- Scientific name: Thunnus thynnus
- Also know as: Tunny, Northern Bluefin Tuna
- Size: Up to 11ft and 1500lb, but average adult is 5ft and 550lbs.
- UK minimum size: N/a – protected species which cannot be targeted by anglers.
- UK shore caught record: N/a
- ICUN Status: NT (Near Threatened) in Europe
- Distribution: Found from the Caribbean Sea and along the east coast of the USA and Canada across the whole of the north Atlantic to the north coast of Africa and the whole of the Mediterranean. Although rare they are increasingly sighted in the waters around the British Isles and are present as far north as the colder waters of the Baltic Sea and the Norwegian Sea.
- Feeds on: Smaller fish and squid.
- Description: Oval shaped powerful body with short fins and long cresent-shaped tail. Small finlets running from dorsal fin to lunate (crescent shaped) caudal fin and two dorsal fins are present. Snout is pointed and mouth is relatively large. Back is dark blue changing to grey on the underside with white dotted lines running upwards from the underside.
Atlantic bluefin tuna is an iconic species the world over. It is one of the most highly prized food fish in the world, and big game anglers target bluefin tuna due to their prodigious power and fighting qualities. Inevitably this has led to intensive commercial fishing of this species and a corresponding large scale decline of bluefin tuna across the world. Despite this warming sea temperatures mean that the distribution of remaining bluefin tuna stocks are changing, and recent years have seen them make a return to the waters around the British Isles. The increasing prevalence of bluefin tuna in British waters has led to calls for a catch-and-release recreational fishery to be established, although this has been opposed by conservationists.
The bluefin tuna has a very wide distribution due to its migratory patterns. Their distribution may be further expanding due to warming sea temperatures (even as tuna numbers are reduced). Bluefin tuna are found from the relatively cold waters around the UK and Nordic countries to the warmer waters of the Mediterranean. Their range extends across the Atlantic where they are found from the coast of Canada to coastline of Brazil and throughout the Gulf of Mexico and the Caribbean Sea. The extent to which tuna populations on each side of the Atlantic Ocean intermix is open to debate, but there are two distinct breeding populations in the west and east of the Atlantic Ocean (see below).
There is some dispute over the maximum size Bluefin tuna can grow to. It is generally accepted that they can certainly reach lengths of 12ft and weigh over 1,500lbs. However, the US National Oceanographic and Atmospheric Administration states that they can reach 13ft in length and 2000lbs, although a Bluefin tuna of this size would be extremely rare. The average size of a fully grown Bluefin tuna is generally 6 – 8ft and between 350b and 550lb in weight.
The largest Bluefin tuna ever caught on rod and line was 1496lb (678.58 kg). It was caught off the coast of Aulds Cove, Nova Scotia, Canada in 1979 by an angler named Ken Fraser. While other, possibly larger, Bluefin tuna may have been caught this is the largest capture which adhered to International Game Fish Association rules.
Diet, Behaviour and Migration
Tuna are a predatory fish which uses its power and speed to catch smaller fish. Juvenile bluefin tuna will pursue smaller fish such as mackerel, sardines and herring, but as they grow they will chase and catch progressively larger prey, although they prefer to consume fish which they can swallow whole which means they avoid the largest species. Bluefin tuna can swim at speeds of up to 40mph and can dive to several hundred metres to find fish to prey on. Bluefin tuna are a highly migratory species. They return to the waters where they were born to spawn, meaning that there are two separate breeding stocks, one in the Mediterranean and one in the Gulf of Mexico. Tuna, therefore may move great distances from the area where they were born during their life but once they reach sexual maturity they will undertake migrations to return to their birthplace to spawn. In the Mediterranean this happens during the summer when the sea temperatures begin to warm up.
Bluefin tuna is officially known as Atlantic bluefin tuna (Thunnus thynnus). There is a similar species found in the Pacific which is now known as Pacific Bluefin tuna (Thunnus orientalis). However, in the past both of these species have been combined together and known as Northen Bluefin Tuna. However, this is rarely done these days and both stocks are generally considered separate species.
Use as Food and Overfishing
Bluefin tuna is one of the world’s most highly prized food fish. It is in huge demand in Japan with some reports stating that as much as 75 – 80% of the bluefin tuna which is commercially caught ends up being sold in Japan as sushi or sashimi. In the UK and other western nation’s fresh bluefin tuna is a ultra-premium fish which can command very high prices.
There are two main commercial methods of catching bluefin tuna: long-lines (where lines containing hundreds, or even thousands, of baited hooks are set out at sea and then retrieved after several days) and purse seining (where a vast net is drawn around tuna and then closed). Other methods include commercial fishing for tuna with rod and line which is mostly practiced for bluefin tuna by fishermen in US waters, and tuna ‘ranching’ involves catching juvenile tuna and then raising them to fully grown marketable fish in open water fish farms.
Due to the demand for bluefin tuna and the price it can reach this species has been subject to intensive commercial exploitation, leading to today’s bluefin tuna stocks being a fraction of previous levels. The International Union for the Conservation of Nature classes bluefin tuna as being Endangered on an worldwide basis with a decreasing population trend. Quota systems which have been introduced across the world have been ineffective in protecting and restoring bluefin tuna stocks, and in the EU eight nations (Spain, France, Croatia, Italy, Greece, Portugal, Malta and Cyprus) share the EU quota for bluefin tuna which was set at 15,850 tonnes for 2018. As the UK has no quota for this species UK commercial fishermen and recreational anglers must return any bluefin tuna which are caught to the sea unharmed and as quickly as possible (see section below).
However, EU nations which have quota for tuna, such as France, can come into British waters to catch bluefin tuna present there. The migratory nature of tuna makes managing and conserving stocks difficult as the fish move across multiple international boundaries. This led to the creation of ICCAT (International Commission for the Conservation of Atlantic Tunas) in 1969. This is an intergovernmental organisation which has the task of managing and conserving stocks of tuna and related species in the northern Atlantic and surrounding seas. Unfortunately ICCAT has developed a poor reputation and is seen as being responsible for mismanaging stocks, favouring the commercial fishing industry and failing to heed scientific advice on quota reductions which are necessary to restore tuna stocks. For these reasons ICCAT is often referred to by conservationists as the International Conspiracy to Catch All Tuna. There have been a few positive moves to protect bluefin tuna stocks, such as the ban on EU nations using driftnets to catch tuna which was introduced in 2002.
While bluefin tuna is one of the most valuable fish in the world UK consumers may be more used to skipjack tuna (Katsuwonus pelamis). This is the species which is much more likely to be found in tinned tuna and pre-packaged tuna products. It is a much smaller species (only growing to around 3ft in length) and its rapid growth and high fecundity mean that it is a far cheaper, and also much more sustainable, choice of tuna. Indeed, skipjack tuna is so common that it is sometimes referred to at ‘the rat of the sea.’ The IUCN class skipkjack tuna as a species of Least Concern in all of the areas where they have carried out stock assessments.
Are Bluefin Tuna Worth Over £1,000,000?
As bluefin tuna are so important in Japanese culture there is a symbolic auction for the first bluefin tuna of the season every January. This auction was held at the famous Tsukiji Fish Market in central Tokyo (until the market was relocated to a different location in Tokyo in 2018). Prices paid for this tuna can reach incredible levels, as wealthy Japanese businessmen bid against each other for the honour and the prestige of purchasing the first bluefin tuna of the season.
In January 2019 Kiyoshi Kimura, the owner of a sushi restaurant chain, set a new record paying £2.5 million for a 612lb bluefin tuna. The price paid for these tunas are highly publicised around the world, and are often used by poorly-informed media outlets to claim that bluefin tuna are a specie where a single fish is worth over a million pounds. This is of course nonsense and although they are a very commercially valuable fish the true market rate of a tuna is only a fraction of the prices paid at the symbolic first tuna Japanese auction of the year. Read more about this in our article on Tsukiji Fish Market by clicking here.
UK Big Game Tuna Fishing and British Record Catch
In the first half of the twentieth century bluefin tuna were relatively common in the North Sea, attracted by the huge shoals of herring which were present. Indeed, in the 1920s and 1930s big game fishing for tuna from Whitby and Scarborough became a fashionable pursuit, attracting the wealthy and famous people of the day to the hotels in the area in the summer and early autumn months.
Multiple tuna over 700lb were caught every year from boats sailing from Scarborough and Whitby from the early 1920s until the outbreak of World War Two in 1939. It was during this time that the biggest ever catch on rod and line from British waters was made when Lorenzo Cecil Vaughan Mitchell-Henry caught a 851lb bluefin tuna when fishing out of Whitby in 1933. In 1947 Bidi Evans caught a 714lb tuna from her father’s yacht off the North Yorkshire coast, a record which still stands as the UK’s women’s record rod and line caught fish.
While big game fishing for tuna continued in the post-war years commercial fishing of mackerel and especially herring expanded dramatically. It was the decline of these prey species (and not the tuna themselves) which led to the Scarborough and Whitby big-game tuna fishing eventually winding down in the 1950s, with the last large tuna of the North Sea big game fishing era reportedly being caught in 1954.
Read our full article on big game tuna fishing in British waters by clicking here.
Tuna’s Return to British waters
Today there is clear evidence that bluefin tuna are returning to the North Sea, with a combination of warming sea temperatures and increasing numbers of herring seen as the most likely reasons for this. The Times reports that there has been over 500 sightings of tuna across the British Isles between 2013 and 2018, and anglers fishing for shark species and commercial fishermen trawling for other species have also inadvertently caught bluefin tuna. In 2018 a 770lbs tuna was caught by a commercial vessel off the coast of Devon, while a 600lb tuna became trapped in a fish pen in a Scottish fish farm but was eventually released by the staff. In the same year a boat angler caught a 500lb, 7ft 7in long bluefin tuna around forty-five miles off the Welsh coast and a “300lb plus” tuna was caught off Plymouth. In summer 2018 a video was posted to YouTube showing tuna breaking the surface in UK waters. The footage was taken from a drone by fishermen targeting porbeagle and blue sharks in an unidentified area off the UK coast. Watch the video by clicking here.
Scientists have put forward the idea that the recent increase of bluefin tuna in British waters is due to a phenomenon called the Atlantic Multidecadal Oscillation. This is a naturally occurring long-term change in the temperature of the North Atlantic. Approximately every sixty to one hundred years the Atlantic Multidecadal Oscillation changes from a negative phase (cooler) to a positive phase (warmer). The current positive phase may explain the growing number of tuna in the usually colder waters of the British Isles and Nordic countries. However, scientists have warned that the current trend of warmer seas in northern Europe could mean a colder Mediterranean Sea, which could have serious impacts on the breeding trends of bluefin tuna. In this way the growing number of bluefin tuna in British waters could mask an overall decline in the number of this species.
The increasing evidence of tuna returning to the UK has led to scientific research being commissioned to confirm that this species is now resident in British waters. Scientists from Cefas (Centre for Environment, Fisheries and Aquaculture Science) and the University of Exeter have started a study which will seek to find out more about the movements and numbers of bluefin tuna in British waters. Funded by Defra and the European Maritime and Fisheries Fund the study will begin in 2018 and last for two years. Read more here.
Big Game Fishing for Tuna to Return to UK Waters?
While a return to the tuna numbers of the 1920s and 1930s may have seemed far-fetched just a few years ago there are now calls for a big game recreational tuna fishery to be re-established in UK waters. In late 2018 the BBC reported that the Angling Trust joined with Bluefin Tuna UK at Westminster to launch the campaign to have a “properly regulated, science-based, live release UK tuna fishery” off the coast of Cornwall. The North Cornwall MP and keen angler Scott Mann backed the proposal, stating “It would be a massive boost to our coastal communities if the government was to take up these proposals and allow local anglers to enjoy world class catch and release big game fishing right on our doorsteps.”
One problem standing in the way is the complicated way in which protection for tuna in UK waters is tied into EU law. Only the eight EU nations with bluefin quota can catch this species in European waters, leaving British fishermen and anglers in the situation where they cannot catch bluefin in their own waters, but foreign fishermen from eight different European nations can come into British waters to catch this species. It will therefore take a change in EU law, or Britain leaving the EU and taking back control of its own fishing waters before a recreational catch-and-release bluefin tuna fishery could be established in British waters.
The current regulations mean that both commercial fishermen and recreational anglers are prohibited from specifically targeting this species and if a bluefin tuna is inadvertently caught it must be returned to the sea alive and unharmed and as quickly as possible. This means that boat anglers who catch a bluefin tuna should not bring it onto the boat to be photographed but should instead unhook and release the tuna while it is still in the water. Sightings of bluefin tuna (including dead tuna) should be reported to either the Marine Management Organisation or Thunnus UK using this link.