The world’s most coveted fish is back in Danish and Swedish waters. New project will tag tuna to find out why they have come back
Bluefin tuna, one of the biggest and fastest bony fishes that lives in the ocean, have returned to waters near Denmark and Sweden in the last few years after nearly 50 years of absence.
Now a new project being conducted by DTU Aqua (Denmark), SLU Aqua (Sweden) and WWF (Netherlands), and supported by the International Commission for the Conservation of Atlantic Tunas (ICCAT; Spain), will learn more about the reasons why they have come back and the factors that could encourage them to keep coming here in the future.
Scientists and recreational fishermen coorperate
Scientists and recreational fishermen will work together to catch bluefin tuna, attach advanced data-storage tags to them and then release the tunas again. The tags will record swimming depth, sea temperature, and other oceanographic information. These data will then be transmitted back to the scientists via satellite and will tell the scientists about the whereabouts of the tuna, reveal their favorite feeding areas and how long they stay at these “seafood restaurants”.
The scientists will also take biological samples from the tuna (e.g. blood) to investigate which of the two spawning groups (the Mediterranean Sea or Gulf of Mexico) they belong to. Both groups have been shown to cross the ocean and return. This information is important because the two groups of fish have different fishery management regulations.
Tunas will be tagged in autumn 2017
The study will be conducted in the Skagerrak-Kattegat and the Øresund, depending on where the tunas are. When bluefin tuna used to be present here in large numbers in the 1930s-early 1960s, they arrived in late summer-early autumn and stayed for a few months.
The new tagging study will be conducted in the autumn of 2017, historically the prime tuna season, and the time of year when most tunas were sighted the last couple of years.
As neither Denmark nor Sweden has permission to catch bluefin tuna, the project has received permission from ICCAT to catch and release bluefin tunas for research purposes in this project.
Contributes to a sustainable bluefin tuna fishery
The new scientific results will help scientists understand how factors such as fishing, climate-ocean variability and local food supplies affect the spatial distribution and migration behaviour of this species, and how, where and why the two groups mix.
The results will contribute to the development of new population dynamics and migration models and to the sustainability of bluefin tuna fisheries throughout the north Atlantic.
Photo: Bluefin tuna. By Rickard Waje.