Good Fish Guide
Method of production - Caught at sea
Capture method - Purse seine (non FAD associated)
Capture area - North West and Central Pacific (FAO 61,71,77)
Stock area - WCPO
Stock detail - All Areas
Certification - None
Fish type - Oily fish
Bigeye tuna have a high susceptibility to fishing pressure. Fishing mortality on the stock in the Western and Central Pacific Ocean has generally been increasing over time. The latest assessment undertaken in 2014 indicates that the stock is being subject to considerable overfishing and recent catches are well above the estimated maximum sustainable yield (MSY). Similar to previous assessments, the assessment indicated that a 36% reduction in fishing mortality is needed in order to return fishing mortality to sustainable levels (Fmsy). Similarly, the biomass has declined over the duration of the fishery and is in an overfished state. 38% of the catch is taken in FAD associated purse seine sets, which encounter high proportions of juvenile tuna and relatively high proportions of bycatch compared with purse seine sets on free schools. The high catch of juvenile bigeye from these fleets has significantly reduced the achievable MSY of the fishery.
The WCPFC has implemented a wide range of management measures, particularly on the FAD purse seine fishery, in order to reduce fishing mortality to sustainable levels by 2017, yet it is not clear how successful these measures will be.
44% of the catch is taken in pelagic longline fisheries. Whilst these fisheries target larger, mature bigeye, they are associated with the bycatch of vulnerable species including sharks, turtles and sea birds. Whilst there are a range of mitigation measures required to be employed, the effectiveness of these measures is yet to be evaluated. Generally, the reporting of interactions with vulnerable species needs to be improved.
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.
Bigeye tuna in the Western Central Pacific Ocean is assessed by the Western and Central Pacific Fisheries Commission (WCPFC). The total bigeye catch in 2015 was 134,084t, which was a 16% decrease over 2014 and a 13% decrease over the average for 2010-14. The last stock assessment was conducted in 2014 and included data from over 60 years. Fishing mortality, F, was estimated to have increased through time, particularly in recent years, and levels were far in excess of sustainable levels (1.57Fmsy), therefore overfishing is occurring. Similar to previous assessments, the assessment indicated that a 36% reduction in fishing mortality was needed in order to return to sustainable levels (Fmsy). The Spawning Biomass, SB, was estimated to have declined over the duration of the fishery and was below the level that would support the Maximum Sustainable Yield (Bmsy at 0.77SBmsy). The fishery is therefore in an overfished state.
The latest estimate of MSY 108,520t is higher than previous assessments though it is noted that this is considerably lower that what could have been achieved prior to the introduction and widespread use of Fish Aggregation Device (FAD) associated purse seining which takes a high proportion of juvenile bigeye.
The bigeye tuna species is assessed as Vulnerable by the IUCN (International Union for the Conservation of Nature).
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 varies significantly between coastal states.
In 2016 the Commission agreed a 10-year timeframe for rebuilding bigeye tuna to the agreed Limit Reference Point of 20% of the unfished biomass (in 2015 it was estimated to be at 17%). The scientific committee in 2016 recommended a 36% reduction in fishing mortality from the average levels for 2008-2011. Whiles there is no Total Allowable Catch (TAC) set for this stock, a range of measures have been implemented to reduce effort with the aim of reducing fishing mortality to sustainable levels (below Fmsy) by the end of 2017. As the FAD purse seine fishery takes a considerable proportion of juvenile bigeye and has a disproportionately large impact on the stock, measures primarily apply to this gear type, including: a 3-month closure of fishing on FADs in EEZ waters and on the High Seas between 20degrees N and 20degrees S; plus, in 2015 and 2016, each member chose between extending this FAD closure to five months, or limit the number of FAD sets to less than the number of sets made by its vessels in a prescribed reference period. In 2017, a prohibition on FAD sets on the high seas will apply, except for vessels purse seine flagged to Kiribati. Additionally 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.
Beyond these measures for FAD fisheries, other measures include: limits for days at sea and a requirement by member states to prevent days at sea increasing; country specific catch limits for bigeye caught by longliners with monthly reporting requirements (total catch limits: 2014: 65,028t; 2015: 60,355t; 2016: 60,355t; 2017: 55,687t); a purse seine landing obligation for bigeye, skipjack and yellowfin between 20N and 20S; and a limit between 20N and 20S in the number of purse seine and longline vessels with freezing capacity.
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. However, observer coverage on purse seiners is poor in areas not specified here. 5% coverage is required on longliners greater than 20m in length.
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.
Only 6% of the total bigeye catch in the WCPO is taken purse seining on free schooling fish (as opposed to using Fish Aggregation Devices, FADs). These fisheries target smaller bigeye that aggregate closer to the surface whereas the longliners target larger fish that inhabit deeper waters. Many juvenile fish are often caught in purse seine fisheries and the method is also associated with bycatch of sharks, turtles and dolphins. Whilst the proportion of this bycatch compared with the total catch is relatively low, the high volume of tuna that is caught means that even a low proportion of this can still be relatively high in terms of total volume or individuals. In 2016 catches of silky sharks in the longline fishery were around three times higher than in the purse seine fishery, while redistribution of effort from FADs to free schools has resulted in substantial reductions in estimated catches of silky shark (by 83%) and oceanic whitetip shark (by 57%). FAD associated purse seine fisheries generally catch higher proportions of juvenile tunas and vulnerable bycatch species. Poorly designed FADs can also entangle such species. In this fishery, the high catch of juveniles has significantly reduced the Maximum Sustainable Yield (MSY) achievable from the stock. The widespread use of FADs is also of concern due to the unknown impacts such gear might have on natural species composition of tuna schools, migratory patterns, growth rates and predation rates of affected pelagic species.
Bycatch mitigation measures such as sorting grids are in place to reduce mortality of turtles, sharks and non-target species in general yet the effectiveness of these measures have yet to be demonstrated. Vessels are prohibited from knowingly setting a purse seine around tuna schools associated with a live whale shark, marine mammal or turtle, and all reasonable steps are required to be taken to ensure the safe release of these animals and details of the interaction are to be recorded if accidentally encircled. Permissible sharks are to be fully utilized and no more than 5% of fins to total shark weight can be retained; and there is a prohibition to land silky and oceanic whitetip sharks. Data on the effectiveness of the WCPFC ban on shark finning is very limited. In 2016, WCPFC adopted 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. The WCPFC have implemented a raft of management measures in recent years to limit and reduce the impacts of the purse seine fisheries on the tuna stocks, specifically skipjack, bigeye and yellowfin. Click on the Management TAB for more information about these measures.
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.
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