Salmon farmers seek cooler waters as climate changes


When the ocean warms, such as during a marine heatwave, cold-blooded salmon move to cooler waters. It could be a simple descent to the same place or a longer migration to another place.

Farmed salmon, however, have no such option. And fish farmers cannot easily move pens when temperatures are higher than expected.

At 14 degrees, salmon thrive.

At 16 degrees, they survive.

* Rising salmon mortality highlights need for culling, but industry urges speed
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* New guide on farming in the high seas drafted by the government
*Climate change affects NZ King Salmon fish stocks and expected profits

At 18 degrees, the enzymes that help them digest food begin to die off. If the water temperature is 18 degrees for a few weeks, the salmon’s immune system collapses. They get sick. They die.

At higher temperatures, for prolonged periods, heat alone can kill them.

That’s what happened this summer, when a sea heat wave killed around two out of five salmon at New Zealand’s King Salmon farms in Marlborough Sounds. More than 1000 tonnes of fish waste was sent to landfill.

King Salmon's Te Pangu Bay New Zealand Farm.

Chloe Ranford/LDR

King Salmon’s Te Pangu Bay New Zealand Farm.

“It was one of the hottest we’ve seen. It started early and ended later. It was often a degree and a half warmer than normal,” said NZ CEO King Salmon, Grant Rosewarne at Newsroom. “There was a very long period of over 18 degrees in Pelorus Sound and in Queen Charlotte as well.”

The company reported a loss of $73 million for the year ending January and is closing most of its farms in the Marlborough Sounds.

Climate hits farms

Marine heat wave conditions – when ocean temperatures are above the 90th percentile for at least five days – were common during the summer, spurred by the La Niña phenomenon.

“What we are starting to see is that we have a changing environment and unfortunately New Zealand King Salmon are suffering some of the consequences,” said Serean Adams, aquaculture group leader at the Cawthron Institute.

This is not the first time that climate change has hit New Zealand fish farms. Ocean temperatures have been rising for decades, although the pace has accelerated more recently.

Salmon are farmed in the Mackenzie region.


Salmon are farmed in the Mackenzie region.

“You hear Niwa and others talk about sea heat waves. For the first seven years of my job I never heard the term sea heat wave and now it’s every two years. And it looks like we’re going to have three La Niñas in an argument now, which again is pretty unheard of,” Rosewarne said.

Other salmon farmers and fishing businesses say they are also seeing the impacts of climate change, although NZ King Salmon’s losses this year are unique in their scale.

This has led to a flurry of research into ways to build resilience by moving to colder waters or changing species.

Maren Wellenreuther is an evolutionary ecologist at the University of Auckland and a seafood scientist at Plant and Food Research in Nelson. The top of the South Island could soon be inhospitable to salmon, but other fish could replace them, she said.

A salmon farm in the High Country near Twizel.


A salmon farm in the High Country near Twizel.

“It’s quite an interesting area because a lot of species are showing their southernmost extent here, like snapper. For them, if you think about climate change, they’re increasing their range in New Zealand, whereas other species, like salmon, are found as far north as Nelson and the Marlborough Sounds, they struggle.”

Wellenreuther worked on a project to breed snappers and prepare them for aquaculture.

“Just looking at the Marlborough Sounds all of a sudden it becomes an area where we might want to farm species like snapper. If you think about the future, this is something that will only accelerate. What are we going to do with this space? With climate change, you always think about winners and losers.

This does not mean the total end of salmon farming in New Zealand. Other companies farm the species further south and NZ King Salmon is still the largest producer of king salmon species in the world.

open ocean

In recent years, therefore, attention has shifted to deep-sea aquaculture, which could unlock a new scale of fish farming while building climate resilience.

Climate change, Rosewarne said, is “the main reason” his company is considering open sea farms. Endeavour. A decision on this request is expected later this year.

“We think this will lead to less stressed fish because the temperature will be cooler. Also, at this site there is something called a thermocline where it gets cooler as you get closer to the bottom We don’t see that in the sounds,” he says.

The Sanford Salmon Farm at Big Glory Bay Stewart Island.


The Sanford Salmon Farm at Big Glory Bay Stewart Island.

“Obviously we can grow to a larger scale, but we can also increase our unit value. We can grow bigger and more valuable fish there. We think we can get a great environmental result – we think we can eventually getting an increase in the natural biodiversity associated with the farm, rather than a decrease that you might see in most farming methods.This has a huge number of benefits.

Wellenreuther said next-generation deep-sea technology could allow enclosures to be moved throughout the year, tracking optimal temperatures for farmed species. It would also limit environmental impacts as the farm would not be concentrated in one space.

At least three other offshore salmon farms are under consideration. Fishing company Sanford, which also runs a few salmon farms, has applied for consent for a deep-sea farm in Southland in 2020. Ngāi Tahu also has plans for its own deep-sea salmon farm in Southland , called Hananui Aquaculture. That program has been referred to the government’s fast-track Covid-19 consent process, according to documents released to the Newsroom under the Official Information Act.

A report commissioned by Fisheries New Zealand last year found that the government’s most valuable intervention would be a new consent process that grants more certainty, faster.

“Feedback from applicants and others on the resource consent request process and the results has been nearly unanimous – it is fraught with pitfalls and uncertainties that have real-world impacts on development schedules, costs and operating flexibility.These impacts are in addition to what many suggest are the high costs typically incurred in obtaining consent;the costs that could be spent more productively on the work required to prove viability in the case of farms in the open sea.

Rosewarne agreed and said that if enabled, deep sea farming will play a vital role in achieving the government’s target of a $3 billion aquaculture industry by 2035. It will also help to the country’s climate goals, allowing us to complement high-emission dairy and meat production with a large-scale, low-emission source of protein. One hectare of land can generate $30 million in revenue on an offshore farm, compared to about $11,000 on a dairy farm.

“We strongly believe that deep sea aquaculture could become New Zealand’s most valuable industry bar none. At the same time, it could be the greenest primary sector we have,” he said. declared.

“The Norwegian salmon industry today is about equal to our dairy industry, depending on where these two products are in their price cycle. space and with a very acceptable environmental footprint.”


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