The bluefin tuna has returned to Swedish waters after being almost completely absent since the 1960s. Now, researchers at SLU will study the tuna population in Skagerrak.
Every summer, the tuna comes to the North Sea and the Baltic Sea to search for food such as mackerel, herring, and garfish. For the rest of the year, it swims in the world’s oceans.
The bluefin tuna was common in Swedish waters during the 1950s but disappeared more and more during the 1960s, probably due to overfishing. However, a few years ago, it reappeared in Swedish waters and has continued to return every late summer.
– The bluefin tuna is an incredibly special and spectacular species. In many ways, it’s the ultimate fish, says Gustav Hellström, a researcher at SLU, to Swedish popular science magazine Forskning & Framsteg.
At the end of August, researchers from the Swedish University of Agricultural Sciences (SLU) have been searching for the tuna at sea in Skagerrak, which is located between Lysekil and Skagen. Tuna are tagged, among other things, so that one can study how they move and how many are caught. The aim is to help preserve the tuna stock.
Last year, there was a lot of tuna in Scandinavian waters, especially in Öresund and Kattegatt. However, Hellström describes today’s stock as vulnerable and emphasizes the importance of studying how the fish move through the oceans.
– They don’t migrate randomly but follow defined corridors in the ocean. It’s important to understand these highways that other species probably also use, he adds.
Tuna can weigh up to 500 kilograms and grow three meters long. Fish tagged by Hellström and colleagues have weighed up to 400 kilograms, but they expect them to grow larger. He also mentions that they hope to find more smaller tunas as it might indicate that younger fish manage to reach the Nordic region.