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What’s the Carbon Catch?
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What’s the Carbon Catch?

Most seafood is more climate-friendly than its terrestrial counterparts. But the latest controversies run deeper than simply wild-caught vs farmed.
September 8, 2023

Let the best of Anthropocene come to you.

Seafood production has quadrupled over the past 50 years, and almost all the extra fish have come from a rapidly growing aquaculture industry. Wild fish catches have remained largely stagnant since the 1990s. So, what does that all mean for carbon? 

Currently, if you swap a weekly beef burger for a fish sandwich, you’ll slash your meal’s carbon footprint by a factor of five and significantly reduce your chance of dying from heart disease to boot. 

That’s great. But there are many moving parts in the blue food equation. Overfishing and declining stocks mean that every fish takes more energy to catch than it did before. Fish farmers promise lower carbon seafood from ever larger operations, but they also have huge problems sourcing sustainable feeds. And then there’s the elusive white whale of zero-carbon seafood alternatives that avoid the ocean altogether.

Here we look at the obstacles your healthy fish sandwich will face in a low carbon world.

• • •

Wild-Caught Fish. The Fuel Problem


1.  There aren’t any electric trawlers. As stocks decline through overfishing, traditional fishing is one of the few modern industries getting less efficient over time. With some deep-sea fishing trips measured in weeks rather than hours, the industry is highly reliant on fossil fuels. Fishing fleets consume over 10 billion gallons of fuel every year, which is about 4% of the world’s carbon footprint for food production. And it isn’t getting any better. Researchers at the University of Tasmania calculated that the emissions per ton of fish caught increased by 21% between 1990 and 2011.

2.  Carbon trawled from the deep. Fishing boats also release carbon from destructive bottom trawling—where the seabed is scraped in search of shrimp, crab and flounder. This process disrupts carbon-rich sediments on the seafloor and releases as much carbon dioxide every year as jet planes, according to a study in Nature. “If we’re adding the entire aviation fleet’s worth of greenhouse gas emissions into the ocean every year just from trawling, that’s going to reduce the ability of the ocean to take up more atmospheric CO2,” one of the study’s authors, Trisha Atwood, told Vox.

3.  Choose the small oily fish. Which wild fish you choose can make a huge carbon difference. A comprehensive study by researchers at American University found that halibut, sole and lobster have about twice the emissions of an equivalent dish of chicken, and four times the carbon footprint of small oily fish like herring, sardines and anchovies. Cod and haddock are also good carbon choices.

The Carbon Footprint of Seafood

Source: Gephart JA et al. 2021. The Environmental Performance of Blue Foods. Nature, 592:397.

• • •

Farmed Fish. The Feed Problem

1.  Inventive diets for fish. Aquaculture now produces more seafood than capture fisheries, well over 100 million tons a year. But all those fish need to be fed, either with soybeans or fishmeal and fish oils for carnivorous fish. Around 70% of the carbon footprint of fish farms comes from their feed, and transporting chilled or frozen farmed fish around the world also has a big impact. But people are working on this, with low-carbon fish feeds that use flies or algae.

2.  Casting a wider net for farmed fish. With wild stocks of many fish in steep decline, fish farmers are trying species that have traditionally been impossible to raise in captivity. The Guardian has a really fascinating feature this week on emerging tuna-fish farms in Europe. It doesn’t delve deeply into their carbon footprint but discusses key issues around environmental and social justice. One aquaculture executive claims that farmed tuna will eat ten times less fish than wild tuna, and is exploring more sustainable plant-based feeds.

3.  Choose shellfish. As with wild seafood, there’s a massive variation in the carbon footprint of farmed fish. Shrimp, tilapia, and carp farmed in ponds in Asia all generate more CO2 than chicken, and can be large sources of methane, another powerful greenhouse gas, according Geoff Lutz of the Louisiana State University Agriculture Center. Farmed salmon and trout have similar emissions to wild-caught. But there are some clear climate wins for farmed seafood. Because clams, mussels, and seaweed don’t require feeding, they have almost negligible CO2 emissions and in fact clean harmful nitrogen and phosphorus from marine ecosystems.


• • •

Alternative Seafoods. The Market Problem

1.  Test-tube tuna. A cell-cultured replica of Pacific bluefin tuna toro, made by San Diego startup BlueNalu, served up a “a butter-soft flavor bomb,” writes Kenny Torella at Vox. Other startups are working on cultured salmon, shrimp, lobster and crab. The flavor seems to be there and the carbon footprint of such lab-grown seafood would be almost zero, but companies are struggling to get prices down, factories built, and regulators convinced.

2.  Beyond the Impossible Burger. Plant-based beefburgers claim to have about one tenth the carbon footprint of their meaty rivals. Plant-based seafood likely won’t match that simply because beef is such a greenhouse gas monster but a few products are already on shelves. The fake salmon burgers, crab cakes, scallops and shrimp are made from chickpeas, algae, lentils and other vegetables. And the taste? NY Magazine didn’t seem entirely convinced by tuna burgers, although Ktchn Rebel enjoyed some vegan shrimp.

3.  Will it move the market? The problem with innovative food products is that consumer behavior can be hard to shift. “I think the hardest hurdle will be getting people to change their consumption behavior – not just to start eating this new product that they are unfamiliar with, but also to stop eating wild-caught fish,” says Benjamin Halpern, a marine biologist at the University of California, Santa Barbara, who studied the link between new foodstuffs and marine ecosystems. For the more established plant-based meats, the jury is still out, according to several studies. A UK campaign last year to promote plant-based alternatives managed to increase families’ consumption of plant-based meat by an impressive 57% – but made no dent in their consumption of actual meat. Why should seafood be any different?

• • •

What To Keep An Eye On


1.  Fossil fuel subsidies for fisheries Last year, the WTO announced a ban on subsidies for illegal fishing and fishing on overfished stocks. But those account for only a fraction of an estimated $22 billion in harmful fishing subsidies around the world, say scientists at the University of British Columbia. They note that subsidies can lead to higher CO2 emissions by making fuel cheaper, and are lobbying for tighter rules. 

2.  Co-farming carbon Some seafood farms could also be ideal locations for carbon sequestration efforts. Carbon Kapture is a UK start-up focused on trapping and locking away carbon in seaweed, which is then processed into stable biochar. This spring, the company partnered with shellfish farmers in County Donegal, Ireland, citing the farmers’ ability to host and scale its seaweed production alongside their own seafood. 

3.  Fish farming on dry land Many problems associated with fish farming, including pollution, escaping fish, and massive water use, arise because aquaculture facilities have historically been located in marine net-pens or outdoor ponds. Moving the whole process indoors to Recirculating Aquaculture Systems (RAS) – think aquariums on steroids – reduces water use by a factor of about five thousand by filtering and recycling it. RAS farms make a lot of sense for maintaining biodiversity and water conservation, but aren’t so hot when it comes to carbon – every kilo of fish produced this way consumes roughly two to six more kilowatt-hours of energy than a traditionally farmed fish, mostly to power pumps. 

Top image: ©Anthropocene Magazine

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