Marine heat waves: how is aquaculture adapting to climate change?


A record-breaking marine heat wave hurt businesses and ecosystems this summer, and there’s new evidence it could happen again next year. How is aquaculture adapting?

A salmon farm (file photo).

Aquaculture is a canary of climate change – particularly vulnerable to its effects. But it also has the potential to take advantage of an international market protein from more sustainable sources.

The ongoing ocean heat wave has pushed ocean temperatures up to 5 degrees above normal in parts of the country.

It caused a massive 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…everything is preventable”

It also forced the country’s biggest salmon exporter, New Zealand King Salmon, to lay off more than 100 staff and close farms in the Marlborough Sounds after killing 1,300 tonnes of fish.

King Salmon New Zealand managing director Grant Rosewarne said it had been an incredibly difficult period.

“It’s all really devastating, and it’s just been a terrible outcome.”

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New Zealand king salmon
Photo: RNZ / Cosmo Kentish Barnes

The government sees the aquaculture industry, which employs about 3,000 people mostly in the regions, as a good bet to produce low-emission protein with international market potential.

In 2019, he published a roadmap increase production by a factor of five, to $3 billion in annual revenue by 2035.

Part of that increase is believed to come from a shift to deep-sea farming – with a decision on New Zealand King Salmon’s resource permit application to farm fish in the colder waters of the Cook Strait in some months.

Rosewarne said practical government support in the form of bespoke legislation to let him farm in open waters would have averted the lengthy RMA process and the hit to his business this summer.

He said the government has made it clear that it wants to act on climate change and develop the aquaculture sector.

Rosewarne said the technology to farm the Cook Strait is now available, so why wouldn’t the government pull every possible lever to make it happen.

“When you have a climate change situation where there is a known solution and it can be done, it’s frustrating not being able to move forward.

“And heaven helps us in other areas [of climate change policy] where there are no known easy solutions, because it’s going to be much more difficult.”

“[The government seems] unable to put the two together and make it work.

“And like I said, it comes at a huge cost to our shareholders, to our team members, to our fish. It’s just a tragedy for us. And it’s all preventable.”

RMA is changing faster than bespoke legislation – government

Rosewarne said the RMA is simply not suitable for aquaculture – it is too slow and too stiff.

A spokesman for Oceans and Fisheries Minister David Parker said there were no bespoke legislation planned at the moment and ongoing RMA reforms would outpace customs rules for the area.

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 anticipate this sort of thing had not taken place.

Rosewarne said that in recent years fish farming operations in other countries have gone from tiny to massive compared to New Zealand, which has stalled.

Deep sea farms and mussel technology are part of the climate future

Deep-sea farming – like New Zealand’s Cook Strait King Salmon’s Blue Endeavor scheme – is being touted as a game-changer and would massively increase production.

Department of Primary Industries Aquaculture Director Mat Bartholomew said you get what you pay for.

“An open sea salmon farm or open sea fish farm of around 10,000 tonnes would take up around 10 hectares of marine space, which is actually a small amount when you think about the huge size of New Zealand. [territorial waters].”

Bartholomew said the current total annual production of farmed fish in Aotearoa is only around 15,000 tons.

He said another promising avenue for tackling 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 offer protection against ocean acidification – another effect of climate change.

A mussel culture.  The aquaculture industry hopes to develop offshore marine farms.

A mussel farm (archive photo)
Photo: Supplied /Cawthron Institute

Expected long-term warming

But climate change means that moving agriculture to colder waters may not make them immune.

University of Otago oceanographer Rob Smith said these places have also experienced strong to severe heat waves this summer.

“It is expected that in these places, as elsewhere in New Zealand, we will continue to see more frequent, longer lasting and more intense heat waves.

“But I certainly recognize that the impacts can be mitigated in those particular places.”

New Zealand’s King Salmon hoped the expansion of its Te Pangu Bay farm could prevent salmon from dying in hotter summers.
Photo: Supplied/ NZ King Salmon

Rosewarne said the deep-sea technology that would be used in Cook Strait would allow farm stock to be dropped deeper into the water, where it’s cooler, but needed flexible resource clearances to be authorized to do so.

He said that although the Blue Endeavor region would always be affected by global warming, he had confidence in the site and the technology available.

Mat Bartholomew said it was all about breeding the right species in the right places, and Rosewarne said the company could consider moving to breeding other species of finfish that would be happier at lower levels. warmer temperatures if the oceans continue to warm.

The La Niña weather pattern – which is a factor driving marine heatwaves as well as climate change – lingers.

NIWA said there was a 60% chance the pattern would continue into next summer, making it a rare La Niña ‘triple dip’ – the third straight summer with warming ocean weather – some something that has only happened a handful of times before.

And in the long term, even in the best of cases, NIWA and Deep South Challenge research has shown that the number of days of marine heat wave per year is expected to double by the end of the century, and in the worst case, the oceans of Aotearoa will be in heat wave almost half the time.

This could wreak havoc on ecosystems and fisheries.

Fisheries New Zealand is commissioning a three-year research program into the risks and impacts of marine heatwaves on fisheries.


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