The true cost of a shrimp sandwich

We are consuming more shrimp than ever, and with the rise of industrial farming and the 'all-you-can-eat' bar, the effect on the marine environment can only get worse

It began with potted shrimp from Morcambe Bay, mutated into prawn cocktails in the Sixties, morphed into prawn curry and is now the substantial stuff of spaghetti à la Jamie Oliver. Such is our culinary relationship with prawns (or shrimps). America has a full-blown love affair, serving them creole-style, as scampi, on the barbie, and now in "all you can eat" shrimp bars. But the West's seemingly insatiable desire for these little crustaceans has come at a price.

Almost every country with a warm coastline has been hit by the fever for pink gold, with 700,000 tons of shrimp being produced annually, mainly for export to the United States and Japan. But some environmentalists claim shrimp farms have destroyed millions of acres of coastal cactus and mangrove forests, and are turning many of the world's estuaries into a prawn cocktail of chemicals.

Shrimp farming began a generation ago when the World Bank underwrote Southeast Asian shrimp operations. Since then America's consumption has increased by 250 per cent; the United States currently imports 600,000 tons of shrimp a year. Restaurants buy the most – the Red Lobster chain sells 5 per cent of all the shrimp farmed in the world. Farmed shrimp production represents just over a quarter of global shrimp production but has increased ninefold since 1982 and is set to rise. At the beginning of this month nearly two hundred countries agreed at the World Summit in Johannesburg to restore fish stocks by 2015, which means that the desire for fish and shrimp will have to be met by aquaculture.

Almost a third of all shrimp farming takes place along the Thai coast and as demand increases, investors are turning to Latin America. In Mexico, for example, the number of shrimp producers nearly doubled between 1993 and 1998. But not without consequences. On the Sonoran coastline, a thousand acres of cactus forest have been cleared. More typically shrimp farms remove mangroves. Mangroves, sometimes called rainforests of the sea, are important centres of biodiversity.

Mangrove swamps contain up to 70 species of tropical trees and shrubs that grow at the boundary between land and sea; they prevent soil erosion and harbour many different species, including manatees, dolphins and turtles; the wood and marine life from mangroves can sustain coastal communities. In a recent study, Greenpeace estimates that shrimp farming has been responsible for clearing a million acres of mangroves. The Global Aquaculture Alliance, based in St Louis, Missouri, an organisation that campaigns on behalf of shrimp farmers, concurs with this figure, but says 60 per cent of the world's mangroves have already been lost due to agriculture, urban development and local communities burning them for fuel.

The organisation adds that this destruction has by and large been halted. To a certain extent this is true: in a landmark case in December 1996 the Supreme Court of India ruled that 100,000 acres of intensive shrimp farms should be shut down, and no new shrimp farms could be situated in mangroves and other wetlands. The problem is that in many countries, like Thailand, the damage has already been done. According to a report by the United Nations Enviroment Programme, only a third of Thailand's mangroves remain and 80 per cent of their coral reefs are at risk, largely due to the effects of major shrimp farms in the region. Ecuador, the world's third largest shrimp aquaculture producer, has demolished 80 per cent of its wetland ecosystem. Dr Jason Clay, a senior research fellow for the World Wildlife Fund based in Washington DC, says: "Virtually nothing is being done to re-establish mangroves that were cleared in the past. At the very least earthworks need to be removed to allow the free flow of water (and seeds) so that mangroves can re-establish themselves. The industry talks a lot about this but has done little."

Traditionally, farmers in Vietnam used to farm shrimp within mangrove swamps for half the year, and then grow rice. However, the stocking densities the industry currently uses are far higher, up to 600,000 larvae per hectare, a hundred times the density of non-intensive farms. This causes a number of problems. The larvae are frequently harvested unsustainably from the wild. Fertilisers have to be added to grow the algae they feed on; in addition they are given fishmeal. Almost half of all fish caught globally – 35 million tons – are turned into fishmeal, nearly a quarter of which is fed to shrimp.

Another consequence of having such high stocking densities is that bacteria build up, which feed on their waste, and consume oxygen. As the larvae are sensitive to dissolved oxygen, they need to have sea water continuously flushed in to the ponds. Over half the pond's volume may be replaced every day – the polluted water from the pond then contaminates adjacent land and water systems. Because the shrimp are highly susceptible to disease, including Taura syndrome and white spot syndrome virus, they are fed antibiotics. This mixture of shrimp waste, antibiotics like terramycin, and pesticides like malathion and endosulfan, could pose a risk to local communities.

The Global Aquaculture Alliance, which is hosting a conference in Bali at the end of the month for delegates from the shrimp industry, has developed a Responsible Aquaculture Programme that includes codes of practice for responsible shrimp farming. It recommends six management practices that include filtering contaminated water. "Filtration would reduce pollution," says Dr Clay, "but", he adds, "It is not practised very much." If the mangroves were actually left intact, they would act as a natural biological filter to some extent but Dr Clay says: "Filtration will become more common in the future as farmers realise that it is cheaper and safer to use the same water over and over rather than bring in potentially tainted or disease-laced water to their farms."

However, the codes of practice are only voluntary and according to Dr Clay, will not help substantially: "In many cases the worst producers will not agree to comply without a parallel regulatory structure, investors that require it, or a certified market that demands it." Dr Clay has been working on an international certification system for farmed shrimp, which includes habitat protection, pollution control, and fair treatment of workers. Members of a UN committee on aquaculture support it, and he hopes he can get shrimp-farming countries to agree on standards within a couple of years. Let's hope it does not take too long before we realise the true cost of a prawn sandwich.