Tuna, bigeye

Thunnus obesus

Method of production — Caught at sea
Capture method — Purse seine (FAD & Free School)
Capture area — Atlantic Ocean (FAO 21,27,31,34,41 and 47)
Stock area — Atlantic
Stock detail — All Areas
Picture of Tuna, bigeye

Sustainability rating five info

Sustainability overview

In 2018 a new stock assessment was carried out for Atlantic bigeye, with more certain and more pessimistic results than the last one and reaffirmed that the stock is overfished (SSB at 0.59SSBMSY) and subject to overfishing (F at 1.6FMSY). The current Maximum Sustainable Yield has been reduced considerably through the harvesting of small bigeye. Spawning stock biomass is estimated to be at its lowest since recording began in the 1950s. Is it advised that as a matter of urgency, catches be appropriately reduced to end overfishing and allow the stock to recover, and particularly to reduce fishing mortality of juveniles. Management measures have failed to keep fishing mortality at sustainable levels and in 2018 it is expected that the Commission will introduce a rebuilding plan, to begin in 2019. In the 2018 assessment, catches consistent with the 2016 TAC (65,000t) were projected to lead to just a 28% chance of the stock being in a good state by 2028, or 44% by 2033. In 2016 and 2017 it was exceeded by 20% (catches around 78,000t) and at this level, there is a 1% chance of the stock being in a good state by 2033. About 29% of the catch is taken in purse seine fisheries, mostly setting on FADs. FAD sets catch a greater amount of juvenile bigeye and yellowfin which is reducing the productivity of these stocks. FADs can also entangle sharks and turtles. The proportion of bycatch of vulnerable species is relatively low in purse seine fisheries, (eg. less than 1.5% for sharks in the Atlantic), yet the overall catch is still significant (especially sharks) and better data collection is needed. The status of some sharks in the area is unknown. FADs can also entangle sharks and turtles, but FAD construction and overall management is improving. Observer coverage is 5%, yet this is not being complied with by several countries and 20% coverage is recommended.

Biology

Tuna belong to the family Scombridae. They are large, oceanic fish and are seasonally migratory, some making trans-oceanic journeys. Bigeye tuna is a tropical and subtropical species, found from the surface down to 250m in the Atlantic, Indian and Pacific Oceans. It is slower growing than skipjack or yellowfin tuna, maturing at about 3 years old and reaching a maximum size of 250cm in length and 200kg in weight, with a maximum age of 11 years. Bigeyes are considered moderately resilient to exploitation.

Stock information

Criterion score: 1 info

Stock Area

Atlantic

Stock information

Atlantic bigeye and other Atlantic tuna stocks are assessed by the International Commission for the Conservation of Atlantic Tunas (ICCAT). It’s generally accepted that there is a single, Atlantic-wide stock of bigeye, but it is possible that there might be a northern and southern stock and this, among other things, creates uncertainty when assessing this species. The stock has been exploited by three major gears (longline, bait boat and purse seine fisheries) and by many countries throughout its range. The total annual catch increased up to the mid-1970s, reaching 60,000 t, and fluctuated over the next 15 years. In 1994 catch peaked at 135,000 t, and then continuously declined to 58,875 t in 2006. Since then, catches have increased and fluctuated between around 75,000 t and 80,000 t. The reductions in catch after 1994 were related to declines in fishing fleet size and CPUE for longline and bait boat, while purse seine catches increased from 2010 onwards. Significant catches of small bigeye tuna continue to be channelled to local West African markets, predominantly in Abidjan, and sold as “faux poisson” in ways that make their monitoring and official reporting challenging.

In 2018 a new stock assessment was carried out for Atlantic bigeye, with more certain and more pessimistic results than the last one. The stock is currently overfished (SSB/SSBMSY =0.59, ranging from 0.42 to 0.80) and undergoing overfishing (F/FMSY = 1.6, ranging from 1.14 to 2.12) with very high probability (99%). The current Maximum Sustainable Yield is estimated at 76,232 t, which has been reduced considerably through the harvesting of small bigeye. Spawning stock biomass is estimated to be at its lowest since recording began in the 1950s. Recent catches (provisionally 78,482t in 2017) continue to exceed the Total Allowable Catch (TAC) of 65,000t (although because this TAC does not affect all countries that can catch bigeye tuna, in theory the total catch removed from the stock could exceed the TAC). If catches stay at around 78,000t, the probability of bringing the stock to a good state by 2033 is 1%. As a matter of urgency, catches must be appropriately reduced to end overfishing and allow the stock to recover. The necessary reduction of fishing mortality can not be achieved with current and previous time area closures and/or changes to fleet allocation alone. Increased harvests on small fishes by FADs and other fisheries, as well as the development of new fisheries, could also have had negative consequences for the stock and in order to increase long-term sustainable yield, there need to be effective measures to reduce fishing mortality of small bigeye tunas. Concern over the catch of small bigeye tuna partially led to the establishment of spatial closures to surface fishing gear in the Gulf of Guinea. This has not been effective at reducing the mortality of juvenile bigeye tuna, and any reduction in yellowfin tuna mortality has been minimal, largely due to the redistribution of effort into areas adjacent to the moratorium area and increase in number of fishing vessels.

The bigeye tuna species is assessed as Vulnerable by the IUCN (International Union for the Conservation of Nature).

Management

Criterion score: 0.75 info

Most tuna stocks range across and are accessed by numerous coastal states, making harmonised and effective management of these individual stocks very difficult. To try and address this, Intergovernmental Regional Fisheries Management Organisations (RFMOs) have been established. There are five main tuna RFMOs worldwide and it is their responsibility to carry out data collection, scientific monitoring and management of these fisheries. This stock is managed and assessed by the International Commission for the Conservation of Atlantic Tunas (ICCAT). Whilst the RFMOs are responsible for the development of management and conservation measures, the degree to which they are implemented, monitored and enforced still varies significantly between coastal states. There remain large data deficiencies in most tuna and billfish fisheries, particularly with regards to fine scale spatial and temporal data for both target and especially for vulnerable bycatch species. For this reason, it is important to choose tuna that has been caught by vessels that are well regulated by their flag state.

Management measures have failed to keep fishing mortality at sustainable levels and in 2018 it is expected that the Commission will introduce a rebuilding plan, to begin in 2019.

The TAC (Total Allowable Catch) for bigeye was 90,000t from 2005-2008, 85,000t from 2009-2015 and from 2016 onwards is 65,000 t, split across various countries. In the 2018 assessment, catches consistent with the 2016 TAC were projected to lead to just a 28% chance of the stock being in a good state by 2028, or 44% by 2033. However, the TAC does not apply to all countries fishing for bigeye, and therefore can be exceeded. In 2016 and 2017 it was exceeded by 20% (catches around 78,000t) and at this level, there is a 1% chance of the stock being in a good state by 2033. The number of vessels fishing for bigeye is limited to the reported number in 2005, and there are country-specific limits on the number of large longline and purse seine boats. As bigeye tuna is a particular target for IUU fishing, catches must be accompanied by Catch Documentation when being imported and exported.

The following measures are in place for bigeye, skipjack and yellowfin:
A multi-annual management programme has been in place for bigeye and yellowfin since 2012, and eastern skipjack since 2015. Fishing for these species using aggregation devices, including FADs, is prohibited from 1st January to 28th February in an area off the west African coast to reduce catches of juvenile bigeye and yellowfin. All vessels fishing during this period must have an observer on board. This measure has failed to reduce the mortality of juvenile bigeye tuna, and any reduction in yellowfin tuna mortality has been minimal, largely due to the redistribution of effort into areas adjacent to the moratorium area.
For the rest of the year, no more than 500 FADs may be active at any one time by any vessel and countries must have FAD Management Plans that improve understanding of FADs and limit their impacts on the ecosystem.
ICCAT maintains a list of vessels over 20m authorised to fish for these species, although other vessels may retain them as bycatch as long as the country sets limits on this and doesn’t exceed its quota.
Countries are encouraged to reduce discards.

It has been noted that increased harvests on FADs could have had negative consequences for the productivity of bigeye tuna fisheries, so to increase long-term sustainable yield the scientific committee continues to recommend that effective measures be found to reduce FAD-related and other fishing mortality of small bigeye tunas. Increased harvests on FADs may also have negative consequences for adult yellowfin and bigeye tuna, as well as other by-catch species.

Other management measures of note include:
There is a mandatory level of observer coverage of 5% (recommendation is for 20%), which may not have been implemented by many fleets, although some fleets are currently implementing voluntary observer programmes that cover 100% of fishing trips. Purse seine and longline vessels over 20m long are encouraged to increase their observer coverage from the required minimum. Vessel Monitoring Systems are required for all vessels over 24m.
In 2015 a working group was formed to look at ways to reduce juvenile catches of bigeye and yellowfin tuna caught in FAD fishing.
Drift nets are banned in the Mediterranean.
ICCAT maintains lists of vessels authorised to fish for tuna and tuna-like species in the ICCAT area, and those caught carrying out Illegal, Unreported or Unregulated activities.
At-sea transhipment is prohibited unless pre-authorised and the vessel has an observer on board.
In 2017 ICCAT banned the discarding of skipjack, yellowfin and bigeye.
In 2016 the Commission passed measures to strengthen and streamline its compliance assessment process and to develop a scheme of responses to non-compliance.

Capture Information

Criterion score: 0.75 info

Approximately 29% of the bigeye catch from the Atlantic is taken in purse seine fisheries that set gear on floating objects including Fish Aggregation Devices (FADs), and 6% by purse seining on free schools. The Atlantic bigeye longline fishery catches medium to large (60kg) bigeye tuna compared with the purse seine fishery which generally catches fish of about 4kg. Average weight of bigeye tuna caught in free schools is more than twice the average weight of those caught around FADs.

Purse seining is commonly an industrial scale fishery used to catch tuna destined for canneries. These fisheries target smaller fish that aggregate close to the surface, whereas longliners target larger fish that inhabit deeper waters. Many juvenile fish are often caught in purse seine fisheries, mainly skipjack, yellowfin and bigeye. When a high proportion of young fish are removed from a population, the potential maximum catch from a fishery is reduced. The method is also associated with bycatch of species such as sharks, turtles and marine mammals, although less so than longlining. Whilst bycatch may comprise a small proportion of the total catch, the high volume of tuna that is caught means that it can still be significant for these vulnerable species. FAD-associated purse seining encounters higher bycatch rates compared with sets on free-schools, and higher proportions of juvenile tuna. The widespread use of FADs is of concern due to the unknown impacts such gear might have on natural species composition of tuna schools, migratory patterns, growth rates and predation rates of affected pelagic species. Poorly designed FADs can also entangle animals.

Fishing for bigeye, skipjack and yellowfin using floating objects is prohibited for two months in an area off the west African coast to reduce catches of juvenile bigeye and yellowfin, with 100% observer coverage required during this time. The scientific committee concluded that closures to date have not been effective at reducing the mortality of juvenile bigeye tuna, and any reduction in yellowfin tuna mortality was minimal, largely due to the redistribution of effort into areas adjacent to the moratorium area.

ICCAT aims to take an ecosystem-based and precautionary approach to fisheries management. In order to minimize the ecological impact of FADs, in particular the entanglement of sharks, turtles and other non-targeted species, and the release of synthetic persistent marine debris, countries must use non-entangling FADs and phase out non-biodegradable FADs. Countries must have FAD Management Plans that improve understanding of FADs and limit their impacts on the ecosystem.

For sharks: Countries are required to develop and submit National Plans of Action for the conservation and management of sharks. Sharks must be fully utilised (e.g. no removal of fins). Sharks must be released wherever possible (if not being directly targeted) and countries must try to minimise bycatch of sharks (although no gear-specific measures are identified). Catching silky sharks, hammerheads, oceanic whitetips, and bigeye threshers is prohibited, and catching other thresher species is discouraged. Shortfin mako can be caught and retained, but as of 2017 the country’s law must require a minimum length of 180cm for males and 210cm for females, otherwise, shortfin makos caught alive must be released unharmed. This is expected to prevent the stock’s currently poor state from worsening, and a rebuilding plan will be developed for 2019. In 2016 additional measures for blue shark were introduced, mainly focussed on improved data recording, with potential to introduce Harvest Control Rules. A catch limit of 39,102 t was also introduced in the north Atlantic (but none for the south Atlantic): if exceeded the commission has committed to reviewing the effectiveness of its blue shark management measures. Preliminary catch in 2016 was 42,117 t. Porbeagle is overfished throughout the Atlantic, significantly so in the northwest, and for the north Atlantic overall it is predicted to take at least 30 years to recover if there was zero fishing mortality. The main porbeagle-directed fisheries (EU, Uruguay and Canada) have closed, and ICCAT have a recommendation to release live porbeagle unharmed, but it is still caught incidentally and discarded, and also landed by other fleets. Currently there is not enough data to properly assess the status of many pelagic sharks (no assessments have been carried out for the Mediterranean) and more work is needed to understand the effects of entanglement in FADs.

For turtles: Purse seiners must avoid encircling turtles and release them when they do so.

There is a mandatory level of observer coverage of 5%, which may not have been implemented by many fleets, in spite of scientific committee recommendation of a minimum of 20% for accurate reporting of bycatch. However, some fleets are currently implementing voluntary observer programmes that cover 100% of fishing trips.

Alternatives

Based on method of production, fish type, and consumer rating: only fish rated 2 and below are included as an alternative in the list below. Click on a name to show the sustainable options available.

Anchovy, anchovies
Arctic char
Herring or sild
Salmon, Atlantic (Farmed)
Salmon, Chinook, King Salmon
Salmon, Chum, Keta, Calico or Dog salmon
Salmon, Coho , Silver, White
Salmon, Pink, Spring , humpback
Salmon, Sockeye , Red Salmon, Bluebacks, Redfish
Sprat, whitebait
Swordfish
Trout, Rainbow
Tuna, albacore
Tuna, bigeye
Tuna, skipjack
Tuna, yellowfin

References

Collette, B., Acero, A., Amorim, A.F., Boustany, A., Canales Ramirez, C., Cardenas, G., Carpenter, K.E., Chang, S.-K., Chiang, W., de Oliveira Leite Jr., N., Di Natale, A., Die, D., Fox, W., Fredou, F.L., Graves, J., Viera Hazin, F.H., Hinton, M., Juan Jorda, M., Minte Vera, C., Miyabe, N., Montano Cruz, R., Nelson, R., Oxenford, H., Restrepo, V., Schaefer, K., Schratwieser, J., Serra, R., Sun, C., Teixeira Lessa, R.P., Pires Ferreira Travassos, P.E., Uozumi, Y. & Yanez, E., 2011. Thunnus obesus. The IUCN Red List of Threatened Species 2011: e.T21859A9329255. Available at http://dx.doi.org/10.2305/IUCN.UK.2011-2.RLTS.T21859A9329255.en [Accessed on 11.12.2018].

Fishery Progress, 2018. Fishery Improvement Project Directory. Available at https://fisheryprogress.org/ [Accessed on 05.12.2018].

ICCAT, 2018. Report of the Standing Committee on Research and Statistics (SCRS) of the International Commission for the Conservation of Atlantic Tunas, 1-5 October 2018, Madrid, Spain. 469 pp. Available at https://www.iccat.int/Documents/Meetings/Docs/2018/REPORTS/2018_SCRS_REP_ENG.pdf [Accessed on 22.11.2018].

ICCAT, 2018. Resolutions, Recommendations and other Decisions. Available at http://www.iccat.es/en/RecsRegs.asp [Accessed on 11.12.2018].

ISSF, 2018. Status of the world fisheries for tuna: October 2018. ISSF Technical Report 2018-21. International Seafood Sustainability Foundation, Washington, D.C., USA. 103 pp. Available at: https://iss-foundation.org/about-tuna/status-of-the-stocks/ [Accessed on 06.12.2018].

Restrepo, V., Dagorn, L., Itano D., Justel-Rubio A., Forget F. and Moreno, G., 2017. A summary of bycatch issues and ISSF mitigation initiatives to-date in purse seine fisheries, with emphasis on FADs. ISSF Technical Report 2017-06. International Seafood Sustainability Foundation, Washington, D.C., USA.