SLU news

Tuna research: Advancing conservation and management knowledge

Published: 23 August 2023
Jumping tuna above the water surface.

All along the Swedish west-coast sightings of jumping giant tunas are being reported. Already in early August an unusually high number of tunas were spotted in Öresund, indicating that the fish arrived here early and quickly migrated south to the strait. This bodes well for this year's fieldwork where tunas will be equipped with transmitters to provide knowledge that can be used in management and conservation efforts.

The return of bluefin tuna to Swedish waters, after nearly 60 years of absence, is often cited as a success story of responsible management that has saved a species on the brink of extinction. At the same time, fishing quotas for bluefin tuna in the Atlantic are increasing once again, and many countries are building up their tuna fleets.

"This makes it even more important to gain knowledge about where and how the 'Swedish' tunas are caught and to map their migrations and survival," says Gustav Hellström, a researcher at the Swedish University of Agricultural Sciences, SLU.

Unpredictable Fieldwork

The tagging, conducted in the Skagerrak and Kattegatt region with a fleet of volunteer fishing teams, began last Saturday and will continue until September 3rd. After that, the tagging operation will move to Öresund for a few days at the end of September.

Strong winds and uncertain forecasts have made planning this year's fieldwork unusually challenging.

"Over the weekend, the wind forced us to fish further east than usual. However, the tunas were present, and five tunas were caught and tagged then. In addition, five more fish were caught and taggedyesterday (22nd). Two of the fish were shorter than 240 cm, which is encouraging as it indicates that new younger age classes have made their way here," says Tomas Brodin, a professor at SLU.

The largest fish of the weekend measured a whopping 286 cm and had an estimated weight of 365 kg.


The tuna project has been going on for several years, and is a collaboration between the Swedish University of Agricultural Sciences (SLU), the Danish Technical University's National Institute of Aquatic Resources (DTU Aqua), The International Commission for Conservation of Atlantic Tuna (ICCAT), and experienced sport fishermen.

Among other things, researchers tag the tunas with satellite transmitters programmed to release after a year. The transmitters then send data on everything from migration routes to spawning areas. To get access to high-resolution data the researchers need to recover the transmitters, which can be very challenging.