For someone looking to make their diet more sustainable, the choices when it comes to eating seafood can be frankly baffling.
It's a vast category of food that includes everything from farmed prawns to wild-caught mackerel, and can have a huge array of environmental impacts, from high carbon emissions to the nasty effects of overfishing, slaughtered bycatch or antibiotic pollution.
Many people seeking to eat more environmentally choose to eschew it altogether and go for the vegetarian or vegan option.
But some seafood can be low-carbon, low environmental impact and also be a healthy source of food. And if you're going to eat fish, making sure you choose a more sustainable option can make a huge difference.
"The category of seafood is really diverse," says Jessica Gephart, assistant professor in environmental science at the American University in Washington DC. "It includes around 2,500 different species produced by farming and capture fisheries. We're really talking about very different production systems there."
Within this, there are some "really great opportunities for finding really sustainable options within that", she says.
To try to untangle my concerns about the sustainability of being a seafood eater, I decided to experiment by tracking my own seafood consumption for a month
I've had a bit of an up and down relationship with eating seafood. Previously a long-time vegetarian, I started eating fish about 10 years ago after a coeliac diagnosis stopped me eating wheat, persuading me to open up some other food options. Living in Britain in 2022, a time when plant-based alternatives to meat are skyrocketing, I actually find I don't rely on fish very often, but I do eat it occasionally.
To try to untangle my concerns about the sustainability of being a seafood eater, I decided to experiment by tracking my own seafood consumption for a month. I noted all the information I could get my hands on about what I was eating, including where and how each fish was caught, to see just what is information is typically available to seafood consumers, at least in the UK.
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I then talked to several experts who spend their lives trying to improve the way we catch, farm and eat fish, to understand where I could be making better choices.
So where to start with the information you can get hold of? And how to make judgement calls about the fish you can't get information on?
A warning: there are few easy answers. But there are some general rules that can be helpful to keep in mind – first and foremost, that warning bells should go off if your supplier can't tell you where your fish comes from, though some types of fish do tend to be more environmentally friendly in general – and some handy sources of information on specific seafood.
Consider this a starting guide to a thorny issue that is not going away.
The amount of fish and seafood caught or farmed globally is set to rise to 202 million tonnes in 2030 (Credit: Munir Uz Zaman / Getty Images)
The seafood industry
Fish and other seafood are a huge source of food globally. Some 178 million tonnes were caught or farmed in 2020, set to rise to 202 million tonnes in 2030, with the rise mainly coming from aquaculture. Per capita consumption of seafood around the world has doubled since the 1960s, to 20kg per person per year.
The people most in need of fish
Seafood is among the most traded commodities globally, but it is crucial to ensure it is not being exported away from local people who need it for nutrition, which research has shown is happening in countries such as Mauritania and Kiribati. Greater transparency around the distribution of fish, and incorporating nutrition into trade agreements, could help address this.
The industry is also a huge source of employment. Around 59 million people work directly for the fisheries and aquaculture industry, but including subsistence fishing and secondary jobs, some 600 million livelihoods depend at least partially on the sector – that's around one in every 13 people on Earth.
Seafood is a crucial source of protein and essential nutrients people around the world, with around three billion people relying on it as a primary source of protein.
At the same time, farmed and wild caught seafood rightfully continue to be a source of huge concern over everything from labour rights and bycatch to environmental damage from trawlers and carbon and nitrogen pollution.
Overfishing of stocks is another big worry: the Food and Agricultural Organization (FAO) estimates that only 65% of fishery stocks in 2019 were operating at biologically sustainable levels.
A guide through the haze
I ate fish six times during the period I tracked. Three times this was haddock in a fish supper (I am Scottish, after all). One restaurant told me the haddock was line-caught in the North Atlantic Ocean. Another named the small fishing village in Scotland the haddock came from but couldn’t tell me the catching method. The third told me their haddock came from Aberdeenshire, Scotland, and was "sustainably trawled".
I also ate salmon in a sushi takeaway in Edinburgh which told me it was farmed in Scotland; cod caught in the Barents Sea using an otter trawl; and mackerel fillets from a supermarket wild caught in the North East Atlantic Ocean (no catching method given). To my knowledge, none of these had any sustainability certificates.
You've got wild, farmed, a dozen different species caught in hundreds of different places with different ways of catching them and farming them – Jack Clarke
Armed with this information, the most useful thing I found to help me understand it was the UK-based Marine Conservation Society (MCS)'s Good Fish Guide. This searchable guide is an incredibly useful source of information on the sustainability of specific fish sources. The US equivalent, Seafood Watch from the Monterey Bay Aquarium, is equally useful.
Where to get seafood ratings for my country?
The Good Fish Guide and Seafood Watch are focused on fish sold in the UK and US respectively, although since seafood is a global industry many of their ratings are relevant for fish sold in many other countries. The wider Global Seafood Ratings Alliance lists similar organisations from around the world.
Both operate on a traffic light system, based on local regulations, how capture fisheries and farms are managed, and the health of fish stocks. These are all aspects of understanding if the resource is "sustainable" – i.e. whether current management means it will continue to be available year after year. The apps both have helpful "best choice" lists.
"With meat, it's a bit easier: you go into the supermarket and you want to buy a chicken and you're faced with maybe three options," says Jack Clarke, sustainable seafood advocate at the Marine Conservation Society (MCS), a UK-based non-profit.
"Seafood is a lot more complicated. There's a lot of variables in there. So you've got wild, farmed, a dozen different species caught in hundreds of different places with different ways of catching them and farming them."
The MCS started the Good Fish Guide to help guide people through this hugely diverse array of seafood, says Clarke.
Around three billion people worldwide rely on fish and seafood as a primary source of protein (Credit: Getty Images)
I found the Good Fish Guide app, which has 600 ratings for around 140 species, relatively easy to use while shopping – so long as I could get hold of the required information about the fish I’m about to buy.
Is farmed or wild-caught fish better?
It's complicated! Farmed fish can leak nutrients like nitrogen and phosphorus into the environment, use up land and freshwater, risk spreading disease and antibiotic resistance, and can be fed on wild-caught fish, but usually have lower greenhouse gas emissions.
Wild-caught fisheries avoid nutrient pollution and don't use up land or freshwater, but emit greenhouse gases from the fuel used in boats, and can have devastating impacts on ocean ecosystems through overfishing, bycatch, seafloor destruction and plastic pollution.
A good starting point is to check the Good Fish Guide and Seafood Watch ratings of the sustainability of different fish sources.
It indicated that the haddock and cod I ate were likely a 2 (out of 5, the best being 1) rating, while the Scottish farmed salmon was a 3 (better than the 5 rating given to wild-caught Atlantic salmon).
The mackerel could have been a 1, 2 or 3, depending on the exact catching method and exactly where it was caught, which I didn’t know.
It’s not terrible, but I realise I could be doing far better on this by looking specifically for the 1-2 rated sources.
Sarah Poon is the associate vice president of the Fishery Solution Center at the Environmental Defense Fund (EDF), a non-profit. But despite her knowledge of fisheries, she says she still struggles with the day-to-day challenges of how to make good decisions about seafood.
"I think it's helpful to look at the guides to understand the nuance," she says. "[They] have looked at not just the species, but where the species come from: what might be a good choice in one place could actually be not a great choice in another place."
Over time using these apps, people can develop a deeper understanding of which gear types tend to be better than others, and which countryies’ fisheries and farms are doing a better job, says Liz Nussbaumer, project director for seafood at the John Hopkins Center for a Livable Future.
Erin Hudson, Seafood Watch programme director, says she tries to remember a few "safe bets" from the Seafood Watch app for when she doesn’t have her phone handy while shopping. "For me personally, when I'm eating on the California Central Coast, that's going to be anything with farmed mussels [...] or farmed rainbow trout or local rockfish species," she says.
The ratings also change over time, though, adds Hudson. "Conditions in fisheries and farming operations do change, and we release new ratings every month. Things are always moving, and that’s great – we want to see improvements happen. And we want to stay on top of when things slide the other way."
Can you trust labels?
Both these apps refer to certificates like the Marine Stewardship Council and Aquaculture Stewardship Council (ASC) in their ratings, which can also be found on fish packets in the supermarket. Despite the criticisms from films like Seaspiracy of these certificates, all the experts I talked to said they are worth taking into account when making choices.
Sustainability on a Shoestring
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"[The Marine Stewardship Council blue tick] means at least they are being audited, and they have to prove things," says Clarke. "It's a great way of just quickly and easily identifying whether something's a sustainable choice."
Certifications like these can also be a protection against fraud, a huge issue in the seafood industry.
A 2016 meta-analysis of DNA identification studies of seafood found that globally there was a 30% rate of misdescription – meaning the fish was not the species stated on the label or menu. But a 2019 DNA study by the Marine Stewardship Council found that seafood bearing its sustainability mark was labelled correctly over 99% of the time.
One issue with these labels, however, is that gaining them can be a significant process for a fishery involving data collection and a lot of paperwork – meaning not every fishery has the resources to receive the stamp, even if they are working sustainably. Some certifications are more accessible to smaller-scale fisheries, such as Fairtrade certification, says Poon.
The highest carbon seafood
It’s worth noting that none of these certificates, nor the apps, currently measure carbon emissions. These can vary significantly between different seafood species, and research has shown some species and farming methods do tend to be better than others on this.
If you're going to eat one kind of seafood, [bivalves are] probably the one to go for from across the board for environmental reasons – Jessica Gephart
In a paper published last year, Gephart and her colleagues surveyed a range of seafood to examine several different dimensions of sustainability more typically considered for land-based agriculture, namely greenhouse gas emissions, nitrogen and phosphorus pollution, land stressors and freshwater use.
"We wanted to be able to compare the aquatic foods [with agriculture and livestock] on a more even basis," says Gephart.
Farmed mussels – the most sustainable seafood?
Farmed bivalves such as mussels are an incredibly sustainable source of seafood less impactful on the planet than some vegetables, says Clarke.
Unlike most farmed seafood, he says, you don't need to feed them or treat them with chemicals or antibiotics to avoid diseases. They’re also low carbon, and don’t use up fresh water or land, and they can form artificial reefs that encourage other kinds of wildlife to congregate. To top it all, they are a great source of micronutrients.
The researchers found that farmed bivalves – a group which includes farmed mussels, oysters, scallops and clams – had the lowest environmental impact across all measures.
When it comes to nitrogen and phosphorus pollution, they actually have a positive effect on pollution – because they absorb these nutrients as they grow.
"They're actually removing nitrogen and phosphorus from the water. And so their emissions are negative for those," says Gephart. "If you're going to eat one kind of seafood, that's probably the one to go for from across the board for environmental reasons."
However, wild-caught bivalves including mussels performed much worse on greenhouse gas emissions, the paper showed. That’s because wild-caught mussels are often caught by mechanical methods like dredging, which use high amounts of energy. It's also well-documented that the methods used to catch some wild bivalves can be devestating for local environments. According to the charity Open Seas, scallop dredging has the most severe impact on the wider ecosystem of any fishery in the UK.
Other fish with low greenhouse gas emissions were farmed silver and bighead carp, salmon and trout, although carp use a lot of land to cultivate.
On the wild-caught side, herrings, sardines and anchovies are fairly low carbon, with cod, hake and haddock not far behind.
But wild-caught flounder, halibut, sole and lobster all fared badly on greenhouse gas emissions, as well as farmed tilapia and both wild and farmed shrimp.
Overall, seafood typically either outperformed or performed similarly to chicken, often viewed as the most efficient form of meat. Predictably, though, it's a different story when considering fish compared to plant-based proteins.
"It is a 'compared to what' when it comes to any dietary question," says Gephart. "What we found is that many of the different species groups are a good choice when it comes to carbon emissions if what you're going to eat instead is some kind of meat."
Farmed mussels are an incredibly sustainable source of seafood - they're low-carbon and don't use up fresh water or land (Credit: Leligny JM / Getty Images)
To look further into the carbon emissions of different seafoods, Monterey Bay Aquarium and Dalhousie University have a handy and searchable seafood carbon emissions tool.
What fish should I avoid?
When I first started eating fish, I found it vexing to learn that farmed fish such as salmon and prawns are often fed on smaller wild-caught fish, like mackerel, sardine and anchovy. It seemed silly to be feeding edible fish to other fish. Why not just eat the smaller fish and avoid the wasted energy?
Is seaweed a good choice?
Farmed seaweed has low greenhouse gas emissions, absorbs nitrogen and phosphorus in a similar way to bivalves, uses no land, freshwater or food input, and has high micronutrients, although it lacks the protein of animal seafood. However, seaweed farming is a relatively new area, Nussbaumer notes, so more needs to be known about its side effects and the best location for it.
Scotland’s farmed salmon industry, for example, is especially reliant on marine feeds, which researchers have criticised as a huge waste of micronutrients which could be feeding people.
However, Gephart says there have been improvements in the raising and rearing of some farmed fish, such as salmon and trout, over the past decade.
"The technology for feeding has improved so much that they are really efficient at turning feed into fish, essentially," she says. She notes that fish meal from sustainably-managed pelagic fisheries can be a better choice to feed fish than, say, soy coming from areas where there's deforestation.
There is also interest in the industry towards moving to other sources of food, such as algae additives, black soldier flies or other insect larvae, says Nussbaumer.
However, generally speaking, lower trophic level species – meaning species that are lower on the food chain – are going to be more sustainable than predators, says Poon. "I would still say you want to know how that fish was caught and where it came from [though]," she adds.
Prawn, shrimp is a great example of a category where you see green, yellow, and red. So it's possible [for it to be sustainable], but you do need to look into where it's from, how it’s being raised – Erin Hudson
There are some species that are usually best completely avoided – shark and bluefin tuna, for example. Prawn and shrimp are another higher impact product to be careful about. Shrimp farms can replace coastal nursery habitats such as mangroves, in turn affecting fish stocks, says Gephart, and can impact coastal protection. Farmers in countries such as Bangladesh are still suffering the unintended impacts of flooding their paddies with salty water to raise tiger prawns, in part as an adaptation to rising sea levels.
"There’s lots of instances of red-rated prawn," says Hudson. "Prawn, shrimp is a great example of a category where you see green, yellow, and red. So it's possible [for it to be sustainable], but you do need to look into where it's from, how it’s being raised."
Seafood includes around 2,500 different species produced by farming and capture fisheries (Credit: Manuel Medir/ Getty Images)
Here again, it’s worth looking out for certifying bodies such as the Aquaculture Stewardship Council, says Clarke. "They stepped in to make sure that these farms are meeting standards in environment, antibiotic use, labour, water use; all these things that we were so worried about, they started introducing them," he says.
But perhaps the best thing to avoid is any place that can’t tell you where its seafood came from, says Poon. "If a restaurant or a supplier or a grocer is not providing you specifics about what species that product is, where it came from, or how it was caught, that’s when a trigger goes off in my head that this could very well be from an unsustainable fishery."
Is it better to eat more diversely?
Some 80% of the seafood eaten in the UK is made up of just five species, namely cod, haddock, salmon, tuna and prawns – statistics which chime with my own choices during my month tracking my seafood consumption.
Where to shop for sustainable fish?
People often assume that local seafood is more sustainable, but this isn’t always the case, says Clarke. Fishmongers can sell "amazingly fresh, high quality, sustainable options", he says, but they can also stock extremely unsustainable seafood. Some supermarkets, meanwhile, are doing a relatively good job on sourcing sustainable fish, says Nussbaumer.
Wherever you buy your fish, it’s always worth checking their sourcing practices, and reading up on what you are buying.
Similarly, in the US, 62% of seafood consumed is shrimp, salmon, canned tuna, tilapia or Alaskan pollock.
This lack of diversity puts pressure on a handful of wild fisheries and a few species that are farmed all over the world, says Clarke.
"Our insatiable appetite for those things is driving unsustainable farming practices. It’s driving these huge fisheries and potentially overfishing of these species," he says.
Swapping some of the usual suspects for less well-known seafood species can therefore have a positive impact, says Clarke.
Farmed trout can substitute salmon, for example, while hake can replace cod. Farmed bivalves such as mussels, which don’t require any feed and can be grown by throwing a seeded line into the sea, are usually an especially good choice, and fare much better across sustainability measures than prawns.
Diversifying can also open opportunities for people to consume local species that may well be being caught in sustainable ways, adds Gephart.
"We have lots of local smaller fisheries [in the US] that are often well managed, but the US consumer is often inclined to eating the same set of species."
Bycatch of sharks and dolphins is minimal in pole and line fisheries (Credit: Mohamed Abdiwahab / Getty Images)
Depending where you live in the world, you may be more or less likely to be able to get information on the catching method from your grocer, but it is always worth asking because it can make a huge difference.
When I realised the cod I was about to eat was caught by trawling, I felt a prod of guilt. Trawling is a controversial method of catching wild fish. It involves dragging cone-like nets along the seafloor bottom, which can damage seafloor habitats. It can also result in large amounts of bycatch, which is often discarded dead or dying back into the ocean, leading to eye-watering amounts of fish waste.
If you’re worried about things like dolphins and shark bycatch, bycatch in pole and line fisheries is minimal – Jack Clarke
Dredging – where a heavy steel frame is towed over the seabed – and to a lesser extent demersal seining, where a net on the seafloor is slowly closed, are other methods which can impact seafloor habitat. Lower-impact methods use less-intensive gear to catch fish, such as pole caught or troll fisheries, says Poon.
Trawling also leads to more greenhouse gas emissions than other catching methods such as line caught fish. "Bottom trawling is, unsurprisingly, going to use a lot more energy as a fishing method," says Gephart. The trawling nets can also drudge up huge amounts of carbon from the seabed floor.
How to stop wasting fish
An incredible one-third of the wild fish caught never gets eaten. Much of this waste happens before fish even reaches our fridges, especially due to trawling, but better planning in our kitchens can also help. Tips include planning in advance how you’ll use the fish you buy and choosing frozen, tinned or smoked seafood over fresh to avoid a fast expiry date.
Scallops are a good example here. They can be caught in the wild by dredging, where they score between 3 and 5 on the Good Fish Guide, or hand diving, where divers pluck them one by one off the seabed, scoring them a 2. They can also be farmed, scoring them a 1.
Pole and line-caught tuna, which are caught one-by-one, similarly tend to score much higher on the Good Fish Guide, says Clarke.
"If you’re worried about things like dolphins and shark bycatch, bycatch in pole and line fisheries is minimal." However, he notes, "you can still catch the last fish in the sea with a hook and a line".
There are ways that this intensive gear can be managed to be less impactful, adds Poon, who recommends asking for any fish caught by a larger net or trawl whether measures are being taken to avoid bycatch and impacts to the habitat.
Clarke also notes that some parts of the sea are less susceptible to damage from trawling. "They have big tidal races, they’re just muddy buttons, where there isn’t that much structure, there aren’t reefs or soft corals."
Trawling and other intensive fishing methods can trap and kill marine animals such as sea turtles (Credit Ulet Ifansasti/Getty Images)
It’s worth keeping in mind in all this that there is only so much you can do as one person. Gephart suggests that the burden needs to be taken off consumers. So advocating for changes on policy, supply chain traceability and sustainable management of stocks at home may be the best place to start for those who want to make a wider impact.
Perhaps my biggest takeaway is that I want to be more vocal when I'm buying fish that I care that it's sustainably sourced
Doing this experiment has made me feel far more engaged with the seafood I’m eating. I’m going to stick to eating it only occasionally – it is still a high-impact food, after all – but I’m also going to make a bigger effort to avoid larger fish higher up the food chain, and instead opt for smaller fish and especially farmed mussels, the seafood superfood. I’ll also keep using the Good Fish Guide to inform my choices.
But perhaps my biggest takeaway is that I want to be more vocal when I'm buying fish that I care that it's sustainably sourced. Simply asking your grocer or local restaurant whether they sell sustainable seafood can make a big difference, says Hudson.
"When customers ask for sustainable seafood, restaurants and retailers begin to seek and demand sustainable options from their suppliers. And, honestly, the answer is not the critical part here; it's the question."
Jocelyn Timperley is a senior journalist for BBC Future. Find her on Twitter @jloistf
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