Marine heatwaves: How is aquaculture adapting to climate change?

A record-breaking marine heatwave hurt business and ecosystems this summer, and there is emerging evidence it could happen again next year. How is aquaculture adapting?

Aquaculture is a climate change canary - particularly vulnerable to its effects. But it also has the potential to cash in on an international market protein from more sustainable sources.

The ongoing ocean heatwave has spiked ocean temperatures 5 degrees above normal in parts of the country.

It caused mass bleaching of tens of millions of sea sponges in the southern fjords, which has scientists deeply concerned.

'It's just been a tragedy for us ... it's all avoidable'

It also forced the country's largest salmon exporter New Zealand King Salmon to lay off more than 100 staff and close farms in the Marlborough Sounds after it killed 1300 tonnes of fish.

New Zealand King Salmon chief executive Grant Rosewarne said it had been an incredibly difficult time.

"All that's quite devastating really, and it has just been a terrible outcome."

The government sees the aquaculture industry, which employs about 3000 people mainly in the regions, as a good bet for producing low emissions protein with international market potential.

In 2019 it released a roadmap to increase output by a factor of five, to $3 billion in annual revenue by 2035.

Part of that increase would come come from a move into open ocean farming - with a decision on New Zealand King Salmon's resource consent application to farm fish in the cooler waters of the Cook Strait due within months.

Rosewarne said practical support by the government in the form of bespoke legislation to let it farm in open waters would have avoided the lengthy RMA process, and the blow to its business this summer.

He said the government has been clear it wants to take action on climate change, and to expand the aquaculture sector.

Rosewarne said the technology for farming the Cook Strait was available now, so why wouldn't the government pull every lever possible to get it to happen.

"When you've got a climate change situation where there is a known solution and it can be done, it is frustrating that we can't make progress.

"And heaven help us in other areas [of climate change policy] where there aren't known easy solutions, because that's going to be a lot harder."

"[The government seems] unable to put the two together and get it going.

"And as I said, that's has a huge cost to our shareholders, to our team members, to our fish. It's just been a tragedy for us. And it's all avoidable."

RMA changes quicker than bespoke legislation - govt

Rosewarne said the RMA simply was not fit for purpose for aquaculture - it is too slow and too inflexible.

A spokesperson for the Oceans and Fisheries Minister David Parker said there were no plans right now for bespoke legislation, and that the RMA reforms underway would be quicker than custom rules for the sector.

In February, Parker said the impact of high water temperature on New Zealand King Salmon was a sharp reminder of the need for RMA reforms, and the strategic planning needed to get ahead of these kind of matters had not happened.

Rosewarne said over the past years other countries' fish farming operations had gone from tiny to massive compared to New Zealand, which has stalled.

Open ocean farms and mussel tech part of climate future

Open ocean farming - like New Zealand King Salmon's Cook Strait plan Blue Endeavour - is being touted as a game changer, and would massively scale up production.

Ministry for Primary Industries aquaculture director Mat Bartholomew said you get lots of bang for your buck.

"An open ocean salmon farm or an open ocean fin fish farm of about 10,000 tonnes would occupy about 10 hectares of marine space, which is actually really quite a small amount when you think about the enormous size of New Zealand's [territorial waters]."

Bartholomew said the current total annual output of farmed fish in Aotearoa is only about 15,000 tonnes.

He said another promising avenue to meet the challenge of global warming was a project the government was investing in to breed mussels in hatcheries to make them more resilient to warmer water, and with shells that provide protection against ocean acidification - another effect of climate change.

Long term warming predicted

But climate change means moving farming to cooler waters may not get them out of harm's way.

University of Otago oceanographer Rob Smith said these places have also seen strong to severe heatwaves this summer.

"It's expected that in these locations, as with elsewhere around New Zealand, we are going to continue to see more frequent, longer lasting, and more intense heatwaves.

"But I certainly acknowledge that the impacts may be lessened in those particular locations."

Rosewarne said the open ocean technology that would be used in the Cook Strait allowed the farm stock to be dropped deeper into the water, where it is cooler, but it needed flexible resource consents to be allowed to do that.

He said that while the Blue Endeavour area would still be impacted by global warming he was confident in the site and the technology available.

Mat Bartholomew said it was all about farming the right species in the right places, and Rosewarne said the company could look to switching to farming other species of fin fish which were happier in hotter temperatures if the oceans continued to warm.

The La Niña weather pattern - which is a factor in causing the marine heatwaves along with climate change - lingers.

NIWA said there was a 60 percent chance the pattern would continue into next summer, making it a rare "triple-dip" La Niña - the third summer in a row with an ocean warming weather pattern - something that has only happened a handful of times before.

And long term, even in the best case scenario, NIWA and Deep South Challenge research showed that the number of days of marine heatwave a year were expected to double by the end of the century, and in the worst case Aotearoa's oceans will be in heatwave nearly half the time.

It could wreak havoc on ecosystems and fisheries.

Fisheries New Zealand is commissioning a three-year research programme on the risk and impacts of marine heatwaves on fisheries.