Tuna, bigeye

Thunnus obesus

Method of production — Caught at sea
Capture method — Purse seine (FAD & Free School)
Capture area — Pacific, Eastern Central (FAO 77), South, East (FAO 87) and West (FAO 81)
Stock area — Eastern Pacific
Stock detail — All Areas
Picture of Tuna, bigeye

Sustainability rating four info

Sustainability overview

EPO bigeye is not currently in an overfished state, but a new stock assessment in 2018 indicates that it is subject to overfishing. The rise of the purse seine fishery has led to higher fishing mortality of younger and smaller fish, and current Maximum Sustainable Yield is about half the level it was in 1993. Bigeye catches in 2017 were about 101,600 t, a 10% increase from 2016 and above MSY. In 2016 interim Harvest Control Rules were brought in for bigeye, skipjack and yellowfin purse seine fisheries, with the aim of preventing fishing effort from exceeding FMSY for the species that requires the strictest management; for other fisheries, management measures will be as consistent as possible with the purse seine fishery. In 2017, it was acknowledged that the commission had failed since 2013 to reduce fishing mortality of yellowfin and bigeye (adjusted for capacity) to a level not exceeding MSY. Some management measures have been improved but remain insufficient to prevent overfishing. Approximately 62% of bigeye tuna in the EPO is caught by purse seiners, almost all of it on floating objects known as Fish Aggregation Devices (FADs). The proportion of bycatch of vulnerable species is low in purse seine fisheries in the EPO (less than 0.5% for sharks), yet the overall catch of sharks is still significant and better monitoring and reporting is needed from the smaller purse seiners. There is 100% observer coverage on large purse seiners.

Commercial buyers should establish what measures the flag state and fleet relating to their source is taking to improve the management of FADs and reduce impacts to and improve reporting of interactions with vulnerable species. Large buyers should consider supporting such improvements. MCS also advocates specifying the need for supplying vessels, to register on the ISSF Proactive Vessel Register.

There are some credible Fisheries Improvement Projects (FIPs) for purse seine fleets operating in this fishery which are making good progress to address some key environmental issues and aim to achieve MSC certification. Further info available, visit fisheryprogress.org.

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 200 kg in weight, with a maximum age of 11 years. Bigeye are considered moderately resilient to exploitation.

Stock information

Criterion score: 0.5 info

Stock Area

Eastern Pacific

Stock information

Eastern Pacific Ocean (EPO) bigeye tuna is managed and assessed by the Inter-American Tropical Tuna Commission (IATTC). Bigeye catches and stock abundance have been strongly influenced by changes to fishing methods over the past few decades. After IATTC tuna conservation resolutions were initiated in 2004 to decrease longline effort, it appears that EPO bigeye stocks began to recover, but then during 2010-2013 the spawning biomass ratio (SBR, the ratio of the current spawning biomass to that of the unfished population) gradually declined to a historically low level of 0.15. This could be related to the below-average recruitments in 2007 and 2008, and coincides with a series of particularly strong La Nia events. SBR increased to 0.23 in 2016, and at 2017 is at 0.21, which corresponds to the maximum sustainable yield (MSY). Meanwhile, the floating-object (FAD) purse seine fishery has expanded and fishing mortality of younger and smaller fish has increased as a result, leading to Maximum Sustainable Yield (MSY) estimates reducing significantly. According to the 2018 assessment, MSY is 95,491 t - about half the level it was in 1993. Bigeye catches in 2017 were about 101,600 tonnes, a 10% increase from 2016 and above MSY.

In 2018 the stock assessment was updated using the same methodology as in 2016. The stock is not in an overfished state, with spawning biomass (S) estimated to be about 2% above the level corresponding to the maximum sustainable yield (S:SMSY=1.02). It is, however, subject to overfishing, with the current level of fishing effort estimated to be about 13% higher than the level of fishing mortality corresponding to MSY (F multiplier=0.87, or F:FMSY=1.13). These interpretations are highly sensitive to the assumptions made about: the stock-recruitment relationship, size-composition data, the growth curve, and rates of natural mortality. There is substantial uncertainty in the assessment, so other indicators were developed as alternative bases for advice until this can be resolved. All the indicators, except catch, show strong trends over time, indicating increasing fishing mortality and reduced abundance, and are at, or above, their reference levels. The increasing number of sets and the decreasing mean weight of the fish that are caught suggests that the bigeye stock in the EPO is under increasing fishing pressure and that the measures in place are insufficient to prevent overfishing. At current levels of fishing mortality, the spawning biomass is predicted to decrease again, towards an SBR of 0.17.

Tagging data indicates it may be more appropriate to have a Pacific-wide assessment, rather than splitting the assessments into west and east.

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 achieve 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 Inter-American Tropical Tuna Commission (IATTC). 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. For this reason, it is important to choose tuna that has been caught by vessels that are well regulated by their flag state.

In 2016 interim Harvest Control Rules were brought in for bigeye, skipjack and yellowfin purse seine fisheries, with the aim of preventing fishing effort from exceeding FMSY for the species that requires the strictest management. For other fisheries, management measures will be as consistent as possible with those for the purse seine fishery. Further evaluation of this HCR and alternatives will be conducted, so that a permanent HCR can be adopted.

In 2017, it was acknowledged that the commission had failed since 2013 to reduce fishing mortality of yellowfin and bigeye (adjusted for capacity) to a level not exceeding MSY: fleet capacity in 2017 was estimated to be about 6.7% greater than the previous three-year average. Management measures were updated accordingly, in line with recommendations: the 62-day closure for large purse seiners was extended to 72 days annually until 2020. However, in 2018 a new bigeye stock assessment indicated that the stock was now subject to overfishing, and while the assessment was too uncertain to recommend further extensions of the closure, indications are that current measures remain insufficient to prevent overfishing. Scientific recommendations are for the total number of purse seine sets (FAD and non-FAD) to be limited to 14,895 in 2019 and 14,498 in 2020, with only dolphin-associated sets allowed once this limit is reached. These have yet to be adopted by the commission, although there are per-vessel limits on the number of FADs that can be active at any one time (between 70 and 450, depending on vessel size) and regular reporting on FAD activity is required.

Until 2020, there is a 30-day closure of an area known as the “Corralito” (west of the Galapagos Islands, where catch rates of small bigeye are high) to the purse-seine fishery for yellowfin, bigeye, and skipjack tuna.

A requirement to retain and land all bigeye, skipjack, and yellowfin tuna caught by purse seine has been extended until 2020, although the degree of enforcement regime may vary depending on the country or authority.

For longliners, maximum total annual catches of bigeye tuna from 2017-2020 are around 55,000t, split between China, Japan, Korea, Chinese Taipei and USA; for other countries up to 500t or their respective 2001 catch is allowed, whichever is more.

There is 100% observer coverage on large purse seiners. The scientific committee continues to recommend 20% observer coverage for small purse seiners, to obtain better data on discards and bycatch, as well as investigations into an electronic monitoring system on all purse seiners for better data on species, sizes, and quantities of target and bycatch species. Since 2011 only 5% observer coverage has been required on large longliners, considered by the scientific committee to be too low for accurate data: a minimum of 20% coverage is recommended. In addition, data recorded by longliners is considered inadequate for scientific purposes and minimum data standards must be identified and introduced.

To help address IUU, the IATTC maintains an IUU Vessel List; maintains a register of authorised fishing vessels; and prohibits transhipments at sea for most vessels (some exemptions apply) and requires most other transhipments to be documented and observed as part of the regional observer programme. Countries are required to report annually on monitoring, control and compliance of management measures. The IATTC and WCPFC endeavour to work together to promote compatibility between their respective conservation and management measures across the Pacific.

Capture Information

Criterion score: 0.75 info

Approximately 62% of bigeye tuna in the EPO is caught by purse seiners, almost all of it on floating objects known as Fish Aggregation Devices (FADs). The discarding of small bigeye in this fishery has a small, but detectable, impact on the depletion of the stock. From 2001-2015 the purse-seine catch of the species discarded at sea has steadily decreased, from 5% in 2000 to less than 1% in 2014.

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 and the method can also be associated with bycatch of vulnerable species, in particular sharks. In the EPO, the bycatch of sharks comprises a small proportion of the total catch of tuna, but as the volume of tuna caught is high, the catch of sharks is still significant.

FAD-associated purse seining generally encounters higher bycatch rates compared with sets on free-schools, and higher proportions of juvenile tuna. The 2018 assessment of yellowfin tuna, often caught with bigeye, indicates that the stock is subject to overfishing. It’s unknown if the widespread use of FADs has other impacts such as on the natural species composition of tuna schools, migratory patterns, growth rates and predation rates of affected pelagic species. Poorly designed FADs can also entangle animals like sharks and turtles.

Bycatch mitigation measures such as sorting grids are in place to reduce mortality of turtles, sharks and non-target species in general. From Jan 2015, all purse seiners using FADs in the EPO must record and report to the authorities details relating to the FAD design, deployment, catch and bycatch summaries for each set. Additionally, FAD design is required to be non-entangling so as to minimise interaction with turtles and sharks and is encouraged to be made from biodegradable materials. Further restrictions to reduce the entanglement of sharks, sea turtles or any other species come into force in January 2019. Vessels are prohibited from knowingly setting a purse seine around tuna schools associated with a live whale shark and if a whale shark is incidentally encircled, all reasonable steps must be taken to ensure its safe release. Details of the interaction are to be recorded, as are details of any interactions with sharks and turtles. Permissible sharks are to be fully utilized and no more than 5% of fins to total shark weight can be retained; landing oceanic whitetip, silky sharks and mobula rays is prohibited and vessels must not fish in silky shark pupping areas. In 2016 IATTC introduced stricter monitoring and reporting of catches of shark species, but the scientific committee continues to advise that shark data collection is inadequate and must be improved - it is currently not possible to assess the state of most sharks and mobulid ray species. The scientific committee also recommends that experiments be conducted on mitigating bycatches of sharks, especially in longline fisheries, and on the survival of sharks and mobulid rays captured by all gear types, with priority given to those gears with significant catches. There is 100% observer coverage on large purse seiners in the EPO so the data coming from these fleets should be useful and of high quality. Data from small purse seiners is very poor and 20% observer coverage is recommended for them as well.

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].

IATTC, 2018. Status of bigeye tuna in the eastern Pacific Ocean in 2017 and outlook for the future. Document SAC-09-05 for the Inter-American Tropical Tuna Commission Scientific Advisory Committee, Ninth Meeting, 14-18 May 2018, La Jolla, California, USA, 12 pp. Available at https://www.iattc.org/Meetings/Meetings2018/SAC-09/9th-Meeting-Scientific-Advisory-Committee.htm [Accessed on 05.12.2018].

IATTC, 2018. Tunas, Billfishes and Other Pelagic Species in the Eastern Pacific Ocean in 2017. Document IATTC-93-01 for the Inter-American Tropical Tuna Commission 93rd meeting, 24 and 27-30 August 2018, San Diego, California. 115 pp. Available at https://www.iattc.org/Meetings/Meetings2018/IATTC-93/IATTC-AIDCP-Annual-Meetings-AUG2018ENG.htm [accessed on 05.12.2018].

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.