Tuna, and related fish, are 40 species in the Atlantic, Indian, Pacific and Mediterranean oceans. Among the best known, we find yellowfin tuna, yellowfin tuna and of course bluefin tuna. Its name, given by the Phoenicians, means “Large animal” and it is deserved!
Tristan Rouyer, researcher at theIFREMER (French research institute for the exploitation of the sea) explain that “It is an animal that can exceed 3.5 meters and reach more than 600 to 700 kg. It’s almost the weight of a cow! “
With its eyes protruding little and its dorsal spicules coming to reduce the turbulence, this animal benefits from an incredible hydrodynamics. Due to its morphology, it can reach 70km / h, a speed rarely reached, even by submarines. Some even say that it would have an acceleration capacity greater than that of a Porsche! A quality that allows him to swim great distances.
According to some data, the tuna has traveled more than 200 km per day. It is a very great migrant which is able to go almost everywhere. It is therefore complicated to follow it, especially since it is able to move according to environmental conditions.
Tristan Rouyer, researcher at IFREMER
This great migrant can even make a double transatlantic in a year! It is 12,000 km covered as well through cold waters, where it feeds, as through warm waters, where it reproduces. Very atypical for a fish, it is said to be hot-blooded! It can have a temperature of 10 ° C higher than the environment where it lives, which allows it to navigate in waters whose temperature can range from 3 to almost 30 ° C!
“Bluefin tuna is endowed with thermoregulation. That is to say, it has a blood system which causes the muscle to warm up the blood system through a network and to be able to transmit heat all over the body. This is what allows it to go to places and latitudes that other tunas cannot reach ”, specifies Tristan Rouyer.
A program led by Ifremer and its partners in the FishNchip and Popstar projects had set the goal of unravel the mysteries of their migratory behavior, but also to study the environmental conditions that punctuate their journey. In 2019, the teams went to the south of Malta, a breeding area, to equip 5 individuals with beacons. These electronic marks have thus made it possible to collect information on parameters such as temperature, light or even the physiology of the fish, in addition to its location. A first !
Very popular in a box or in sushi, each year more than 7 million tonnes of tuna are caught. They even represent more than 8% of world seafood production. To the extent that, “according to the latest estimates, a third of stocks of the seven main tuna species were being exploited at a biologically unsustainable level ”. Fishing quotas made it possible to recover stocks after the collapse of the late 2000s.