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Vanishing fish putting tuna industry at risk

Ben Endean

South Australia’s bluefin tuna ranchers say fish have vanished from their usual haunts. The industry is desperate to understand why. 

The changing patterns of fish behaviour have thrown a spotlight back on the oil and gas industry as a possible culprit just weeks after Norwegian oil major Equinor pulled out of drilling in the Great Australian Bight

“In recent years the behaviour of the fish coming into the Great Australian Bight from the Western Indian Ocean has changed,” says Brian Jeffriess, CEO for the Australian Southern Bluefin Tuna Industry Association (ASBTIA). 

“The fish seem to be moving more quickly through the Great Australian Bight to the southeast and into Tasmania and on to the east coast. That’s made it less predictable in terms of where they congregate.” 

The tuna ranching industry is the largest aquaculture exporter in Australia, worth 150 to 200 million dollars a year and creating more than 1000 jobs directly. A further1200 to 1400 jobs are associated with the industry, so there’s a lot at stake. 

Southern bluefin tuna are highly mobile. Not only do they travel long distances between the Indian Ocean and the Great Australian Bight, they also migrate vertically through the water column from the surface to 2500 metres in depth. 

They start arriving in the Bight towards the end of October and can be expected to surface off the eastern coast of Kangaroo Island until the end of March. 

“It’s a very discrete window,” says Kirsten Rough, a research scientist with ASBTIA. 

“The whole lot of them come here year in, year out for multiple years of their life. In the Bight, they display a unique behaviour, which is to form large schools at the sea surface,” she says. “And that behaviour is critical for the tuna ranching industry.” 

Tuna of a specific age and size are meant to be caught during a brief, but predictable, window. 

Target fish are between two and four years old weighing around 15 to 16 kilograms. They are then penned and towed to waters near Port Lincoln to be fattened up for sale over about six months in the same way as land-based farmers would agist cattle. 

Until recently that has worked like clockwork. 

But if the fish aren’t there when they are expected, the whole system breaks down. Now tuna are moving through the region so quickly that they’re in the southeast of South Australia by January when they should only be there at the end of March. 

“If you can’t follow the normal, predictable path of these fish it adds enormous costs,” says Jeffriess. “It means we have to have a lot more boats out there ready to catch the fish.” 

Added costs are one thing. “But the real problem is whether they’ll be there at all,” he says. 

Luke Stevens

The association has been busy assessing all potential explanations for the change in behaviour of the fish, eliminating as many factors as they can. They now believe seismic surveys associated with the oil and gas industry may be the culprit. 

“We’ve eliminated water temperature,” says Jeffriess. “The Great Australian Bight has remained about the same for the last 30 years. 

“The catch quota is set by a scientific formula, and stock is increasing very fast at the moment. So we know it can’t be a shortage of fish.” 

That leaves seismic surveys as one of the few variables. 

The surveys are designed to capture images of the geology kilometres below the seabed by discharging very loud pulses of sound from air guns near the surface. 

International oilfield services giant Schlumberger was given the go-ahead by industry regulator the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) to carry out a survey over a 93,000 square kilometre area which begins about 190 kilometres southeast of Kingscote. It was given an operational window of 100 days between November last year and June. 

These surveys have been shown to damage wildlife. Associate Professor Robert McCauley of Curtin University has studied the effect of this noise through experiments with plankton, scallops, lobster, squid, fish, sea turtles and humpback whales – although not specifically tuna. 

“We did experiments with plankton and got some startling results that looked like the smaller plankton were killed out to a kilometre from a single airgun,” says McCauley. 

Last year, a study published in a UK biology journal showed how the surveys impacted the ability of rock lobsters to right themselves when they fell over. 

“They really rely on this ability to right themselves and to control when they are escaping from a predator,” one of the researchers, Ryan Day, said at the time. 

In the case of the tuna, Kirsten Rough speculates the sound may be spooking fish and affecting their normal schooling and sunbaking behaviour. 

“We think that the fish are finding the Bight over thousands of kilometres by following the sounds which are made by other fish, and possibly whales,” she says. 

“If you have an activity which generates a huge amount of sound and that is broadcast over a very wide area, there’s a very real risk that the swimming tuna won’t hear the quieter sounds made by their prey,” she says. 

Schlumberger did not respond to a request for an interview, but Jeffriess says the company has responded well to his association’s concerns. 

“If we asked them to move away from a particular area of the fishing ground, because that’s where we know the fish are, then they did so readily, at some cost to themselves. Frankly it is a very impressive level of cooperation that we are not always used to.” 

With a senate inquiry into the effects of seismic surveys on fisheries due to report in May, Jeffries would like to see that sort of co-operation enshrined in law. He is seeking a level playing field between all resource industries, including his own. 

The industry also wants an end to repeating seismic surveys in areas that have previously been covered and in areas oil companies themselves say are not viable or too expensive to develop. 

“We want the same rules to apply to everybody. If you apply for an aquaculture site and you don’t start within the year, for example, you lose the site. Currently with seismic surveys and drilling, you get approval for two, four, five, ten years. Over that sort of time period it’s just sort of random whether it’s going to be that year or not. It just creates massive uncertainty for other resource users. 

“So we don’t want any special deals. We just want the same rules to apply to all natural resource users.” 

Bill Condie

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Bill Condie has been a journalist for more than 30 years, working as a writer and editor in Europe, Asia and Australia for newspapers including The GuardianThe Observer and The Times. He is a former publisher of Cosmos magazine.

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