The Chatham Rise is one of our most productive fishing grounds. So, in 2007, the Government accepted fishing industry proposals to ban bottom trawling there.

It was one of 17 large areas of ocean the industry agreed to protect, since damaging the seabed diminished the health of the fisheries.

On Wednesday, the Government rejected a proposal from Chatham Rock Phosphate to dredge a huge swathe of the Chatham Rise’s protected seabed. The company was after phosphate nodules to turn into fertiliser for farming.

‘‘The view that mining the seafloor in an area in which a comparable activity is prohibited would be, at the very least, contradictory,’’ the Environmental Protection Authority’s decisionmaking committee gave as one of its many grounds for rejecting Chatham Rock’s application.

Moreover, there was no way to fix the damage that mining would do.

In response to the rejection, Business New Zealand and Strattera, the mining industry association, expressed outrage about the economic opportunity lost. They called for radical reform of the whole consenting process on land as well as at sea.

Yet they exaggerated wildly. The economic evidence at the hearings told a very different story.

In its decision document, the committee said it seemed generally agreed that a price of around US$125 (NZ$169) per tonne of phosphate would constitute a break-even point for the proposal.

However, the world phosphate price would range below that – from US$110 per tonne in January 2014, to US$90 per tonne in 2025 – according to a World Bank forecast submitted as evidence.

Nonetheless, Chatham Rock’s commissioned report from NZIER showed a moderate economic benefit for the project. This was heavily challenged in the hearings for a range of reasons, including its failure to quantify losses others might suffer.

Alex Sundakov, a former NZIER chief executive giving evidence on behalf of Ngai Tahu, estimated the potential costs to the fishing industry at $270 million to $1.5 billion a year.

The heart of the matter is that we know so little about our extremely complex marine environment. That’s why the legislation governing activity in our Exclusive Economic Zone (EEZ) is founded on the precautionary principle.

Consequently, the authority has rejected the first two applications for seabed mining; Chatham Rock’s, and Trans-Tasman Resources’ application last year to dredge for iron sands off Taranaki.

Business New Zealand and Strattera are right about one thing. It was madness for Crown Minerals to award mining licences to the two applicants without any regard for the environmental impacts.

But the business lobbyists are dead wrong to argue the Government should back off significantly on environmental precaution. Too little is known. Too much is at stake.

There is a much better way. Marine spatial planning would identify what activities are appropriate where, as such planning already does on land.

Once such clarity was given, companies seeking to benefit from our marine wealth in sustainable ways would have a much more certain consenting process.

Such planning, though, is a phenomenally big task.

Our EEZ, at 5.8 million square kilometres, is the fourth-largest in the world. We know astonishingly little about it.

Niwa says there are some 5000 known species in our waters, but of the species we know, 60 per cent are unique to them.

Humankind has barely begun to understand the value of marine life. For example, of 31 marine leads for anti-cancer drugs, New Zealand has contributed three. One is a breast cancer drug in preclinical development from a local sea sponge.

Likewise, we have studied less than 6 per cent of our seabed so far, estimates Dr Michael McGinnis, formerly of Victoria University. Government funding for marine science is barely $5m a year.

Yet, if we began the long work of marine spatial planning we could make some very good, immediate decisions. For example, we ban mining in national parks. So we should ban seabed mining in protected fishing grounds.

There will still be howls of protest from business. The minerals they want for farming on land are the ones that help make the fishing grounds so fertile. We need to make logical choices. Threatening fishing to further farming is not one.

Best practice on ocean policy around the world is based on the principles of ecosystem management and integrated tools to achieve it. In addition to spatial planning, another key discipline is establishing representative networks of marine protected areas.

Canada was the pioneer of this approach with its Oceans Act of 1997, followed by Australia in 1999, the US in 2000 and the UK in 2009.

Yet our Government has no interest in taking such a sensible approach. The EEZ legislation it rushed through parliament in 2012 is riddled with the sorts of holes in logic, principle and practice that have tripped up Chatham Rock and Trans-Tasman Resources.

If the Government had a strategic bone in its body, it would start New Zealand on the long, hard journey to becoming a world leader in marine sciences and management, thereby generating substantial, sustainable wealth.