Who doesn't love a nice basket of fish and chips an a beautiful summer day at the beach? But as you munch on your fillet of battered flake, did you stop to think where it came from?

"People say 'I'll have fish and chips' without thinking," says Craig Bohm from the Australian Marine Conservation Society (AMCS). According to Bohm, we should be asking questions in the fish shop: What type of fish is it? How was it caught? How long does it live?

This is the only way we can make environmentally informed decisions about the seafood we buy, he says. In Australia, with several hundred species of seafood to choose from and little support from major retailers, making a green choice can be confounding.

To help us make real choices about the seafood we buy, the AMCS has published a Sustainable Seafood Guide. It recommends we say "no thanks" to gemfish and tuna, "think twice" before we tuck into prawns, and make a "better choice" by buying Western Australian rock lobster instead of tropical rock lobster.

But why should we give some varieties of seafood a tick and others the flick? The AMCS base its decisions on the status of fish populations or 'stocks' - whether they are "faring well", "on the edge" or "overfished".

But trying to unravel the status of Australian fish stocks is a tricky task, with different species monitored by governments and agencies both local and international. There are no independent assessments of fish stocks managed by Australian states or territories. Only fisheries managed by the Commonwealth Government get an annual report card from the Bureau of Rural Sciences.

Worryingly, the latest Bureau report in 2006 found that 20 per cent of the stocks managed by the Australian Fisheries Management Authority (AFMA) on behalf of the Australian Government were overfished or subject to overfishing.

There's still overfishing of some stocks jointly managed through international agreements, including big-eye tuna, southern bluefin tuna and yellowfin tuna.

Environmental burden

Another reason to cut down our consumption of tuna and swordfish is that harvesting such predatory species burdens the environment with greenhouse gases to a greater extent than taking smaller fish does, according to recent research by Gidon Eshel and Pamela Martin from the University of Chicago.

Eshel and Martin calculated that the harvesting of tuna and swordfish produced similar greenhouse gas emissions to those generated by harvesting beef. "Eating fish can be environmentally entirely benign and really advantageous or it can be the dietary equivalent of driving a Hummer. It spans the entire range," says Eshel.

At the other end of the spectrum for greenhouse gas emissions, according to Eshel and Martin, are sardines and anchovies, which are low on the food chain because they feed on small plankton. Catching these small fish produces far less greenhouse gas emission because boats needn't venture far from shore. The short lifespan of these fish means the stocks have a high turnover, and less energy is taken out of the food chain with each fish.

Collateral damage

Harvesting seafood has additional environmental costs. Dragging a trawl net along the ocean floor changes seabed communities - each pass of a trawler can remove up to a quarter of the life from the seabed, with repeated trawls stripping away up to 90 per cent of life. The seabed life can take up to two decades to recover.

For every tonne of useful seafood caught by trawling, 2 to 15 tonnes are discarded. Wrenched from the seabed, the unwanted marine life (called the bycatch) gets hauled from hundreds of metres below the surface and spends several hours crammed in a trawl net with thousands of thrashing fish and assorted marine animals.

Much of the bycatch doesn't survive the trauma of breathing out of water or being washed off the heaving decks of the fishing boat. The scientists offered a glimmer of hope, saying that we could restore marine biodiversity if we manage our fisheries sustainably, take care of marine habitats and create marine reserves.

So is Australia on track to save our seafood? "Australia's fisheries management system is very good by world standards," says Keith Sainsbury, an internationally awarded fisheries scientist and board member of AFMA. He believes that "serious efforts are being made to redress our mistakes".

Just before Christmas in 2005, after a series of very bad report cards, the AFMA received an ultimatum from the Government, which insisted it do a better job in ensuring the sustainability of Australian fish stocks and secure a future for the fishing industry.

Fortunately, the Government backed its demand with $220 million in funding. The money is being used to reduce competition by buying out fishing licences, helping to relocate or retrain fishermen so they can get new jobs, and supporting businesses so they can diversify their fishing-related operations.

In theory, knowing that a fish stock is being overfished should trigger a rapid reduction in effort: fewer boats catching fewer fish, or even a ban on commercial fishing until the stock recovers. Yet, even the most basic information about our fisheries resources can be full of uncertainty. "It's very difficult and very expensive to estimate how many fish are in the sea and how many fish can be taken safely," says Sainsbury.

The more information available about the fish stock, the better the estimates: lifespan, migration patterns, growth rate and breeding age are all useful indicators of the success of the stock. For some stocks, it was a case of too much fishing too soon, before crucial information about their biology was known. "There are a number of cases where we went from having poor understanding of the stock, straight to [it] being overfished," says Sainsbury.

Sustainable management

Stricter harvesting rules also set out much more clearly the criteria for limiting fishing in a particular area, or stopping it altogether. There's also a process to assess the risks of target species and the bycatch. Zoning of fisheries has also been improved. Marine reserves are being used to concentrate stock depletion and seabed damage in some areas, while protecting marine biodiversity, including fish stocks, in others.

In addition to his role on the board of AFMA, Sainsbury is on the Technical Advisory Council of the Marine Stewardship Council (MSC), an independent organisation that assesses fisheries around the world for their sustainability.

"I don't want to paint an overly rosy picture," says Sainsbury. "There are a lot of fisheries that aren't well managed, but there are also ones that are. That's what the MSC is about. MSC recognises and rewards fisheries that are well managed." The MSC accreditation process considers the sustainability of the stock, the effect of fishing on the marine ecosystem and the management of the fishery.

The Western Australian rock lobster fishery is one of only 24 fisheries worldwide that has sought and achieved MSC certification. It means that Western Australian rock lobsters can proudly display the blue eco-label from MSC, making it simple for consumers to choose sustainable seafood.

"People are concerned that overfishing is a part of life in Australia. People don't want to be part of it," says Bohm. "We're at the beginning of what I'd like to call a sustainable seafood revolution. We want people to think about it more, to ask about it," adds Bohm.

By asking questions and becoming seafood 'snobs', we can all be part of the sustainable seafood revolution.

Adapted from "Sustainable Seafood", written by Louise Goggin in G Magazine.