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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 (FAD associated)
Capture Area Atlantic  FAO 34,47
Stock Area Atlantic
Stock Detail All Areas
Summary
The stock is at about the level which can produce the maximum sustainable yield (Bmsy), with fishing mortality below safe levels (Fmsy), indicating the fishery is in a healthy state. It is important for the individual Member nations to adopt catch levels in accordance with scientificly recommended TAC of 85,000t (for 2012-15). ICCAT managment has only been partially effective at controlling catch and effort, and Illegal Unreported and Unmonitored (IUU) fishing is believed to be occurring in some regions. Bycatch and discards for the longline and FAD associated purse seine fisheries are thought to be significant and both fisheries are need to adopt better measures to mitigatee this and improve monitoring. The best choice is from the surface fisheries, such as pole & line and non-FAD purse seine fisheries. Bigeye is assessed as Vulnerable by the IUCN - the World Conservation Union.
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. Bigeyes are considered moderately resilient to exploitation.
Stock Information
Atlantic bigeye and other Atlantic tuna stocks are assessed by ICCAT - the International Commission for the Conservation of Atlantic Tunas. The bigeye stock declined rapidly in the 1990s due to high catch levels, but has recently stabilized at approximately Bmsy. The latest stock assessment was undertaken in 2010 and has been updated to include 2011 data. The ICCAT Scientific Committee on Reporting and Statistics (SCRS) note that (like previous ones) there is considerable uncertainty in the assessment. Median biomass (2009) was about equal to that which could support Maximum Sustainable Yield (1.01Bmsy, range 0.72-1.34Bmsy); this suggesting that the stock is not overfished. Results for fishing effort suggest that the stock is not being subject to overfishing, with median fishing mortality at 0.95Fmsy (Range 0.65-1.55Fmsy). A TAC of 90,000t was in place between 2005-2008, yet this was lowered to 85,000 t for ?08-?11 and remains in place for 2012-2015. Reported catches have always been lower than the TAC, yet the Committee note that if major countries were to take the entire catch limit set under their current individual quotas, then the total catch could well exceed 100,000 t. MSY is currently estimated at about 92,00t - a provisional catch for 2011 was 77,795 t. There are concerns regarding IUU catches of bigeye from the Atlantic. There are a number of conservation measures in place, including a 3.2kg minimum size, limits on the numbers of vessels and restrictions on the use of Fish Aggregating Devices (FADs). Bigeye is assessed as Vulnerable by the IUCN (International Union for the Conservation of Nature).
Capture Information
21% of the bigeye catch from the Atlantic is taken in purse seine fisheries that set gear on floating objects including Fish Aggregation Devices (FADs). Many juvenile fish are discarded in purse seine fisheries and the method is also associated with bycatch of sharks and turtles. 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, yet on a much smaller scale compared with FAD fisheries. There are measures employed to reduce bycatch such as sorting grids, in addition to spatial and temporal closures and yet continued monitoring is required to assess their effectiveness.
References
ICCAT, 2012. Bigeye executive summary report 2012-13. Available at http://www.iccat.int/Documents/SCRS/ExecSum/BET_EN.pdf [Accessed Dec 2012]. ICCAT, 2010. Report of the 2010 ICCAT bigeye tuna stock assessment session . Pasaia, Gipuzkoa, Spain - July 5 to 9, 2010. Available at http://www.iccat.int/Documents/Meetings/Docs/2010_BET_Assessment_REP_ENG.pdf [Accessed Dec 2012]. ISSF, 2011. Bigeye: Atlantic 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.
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.