Bigeye Tuna - Sustainabililty
WILD HARVEST FISHERIES
All bigeye tuna production is from wild harvest fisheries. Bigeye tuna is a moderately fast-growing, widely distributed and very fecund species. It is heavily fished by many different methods and, despite its high productivity, its stocks face future challenges due to a high demand. Both stocks in the Western and Central Pacific Ocean (WCPO) and the Indian Ocean (IO) are currently not overfished. In both oceans areas, the problem of bycatch from longline, gillnets (IO), purse seine fishing with drifting fish aggregating devices (FADs), and the impact of pole and line fishing on baitfish stocks cause environmental problems that are being addressed by several conservation management measures. The effects of these measures are not considered adequately monitored except in the case of the WCPO purse seine fishery.
IUCN Red List Status
Vulnerable (globally) http://www.iucnredlist.org/details/21859/0
Because the maximum sustainable yield (MSY) of the Western and Central Pacific bigeye tuna stock represents more than 20% of the global populations, bigeye tuna is listed as 'vulnerable' globally under Category A2: "Population reduction observed, estimated, inferred, or suspected in the past where the causes of reduction may not have ceased OR may not be understood OR may not be reversible."
State of the Stocks and Impacts of Fishing
The updated assessment shows the bigeye tuna stock in the WCPO appears not to be overfished nor subject to overfishing (Vincent, Pilling & Hampton, 2018). However, the stock is estimated to have declined substantially over most of the assessment period and remains in a state somewhat more depleted than most other tuna stocks in the WCPO (McKechnie et al., 2017). Most of the catch is taken by fishing methods that entail significant bycatch (longlines and surface purse seining on fish aggregating devices (FADs), or, in the case of the small amount of bigeye tuna taken by pole and line, methods that may negatively impact local baitfish species. Monitoring of purse seine fishing is comprehensive and adequate. Monitoring of longline fishing is not as comprehensive as that for purse seine fishing, having lower coverage of logsheet data submitted to the Western and Central Pacific Fisheries Commission (WCPFC) and lower observer coverage of fishing trips. The vessel monitoring system (VMS) coverage of longline fishing, however, is close to 100%.
The bigeye tuna resources of the IO are not overfished, nor subject to overfishing. The majority of the catch is taken by longline, purse seine around FADs and gillnet. These are methods with significant bycatch problems.
The following bigeye tuna stock status information, by ocean, is drawn from the scientific reports of the regional fisheries management organisations and from the International Seafood Sustainability Foundation’s (ISSF) overview of stock status, rankings of management measures and impacts of fishing on bycatch (Status of the Stocks Technical Report).
WCPO BIGEYE TUNA
In stock assessments, bigeye tuna in the WCPO is considered a single stock.
Stock abundance
Green - SSB > SSBMSY The spawning biomass is above the MSY level..
Fishing mortality
Green - F < FMSY F is below the MSY level.
Environment
Green – 8% of the catch is made with purse seining on free schools, with little impact on non-target species.
Yellow – 36% of the catch is made by purse seining on floating objects (including FADs). Several bycatch mitigation measures are in place (turtles, sharks). There is 100% observer coverage on part of the purse seine fleet.
Yellow - 3% of the catch is made by pole-and-line fishing, with unknown impacts on baitfish stocks.
Orange – 43% of the catch is made by longlining. Several mitigation measures are in place (sharks, turtles, sea birds). Monitoring is deficient.
IO BIGEYE TUNA
Stock abundance
Green – SSB > SSBMSY
Fishing mortality
Green – F < FMSY
Environment
Green - 7% of the catch is made with purse seining on free schools, with little impact on non-target species.
Yellow – 21% of the catch is made by purse seining on floating objects (including FADs). Several bycatch mitigation measures are in place (turtles, sharks).
Orange – 54% of the catch is made by longlining. Several mitigation measures are in place (sharks, turtles, sea birds). Monitoring is deficient.
Orange – 17% of the catch is made by other gears such as gillnet. Reporting by these fisheries, which are thought to have substantial amounts of bycatch, is poor.
Certificates for sustainability of wild harvest fishery
Marine Stewardship Council (www.msc.org)
No bigeye tuna fisheries are certified although two fisheries, in combination with yellowfin, are under assessment. One of these, SZLC CSFC & FZLC FSM EEZ Longline Yellowfin and Bigeye Tuna, was certified in October 2018 with component(s) in assessment. The certificate expires in October 2023..
Sea (www.friendofthesea.org)
Friend of the Sea does not certify fisheries, but audits and certifies companies in the fish supply chains to adopt selective fishing methods, reduce ecosystem impact and manage within maximum sustainable yield. The certification also deals with quality standards for energy efficiency and social accountability. A list of currently certified fleets for bigeye fishing in the Indian Ocean can be found through this link. and social accountability.
Several conservation and sustainable/fair food organizations also promote sustainable tuna campaigns, e.g., see the Pew Charitable Trusts Global Tuna Conservation campaign.
FISHERIES ASSESSMENTS
The status of bigeye tuna stocks is difficult to assess because each stock is harvested by many different fishing gears, over a wide geographic area with each gear type tending to catch fish of a different size range. Longline fishing mainly harvests adult bigeye tuna whereas purse seines and gillnets harvest a wide size range of bigeye tuna, including many juveniles.
Compared to skipjack and yellowfin tuna stocks, those of bigeye tuna are more vulnerable to overfishing and take longer to recover after a population decline because they are relatively long-lived and mature later than these other tunas. The large and increasing catches of bigeye juveniles by surface fisheries are reducing the size of the spawning stock of large fish caught in the deeper waters by longlines, and reducing the maximum sustainable yield of the whole fishery.
Fisheries catch data, which are essential to bigeye tuna assessments, have several shortcomings. In particular, reporting of bigeye tuna catches is inconsistent among fleets and gears. For some gear types, such as gillnets and those used in artisanal fishing, reporting of catch and effort is limited, e.g., despite their importance, the catches of bigeye tuna in Indonesia, Philippines, and Vietnam are not fully monitored. Bigeye tuna catches are under-reported for several gear types, especially purse seines, because juvenile bigeye join schools and are harvested with other tuna species of similar size, especially skipjack and yellowfin tuna. Log sheets from purse seine fisheries tend to be biased towards recording most small tunas as skipjack. Observer sampling in port and at sea has revealed under-reporting of yellowfin and bigeye of up to 15% (for sets associated with floating objects). Such under-recording of juvenile yellowfin and bigeye tuna occurs both in the WCPO and the IO fisheries and the logbook estimates are adjusted using port - or at sea - samples of fish to help reduce the bias. Difficulties in distinguishing juvenile bigeye from juvenile yellowfin tuna also cause data problems (see Biology).
Western and Central Pacific Ocean
The 2018 re-evaluation of bigeye tuna in the WCPO using an updated new growth model (similar to the model presented in 2017) again provided a more optimistic stock status estimates than the old growth model. The Scientific Committee recommends, however, a precautionary approach that the fishing mortality on bigeye tuna stock should not be increased from current levels to maintain current or increased spawning biomass until the Commission can agree on an appropriate target reference point (WCPFC, 2017).
While trying to maintain/reduce fishing on bigeye (and yellowfin) tuna, management agencies have to deal with the economic losses that the purse seine fisheries primarily catching skipjack tuna would suffer. With a view to controlling fishing levels on bigeye tuna in the face of increasing fishing pressures and fishing fleet dynamics, the WCPFC continues to develop and encourage implementation of annually revised Conservation and Management Measures (CMM). CMM 2018-01 and its precursors contain articles to control skipjack, yellowfin and bigeye fishing rates by: controlling fishing levels at the average SB/SBF=0 2012-2015 levels (bigeye and yellowfin) and at 50% of the spawning biomass in the absence of fishing (skipjack interim target reference point – CMM 2015-06); management of fishing on FADs and floating objects including seasonal closures; effort controls; high seas controls; overlap area controls; retention policies; charter, compliance and observer arrangements; and bigeye longline catch limits by fishing flag states.
Longlines take about 45% of the bigeye tuna catch, and purse seines take about 45%, with pole-and-line; handline and other gears taking small shares (Brouwer, et al, 2018). In 2013, the record purse seine catch of bigeye tuna exceeded that of longlines for the first time. The purse seine and other surface fisheries have slightly greater impact on bigeye stocks than does the longline fisheries. The purse seine and Philippines and Indonesian domestic fisheries impact the western Pacific fishery around the equator, and the Japanese coastal pole-and-line and purse-seine fisheries impact the bigeye fishery in the north.
Indian Ocean
For bigeye tuna in the IO, the stock is assessed by the Scientific Committee of the IOTC. The Scientific Advisory Committee of the ISSF takes the IOTC stock assessments, plus other reliable information, to make their sustainability assessments based on the IOTC estimates of stock abundance, fishing mortality and environmental impact. Tag recoveries suggest that bigeye tuna in the Indian Ocean belong to a single stock.
Indian Ocean bigeye tuna stock is not overfished and is not experiencing overfishing. The MSY for the Indian Ocean bigeye stock size is 104,101 tonnes, compared to a recent average of 95,997 tonnes (IOTC, 2018). Catches increased after 2011, however, as the piracy threat in the western Indian Ocean decreased. Stock estimates for the IO are compromised by the lack of detailed catch statistics from some coastal fisheries, the gillnet fisheries of Iran, Pakistan and Sri Lanka and some industrial longline fleets (e.g. from India, Philippines).
FISHERIES MANAGEMENT
Bigeye tuna fisheries are managed by regional fisheries management organizations (RFMOs) and by national governments. Reaching agreement on management measures is difficult due to competing interests of countries and fleets and preferences for different types of management choices, e.g., controls on the number of licenses, total allowable catch limits, vessel day limits, and restricting access to fishing areas.
As for the stock assessments, the management of bigeye tuna fisheries is complicated by the mix of gears and fleets exploiting the stocks in both oceans, and problems in under-reporting of catches of bigeye (and yellowfin), especially in purse seine fisheries.
Industrial tuna fisheries are managed by the WCPFC in the WCPO, the IOTC in the IO, and the Inter-American Tropical Tuna Commission (IATTC) in the Eastern Pacific Ocean (EPO). There is some overlap between the WCPFC and IATTC Convention Areas with respect to management of bigeye tuna. The RFMOs meet annually to consider and endorse recommended management actions. [See Gallery for convention area maps].
Regional associations of countries are increasingly influential in tuna fisheries management, more so in the WCPO than the IO. Individual island countries also manage their tuna resources, through national tuna management plans.
Each of the RFMOs has a scientific committee that provides advice on stock status, monitoring and management implications, using their own and additional scientific expertise. In the case of the WCPFC. SPC is the data management service provider, and holds all of the data used in assessments. WCPFC has the parts of this that are designated as WCPFC data.
Through negotiations, the RFMOs recommend management measures (‘Conservation and Management Measures’ or CMMs) aimed at securing the sustainability of tuna stocks and, more recently, bycatch stocks and the marine environment. However, because the RFMOs use consensus-based decision-making, it is increasingly difficult for agreement to be reached between science, politics and economics on the implementation of effective stock management measures.
In the European Union countries, which are important tuna markets for WCPO and IO tuna, regulations against illegal, unreported and unregulated (IUU) fishing vessels (Council Regulation (EC) No. 1005/2008 and Commission Regulation (EU) No 468/2010) act, in effect, as management drivers.
In addition, campaigns by international environment organizations, such as Greenpeace, the Pew Environment Group and the World Wide Fund for Nature (WWF), advocate against the catch of juvenile bigeye and yellowfin tuna, especially by purse seiners in association with drifting FADs. These campaigns have led to some marketing chains (in Australia, UK, USA) imposing bans or foreshadowing bans on canned tuna harvested around FADs.
Western and Central Pacific Ocean
Although the new assessment is a significant improvement in relation to the previous one, the WCPFC Scientific Committee advises that the amount of uncertainty in the stock status results for the 2017 assessment is higher than for the previous assessment due to the inclusion of new information on bigeye tuna growth and regional structures. The Scientific Committee recommends a precautionary approach that the fishing mortality on bigeye tuna stock should not be increased from current levels to maintain current or increased spawning biomass until the Commission can agree on an appropriate target reference point (WCPFC, 2017).
While trying to maintain/reduce fishing on bigeye (and yellowfin) tuna, management agencies have to deal with the economic losses that the purse seine fisheries primarily catching skipjack tuna would suffer. With a view to controlling fishing levels on bigeye tuna in the face of increasing fishing pressures and fishing fleet dynamics, the WCPFC continues to develop and encourage implementation of annually revised Conservation and Management Measures (CMM). CMM 2017-01 and its precursors contain articles to control skipjack, yellowfin and bigeye fishing rates by: controlling fishing levels at the average SB/SBF=0 2012-2015 levels (bigeye and yellowfin) and at 50% of the spawning biomass in the absence of fishing (skipjack interim target reference point – CMM 2015-06); management of fishing on FADs and floating objects including seasonal closures; effort controls; high seas controls; retention policies; compliance and observer arrangements; and bigeye longline catch limits by fishing flag states.
A subset of WCPFC member countries, the Parties to the Nauru Agreement (PNA), also place limits on purse-seine fishing effort within their Exclusive Economic Zones (EEZ) through a ‘vessel day scheme’ (VDS) that only licenses those purse-seine vessels that do not fish in the high seas between 100N and 200S, including the two tropical high-seas pockets within their region.
Pacific island countries also have to balance domestic development aims for national tuna fishing and onshore processing facilities with sustainable use of tuna resources. Groups of countries have been formed to help foster collective country interests. Regional inter-governmental and industry organizations concerned with tuna in the WCPO are:
Pacific Islands Forum Fisheries Agency (FFA) (https://www.ffa.int/) - (member countries: Australia, Cook Islands, Federated States of Micronesia, Fiji, Kiribati, Marshall Islands, Nauru, New Zealand, Niue, Palau, Papua New Guinea, Samoa, Solomon Islands, Tokelau, Tonga, Tuvalu and Vanuatu)
Parties to the Nauru Agreement (PNA) (http://www.pnatuna.com/) - (member countries: Federated States of Micronesia, Kiribati, Marshall Islands, Nauru, Palau, Papua New Guinea, Solomon Islands and Tuvalu). The influence of the PNA in tuna management in the WCPF Convention Area has been significant because, as a group, the zones of the member countries host significant yellowfin tuna resources.
TeVaka Moana Arrangement (TVMA) (http://www.tevakamoana.org/) - (member countries: Cook Islands, New Zealand, Niue, Samoa, Tokelau and Tonga).
Pacific Islands Tuna Industry Association (PITIA) (http://pacifictuna.org/) - (member countries: Cook Islands, Federated States of Micronesia, Fiji, Kiribati, Marshall Islands, Nauru, Niue, Palau, Papua New Guinea, Solomon Islands, Tonga, Tuvalu and Vanuatu).
Indian Ocean
The annual IO catches of bigeye tuna are well below the maximum sustainable yield (MSY) level, and at present immediate management measures are not required. However, continued monitoring and improvement in data collection, reporting and analysis are required to reduce the uncertainty in assessments. The International Seafood Sustainability Foundation recommends that the fishery should be limited entry, accompanied by a closed vessel registry with the aim of reducing the number of fishing vessels targeting the stock.
As yet, the IOTC has not established particular conservation measures for bigeye. More generally, bigeye are subject to CMMs of other species. These measures include providing catch data, limiting fishing capacity and keeping a record of licensed foreign and local fishing vessels, and catch retention, e.g., Resolution 17/04. The main binding conservation measures requires that total catch should not exceed 110,000 tonnes and that vessels longer than 24 m, and smaller vessels if they fish on the high seas, should respect a one-month closure for purse seiners and longliners in an area of size 10°x20°.
In addition to the IOTC management of bigeye and other tuna in the Indian Ocean, the Maldives Seafood Processors and Exporters Association and the Western Indian Ocean Fisheries Directors Forum represent the interests of industry or sub-regional country groups.
AQUACULTURE
Although approval has been given for a yellowfin and bigeye tuna farm off Hawaii, it is not yet operational. Cage grow-out of bigeye is not conducted. The life-cycle of bigeye tuna has not been closed.
GUIDE TO FURTHER READING
For comments on tuna in IUCN Redlist, see Restrepo et al (2011)
For stock status updates, see the International Seafood Sustainability Foundation’s (ISSF) Status of the Stocks Technical Report, IOTC (2018) and IOTC Stock Status Dashboard (http://www.iotc.org/science/status-summary-species-tuna-and-tuna-species-under-iotc-mandate-well-other-species-impacted-iotc), Brouwer et al. (2018) and McKechnie et al. (2017).
For biological and fishery factors affecting bigeye tuna fishery assessments, see Babaran (2006), Brouwer et al. (2018), Colette et al. (2011), Hampton & Williams (2011), Lawson (2010) and Miyake et al. (2010).
For information on the Western and Central Pacific Ocean bigeye tuna assessments, see Brouwer et al. (2018), WCPFC (2017) and Willams et al. (2017).
For information on the Indian Ocean bigeye tuna assessments, see IOTC (2018), IOTC (2016) and ISSF (2017).
For views on achieving effective regional management, see Hamilton et al. (2011) and Polacheck (2012).
For Western and Central Pacific Ocean bigeye tuna management arrangements, challenges and opportunities, including climate see Davies et al. (2011), Hamilton et al. (2011), Brouwer et al. (2018), ISSF (2017), Miyake et al. (2010), Restrepo et al. (2014) and Lehodey et al. (2011).
For Indian Ocean management IOTC (2012) and IOTC (2018).
REFERENCES
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