Fisheries and aquaculture are confronted with continuing problems such as climate change, growing human populations, low income of small scale fishers and fish farmers, and competitive production and trading conditions. People should be confronting and discussing the challenges in order to come up with solutions on how we can respond; and the community should be resilient and adaptive in combatting the challenges. We cannot immediately solve some problems, such as overfishing, illegal fishing, depletion of marine resources, as they have deep root causes, but we are learning how to address them. Governments do their best to manage fishery resources to meet these challenges. Decision makers and the public also need to continually listen to new information so that they are equipped with knowledge for sustaining marine and aquaculture resources and protecting people who depend on them for nutrition, livelihood and business. Research is an important information gathering tool that contributes to policy and decision-making. The Asian Fisheries Society and its partners are taking a lead in making new information accessible through its platform AsiaPacific-FishWatch providing essential information on fish harvested or farmed for food in Asia-Pacific. I am pleased that AsiaPacific-FishWatch gives attention in its profiles and posts to the critical social, economic and market character of the value chains. The Asian Fisheries Society emphasises equally social and economic knowledge and biological, physical and technical knowledge.

Prof. Alice Joan G. Ferrer, PhD, President, Asian Fisheries Society

 
 
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Bigeye Tuna

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 10oN 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

CALORIES 130
PROTEIN 27g
FAT, TOTAL 2g
SATURATED FATTY ACIDS, TOTAL 0.5g
CARBOHYDRATE 0g
SUGARS, TOTAL 0g
FIBER, TOTAL DIETARY 0g
CHOLESTEROL 45mg
SELENIUM 160% daily value
SODIUM 70 mg

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

Bigeye tuna live in tropical and warm temperate waters of the Atlantic, Pacific and Indian oceans. They are pelagic and exhibit several dispersion patterns. The Western and Central Pacific Ocean and the Indian Ocean bigeye are each considered single and separate stocks; although considerable mixing occurs, Western and Central Pacific Ocean and Eastern Pacific Ocean bigeye tuna populations are assessed separately for management purposes.

Bigeye tuna form free schools or may swim associated with floating objects such as logs. Juvenile bigeye will form schools with juvenile yellowfin and skipjack tunas. Bigeye tuna tolerate warmer and deeper waters and lower oxygen and salinity levels than other tropical tunas. They may live to at least 15 years of age. They grow more slowly than yellowfin tuna, have lower natural mortality, and are less abundant.

FISHERIES

Bigeye tuna is important in commercial fisheries around the world, accounting for nearly 10% of the world’s catch of major tunas. In the Central and Western Pacific Ocean, 6% of the tuna caught are bigeye and, in the Indian Ocean, 9% are bigeye. Juveniles are caught by both surface gears such as purse seines and, in the Indian Ocean, by gill nets. As valuable adult fish, they are caught by longline and other gears. They are a principal target species of both the large, distant-water longliners from Japan, Korea, China, Taiwan and the smaller, fresh sashimi longliners based in several Pacific Island countries.

SUSTAINABILITY AND MANAGEMENT

The bigeye tuna stock of the Western and Central Pacific appears not to be overfished nor subject to overfishing. However, the stock is considered to remain in a state somewhat more depleted than most other tuna stocks in the Western and Central Pacific. The Indian Ocean bigeye stock is not overfished, nor subject to overfishing. The catch of juvenile bigeye in surface fisheries that target skipjack and yellowfin tuna, e.g., purse seine and gillnet fisheries, is increasing, thus decreasing the biomass of adults in the deeper water longline fisheries and the maximum sustainable yield of the stocks.

Bigeye tuna resources are managed by the Western and Central Pacific Fisheries Commission (WCPFC), the Indian Ocean Tuna Commission (IOTC), and national governments. Sub-regional fishing interest groups, international environmental organisations and market controls also have a strong influence on the governance of bigeye tuna fisheries.

VALUE CHAINS

The meat of bigeye tuna is highly prized and is processed into sashimi in Japan (and western countries). Bigeye is marketed mainly in canned, frozen, or fresh forms. Prices paid for both frozen and fresh product on the Japanese sashimi market are the highest among all the tropical tunas.

FOOD

As food, bigeye is a very good source of low-fat protein and is low in sodium, but has a moderate level of cholesterol. Fat content in bigeye tuna is higher than in other tuna species, yet it is a good choice for low-fat diets.

ECOSYSTEM AND CLIMATE

Bycatch of fishing for bigeye tuna and other pelagic species includes bigeye tuna juveniles, and also sea turtles, sharks, seabirds and other marine fish species and is a significant environmental issue. Among all fishing gears used for bigeye tuna, longlines and gillnets have the greatest bycatch rates.

Longline and purse seine fishing are among the most energy intensive fishing operations as measured by greenhouse gases produced per tonne of fish landed. Also, unless strictly managed, fish canneries may have negative effects on surrounding land and sea environments and the resources they support.

The area of suitable bigeye tuna habitat changes with seasons and with inter-annual climate variability and this is reflected in the catches of bigeye tuna. In the Western and Central Pacific Ocean, the El Niño Southern Oscillation events affect catches of bigeye tuna which are higher during the warmer El Niño period and lower during the cooler La Nina periods.

Global warming affects the distribution and catchability of bigeye tuna stocks which are sensitive to changes in oceanic circulation, the stratification of the water column and water temperature and density.

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