Atlantic bluefin tuna feeding in the Mediterranean Sea. Copyright Credit: © Frédéric BASSEMAYOUSSE / WWF-Mediterranean

Tuna tagging for the first time ever in Denmark and Sweden

Saturday 09 Sep 17

Facts about bluefin tuna

  • The officially registered maximum weight of a bluefin tuna is 725 kg, with a size of 3.3 meters and can reach a speed of over 80 km/h
  • Female Atlantic bluefin tuna can produce up to 10 million eggs per year.
  • The Bluefin Tuna is warm blooded which is a rare trait among fish
  • Bluefin tuna species and stocks, including the one in the Northeast Atlantic-Mediterranean, are endangered and on the IUCN Red List; however recent conservation actions are helping this one to recover and support sustainable fisheries.


DTU Aqua, Technical University of Denmark
Project Leader, Professor 
Brian R. MacKenzie
Tel. +45 2131 5814

SLU Aqua, Swedish University of Agricultural Sciences
Dr. Andreas Sundelöf
Tel. +46 10 47 84 069

WWF Netherlands
Ocean Expert Ingvild Harkes
Tel. +31 6 1255 6767 /
+31 6 1139 0691

Press officer Dylan de Gruijl
Tel. +31 6 2260 7633 

WWF Denmark
Press Officer Cecilie Weinholt
Tel. +45 3176 1200 

Today DTU Aqua, SLU Aqua and WWF will start tagging bluefin tuna to get a better understanding of why the fish have begun returning to Danish and Swedish waters, after more than 50 years of absence.

Saturday 9 September 2017 this unique tagging operation of the iconic bluefin tuna will kick off in Denmark and Sweden. It is the first time ever that Bluefin tuna will be tagged with advanced data-storage tags in Scandinavia.

The project is conducted by Technical University of Denmark (DTU Aqua), the Swedish University of Agricultural Sciences (SLU Aqua) and World Wide Fund for Nature (WWF), supported by the International Commission for the Conservation of Atlantic Tunas (ICCAT). The tagging will take place in the Skagerrak-Kattegat off the Danish-Swedish coasts.

The tuna disappeared from Danish and Swedish waters in the 1960s, probably due to a combination of high fishing pressure on both the tunas and their prey, and changes in ocean conditions.

"We don’t know why they now have begun to return but probably improved management and conservation measures are helping. This exciting tagging project is the first of its kind in Scandinavia and will hopefully reveal some secrets about the bluefin tuna," says Project Leader, Professor Brian MacKenzie from DTU Aqua.

Dr. Andreas Sundelöf from SLU Aqua adds:

"If we understand the reasons why the tuna has returned, we might be able to identify the factors that will enable them to keep coming here in the future. Bluefin tuna is a large predator at the top of the food chain which makes them essential for a healthy ecosystem".

The east Atlantic-Mediterranean bluefin tuna has been on the verge of extinction due to decades of heavy overfishing. After years of intensive advocacy for sustainable management, the population in the Mediterranean is now showing signs of recovery. If the bluefin tuna return to the north, we need proper management measures to preserve this species, WWF-ocean expert Ingvild Harkes stresses:

"This amazing animal is one of the most commercially valuable fish in the world. For this reason, bluefin tuna has been heavily overfished for decades and has fallen victim to widespread illegal fishing especially in its main spawning grounds across the Mediterranean. Now that it seems to be back, it is important to find out how to preserve the bluefin tuna for future generations".

Scientists and recreational fishers will now work together to catch 40 Bluefin tunas and tag them by attaching advanced electronic data-storage to the fish before releasing the tunas again. This operation will take place over a period of two weeks starting today. The tags will record location, swimming depth, sea temperature and light. When the tags detach from the tunas after a year, they will rise to the surface and transmit their data back to the scientists via satellite. The data will reveal the migration patterns of the tuna and the potential spawning and feeding grounds.

The scientists will also take DNA samples from the tuna to identify which of the two stocks they belong to: the one spawning in the Mediterranean Sea or in the Gulf of Mexico. This information is important because the two groups of fish have currently different management regimes.

As neither Denmark nor Sweden has quotas for targeted bluefin tuna fishing, this project has been allocated a special permission from ICCAT for research purposes only to catch and release bluefin tunas for tagging. The tunas will be caught by anglers having experience with big-game fishing methods to support as harmless catch as possible and will be tagged by experts trained in tagging bluefin tuna.  

Photo: Atlantic bluefin tuna (Thunnus thynnus) feeding in the Mediterranean Sea. Copyright Credit: © Frédéric BASSEMAYOUSSE / WWF-Mediterranean.