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Tuna, bigeye

Thunnus obesus

Method of production - Caught at sea
Capture method - Longline
Capture area - Western & Central Pacific - WCPO (FAO 61,71,77)
Stock area - WCPO
Stock detail - All Areas
Accreditation -
Fish type - Oily fish

Sustainability rating Click for explaination of rating

This fish, caught by the methods and in the area listed above, is the least sustainable fish to eat and should be avoided. Click on the rating icon above to read more and on the alternatives tab below to find sustainable fish to eat.


Sustainability overview

Bigeye tuna are currently being overfished in the Western and Central Pacific Ocean and it is probable that the stock is also in an overfished state. Management by WCPFC is ineffective in preserving the stock and overcapacity is an issue. The WCPFC Scientific Committee recommended reducing catches by 30% in line with Fmsy, yet this failed to be incorporated into management agreements for 2013. Both longlining and FAD associated purse seine fisheries are associated with negative impacts to target and bycatch species. Avoid eating bigeye tuna from WCPO unless sure it is from the minority pole & line and non-FAD purse seine fishery.

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

Stock area
WCPO

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Stock information
Tuna management and assessment in the Western Central Pacific Ocean is undertaken by the Western and Central Pacific Fisheries Commission (WCPFC). The last stock assessment was conducted in 2011 and included data from the last 58 years. Fishing mortality is estimated to have increased through time, particularly in recent years, and current levels are far in excess of sustainable levels (1.46Fmsy), therefore overfishing is occurring. The total catch of bigeye in 2012 of 161,679t was a 2% increase over 2011 and a 7% increase over the previous five year average. The spawning biomass is estimated to have declined over the duration of the fishery and is now approaching or possibly below that which could sustain Maximum Sustainable Yield (SBmsy). Therefore it is possible the fishery is in an overfished state. Different models indicate that spawning biomass (SB) between 0.61-1.19SBmsy. The estimate of MSY is 76,800t (half that of the 1970s) with current catches (116,900 t) 51% greater than MSY. Reducing the catch of small bigeye would increase the overall level of catches that could be obtained sustainably. The WCPFC Scientific Committee recommended a reduction of at least 32% in fishing mortality from the average levels for 2006 to 2009 to return the fishing mortality rate to Fmsy. In March 2012, WCPFC members were unable to agree on additional measures to reduce bigeye mortality.

A new stock assessment is scheduled for 2014.

Management

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 bigeye tuna fishery in the Western and Central Pacific Ocean (WCPO) is 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. In this instance though, bigeye from other fisheries should be sourced.

There is no Total Allowable Catch (TAC) set for this stock although a range of measure have recently been implemented to try and reduce effort with the aim of reducing fishing mortality to sustainable levels (below Fmsy) by the end of 2017. These include: limits for days at sea and a requirement by member states to prevent days at sea increasing; in addition to a purse seine landing obligation for these species between 20N and 20S. Specifically regarding the use of Fish Aggregation Devices (FADs): there is a 3-month closure of fishing on FADs in EEZ waters and on the High Seas between 20N and 20S; plus each member shall choose between extending this FAD closure through October, or limit the number of FAD sets to less than the number of sets made by its vessels in prescribed reference period; and, there is a requirement to submit FAD management plans, including information on strategies used to implement the closure and other measures for reducing mortality of juvenile bigeye. It isn't clear how successfully these measures have been implemented yet.

100% regional observer coverage is required for all purse seine vessels fishing on the high seas and in waters under the jurisdiction of one or more coastal States, or vessels fishing in waters under the jurisdiction of two or more coastal States during the same trip; and on all purse seiners fishing between 20N and 20S.

Specifically regarding longline bycatch: there is a requirement for longliners to use at least 2 prescribed seabird mitigation measures (eg tori line, dyed bait, weighted branch line, night setting, underwater setting chute); for vessels to carry line cutters and de-hookers to promptly release turtles or to foster to recovery any sick or comatose turtles captured; for permissible sharks to be fully utilized with no more than 5% of fins to total shark weight to be retained. Monitoring of these measures is deficient.

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.

Capture information

57% 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 100 GRT) offshore vessels, usually domestically based. Pelagic longlining in the WCPO is associated with the incidental capture and mortality of sharks, turtles and sea birds. There are a range of measures that can be employed to reduce bycatch of these species including: circle and/or barbless hooks to prevent turtle and shark capture, and weighted branchlines, bird scaring lines, and night setting to reduce the capture of birds. These different measures are available yet not regulated in many of these fisheries. Monitoring in these fisheries is deficient. Of the 22 species of albatross 17 are threatened with extinction, largely because of longlining. See www.savethealbatross.net for more information.

Read more about capture methods


References
ISSF, 2013. ISSF Tuna Stock Status Update, 2013(2): Status of the world fisheries for tuna. ISSF Technical Report 2013-04A. International Seafood Sustainability Foundation, Washington, D.C., USA. Available at http://iss-foundation.org/resources/downloads/?did=487 [Accessed Nov 2013].
WCPFC, 2013. Scientific committee ninth regular session: summary report. 6-14 August 2013, Pohnpei, Federated States of Micronesia. Avaiilable at http://www.wcpfc.int/meetings/9th-regular-session-scientific-committee [Last accessed Jan 2014].
IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. . [Accessed December 2012].
WCPFC, 2012. The Western and Central Pacific tuna fishery: 2010 overview and status of stocks. scientific committee eighth regular session. 7-15 august 2012, Busan, Republic of Korea.
www.fishbase.org [Accessed Nov 2013].

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