Bluefin tuna has been extinct by predatory fishing for decades, and since 2009 it has been internationally classified as threatened. Fishing is still allowed according to regulated quotas, but in order to set quotas, researchers need facts about how many they are and how they move in the Atlantic. Therefore, tuna is noticed and re-tested in the Atlantic.

Riddle how they swim

Since the tuna has returned to the West Coast in 2016, marking has been carried out the last two summers, but so far the results are unclear. Only three transmitters have worked and the information is not clear. One fish has been swimming to New Foundland off the east coast of Canada, one has been swimming south to the sea off Morocco, and one has been swimming into the Mediterranean and turned.

- Although this is a recognized species of great value, biological knowledge is actually not that great, so we hope to strengthen science with it, says fisheries researcher Andreas Sundelöf at SLU Aqua, who now labels fish for the third summer in a row.

Inigo Onianda gets ready to tag a tuna. The eyes are covered, the hook is removed and the fish gets water in a hose. It is measured before being released back into the water. Photo: SLU

Origin: Mediterranean

Bluefin tuna plays and propagates in the warm waters of the Gulf of Mexico and the Mediterranean. How these two stocks are interconnected and how the tuna swim is unclear, but the gene tests have shown that 95 percent of the tuna caught on the west coast originated in the Mediterranean stock.

- That's what we expect, says Andreas Sundelöf.

Gets to catch protected fish

The researchers are now collaborating with Swedish and Danish anglers who now have the chance of their lives to catch one of the largest fish that can be found in Sweden, a fish that is otherwise completely protected for the sake of research. The goal this year is to label 26 tuna with one or more transmitters and labels on the Swedish side.

- Ernest Hemingway called the bluefin tuna for the king of all fish for its strength and speed. It goes without saying that you want to hook a bluefin tuna at some point in your life. Sport fishing is the best method to collect this data, says Markus Lundgren of the organization Sportfiskarna.

May continue to increase in Sweden

How much tuna there is now on the West Coast is difficult to estimate and Sweden currently has no fishing quota. The anglers hope that it will continue to increase so that it is no longer classified as threatened and can then be fished in Sweden again.

It is based on the fact that the population of the Mediterranean continues to increase and spread northward. Although fishing is now increasing again in the Mediterranean, it still looks bright for tuna in Sweden according to fisheries researcher Inogo Onianda.

- Yes, when you see such large individuals it is a good sign of good status on the stock, he says.