SPECIES IMPORTANCE

Bigeye tuna is of major commercial interest, caught primarily for sashimi (larger fish) and to a lesser extent, for canning (small fish).

Bigeye tuna occurs in the tropical and subtropical waters of the Atlantic, Indian and Pacific Oceans, but is absent from the Mediterranean Sea. Production is from all of these regions, Japan and the Republic of Korea being the major countries reporting catches.

In the Western and Central Pacific and Indian Oceans, bigeye tuna is targeted in the industrial and smaller scale tuna longlining fisheries and is taken also in non-targeted catches in the purse-seine and pole and line fisheries. Juvenile bigeye tuna caught in the purse seine fishery is either canned (although not invariably and may be diverted to fish meal, flakes etc. because of blood spots in the meat, and increasing traceability requirement for one species in the can as occasionally verified by DNA) and fresh in local markets; mature adults from the longline fishery generally are sold as sashimi or good quality steaks. Juvenile bigeye and yellowfin tuna are similar in appearance and as a result bigeye tuna is likely to be counted as yellowfin. Bigeye tuna catches, therefore, may be slightly underreported.

More than 80% of the world’s bigeye tuna is caught in the Indian and Pacific Oceans (Western and Central and Eastern areas). The catch was highest in the Western and Central Pacific Convention Area (around 150,000 t); followed by around 100,000 t in the Eastern Pacific Ocean area, and around 90,000 t in the Indian Ocean (recent five year averages).

FISHING METHODS

Bigeye tuna is caught predominately by longline and purse seine (both targeted and non-targeted). Other gears also used, but accounting for a significantly smaller proportion of the catch, are pole and line (limited), handline and troll, and gillnet.

Western and Central Pacific

Bigeye tuna of sashimi size and quality is the most valuable of the tropical tunas and is the principal target of large distant-water longliners which freeze catches, and of the smaller, locally-based fresh sashimi vessels (National Oceanic and Atmospheric Administration, 2007). Within the Pacific Ocean, bigeye tuna is distributed through the basin but the bulk of the catch is made towards the eastern and western ends of the ocean basin. Bigeye tuna fisheries in the Western and Central Pacific Ocean (WCPO) are diverse, ranging from small-scale artisanal operations in the coastal waters of Pacific states, Indonesia and Philippines, to industrial purse-seine, pole and line, and longline operations in the exclusive economic zones of Pacific states and in international waters.

The majority of the catch in the WCPO is taken in equatorial areas, by both purse-seine and longline. The longline catch is predominately taken in the central Pacific, contiguous with the important traditional bigeye tuna longline area in the eastern Pacific. Some of the longline catch is within sub-tropical areas, for example, east of Japan and off the east coast of Australia.

The domestic surface fisheries of the Philippines and Indonesia take large numbers of small bigeye in the range 20-50 cm. In addition, large numbers of 25-75 cm bigeye tuna are taken in purse seine fishing on Fish Aggregating Devices (FADs), which along with the fisheries of the Philippines and Indonesia account for the bulk of the catch by number.

Large bigeye tuna are rarely taken in the WCPO purse-seine fishery, and only a relatively small amount comes from the handline fishery in the Philippines. This contrasts with large yellowfin tuna, which, in addition to the longline catch, is also taken in significant amounts from unassociated schools in the purse-seine fishery and in the Philippines and Indonesian handline fishery.

By weight, the longline fishery accounts for most of the bigeye tuna catch. Bigeye tuna sampled in the longline fishery are predominantly adult fish, with a mean size of approximately 130 cm; most fish are between 80 and 160 cm. Bigeye tuna are generally caught in waters of about 10-15°C, at 100–400m depth, although substantial commercial catches are made where the temperature range is 13–27°C and at depths of at least 200-400m. The best fishing is usually a few days before, during and a few days after a full moon, taking advantage of the fact that large bigeye come close to the surface (50 to 100 m) to feed at night in equatorial waters.

The area fished is determined to some extent by access agreements and the cost of those agreements. The Japanese longline distant water fleet predominately catch bigeye tuna, the majority of which is taken in high seas areas (60% in 2015 and close to 60% on average 2011-2015). A large proportion of Japanese longline distant water fleet catch also occurs within Japan, FSM, Marshall Islands, Palau and Solomon Islands EEZs. Effort shifts seasonally tending north of 10^oN and towards high seas areas and the Japan EEZ. Other distant water fleets, such as the Taiwanese large-scale tuna longline fleet also catch the majority of its tuna (mostly albacore and bigeye) in the high seas (average catch in 2011-2015 was 74%). Effort has also shifted between the high seas and within EEZs (and also between EPO and WCPO) for the Korean longline fleet reflecting changes in access arrangements.

Bigeye tuna are also caught by handlining, often around anchored FADs, or by longlining in domestic fisheries in some regions, such as Indonesia, Philippines, and operated by large artisanal fishing vessels. Their catches of quality bigeye tuna are exported as quality fresh chilled product.

Eastern Pacific Ocean

Despite little gene flow between populations of bigeye tuna in the Eastern and Western Pacific Ocean (Philippines and Ecuador), bigeye in the Pacific Ocean appear to comprise a single Pacific-wide population (see more in BIOLOGY). The majority of the bigeye tuna catch in the Eastern Pacific Ocean (EPO) was initially taken by longline vessels, however with the expansion of purse-seine fishing on fish-aggregating devices since 1993, the purse-seine fishery has taken an increasing component of the bigeye catch. Subsequently, fishing mortality of juvenile fish has increased alongside the expansion of the purse-seine fishery catching tuna associated with FADs, although the average size taken is relatively larger in the EPO than the WCPO relating to the shallower EPO thermocline.

Effort has shifted towards the EPO for the distant water Japanese longline fleet with the trend for fishing outside of PICs EEZs and a much higher quota in the EPO (32,372 mt cf. 16,860 mt in 2017).

Indian Ocean

In the Indian Ocean (IO), the distant-water longline fishery commenced operation during the early 1950s and reached a peak in the late 1990s–early 2000s. During the mid-2000s, the total annual bigeye tuna catch declined considerably, primarily due to a decline in the longline catch in the western equatorial region in response to the threat of piracy off the Somali coast. This has recovered somewhat over the following years.

Industrial fisheries account for the majority of catches of bigeye tuna including from vessels equipped with deep-freezers (-600C) and fresh longline and purse seine fisheries by Indonesian, Taiwanese, Chinese, Seychelles, and EU-Spanish fleets mainly in the Western Indian Ocean but also in the Eastern Indian Ocean. The fishery by deep-freezing longliners is dominated by Taiwanese fleets accounting for as much as 40-50% of the total longline catch in the IO. Bigeye tuna caught by purse seiners in the IO are dominated by the EU and Seychelles fleets and are mainly small juvenile bigeye tuna (around 5 kg).

The sizes exploited in the IO range from 30 cm to 180 cm fork length. Newly-recruited fish are primarily caught by the purse seine fishery on floating objects where they form mixed schools with skipjack tuna and juvenile yellowfin and are mainly limited to surface tropical waters, while larger fish are found in sub-surface waters.

Bigeye tuna are also caught by handlining, often around anchored FADs, or by longlining in domestic fisheries in some regions, such as Maldives, Sri Lanka and (presumably) other coastal IO States, and operated by large artisanal fishing vessels. Their catches of quality bigeye tuna are exported as quality fresh chilled product.

Gillnet fisheries also take a substantial catch but reporting is minimal.

INDUSTRIAL-SCALE FISHERIES

The industrial scale longline industry is characterised by two main vessel types – large-scale distant water vessels (supplying frozen tuna) and small-medium scale offshore vessels (supplying fresh tuna). Longline vessels targeting albacore or other species may also supply incidental bigeye catch to the fresh sashimi market.

Bigeye tuna caught in the longline fishery (and Japanese pole and line fishery) are placed in ultra-low temperature (ULT) freezers capable of reaching temperatures of -55oC to -60°C for storing catch, and after arriving at port, may be air-freighted to Japanese, European or US markets where they are sold as sashimi or fresh chilled fish or sold and transported to local markets.

SMALL-SCALE FISHERIES

Artisanal fisheries are defined as those undertaken by fishing boats having overall length (LOA) of less than 24 m and operated full-time within the EEZ of their flag States. In most coastal States such vessels engage in fully commercial fishing – notably in the 18 member States of the IOTC, and in Indonesia, the Philippines and Vietnam. Fishing fleets in developing countries are very diverse, some fleets are multipurpose and artisanal or traditional in nature. Unless hand-lining at night, truly subsistence fleets are less likely to catch bigeye tuna in commercial quantities.

The domestic Indonesian and Philippine fisheries employ various gears for catching bigeye (targeted and non-targeted) including ring net, pole and line, handline, longline, and purse seine. These fisheries, such as the Philippine domestic purse seine and ring net fisheries, are FAD-based fisheries and, within Philippine waters, mainly catching juvenile tunas. The domestic fisheries catch juvenile bigeye tuna from 15 to 78 cm in length (average 28 cm). Enhancements have been made to some small scale longline vessels to improve their freezing and fish hold capacity to access high-quality markets and increase autonomy at sea (e.g. Taiwanese longline fleet).

RECREATIONAL FISHING

Bigeye tuna is an excellent sport fish. Recreational fishing methods are: trolling deep with squid, mullet or other small baits, and artificial lure and live bait fishing in deep waters.

AQUACULTURE

Although approval had been given for a yellowfin and bigeye tuna farm off Hawaii, it never began commercial operations before closing down in 2017. The Research Institute for Mariculture in Gondol, Bali conducted research from 2003 to 2010 to analyse to develop techniques for tuna species resource enhancement however has since closed. Cage grow-out of bigeye tuna is not conducted. The life-cycle of bigeye tuna has not been closed.

GUIDE TO FURTHER READING

Note: Details of all sources are given in References below.

On species importance, see: FAO Species Fact Sheet for bigeye tuna http://www.fao.org/fishery/species/2498/en, and ISSF (2018).

On fishing methods, see for the WCPO, see: National Oceanic and Atmospheric Administration (2007), Brouwer and others (2017), Leroy and others (2013), Hanamoto (1987), Farley and others (2006), Lehodey and others (2011), Boggs (1992), Beverly and others (2003 in McCoy & Gillett, 2005), Campling and others (2017), Babaran (2006), and Harley and others (2009).

For the EPO, see IATTC (2016), and Campling and others (2017).

For the IO, see: IOTC (2016), IOTC (2017), and IOTC (2011).

For industrial-scale fishing, see: Hamilton and others (2011).

For small-scale fishing, see: Miyake and others (2010), USAID (2017), WCPFC (2017), and Campling and others (2017).

For recreational fishing, see: the International Gamefishing Association (www.igfa.org).

General descriptions of the main gear types used for the capture of bigeye tuna can be found at: http://www.fao.org/fishery/fishtech/1010/en.

REFERENCES

• Babaran, RP. 2006. August. Payao fishing and its impacts to tuna stocks: A preliminary analysis. In Second regular scientific meeting. WCPFC. Manila (pp. 7-8).
• Boggs, CH. 1992. Depth, capture time, and hooked longevity of longline-caught pelagic fish: timing bites of fish with chips. Fish. Bull., 90, pp.642-658.
• Brouwer, S, G Pilling, J Hampton, P Williams, S McKechnie & L Tremblay-Boyer. 2017. The Western and Central Pacific tuna fishery: 2016 overview and status of stocks. Noumea, New Caledonia: Pacific Community. https://www.wcpfc.int/node/30158
• Campling, L, A Lewis, & M McCoy. 2017. The Tuna Longline Industry in the Western and Central Pacific Ocean and its Market Dynamics. Honiara: Pacific Islands Forum Fisheries Agency. http://www.ffa.int/system/files/Campling-Lewis-McCoy%202017%20The%20Tuna%20%20Longline%20Industry.pdf
• FAO (Food and Agriculture Organisation of the United Nations) Fisheries and Aquaculture Department. 2017. Species fact sheets: Thunnus obesus. http://www.fao.org/fishery/species/2498/en
• Farley, JH, NP Clear, B Leroy, TL Davis, & G McPherson. 2006. Age, growth and preliminary estimates of maturity of bigeye tuna, Thunnus obesus, in the Australian region. Marine and freshwater Research, 57(7), pp.713-724.
• Hamilton, A., A Lewis, M.A. McCoy, E Havice, & L Campling. 2011. Market and industry dynamics in the global tuna supply chain. Honiara, Solomon Islands: Pacific Islands Forum Fisheries Agency. https://www.ffa.int/system/files/Global%20Tuna%20Market%20%26%20Industry%20Dynamics_Part%201a.pdf
• Hanamoto, E. 1987. Effect of oceanographic environment on bigeye tuna distribution. Bull. Japan. Soc. Fish. Oceanogr, 51:213-216.
• Harley S, S Hoyle, A Langley, J Hampton & P Kleiber. 2009. Stock assessment of bigeye tuna in the Western and Central Pacific Ocean. Western and Central Pacific Fisheries Commission Scientific Committee Fifth Regular Session, 10-21 August 2009, Port Vila, Vanuatu. WCPFC-SC5-2009/SA-WP-4. 98 p.
• IATTC (Inter-American Tropical Tuna Commission). 2016. Tunas, billfishes and other pelagic species in the Eastern Pacific Ocean in 2015. La Jolla, California: Inter-American Tropical Tuna Commission.https://www.wcpfc.int/system/files/GN-WP-02%20IATTC%20Tunas-billfishes-and-other-pelagic-species-in-the-EPO-2015.pdf
• IOTC (Indian Ocean Tuna Commission). 2011. Executive Summary: status of the Indian Ocean bigeye tuna (Thunnus obesus) resource. IOTC-2011-SC14-09. 9 p.
• IOTC (Indian Ocean Tuna Commission). (2017). Status summary for species of tuna and tuna-like species under the IOTC mandate, as well as other species impacted by IOTC fisheries. Victoria Mahé, Seychelles: Indian Ocean Tuna Commission. http://www.iotc.org/science/status-summary-species-tuna-and-tuna-species-under-iotc-mandate-well-other-species-impacted-iotc
• IOTC (Indian Ocean Tuna Commission). (2016). Stock assessment of bigeye tuna in the Indian Ocean for 2016 — model development and evaluation IOTC-2016-WPTT18-20. Victoria Mahé, Seychelles: Indian Ocean Tuna Commission. http://www.iotc.org/documents/stock-assessment-bigeye-tuna-indian-ocean-2016
• ISSF (International Seafood Sustainability Foundation). 2018. Status of the world fisheries for tuna. February 2018. ISSF Technical Report 2018-02. International Seafood Sustainability Foundation, Washington, D.C., USA.
• Leroy, B, J Scutt Phillips, S Nicol, GM Pilling, S Harley, D Bromhead, S Hoyle, S Caillot, V Allain, & J Hampton. 2013. A critique of the ecosystem impacts of drifting and anchored FADs use by purse- seine tuna fisheries in the western and central Pacific Ocean. Aquat. Living Resour. 26, 49–61.
• Lehodey P, J Hampton, RW Brill, S Nicol, I Senina, B Calmettes, HO Portner, L Bopp, T Ilyina, JD Bell & J Siebert. (2011). Vulnerability of oceanic fisheries in the tropical Pacific to climate change. In: Bell JD, Johnson JE, Hobday AJ (eds) Vulnerability of Tropical Pacific Fisheries and Aquaculture to Climate Change. Secretariat of the Pacific Community, Noumea, New Caledonia, pp. 433–492.
• McCoy, MA & RD Gillett. 2005. Tuna Longlining by China in the Pacific Islands: a description and considerations for increasing benefits to FFA member countries. Pacific Islands Forum Fisheries Agency.
• Miyake MP, P Guillotreau, CH Sun & G Ishimura. 2010. Recent developments in the tuna industry: stocks, fisheries, management, processing, trade and markets. FAO Fisheries and Aquaculture Technical Paper. No. 543. Rome, FAO. 125 p.
• National Oceanic and Atmospheric Administration. 2007. Fishery Management Plan for U.S. West Coast Fisheries for Highly Migratory Species. As amended. Appendix A: Description of the fishery. Portland, Oregon: National Oceanic and Atmospheric Administration. http://www.pcouncil.org/wp-content/uploads/2017/03/HMS_AppA_pt1.pdf
• USAID (United States Agency for International Development). (2017). Value Chain Assessment: General Santos City, Philippines. Manila, Philippines: United States Agency for International Development/Regional Development Mission for Asia. 
• WCPFC (Western and Central Pacific Fisheries Commission). 2017. Western and Central Pacific Fisheries Commission Tuna Fishery Yearbook 2016. Noumea, New Caledonia: Oceanic Fisheries Programme Pacific Community. https://www.wcpfc.int/statistical-bulletins

POST HARVEST

Bigeye tuna is one of the most valuable tuna species and is the most highly targeted species, followed by yellowfin tuna and, to a lesser extent, albacore. Bigeye tuna generally has less fat than bluefin tuna but is popular for its bright red flesh.

CANNING

Bigeye tuna is predominately used in the sushi and sashimi market, however, some bigeye tuna is canned by default. In 2007, approximately 2% of total canned tuna was bigeye tuna.

SASHIMI AND OTHER PRODUCTS

Japan is the major global market for sashimi quality tuna (around 100% of global consumption in 2010). In 2014, bigeye accounts for 38% of the total supply volume (imports and landings) of sashimi grade tuna. In 2015, over 90% of bigeye landings to Japan is frozen.

Longliners and some purse seiners, especially those from Japan, have ultra-low temperature (ULT) freezing capability at -60 or -35-40o freezing capacity (ULT commands a higher price premium) allowing for the production of sashimi-quality tuna. Most fish caught by purse seining is canned but larger fish such as bigeye tuna caught by Japanese purse seine vessels with ULT freezers is sold as a product termed ‘purse seine special’ on the lower-quality sashimi market, still fetching a higher value than that for canning. Fish that is unsuitable for top or export markets is sold on domestic markets.

Adult bigeye tuna is caught by coastal longlining, pole-and-line, and handline and is sold fresh chilled, generally as sashimi or as fresh steaks.

Eating fresh tuna has been popular in the large United States market since the late 1990s. The most popular tuna fresh is the so-called ‘ahi’, the Hawaiian name for bigeye tuna, but ‘ahi’ may be either yellowfin or bigeye tuna.

COMMON MARKET NAMES

The FAO names for bigeye tuna: bigeye tuna (English); Thon obese (French); and Patudo (Spanish). Bigeye tuna is known by many local common names (e.g., see FishBase – http://www.fishbase.org – for lists). In the USA, the Hawaiian word for both yellowfin and bigeye tuna, "ahi," has been used as a marketing tool irrespective of fish origin and has gained general acceptance at the wholesale and retail level.

NUTRITIONAL VALUE

Fat content in bigeye tuna is higher than in other tuna species, yet, relative to other animal-based foods, it remains a good choice for low-fat diets. The fish has firm, red-pink flesh and a mild flavour. A c.100 g. serving contains 108 calories, roughly 500 mg of omega-3 fatty acids and 1 g of fat.

Nutrition Facts, 1 serving, of weight 113g

TRADE AND MARKETS

Japan is the world’s principal market for fresh-chilled and frozen sashimi-grade tuna accounting for around 100% of the global sashimi consumption in 2010. The USA is the second market in volume for sushi and sashimi with an estimated 8-10 percent of global sashimi consumption. Sushi consumption is now a global trend and consumers in more countries are eating it. Longline-caught bigeye tuna are exported fresh or frozen mainly to sashimi markets in Japan, the USA and Europe. Sashimi-grade portions of catches are offloaded in ports with good air-freight connections to Japan and other markets, while the non-sashimi grade portion is either sold in local markets, processed into export-grade value-added fresh and frozen tuna products, or frozen whole round for export or shipping back to home ports.

Indonesia has long been a major exporter of fresh-chilled sashimi grade tuna, mainly to U.S. markets. A large number of Taiwanese and Indonesian joint-venture vessels have been based in Jakarta and Benoa and mostly fish in the Indian Ocean. The Philippines, Vietnam and Fiji are other major bigeye exporters to the U.S.

Recent national and international management controls for longline vessels catching bigeye tuna and other species, such as yellowfin tuna, require registration and traceability certificates for import clearance to the market countries, especially Japan, the EU and the USA.

EMPLOYMENT, SOCIAL FACTORS AND GENDER

Much of the fishing for bigeye tuna takes place outside exclusive economic zones and so employment and social factors concern mainly those in countries of vessel owners, crews and markets. In the case of the longline fisheries, developing countries, such as those in the Pacific and Indian Ocean, have gained only small economic returns. Longline vessels are said to have low profit margins, including from rising operating costs such as from fuel that are not accompanied by rising tuna prices.

Men comprise the fishing crews on tuna fishing vessels. The majority of cannery production workers are women although men are engaged in heavy tasks. Men have a significant role in bigeye tuna production, simply because the adult fish are large, from catching, moving fish around at landing places and in processing facilities, and in some fresh chilled and sashimi markets (e.g. in Japan).

In the Philippines and Indonesia, small bigeye tuna are usually sold in local markets by women. Women have established niche spaces in the Fish Port Tambler Complex of General Santos City, Philippines.

Women are beginning to enter non-traditional areas of work, for example, as observers and tuna taggers on board fishing vessels – e.g. in the Solomon Islands and Fiji.

FISHING

Labour on fishing vessels has received much greater attention in recent years as labour and human rights groups have uncovered many instances of rights abuses, especially on those vessels that spend protracted periods at sea, such as longliners and even large purse seine vessels. The operating costs squeeze on such vessels has led to extensive hire of migrant crew, some quite young, from poor backgrounds in countries such as Cambodia, Indonesia, Myanmar, Philippines and Vietnam who are paid little and who work under bonded labour conditions. Some are trafficked as forced labour.

Large-scale distant water longline fishing vessels present the most challenging labour conditions as the vessels can be at sea for as long as 18 months and the work entails long hours under arduous conditions. Although nominally covered by the new ILO Work in Fishing Convention No. 188(2007) that came into force on 17 November 2017, more minimum requirements are needed: minimum age; medically fitness; conditions of service such as adequate crewing and rest periods, employment contracts, repatriation, recruitment and placement; accommodation and food; and, medical care, health protection and social security.

Socially responsible labour conditions are becoming recognised as reasons, alongside conservation issues, for restricting tuna imports, including of high value species such as bigeye tuna. Flag states and market ports, e.g., Taiwan, Hawaii (USA) have had to pass domestic laws addressing hiring of foreign crew and protecting the workers’ rights.

Social standards for supply chains free of forced and child labour are beginning to enter the requirements of the certifying bodies such as the Marine Stewardship Council (MSC), Pacifical (Parties to the Nauru Agreement MSC certified fisheries), and OPAGAC (the fishing association representing the Spanish purse seine tuna fleet). Major tuna retailers are now requesting social audits although, in the case of key bigeye tuna markets, Japanese and other Asian sashimi markets are not applying much pressure for longline social standards. In 2017, Thai Union Group introduced a fishing vessel improvement program and vessel code of conduct to provide guidance to vessels from which the company sources as well as improve labour and ethical performance in the fishing sector.

PROCESSING FACILITIES

In the bigeye tuna value chain, women are mostly engaged in fish processing (canneries) and trimming and preparing fish pouches and steaks for export; they also engage in domestic and non-commercial marketing of small fish. Women may join men as production managers and the like in processing operations.

GUIDE TO FURTHER READING

Note: Details of all sources are given References below.

For comprehensive post harvest information see Campling, Lewis & McCoy (2017).

For canning, see: Hamilton and others (2011).

For sashimi and other products, see: Campling and others (2017), Miyake and others (2010), and Hamilton and others (2011).

For common market names, see: FAO bigeye tuna Species Fact Sheet (http://www.fao.org/fishery/species/2498/en) and for many local common names, see FishBase for lists (http://www.fishbase.org).

For nutritional value, see FishChoice (2018) and Fishwatch (2017).

For trade and markets, see: Campling and others (2017), FAO (2017) and Hamilton and others (2011).

For employment, social factors see: Campling and others (2017).

For gender, see Tuara & Passfield (2011), Ram-Bidesi (2010), and Pavo & Digal (2017).

On labour in fishing, see: Campling and others (2017), de Coning (2011).

REFERENCES

• Campling, L, A Lewis, & M McCoy. 2017. The Tuna Longline Industry in the Western and Central Pacific Ocean and its Market Dynamics. Honiara: Pacific Islands Forum Fisheries Agency. http://www.ffa.int/system/files/Campling-Lewis-McCoy%202017%20The%20Tuna%20%20Longline%20Industry.pdf
• de Coning, E. 2011. Transnational organised crime in the fishing industry: Focus on: Trafficking in persons smuggling of migrants illicit drugs trafficking. Vienna, Italy: United Nations Office on drugs and crime. http://www.unodc.org/documents/human-trafficking/Issue_Paper_-_TOC_in_the_Fishing_Industry.pdf
• FAO (Food and Agriculture Organisation of the United Nations). 2017. An overview of the global tuna market. http://www.fao.org/in-action/globefish/fishery-information/resource-detail/en/c/880744/
• FishChoice. 2018. Bigeye. http://www.fishchoice.com/buying-guide/bigeye-tuna
• FishWatch. 2017. Pacific bigeye tuna, Thunnus obesus. https://www.fishwatch.gov/profiles/pacific-bigeye-tuna
• Hamilton, A, A Lewis, MA McCoy, E Havice, & L Campling. 2011. Market and industry dynamics in the global tuna supply chain. Honiara, Solomon Islands: Pacific Islands Forum Fisheries Agency. https://www.ffa.int/system/files/Global%20Tuna%20Market%20%26%20Industry%20Dynamics_Part%201a.pdf
• Miyake, M.P., Guillotreau, P., Sun, C.H., & Ishimura, G. (2010). Recent developments in the tuna industry. Rome, Italy: Food and Agriculture Organisation of the United Nations. http://www.fao.org/3/a-i1705e.pdf
• Pavo, R & LN Digal. 2017. Women’s Space in the Fish Port Tambler Complex and the Value-Chain Nodes of the Fishing Industry in General Santos City, Philippines. Asian Fisheries Science 30S:33-58. http://www.asianfisheriessociety.org/publication/abstract.php?id=1163
• Ram-Bidesi, V. (2010). Employment opportunities for women in the tuna industry in small islands: is it really restrictive? A case study of Fiji Islands. South Pacific Studies, 31(1), 17-42
• Tuara, P. & Passfield, K. (2011). Gender in oceanic and coastal fisheries science and management: Based on case studies in Solomon Islands, Marshall Islands and Tonga. Noumea, New Caledonia: Secretariat of the Pacific Community. http://www.spc.int/fame/en/fame-digital-library

DESCRIPTION

Bigeye is a large tuna with a long, robust, and tapered body. Its pectoral fins are moderately long (22-31% of fork length) in fish larger than 110 cm fork length, but very long (30% or more of fork length) in smaller fish. It differs from yellowfin tuna (Thunnus albacares), in its colour, and by: 1) 23-31 rakers on the first gill arch (26-34 in yellowfin), 2) striated ventral surface of the liver (not striated in yellowfin), and 3) approximately equal liver lobes (in yellowfin, the right lobe is much longer than the other lobes). The second dorsal and anal fins of bigeye tuna do not grow as long as those of yellowfin tuna.

At a comparable size, the swim bladder of a bigeye tuna is larger than that of a yellowfin tuna.

The back is dark metallic blue and the sides and belly are whitish; when the fish is alive, an iridescent blue band runs along the sides. The first dorsal fin is dark yellow and the second dorsal and anal fins are pale yellow. The finlets are bright yellow with a black edge. The tail is plain and does not have a white trailing edge (as has albacore, T. alalunga).

ECOSYSTEM ROLE

Together with the other species of tropical tuna, bigeye tuna is near the top of the pelagic food chain. Tunas typically follow the daily vertical movement of their preferred prey (micronekton), moving to deeper habitats during the day and to shallower habitats at night. The physiology of bigeye allows them to feed deeper in the water column and for longer periods than other tropical tunas. Bigeye tuna foraging behavior also changes as they grow, with larger individuals able to more frequently use deeper habitats.

Predators of bigeye include other tunas, sharks, dolphins, sailfish, marlins, and toothed whales.

HABITAT AND DISTRIBUTION

Bigeye tuna occur worldwide in tropical and subtropical waters but are absent from the Mediterranean Sea. In the Western and Central Pacific and Indian oceans, bigeye are found between Latitudes 40º N and 40 ºS.

They are found predominantly in tropical open ocean ecoregions, in waters extending from the surface to below the mixed layer and thermocline. In coastal waters, bigeye tuna are most commonly found in waters around the bottom of the mixed layer, which varies with place and season. [See gallery for bigeye tuna distribution map and diagram]. Bigeye are rarely found over shallow coastal shelves where the ocean depth is less than about 50 m.

Despite little gene flow between populations of bigeye in the eastern and western Pacific Ocean (Philippines and Ecuador), bigeye in the Pacific Ocean appear to comprise a single Pacific-wide population. Recent analyses of bigeye tagging studies supports these genetic observations, with little mixing observed between fish tagged in the extreme east and west of the Pacific. Higher rates of mixing were observed in the central Pacific. The bigeye tuna showed little dispersal by latitude (N-S), some regional retention and some large eastward longitudinal movements. From the tagging results, three possible Pacific stocks may be inferred but for management purposes, to the present, the bigeye tuna eastern and western Pacific fisheries are assessed separately.

During mark-recapture studies, bigeye tuna in the Pacific have been recovered up to 5,372 nautical miles from their release points, after periods at liberty from one to nearly five years. In the Pacific Ocean, three types of movement patterns are identified: (1) fish that reside within 1,000 nautical miles of their release location, (2) fish that are residents, yet undertake excursions outside the residence area, to which they return, and (3) fish that are nomadic and have other movement patterns. In the Indian Ocean, tagged juveniles moved 657 nautical miles, on average, between release and recapture. In general, however, the understanding of bigeye movement and its relationship with fish size is still poor.

The higher tolerance of bigeye tuna to variation in water temperature and O² levels allows them to use a wide range of ocean habitats. As with other tuna, the blood circulation system of bigeye tuna has a heat exchanger that rapidly lessens heating and cooling rates. This enables these fish to maintain muscle temperatures significantly above those of the environment; increasing both their swimming efficiency and the range of temperatures in which they can live. Adult bigeye tuna (>100 cm FL (fish length)) can live in water with dissolved oxygen (O²) levels as low as 1.5 ml/L and in cool water (5⁰C - 15⁰C). However, bigeye tuna spend little time in water temperatures below 7⁰C and oxygen levels less than about 2 ml/L.

The characteristic daily behavior of bigeye tuna is to feed above the thermocline in the mixed layer starting at dusk, and descend below the thermocline at dawn to feed at depth in cooler waters. Bigeye tuna appear to have flexible feeding strategies, enabling them to succeed in a patchy environment. Given this flexibility, the behavior of individual fish can vary considerably with location, season, moon phase and food availability. Juvenile bigeye can school at the surface underneath floating objects, along with yellowfin and skipjack tunas. Older bigeye tuna are less commonly found near floating surface objects.

GROWTH, REPRODUCTION AND DIET

Although much is known about bigeye tuna growth, variations in growth rates between fish in different stock assessment areas and across the full size range are still under study, using several methods and sometimes integrating these: growth increments on otoliths (ear bones), tag-recapture and length frequency analysis. In the WCPO, IO and other oceans, younger bigeye tuna are relatively fast-growing but growth slows in the second year of life, when the fish are between 40 and 70 cm FL.

In the WCPO, bigeye tuna growth appears to be faster than that in other oceans up to the size of the growth slow down and slower than that in other oceans for fish at sizes larger than about 100 cm. Except for the very early growth, in the Western Indian Ocean, bigeye tuna growth rates were similar to those of bigeye tuna in the Western Pacific Ocean. The bigeye tuna in the eastern Indian and south-west Pacific oceans display different growth rates from those in the Eastern Pacific Ocean.

In the WCPO, bigeye tuna mature after 2.5 years and begin spawning at 3-4 years of age (about 100-130 cm FL, 30 Kg). Indian Ocean bigeye tuna mature at three years of age at about 100 cm FL. Maximum size is 200 cm FL, commonly to 180 cm FL, and maximum weight is 210 kg.

In the Pacific Ocean, many fish survive until 8-16 years of age. The life span of bigeye in the Indian Ocean has been estimated at 15 years.

Bigeye tuna are batch spawners, capable of spawning daily and releasing batches of about 1 to nearly 10 million eggs. The eggs and larvae are pelagic.

Bigeye spawn year-round in warm surface waters (>24°C), although spawning is generally restricted to the summer months of December to January in the tropical western Pacific and Indian oceans. However, spawning also takes place in June in the eastern Indian Ocean, and mature females are found off north-eastern Australia in August. Spawning occurs between about 30°N and 20°S in the Western Pacific. Spawning is undertaken mainly at night, between about 1900 h and 0400 h.

Bigeye tuna forage successfully, during day and night, on a range of organisms. The diet of bigeye tuna includes shallow-water squid, crustaceans and fish (mullet, sardines, small mackerels), as well as deep water micronekton (squid, euphausiids and mesopelagic fish).

GUIDE TO FURTHER READING

Note: Details of all sources are given in References below.

For bigeye tuna descriptions, see Collette 2001, Schaefer (1999), Bertrand and Josse (2000), the Indian Ocean Tuna Commission (IOTC) species identification card (http://www.iotc.org/science/species-identification-cards) and the International Game Fish Association (http://www.igfa.org/).

For the most comprehensive guides and handbooks to the identification of yellowfin and bigeye tuna, from fresh to frozen and damaged, see the Secretariat for the Pacific Community FAME Digital Library, and enter "yellowfin" AND "David Itano" (author) into the search boxes to obtain the guides, many in several languages.

For the use of habitat, see Musyl et al. (2003) and Brill et al. (2005). Predators are given in FishBase (www.fishbase.org).

For descriptions of habitat and geographic distribution, see Reygondeau et al. (2012), Collette (2001) and Lee, et al. (2005). Grewe & Hampton (1998), IOTC (2011) and Schaefer et al. (2015) address stock structures, movement and dispersion.

For information on biology, physiology and distribution, see Musyl et al. (2003), Boye et al. (2009), Lehodey et al. (2011).

For daily behavior patterns and their variability, see Evans et al. (2008) and Schaefer and Fuller (2010). For juvenile schooling behavior, see Collette (2001) and IOTC (2011).

For growth see: Lehodey et al. (1999), Farley et al (2006) and Fonteneau and Hallier (2015) on growth rates of young fish. For comparative growth rates by ocean from tagging studies, see Fonteneau and Hallier (2015); for IO growth Stéquert & Conand (2004); for WCPO and EPO, Farley et al. (2006), Nicol et al. (2011), and Fonteneau and Hallier (2015).

For information on maximum size, see Lehodey et al. (1999), Collette (2001), and Fishbase (www.fishbase.org). For life span and age information, see Farley et al. (2006), Lehodey et al. (1999), Harley et al. (2009) and IOTC (2011).

On maturation and reproduction of bigeye tuna, see Schaefer et al. (2005); for WCPO, see Lehodey et al. (1999), Farley et al. (2006), SPC (2009), and Sun et al. (2013); and for IO, see IOTC (2011). For bigeye tuna diet, see Musyl et al. (2003), Evans et al. (2008), and Collette (2001).

REFERENCES

• Bertrand, A, and E Josse. 2000. Tuna target-strength related to fish length and swimbladder volume. ICES Journal of Marine Science: Journal du Conseil 57:1143-1146.
• Boye J, M Musyl, R Brill & H Malte. 2009. Transectional heat transfer in thermoregulating bigeye tuna (Thunnus obesus) - a 2D heat flux model. The Journal of Experimental Biology, 212:3708-3718.
• Brill RW, KA Bigelow, MK Musyl, KA Fritsches & EJ Warrant. 2005. Bigeye tuna (Thunnus obesus) behaviour and physiology and their relevance to stock assessments and fishery biology. Collective Volume of Scientific Papers of the ICCAT, 57(2):142-161.
• Collette BB. 2001. Tunas (also, albacore, bonitos, mackerels, seerfishes, and wahoo). pp 3721-3756, in K.E. Carpenter & V.H. Niem (eds), FAO species identification guide for fishery purposes. The living marine resources of the Western Central Pacific. Vol. 6: Bony Fishes Part 4 (Labridae to Latimeriidae), Estuarine Crocodiles, Sea Turtles, Sea Snakes and Marine Mammals. Rome, FAO.
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• Schaefer, KM. 1999. Comparative study of some morphological features of yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tunas. Bulletin/Inter.-American Tropical Tuna Commission, 21:491-525.
• Schaefer, KM, DW Fuller, & N Miyabe. 2005. Reproductive biology of bigeye tuna (Thunnus obesus) in the eastern and central Pacific Ocean. Inter-American Tropical Tuna Commission. Bulletin 23:3-31.
• Schaefer, K & D. Fuller. 2010. Vertical movements, behavior, and habitat of bigeye tuna (Thunnus obesus) in the equatorial eastern Pacific Ocean, ascertained from archival tag data. Marine Biology 157:2625-2642.
• Schaefer, K, D Fuller, J Hampton, S Caillot, B Leroy, & D Itano. 2015. Movements, dispersion, and mixing of bigeye tuna (Thunnus obesus) tagged and released in the equatorial Central Pacific Ocean, with conventional and archival tags. Fisheries Research 161:336-355.
• SPC, OFP (Secretariat of the Pacific Community’s Oceanic Fisheries Programme). 2009. Tuna fisheries in the western and central Pacific: an update. SPC Fisheries Newsletter #129 - May/August 2009: 8-9.
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• Sun, CL, SZ Yeh, YJ Chang, HY Chang & SL Chu. 2013. Reproductive biology of female bigeye tuna Thunnus obesus in the western Pacific Ocean. Journal of Fish Biology, 83: 250-271.