Is seafood sustainable?

The objection

“The ocean replenishes itself. Most of the fish we buy comes from well-managed stocks, and fish farms are taking the pressure off the wild ones, so sustainable seafood is a real thing.”

The answer

Plenty of seafood does come from fisheries that are well run by the official measure, but the ocean’s capacity to replenish itself has limits, and the global catch has been pressing against them for decades. In its 2026 report the UN’s Food and Agriculture Organization (FAO) describes the world’s wild catch as relatively stable since the late 1980s, because a number of wild stocks had reached their biological and ecological limits; catches from the sea peaked at 86.4 million tonnes in 1996 and were 79.6 million tonnes in 2024 [1].

How many of the world’s fish stocks are overfished?

More than a third of assessed marine fishery stocks were overfished in 2023, according to the FAO’s 2026 report [1]. Of the 2,665 stocks it assessed, 37.6% were overfished and 62.4% were within biologically sustainable levels [1]. Under the FAO’s older method, the overfished share rose from around 10% in the 1970s to about a third, where it has hovered in recent decades (Our World in Data, 2021) [2]. A stock passes if its biomass is at least 80% of the level that gives its maximum sustainable yield, a margin the FAO allows for natural swings, and most that pass sit around that level: 46.9% of all assessed stocks were rated maximally sustainably fished and 15.5% underfished [1].

Weighted by catch the picture looks better: the largest stocks tend to be the best managed, and 72.6% of landings from assessed stocks came from sustainably fished ones in 2023 [1]. Many stocks have no rating at all, though, and the FAO says nearly 45% of the monitored stocks targeted by small-scale fisheries were still of unknown status in 2024 [1]. The Mediterranean and Black Sea had the lowest share of sustainable stocks of any region in 2023, 45.7%, but that was up from 35.1% in 2021, the biggest improvement anywhere, which the FAO credits to management that cut fishing pressure [1]. In the Northeast Atlantic fewer than 40% of Atlantic cod, beaked redfish and whiting stocks passed [1].

Isn’t farmed fish the sustainable alternative?

Fish farming now produces more than half the world’s fish and other aquatic animals, but it still draws on the wild catch. Farms inland and at sea, such as the floating salmon cage in Macquarie Harbour, Tasmania, Australia, filmed from inside in 2017, produced 103 million tonnes of aquatic animals in 2024, against 92 million tonnes from capture fisheries [1]. That year more than 18 million tonnes of wild fish, about a fifth of the world’s catch, was ground into fishmeal and fish oil, and the industry body IFFO estimates that over 90% of the fishmeal and about 64% of the fish oil went to fish farms (2024) [1]. The tonnage of wild fish ground up has moved between about 14 and 18 million tonnes a year since 2014, down from about 30 million in 1994, and from that fall the FAO concludes that farming’s growth has not increased the pressure on these fisheries globally [1]. IFFO estimates that by-products such as trimmings and offal supplied about a third of the fishmeal and over half of the fish oil in 2024 [1].

Salmon farms in the Northeast Atlantic also pass parasites to wild fish, because large farms raise local numbers of sea lice. The main evidence comes from trials that release tagged young salmon, usually hatchery-reared, in paired groups, one protected by an anti-lice drug and one not, and compare how many return as adults [6][7]. A meta-analysis of 24 such trials in Ireland and Norway (2013), with 283,347 fish released between 1996 and 2008, estimated that lice cut adult returns by 39% (95% confidence interval 18 to 55%), the lice probably picked up as the fish migrated past areas with large salmon farms [3].

A larger meta-analysis (2025), of 43 paired releases from 2001 to 2019, found 18% fewer adults returning among the untreated fish, with losses rising as lice pressure from farms rose, and its authors note that the drug may not fully shield the treated fish, so the true loss may be larger [6]. In a 19-year series of these trials on a river in western Norway (2023), the drug’s measured benefit faded towards zero while returns of wild salmon to the region still fell in years with more lice, and the authors concluded that such trials can miss a large effect on wild populations [7].

What else does fishing harm besides the fish it targets?

Fishing also catches animals nobody set out to catch and drags nets across the sea floor, and a stock can be rated sustainable whatever bycatch or seabed damage its own fishery causes, because the FAO’s rating compares only that stock’s biomass with the level that gives its maximum sustainable yield [1]. An FAO assessment, as summarised by Our World in Data (2021), put discards, the unwanted catch thrown back into the sea, at about 9.1 million tonnes a year over 2010 to 2014, or 10.8% of the total catch [2]. A large share of the ocean-going sharks brought ashore are caught by accident on tuna and swordfish longlines, and of the shark stocks the FAO assessed, 60% were rated sustainable in 2023 [1]. A global review (2014) mapped hotspots of seabird, marine mammal and sea turtle bycatch across the three most widely used kinds of fishing gear [4].

Bottom trawls sweep about 5 million square kilometres of seabed each year, by a 2021 estimate in Nature that Our World in Data summarises [2]. A single pass kills or removes from about 6% of the organisms living there with otter trawls and 14% with beam trawls to 41% with hydraulic dredges, and the seabed’s life takes 1.9 to 6.4 years on average to recover, but only if the ground is left alone (Our World in Data, 2021) [2].

Is any seafood sustainable?

Some seafood does well on both stock health and pollution. Every assessed Antarctic stock and 89.3% of those in the Northeast Pacific were rated sustainable in 2023, as were 91.3% of assessed tuna stocks [1]. A 2021 analysis in Nature of aquatic foods’ greenhouse gas, nitrogen and phosphorus emissions and their use of freshwater and land found the lowest impacts of all in farmed bivalves, such as mussels and oysters, and seaweeds [5]. Among wild catches, small pelagic fish such as anchovies and sardines had lower emissions than any fish or shellfish farmed on feed, and flatfish and crustaceans the highest [5], though small pelagics are also the main fish ground into fishmeal [1]. These measures cover tonnes and emissions only; the welfare questions, whether fish feel pain and how they are killed, have pages of their own.