Bluefin Tuna are back in the seas around the UK after decades of decline and absence. It has been proposed this could be due to warming seas rather than species recovery. After generations of overfishing, pollution and lack of food, it is astonishing how resilient these Tuna and other species are in their survival and wondrous that they should be able to return at all. What is not so wondrous is human nature. The Angling Trust are now petitioning for the protection status for these fish to be changed to establish a catch and release licensed fishery in what seems to me to be a case of self gratification and financial profit over sensible environmental concern.
New research by Dr Robin Faillettaz from the University of Lille (France), his French co-workers Drs Gregory Beaugrand and Eric Goberville, and Dr Richard Kirby from the UK – as part of the scientific programme CLIMIBIO (www.climibio.univ-lille.fr/) – has revealed that warmer seas can explain the reappearance of tuna around the UK.
Dr Richard Kirby says “Bluefin tuna have been extensively overfished during the 20th century and the stock was close to its lowest in 1990, a fact that further indicates the recent changes in distribution are most likely environmentally driven rather than due to fisheries management and stock recovery. Before we further exploit bluefin tuna either commercially or recreationally for sport fishing, we should consider whether it would be better to protect them by making the UK’s seas a safe space for one of the ocean’s most endangered top fish.”
I asked him for more information and he sent me the following report:
“Bluefin tuna are back in the sea around the UK after decades of absence and a new study says that warming seas can explain why. Bluefin tuna are one of the biggest, most valuable, most sought after, and most endangered fish in the oceans. Sport fishermen excited at the prospect of catching a fish that can grow to over 900kg have already launched a UK campaign to allow recreational fishing for one of game fishing’s top targets. But should we catch and exploit this endangered species or should we make UK waters a safe space for this incredible fish? Important questions to answer are why has this endangered fish suddenly returned to the UK after an absence of nearly 40 years and are bluefin tuna now more abundant or have they just changed in their distribution?
CLIMIBIO’s research shows that the disappearance and reappearance of bluefin tuna in European waters can be explained by hydroclimatic variability due to the Atlantic Multidecadal Oscillation (AMO), a northern hemisphere climatic oscillation that increases the sea temperature when in its positive phase like it is now.
To come to their conclusion, the scientists examined the changing abundance and distribution of bluefin tuna in the Atlantic Ocean over the last 200 years. They combined two modelling approaches, focusing on the intensity of the catches over time and on the distribution of the fish’s occurrence, i.e. when it was observed or caught. Their results are unequivocal: the AMO is the major driver influencing both the abundance and the distribution of the bluefin tuna.
The Atlantic Multidecadal Oscillation affects complex atmospheric and oceanographic processes in the northern hemisphere including the strength and direction of ocean currents, drought on land, and even the frequency and intensity of Atlantic hurricanes. Approximately every 60 to 120 years the AMO switches between positive and negative phases to create a basin-scale shift in the distribution of Atlantic bluefin tuna. During a warm AMO phase, such as since the mid-1990s, bluefin tuna forage as far north as Greenland, Iceland and Norway and almost disappear from the central and south Atlantic. During its previous warm phase – at the middle of the 20th century – the North Sea had a bluefin tuna fishery that rivalled the Mediterranean and the Bluefin Tunny sportfishing club – known worldwide – was founded in Scarborough. However, during a cold AMO phase, such as that between 1963-1995, bluefin tuna move south and are more frequently found in the western, central, and even southern Atlantic, with few fish caught above 45°N. Dr Faillettaz says that “The ecological effects of the AMO have long been overlooked and our results represent a breakthrough in understanding the history of bluefin tuna in the North Atlantic.”
In fact, the most striking example of the effect of the AMO on bluefin tuna is the sudden collapse of the large Nordic bluefin tuna fishery in 1963. The collapse coincides perfectly with the most rapid known switch in the AMO from its highest to its lowest recorded value in only two years. After that switch tuna also vacated the North Sea, and the conditions remained unfavourable for bluefin tuna in the northern Atlantic until the late 1990s when it started to reappear around the UK.
The scientists expect that bluefin tuna will continue to migrate to the UK and North Sea waters every year until the AMO reverses to a cold phase. However, they also highlight that the additional effect of global warming on sea temperatures will make the future response of bluefin tuna to changes in the AMO uncertain. Further to the effect of the AMO on where and when bluefin tuna occur in the Atlantic, the study also found that this climatic oscillation influences their recruitment, i.e., how many juvenile bluefin tuna grow to become adults.
Dr Faillettaz said that “when water temperature increases during a positive AMO, bluefin tuna move further north. However, the most positive phases of the AMO also have a detrimental effect upon recruitment in the Mediterranean Sea, which is currently the most important spawning ground, and that will affect adult abundance a few years later. If the AMO stays in a highly positive phase for several years, we may encounter more bluefin tuna in our waters, but the overall population could actually be decreasing.”
Consequently, Dr Beaugrand warns that “global warming superimposed upon the AMO is likely to alter the now familiar patterns we have seen in bluefin tuna over the last four centuries. Increasing global temperatures may cause Atlantic bluefin tuna to persist in the Nordic region and shrink the species distribution in the Atlantic Ocean, and it may even cause the fish to disappear from the Mediterranean Sea, which is currently the most important fishery.”
Dr Goberville also raises another important observation saying that “because bluefin tuna are so noticeable, they are also an indicator of current temperature driven changes in our seas that are occurring throughout the marine food chain, from the plankton to fish and seabirds”.
The Atlantic bluefin tuna fishery indeed encompasses most of the problems seen in fisheries around the world, including fleet overcapacity and political mismanagement; the species’ distribution crosses exclusive economic zones and spans international, open-access waters (i.e. the entire North Atlantic, from the Mediterranean Sea to the Gulf of Mexico). Added to that, the long-term fluctuation in Atlantic bluefin tuna abundance was hitherto understood poorly, which represents a fundamental gap in this fish’s sustainable management.
Dr Kirby says that “we have shown why bluefin tuna occur when and where in the North Atlantic and what may influence their recruitment and abundance, and this is fundamental to understanding the management of a fish that is endangered due to overfishing. Bluefin tuna have been extensively overfished during the 20th century and the stock was close to its lowest in 1990, a fact that further indicates the recent changes in distribution are most likely environmentally driven rather than due to fisheries management and stock recovery.”
Before we further exploit bluefin tuna either commercially or recreationally for sport fishing, we should consider whether it would be better to protect them by making the UK’s seas a safe space for one of the ocean’s most endangered top fish.”
The lead author Dr Faillettaz concludes: “Our results demonstrate that local changes in Atlantic bluefin tuna abundance can reflect large-scale shifts in a species’ distribution that are unrelated to improvements or worsening of a stock’s abundance. In this context we hope that our study will highlight the need to consider the environment when planning the sustainable management of all migratory fish species.”
For further information
Dr Richard Kirby
Dr Robin Faillettaz
For further reading
The BiG Scuba Podcast… with Paul Rose
Next in a new series of podcasts shared by our friends Gemma and Ian aka The BiG Scuba Podcast…
Ian and Gemma chat to Paul Rose. A man at the front line of exploration and one of the world’s most experienced divers, field science and polar experts, Paul Rose helps scientists unlock and communicate global mysteries in the most remote and challenging regions of the planet.
He is an experienced television presenter and radio broadcaster. With a proven track record in business engagements, Paul is a sought-after speaker, chairman, host and moderator for industry, government and NGO events.
Former Vice President of the Royal Geographical Society(link is external) and Chair of the Expeditions and Fieldwork Division, Paul is currently Expedition Leader for the National Geographic Pristine Seas Expeditions.
He was the Base Commander of Rothera Research Station, Antarctica, for the British Antarctic Survey for 10 years and was awarded HM The Queen’s Polar Medal. For his work with NASA and the Mars Lander project on Mt Erebus, Antarctica, he received the US Polar Medal.
Paul is a mountain and polar guide leading Greenland Icecap crossing and mountaineering expeditions and polar science support logistics. He worked for four years as a Mountain Safety consultant to the oil industry in the Middle East.
On his 2012 Greenland expedition, Paul led the first expedition to successfully traverse a new 275km icecap route of Knud Rasmussen Land and repeated his first ascent of the north face of Gunnsbjørnfjeld, the highest mountain in the Arctic.
His professional diving work includes science support diving in Antarctica as the British Antarctic Survey’s Institute Diving Officer. He ran the US Navy diver training programme at Great Lakes Naval Training Centre and trained many emergency response dive teams including the Police, Fire Department and Underwater Recovery Teams. He remains a current and active PADI Dive Instructor.
Find out more about Paul Rose at www.paulrose.org
Find more podcast episodes and information at www.thebigscuba.com and on most social platforms @thebigscuba
How can we do what you do at Blue Planet?
We at Blue Planet Aquarium usually get asked how people can do what we do; this question usually comes from young adults and children who are dreaming of careers in Marine Biology or Diving, and we make sure to help along the way as much as we can.
If you ask anyone in the industry how they got to where they are, you will always hear a different story, you will hear similarities but there will always be something different. Thus, I would always suggest for people to carve their own path in the industry, and of course this industry is huge with many different areas and avenues for you to go down, which is also what makes the industry so amazing, it allows everyone to have a speciality and to be able to do their part for the single goal of preserving our natural world.
Working as a Diver at Blue Planet is amazing for anyone who wants to make a career in the industry, for several reasons, it is good as it helps you gain diving experience both with animals and teaching students. It gives you chance to practice diving skills in what could be considered difficult diving due to the tasks we have to carry out, and it also allows you to learn about HSE regulations and laws which also helps makes you safe and aware.
Here at Blue Planet, we have people spanning a multitude of different careers, from Marine Biology, Military Diving, Photography and Dive Guiding, it is this that makes the team so amazing as we have a go to person for everything.
The best advice I can give to anyone who wanted to work on the dive team or in an aquarium, would be to have a decent amount of diving experience and be able to demonstrate good diving knowledge, along with being respectful to the environment and animals and being able to work well in a team. It is also helpful to be outgoing and confident as although we work behind the scenes, we are still in the view of guests when we do our feeds or public dives.
For more information about Blue Planet Aquarium please visit their website by clicking here.
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Jump on board the latest addition to the Emperor fleet and enjoy diving the famous sites of the Red Sea with this fantastic special offer. This itinerary takes in the wonderful South & St Johns from 26 February – 05 March 2021.
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