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Sustainable Seafood

seafood

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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.

Long-distance voyages are needed to catch these large ocean-going fish. Predatory fish are also high on the food chain - they eat smaller animals, which in turn eat smaller animals, and so on, which means it takes a lot of energy from the ecosystem to produce a kilo of tuna or swordfish steak.

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.

In 1996, the United States stopped importing prawns from countries that didn't use devices on trawl nets to limit the accidental capture of turtles - including, at the time, Australia.

Such devices are now compulsory on all trawlers in Australia, but AMCS still recommends we "think twice" before purchasing prawns even though the US market re-opened to Australian wild-caught prawns in 2004.

Last year, an international team of researchers reported in the US journal Science that - if we continue to do as we are doing - all the world's fish and seafood species will collapse in 40 years.

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.

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