Marine heatwave looming this summer, with potential to impact some much-loved Aussie seafood

Marine heatwave looming this summer, with potential to impact some much-loved Aussie seafood

A heightened risk of bushfires, drought and now marine heatwaves are on the cards for this summer, with the forecast warmer waters having the potential to impact Australians’ access to seafood. 

The weather events will likely hit Tasmania just as seafood operators are harvesting oysters, abalone, and salmon for the Christmas dinner table.

The triple whammy is making its way to the Tasman Sea as a result of the impending, but as yet undeclared, El Niño.

Forecasts from the Bureau of Meteorology indicate above-average ocean temperatures around the country, particularly off the coast of Tasmania and Victoria.

This could lead to coral bleaching and changes in fish migration and aquaculture production.

The warmer waters could lead to coral bleaching.(Supplied: CSIRO)

Heatwave modelling helps fisheries

For the past two years, CSIRO and the BOM have been developing a more accurate way to forecast marine heatwaves.

It’s hoped the early warning system will aid in minimising disruptions to seafood supplies across the east coast of the country.

CSIRO research director for Sustainable Marine Futures Alistair Hobday said that an El Niño typically led to a redistribution of heat in the ocean.

“In the South Pacific we expect to see more heat and that would lead to more heatwaves in the Tasman Sea,” Dr Hobday said.

“That’s the ocean off Victoria and off Tasmania’s coast.”

Map of marine heatwave forecast for September 2023.(Supplied: CSIRO)

Dr Hobday said the heatwave modelling drew on data from the BOM’s ocean atmosphere model.

The model pulled together information on wind, ocean, and air temperatures to produce daily weather forecasts.

“That model is also now being used to project conditions six months into the future and we’ve used that technology to produce heatwave forecasts,” Dr Hobday said.

This summer, marine heatwave risks are higher on Australia’s east coast and lower risk on the west coast.

Alistair Hobday says the heatwave could impact fish movements.(Supplied: Alistair Hobday)

CSIRO and the BOM have been providing briefings to the fisheries sector to help the industry prepare for severe impacts.

“Abalone fishers on the coast of New South Wales and Victoria are starting to think about what to do if the summer is warmer,” Dr Hobday said.

“Warmer waters hold less oxygen, so salmon growers might be choosing to do more oxygenation of their waters or begin ordering food that the animals prefer to eat when the water is warmer.”

Like an underwater bushfire

Swimming in warmer water might sound appealing to some, but for the species that live in it, it’s bad news.

Any increase in water temperature can kill off marine habitats, such as sea grass and kelp, and, as a result, disrupt the food chain.

Underwater forests along the Great Southern Reef are likely to be impacted by warmer waters.(Supplied: Great Southern Reef Foundation/Stefan Andrews)

David Maynard is an extension officer with the Fisheries Research and Development Corporation. He said a marine heatwave was akin to an underwater bushfire rolling through.

“We’ve all seen what a devastating bushfire looks like on the news,” he said.

“You lose the forest; you lose all the animals in that.

“It’s pretty much the same below the waterline.

“It’ll affect everything from the smallest invertebrate to our larger predatory species and our target species.”

Many east coast marine animals have a low temperature tolerance.

While some species could move to deeper water or migrate further south to avoid the heat, in Tasmania, the migratory options were limited.

“It’s Macquarie Island or the Antarctic peninsula,” Dr Hobday said.

“Generally, if it gets too hot, we will see mortality or death of animals.”

Tassie in the firing line

Research has shown that Tasmania’s waters have been warming at a rate four times the global average.

For years, researchers have referred to it as a global ocean hotspot.

Tasmania’s marine ecology would change with warming waters.(Supplied: IMAS/Cayne Layton)

“In part, it’s due to the East Australian Current growing stronger and bringing warmer water further south,” Dr Hobday said.

“Then, when we have very hot days or atmospheric conditions, it puts a lot of heat into the ocean.

“So we get this double whammy of heating off the east coast of Tasmania.”

Josh Poke hopes the industry is better prepared this summer.(Supplied: Josh Poke)

Lessons learnt from El Niño

This year’s heatwave prediction has some Tasmanian shellfish growers worried.

The last time there was a marine heatwave, it cost Josh Poke’s oyster business a million dollars in lost revenue.

It was 2016 when his oysters in southern Tasmania began dying in the water.

“There was no warning at all, really,” Mr Poke said. 

“We knew it was warm, but that was about it.”

The Pacific Oyster Mortality Syndrome (POMS), which becomes active when water temperatures rise, had taken hold across most of the state’s oyster-growing regions.

There were heavily casualties to oyster spat in the 2016 POMS event.(ABC News: Michael Atkin)

It wiped out more than 60 million Pacific oysters, cut supplies of baby oysters to South Australia and New South Wales, and bumped up the retail price.

“We watched the disease sweep through our stock, the millions of oysters that we lost and the subsequent job cuts we had to make to survive,” Mr Poke said.

“It’s still pretty vivid in the mind.”

Mr Poke is now involved with Tasmanian Oyster Company, which farms 220 hectares of water across the state.

Marine heatwaves can lead to major fatal disease outbreaks.(ABC Rural: Laurissa Smith)

He said the heatwave forecasts were an invaluable tool for the industry.

“So we can get on top of grading schedules, planned maintenance, and make sure our oysters are as happy and healthy as they can be,” he said.

“They take two-and-half years to go from a baby oyster to maturity on average.

“You can’t just empty your farm and pick it up next year.

“You’ve got to try to get as much stock through each summer as you can.”

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