Tuna, bigeye

Thunnus obesus

Method of production — Caught at sea
Capture method — Longline
Capture area — Pacific, North West (FAO 61) and Central (FAO 71,77)
Stock area — Western and Central Pacific
Stock detail

All Areas


Picture of Tuna, bigeye

Sustainability rating three info

Sustainability overview

A new stock assessment was conducted for bigeye tuna in the Western Central Pacific Ocean in 2017, and updated in 2018 to reduce some of the uncertainty. This indicated the stock is not in an overfished state and not undergoing overfishing. Preliminary 2017 catch is 126,929 t, a 17% decrease from 2016, and a 19% decrease from the average 2012-2016. The estimate of MSY is 159,000 tonnes. MSY has been reduced to less than half its levels prior to 1970 through harvest of small bigeye (‘growth overfishing’). Levels of fishing mortality and depletion differ between regions, and fishery impact was higher in the tropical region, and the scientific committee has recommended reducing mortality in these regions. As of January 2018, a bridging measure is in force to manage bigeye, yellowfin and skipjack - all caught together. As part of this, spawning biomass depletion ratios for bigeye and yellowfin are to be maintained at recent levels (the average from 2012-2015). Whiles there is no Total Allowable Catch (TAC) set for this stock, a range of measures have been implemented to reduce effort and includes flag-specific catch limits for bigeye caught by longliners. 43% of bigeye catches in the WCPO are taken in pelagic longline fisheries. Pelagic longlining in the WCPO is associated with the incidental capture and mortality of vulnerable species including sharks, turtles, sea birds and billfish. Whilst there are some mitigation measures in place to reduce the impact, monitoring and reporting of interactions is insufficient to evaluate the effectiveness of these measures. There is 5% observer coverage on large longliners, but a review of coverage has been advised.

Commercial buyers should establish what measures the flag state and fleet relating to their source is taking to reduce impacts to and improve reporting of interactions with vulnerable species. Large buyers should consider supporting such improvements. There are a number of Fishery Improvement Projects (FIPs) in the WCPO making improvements in longline fisheries for bigeye. More information about these FIPs is available from 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 200kg in weight, with a maximum age of 11 years. Bigeye are considered moderately resilient to exploitation.

Stock information

Criterion score: 0.25 info

Stock Area

Western and Central Pacific

Stock information

Bigeye tuna in the Western Central Pacific Ocean is assessed by the Western and Central Pacific Fisheries Commission (WCPFC).

A new stock assessment was conducted in 2017, and updated in 2018 to reduce some of the uncertainty (although more work is needed on that area). It is considered to be the most advanced and comprehensive assessment yet conducted for this species, with improvements to both the data and the model used. It shows that the bigeye stock may be in better condition than previously thought. The stock is not in an overfished state, with the ratio of recent Spawning Biomass (SB) to unfished levels (SB/SBF=0) at 36% (or 1.23 SBMSY) as opposed to 20% in 2014. It is also thought that the stock is not undergoing overfishing, with the ratio of recent fishing mortality (F) to FMSY at 0.77 (in 2014 it was 1.57). The significance of the recent high recruitment and the progression of these fish to the spawning potential component of the stock are encouraging, but the cause is unknown: it could be one or a combination of environmental conditions or management measures, or other factors. Recent recruitment improvements for Pacific yellowfin, skipjack and bigeye tunas, as well as observations that strong recruitment levels in the East Pacific Ocean had been recorded in 2015 and 2016, associated with a major El Nino event, lend weight to the environmental hypothesis. The management target is to maintain spawning biomass depletion ratio (SB/SBF=0) at or above the average SB/SBF=0 for 2012-2015. Any predictions on future stock trends are strongly influenced by assumed future recruitment levels. Positive recruitments lead to an increase in SB/SBF0, and a decrease in F, while less positive recruitments lead to a decline in SB/SBF0 and F increases to well above FMSY.

Consistent with previous assessments, the latest one shows that the stock has been continuously declining for about 60 years, since the late 1950’s, except for a recent small increase. Preliminary 2017 catch is 126,929 t, a 17% decrease from 2016 and a 19% decrease from the average 2012-2016. The estimate of MSY is 159,000t. MSY has been reduced to less than half its levels prior to 1970 through harvest of small bigeye (“growth overfishing”). Recent catches (2013-2017 average = 141,800 tonnes) are below MSY. Levels of fishing mortality and depletion differ between regions, and fishery impact was higher in the tropical region, with particularly high fishing mortality on juvenile bigeye tuna in these regions. The scientific committee therefore continues to recommend a precautionary approach to management, including reducing fishing mortality of juveniles. It is also recommended that fishing mortality is maintained at 2011-2014 levels (in order to maintain SB at the 2012-2015 levels) until further management objectives and a target reference point are agreed.

Management

Criterion score: 0.5 info

Most tuna stocks range across and are accessed by numerous coastal states, making harmonised and effective management of these individual stocks very difficult. As a result, 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. The tuna fisheries in the Western and Central Pacific Ocean (WCPO) are managed by the Western and Central Pacific Fisheries Commission (WCPFC). 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.

WCPFC has put in place a lower limit for the spawning biomass of bigeye, skipjack, and yellowfin tuna of 20 percent of unfished levels (SB/SBF=0, aka spawning biomass depletion ratio), below which the stock should not fall. For skipjack there is also an interim target of 50 percent of unfished levels, which was adopted in 2015 and has been reached. The scientific committee recommends reducing fishing mortality on juvenile bigeye and yellowfin in the tropics, through preventing increases in overall fishing mortality, until targets for these two stocks can be agreed. The commission is looking to establish harvest strategies for key fisheries and stocks but has not yet completed this work and so, as of January 2018, a bridging measure is in force to manage bigeye, yellowfin and skipjack - the measure lasts until harvest strategies are in place or until February 2021. As part of this, spawning biomass depletion ratios for bigeye and yellowfin are to be maintained at recent levels (the average from 2012-2015) and skipjack at 50 percent. The bridging measure includes a number of new measures and consolidates some pre-existing ones, and is outlined below.

In the tropical region, between 20 degrees North and 20 degrees South, the following applies:
The use and deployment of FADs is prohibited for 5 months of the year (3 months for Kiribati and the Philippines). VMS polling frequency increases to every 30 minutes during the FAD closure.
Effort limits (in vessel days) apply to purse seining on the high seas (excluding Small Island Developing States, SIDS): limits vary by country. In order not to undermine the effectiveness of this, countries cannot transfer effort into areas outside of this region.
To create an incentive to reduce the non-intentional capture of juvenile fish, to discourage waste and to encourage an efficient utilization of fishery resources, purse seiners must retain on board and then land or transship at port all bigeye, skipjack, and yellowfin tuna (also applies to national waters).
All purse seine vessels operating on the high seas or within national waters in this region must carry an observer. This also applies to purse seiners anywhere in the convention area fishing in waters under multiple countries’ jurisdiction or moving between the high seas and national waters.
The number and capacity of large (over 24m) purse seiners and longliners (with freezing capacity and ice-chilled) operating in this area is frozen to 2016 levels (excluding SIDs and Indonesia).

Other measures that apply to the wider convention area:
The number of drifting FADs with activated instrumented buoys deployed at any one time is limited to 350 per purse seine vessel.
Catch and/or effort limits apply for purse seining within national waters (both the type of limit and the amount vary by country).
There are country-specific limits on longline bigeye catch, and by 2020 hard limits for bigeye and a framework to allocate them amongst countries shall be developed.
Catches by other commercial tuna fisheries for bigeye, yellowfin or skipjack tuna (excluding those taking less than 2,000 tonnes) shall not exceed either the average level for the period 2001-2004 or the level of 2004.

More generally:
There is a requirement to submit FAD management plans, including information on strategies used to implement closures and other measures for reducing mortality of juvenile bigeye. A number of aspects in the bridging measure have been brought forward from previous management measures, and it isn’t clear how well they have been implemented, especially given the ongoing increases in total catch of skipjack. The scientific committee recommends more comprehensive data collection relating to FADs.
Observer coverage on purse seiners is poor in areas not specified in the bridging measure and only 5% coverage is required on longliners greater than 20m in length. 20% is considered to be the minimum to be effective.
To help address IUU, the WCPFC maintains an IUU Vessel List, prohibits transhipments at sea between purse seiners (some exemptions apply) and requires all other transhipments to be documented and 100% observed as part of the regional observer programme.
In 2017 a Compliance Monitoring Scheme was introduced to assess and improve compliance with obligations, and penalise non-compliance.

Capture Information

Criterion score: 0.75 info

43% of bigeye catches in the WCPO are taken in pelagic longline fisheries. The number of boats in the fishery fluctuates between 4,000 and 5,000 and involves large, distant, water freezer vessels and smaller (typically less than 100t) offshore vessels, usually domestically based. Pelagic longlining in the WCPO is associated with the incidental capture and mortality of vulnerable species including sharks, turtles, sea birds and billfish.

There is concern that some seabird species, notably albatrosses and petrels, are threatened with global extinction. Of critical concern is Antipodean wandering albatross, which is expanding foraging range into tuna fishery areas and has experienced a high and sustained rate of decline - it is now in New Zealand’s “Nationally Critical” conservation status category. High bycatch of seabirds, especially albatross, continue to be reported by some countries fishing south of 30 degrees South. The Commission for the Conservation of Antarctic Marine Living Resources advises that, together with illegal, unreported and unregulated fishing, the greatest threat to Southern Ocean seabirds is mortality in longline fisheries in waters adjacent to its Convention Area. Countries are expected to implement the International Plan of Action for Reducing Incidental Catches of Seabirds in Longline Fisheries (IPOA-Seabirds) and report back on this. South of 30 degrees South and north of 23 degrees North, longliners must use at least 2 mitigation measures. In the area between, longliners need only use 1. The simultaneous use of 3 measures (weighted branch lines, bird scaring lines and night setting) remains the best practice approach. Further research is being done on hook shielding devices, and countries are encouraged to develop and refine measures to mitigate seabird bycatch, including safe release of seabirds captured alive. Scientific advice is to review observer coverage rates (used to estimate total seabird interactions), which is not currently being done.

The five marine turtle species in the WCPFC Convention Area are threatened or critically endangered, and WCPFC does not hold sufficient information to quantify the severity of the threat posed by longline fisheries to sea turtle populations. Measures to mitigate turtle bycatch, from 2008, are: to safely recover and release captured turtles, for purse seiners to avoid encircling them, for longliners to carry cutters and dehookers for releasing them, and for shallow-set swordfish longliners to use circle hooks and whole finfish bait (some exemptions to the latter measure apply, e.g. if there is 10% observer coverage). Under this measure, less than 1% of Western and Central Pacific Ocean (WCPO) longline effort is subject to mitigation, even though approximately 20% of the WCPO longline effort consists of shallow sets. To improve current management measures, research into turtle bycatch mitigation is ongoing. Research includes, but is not limited to, the wider use in longline fisheries of large circle hooks and/or whole finfish for bait. Improvements in data collection on interactions with sea turtles are needed. Although interaction rates are higher in shallow-set longlines, mitigation for deep-set longlines would deliver greater reductions in total interactions because effort in deep-set longline fisheries is 4 times that of shallow sets. Similarly, introducing mitigation to deep-set longlines would deliver greater reductions in at-vessel mortality compared to shallow-sets, because sea turtles have a higher probability of asphyxiation in deep sets.

In 2016, catches of silky sharks in the longline fishery were around three times higher than in the purse seine fishery. Shark measures include: full utilisation of permissible sharks and retention of no more than 5% of fins to total shark weight, a prohibition to land silky and oceanic whitetip sharks, and a prohibition on the use of shark lines. The effectiveness of these measures are difficult to evaluate owing to lack of data. As of 2014, shark management plans are required where sharks are being targeted, although to date only 2 countries have developed them. There are measures to improve recording of manta and mobula rays discarded and released, and to treat these species as key shark species for assessment and research. In 2017 the scientific committee recommended guidelines for safe release of manta and mobulid rays, which were adopted by the WCPFC. The commission is also looking to develop guidelines for other rays and sharks, especially silky shark and oceanic whitetips, as well as develop stronger and more comprehensive management measures for sharks, but there is no stated deadline for this. It is recommended that target and limit reference points are established for pelagic sharks.

In general, the effectiveness of the above measures has not been evaluated. Monitoring is deficient and the reporting of interactions with vulnerable species is poor. The scientific committee has recommended a continuation of the work on purse seine bycatch estimates and extension of this work to producing estimates of bycatch in the longline fisheries for 2018, acknowledging the issues related to the 5% observer coverage in these fisheries.

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].

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].

Pilling, G., Vincent, M., Williams, P., Hampton, J., 2018. Evaluation of CMM 2017-01 for bigeye tuna, WCPFC-SC14-2018/ MI-WP-08 for the Fourteenth Regular Session of the Scientific Committee of the Commission for the Conservation and Management of Highly Migratory Fish Stocks in the Western and Central Pacific Ocean, 8-16 August 2018, Busan, Republic of Korea. 14 pp. Available at https://www.wcpfc.int/meetings/14th-regular-session-scientific-committee [Accessed on 06.12.2018].

WCPFC, 2018. Conservation and Management Measures of the Western and Central Pacific Fisheries Commission. Available at https://www.wcpfc.int/conservation-and-management-measures [Accessed on 06.12.2018].

WCPFC, 2018. Outcomes Document from the Fourteenth Regular Session of the Scientific Committee of the Commission for the Conservation and Management of Highly Migratory Fish Stocks in the Western and Central Pacific Ocean, 8-16 August 2018, Busan, Republic of Korea. 34 pp. Available at https://www.wcpfc.int/meetings/14th-regular-session-scientific-committee [Accessed on 06.12.2018].

WCPFC, 2018. Summary Report of the Fourteenth Regular Session of the Scientific Committee of the Commission for the Conservation and Management of Highly Migratory Fish Stocks in the Western and Central Pacific Ocean, 8-16 August 2018, Busan, Republic of Korea. 34 pp. Available at https://www.wcpfc.int/meetings/14th-regular-session-scientific-committee [Accessed on 06.12.2018].