sense of it, given what they been saying recently about things like climate change, is that they would certainly be open to the idea."
TTR's proposal received 13,733 submissions, most opposed to granting consent.
Mr Shaw said he believed there was huge Government pressure to allow it through.
The Department of Conservation should have opposed the application, he said.
"It's pretty clear that DoC's advocacy for nature role has been pretty heavily subverted by the current Government," he said.
"DoC are under tremendous pressure to allow economic development."
The policy announcement was made alongside Ngāti Ruanui after hundreds had formed a human chain alongside the Waihi circuit in opposition to seabed mining.
"It was an awesome response. We are really humbled," Ngāti Ruanui kaiarataki Debbie Ngarewa-Packer said.
She backed the sanctuary proposal as an alternative to mining.
"I think it's palatable to mainstream New Zealand who are concerned about these activities," she said.
"I think it's not only going to bring about protection, but it can also make money. I think the Green Party are acutely aware of opportunities."