Fishing’s Hidden Carbon Footprint

Harvesting large fish like yellowfin tuna prevents the carbon in their bodies from sinking to the seafloor when they die. (Photo: Jeff Muir / NOAA)
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By Harrison Tasoff, UC Santa Barbara

A fish that dies naturally in the ocean sinks to the depths, taking with it all the carbon it contains. Yet, when a fish is caught, most of this carbon is released into the atmosphere as CO2. 

An international research consortium including scientists from UC Santa Barbara has estimated that because of this overlooked phenomenon, carbon emissions from fishing are actually 25% higher than what up to now was considered from fuel consumption alone. What’s more, part of the carbon extracted from the oceans comes from areas where fishing is not economically profitable in the absence of government subsidies. This study is published in Science Advances.

Carbon is a major component in the molecules that make up living tissue. Large fish like tuna, sharks and swordfish are composed of 10 to 15% carbon. When they die, they quickly sink to the deep sea. As a result, most of the carbon they contain is locked away for thousands or even millions of years. They are therefore literal carbon sinks, the size of which has never been estimated before.

This natural phenomenon, a blue carbon pump, has been greatly disrupted by industrial fishing.

“When we catch fish for our consumption, we also extract the carbon in their bodies, a fraction of which would have naturally sunk to the bottom of the ocean where it would have otherwise stayed, sequestered for many years,” said coauthor Juan Mayorga, a marine data scientist at UC Santa Barbara’s Environmental Market Solutions Lab.

Scientists had never estimated the amount of carbon extracted and released into the atmosphere as a result of fishing. “This is a step forward toward more holistic, science-based assessments of the status of fisheries management,” Mayorga said, “and opens the door to innovative financing models including tapping into carbon markets.”

Industrial fishing would therefore emit a double amount of CO2 into the atmosphere: not only do the boats massively emit greenhouse gases by consuming fuel oil, but in addition, by extracting fish from the sea, they release CO2 which would otherwise remain captive in the ocean.

"This is the first time that we have estimated the quantity of this ‘blue carbon’ that is released into the atmosphere by fishing," explained coauthor David Mouillot, a professor at the University of Montpellier. This estimate is far from negligible since researchers consider this carbon sequestration deficit in the deep ocean would represent more than 25% of the previous carbon balance of industrial fishing activities.

The researchers’ findings imply that estimates of carbon emissions from industrial fishing should be revised upwards. "Three quarters of these real emissions are related to fuel consumption, and one quarter comes from the fact that the carbon contained in the fish caught is released as CO2 into the atmosphere instead of remaining buried in the seabed," the researchers said.

For the authors of the study, these new data bring another strong argument in favor of more reasoned fishing: "The annihilation of the blue carbon pump represented by these large fish suggests that new protection and management measures must be put in place, so that more large fish can remain a carbon sink and no longer become an additional CO2 source,” said lead author Gaël Mariani, a doctoral student at the University of Montpellier.

Above all, we need to fish better, added Mouillot. Fishing boats sometimes go to very remote areas, which causes enormous fuel consumption, even though the fish caught in these areas are not profitable and fishing is only viable thanks to subsidies. Researchers estimate that 43.5% of this "blue carbon" extracted by fishing comes from such areas.

“We do not have to stop fishing to regain many of these carbon sequestration benefits,” said coauthor Steve Gaines, director of UCSB’s Bren School of Environmental Science & Management. “If we fish in the right places and at sustainable rates, we can rebuild a significant amount of this natural blue carbon sink."

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yacht rocked Jan 11, 2021 07:46 PM
Fishing’s Hidden Carbon Footprint

Perhaps the way to look at this is that we need to raise more Tuna as an NBS (nature-based solution), and stop government subsidies for tuna fishing, which would otherwise be unprofitable. It's a noble goal, but I admit I'm conflicted when I see that pallet of solid albacore tuna in Costco near the two-pack of quart size wasabi mayonnaise. Sometimes it sucks to be human....

Happy to have my body dropped off in the deep blue sea to make amends. I'm just not quite done with it yet.

BDM 1868 Jan 11, 2021 06:15 PM
Fishing’s Hidden Carbon Footprint

Fish that sink to the bottom get eaten by crabs.
Then the crabs get gas and fart. The bubbles float back to the surface and then Climate change!

fishnsurfn Jan 11, 2021 06:08 PM
Fishing’s Hidden Carbon Footprint

Pelagics follow and feed on schools of bait fish. Bigger fish feed on them. The sharks show up to the party and make sure almost nothing goes to waste, not even other sharks. Other creatures(to many to list) get the rest. This occurs mostly in the shallow regions i.e. on the continental shelves.

chico berkeley Jan 12, 2021 10:28 AM
Fishing’s Hidden Carbon Footprint

For someone who claims logic/science for your religion you really don't know what your talking about.
Absolute Zero is an impressive -460 degrees fahrenheit which is the temp I was taught was a temp that nothing can live.
Big diff between that and whatever you think is the "bottom" of the ocean.
Edhat needs some different PAID antagonists because the same 5 people are getting old.
Chow take nap.

dukemunson Jan 11, 2021 08:02 PM
Fishing’s Hidden Carbon Footprint

In pits defense... he/she is always wrong... so... as Leslie Neilson would say, “nothing to see here”. Notably I did recommend a while back that they go Costanza on, everything! but... no... they’ve stuck to their guns...

ChemicalSuperFreak Jan 11, 2021 07:35 PM
Fishing’s Hidden Carbon Footprint

Pit, sorry but you're totally wrong here. "... sinking down to really cold depths where bacteria can't go to work." In case you haven't heard, there are lots of extremophilic bacteria that function in the most inhospitable environments, include the cold ocean depths (psychrophiles). Here's one example: "Characterization of Psychrotrophic Bacteria in the Surface and Deep-Sea Waters from the Northwestern Pacific Ocean Based on 16S Ribosomal DNA Analysis" (

PitMix Jan 11, 2021 01:08 PM
Fishing’s Hidden Carbon Footprint

Are most fish in shallow coastal waters? Because the researchers must be talking about fish dying in the open ocean and sinking down to really cold depths where bacteria can't go to work.

fishnsurfn Jan 11, 2021 09:21 AM
Fishing’s Hidden Carbon Footprint

Natural death for fish in the ocean is that fish being preyed oppon. Flawed models,
flawed science. These "science" papers are just ways to perpetuate their ideology.

PitMix Jan 11, 2021 07:45 AM
Fishing’s Hidden Carbon Footprint

Fishing is one of the few industries left where the extractor doesn't have to put any inputs back to keep the industry going. Loggers have to plant trees, miners have to reclaim the mine sites, etc. As such, it is unsustainable and the factory ships from China and Japan will clear the oceans in the coming years.

Ahchooo Jan 10, 2021 08:51 PM
Fishing’s Hidden Carbon Footprint

The article doesn’t say we shouldn’t eat fish. Mostly it says we shouldn’t subsidize fishing in remote waters. The defensive comments are irrational.

a-1610346858 Jan 10, 2021 10:34 PM
Fishing’s Hidden Carbon Footprint

sounds reasonable to me to not subsidized fishing in remote waters; not only should there be some sanctuary for ocean dwellers but the ity concil amount of fuel expended must be sizable. ...Not so convinced about the move that's before the SB city council on Tuesday to ban non-electric utilities in new construction, a propos of greenhouse gases.

Sail380 Jan 10, 2021 07:05 PM
Fishing’s Hidden Carbon Footprint

How much carbon could be reintroduced into the ocean from burial at sea instead of a cemetery? Dispose of dead livestock the same way? Win win for the environment

MountainMan4865 Jan 11, 2021 07:19 PM
Fishing’s Hidden Carbon Footprint

Guess I should stop telling my relatives to just throw my body on one of the burn piles when I go....

MountainMan4865 Jan 10, 2021 11:39 PM
Fishing’s Hidden Carbon Footprint

Dead people sink. I would sink... but then gasses. And then I would be a floater, unless the yellow tuna ate me first, and then we would both be sinkers? I'm not sure how that works.

Sail380 Jan 10, 2021 10:08 PM
Fishing’s Hidden Carbon Footprint

Really? Why do divers recover bodies from the bottom of lakes and oceans? Do you ever watch the nature channels? There are several showing how a whale falls after death and supplies food to several creatures.

Ahchooo Jan 10, 2021 08:47 PM
Fishing’s Hidden Carbon Footprint

That’s an interesting concept. I was surprised that they said the large fish sink to the bottom when they die, and stay there, holding on to their carbon. Are there no scavengers or bacteria that eat up the dead fish? How long does the carbon stay there in the dead fish bodies? Very odd.

a-1610334324 Jan 10, 2021 07:05 PM
Fishing’s Hidden Carbon Footprint

Mere ignorance, such as repeatedly misspelling a word, isn't too offensive, because it can presumably be corrected by education. Willful ignorance however, such as denying the reality of AGW by ignoring an overwhelming body of facts, is worse than stupidity. Unfortunately, we're witnessing how that behavior has become widespread in an age where people don't apply critical analysis to what they are told by politicians, even when it is absent any evidence at all.

ChemicalSuperFreak Jan 10, 2021 04:31 PM
Fishing’s Hidden Carbon Footprint

"Yet, when a fish is caught, most of this carbon is released into the atmosphere as CO2." Sure, if you put the fish in an oxygen furnace and incinerate it. The truth is that someone will eat that fish and the carbon in that fish will be used to fuel the person who ate it and help to rebuild their carbon-rich tissues. What is not used is excreted as solid and liquid waste, not CO2. During metabolism (Kreb's cycle) some of those carbon units (acetyl groups) will be released as CO2 units and exhaled from the lungs as gas. I suppose denying the person this fish and starving them to death would put an end to this CO2 release. I wonder if these same scientists will do a similar study on the consumption of plants. Each plant that is harvested for food and materials is also a loss of a carbon sink. Think of all those carbon units in cellulose and starch can potentially be released into the atmosphere.... Where does the madness end?

a-1610391219 Jan 11, 2021 10:53 AM
Fishing’s Hidden Carbon Footprint

It's really much more useful to think a little more deeply about the problem. The biosphere has a number of carbon release/sequestration systems that have been operating for billions of years. Suddenly we are vacuuming up billions of tons of carbon that were in the oceanic cycle, and dumping them into another set of carbon cycles that were largely separate from that oceanic cycle. It makes a lot of sense to look at the implications, rather than deflecting, obfuscating, and dismissing them.

shorebird Jan 10, 2021 04:10 PM
Fishing’s Hidden Carbon Footprint

As a carbon unit myself, I’m going to continue to eat carbon units. And on top of that I’m going to continue to exhale. It’s a long term habit. Sorry.

a-1610320765 Jan 10, 2021 03:19 PM
Fishing’s Hidden Carbon Footprint

Title should read “UCSB’s Hidden Carbon Footprint.” All these global warming publications must have a huge carbon footprint.

Sail380 Jan 11, 2021 09:49 AM
Fishing’s Hidden Carbon Footprint

Absolutely true. How many electrons were killed running lights and computers while the scientist ate fish for dinner?

Chip of SB Jan 10, 2021 03:29 PM
Fishing’s Hidden Carbon Footprint

That’s for sure! And beyond that, think of how much good could be done addressing real environmental and humanitarian challenges around the world if we were not wasting so much effort on our Quixotic pursuit of CO2.

Chip of SB Jan 10, 2021 03:17 PM
Fishing’s Hidden Carbon Footprint

The philosophy behind “climate change” is to play on the guilt and insecurities that are inherent in human nature. The idea is to make people feel guilty for all that they enjoy in life. This guilt can then be exploited by governments to seize additional power and by businesses to make profits. The example of this article addresses seafood, which helps those who enjoy seafood feel guilty about it. However, a similar approach could be applied to anything. CO2 is a very carefully chosen “toxin” to focus on, because virtually everything related to life on earth releases or absorbs it. Think of something that you enjoy doing in life, and I bet I could articulate a reason why it contributes to the release of CO2. The endgame is that you are supposed to feel guilty whenever you experience pleasure. I see things a bit differently, so I will make a point of enjoying a delicious wild-caught fish this evening. And I won’t even feel guilty about it...

Chip of SB Jan 10, 2021 03:47 PM
Fishing’s Hidden Carbon Footprint

This is exactly what I was driving at Thomas. More regulations (government power) will be required to save us from the quixotic CO2 menace. Some businesses will naturally profit from the new regulations (typically larger more politically connected businesses). Other businesses will suffer (likely small ones, or your local fisherman). At the end of the day, the government will have more control over another aspect of life, large corporations will expand their dominance in another sector of the economy, and you will have to pay more for yet another product than you used to. But, as long as you go along with all that I guess you can feel a little less guilty...

Thomas John Jan 10, 2021 03:37 PM
Fishing’s Hidden Carbon Footprint

"“We do not have to stop fishing to regain many of these carbon sequestration benefits,” said coauthor Steve Gaines, director of UCSB’s Bren School of Environmental Science & Management. “If we fish in the right places and at sustainable rates, we can rebuild a significant amount of this natural blue carbon sink.""

Where is the guilt in this?

yacht rocked Jan 10, 2021 03:08 PM
Fishing’s Hidden Carbon Footprint

I would guess that dairy cows, cattle, and now Covid-19 deaths are having much more impact on carbon emissions.

ginger1 Jan 10, 2021 02:36 PM
Fishing’s Hidden Carbon Footprint

Here. Allow me to boil (or broil, or bake) this down for you: Using diesel-fueled/fossil-fueled boats to travel hundreds of miles out to sea to catch a few dozen large fish (or even a larger catch of smaller fish) is not cost-effective, fuel efficient and produces greenhouse gases and excess carbon far in excess of any benefits, along with the reality that sequestering that carbon at the bottom of the sea is better than releasing the from your barbecue.

No one is saying to not eat fish, just to gather them more sustainably. Which in this case is also generally more profitable in the end. In so many ways. Simple enough?

sacjon Jan 10, 2021 02:05 PM
Fishing’s Hidden Carbon Footprint

Glad I practice catch and release! Also, I hate the taste of fish, so not eating any commercially caught fish.

dukemunson Jan 10, 2021 01:55 PM
Fishing’s Hidden Carbon Footprint

Edhat : you jumped the gun and posted this too Early... this was obviously meant to be posted April 1st!!!

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