Atlantic bluefin tuna

Thunnus thynnus

5: Avoid How we work out the ratings

What to check for

Location

All areas

Production method

Marine net pen, capture-based

Rating summary

Farming or ranching of Bluefin tuna relies on capture of juvenile wild tunas for on-growing and fattening in open net cages until harvest. Therefore this process is completely reliant on wild fish stocks. There is still concern for the biomass of the stock as the stock is still recovering from very low levels and there is a lack of reference points. Farming in this way will not lessen the pressure on the species. In the case of Mediterranean sea ranching operations, the capture of tuna for ongrowing is an increasing part of the catch. The ranching of tuna requires large amounts of fresh fish for feeding, with an average of 20 kg of wild fish required to produce 1 kg of Bluefin. There are currently no known procedures in place to ensure animal welfare and humane slaughter. Tuna resulting in a significant net loss of fish protein. Management and regulation of ranched tuna in the Mediterranean is only partially effective in mitigating the negative environmental impacts from aquaculture. However, it does seem that farming is incorporated in marine spatial planning.Rating last updated January 2025.

Technical consultation summary

How we worked out this Rating

Ranched Atlantic Bluefin tuna are fed a diet of whole fish that are untraceable and are a net consumer of protein.Ranched Bluefin tuna are classified as a fed species. However, unlike other farmed fish, they do not receive commercial pelleted feed but are instead fed whole fish. This is primarily composed of a variety of small, pelagic species such as round sardinella, herring, chub mackerel horse mackerel, bogue, and squid. Japan is the primary market for Bluefin tuna, where it is believed that feeding them whole fish enhances both the taste and oil content of the flesh.While the types of fish used for feeding in tuna ranching are generally known, the specific composition of feed fish is not known in most cases because of the commercial nature of the tuna farming industry. It is challenging to determine the exact species and their proportions in the diet, as this information is proprietary to individual companies, hindering transparency and traceability. Some farms are experimenting with alternative feeds, with some incorporating soy, to reduce reliance on baitfish, but the extent of this adoption is unclear.Bluefin tuna have a high protein requirement due to their diet of whole fish, leading to a significant dependence on feed fisheries. Their fast metabolism, combined with a higher blood temperature than most fish, supports their muscle function, aiding in speed and agility. They require far more protein than they produce with an average The feed fish dependency ratio of 20:1, making them a net consumer of protein.

Bluefin Tuna ranching in marine open net pens has a negative impact on the environment.There is limited data on chemical use in tuna ranches, but it is generally believed that the use of chemicals is minimal, and the risk of chemical impacts is considered low. However, there is a lack of regulation and monitoring regarding the discharge of organic waste, which could be significant due to the high demand for feed. While tuna fattening pens are typically located in areas with high water movement and flushing rates, this cannot be confirmed due to insufficient monitoring.Bluefin tuna aquaculture relies on the wild capture of juvenile fish for fattening, meaning it is not a true farming operation that raises fish from hatcheries. This practice does not reduce pressure on wild tuna populations but instead depends on them to supply the farms. Although there have been improvements, concerns remain about biomass levels, as there is no clear indication of the stock's status. The population is recovering from long-term depletion, but uncertainty persists about the extent of this recovery. Overall, the stock is still considered at risk, and further depletion to support tuna ranching is not sustainable.The incidence of parasite transfer to nearby species and regional disease outbreaks is low, but there is a lack of regulation, data, and monitoring on these issues. Similarly, the rate of escapes from tuna farms is low, and since the fish are wild caught, any escapes are unlikely to have a harmful impact on local species.Data on predator control is lacking, and while bycatch occurs during the capture of juvenile tuna, the extent of this bycatch remains unknown.

There are currently no known procedures in place to ensure animal welfare and humane slaughter.There are currently no known operating procedures in place for Atlantic Bluefin tuna ranching which are specifically tailored to promote animal welfare and adhere to definitions of humane slaughter. The lack of established reporting procedures means that this area of farming remains data deficient.

Management and regulation of ranched tuna in the Mediterranean is only partially effective in mitigating the negative environmental impacts from aquaculture. However, it does seem that farming is incorporated in marine spatial planning.A Multi-Annual Management Plan for Bluefin Tuna in the Eastern Atlantic and the Mediterranean entered into force in 2022 and was updated in 2023. This plan has incorporated several regulations for the tuna aquaculture sector including caging rules, farming capacity and establishing farming management plans.Despite this the overall regulation of the Bluefin tuna production sector appears to be lacking, despite their being a requirement for an Environmental Impact Assessment, all other regulations expected to be in force, in relation to chemical use, discharges, biosecurity and disease management are either not in place or no data is publicly available in relation to them.This assessment is for the uncertified production of Bluefin tuna.

References

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Report of the 2024 ICCAT Intersessional Meeting of Bluefin Tuna Species Group (BFTSG), 2024. Available at: https://www.iccat.int/Documents/Meetings/Docs/2024/Reports/2024_BFT_ENG.pdf [Accessed on 09.12.2024].

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Vita, R. and Marín, A., 2007. Environmental impact of capture-based bluefin tuna aquaculture on benthic communities in the western Mediterranean. Aquaculture Research, 38, pp.331–339.

Vizzini, S. and Mazzola, A., 2012. Tracking multiple pathways of waste from a northern bluefin tuna farm in a marine-coastal area. Marine Environmental Research, 77, pp.103–111.