Atlantic bluefin tuna

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Description

Atlantic bluefin Tuna, Thunnus thynnus is a giant of the fish world growing to a maximum size of 3meters and weighing up to 250 kilos. The largest species of tuna in the world these torpedo shaped fish are built for speed and power and travel huge distances in the open ocean. Unlike most fish they are warm blooded with heat generated in their powerful swimming muscles that enable them to accelerate rapidly, and gives them improved cognitive power and reactions. They are incredible top predators and are at the top of the oceanic food chain.

Sustainability Overview

Atlantic bluefin tuna are a fast simming and wide ranging species that has always occasionally ventured into UK waters but they became an extremely rare sight through the latter half of the 20th century when this higly valuable species was fished near to extinction. Thanks to improved international management stocks appear to have recovered. Atlantic bluefin tuna began reappearing in UK coastal waters in 2014 and since then they have been regularly sighted in increasing numbers around the coasts of Cornwall, and further along the south coast into Devon and Dorset waters. The return of this incredible species is most likely due to the increase in their prey in our waters, small pelagic fish such as sardines. Bluefin tuna appear in Cornish waters in mid-summer and are seen well into autumn. From 2021 the UK government allowed commercial fishermen who accidentally catch bluefin tuna in trawls or ring nets to land one fish per day per boat and they can be sold for human consumption. In 2023 the MMO announced a limited hook and line fishery for bluefin tuna in UK waters. We hope that this newly opened fishery is well managed and rules are strictly enforced as this is a top predator that is very easily over fished and has only recently recovered from the brink of near extinction.

In 2021, 1.3 tonnes of Atlantic Bluefin tuna was landed to Cornish ports with a value of over £4000.

Updated July 2023

Biology

Tuna belong to the mackerel family, Scombridae. They are large, oceanic fish and are seasonally migratory, some making trans-oceanic journeys. Able to tolerate both warm and cool temperatures, bluefin tuna range throughout the entire north Atlantic and adjacent seas, (primarily the Mediterranean Sea) and can frequent depths to 1000m. Despite this thermal tolerance, a recent analysis of present vs. historical ranges concluded that Atlantic bluefin tuna has shown range contractions of 46% since 1960 - more than any other pelagic species . Despite poorly understood movements from east to west, a distinction in populations is made between the two regions. Interestingly, life history characteristics differ greatly between them. In the Mediterranean, bluefin tuna is assumed to mature at approximately 25 kg (age 4), whereas in the Gulf of Mexico in the West Atlantic, maturity occurs at approximately 145 kg (age 9). Northern bluefin grow slowly compared with other tunas and billfish but can reach more than 450cm in length and 680kg in weight with a maximum age of approximately 40 years. Spawning occurs from April to June in the Gulf of Mexico and June to August in the Mediterranean.

Stock Info

There are two stocks of Atlantic bluefin tuna: west Atlantic (western stock), and East Atlantic and Mediterranean (eastern stock). This rating is for the eastern stock. There has been a lot of uncertainty about the size and health of the Atlantic bluefin stock, and while it has recently improved, it is not clear whether it has reached sustainable levels. MCS considers there to be concern for the biomass, because it is recovering from an historically low level. The stock is not thought to be subject to overfishing, and so there is no concern for fishing pressure.

Atlantic bluefin tuna are assessed and managed by the International Commission for the Conservation of Atlantic Tunas (ICCAT). The eastern stock was heavily fished from the 1950s until 1996, after which, catch limits and a limit in the size of tuna that could be taken caused catches to drop from 60,000 tonnes to 10,00 tonnes. The stock declined from the 1970s until 1991, staying at a low level and coming close to stock collapse until it began to increase in the mid-2000s. A new stock assessment was produced in 2020 but depends on recruitment estimates, which are highly unstable, and is also closely related to assumptions made about stock structure and migratory behaviour, which are poorly known. Nonetheless, compared to 2017, the extra data now available confirm a recent stock biomass increase, although the magnitude of the increase remains difficult to quantify. Fishing pressure appears to be clearly below the target level of F0.1, which is a proxy for FMSY and has been set with the aim of maintaining the biomass at B0.1 (BMSY). The average fishing pressure from 2015-2017 is 42.6% of the target level, indicating that overfishing is not taking place. Given the levels of uncertainty, and that the stock is recovering from very low levels, MCS considers that there is still concern for the biomass. The stock is not thought to be subject to overfishing, and so there is no concern for fishing pressure.

Projections on the future of the stock could not be made owing to the uncertainty in the data. However, an analysis of the effect of the current and future catch limits (32,240t in 2019 and 36,000 t in 2020-2022) suggests that there is no cause to change them. The projections from the 2017 advice have been reiterated in the 2020 assessment: a constant catch of 36,000 tons from 2018 onwards would keep fishing pressure below the target level with a probability higher than 60% in 2021 and in 2022.

The introduction of fattening and farming activities into the Mediterranean in 1997 and good market conditions resulted in rapid changes in the Mediterranean fisheries for bluefin tuna, mainly due to increasing but unknown catches of juveniles going into farms. There have been considerable improvements in data quality and quantity over the past few years but important gaps remain in the temporal and spatial coverage for detailed size and catch-effort statistics for several fisheries, especially in the Mediterranean before the implementation of stereo video cameras in farms in 2014. It still remains unclear how much of the Eastern Atlantic stock mixes with and supports the Western Atlantic stock.

In 2021 the IUCN changed the status of Atlantic bluefin tuna from Critically endangered to Least concern. Read more here.

Management

In 2021 a small quota for Atlantic bluefin tuna has been allocated to the UK government. This quota is being used in 2021 to open up a catch and release tagging sport fishery which is strictly licenced and controlled with only 15 licences being issued in 2021 (see CHART website). Mortalities are to be avoided but any unitentional mortalities will have to be reported and the fish will be landed for research purposes and given to the MMO. (for more info visit government page)

In 2023 a Commercial hook and line fishery for Atlantic bluefin tuna was opened by the MMO as a trial small scale fishery. This is a selective fishing method and all fish caught have to be reported and data collected will be used to build information on tuna stocks in UK waters.

Recreational fishing for tuna withouth a licence is illegal. Any incidental catch must not be brought onto the vessel it must be released alive, unharmed to the greatest extent possible. Recreational sea anglers must not land bluefin tuna. The MMO must be informed of any accidental mortality and they may request the fish to be landed to them for research purposes.

Commercial fishermen are not allowed to target Atlantic bluefin tuna but if they are accidentally caught in ring nets, gill nets or trawls they can be landed as long as they are above the Minimum conservation reference size (30kg or 115cm fork length) and can then be sold for human consumption. Only one fish per commercial boat can be landed per day.

There is serious concern that these rules may not be enforced adequetly and that some recreational and commercial fishers may be tempted to illegally land tuna. Always be careful if buying tuna to ensure you know it was caught legally.

After the eastern Bluefin tuna stock came close to collapse in the early 2000s, a 15-year recovery plan was initiated in 2007-2022, with the aim of recovery biomass levels (B) to those associated with a maximum sustainable yield (MSY) with at least a 60% probability. Total Allowable Catches (TACs) were reduced from 32,000 tonnes in 1998 to 12,900 t in 2010, and have since gradually increased. Meanwhile, the minimum size was increased from 6.4kg in 2002 to 10kg in 2004 and is now at 30kg / 115cm (with a few exceptions). The ICCAT scientific committee has stated that, while it is too early to know the effect of the recent catch limits from 2018 onwards, the combination of size limits and the reduction of catch certainly contributed to a rapid increase in the abundance of the stock. As a result, in 2017, the scientific committee advised moving from the rebuilding plan to a management plan. However, it should be noted that there is no reliable estimate of biomass in relation to any reference points, and so while fishing pressure (F) has been brought below FMSY, the stock is not confirmed to have reached BMSY. Management is based on keeping F at F0.1, which is assumed to maintain B around B0.1.

In its 2020 report, the Scientific Committee noted that reported catches are in line with recent TACs, but had been informed of the existence of unquantified illegal catches of unknown magnitude. TACs have increased from 16,142 t in 2015 to 32,240t in 2019 and 36,000 t for 2020. The projections from the 2017 advice have been reiterated in the 2020 assessment: a constant catch of 36,000 tons from 2018 onwards will keep fishing pressure below the target level with a probability higher than 60% in 2021 and in 2022. The current 2020 TAC is therefore expected to keep fishing pressure below the target levels and will be carried forward to 2021. Owing to COVID disruption and the high levels of uncertainty in the 2020 stock assessment, further management recommendations for future TACs could not be made in 2020 and will be revisited in 2021. It should be noted that the 2017 assessment also projected that while catches of 36,000t would keep fishing pressure below the target level, constant catches of over 32,000t were projected to cause the biomass to decline. The TAC of 36,000t does not therefore seem precautionary, given the high levels of uncertainty around the status of the stock and the unquantified level of the recent illegal catches. In addition, 75% of the catch is by purse seiners, mostly on juveniles which are taken alive to tuna farms for growing on. While there is no data in the latest stock assessment relating to ages and sizes of tuna caught, a high catch of juveniles would be very concerning for the long-term growth of the stock.

Capture Info

2021 sees the first legal landing of Atlantic bluefin tuna in UK waters in many years.

Commercial fishers are not allowed to target bluefin tuna but if they accidentally catch them they are permitted to land one fish per vessel per day.

The fish can only be landed if they are above the Minimum size of 30kg or 115cm fork length, and can only be caught using Ring nets, demersal trawls, gill nets pelagic trawls and seine nets. More details are published here.

A commercial Bluefin Tuna hook and line trial fishery was opened in 2023 by the MMO -10 licences have been issued to UK commercial vessels who have a limited quota of 39 tonnes for 2023. All fish caught have to be recorded and data submitted to MMO. Line fishing for tuna is a selective method of capture that has minimal risk of harm to other species and has no impact on the seabed or wider environment. A rating for this fishery in Cornwall will be consulted on in our winter ratings review 2023/2024.