The food we eat accounts for about a quarter of the world’s carbon footprint, mostly from farming crops and raising livestock. While wild seafood caught from the ocean is a small slice of that pie, the greenhouse emissions tied to global fishing have increased in recent decades, a new study has found.

Around 3 billion people depend on seafood for protein. Yet marine fisheries’ emissions have often been either excluded from food production emissions calculations or estimated from a limited number of case studies, according to Robert Parker, a postdoctoral fellow at the University of British Columbia’s Fisheries Economic Research Unit.

In a recent paper, Parker and his coauthors compiled more data to calculate a more accurate global estimate of fisheries emissions. In 2011, marine fisheries made up 4 percent of carbon emissions from global food production, the study found – and emissions had grown by 28 percent since 1990. A large portion of that growth was related to more fishing for crustaceans. These fisheries had by far the most emissions per landing – or metric ton of fish caught – while small fish, such as anchovies and herring, had a lighter carbon impact.

Although Parker said the emissions are relatively small on a global scale, individual nations that rely on seafood may be able to use this information to meet their own national greenhouse gas emissions goals. For example, most of Iceland’s food production-related emissions are from marine fishing.

Oceans Deeply spoke to Parker about the source of fisheries emissions and what can be done to reduce them.

Oceans Deeply: Why have fisheries been left out of food production emissions data?

Robert Parker: I think the focus on fishery science has always been on the biological measures – knowing how many of a certain species are in the ocean to determine how many we could take out.

But because fuel use and greenhouse gas emissions aren’t really related – directly, anyways – to those biological measures, they haven’t been looked at as much when it comes to studying fisheries. So the data just weren’t available to underpin those analyses. As climate change has become a more important issue, that has been the impetus to then look at fisheries again from these other perspectives.

Oceans Deeply: The most obvious emissions in fisheries come from fuel used in boats to catch fish. But in this paper, you also look at non-fuel-use emissions. What are non-fuel-use emissions in fisheries?

Parker: The inputs to vessel construction, the provision of steel and aluminum and other materials to build a vessel. What are the emissions associated with that? What are the emissions associated with providing the gear, the trawls or the traps or the purse seine nets? What are the emissions associated with the use of different chemicals on board, or generating electricity on board or the use of refrigerants to keep your product cool on its way back to port?

All of these different things could be associated with greenhouse gas emissions. Generally, we see that somewhere between 60 and 90 percent of the carbon footprint of a fishery is associated with the fuel itself. So, the other 10–40 percent is these non-fuel sources of emissions.

Oceans Deeply: Fishing for crustaceans, such as lobster, seems to have an especially high amount of emissions per landing. What is happening there?

Parker: It largely just comes down to catch rates. These are species that we’re not going out and catching tons and tons at a time and bringing them in with a great big net like we do anchovies and herring. Just that difference in catch rate would explain the larger amount of fuel per unit of catch for the crustacean fisheries.

Oceans Deeply: You show that other places, such as the west coast of South America, have particularly low emissions per landing. Why is that?

Parker: It’s all completely explained by one fishery. It’s called the anchoveta, or Peruvian anchovy, fishery. In most years, it’s [one of] the largest fisheries in the world.

They do it with purse seine vessels, where you have a large net that circles around a school of fish and then you scoop them up. They target this very small pelagic fish that schools in very large groups and you catch thousands or millions of individual fish quite quickly with a small number of vessels. It just doesn’t use very much fuel – around 15–20 liters [4–5 gallons] per ton [of fish].

Oceans Deeply: If fisheries want to decrease their emissions, should they focus more on these smaller pelagic fish?

Parker: I’m not going to suggest that we should be catching more of any individual fish because those fishery management decisions need to be based on ecological and biological [data]. But one thing that we could do is eat more of those small pelagic fish.

Most of the anchovies and a lot of other small pelagic fish that we catch are used for industrial purposes – reduced into fish meal and fish oil for aquaculture feed – which is important because we like to eat aquaculture fish and we need to feed them something. But we should recognize that if we ate those anchovies and herring and mackerel directly, rather than feeding them to other animals, we would get more food for less carbon.

Oceans Deeply: How can fisheries reduce those non-fuel-use emissions?

Parker: There are three things. One is that improving catch rates and improving [fish] populations where they’re low is going to reduce emissions from all sources.

Another one is reducing the use of certain refrigerants. We’ve switched from using CFCs, which are ozone-depleting refrigerants, to things like HCFCs – but those are greenhouse gas refrigerants. Finding and using refrigerants that are not potent greenhouse gases can reduce these non-fuel emissions.

And another one is avoiding flying your product by air. Lobster fisheries in Australia are selling lobster to China. Largely, they’re flying those products. That flight alone doubles the carbon footprint of the product – a product that already has a lot of emissions from the fishing stage. And that’s something that we see with a lot of crustacean fisheries because they have a high [economic] value, so it’s worth it to fly them because the price makes up for it.