The Atlantic tuna had disappeared from the Öresund for more than half a century. Overfishing had brought the stock in the Atlantic and Mediterranean to the brink of collapse. International conservation measures have now been in place for over ten years. Catch quotas and fishing breaks are now proving successful. The IUCN removed the species from the Red List in 2026.
Special conditions for tuna in the Öresund
The strait between Denmark and Sweden offers the tuna a unique habitat. The seabed is shallow and funnel-shaped. At the narrowest point between Helsingør and Helsingborg, the passage measures just four kilometres. The water depth there is between 20 and 40 metres. For tuna, which normally dive several hundred metres deep, the Öresund is like a bottleneck. When hunting herring, mackerel and garfish, the fish can reach speeds of over 50 kilometres per hour. This speed can no longer be slowed down in shallow water. The animals break through the surface and jump metres out of the water.
Strict safety rules in use
There is a commercial fishing ban on tuna in the Öresund. Its prey fish are also subject to strict protective measures. Herring, mackerel and garfish may only be caught during set periods. The heavily overfished Baltic Sea is slowly recovering from decades of exploitation. Jens Peder Jeppesen is head of the Öresund Aquarium in Helsingør. The marine biologist has been observing the development for years. On some days, he counts schools of several hundred jumping tuna. The sightings are documented and passed on to environmental associations, fishing organisations and Copenhagen University.
Tuna safaris provide research data
The aquarium offers tuna-watching tours. The excursions are not just for tourism. They provide valuable data on stock development. Every sighting is counted and documented. The information flows into conservation management. The animals pass through the strait from late summer onwards. This is the best time for observations. The adult tuna weigh around 300 kilograms and measure around three metres in length. Their leaps out of the water can be seen from a great distance.
Global protection not yet secured
The Atlantic tuna is considered a conservation success story. The situation is different in the Pacific. Related species are still endangered there. They are among the most expensive edible fish in the world. World Tuna Day on 2 May draws attention to the problem. Environmental organisations are calling for sustainable fishing and consistent conservation measures. The recovery of the Atlantic tuna shows that protective measures work. However, they must be maintained in the long term.
Geological features shape behaviour
The shallow topography of the Öresund strongly influences the behaviour of tuna. In deeper waters, they usually hunt below the surface. In the Öresund, they lack the space to escape. The high speed at which they hunt inevitably causes them to break the surface of the water. Jeppesen observes this phenomenon more intensively every year. The population is growing continuously. The number of sightings is increasing. This confirms the success of the protection measures.
Food supply crucial for return
The recovery of prey fish stocks was a prerequisite for the return of tuna. Herring and mackerel were also under enormous fishing pressure. Closed seasons and catch quotas have also stabilised these stocks. The Öresund once again offers sufficient food. However, the heavily travelled strait still poses a challenge. Shipping traffic and limited water depth restrict the habitat. Nevertheless, the tuna regularly utilise the passage.
Long-term tuna monitoring necessary
Stock recovery is not a sure-fire success. Continuous monitoring remains necessary. The data from the Öresund is fed into international conservation programmes to help assess population trends. This enables scientists to recognise changes at an early stage. If necessary, conservation measures can be adapted.
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Jan-Ole Puls
Editor Test & Technology
