Danish tagging team. Photo: Thomas Petersen Eldor

Successful tagging of 18 bluefin tuna in Denmark and Sweden

Wednesday 18 Oct 17


Prof. Brian R. MacKenzie
DTU Aqua, Technical University of Denmark
+45 21 31 58 14

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

Press officer Maria Hornbek
+45 53 88 43 21

For the first time ever tagging of bluefin tuna has taken place in Danish and Swedish waters. The tags will collect important knowledge of the tuna that are present in Scandinavia after more than 50 years of absence.

DTU Aqua, SLU Aqua and WWF completed a successful tagging operation, supported by the International Commission for the Conservation of Atlantic Tunas (ICCAT), and now look forward to collecting the results from all 18 tags that have been placed on the backs of the big predatory fish. The tunas that were caught and released during the tagging project are bluefin tunas weighing from 130 kilos to 300 kilos. Despite challenging weather conditions, four were tagged in Denmark and 14 in Sweden. 

It is the first time ever that bluefin tuna have been tagged with advanced data-storage tags in Scandinavia. The tags on the tuna are now recording swimming depth, sea temperature and light. In about a year’s time, the data back will be sent back via satellite. This will show where the tuna have gone, including potentially where they spawn and feed. This new knowledge will help improve the sustainability of both the bluefin tuna and relevant fisheries.

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) in cooperation with dozens of volunteer recreational fishermen. The tagging took place in the Skagerrak-Kattegat off the Danish-Swedish coasts. 

"It has been a fantastic project. We have been able to tag 18 bluefin tunas, and we have had great support from the angling communities in Denmark and Sweden. Now we must wait for the data to come back to us. When it does, we will learn much more about why the tuna have returned and what actions we could take to encourage them to keep coming back," states Professor Brian MacKenzie from DTU Aqua. 

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

"The 18 tagged fish will contribute to the data on migration and genetics which will be fundamental for the management of bluefin tuna in the future. It will help us improve the sustainability of both the bluefin tuna and their fisheries. The stocks have grown and hopefully our chances are good to see them in Scandinavian waters in the years to come," states Dr. Andreas Sundelöf from SLU Aqua.

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

CEO Bo Øksnebjerg from WWF Denmark adds:
"Decades ago the bluefin tuna was a natural part of the marine life in Denmark and Sweden, but because of poor management of the fisheries the tuna fish totally disappeared from these waters. Now we have a unique chance to correct that mistake. If we can ensure a permanent return of the tuna, we are not only restoring Danish and Swedish nature – we are also bringing back an iconic species that naturally belongs to the food chains in our waters."

The tunas have been caught by anglers having experience with big-game fishing methods to support as harmless catch as possible and have been tagged by experts trained in tagging bluefin tuna. 

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 tagging took place over two weeks in September.

Facts about bluefin tuna

  • The maximum (officially) recorded weight for bluefin tuna is 725 kg, with a length of 3.3 meters.
  • The large pelagic fish can reach velocities of 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, have been classified in 2010 as endangered and were thus included on the IUCN Red List; however recent conservation actions since then have helped the recovery of this stock, which in 2017 supports sustainable fisheries.