Atlantic Bluefin Tuna
Thunnus thynnus
A warm-bodied fish that can outweigh a horse — and one of the ocean's great comeback stories.
Bluefin tuna are built for speed and distance: a torpedo body, a crescent tail and fins that fold into slots to cut drag. They cross whole oceans and stay warmer inside than the water around them. They were fished so hard that scientists feared for them — then countries agreed to catch less, and the fish came back.
On the conservation status
Moved from Endangered to Least Concern by the IUCN in 2021, after catch limits let the fish recover. It stays a good-news story only as long as those limits are kept.
- Length
- Up to about 4 m (13 ft)
- Weight
- Usually 225–250 kg (500–550 lb)
- Lifespan
- 20 years or more
- Diet
- Herring, mackerel, squid, crustaceans
- Dives
- 500–1,000 m deep
- Breeds in
- The Gulf of Mexico and the Mediterranean
The good stuff.
A warm fish
Bluefin tuna can keep their bodies warmer than the water around them — better than any other fish. That lets them hunt in cold northern seas, then swim south to breed.
Built for speed
The spiny fin on its back and the fins on its sides fold down into grooves, turning the fish into a smooth torpedo. The little yellow finlets running back to the tail are thought to help water flow smoothly past it.
Ocean crossers
Bluefin migrate thousands of kilometres, and some cross the whole Atlantic. A small window in the top of the head lets light reach part of the brain, which may help them find their way.
Two nurseries
Western bluefin breed in the Gulf of Mexico; eastern bluefin breed in the Mediterranean. Then they mix across the Atlantic to feed.
Ten million eggs
A female can release up to 10 million eggs a year — but most bluefin don't start breeding until they're about 8 years old.
The comeback
Over 40 years, bluefin numbers crashed by more than 70% in parts of the Atlantic. Countries agreed on strict limits to how many could be caught, and in 2021 the IUCN moved the species from Endangered to Least Concern.
Wait, really?
- ✦
Tuna have to keep swimming to breathe: moving forward is what pushes water over their gills.
- ✦
It's the biggest of all the tunas.
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A bluefin can dive 1,000 m down and come back up, swapping warm surface water for the cold and dark below.
What it sounds like
Silent, as far as anyone knows. Like sharks, tuna have no known calls.
Where you might see one
The Gulf of Mexico in spring, where the western ones breed; off Nova Scotia and New England in late summer; and around the Balearic Islands in the Mediterranean.
The trouble
- Overfishing, if catch limits aren't kept
- Illegal and unreported fishing
- Getting caught by accident on lines set for other fish
One real thing
If your family eats tuna, ask where it was caught and how — and remember the bluefin. It came back because people agreed to take less.
More ways to help