The marking of a bluefin tuna -

Ifremer

  • The migratory wanderings, aimed at feeding and reproducing, of bluefin tuna, remain an enigma for scientists.

  • Researchers from Ifremer have thus placed electronic chips on several fish to try to understand their incredible journeys.

  • One of them did a double transatlantic before returning to the Mediterranean.

Bluefin tuna, tireless swimmers, are great travelers.

But their migratory peregrinations, aiming to feed themselves, in cold waters, and to reproduce, in warm waters, remain an enigma for scientists.

In an attempt to unravel their mysteries, Montpellier researchers from the French Research Institute for the Exploitation of the Sea (Ifremer) launched a new campaign two years ago, which has just provided some answers to their questions.

"An impressive journey"

It is in the south of Malta, on a fishing vessel, that these scientists captured tuna, to equip them with an electronic chip, before releasing them.

“Tagging on board a purse seine [a fishing vessel] is a real logistical challenge,” explains Tristan Rouyer, researcher at the Mediterranean fisheries laboratory in Montpellier.

It is necessary to go back on board the tuna that weigh more than 200 kg, place the anchor of the electronic mark at a specific location on the back, all in as little time as possible to limit the stress of the fish as much as possible and free them at faster.

We are the only team to carry out these markings during purse seine fishing campaigns in the breeding areas, where the largest catches in the world are made.

"

The researchers then crossed their fingers for the fleas to hold onto these large fish.

"Of the five individuals that we had equipped, three brands lasted more than ten months, including two one year, without falling off," continues the researcher.

A double transatlantic

Scientists were able to elucidate their trajectories: two tuna, more cushy than its congeners, remained in the Mediterranean Sea, while another was found in Ravenna, in the north of the Adriatic.

“The more adventurous has reached the Atlantic to the south of Iceland before continuing his crossing to Canada, heading south and then starting a return to the Mediterranean, where he returned in June, a year after being marked.

An impressive journey!

», Underlines Ifremer.

A double transatlantic, which particularly surprised scientists.

In addition to the details of the journeys of these bluefin tuna, the electronic marks have also allowed researchers to measure other parameters, such as temperature and light.

These data are all the keys to understanding the surprising behavior of this fish.

And to study their migratory dynamics, in the face of climate change.

Other chips will soon be placed on other tuna, indicates Ifremer.

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