Climate-Friendly Seafood - Is There Such a Thing?

Wollwerth Imagery @ Adobe Stock

Editor's Note: We're continuing our coverage of all things ocean and seafood for this year's World Ocean's Day with this piece on the connections between seafood and climate change. You can do your part to help by taking the Sustainable Seafood Shopper's Pledge!   

Discussions around the carbon footprint of our diets tend to focus on burping cows and ever-expanding fields of corn and soy. It can be tempting to point towards fish as a universally climate-friendlier alternative. Just think: no belching or fields to fertilize! However, fish both wild-caught and farmed are indeed responsible for greenhouse gas emissions. That impact can vary widely depending on a large and complex number of factors including the health of fisheries, what fish eat, how they are caught (or farmed) and how they make their way to your plate. Fish consumption around the world is growing, and a third of commercial fisheries around the world are being fished at unsustainable levels. Long term, climate change is leading to rising ocean temperatures and acidifying waters. With these pressures mounting on already stressed supplies of seafood, it's time to take a closer look at how the fish we eat might play a role in climate change, and how climate change may ultimately harm fish.

Emissions Through the Seafood Supply Chain

The fish we eat can be either wild-caught or farmed, and in both cases the first portion of the supply chain - either catching or farming - represents the biggest portion of their carbon footprints. For wild-caught fish, emissions are largely from the fuel burned to power a fishing vessel and freeze or cool the fish once they're onboard. Emissions from farmed fish, on the other hand, primarily come from feed. For both kinds of fish, a sometimes significant source of emissions is produced by transportation, depending on the distance that fresh or frozen fish travel and what mode of transportation is used. Estimating the carbon footprint of fish is fraught with a large number of variables in an industry not exactly known for transparency. Still, there is much to be learned by looking at the key components of carbon footprints of wild-caught and farmed fish.

The Carbon Footprint of Wild Fisheries

The carbon footprint of wild fish primarily comes from the burning of diesel fuel. Fishing vessels use large amounts of fuel for processing fish onboard, refrigeration and freezing, but most of their fuel goes towards powering ships to, from and around fishing grounds. Due to the decline of many popular fish species, vessels are traveling further and for a longer time from port to pursue species that once were abundant and easy to catch, requiring more fuel than before.

But beyond changes to the health of fisheries, different species and how they are typically caught require widely differing amounts of fuel. A study that looked at 1,600 fishing vessels from around the world added up the fuel used to catch and bring various types of fish and seafood to port. On the low end, sardines and other forage fish like herring and anchovies tend to school together and are found close to shore, making it easy for fishermen to catch them with enormous nets called purse seines. In turn, it doesn't take a whole lot of fuel to land these species. On the extremely high end, some shrimp and lobsters (make that Norway lobsters; their Maine counterparts are relatively fuel efficient to catch) are small in size and scarce, so fishing boats have to pull their nets for long distances to catch them, which requires a lot of fuel.  

One would think that higher fuel use would encourage changes in how and which fish are caught given that it's getting more expensive for fishermen to catch the same amount of fish.  The problem is that many nations still subsidize their fishing fleets, specifically fuel costs, which keeps the economic realities at bay and encourages overfishing and continued pressure on rapidly depleting fish stocks, particularly on the poorly-regulated high seas. It's a bad cycle: subsidies encourage more fuel use and more CO2 emissions without factoring in the impacts to fisheries from both overfishing and future climate change.

The Carbon Footprint of Farmed Fish

While most of the carbon footprint for wild-caught fish comes from fuel use, for farmed fish the culprit is feed. The notable exception, however, are land-based fish farms where energy use to regulate temperatures and circulate water can be the top source for greenhouse gas emissions. To understand the emissions impact of feeding fish, you need to know what kind of feed is used and how efficiently the fish converts food into growth, known as the feed conversion ratio. Feed conversion ratios for farmed fish are generally lower, sometimes significantly so, than livestock and poultry.

Exactly what farmed fish are being fed is also an important factor. Most commonly, carnivorous farmed fish species like salmon are fed a mix of fish meal and fish oil (made from of small forage fish like anchovies, herring and menhaden) along with plant proteins from corn and soy. Because forage fish are of course wild fish, the fuel used to power the boats that catch them also plays a big factor in the size of the carbon footprint of farmed fish. Unique to farmed fish, however, are the emissions from corn and soy production as a result of fertilizer use and deforestation, for example.

Feed conversion ratios and feed types shouldn't be viewed in a vacuum.  A quarter of the world's fish catch is used for fish meal production, and 90 percent of that catch could be used for direct consumption by humans. Instead of preparing delicious and nutritious - but yes, small - fish for dinner, we're  less efficiently feeding them to other fish that we've developed a taste for, like salmon. Unfortunately, some farmed fish that naturally eat a vegetarian diet are unnecessarily being fed fish oil to speed their growth, like tilapia and carp at Chinese fish farms. So the choice of farmed fish species that we eat, as well as what we feed them, has a direct impact on not just their carbon footprint but also the health of wild fish species towards the base of the oceanic food chain.

How to Make Climate Friendly Fish Choices

The good news is that if you eat fish, in general you have a lower carbon footprint than someone who eats meat. A UK study found that fish eaters on average have a 46 percent smaller carbon footprint than those who eat a lot of  meat each day, and 16 percent smaller than those who eat just a little meat. But the devil can be in the details, because farmed salmon, for example, has been found in some cases to have a higher footprint than chicken, which in turn has a nominally larger footprint than canned tuna. As you've already read here, different methods of catching, farming, processing and shipping the fish can lead to very different results.

With that in mind, the best way to choose climate-friendly fish might be to look beyond the limited number of carbon emission estimates, and pay more attention to the health of wild fisheries and the impacts of farming techniques. As it turns out, there's a good amount of overlap between typical measures of sustainable fish and lower greenhouse gas emissions. So what should you look for?

  • If you have access to locally caught fish in the US, especially species besides the usual shrimp, tuna and salmon trifecta, try them out! This way you support local fishermen who are following strict federal sustainability guidelines. That said, if there doesn't happen to be a fishing pier nearby, choose US-caught fish since we have the most advanced fisheries management system around.
  • If you're choosing fish that is shipped from far away, go with frozen instead of fresh. At least one study has found that transporting fish that is flash-frozen at sea has a lower carbon footprint than transporting fresh fish.
  • Eat fish lower on the food chain. For wild fish, try eating small fish like sardines, anchovies and herring. For farmed species, focus on tilapia, catfish and carp which only require vegetarian feed, not ground-up small fish from the ocean. If grown in on-land, recirculating systems, there's no danger of them escaping in to the wild or passing along diseases to wild fish.
  • Follow the sustainable fish guides! There are lots of different ones to try, but they can be a valuable tool to help you do some carbon footprint sleuthing. Fisheries in good health and caught sustainably tend to use less fuel because fishermen don't have to search for dwindling fish or use fuel-intensive and destructive technologies like bottom trawling. In fact some fishery eco-labels may soon include information on the carbon footprints of specific fish.
  • Farmed oysters, mussels and clams and other shellfish are all great options. They have very small carbon footprints because they don't need any additional feed (free-floating plankton work just fine, thank you), and in fact they can sequester carbon as they build their shells. As a bonus, these filter feeders are great at cleaning up the water around them.

There are no global estimates of greenhouse gas emissions from commercial fishing and aquaculture. But we do know that the industry's contributions of greenhouse gasses are self-sabotage. The ocean stores nine-tenths of emissions-driven heat on Earth, and already fish and other marine organisms are migrating towards cooler waters of the North and South Poles. Acidifying waters due to carbon emissions are threatening corals and animals that grow shells like crabs, oysters and clams. Much of the world's aquaculture is not immune from these oceanic threats thanks to its dependence on wild forage fish for feed. Policy shifts, international cooperation, improved technology and assistance for fishermen are all necessary changes. But don't discount your power as a consumer. Signaling that we want sustainably caught and yes, low carbon fish is important not just to help fight climate change, but to help preserve the fish we want to see on our plates.