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
Creature Feature: Porbeagle
In this series, the Shark Trust will be sharing amazing facts about different species of sharks and what you can do to help protect them.
This time we’re showcasing the robust Porbeagle, one of the only known sharks that may love to play..
Shaped like a rugby ball, this muscular stocky shark is incredibly hydrodynamic and built for endurance. Dark grey-blue in colour with a white belly, they have a pointed snout and large black eyes.
Porbeagle’s belong to an elite group of sharks known as the mackerel sharks. These include some of the most powerful and agile sharks in the world, such as the White Shark and Shortfin Mako. This group are endothermic, so can keep themselves nice and warm, due to a remarkable adaptation known as a rete mirabile. This makes them more efficient hunters and able to tolerate colder waters.
Porbeagle’s look a lot like White Sharks, so are often mistaken for them. As they’re found in UK waters, this has led to many false reports of White Sharks in the UK. But Porbeagle’s are around half the size. Although still a large shark, the biggest Porbeagle on record is 3.6m. While the largest White Shark is 6m.
Found worldwide in cold-temperate waters, Porbeagle’s are strong swimmers. Travelling thousands of miles in search of food and to give birth. One individual, tagged in Irish waters, journeyed over 2,000 miles to Newfoundland in Canada. A known mating ground for Porbeagle’s.
Porbeagle’s may live on their own, or in small groups made up of similar sized or same sex individuals. With males and females coming together usually in September-November to mate. Yet in some places this can take place in January.
These sharks reproduce slowly, so are extremely vulnerable to destructive fishing. Females take 12-16 years to reach sexual maturity, males 6-10 years. After 8-9 months, females will give birth to litters of just 1-5 pups, which are relatively large at 60-80cm long.
Two distinct populations exist – the north Atlantic and south Pacific. Individuals from these areas don’t seem to mix, resulting in key differences. North Atlantic Porbeagle’s get a lot bigger, and don’t tend to live as long as those in the south Pacific.
During the day Porbeagles tend to spend their time in deeper waters, rising to the surface at night. They’re opportunistic feeders, mostly eating small fish – such as mackerel, whiting and herring – as well as octopus, squid and cuttlefish.
Highly inquisitive, Porbeagles have been seen chasing each other, rolling at the surface, and even pushing around floating objects and kelp. Could they be playing? Currently there are no scientific studies to back this up. But what an interesting study that would be…!
- SCIENTIFIC NAME: Lamna nasus
- FAMILY: Mackerel Sharks (Lamnidae)
- MAXIMUM SIZE: 3.6m
- DIET: Small fish & squid
- DISTRIBUTION: Wide-ranging in temperate waters (except North Pacific).
- HABITAT: Coastal and oceanic waters from 0-1,800m deep. Prefers temperatures below 18°C but can tolerate -1–23°C.
- CONSERVATION STATUS: Vulnerable
For more amazing facts about sharks and what you can do to help the Shark Trust protect them visit the Shark Trust website by clicking here.
Header Image: Doug Perrine / Alamy
Top Destinations to dive with Manta Rays
In their mission to create a billion Torchbearers to explore and protect the ocean, PADI is encouraging divers to seek adventure and experience first-hand the vital eco-systems below the surface of the ocean.
To further raise awareness of this mission on International Manta Ray Day (17 September 2021), PADI has rounded up the top destinations in the world that are currently open to divers.
Machadilla National Park, Isla de la Plata, Ecuador
Diving in Ecuador offers a special paradise for scuba divers, in which the chance of encountering marine species nowhere else on earth is extremely high due to the heavy currents and nutrient rich waters. And for those keen to dive with manta rays, head out with PADI 5 Star Dive Center Exploramar Diving, or PADI 5 Star Dive Center Mares Ecuador here they take divers out to Machadilla National Park in Isla de la Plata for a chance to greet these graceful creatures every July to September.
Find out more with PADI’s Dive Guide for Ecuador
Kona, Big Island, Hawaii
Hawaii’s volcanic origins and isolated geographical location makes for a whirlwind of scuba diving encounters underwater, with manta ray encounters being likely all year long. For those looking for an extra special experience, PADI 5 Star Dive Center Jack’s Diving Locker offers a manta ray night dive and a PADI Distinctive Specialty Course called Manta Ray Diver, which covers everything from the manta ray anatomy to cleaning habits, reproduction and how to identify individual rays in the local population.
Find out more with PADI’s Dive Guide for Hawaii
Bryon Bay, Australia
For those who are currently in Australia, they can have their backyard manta ray encounter with PADI 5 Star Dive Center Sundive Byron Bay. The summer months of December to May bring manta rays to the nearby Julia Rocks Marine Reserve, which National Geographic once acknowledged as one of the top 20 dives in the world.
Find out more with PADI’s Dive Guide for Australia
Manta Point, Nusa Penida, Bali
The name speaks for itself. Manta Point in Bali is a haven for manta rays all year long, with the best time to see them being from April to May. PADI 5 Star Dive Center and Resort Scuba Junkie Penida offers the ultimate manta ray diving experience in the area, adding coral dives and drift dives to the day’s adventure.
Find out more with PADI’ Dive Guide for Bali
Komodo National Park, Labuan Bajo, Indonesia
One of Indonesia’s most famous diving destinations is also one of the best places to dive with manta rays! PADI 5 Star Dive Resort Blue Marlin Komodo is the perfect place for a manta ray holiday, where divers can stay at the dive resort while getting their PADI Open Water Diver certification and then hop aboard their dive vessel for a day of diving out at sea with manta rays!
Find out more with PADI’s Dive Guide for Indonesia
Six Senses Manta Point, Laamu Atoll, Maldives
Crystal clear warm waters, white sandy beaches and manta rays—PADI 5 Star Dive Resort Six Senses Laamu offers the ultimate luxurious manta ray holiday. As the only dive resort in the Laamu Atoll, divers of all levels will have extremely personable encounters with manta rays every month of the year in this world-class diving area. There are also more than 180 PADI Dive Centers and Resorts in the Maldives that can take divers out to have a manta ray encounter.
Find out more with PADI’s Dive Guide for the Maldives
The islands that make up the Azores off the coast of Portugal are one of the most diverse for marine life. One specific type of manta rays known as the Mobula birostris is known tohang out in large groups around the island of St. Maria between June and October, with PADI 5 Star Haliotis Dive Center offering guided boat trips to the island.
Find out more with PADI’s Dive Guide for Portugal
Diving with whale sharks and manta rays can make a difference in protecting these incredible species for future generations – dive tourism encourages protection from local communities and governments. But its important to always adhere to local guidelines and best practices to ensure these creatures’ well-being is always at the forefront. PADI dive operators understand the importance of using the proper equipment, the time of day to dive with sharks, and the maximum number of operators that should be on the water at any given time. To learn more about responsible shark and ray tourism and other ways you can support the protection of these incredible animals, visit padi.com/aware/sharks.
Win a PADI Drift Diver eLearning Course – two to give away!!!
For this week’s competition, we’ve teamed up with our good friends at PADI to give away a couple of their Drift Diver eLearning...
Win a Mares Magnetic Connector BCD Accessory!!!
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WIN an XDEEP Radical Frameless Mask!!!
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WIN a Bigblue Expandable Tray!!!
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Red Sea Northern Wrecks & Reefs plus Tiran
Custom built itinerary scheduled to include Abu Nuhas wrecks, the SS Thistlegorm, the fabulous reefs at Ras Mohamed including Shark Reef, then over to Tiran to dive Gordon, Jackson, Thomas and Woodhouse reefs.
You’ll visit any number of other wrecks including the beautiful Carnatic and the wrecks of the Giannis D, the Chrisoula K and the Marcus, all at Abu Nuhas. And you can’t miss the Rosalie Moeller and the Dunraven!
But this trip isn’t just about wrecks – far from it! Ras Mohammed, the protected marine reserve of the Red Sea, delivers schooling fish, spectacular corals, and we drop-in numerous times on the best sites before heading over to Tiran to dive the immense reefs of Gordon, Jackson and Woodhouse.
What are you going to see? The most stunning corals, abundant marine life, and exceptional wrecks. Turtles, Napoleon wrasse, morays, dolphins, maybe a manta, and perhaps even whale sharks. Hammerheads off the back of Jackson Reef are a possibility, and don’t forget the little critters either! This trip delivers, time and time again.
From £1599 per person based on double occupancy. Full board basis, buffet meals with snacks, tea and coffee always available. Add a week on at Roots Red Sea Resort before or after the liveaboard for just £695pp. Stay in a deluxe chalet on a soft all-inclusive basis and enjoy 10 guided shore dives and unlimited, unguided house reef diving. Flights and transfers are included. See our brochure linked above for the full itinerary.
This trip will be hosted by The Scuba Place. Come Dive with Us!
Call 020 3515 9955 or email email@example.comMore Less
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