When the ocean heats up, like it does during a marine heatwave, cold-blooded salmon move to cooler waters. That could be a simple descent in the same location or a longer migration to someplace else.
Farmed salmon, however, have no such option. And fish farmers can’t easily move pens when temperatures are higher than expected.
At 14 degrees, salmon thrive. At 16 degrees, they survive.
At 18 degrees, the enzymes that help them digest food start to die off. If water temperatures are at 18 degrees for a few weeks, the salmon’s immune system breaks down. They get sick. They die.
At higher temperatures, for prolonged periods of time, the heat alone can kill them.
That’s what happened this summer, when a marine heatwave left about two in every five salmon in New Zealand King Salmon’s Marlborough Sounds farms dead. More than 1000 tonnes of fish waste were sent to landfill.
Related Posts
“It was one of the hottest ones we’ve seen. It started early and it finished later. It was often a degree and a half warmer than normal,” NZ King Salmon’s CEO Grant Rosewarne told Newsroom. “There was a very extended period over 18 degrees in the Pelorus Sound and in the Queen Charlotte as well.”
The company reported a $73 million loss for the year ending in January and is closing most of its farms in the Marlborough Sounds.
“What we’re starting to see is that we do have a changing environment and unfortunately New Zealand King Salmon is bearing some of the consequences of that,” Serean Adams, the aquaculture group manager at the Cawthron Institute, said.
This isn’t the first time climate change has hit New Zealand’s fish farms. Ocean temperatures have been rising for decades, although the pace has sped up more recently.
Other salmon farmers and fishing companies say they’re seeing the impacts of climate change as well, though NZ King Salmon’s losses this year are unique in their scale.
That’s driven a flurry of research into ways to boost resilience through relocating to cooler waters or switching species.
In recent years, the focus has therefore shifted to open ocean aquaculture, which could unlock a new scale of fish farming while also boosting climate resilience.
