What’s Behind the Prawn Sandwich?

Your cheap prawn sandwich may be destroying Sri Lanka's mangroves. PHOTO: Aldi

Your cheap prawn sandwich may be destroying Sri Lanka’s mangroves. PHOTO: Aldi

A swelling appetite for shrimps and prawns in America, Europe and Japan has fuelled industrial farming of shellfish in the past few decades. The industry now has a farm-gate value of $10 billion per year globally and the prawn in your sandwich is much more likely to have come from a pond than from the sea. While the industry is dominated by the likes of China, Vietnam and Thailand, a large number of other countries have invested heavily in cultivation too.

 One is Sri Lanka, which saw the industry as a passport to strong economic growth and widespread employment. Just outside the world’s top ten producers, it accounts for approximately 50% of the total export earnings from Sri Lankan fisheries. More than 90% of the harvested cultured prawns are exported, going mostly to Japan.

Prawn aquaculture has been likened to slash-and-burn cultivation—find a pristine spot, remove the vegetation and farm it for a few years before moving on. But the analogy is misleadingly benign. Slash-and-burn systems on a small scale can be sustainable, since the cut plots can recover afterwards.

Prawn aquaculture has been likened to slash-and-burn cultivation—find a pristine spot, remove the vegetation and farm it for a few years before moving on. But the analogy is misleadingly benign. Slash-and-burn systems on a small scale can be sustainable, since the cut plots can recover afterwards.
In the case of prawn farming, a better phrase would be “slash and sink”. Mangroves are among the most carbon-dense of all ecosystems, often storing more than 2,000 tonnes of carbon per hectare in sediments beneath the forest floor, according to research that our group has yet to publish. Cut them down and this carbon is oxidised and emitted into the atmosphere as carbon dioxide.

An additional issue is the sinking shoreline. In the face of global rising sea levels of more than 3mm a year, healthy mangrove forests are among the best protection since they bind together sediments and even elevate their soils to match the rising tide. Lose them and the chances of coastal subsidence, erosion and storm damage goes up.

In fact, mangroves are such useful ecosystems that destroying them almost never makes sense, even from a narrow economic perspective. Arecent analysis in southern Kenya showed that conserving and restoring the forests was worth at least $20 million more in present value than allowing current cutting to continue.
Read more on what Sri Lanka has to do to preserve its coastlines and marine stock.

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