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Bigeye tuna (Thunnus obesus)

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Common name - Bigeye tuna
Scientific name - Thunnus obesus
Rating
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Caught at sea Purse seine (non FAD associated)
Capture Area Western & Central Pacific - WCPO  FAO 61,71,77
Stock Area WCPO
Stock Detail All Areas
Summary
Bigeye tuna are currently being overfished (F>FMSY) in the Western and Central Pacific Ocean and is possible that stocks are in an overfished state. Management by WCPFC is ineffective in preserving the stock and overcapacity is an issue among many. The WCPFC Scientific Committee recommended reducing catches by 30% in line with Fmsy, yet this has 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 fisheries.
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
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 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 1970?s) 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?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.
Capture Information
Only 4% of the total bigeye catch in the WCPO is taken purse seining on free schooling fish (as opposed to using Fish Aggregation Devices, FADs). FADs are known to attract juvenile fish and are also associated with bycatch of turtles, sharks and marine mammals. FADs are thought to have negative ecosystem effects and have been linked to changes in migratory patterns, growth rates and predation rates of affected pelagic species. Non FAD associated purse seiners still encounter bycatch of shark and turtles and juvenile fish, yet on a much smaller scale compared with FAD fisheries. There are measures employed to reduce bycatch such as sorting grids, yet continued monitoring is requried to assess their effectiveness. There is 100% observer coverage in parts (larger vessels) of these fisheries in addition to spatial and temporal closures and the requirement to submit FAD management plans. Bigeye from FAD free purse seine fisheries represent a more sustainable choice.
References
IATTC, 2012. Scientific meeting. La Jolla, California (USA), 15-18 May 2012. Available at http://www.iattc.org/Meetings/Meetings2012/May/PDFs/SAC-03-Meeting-report.pdf [Accessed Dec 2012]. ISSF, 2011. Bigeye: Western & Central Pacific Ocean. Available at http://iss-foundation.org/science/status-of-the-stocks/ [Accessed Dec2012]. IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded 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. WCPFC, 2012. Overview of tuna fisheries in the Western and Central Pacific Ocean, including economic conditions ? 2011. Scientific committee eighth regular session. 7-15 august 2012, Busan, Republic of Korea.
Alternatives
(Based on method of production, fish type, and consumer rating: only fish rated 3 and below are included.)
Read what the consumer pages of the Good Fish Guide say about this species.