Just off the rugged coast of Cornwall, the sea rolls blue and glassy under a pale morning sky. A research boat rocks gently in the swell, instruments ticking softly as the team scans the horizon. Then, suddenly, the water erupts. A school of baitfish flashes to the surface in a frenzy of silver panic.
Out of nowhere, it hits like a torpedo. A blur of blue-black muscle and raw speed, slicing through the sea with terrifying grace. It twists; each turn impossibly tight for a creature the size of a tall human! A creature that, until recently, was a rare sight in British waters.
The baitball fragments, desperate, but the tuna is already there, anticipating its movements. It strikes forward, faster than the eye can track. With each powerful sweep of its tail, it carves through the chaos, feeding with ruthless precision.
The researchers can only watch as the ocean turns into a theatre of speed and power. The water boils with the chaos of the hunt.
The return of a vanished giant
The Atlantic bluefin tuna is an extraordinary animal defined by pure speed and power. However, largely due to overfishing, they disappeared from UK waters in the 1960s1. Sadly, this has been the case for many species in UK waters. Over the past 150 years, advancements in fishing practices and technology have dramatically increased how far and how much we can fish.2
But, unlike many of its fallen comrades, unexpectedly and of its own accord, the Atlantic Bluefin Tuna has returned! A true story of hope for British waters! But to avoid history repeating itself, we must protect these incredible species.
This is easier said than done as tuna are known to dive to incredible depths and roam thousands of miles each year! So, to better understand how we can protect the tuna sighted off the Cornish coast, a team of researchers from the University of Exeter decided to track their movements and migration to see where they go and what they get up to!
Following the fish
Obviously, tracking a creature like the Atlantic bluefin tuna is no small task and following their movements requires more than patience; it requires technology built for the high seas. Luckily, the researchers had just the device up their sleeve: the pop-up satellite archival tag. Once attached to a fish, these tags follow it around and, through a satellite, send the data that they collect straight to the researchers. This is a major step up from older tags, which had to be retrieved first to get the data. It’s the difference between receiving an SMS and having to go to your friend’s house to ask for their notes!
So, between 2018 and 2021, the researchers set to work attaching these tags to 68 individual tunas found in British waters, collecting information about their position, depth, temperature and other factors that the tuna was experiencing.
Tuna tracking
Out of the 68 tags that were attached, an impressive 56 successfully transmitted data to the researchers. However, in the end, only 25 of the tuna were tracked for more than 300 days. But this still left the team with an incredible 12,738 days’ worth of data!
This is because sometimes the tagged tuna get fished, eaten by other animals, or die from other natural causes. Although, this in itself can make for very interesting data! One tag in particular accidentally collected the longest tagging dataset of one of the tuna’s primary predators…but that’s a story for another article!!
The data collected from the tags confirmed something very exciting! Not only had tuna returned to British waters, they were returning year after year. This shows that the tuna seen off the coast of the UK were not just passing through, they were choosing to be there!
They also found that these tuna seemed committed to a three-phase migration pattern. They appeared to spend autumn in shallower coastal waters like the UK, winter in deeper offshore waters like the High Seas, and summer in known spawning groups around the Mediterranean or in the south of the Bay of Biscay.
This is really important information as the tuna seen at all of these different locations can be considered from the same ‘stock,’ a term often used when discussing the management of a species when it comes to fishing. With this knowledge, conservation efforts can be made more effective, ensuring that crucial habitats are protected during key phases of the tuna’s life cycle. It also opens the possibility of smarter policies that balance conservation with fishing interests.
* For the purpose of this article, autumn refers to August–December, winter to December–April, and summer to May–July.
But why have they returned?
Among the most exciting outcomes of this research is the confirmation that the Channel is once again a seasonal home for Atlantic bluefin tuna. During summer and autumn, a sizeable population now regularly swims between England and France, and they seem to like the area enough that they come back every year after completing their lengthy migrations. But how did this happen without extensive conservation intervention? There are two main possibilities, perhaps working together!
As temperatures increase around the globe, animals travel further and further north to escape the heat3, and fish are no exception to this phenomenon. The European sardine and the European anchovy, two key components of the tuna’s menu, currently thrive in the Channel because of this, and your food moving somewhere else seems a compelling enough reason for you to follow!
Alternatively, it could also be that the Atlantic bluefin tuna population has increased enough that some tuna have relocated to the Channel in search of a less crowded, more favourable environment.
Protecting a part-time visitor
Regardless of why they’ve returned, what matters now is that the Channel has become a key seasonal habitat for these tuna, and that brings responsibility. Protecting them, however, isn’t straightforward. How do you safeguard a species that only visits your nation’s waters for part of the year? If they’re only protected in a fraction of their range, they may be caught or harmed elsewhere before making it back to the safe zone, rendering local efforts ineffective.
The answer is cooperating with other countries that the species visits on its migrations.4-5 In the Atlantic Bluefin Tuna’s case, this would be other European waters. Developing a conservation plan of such magnitude would inevitably take time, but luckily, the UK and EU have many similar cases that they can draw from, as well as the support of knowledgeable marine biologists and fishery experts.
The Atlantic Bluefin Tuna has historically been admired for its size, strength, and speed. Fishermen commend them, and writers recount anecdotes of their prowess. Merely seeing them as food yet to be caught and prepared would be undervaluing their existence. So, perhaps it’s time we reconnect with them, not just as resources, but as magnificent animals worthy of the same awe we reserve for whales or dolphins!
Article written by Giulia Checchi and Nia Clarke
Primary paper:
Horton, T.W. et al. (2025) ‘Annual migrations, Vertical Habitat use and fidelity of Atlantic bluefin tuna tracked from waters off the United Kingdom’, Scientific Reports, 15(1). doi:10.1038/s41598-024-80861-w. https://www.nature.com/articles/s41598-024-80861-w
Other references:
- Horton, T.W., Block, B.A., Davies, R., Hawkes, L.A., Jones, D., Jones, H., Leeves, K., Maoiléidigh, N.Ó., Righton, D., van der Kooij, J. and Wall, D., 2021. Evidence of increased occurrence of Atlantic bluefin tuna in territorial waters of the United Kingdom and Ireland. ICES Journal of Marine Science, 78(5), pp.1672-1683. https://academic.oup.com/icesjms/article/78/5/1672/6231587?login=false
- Mansfield, B., 2010. “Modern” industrial fisheries and the crisis of overfishing. In Global political ecology(pp. 98-113). Routledge.
- Parmesan, C., Gaines, S., Gonzalez, L., Kaufman, D. M., Kingsolver, J., Townsend Peterson, A., & Sagarin, R. (2005). Empirical perspectives on species borders: from traditional biogeography to global change. Oikos, 108(1), 58-75.
- Martin, T. G., Chadès, I., Arcese, P., Marra, P. P., Possingham, H. P., & Norris, D. R. (2007). Optimal conservation of migratory species. PloS one, 2(8), e751.
- Lascelles, B., Notarbartolo Di Sciara, G., Agardy, T., Cuttelod, A., Eckert, S., Glowka, L., … & Tetley, M. J. (2014). Migratory marine species: their status, threats and conservation management needs. Aquatic Conservation: Marine and Freshwater Ecosystems, 24(S2), 111-127.
