The Carbon Footprint of Fish

Is eating fish a more environmentally friendly alternative to eating meat? In this blog, we unpack the carbon footprint of fish.

Fishing boat dragging a net throught the water of the Waddensea, The Netherlands. Lots of seagulls
Image Credit: AdobeStock

Discussions about diet and climate impact tend to focus on cows, who are (through no fault of their own) the biggest contributors to climate-changing emissions in agriculture.

However, they are by no means the only contributor. Increasingly the impact of fish – both farmed and wild-caught – is coming under scrutiny.

How does bottom trawling drive climate change?

The ocean is the world’s biggest carbon sink and absorbs about 31% of global CO2 emissions each year.1 Mangroves, kelp forests and seagrass meadows all play a role in capturing carbon but are being destroyed to satisfy the world’s demand for seafood.

While these are serious issues that must be addressed, it is bottom trawling that causes the greater climate problem. The ocean floor, which is a vital carbon sink, is being ploughed over and over by bottom trawlers. Their weighted nets gouge scars in the sea floor, releasing stored carbon back into the ocean. If the ocean is saturated with CO2 from the seabed, it is less able to absorb it from the atmosphere.

A 2024 study estimated that a staggering 8.5 to 9.2 billion tonnes of CO2 have been released from trawling into the atmosphere between 1996-2020. The researchers also found that 55-60% of the CO2 released by trawlers will be in the atmosphere within nine years.2 A 2021 study published in Nature calculated the impact of bottom trawling as one gigaton of carbon each year – more than all (pre-pandemic) aviation emissions combined.3 But the damage caused by bottom trawling doesn’t stop there.

Fishing vessel. Great catch of fish in thrall. The process of casting the fish in the tank. Large freezer trawlers.
Image Credit: AdobeStock

Bycatch Drives Climate Change

The nets dragged along by trawlers are immense – some are big enough to fit 10 jumbo jets inside – and they scoop up any creature unlucky enough to be in their path. This includes whales, dolphins, sharks and porpoises, and the deaths of these creatures are not only a tragedy – it’s a climate issue, too.

A 2019 International Monetary Fund report found that protecting large sea creatures is actually more important for the climate than planting trees because the animals accumulate carbon in their bodies throughout their long lives, and when they die, the carbon remains locked away in their bodies at the bottom of the ocean.4 Scientists have called destructive practices such as bottom trawling ‘marine deforestation’ because of the extent of the damage they cause.5

If we stopped fishing, we would stop bycatch, which would allow carbon to accumulate in large creatures, and the seabed with its carbon stores would remain intact.

Green Sea turtle entangles on a discarded fishing net
Image Credit: AdobeStock

Is fish farming better for the environment?

It would be tempting to think that fish farming could solve the climate impact of the fishing industry, but this is not the case because many farmed fish – particularly salmon and trout – are fed wild-caught fish. Farmed salmon, for example, has a bigger carbon footprint than chicken or turkey and generates more than 4kg of carbon emissions per kilogram of salmon.6

About half of the fish consumed today comes from fish farms and these are far from environmentally friendly. Like all factory-farmed animals, fish live in crowded, squalid conditions and are fed an array of drugs to try to control the viruses, bacteria and parasites that infect them. These drugs are toxic and cause serious pollution in the wild.7 One report found that pollution of one such toxic pesticide in Scottish lochs had increased by 72 percent in a year.8

Shrimp farms also cause problems for the environment. Production has increased by 1,000 percent over the last 30 years and it is a key driver in mangrove forest loss.9,10 Mangroves are a type of tropical forest, rich in biodiversity and important for mitigating climate change. A quarter of mangrove forests have been lost in the last 40 years.11

When Oxford University researcher Joseph Poore undertook the biggest study to date of the environmental impact of different foods, he was surprised by the impact of freshwater fish farming, which provides two-thirds of such fish for the Asian market and 96 percent for the European market.12

Poore told The Guardian: “You get all these fish depositing excreta and unconsumed feed down to the bottom of the pond, where there is barely any oxygen, making it the perfect environment for methane production.” Methane is a potent greenhouse gas commonly associated with cow burps, but it is also an issue in the fishing industry.

Dead corals after bleaching,  Raja Ampat Indonesia
Image Credit: AdobeStock

Is the fishing industry sustainable?

Taking vast numbers of animals out of their habitat causes significant damage to ecosystems. It causes whole populations to collapse, which triggers collapses in the species who rely on them for food and a boom in the number of species that are preyed upon by them. In this way, the entire ecological system is destabilised.

Add to this the destruction of the ocean floor, seamounts and coral reefs by trawlers and the plastic pollution which comes in large part from the fishing industry13,14, and we start to see the immensity of the damage caused by our over-consumption of fish.

Renowned marine biologist Dr Sylvia Earle says: “I have looked long and hard, seriously, at trying to find an example of where a large-scale extraction of wildlife is sustainable. It just doesn’t exist.”

The climate impact of farmed fish is far larger than for plant-based foods such as tofu, nuts and legumes. To protect our planet, its inhabitants and our future, we should be choosing plants.

For more information about choosing plant-based alternatives to fish, check out our Choose Fish-Free campaign.


1. Gruber, Nicolas, et al. “The Oceanic Sink for Anthropogenic CO2 from 1994 to 2007.” Science, vol. 363, no. 6432, 14 Mar. 2019, pp. 1193–1199, Accessed 28 May 2024.

2. Atwood, Trisha B, et al. “Atmospheric CO2 Emissions and Ocean Acidification from Bottom-Trawling.” Frontiers in Marine Science, vol. 10, 18 Jan. 2024, Accessed 28 May 2024.

3. Sala, Enric, et al. “Protecting the Global Ocean for Biodiversity, Food and Climate.” Nature, vol. 592, no. 592, 17 Mar. 2021, pp. 397–402, Accessed 28 May 2024.

4. Chami, Ralph, et al. “Nature’s Solution to Climate Change.” International Monetary Fund, Dec. 2019, Accessed 28 May 2024.

5. McVeigh, Karen. “Carbon Released by Bottom Trawling “Too Big to Ignore”, Says Study.” The Guardian, 18 Jan. 2024, Accessed 28 May 2024.

6. Environmental Working Group. “Meat Eater’s Guide to Health and Climate.” EWG, 2011, Accessed 28 May 2024.

7. Wild Fish. “Responsibly Farmed? Investigating the Certification of Scottish Farmed Salmon.” Wild Fish, Sept. 2023, Accessed 28 May 2024.

8. Edwards, Rob. “Fury as Fish Farm Pesticide Pollution Rises 72% in a Year.” The Ferret, 7 Oct. 2020, Accessed 28 May 2024.

9. Food and Agriculture Organization. “FAO Fisheries & Aquaculture.” FAO, Accessed 28 May 2024.

10. Environmental Justice Foundation. “Farming the Sea, Costing the Earth: Why We Must Green the Blue Revolution.” EJF, 2004, Accessed 28 May 2024.

11. UN Environmental Programme. “5 Facts about Mangroves and Why We Must Protect Them.” UNEP-WCMC, 26 July 2020,

12. Carrington, Damian. “Avoiding Meat and Dairy Is “Single Biggest Way” to Reduce Your Impact on Earth.” The Guardian, 20 Nov. 2018, Accessed 28 May 2024.

13. WWF. “Stop Ghost Gear: The Most Deadly Form of Marine Plastic Debris.” 2020, Accessed 28 May 2024.

14. Greenpeace. “Ghost Gear: The Abandoned Fishing Nets Haunting Our Oceans.” Greenpeace, 2019, Accessed 28 May 2024.

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