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Can Shrimp Farming be Sustainable?

Per kilogram, shrimp themselves emit a miniscule amount of carbon dioxide equivalent emissions. This is according to some good scholarship by Rifqi et al. (2020), but it flies in the face of what most climate-savvy consumers believe.

Headlines such as "The jumbo carbon footprint of shrimp" might imply that the organisms themselves are vast polluters, but this is a mistake. It is the shrimp industry that has a massive carbon footprint and it is for one simple reason that this is the case.

a mangrove forest
a lovely mangrove

The beautiful, highly respectable mangrove.

A mangrove is a type of forest that is found on coastlines in brackish environments (which just means the water is not as salty as the sea, but is still salt water). See the tangling, complicated root structures? They mean that mangroves are among the safest places for fish, who often visit them to raise their young in safety.

Mangroves are also a haven for trapped carbon in such a way that even dwarves the rich soils of the Amazon. The Center for International Forestry Research conducted a longitudinal study investigating the carbon credentials of mangrove forests and they are jaw-dropping. Mangrove forests rely on a lot of mud and unusually it is in this mud that most carbon stocks in the ecosystem are found. This carbon is not just stationary, it is part of the ecosystem's carbon cycle.

Okay, so what has this got to do with shrimp? You might have an inkling. The most popular farmed shrimp species in the world, the vannamei, is a delicate creature and can only grow in brackish water (of a particular pH, oxygen level and stocking density). Farmers wanting to cash-in on high shrimp prices would be incentivised to avoid the high costs of building an maintaining a proper shrimp farming system (e.g. RAS) and would instead go for a cheaper, shorter term solution: buying a patch of land near the coast with brackish water and then digging a shrimp pond.

fishing nets
a tricky situation to untangle

To make space for the shrimp pond, the mangrove is destroyed. All the carbon in the soil is released - up to three meters below the ground. That is why mangrove forests are estimated to emit over 10% of tropical deforestation's total carbon emissions, despite making up less than a percent of tropical forest area. The impact of mangrove deforestation doesn't stop there either - remember all those fish that make mangroves their nursing grounds? They'll lose out, impacting almost all of the ocean's trophic level flow in the process.

What makes all this even worse is that mangrove shrimp ponds aren't used for a very long - 5 years on average in the aquatic version of slash and burn agriculture. The consequence is that if you eat a 100 gram shrimp cocktail with shrimp that came from a former mangrove, that shrimp cocktail has the same carbon footprint as burning 90 litres of petroleum according to Boone Kauffman of Oregon State University.

How depressing.

But shrimp farming doesn't need to be unsustainable, quite the opposite. We've seen that shrimp don't emit much CO2 themselves and, if they're reared in proper long-term ponds with water treatment systems and if they are fed sustainable sources of protein (the lower carbon the better), they have the potential to be one of the most environmentally friendly sources of animal protein out there. People just need incentives to avoid deforestation, which can be achieved through responsible governance as well as effective use of carbon markets. When you put a price on carbon produced, the financial incentive to farm in a mangrove region is reversed.

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