Atlantic bluefin tuna

Atlantic bluefin tuna live in the Atlantic Ocean.

They swim in the open sea, far from land. They also swim into the Mediterranean Sea.

Atlantic bluefin tuna live in much of the North Atlantic Ocean, from Canada and Norway south to Brazil and West Africa, and in the Mediterranean Sea. They swim near the surface but often dive deep, to 500 to 1,000 meters.

They are great travelers. Some cross the whole Atlantic Ocean, thousands of kilometers. As the oceans have warmed, bluefin tuna have even been seen near Greenland and Iceland.

The IUCN describes a range across much of the North Atlantic, reported also from the South Atlantic: historically from Canada to Brazil in the west (though the population off Brazil has almost disappeared), and from Norway to Cabo Verde and West Africa in the east, plus the Mediterranean and, rarely now, the Black Sea. Rising temperatures have brought it into Greenland waters and the Icelandic Basin.

It is pelagic and oceanodromous, found to at least 1,015 meters, and tolerates 1 to 29 °C, the widest range of any tuna; large adults feed as far north as the Norwegian Sea and the Gulf of St. Lawrence (IUCN). Fish from both stocks mix across the Atlantic outside the spawning grounds.

Bluefin tuna eat other fish and squid.

They chase schools of small fish, like herring and mackerel.

Bluefin tuna are predators. Young ones eat fish, squid and crustaceans, and adults feed mainly on schools of smaller fish, such as herring, mackerel and bluefish.

What they eat changes as they grow. In the Mediterranean, young tuna eat mostly tiny drifting animals and small fish, while big adults catch squid and larger fish.

The IUCN lists prey including small schooling fishes (anchovies, sauries, hakes), squids and red crabs. A Mediterranean study found a diet shift with age: juveniles mainly zooplankton and small coastal fishes, subadults medium pelagic fishes, shrimps and cephalopods, adults mainly cephalopods and larger fishes.

In the Gulf of St. Lawrence, Atlantic herring and Atlantic mackerel dominate the diet. In the Icelandic Basin, 36 prey species were found, the most important being European flying squid, barracudinas and gonate squids. NOAA adds that juveniles eat fish, squid and crustaceans, and adults mainly baitfish such as herring, bluefish and mackerel.

Bluefin tuna swim together in groups called schools.

They travel very, very far across the ocean.

Bluefin tuna swim in schools, groups of fish of about the same size. Sometimes they share a school with other tunas, such as albacore and yellowfin.

They are highly migratory: electronic tags show that some swim thousands of kilometers, crossing the Atlantic. Each year, eastern fish swim into the Mediterranean through the Strait of Gibraltar in May and June and leave in July and August.

Bluefin school by size, sometimes with albacore, yellowfin, bigeye or skipjack tunas (IUCN). NOAA describes them as highly migratory, capable of crossing an ocean, with tagged fish moving across the east-west management boundary.

Eastern fish enter the Mediterranean through the Strait of Gibraltar in May and June and leave in July and August. Tags show behavior changes around spawning: western fish entering and leaving the Gulf of Mexico dove to 568 to 580 meters daily, but during the likely breeding phase their deepest daily dives averaged about 203 meters. Predators include sharks, killer whales, pilot whales and large fish (NOAA).

People caught too many bluefin tuna.

Now countries work together and set limits on how many can be caught.

Bluefin tuna are very valuable as food, especially for sushi, and for many years far too many were caught. The western population fell sharply.

Now the countries that fish in the Atlantic work together in a group called ICCAT. They set limits on how many tuna can be caught each year. In ICCAT's latest check, overfishing was not happening in either the eastern or the western stock, and the eastern stock grew after stricter rules began in 2008. The IUCN lists the species as Least Concern.

The IUCN assessed Thunnus thynnus as Least Concern (assessed January 2021; Endangered in 2011), because the larger eastern stock, about 80 percent of the population, may be increasing, while the western stock declined by up to 83 percent over three generations. Eastern catches peaked above 60,000 tonnes around 2007, before stricter ICCAT management from 2008.

ICCAT's 2025 executive summary keeps the status from its most recent assessments (west 2021, east 2022): overfishing is not occurring in either stock, and biomass reference points for the west are unknown. Catch limits for 2023 to 2025 were 40,570 tonnes (east) and 2,726 tonnes (west). NOAA likewise reports the western stock is not subject to overfishing, with overfished status unknown (2021 assessment), and US rules ban targeted bluefin fishing in the Gulf of Mexico spawning area (NOAA's page uses the name Gulf of America).