Chapter 10 preface: Bluefin fact sheet

Meet the amazing Atlantic bluefin tuna (Thunnus thynnus)

AKA: Northern bluefin tuna, horse mackerel, giant tuna, maguro, atun de aleta azul, thon rouge

A giant amongst fish
Adults are typically 2 metres long but can reach over 4 metres, making the Atlantic tuna one of the largest bony fishes and the largest of all tuna species. Adults average around 250kg, but the largest recorded specimen was a massive 679 kg - that’s heavier than a horse!

Faster than a speeding bullet
So how fast can these tuna swim? They usually cruise around at 2.8-7.4 km/hour (that’s a slow to reasonably brisk walking pace for us), but can speed up to 14.8 km/hour (an average running pace) for some time.

But it’s when they’re chasing their prey (or avoiding a hungry shark) that they really let fly, accelerating faster than a Porsche and reaching speeds of 70, and maybe even 100 km/hour! No surprise then that the word tuna comes from a Greek word meaning “to rush”.

Long distance champions
Atlantic bluefin tuna are not just fast sprinters - they are also champion long-distance swimmers.

These fish are found on both sides of the North Atlantic Ocean, from Brazil to Newfoundland in the west and from West Africa to Norway in the east. Throughout their lives they roam this vast area searching for prey, returning each year to their spawning grounds in either the Gulf of Mexico or the Mediterranean Sea.

These travels include trans-Atlantic crossings, which a bluefin can complete in less than 60 days. Up to 30% of the total population makes this voyage, with some individuals even making multiple crossings in a single year.

Warm hearted
You probably learnt at school that fish are cold-blooded, right? That’s mostly true - but not for bluefin tuna. Their specialized circulation system allows these fish to retain up to 95% of the heat generated by their muscles. This means they can keep themselves much warmer than the surrounding water - essentially making them a warm-blooded fish!

Built for speed
Bluefin tuna are built like torpedoes. Not only do they have a hydrodynamic shape, their pectoral (side) fins can be retracted and, unlike other fish, their eyes are set flush to their body. This means their bodies create little drag as they swim through water.

A warm body temperature also helps these fish swim fast, as does a stiff body that channels muscle energy directly to a highly efficient, crescent-shaped tail.

Constantly on the move
Atlantic bluefin tuna must literally swim for their life. Their rigid head helps them to swim fast, but doesn’t allow them to pump water over their gills like some other fish. Instead, water is forced over their gills as they swim with their mouths open. But this means they need to keep swimming - like some sharks, if they stop they will suffocate.

Voracious predators
Tuna are fearsome predators from the moment they hatch. They hunt by sight, and have the sharpest vision of any bony fish.

Adult Atlantic bluefin tuna eat schooling fish like herring, mackerel, flying fish, and anchovies, as well as squid, eels, and crustaceans - and occasionally starfish and even kelp. They can dive down to around 1,000m to find food.

A long life - for those that make it
Atlantic bluefin tuna larvae have only a 1 in 40 million chance of reaching adulthood. But these lucky few are amongst the ocean’s top predators. They can expect to live for at least 15 years, and even as long as 30.

They’re not quite at the top of the food chain though. Their fast speed allows them to escape most predators - except for large sharks, toothed whales like killer whales and pilot whales… and humans.

The world’s most valuable fish
The Atlantic bluefin tuna can’t make the claim of the world’s most expensive fish. That honour goes to its cousin, the Pacific bluefin tuna (T. orientalis). In 2001, a 200kg specimen sold for a record-breaking $US 173,600 at Tokyo's Tsukiji fish market. That’s over $800 per kilogram!

Records aside however, Atlantic bluefin tuna are just as valuable as their Pacific cousins.
One of the most endangered fish
Bluefin tuna populations have declined alarmingly over the past few decades - not just Atlantic bluefin tuna, but also Pacific bluefin tuna and southern bluefin tuna.
In all cases, the decline has largely been driven by Japanese demand for sushi and sashimi.

There are 2 populations of Atlantic bluefin tuna. The smaller western stock has declined by nearly 90% since the 1970s and is classified as Critically Endangered. The larger eastern stock, which spawns in the Mediterranean Sea, is currently classified as Endangered but in fact is in danger of complete commercial and biological extinction. Both populations are classified as overfished, but overfishing continues.

Source: World Wildlife Foundation