New Zealand King Salmon has a problem most businesses can only dream of.

That is to decide which of its many customers it cannot supply.

The premium product is in such demand, deliveries have to be rationed.

That is why the company earlier this year took the unusual step of becoming a salmon importer, bringing in the more common Atlantic salmon.

That is a cheaper and less palatable product, but inferior salmon is better than no salmon at all to small businesses reliant on it, as long as the distinction is made clear.

King Salmon is severely constrained by its access to water space.

The company has eight farms covering 17 surface hectares in the Marlborough Sounds, which produce 8000 tonnes of salmon per year.

No other means of protein production is as efficient, or has as little environmental impact.

Agricultural production, with its substantial water and fertiliser and chemical inputs as well as the loss of natural habitat and wildlife when the land was cleared cannot compare.

Despite this, King Salmon faces multiple challenges.

These include objections from environmental groups, bach owners and other aquaculture interests; lack of strong water flow in the inner Sounds; fouling of the seabed from faeces and nutrients; increasing water temperatures that have caused mortalities as high as 50 percent at the height of summer.

King salmon, also known as quinnat or chinook in its native North America, was first farmed here at the famed Te Waikoropupu Springs outflow in Takaka in 1976.

It is the only salmon species farmed in New Zealand and this country has become the world’s top producer of a species generally regarded as the premium in terms of taste, nutritional quality, colour, fat, Omega 3 oil content, fillet size and texture.

King Salmon produces just over half the New Zealand total.

Sanford is the next biggest producer, based at Big Glory Bay in Stewart Island, followed by Mount Cook Alpine Salmon, farming in freshwater hydro canals.

King Salmon has sought approval to move several farms to higher flow sites in the outer Sounds and is awaiting a decision from Fisheries Minister Stuart Nash.

But the long-term solution in King Salmon managing director Grant Rosewarne’s mind is to look to the open ocean.

He favours submersible pens anchored 6-12 kilometres offshore in the region surrounding the Cook Strait, despite its wild weather.

The frigate Wellington sunk off the Island Bay coast was soon torn apart by southerly storms. A 14-metre wave has been recorded by the fixed beacon at the entrance to Wellington Harbour. Offshore salmon farming is expected to be much further away from land.

Rosewarne is undeterred.

He says the pens would be like underwater silos, submerged 20 metres below the waves, where the water would be much calmer than on the surface.

“There’s a very real possibility it could become New Zealand’s biggest industry,” he said.

“In Norway they’ve already used aquaculture to replace their $70 billion oil and gas industries.”

He sees long-term potential for up to 100 submerged pens holding 1000 tonnes of salmon each, that still leaves plenty of room for marine mammals and sea-based activities in a significantly sized ocean area. This opportunity for low-impact growth over the next few decades could lift revenue to $2.5 billion annually, more than is currently gained from the entire seafood industry’s domestic and export sales.