The real cost of sushi

04 May 2023

A scandal erupted in Japan recently.

Viral videos showed young diners deliberately engaging in “sushi terrorism”—licking communal bottles, putting cigarette butts into plates of ginger—forcing restaurants to stop their famous conveyor belts, for decades a symbol of hi-tech fast food in the dish’s homeland.

This curious episode of antisocial behavior among Japanese youth does not appear to be a politically-motivated protest against the massive environmental damage caused by the sushi industry, yet it has unwittingly disrupted a multibillion-dollar global industry that is in dire need of a reality check. The negative externalities of the sushi industry make its consumption completely incompatible with any notion of sustainability, and its continued success poses an existential threat to coastal communities worldwide.

A global phenomenon

Sushi, like pizza, hamburgers and kebabs, is a globalized product, completely divorced from its place of origin: a simple template that can be replicated anywhere. Its hundreds of years of history in Japan as an outdoor snack sold by street vendors with carts are largely irrelevant to modern consumers who see it as a healthier and more refined alternative to the other fast food formats mentioned above.

The popularity of sushi has exploded since it first arrived in Los Angeles in 1966, and there are now around 20,000 sushi restaurants in the US alone, and more than 100,000 worldwide. The small town of Bra, home to less than 30,000 people and the historic headquarters of Slow Food, has four separate sushi restaurants. Milan has 400—even more than LA!—yet it didn’t even make it into the top 10 of a survey of the most “sushi-crazed” cities outside Japan conducted in early 2022[1].

So what are people eating at sushi restaurants? There are two species which dominate menus worldwide, each with their own set of problems: tuna and salmon.


Tuna is an apex predator[2] and consumes a wide variety of other fish, making it a vital component of the marine ecosystems where they are present. It’s also one of the most commercially valuable fish on the planet: the record price was set in 2019 at the auction at Tokyo’s Toyosu Fish Market, when sushi magnate Kiyoshi Kimura paid over $3 million for a single fish of the Pacific bluefin variety. Yet tuna is also an affordable and widely-available source of protein around the world, and herein lies the problem.

An estimated 80% of all the bluefin tuna caught around the world ends up in Japan, and some varieties, like the Pacific bluefin, have seen their numbers reduced by more than 96% since the onset of industrial fishing in the 1950s, according to a stock assessment conducted in 2013[3]. The global demand for tuna, partly driven by the increasing popularity of sushi around the world, increases pressure on other tuna populations too—the yellowfin, albacore, skipjack and bigeye varieties in particular—partly as a replacement for the overfished bluefin. It has also changed the way we fish for tuna, with a range of ecological impacts.

Dolphin-safe doesn’t mean ocean-safe

The most traditional method of catching tuna, using the pole-and-line method, used scattered bait fish to attract tuna and then catch them one by one, often with handlines. This method is still in use throughout small-scale artisanal fisheries today, and has a low incidence of bycatch.

Over the last 50 years this method has all but disappeared in commercial fisheries, replaced by much more “productive” techniques. From the 1970s there was a sharp increase in the use of the purse seining method, which involves massive vertical nets being set around whole schools of fish and then pulled together like a drawstring bag. This led to a catastrophic rate of bycatch, particularly of dolphins and sea turtles. There was public outrage following the release, in 1988, of documentary footage by American biologist Samuel LaBudde showing dolphins being killed by tuna fishers using purse seine nets in the Eastern Pacific. This led to the establishment of “dolphin-safe” labels on American canned tuna in the 1990s.

Vague labels

Dolphin-safe fishing is not necessarily as environmentally friendly as it sounds, as all it guarantees is compliance (often self-reported by the ship’s operator) with policies meant to minimize dolphin bycatch: these labels have been described as a fraud by Forbes: “Most Americans think that the existence of a dolphin-safe label means that no dolphins were harmed when the tuna were caught. In truth, the label only means that one particular fishing method was not used in one particular part of the ocean.”[4]

An alternative method to purse seining which has become increasingly popular in commercial fisheries around the world over recent decades is longline fishing, which targets so-called “sashimi-grade” tuna in warm and tropical waters. Here, again, bycatch is a major issue: according to the International Seafood Sustainability Foundation, the average bycatch rate is more than 20% of the total catch, killing untold numbers of sharks, turtles and seabirds every year. The same organization also conducted a study into the amount of fuel used in longline fishing, finding that more than 1000 liters of fuel are burnt to catch a ton of tuna, or more than one liter per kilo.

Aquaculture: a viable alternative?

It’s well known that nearly all of the world’s salmon comes from intensive aquaculture nowadays—and more on that later!—but did you know that we’re now attempting to raise tuna in aquaculture too? That’s right: tuna ranching is a practice whereby young tuna are caught and, instead of being killed, are transported to enclosed areas where they are fattened up with a constant supply of their favorite foods: sardines, squid, mackerel, etc.[5] Tuna ranching is mainly found in the Mediterranean, with most of the fish being exported to Japan.         

So what’s the issue? Pumping enclosed areas of water with nutrients (i.e. the smaller fish used to feed the tuna) creates an overabundance, leading to nutrient pollution, eutrophication, the death of Neptune grass (Posidonia oceanica), and a loss of biodiversity, as well as the obvious impacts all this has on local, small-scale artisanal fishers. It’s also a highly inefficient method of producing meat for human consumption, as the ratio of fish feed required is 28:1 (i.e. 28kg of feed to provide 1kg of tuna). Researchers have worked with the idea of feeding tuna soy-based feed instead of sardines, which would reduce the ratio to just 4:1, but these experiments are not yet the reality in Mediterranean tuna farms.


Tuna is the premier fish species in authentic Japanese sushi, and its Japanese market plays a predominant role in global demand, but salmon is altogether a different kettle of fish. Its use in sushi is a Western invention, and the arrival of sushi in the West roughly coincides with the establishment of the first functional salmon farms in Norway and Scotland, in the late 1960s. The popularity of farmed salmon has increased massively since, reaching around 2.8 million tons in 2021, or four times the volume of wild salmon caught.

While not all of this salmon ends up in sushi restaurants, a cursory glance at any sushi menu restaurant from Canada to Ukraine will show that the industry—outside Japan—is dependent on the steady supply of farmed salmon. And even Japan has acquired a taste for it, too, increasing its salmon imports from Norway by a magnitude of 20 times over a 15-year period from 1992 to 2017.[6]

Salmon farms produce millions of tons of fish a year, much of which ends up in sushi.

But what do the salmon eat?

Salmon, like tuna, is a carnivorous fish, and in order to farm million tons of salmon a year, we need three times as much wild fish to feed them.[7] Those wild fish (generally sardines, sardinella, anchovies and mackerel) are caught in waters far from the farms, meaning that local, small-scale fishing communities struggle to survive as their coastal waters are ransacked by the dragnets of multinationals for the aquaculture industry. We’ve explored this topic before, and the knock-effects of this overfishing are being keenly felt in every sea, from an explosion in jellyfish populations to the arrival of invasive species. The collapse of local fisheries in West Africa, driven indirectly by salmon consumption in the Global North, is another push factor that leads people on perilous migration journeys to Europe.

A dirtier business than you’d like to imagine

That’s before we consider the pollution caused by the salmon farms themselves. A farm containing 10 cages, each with as many as 100,000 fish each, creates as much excrement and chemical residue as a city of 65,000 people.[8] But while human wastewater is subject to sewage treatment, the waste from salmon farms simply drifts into the surrounding sea, causing massive damage to the surrounding ecosystems.

The practice of stacking a million fish into a small area naturally produces atrocious sanitary conditions, with predictable consequences for the health of the fish. In their book Salmon Wars: The Dark Underbelly of our Favorite Fish, authors Catherine Collins and Douglas Frantz describe how parasites like sea lice are so prevalent on salmon farms that “at some fish-processing plants workers use Shop-Vacs to remove them from incoming salmon.” And when (sadly now increasingly common) extreme weather events destroy the cages and allow these thousands of farmed salmon back into the wild, the results for the ecosystems are even more catastrophic, as we saw in Washington State in 2017.

What can we do?

First and foremost, the answer is simple: we must stop buying and eating farmed salmon, and massively reduce our collective consumption of tuna. At the same time, we need to encourage greater public awareness of the environmental damage that our overfishing — symbolically represented by the sushi industry — causes. Greater awareness leads to political pressure on policy makers, who we urge to act with the interests of the seas given greater priority than those of industry.

But most of all, we need to listen to our fishers, and to support short supply chains wherever possible. If we reduce our support for sushi, and all the industrialized fishing systems that it depends on, we guarantee a future for the small-scale fishers and coastal communities who depend on the bounty of their local waters. The alternative doesn’t just represent an increase in economic inequality, but promises an ecological disaster.

You can come and learn more about the struggles of small-scale fishing communities and the myriad interconnections between human activity and marine ecosystems at Slow Fish, particularly at the Conferences and at the Fisher’s Platform.

by Jack Coulton,

Slow Fish 2023 is organized by Slow Food and the Liguria Region, with the support of the City of Genoa. We’re in the Porto Antico of Genoa from June 1-4. Sign up to the Slow Food newsletter for the latest updates. #SlowFish2023


[1] Vancouver ranked number one. It is possible that Milan is now among the top 10, given that many of the cities above it in the rankings were in Ukraine.

[2] Which is, in itself, an issue: humans generally don’t eat apex predators in the mammal, reptile or bird classes. By their nature, predators have a smaller biomass than their prey species, so our taste for apex predator fish implies and necessitates the existence of a sufficient biomass of prey species to support the predator population. In other words: if we want to eat a lot of tuna, we need there to be a significantly greater biomass of their food, too.

[3] This figure of a reduction of 96% dates to a stock assessment conducted in 2013. Since then, action to reduce overfishing has led to a rebound in numbers, but the situation remains critical.


[5] Young tuna are caught and trapped in these ranches only after they have reached a certain size, i.e. when they are large enough to eat full-sized prey. Newborn tuna are too small to be fed artificially, and tuna will not eat anything that is left dead in the water for them: only live prey is considered edible. This is the only reason why intensive, full-cycle tuna aquaculture is not widely practiced, though there are continuing experiments in this area, particularly in Japan.

[6] Norway, by far the largest producer of farmed salmon in the world, accounting for around half of the global total, has been hard at work trying to convince the Japanese of the merits of salmon since the 1980s, and has largely succeeded: its salmon exports to Japan grew from 5000 tons in 1992 to over 114,000 tons in 2017.

[7] From the Guardian: “They calculated that in a single year, 179,000 tonnes of salmon produced in Scottish aquaculture farms consumed fish meal and fish oil produced from 460,000 tonnes of wild-caught fish, 76% of which was edible.”

[8] From an interview with Collins and Frantz at

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