Australians love seafood. We eat about 400,000 tonnes of it every year.

And we have one of the better-managed fisheries in the world.

But about 70 per cent of the seafood we eat comes from overseas where issues like overfishing and even slave labour can be present in the supply chain.

And Australian-grown seafood isn't completely without its issues: we still have tarnished species like orange roughy on our menus, and some fisheries use controversial methods like longlining and bottom trawling, which can damage habitat and kill things like turtles and other protected species.

So if we want to enjoy seafood sustainably, are there species we should favour, others we should avoid, and how can we find out where our food comes from?

What makes a sustainable species?

Mahi-mahi can be a very sustainable fish, depending on how it's caught. ( Getty Images )

There's a beautiful looking, phenomenal athlete of a fish called mahi-mahi — sometimes called dorado or dolphinfish — that's found around the world, including off Australia.

It can swim at lightning speeds of up to 90 kilometres an hour. It uses its pace to catch the prey it needs to fuel its relentless growth.

It can grow at up to 4 millimetres a day, 3 centimetres a week, and can reach lengths of more than a metre in its first year or two. It's able to start reproducing by about 4 to 5 months of age.

On paper, it has all the biological characteristics of a model fish for sustainable harvest. And it can be.

Longlining is known to cause bycatch, where creatures such as turtles and seabirds are caught as well as the fish that is intended to be harvested.

But in some fisheries, including some in Australia, it's caught by longlining — a method of fishing where thousands of baited hooks attached to a mainline are set adrift, and which some conservation groups say has an unacceptable bycatch of turtles, seabirds, sharks, and other threatened species.

While industry members say they work hard to minimise bycatch, online advice from the Australian Fisheries Management Authority (AFMA) acknowledges it is an issue.

Longlining is also used in some fisheries to catch tuna, and fish like sailfish and marlin, where the bycatch can be as high as 20 per cent of the total take.

So while biology is important in choosing sustainable seafood, if you want to be really careful, the fishing or harvesting method should also be taken into account.

How do I know what seafood to choose?

The FRDC reports on whether different fisheries are depleted, recovering or sustainable. ( Supplied: FRDC )

The level of caution you want to exercise in selecting your seafood is a personal choice.

If your concern is whether a fish species is declining or sustainable, the Fisheries Research and Development Corporation (FRDC) — a co-funded industry and Government body — publishes an Australian Fish Stocks Report every year.

Species are assigned to one of six categories including Sustainable, Depleted, Depleting, or Recovering.

The Sustainable Seafood Guide recommends avoiding Orange Roughy. ( Supplied: AMCS )

Each species is also broken down into its fishery. So for instance, the Queensland snapper fishery is listed as Depleted, whereas New South Wales is Sustainable.

You can also get information via an app called SAFS, or the Status of Australian Fish Stocks.

While this information is industry approved, the Australian Marine Conservation Society (AMCS) said a more environmentally cautious approach is needed.

AMCS publish the Sustainable Seafood Guide, which is available as an app too.

The guide breaks down seafood into fisheries similar to the Fish Stocks Report, but also considers how the seafood is caught and gives them an overall "traffic light" rating — green, amber, red.

For instance, many whiting, yellowfin bream, and Spanish mackerel fisheries have healthy stocks and are caught using low-impact methods, and fall into the green, "Eat More" category.

But some gill-netted and bottom-trawled fish, some trawled fish and prawns, and farmed Atlantic salmon are red-listed as "Say No" species according to the AMCS sustainable seafood manager Adrian Meder.

"Recently and disappointingly we had to downgrade Atlantic salmon that has been farmed in Australia," Mr Meder said.

"That was due to an ongoing series of serious environmental issues as a result of the industry looking to expand their production farther and faster than the local environment was able to support."

But Seafood Industry Australia CEO Jane Lovell said the Tasmanian salmon industry had made improvements to its practices in the last 15 months.

"These investments include ongoing innovation to seal-proof pens ... investments into multi-trophic farming to reduce environmental impacts, and substantial funding of marine-debris partnerships to further reduce impacts in waterways," Ms Lovell said.

While she also pointed to the industry's certification under the Aquaculture Stewardship Council, two experts quit a review panel in November last year over concerns about the approval process for Tasmanian salmon farms.

The Australian Marine Conservation Society regularly update their guide, and reward fisheries that are doing the right thing, according to sustainable seafood manager Adrian Meder.

"We've been able to put in our green ranking barramundi that is farmed in Australia. [And] elsewhere, we've seen great progress in the management of sardine fisheries in Australia, so we're happy to recommend the wild sardine fisheries."

What about imported stuff, like canned tuna?

Pole and line fishing for tuna can reduce the bycatch associated with longlining. ( Supplied: Paul Hilton/Greenpeace )

Slave labour isn't something at the front of most of our minds when we go to grab a tin of tuna off the shelf.

But a significant portion of our imported seafood comes from countries where there is a "high risk" of slavery being used in the supply chain, Professor Jessica Meeuwig of the University of Western Australia told 7.30 recently.

"Definitely a percentage of the fish we eat is tainted by slave labour," she said.

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Added to that, many international tuna fisheries are poorly regulated, over-harvested, and use things like FADs — Fish Aggregating Devices to catch fish.

FADs are floating structures that attract all sorts of marine life, which is then longlined or netted, with high rates of bycatch.

But again, resources are available if you want to make more sustainable canned tuna choices.

One of those is the Change Your Tuna guide from Greenpeace, which lists 10 Australian brands from best to worst.

Tuna brands that rate highly use pole and line fishing, uphold human rights and labour commitments, use species like skipjack tuna instead of yellowfin, and have transparent labelling.

Another option is to look for sustainability accreditation labels.

One of those which can be found on canned tunas and a range of seafoods available in Australia, is the Marine Stewardship Council (MSC) certification.

The MSC logo can be found on a range of certified seafoods in Australia. ( Supplied: MSC (Jason Thomas) )

The MSC assesses fisheries broadly on the health of the fish stock, the wider environmental impacts of the fishing method, and how robust the management systems are, according to MSC's Oceania Program Director Anne Gabriel.

"Worldwide, there are over 100 species certified to the MSC standard for sustainablity with over 35,000 MSC labelled products now available," she said.

There are plenty of options to choose from if we want to eat sustainable seafood, including crabs, prawns, abalone, crayfish, oysters and fish.

As our fisheries come under increasing pressure from climate change and growing populations, making sustainable choices now can give us the best chance of being able to enjoy seafood in the future.