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Tuna, northern bluefin

Thunnus thynnus

Method of production - Caught at sea
Capture method - All applicable methods
Capture area - Worldwide (FAO All Areas)
Stock area - Atlantic
Stock detail - All Areas
Accreditation -
Fish type - Oily fish

Sustainability rating Click for explaination of rating

This fish, caught by the methods and in the area listed above, is the least sustainable fish to eat and should be avoided. Click on the rating icon above to read more and on the alternatives tab below to find sustainable fish to eat.


Sustainability overview

Northern or Atlantic bluefin tuna is slow growing and long lived, making it vulnerable to overfishing. The Atlantic stock is estimated to have decreased by 90% since the 1970s. There is significant uncertainty in this and previous stock assessments yet east Atlantic stocks are estimated well below safe levels. IUU has been a serious problem in these fisheries in the past as individual fish can regularly be sold in excess of tens of thousands of pounds. Recent improvements in monitoring, enforcement and control are positive yet it will be several years before these measures are reflected in the stock. A new stock assessment is scheduled for 2014.

The species is listed by IUCN as Endangered and should be avoided until the stock has recovered to healthier levels.

Biology

Tuna belong to the 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 information

Stock area
Atlantic

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Stock information
The bluefin tuna stock in the East Atlantic and Mediterranean are assessed by the International Commission for the Conservation of Atlantic Tunas (ICCAT). Reported catches in the East Atlantic and Mediterranean reached a peak of over 50,000 t in 1996 (With additional unreported catches possibly equal to that), severely overfishing the stock. Since then, reported catches have steadily decreased, stabilising according to Total allowable Catches (TACs) in the last few years. The 2012 reported catch of 10,852t was less than the TAC of 12,900t and 35% less than the previous five year average of 19,843t. This stock represents the overwhelming majority of the whole Atlantic stock and is therefore vital for the future recovery of the species. The most recent stock assessment was carried out in 2012 and in spite of recent improvements in the data quantity and quality, there remain important data limitations for this assessment, primarily as a result of the mis-reporting that took place until 2007. Using reported catch data, the assessment indicated that spawning biomass, SB, was between 0.37 and 0.89SBmsy, indicating that the stock was considerably overfished. Fishing mortality, F, was between 0.36 and 0.7Fmsy, and as reported catches in recent years have been below the TAC , the stock is likely no longer being subject to overfishing.

Management

Tuna fisheries in the Atlantic are managed by the International Commission for the Conservation of Atlantic Tunas (ICCAT). Bluefin tuna has been badly managed in the past with a lack of regulation and enforcement across its range. Contributing to this has been its extremely high market value. Information available has demonstrated that catches of bluefin tuna from the East Atlantic and Mediterranean were seriously under-reported between the mid-1990s through to 2007. The ICCAT scientific committee views this lack of compliance with TAC and underreporting of the catch as a major cause of stock decline over that period. Bluefin is still reportedly captured in illegal gill net fisheries in Italy and is still officially permitted in Morocco. In recent years, ICCAT have implemented a range of management measures to reduce IUU fishing for bluefin and to aid the recovery of the stock. A stock rebuilding program has been in effect since 2006 which aims to recover (with over 60% probability) the stock to Bmsy by 2022.

Additional management measures of note include:

A current TAC of 13,500t; Limits on capacity; Closed fishing seasons for longliners (six months), purse seiners (11 months), and for pole and line, pelagic trawl and sport fishing vessels (eight months each); Minimum sizes of 8 and 30 kg, depending on the fishery; A register of authorized fishing vessels and authorized farming facilities; A requirement for weekly catch reports to national agencies and monthly catch reports to ICCAT; 100% observer coverage for purse seiners and for transfers to sea pens; VMS on every vessel over 15 m in length; and the prohibition of trade of bluefin not accompanied by valid catch documents.

General ICCAT management and conservation measures of note that apply to vessels in ICCAT jurisdiction include:

A prohibition to retain at risk shark species including: bigeye thresher, oceanic whitetip, hammerhead and silky sharks. This has been in place for over three years, yet ICCAT has not received records of compliance from the majority of member states.

A combination of at least two bird mitigation measures are required to be used for pelagic longline fisheries, yet monitoring and data relating to this and other vulnerable bycatch species is deficient.

ICCAT have developed an IUU vessel register and a register of vessels authorised to undertake transhipments at sea.

Capture information

Approximately 44% of the bluefin in the East Atlantic and Mediterranean is caught in purse seine fisheries that target free schooling fish (as opposed to using Fish Aggregation Devices, FADs). These fish are live captured to then be transported to sea pens where they are held and fattened for later sale on the Asian sashimi market. Purse seining on free schools is a relatively clean method of fishing and does not attract much bycatch compared with FAD associated fisheries. Approximately 21% of the catch is taken in pelagic longline fisheries. Pelagic longlining can encounter considerable bycatch of vulnerable species, including sharks, turtles and sea birds. The bycatch of sharks in the Atlantic is of serious concern. There are a range of measures that can be employed to reduce bycatch including: circle and/or barbless hooks to prevent turtle capture; chemical, magnetic and rare earth metal shark deterrents; and weighted branchlines, bird scaring lines, underwater chutes and night setting to reduce the incidental capture of seabirds. ICCAT specify that at least two of these different measures should be employed yet their use is not well monitored or enforced in these fisheries. Monitoring of bycatch is deficient in these fisheries.

Approximately 13% of the catch is taken in fixed net traps that reportedly have a low impact on non-target species. Approximately 6% of the catch is taken in pole and line fisheries. This is a very selective method of fishing yet uses a lot of baitfish, and the impact of this on baitfish stocks is unknown. To a lesser extent, bluefin is also captured in illegal gill net fisheries. For EU Member States, driftnet fishing for tuna has been banned since January 2002, yet remains a problem in some Italian fisheries and is still officially permitted in Morocco.

Read more about capture methods


References
ICCAT, 2013. Report of the standing committee on research and statistics. Madrid, Spain, 30 Sept to 4 Oct, 2013. Available at http://www.iccat.int/Documents/Meetings/Docs/2013-SCRS-REP_ENG.pdf [Last accessed Dec 2013].
ICCAT, 2013. Report of the 2012 Atlantic bluefin tuna stock assessment session. Madrid, Spain, September 4 to 11, 2012. Doc. No. SCI-033/2012. Availabel at http://www.iccat.int/Documents/Meetings/Docs/2012_BFT_ASSESS.pdf [last accessed Jan 2014].
ISSF, 2013. ISSF Tuna Stock Status Update, 2013(2): Status of the world fisheries for tuna. ISSF Technical Report 2013-04A. International Seafood Sustainability Foundation, Washington, D.C., USA. Available at http://iss-foundation.org/resources/downloads/?did=487 [Accessed Nov 2013].
Collette, B. et al. 2011. Thunnus albacares. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. . [Accessed Nov 2013].
www.fishbase.org [Accessed Nov 2012].

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