© Wild Wonders of Europe /Zankl / WWF
If we were to name an iconic species of the Mediterranean sea, it would no doubt be the Atlantic bluefin tuna. Strangely, not many people know about this amazing animal, which is one of the biggest and one of the most commercially valuable fish in the world. Precisely for this reason bluefin tuna has been heavily overfished for decades and has fallen victim to widespread pirate fishing especially in its main spawning grounds across the Mediterranean.
A giant amongst fishAdults 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 the 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 bulletHow fast can tuna swim? You`ll usually find them cruising around at 2.8-7.4km per hour, but can swim double that, nearly 15km per hour, 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 100km per hour! No surprise then that the word tuna comes from a Greek word meaning “to rush”.
Long distance championsAtlantic 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 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 heartedYou probably learnt at school that fish are cold-blooded, right? That’s mostly true – but not for bluefin tuna. Their specialized circulation system allows them 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!
Constantly on the moveAtlantic 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 other fish. Instead, water is forced over their gills as they swim with their mouths open. This means they need to keep swimming – like some sharks, if they stop they will die.
Voracious predatorsTuna 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 1000m to find food.
A long life for those that make itAtlantic bluefin tuna larvae have only a 1 in 40 million chance of reaching adulthood. But the 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.
© WWF Mediterranean