Yellowfin tuna is a highly migratory fish species. It lives in tropical and subtropical oceanic waters, above and below the thermocline. It is found throughout the Indian Ocean (IO) and Western and Central Pacific Ocean (WCPO) except in areas where ocean depth is less than about 50m. Yellowfin tuna also lives in the Atlantic Ocean.
Smaller yellowfin tuna are mainly limited to surface waters, while larger fish are found in both surface and deeper waters, but rarely below 250m.
Globally, yellowfin tuna comprise about a quarter of the total tuna catch (all species), and Asia-Pacific yellowfin tuna are more than 70% of the global yellowfin tuna catch. Yellowfin tuna comprises 22.5% of the total tuna catch of the WCPO and about 34% of the IO tuna catch. The main production areas are in the north and west of Madagascar (IO) and the western equatorial belt (WCPO).
Using many different fishing gears, yellowfin tuna are caught by local fishers (including artisanal and traditional coastal fishery fleets) and foreign licensed vessels. The artisanal fleets of Indonesia and the Philippines often operate around anchored FADs. Juveniles are caught by purse seine, pole and line, handline, trolling, and - especially in the Indian Ocean - gillnets. Adult yellowfin tuna are caught mainly by pelagic longline and handline. Yellowfin tuna are also a popular recreational species with game-fishing (angling) clubs and with tourists in many Asian-Pacific countries, e.g. Indonesia, Malaysia, Philippines and Australia.
SUSTAINABILITY AND MANAGEMENT
Yellowfin tuna is a fast-growing and highly productive species. Although heavily fished, the yellowfin tuna stock of the Western and Central Pacific Ocean is not overfished. In the Indian Ocean, however, the yellowfin tuna stock is now assessed as overfished, due to an increase in catch levels in recent years. In both oceans, scientific assessments indicate concern for the levels of fishing mortality, increasing surface fisheries on juveniles, and on the environmental effects of fishing by certain of the main fishing gears, especially purse seining on floating objects including fish aggregating devices (FADs), longlining and gillnetting.
Yellowfin resources are managed by the Indian Ocean Tuna Commission (IOTC), the Western and Central Pacific Fisheries Commission (WCPFC), the Pacific Islands Forum Fisheries Agency (FFA) and national governments. International environmental organisations and market controls also have a strong influence on the governance of yellowfin tuna fisheries.
Yellowfin tuna is marketed mainly frozen (whole fish, loins) and canned, but also fresh (chilled whole fish, loins, fillets) and smoked. Juvenile yellowfin tuna caught in the purse seine fishery are canned. Very small juveniles are sold in local markets in the Philippines and Indonesia as plate-sized small pelagic fish. Throughout its range, yellowfin tuna is consumed by local urban and rural communities. It is served raw (as prime sashimi and sushi), grilled, barbecued, deep or lightly-fried, and smoked.
The yellowfin tuna fishery provides tens of thousands of jobs in fishing and processing – including for women – although many fishing crew and processing workers are low-paid and their work is arduous. Men comprise the crews and officers of fishing and fish cargo vessels. The majority of cannery production workers are women, although men are engaged in heavy factory tasks. Women may join men in positions such as processing factory production managers; they are also the main sellers at domestic markets. Women are also beginning to enter non-traditional areas of work in the tuna fishing industry, e.g. as observers on purse seine vessels and as staff on tuna tagging research programmes.
Key benefits of the local and oceanic tuna fisheries are economic development, government revenue, significant contributions to food security and employment. Governments of small island developing states in the Pacific and Indian Oceans receive substantial revenue from granting fishing licences to foreign vessels. For countries with onshore processing facilities, greater benefits are received by those with direct air links to the USA and Japan and those that offer suitable port facilities.
As food, yellowfin tuna is a very good source of low-fat protein and is low in sodium, but has a moderate level of cholesterol. It is a very good source of thiamin, selenium, vitamin B6, and omega-3s. While frequent consumption of fish with high concentrations of mercury by pregnant and lactating women can affect neurodevelopment in children, yellowfin tuna caught from the Pacific ocean have relatively low levels of mercury, and high levels of selenium which gives a protective effect against mercury toxicity.
ECOSYSTEMS AND CLIMATE
The capture of bycatch, including juveniles of bigeye tuna and also of sea turtles, sharks and other marine fish species, during tuna fishing operations is a significant environmental issue. Also, unless strictly managed, regional fish canneries may have negative effects on surrounding land and sea environments and the resources they support.
Global warming affects the distribution and catchability of yellowfin tuna stocks which are sensitive to changes in oceanic circulation, the stratification of the water column and water temperature and density. The effects of ocean acidification on yellowfin tuna have yet to be assessed, although preliminary research has commenced by the Inter-American Tropical Tuna Commission (IATTC) and the Oceanic Fisheries Programme (OFP) at the SPC.
The area of suitable yellowfin tuna habitat changes with seasons and with inter-annual climate variability. For example, the deepening of the thermocline in the eastern Pacific and shoaling of the thermocline in the west during El Niño events changes the catchability of yellowfin tuna.
WILD HARVEST FISHERIES
All yellowfin tuna production is from wild harvest fisheries. Yellowfin tuna is a fast-growing, widely distributed and very fecund species. It is heavily fished by many different methods and, despite its high productivity, its stocks face future challenges due to a high demand. Stocks are currently being fully exploited, and there is little potential for increasing catches.
IUCN Red List Status
Near Threatened (globally) http://www.iucnredlist.org/details/21857/0
Presently, the yellowfin tuna resources in the Western and Central Pacific Ocean (WCPO) and Indian Ocean (IO) are in better condition than those in the Atlantic. However, yellowfin tuna was probably overfished in the IO in the past (2003-2006).
State of the Stock(s) and Impacts of Fishing
The yellowfin tuna stock of the WCPO is not overfished but the scientific assessments indicate concern about the levels of fishing mortality, increasing surface fisheries on juveniles, and on the environmental effects of fishing by some of the main gears used, especially purse seining on floating objects including fish aggregating devices (FADs), longlining and gillnetting. The IO yellowfin tuna stock is now considered overfished. Concerns are expressed on the envrionmental impacts of gears that take the majority of the catch, especially purses on floating objects, longline and gillnets.
The International Seafood Sustainability Foundation’s (ISSF) overview assessment of the resource (Status of the Stocks Technical Report - Stock Status Report) for each ocean states:
- Green –Biomass (B) is at or above stock biomass at maximum sustainable yield (BMSY).
- Yellow – F < FMSY. The overall estimate of current F is below FMSY, and therefore the rating could be Green. However, due to heavy fishing effort in the tropical region, there is little or no room for increased fishing pressure on the stock overall.
- Green – 34% of the catch is made with purse seining on free schools, with little impact on non-target species.
- Yellow – 25% of the catch is made by purse seining on floating objects (including FADs). Several bycatch mitigation measures are in place (turtles, sharks). There is 100% observer coverage on part of the purse seine fleet.
- Orange – 20% of the catch is made by other gears such as gillnets, with unknown impacts on non-target stocks
- Orange - 16% of the catch is made by longlining. Several mitigation measures are in place (sharks, turtles, sea birds). Monitoring is deficient.
- Orange – SSB < SSBMSY. The low level of stock biomass is attributable to increased catch levels in recent years.
- Orange – F>FMSY.
- Green - 18% of the catch is made by handlines, expected to have little impact on bycatch species.
- Green - 12% of the catch is made with purse seining on free schools, with little impact on non-target species.
- Green - 3% of the catch is made by trolling, expected to have little impact on bycatch species.
- Yellow – 23% of the catch is made by purse seining on floating objects (including FADs). Several bycatch mitigation measures are in place (turtles, sharks).
- Yellow - 5% of the catch is made by pole-and-line fishing, with small bycatch of non-target species but unknown impacts on baitfish stocks.
- Orange – 20% of the catch is made by longlining. Several mitigation measures are in place (sharks, turtles, sea birds). Monitoring is deficient.
- Orange – 16% of the catch is made by gillnets, which are poorly monitored. Gillnets are thought to have high bycatch rates. No mitigation measures are in place and monitoring is extremely deficient.
CERTIFICATES FOR SUSTAINABILITY OF WILD HARVEST FISHERY
Marine Stewardship Council (www.msc.org):
- PNA Western and Central Pacific skipjack and yellowfin tuna; for purse seine setting on unassociated/ non FAD free schools; from 2011 for 5 years.
- FZLC Cook Islands EEZ South Pacific albacore & yellowfin longline: certified June 2015 for 5 years.
- Walker Seafood Australia albacore, yellowfin tuna and swordfish; for pelagic mid-set longline; from August 2015 for 5 years.
- Tri Marine Western and Central Pacific Skipjack and Yellowfin Tuna: certified June 2016 for 5 years.
- Solomon Islands skipjack and yellowfin tuna purse seine and pole and line: certified July 2016 for 5 years.
Several other yellowfin fisheries are under assessment.
Friends of the Sea (www.friendofthesea.org)
- Friend of the Sea does not certify fisheries, but rather tuna fishing fleets, including some company fleets fishing for yellowfin and other tunas in the Asia-Pacific region. A list of currently certified fleets can be found through this link.
Several conservation and sustainable/fair food organizations also promote sustainable tuna campaigns, e.g., see the Pew Charitable Trusts Global Tuna Conservation campaign.
The status of yellowfin tuna stocks is difficult to assess because the species is harvested by many different fishing gears, over a wide geographic area with each gear type tending to catch fish of a different size range. Longline fishing mainly harvests adult yellowfin tuna whereas purse seines harvest a wide size range of yellowfin tuna, including many juveniles.
Fisheries catch data, which are essential to yellowfin tuna assessments, have several shortcomings. In particular, reporting of yellowfin tuna catches is inconsistent among fleets and gears. For some gear types, such as those used in artisanal fishing, reporting of catch and effort is limited, e.g., despite their importance, the catches of yellowfin tuna in Indonesia, Philippines, and Vietnam are not fully monitored. Yellowfin tuna catches are under-reported for several gear types, especially purse seines, because juvenile yellowfin tuna school and are harvested with other tuna species of similar size, especially skipjack (Babaran, 2006). Log sheets from purse seine fisheries tend to be biased towards recording most small tunas as skipjack. Observer sampling in port and at sea has revealed under-reporting of yellowfin and bigeye of up to 15% (for sets associated with floating objects) (Lawson, 2010; Hampton & Williams, 2011). Such under-recording of juvenile yellowfin (and bigeye) tuna occurs both in the WCPO and the IO fisheries and the logbook estimates are adjusted using port - or sea - samples of fish to help reduce the bias.
Western and Central Pacific Ocean
For yellowfin tuna in the WCPO, stock assessment and data management services are provided by the Oceanic Fisheries Programme of the Secretariat of the Pacific Community (SPC) and reviewed by the Scientific Committee of the Western and Central Pacific Fisheries Council. Yellowfin tuna assessments are based on catch, effort, fish size and tagging data from the major component fisheries – longline and purse seine fleets - and defined fishing regions of the management area of the Western and Central Pacific Fisheries Commission (WCPFC). Corrections and adjustments are made in the assessment models to account for the estimates of catch composition by species and biases in the monitoring data. Increasing attention is being paid to analyses of data from the fisheries conducted in the intensively fished Indonesian and Philippine waters (Langley et al., 2011). The Scientific Advisory Committee of the ISSF takes into consideration the WCPFC stock assessments, plus other reliable information, in making its sustainability assessments of stock abundance, fishing mortality and environment (ISSF, 2013).
Based on average annual harvests of ≥550,000 tonnes, overfishing is not occurring but current catches are about at maximum sustainable yield (MSY) levels. The geographic patterns of exploitation, however, are of concern. Ninety-five percent of the catch of yellowfin tuna in the WCPO is taken in the equatorial zone (Langley et al., 2011), with a particular concentration in the western equatorial zone (over 80% of WCPO yellowfin tuna catch) (WCPFC, 2012). In the western equatorial Pacific part, the fishery will not be sustainable if the catch increases further (ISSF, 2013; WCPFC, 2012). Historical analyses indicate that MSY has been reduced to approximately 60% of its levels prior to 1970 through increased harvesting of juveniles (WCPFC, 2012). Most of the increase in juvenile harvesting is from the Philippines and Indonesian surface fisheries (purse seine, troll and various artisanal gears) (WCPFC, 2012). The spawning biomass in that region appears to have declined to about 31% of the unexploited level (WCPFC, 2012). If mortality of juveniles were reduced, MSY levels would increase (WCPFC, 2012).
The purse-seine fishery on tuna schools associated with floating objects (including FADs) and the Philippines and Indonesian domestic fisheries have the greatest effect on yellowfin tuna stocks. These fisheries are conducted in western equatorial waters, including Indonesia, Philippines, the Federated States of Micronesia (FSM), the Republic of the Marshall Islands (RMI), Palau and the Solomon Islands. The purse-seine fishery on unassociated schools has a moderate effect. These western equatorial fisheries also influence yellowfintuna fisheries in all other parts of the WCPO (WCPFC, 2012). In their home region in the north, the coastal Japanese pole-and-line and purse-seine fisheries have significant effects on biomass levels but the longline fishery (all fishing areas) has only reduced yellowfin stocks by 5% (Langley et al., 2009).
Although tagging data indicate that yellowfin tuna in the WCPO are a single stock, sub-regional biological differences are possible. The biological characteristics of yellowfin tuna in the Western equatorial region need further investigation as growth rates, spawning and maturity schedules may differ from those elsewhere in the region (WCPFC, 2012).
For yellowfin tuna in the IO, the stock is assessed by the Scientific Committee of the Indian Ocean Tuna Commission (IOTC). The Scientific Advisory Committee of the ISSF takes the IOTC stock assessments, plus other reliable information, to make their sustainability assessments of stock abundance, fishing mortality and environmental impact (ISSF, 2013). In the IO, tagging data support the assumption that yellowfin comprises a single stock (Langley, et al, 2009). Stock estimates for the IO are compromised by the lack of detailed catch statistics from some coastal fisheries, the gillnet fishery of Pakistan and some industrial longline fleets (e.g. from India).
For the five years 2007-2011, the average catch has been about 300,000 tonnes, a decline since the peak of about 500,000 tonnes between 2003 and 2006 (IOTC, 2012). The decrease in longline and purse seine effort has substantially lowered the pressure on the IO yellowfin stock. However, if the security situation in the western IO were to improve, a rapid reversal in fleet activity in this region may lead to an increase in effort which the stock might not be able to sustain. Catches would then be likely to exceed MSY levels (IOTC, 2013a).
The catches are within the lower range of MSY values. In the 2011 assessment of the IOTC Scientific Committee, the stock is currently not overfished (B2009>BMSY) and overfishing is not occurring (F2009<FMSY) (IOTC, 2012). A greater proportion of smaller fish in the catch (mainly from the purse seine FAD fishery) has led to declines in expected yield over the past five years (IOTC, 2012). However, based on the estimated levels of recruitment during the last 15 years, the stock is unlikely to support much higher yields than at present (IOTC, 2012).
The yellowfin tuna fisheries are managed by regional tuna fisheries management organizations (RFMOs) and by national governments. Reaching agreement on management measures is difficult due to competing interests of countries and fleets and preferences for different types of management choices, e.g., total allowable catch limits, vessel day limits, and restricting access to fishing areas.
As for the stock assessments, the management of the yellowfin tuna fisheries is complicated by the mix of gears and fleets exploiting the stocks in both oceans, and problems in under-reporting of catches of yellowfin (and bigeye), especially in purse seine fisheries.
Industrial tuna fisheries are managed by the IOTC and the WCPFC. The Inter-American Tropical Tuna Commission (IATTC) management area encompasses the Eastern Pacific, with some overlap with the WCPFC Convention Area. The RFMOs meet annually to consider and endorse recommended management actions. [See Slide Show for convention area maps]
Regional associations, such as the Pacific Islands Forum Fisheries Agency (FFA) and the Parties to the Nauru Agreement (PNA) are increasingly influential in tuna fisheries management. Individual island countries also manage their tuna resources, through national tuna management plans.
Each of the tuna RFMOs has a scientific committee that advises the RFMO management on stock status, monitoring and management advice and implications using their own and additional scientific advice provided by specialist organizations and individual national experts. The scientific committees also maintain databases for the catch, effort, size frequency, tagging, biological data, observer, sampling and other data.
In the European Union countries, which are important tuna markets, regulations against illegal, unreported and unregulated (IUU) fishing vessels (Council Regulation (EC) No. 1005/2008 and Commission Regulation (EU) No 468/2010) act, in effect, as management drivers. Campaigns by international environment organizations, such as Greenpeace, the Pew Environment Group and the World Wide Fund for Nature (WWF), advocate against the catch of juvenile yellowfin (and bigeye) tuna, especially by purse seiners in association with drifting FADs. These campaigns have led to some marketing chains (in Australia, UK, USA) imposing bans or foreshadowing bans on canned tuna harvested around FADs
Western and Central Pacific Ocean
Western and Central Pacific Convention Area conservation and management measures have the objective of ensuring that the fishing mortality rate of yellowfin tuna is not greater than Fmsy, i.e. F/Fmsy ≤ 1. Specific measures include port and at-sea inspections, an observer programme for purse seine and longline vessels, positive vessel list (vessels authorised to fish in flag States of RFMO member countries), IUU vessel lists, release tool for sea turtles, fishery closures, total allowable catch and effort, “freezing” vessel capacity, reducing excess fleet capacity, reducing “trading” of fishing effort, and obligatory carrying of satellite-linked tracking devices (http://www.wcpfc.int/conservation-and-management-measures/).
Regional inter-governmental and industry organizations concerned with tuna in the WCPO are:
- Pacific Islands Forum Fisheries Agency (FFA) - (member countries: Australia, Cook Islands, Federated States of Micronesia, Fiji, Kiribati, Marshall Islands, Nauru, New Zealand, Niue, Palau, Papua New Guinea, Samoa, Solomon Islands, Tokelau, Tonga, Tuvalu and Vanuatu)
- Parties to the Nauru Agreement (PNA) (http://www.pnatuna.com/) - (member countries: Federated States of Micronesia, Kiribati, Marshall Islands, Nauru, Palau, Papua New Guinea, Solomon Islands and Tuvalu). The influence of the PNA in tuna management in the WCPF Convention Area has been significant because, as a group, the zones of the member countries host significant yellowfin tuna resources.
- TeVaka Moana Arrangement (TVMA) (http://www.tevakamoana.org/) - (member countries: Cook Islands, New Zealand, Niue, Samoa, Tokelau and Tonga).
- Pacific Islands Tuna Industry Association (PITIA) - (member countries: Cook Islands, Federated States of Micronesia, Fiji, Kiribati, Marshall Islands, Nauru, Niue, Palau, Papua New Guinea, Solomon Islands, Tonga, Tuvalu and Vanuatu).
IOTC conservation and management measures include port inspections, an observer programme, transshipment controls, use of vessel monitoring system (for vessels greater than 15 m and fishing on the high seas), limitations on fishing capacity, gear and area closures, retention polices, electronic logbooks for purse-seiners, a vessel registry, positive vessel list, IUU vessel list, required use of a release tool for sea turtles, and other conservation measures for sea birds and sharks (http://www.iotc.org/cmms).
The IOTC is considering a total allowable catch and catch allocation system (IOTC, 2013b).
Yellowfin tuna is not produced in aquaculture. It has been spawned in captivity in Panama and also in Bali but larval rearing has proven difficult so far (Hutchinson et al., 2012).
- Babaran, RP. 2006. Payao fishing and its impacts to tuna stocks. A preliminary analysis. Western & Central Pacific Fisheries Commission, 2nd Scientific Committee Regular Session, 7-18 August 2006, Manila, Philippines, Paper FT-WP7. 13p.
- Hampton, J & P Williams. 2011a. Misreporting of purse seine catches of skipjack and yellowfin-bigeye on log sheets. WCPFC Scientific Committee Seventh Regular Session, 9-17 August 2011, Pohnpei, Federated States of Micronesia. Paper T-WP-02. 11p.
- Hutchinson, W, G Partridge & J Hutapea. 2012. Achieving consistent spawning of captive yellowfin tuna (Thunnus albacares) at Gondol Research Institute of Mariculture, Bali, Indonesia. Final report, ACIAR project number FIS/2006/140. 31p.
- IOTC (Indian Ocean Tuna Commission). 2012. Report of the Fourteenth Session of the IOTC Working Party on Tropical Tunas, held at Mauritius, 24-29 October 2012. IOTC–2012–WPTT14–R[E]. 88 p.
- IOTC (Indian Ocean Tuna Commission). 2013a. Report of the Sixteenth Session of the IOTC Scientific Committee. Busan, Rep of Korea, 2–6 December 2013. IOTC–2013–SC16–R[E]. 312p.
- IOTC (Indian Ocean Tuna Commission). 2013b. Report of the Seventeenth Session of the Indian Ocean Tuna Commission. Mauritius, 6–10 May, 2013. IOTC–2013–S17–R[E]. 129p.
- ISSF (International Seafood Sustainability Foundation). 2013. Status of the world fisheries for tuna. Stock status ratings - 2013. August 2013. ISSF Technical Report 2013-04A. 86p. http://iss-foundation.org/science/status-of-the-stocks/
- Langley, A, M Herrera, J-P Hallier & J Million. 2009. Stock assessment of yellowfin tuna in the Indian Ocean using MULTIFAN-CL. Indian Ocean Tuna Commission, 11th Session of the Working Party on Tropical Tunas, 10-23 October 2009, Kenya. Working paper 10. 66p.
- Langley, A, S Hoyle, & J Hampton. 2011. Stock assessment of yellowfin tuna in the Western Central Pacific Ocean. Western & Central Pacific Fisheries Commission 7th Scientific Committee Regular Session, 9-17 August 2011, Pohnpei, Federated States of Micronesia, Paper SA-WP-03 (Revision 1–03 August 2011). 135p.
- Langley, A, M Herrera & J Million. 2012. Stock assessment of yellowfin tuna in the Indian Ocean using MULTIFAN-CL. IOTC–2012–WPTT14–38 Rev_1. 21p.
- Lawson, T. 2010. Update on the estimation of selectivity bias based on paired spill and grab samples collected by observers on purse seiners in the Western and Central Pacific Ocean. Sixth Regular Session of the Scientific Committee of the Western and Central Fisheries Commission, 10-19 August 2010, Nuku’alofa, Tonga. Working Paper SC6-WP02. 19p.
- WCPFC (Western and Central Pacific Fisheries Commission), 2012. Summary Report of the Scientific Committee, the Commission for the Conservation and Management of Highly Migratory Fish Stocks in the Western and Central Pacific Ocean. 7th Regular Session, 9-17 August 2011, Kolonia, Pohnpei, Federated States of Micronesia. 211p.
Yellowfin tuna is a globally important commercial species. It accounts for more than a quarter of the world’s tuna catch. More than 70% of the world yellowfin tuna catch is taken from the Western and Central Pacific and Indian oceans.
Currently, about 0.9 million t of yellowfin tuna are harvested from the Asia-Pacific: about 0.5 million tonnes (t) from the Western and Central Pacific Ocean (WCPO) (valued at just over US$0.5 billion) and nearly 0.4 million t from the Indian Ocean (IO). Yellowfin tuna comprises nearly a fifth of the total tuna catch of the WCPO and nearly half (about 44%) of the IO tuna catch.
The main production areas are the western equatorial belt of the WCPO and in the north IO and to the west of Madagascar.
In its oceanic environmental range, (see Biology), yellowfin tuna is caught by local and foreign licensed fishing vessels using a wide range of fishing gears of artisanal, semi-industrial, industrial and recreational types. Surface-oriented fishing methods such as purse seines and gillnets catch a wide size range of yellowfin tuna (juvenile and adult fish), whereas the deeper fishing methods such as longline and handline take mainly adult fish. In purse-seine sets on free schools (not associated with fish aggregating devices (FADs)), yellowfin dominate in the Indian Ocean, but form a minor component of such schools in the Western and Central Pacific Ocean, where skipjack typically dominate. However, free-swimming schools of large yellowfin tuna are sometimes present in the WCPO.
The tuna fishing fleets of developing countries are very diverse and range from coastal and artisanal, through semi-industrial to industrial-scale vessels; developed country fleets are industrial scale and much less diverse.
In the WCPO, yellowfin tuna is caught by purse-seine nets, handline, longline, pole-and-line and troll line. In the IO, yellowfin tuna is caught by purse seine, longline, gill nets, pole-and-line, handline, troll line and sundry other artisanal gear. A substantial amount of juvenile yellowfin tuna is taken off Indonesia, in particular off Sumatra, using various types of artisanal gears, in particular liftnets.
In both ocean areas, the relative importance of the different gears used for yellowfin tuna has shifted over recent decades. In particular, purse seine fishing has increased in importance; considerable quantities of yellowfin tuna are now caught by purse-seine fleets fishing for free schools or targeting skipjack tuna around fish aggregating devices (FADs) and other floating objects. In the Indian Ocean fishing with artisanal and semi-industrial gears have increased in some coastal countries including coastal longlines and handlines in Maldives, India, Indonesia, and other countries, and the liftnet fisheries referred to above.
SMALL-SCALE AND INDUSTRIAL-SCALE FISHERIES
Since the early 1990s in both the WCPO and IO, the share of the yellowfin catch by vessels from distant water countries has declined, while catches by coastal States, using industrial gear such as purse seine and longline, as well as a variety of artisanal gear, has increased rapidly.
WESTERN AND CENTRAL PACIFIC OCEAN
In the Western and Central Pacific Ocean (WCPO), purse seiners take the majority of the yellowfin tuna catch (over 60% in recent years); the longline fleet takes about 15% and most of the remainder is taken by the domestic fisheries of Philippines and Indonesia that use a variety of gears. More than half of the total yellowfin catch from the WCPO comes from within the Exclusive Economic Zones (EEZs) of the eight Pacific Island countries that are the members of the Parties to the Nauru Agreement (PNA) (Federated States of Micronesia, Kiribati, Marshall Islands, Nauru, Palau, Papua New Guinea, Solomon Islands and Tuvalu).
Due to the large increase in numbers and size of purse-seine fishing vessels targeting skipjack tuna since the late 1970s, the average annual yellowfin tuna catch in the Western and Central Pacific Convention Area increased from 100,000 tonnes in 1970 to around 500,000 tonnes in recent years. Because small yellowfin and bigeye tuna are difficult to distinguish, yellowfin tuna may not always be reported accurately in catches dominated by skipjack tuna. Reported catches may need to be adjusted by factors up to 15-20% to correct for sampling and reporting bias.
In the WCPO, the number and average size of purse-seine vessels targeting skipjack, yellowfin and bigeye tuna have been increasing. The current industrial purse-seine fleets (nearly 300 vessels) come from the 3 main groups of countries: 1) the historically strong tuna fishing nations, i.e., Japan, Republic of Korea, Taiwan and United States of America; 2) Pacific Island countries that either have their own fleets or register foreign-owned vessels under their flags (Federated States of Micronesia, Kiribati, Marshall Islands, Papua New Guinea, Solomon Islands, Tuvalu and Vanuatu); and 3) newer tuna fishing nations (China, Ecuador, El Salvador, New Zealand and Spain).
In the WCPO, yellowfin tuna caught in purse-seine sets on free schools are often adult fish (> 100 cm fork length - FL), whereas smaller yellowfin tuna are generally caught in sets on FADs and logs. In the domestic surface fisheries of the Philippines and Indonesia, the catch includes many small yellowfin tuna in the size range of 20-50 cm FL. The association of tuna with floating or anchored devices has become a prime issue in tuna fisheries management, most notably for the need to control the catches of bigeye tuna which are an order of magnitude higher than those of bigeye tuna from unassociated sets.
The longline catch of yellowfin tuna is comprised almost entirely of adult fish (>100 cm FL). The catch of adult yellowfin tuna by purse-seine (by weight) is usually higher than that of the longline adult yellowfin tuna catch.
Longline fishing for yellowfin tuna is carried out by 3-6,000 vessels, from China, Federated States of Micronesia, Japan, Republic of Korea, Indonesia, Papua New Guinea, Philippines, Solomon Islands, Taiwan, Vanuatu, and Vietnam. However, because the catch supplies the high-value sashimi tuna market, the value of yellowfin tuna from longline fishing is similar to that of the larger volume from purse-seine fishing. Pole and line fishing, largely in the western part of the WCPO, accounts for about 4% of the total yellowfin catch.
In the WCPO, artisanal gears for yellowfin tuna include handline, small coastal longline and troll. The domestic fleets are diverse and multipurpose, from artisanal and traditional coastal fishery fleets especially in Indonesia and Philippines, and including composite industrial and small-scale fisheries. In Indonesia, Papua New Guinea, Philippines and Vietnam, artisanal fleets of small vessels operate around anchored FADs using handlines and small vertical longline gears. The commercial handline fleets target large yellowfin tuna which comprise the majority of their catch (> 90%).
Collecting accurate catch statistics from fleets using composite fishing gears (FADs and small-scale gear) is very difficult due to the diverse and unregulated nature and the rate of expansion. The Western and Central Pacific Fisheries Commission (WCPFC) are making concerted efforts to collect such data with considerable progress in recent years.
In the Indian Ocean (IO), the yellowfin tuna catch is a high proportion (44%) of the total IO tuna catch. IO yellowfin tuna are caught by a wide variety of gears and scales of operations. The long-dominant fishing methods for yellowfin tuna, purse seine (currently just over a third of the catch) and longline (one fifth), are declining in relative importance. Artisanal and semi-industrial gears, especially gill nets (one sixth of yellowfin tuna catch) and miscellaneous types (one fifth) are increasing rapidly as more countries in the IO target yellowfin tuna. Pole and line, one of the minor gear types, takes about 5% of the catch.
In the most productive Western Indian Ocean areas, pirate activity off Somalia, Kenya, Tanzania and Seychelles has depressed longline fishing and to some extent purse seine fishing for several years, but this disruption has now largely ended.
In tropical areas, both surface and longline fisheries occur year-round, but in the higher (subtropical/temperate) latitudes, the longline fisheries are seasonal.
The main fleets catching yellowfin tuna in the IO are from Spain (purse seine), France (purse seine), Sri Lanka (gillnet, longline, pole and line, troll, handline and other various artisanal gears), Maldives (pole and line and, increasingly in recent years, handline), Indonesia (purse seine, longline, handline, gill net, troll, pole and line, liftnet and various other artisanal gears), Iran (gill net, purse seine), Republic of Korea (purse seine, longline), Seychelles (purse seine, longline), Yemen (handline and troll), India (many gears), Comoros (hand and troll lines), and other countries with longline fleets (Japan, Taiwan, China, Philippines, South Africa).
Most of the yellowfin tuna purse-seine catch is taken in the Western Indian Ocean, around Seychelles and off the coast of Somalia and in the Mozambique Channel. Vessels of the European Union distant water fleet (France and Spain) take most of the catch and land the fish in the Seychelles.
In the IO, purse seiners take both small and adult fish (40 – 140 cm FL). Fishing uses two different modes: fishing on floating objects (FADs) that yields large numbers of skipjack tuna along with juvenile yellowfin and bigeye tunas, and fishing on free swimming schools that catches larger yellowfin tuna, with or without other tuna species. The majority of the purse seine catches of yellowfin are sold for canning with a small but increasing amount of yellowfin tuna is preserved deep-frozen on board and sold for the sashimi markets.
The IO longline fishery takes predominately large fish (80 - 160 cm FL), except for catches by Taiwanese longliners (and gillnetters from IO countries) in the Arabian Sea, where smaller fish (60– 100 cm FL), dominate catches. In tropical waters, yellowfin and bigeye tuna are the main longline target species.
While in the past the majority of the yellowfin tuna was caught by deep-freezing longliners for the sashimi market, in recent years the majority of the catches of yellowfin tuna have come from the fresh-tuna longline fleets of Indonesia and Taiwan, which export the catch chilled for the sashimi market or sell it to the fresh market.
In the IO, the artisanal and semi-industrial fisheries take a substantial and increasing component (20-30%) of the yellowfin tuna catch. Among these fisheries, gillnets are the most common method taking much (about 80,000 tonnes) of the juvenile or pre-adult yellowfin tuna. Other gears include pole-and-line, which also takes juvenile yellowfin tuna, and troll and handline. Large catches are landed by fleets from Sri Lanka (gillnet and longline combination), Pakistan and Iran (gillnet), the Maldives (pole-and-line, handline), and Indonesia (longline and various artisanal gears) and India (longline and trolling). A substantial amount of juvenile yellowfin tuna is caught in association with anchored-FADs, especially in Indonesia and, to a lesser extent, Maldives.
The Maldives catch of yellowfin tuna is about 23,000 tonnes annually, caught by two gears: pole-and-line and handline. Pole-and-line fishing catches juveniles.
Yellowfin tuna is a popular recreational species for game-fishing (angling) clubs in many countries bordering the Pacific and Indian oceans. The annual recreational angling catch of yellowfin tuna just from New South Wales (eastern Australia) is between 50 and 350 tonnes.
Yellowfin tuna is not produced in aquaculture, although the technology for producing the species in captivity has been developed.
GUIDE TO FURTHER READING
Note: Details of all sources are given in References below.
For overview of tuna fishing, see Makoto Peter Miyake and colleagues (2010).
For fleets and fishing methods for yellowfin tuna in the WCPO, see John Hampton & Peter Williams (2011a, 2011b), Peter Williams & Peter Terawasi (2014), and Shelton Harley and colleagues (2015). For fleet size dynamics, see Kate Barclay & Ian Cartwright (2007). For FAD fishing in Indonesia and Philippines, see Ricardo Barbaran (2006). For data corrections, see John Hampton & Peter Williams (2011a), and Tim Lawson (2010). For 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 Indian Ocean IOTC catches, see Stock Status Dashboard summary, M. Renaud Pianet and colleagues (2011), IOTC (2014). For IO fishing capacity, see Guillermo Moreno & Miguel Herrera (2013). For Maldives fisheries, see M. Shiham Adam & A. Riyaz Jauharee (2009).
For recreational fishing statistics in New South Wales, see I & I NSW (2010). For game fishing information on yellowfin tuna, see International Game Fish Association.
- Adam, MS & AR Jauharee. 2009. Handline large yellowfin tuna fishery of the Maldives. Indian Ocean Tuna Commission 10th Session of the Working Party on Tropical Tunas, Mombasa, Kenya, 15-23 October 2009, Working Paper 15. 14 p.
- Babaran, RP. 2006. Payao fishing and its impacts to tuna stocks. A preliminary analysis. Western & Central Pacific Fisheries Commission, 2nd Scientific Committee Regular Session, 7-18 August 2006, Manila, Philippines, Paper FT-WP 7. 13 p.
- Barclay, K & I Cartwright. 2007. Governance of tuna industries: The key to economic viability and sustainability in the Western and Central Pacific Ocean. Marine Policy 31: 348–358.
- Hampton, J & P Williams. 2011a. Misreporting of purse seine catches of skipjack and yellowfin-bigeye on logsheets. WCPFC Scientific Committee Seventh Regular Session, 9-17 August 2011, Pohnpei, Federated States of Micronesia. Paper T-WP-02. 11 p.
- Hampton, J & P Williams. 2011b. Analysis of purse seine set type behaviour in 2009 and 2010. WCPFC Scientific Committee Seventh Regular Session, 9-17 August 2011, Pohnpei, Federated States of Micronesia. Paper MI-WP-01. 18 p.
- I. & I. NSW (Industry & Investment NSW Government). 2010. Yellowfin tuna, pp 377-379, In Status of Fisheries Resources in NSW, 2008/09, Wild Fisheries Research Program.
- IOTC (Indian Ocean Tuna Commission). 2014. Status of the Indian Ocean yellowfin tuna (YFT: Thunnus albacares) resource. IOTC Stock Status Dashboard. 20 p.
- Lawson, T. 2010. Update on the estimation of selectivity bias based on paired spill and grab samples collected by observers on purse seiners in the Western and Central Pacific Ocean. Sixth Regular Session of the Scientific Committee of the Western and Central Fisheries Commission, 10-19 August 2010, Nuku’alofa, Tonga. Working Paper SC6-WP02. 19 p.
- 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.
- Moreno, G. & M Herrera. 2013. Estimation of fishing capacity by tuna fishing fleets in the Indian Ocean. Report presented at the 16th Session of the Scientific Committee of the Indian Ocean Tuna Commission. Busan, Republic of Korea, 2–6 December 2013. IOTC–2013–SC16–INF04.
- Pianet R, A Delgado de Molina, P Dewals, V Lucas, L Floch, E Chassot, & J Ariz. 2011. Statistics of the main purse seine fleets fishing in the Indian Ocean (1981-2010). Thirteenth Session of the IOTC Working Party on Tropical Tunas. Lankanfinolhu, North Malé Atoll, Republic of Maldives, 16–23 October 2011. IOTC-2011-WPTT13-24 Rev_1. 30 p.
- WCPFC (Western and Central Pacific Fisheries Commission). 2014a. Summary Report of the Tenth regular session of the Scientific Committee. Majuro, Republic of the Marshall Islands, 6-14 August 2014, 229 p.
- WCPFC (Western and Central Pacific Fisheries Commission). 2014b. Summary Report of the Eleventh Regular Session. Apia, Samoa, 1-5 December 2014.
- Williams, P & P Terawasi. 2014. Overview of tuna fisheries in the Western and Central Pacific Ocean, including economic conditions – 2013. WCPFC Scientific Committee Tenth Regular Session, 6-14 August 2014, Majuro, Republic of Marshall Islands. WCPFC-SC10-2014/GN WP-1. 60 p.
Yellowfin tuna is traded in many forms including small whole fresh fish for local wet markets, small and large frozen fish from industrial purse seiners for loining, canning and higher value specialty markets, large frozen or fresh fish from longliners and handliners, flown or shipped to high value export markets for sashimi and steaks, and lower value derived products.
Changes in yellowfin tuna supply chains are driven by strong domestic and international markets especially in Japan, USA, Europe, Indonesia and Philippines, and technology developments that have improved on-board handling of fish in order to maximize its value.
Yellowfin tuna is processed for different markets on the basis of quality, size and method of capture (see Production). In local markets, small yellowfin tuna (e.g., in India, less than 50 cm in length) is sold mainly as whole fresh fish; large fish are sold as sashimi and steaks in urban and tourist centers. In international markets, yellowfin tuna is sold as whole frozen fish, loins, fresh, chilled fish and canned and pouched fish. More yellowfin tuna is sold in cans and pouches than as fresh, frozen or other products. Nearly every part of yellowfin tuna is used during processing and little is discarded.
FRESH AND FROZEN FISH AND BYPRODUCTS
Depending on available transport options, the quality and appearance of the fish flesh will determine the price and destination. Its quality depends largely on how it is caught and handled from the moment of landing on the fishing vessel. Grading of individual fish destined for high value sashimi markets, e.g. Japan, can take place at several points in the supply chain. Adult yellowfin tuna has red or pink flesh.
The higher grades of longline caught yellowfin tuna over about 20 kg round weight is sold mostly for sashimi and fresh-chilled products such as loins or steaks. Lower grades landed in some Philippine and Indonesian ports are treated with carbon monoxide (CO) and frozen for export. The USA is a major destination for CO-treated yellowfin. Several other jurisdictions including the EU and Japan prohibit its importation.
Large distant water longliners with super freezers operating at -55o to -60oC supply frozen yellowfin tuna to distant markets. The whole or gilled and gutted fish are frozen within minutes of landing on the vessel to maintain optimum quality. Small and medium scale offshore and coastal longliners utilize ice or refrigerated seawater to supply fresh tuna. Fresh yellowfin is sent to major markets in the EU, Japan and the USA from offloading ports with the required air freight capacity.
Yellowfin tuna caught by handline e.g. from Indonesian, Maldivian, Vietnam and Philippine fleets, is sold fresh chilled for sashimi to major domestic and international markets or may be frozen onshore where air freight is not a good option or where some processing into secondary products e.g., steaks and saku blocks occurs Yellowfin tuna caught by longline or handline but unsuitable for export markets is sold in domestic markets. In the more eastern areas of the Western and Central Pacific Ocean, purse seiners are catching increasing volumes of large yellowfin tuna, especially when fishing on non-FAD (unassociated) schools. To maximize value, the catch is often high graded by sorting on board or during transshipment, and good quality large fish sent to higher priced European (Spain, Italy) specialty markets or processed as cooked loins.
In the more eastern areas of the Western and Central Pacific Ocean, purse seiners are catching increasing volumes of large yellowfin tuna, especially when fishing on non-FAD (unassociated) schools. To maximize value, the yellowfin tuna catch by purse seiners is often sorted on board or during transshipment, and good quality large fish sent to higher priced European (Spain, Italy) specialty markets. Japanese purse seiners have the ability to freeze a certain portion of their larger yellowfin and bigeye tuna catch at ultra low temperatures and sell to the lower-end sashimi market in Japan. Worldwide, a few of the newer large purse seiners are being equipped with super freezers to likewise quickly freeze and hold the large yellowfin for higher value markets. Gillnets, that are increasingly important in the Indian Ocean, e.g., Sri Lanka, Pakistan and Iran fleets, provide fresh tuna, and in the case of some vessels, frozen yellowfin tuna, to domestic and foreign markets, depending upon the quality of fish achieved. The majority of the gillnet catch, however, is thought to go to local markets or possibly canning; its quality is often poor.
Various products are utilized from the processing of lower grade large yellowfin, particularly in Philippines, Vietnam and Indonesia. In decreasing order of value, these products include: tuna blocks or "saku blocks" of lower grade loin tuna often used in mass-produced sushi products; cubes of flesh (from loins) that are smaller pieces than a saku block; tuna chunks of meat lower in grade than sashimi; tuna cubes or "poke" cubes; tuna scrape meat (or "naokochi" scrape) consisting of small, odd sized pieces of meat pulled from the fish skeleton; tuna belly flaps; and opercula (gill covers). Most of these products are vacuum packed in plastic bags and frozen for easy transport. Most come in two forms, either bright red due to treatment by carbon monoxide, or darker if untreated. Heads, gills and offal are often rendered and used in fish meal for fertilizers or feed, or, in some South and Southeast Asian countries, used in fish head curry dishes. Bones are usually used for extraction of calcium and protein concentrate may be recovered from wash and cooking water. Fish oil is often another important by-product. Dark meat may be used in low value canned product or petfood.
CANNED AND POUCHED TUNA
Tuna sold in cans or pouches can be transported in their final form without refrigeration and are refeered to as ambient tuna.
Canned yellowfin tuna can be legally sold as “light meat tuna,” although other species (skipjack, longtail and bigeye tuna) and even bonito can also be labelled the same way in some markets.
Caught by purse seiners, frozen small yellowfin tuna are unloaded directly to canneries or transhipped on carrier vessels. Yellowfin tuna caught by purse seine in the Western and Central Pacific and Indian Oceans is canned or loined for canning elsewhere, as is skipjack tuna, in factories in Thailand, Seychelles, Mauritius, Madagascar, Kenya, China, India, Philippines, Indonesia, Vietnam, Papua New Guinea, Solomon Islands, Fiji, Marshall Islands, American Samoa, and Costa Rica, Ecuador, El Salvador, Guatemala, and Mexico.
At the cannery, the fish is sorted, headed and gutted, then cleaned before cooking and subsequently being processed into loins. Cooked loins may be packaged and frozen for canning elsewhere or placed into shelf-stable packages (cans or pouches) before cooking under pressure in a retort. Various additives or flavourings may be added to the cans before sealing and retorting. Tuna in pouches are more easily transported and require less packaging material than cans. Such products are slowly gaining consumer acceptance in major markets, Much of the large yellowfin tuna processed by Indian Ocean canneries is packed in the “raw pack” (tuna “au naturel” – in brine or oil) form preferred by the French market. In this method, raw fish is placed into a can, covered with brine or oil, sealed and cooked in an autoclave.
SALTED AND DRIED PRODUCTS
In the Indian Ocean, traditionally, Pakistan gillnetters supplied Sri Lanka with salted dried yellowfin tuna, but this has reduced in recent years in favour of selling to higher value markets in Iran and other Middle East countries.
In the Western and Central Pacific Ocean, yellowfin tuna is not used in salted and dried products.
COMMON MARKET NAMES
The FAO names for yellowfin tuna are: yellowfin tuna (English), thon albacore (French), and rabil (Spanish). Yellowfin tuna is also known by many local common names (e.g., see FishBase http://www.fishbase.org for lists) but, due to its large global market, is usually known also at country level as "yellowfin tuna." 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.
Yellowfin tuna is low in saturated fat and sodium and is a very good source of protein, thiamine, selenium, vitamin B6, and the health-benefitting omega-3 long-chain (containing 20 or more carbon atoms) polyunsaturated fatty acids.
Nutritional data for yellowfin tuna sourced from Australian, Eastern Pacific and Western Atlantic yellowfin tuna are as given below (per 100g of raw product):
|Total fat (oil) (g)||
|Total fatty acids (mg)||
|Omega 3 EPA (mg)||
|Omega 3 DHA (mg)||
|Omega 6 AA (mg)||
Sources: NOAA FishWatch Pacific Yellowfin Tuna Table of Nutrition; Nichols et al. (1998),* Fishfiles (http://www.fishfiles.com.au/knowing/species/finfish/tuna-billfish/Pages/Yellowfin-Tuna.aspx)*, Burger and Gochfeld (2011) (for western Atlantic yellowfin tuna**
Top quality yellowfin tuna is desirable for use as sashimi and is also used in sushi in Japan and many other Asian countries. It is gaining popularity as sashimi and sushi in western countries where the more expensive bigeye tuna is either not available or uneconomical to use. Yellowfin is also served seared, grilled, broiled, sautéed, dried and smoked. In the Maldives and South Asian countries, it is used in several traditional products such as the cooked, smoked and sun-dried hikimas and Maldive fish.
MERCURY IN TUNA
The health and environmental risks of methylmercury accumulation in the tissues of predatory fish such as yellowfin tuna have received public and scientific attention. Methylmercury is a water soluble compound of mercury (a heavy metal) and has toxic biological impacts. The mercury content of yellowfin tuna, where it has been analysed, is generally well below the recommended Codex Alimentarius guideline (predatory fish species) of 1.0 mg mercury per kg of fish. The mercury content of yellowfin tuna varies with location, fish size and season and typically is lower than that in other tunas that are either longer lived or with higher fish diets, e.g., bigeye tuna and albacore. Large yellowfin tuna have the highest levels of mercury. In 2004 in Fiji, the average methylmercury levels in yellowfin tuna were 0.11 mg/kg.
The FAO/WHO Codex Committee on Contaminants in Food (CCCF) is reviewing the current guidelines, taking into account information on the benefits of fish consumption as well as the risks of mercury ingestion. Country and consumer specific advice needs to be specific to the risk of mercury exposure from the diet, depending on factors such as the patterns of fish consumption (types, sizes, frequency of consumption). Typically, dietary advice is given separately for children, women of child-bearing age and the general population.
In the Seychelles (Indian Ocean) where fish (including tuna) is consumed daily, a preliminary study of children to 9 years old found no consistent pattern of negative associations with prenatal methylmercury exposures. This suggested that the beneficial influence of nutrients from fish (including omega-3 long-chain polyunsaturated fatty acids, iodine, iron, and selenium) are generally considered to have far outweighed adverse effects of methylmercury on the developing nervous system of the children. Yellowfin tuna has a high selenium content relative to its mercury content, perhaps helping mitigate the impact of mercury on human health.
TRADE AND MARKETS
In the Western and Central Pacific and Indian Oceans, yellowfin tuna is a major food commodity of political and economic importance. It is harvested in large volumes; it has a wide range of valuable products and markets; and international fishing and market access arrangements have impacts on and beyond the fisheries sector.
Price premiums, the spread of technology such as on-board ultra low temperature (ULT) freezers and availability of air transport out of certain landing ports are delivering more fresh and frozen yellowfin tuna products into high value markets. The increase in longline fishing by coastal states has improved the supply of fresh yellowfin to international markets, e.g., by air freight from Indonesia, Vietnam, Malaysia, Marshall Islands, Singapore, Mexico, Fiji, to consumer markets for fresh tuna. Major primary markets are in Japan, mostly Tokyo and Osaka, and Los Angeles in the USA. Domestic urban and tourist markets have also increased demand for fresh and frozen yellowfin tuna of an intermediate value. Small fresh fish caught by artisanal fishers also find ready outlets in local wet markets. Canned and pouched yellowfin tuna are the other major trade products.
Along with other tuna, particularly skipjack tuna, yellowfin tuna is the subject of several international market access and trade preference agreements.
In the case of canned tuna, Pacific island and Indian Ocean countries rely primarily on European and USA markets, both of which are changing. The USA canned tuna market is declining, and the European market presents challenges from regulations on illegal, unreported and unregulated fishing, and food safety requirements. Consequently, the Pacific island countries, with their high dependence on exports, are looking to alternative markets in the Middle East, Latin America and emerging markets such as Eastern Europe. The form of traded product is also evolving, with increased exports of tuna in pouches as the pouches are easier to transport to factories in the Pacific than are empty cans.
In many OECD countries, canned yellowfin tuna products are the subject of seafood rating schemes, based mainly on the conservation policies of the rating group and its campaign principles, such as FAD-free, pole-and-line and handline-caught fish, stock sustainability rating, certificates achieved, e.g., MSC certified. To date, environmental conservation has been the main focus of ratings, but this is broadening. Several conservation and social campaigns and trade measures are exerting greater influences on tuna supply chains and markets: tuna satisfying fair trade principles, not caught by IUU fishing, caught by local producers using low impact fishing methods, and tuna produced under fair employment conditions, e.g., no human trafficking. In the case of fresh and frozen yellowfin tuna on the export markets, individual traded quantities are smaller than is the case for canned fish, and multiple pathways are used. For commodities such as derived products, such as saku blocks, cubes and scrape, internet market sites such as Alibaba appear to be gaining importance in linking sellers to buyers, often via agents. These sites also deal in non-branded and lesser brands of canned tuna.
EMPLOYMENT, SOCIAL FACTORS AND GENDER
The yellowfin supply chains, from pre-production services to consumption and waste removal, provide jobs for thousands of people, although many of these jobs are intermixed with those for other tuna and even non-tuna species. In 2008 in the Western and Central Pacific, nearly 10 times as many local jobs for Pacific island people were in shore-based processing (about 11,000 vs 1,100) compared to local jobs on tuna vessels. In 2010, about 5,800 crew from non-Pacific Island countries were employed on distant water fishing vessels operating in the PIC region. Additional professional jobs in tuna fisheries management and support services provide additional jobs, e.g., over 600 jobs for fisheries observers in the Western and Central Pacific Ocean. Total employment statistics for all vessels, enterprises and from all countries, however, is not available, and nor are statistics for employment on artisanal and domestic vessels and in the local supply chains. For the Indian Ocean, estimates for employment in tuna fishing, all species, are not available.
In the large industrial fisheries, pre-production services include the logistics of food supply, bait, crew recruitment and rotation, wharf access, establishment of markets and bunkering, vessel registration, licensing, and international negotiations. The purse seine catch may be transhipped to fish carriers or reefers in port (Western and Central Pacific) and/or close to port (Indian Ocean), to convey the catch to the canneries. This facility enables the seiners to keep on fishing, and also separates the fishing roles of capture and transport, as an efficiency measure. To reduce IUU, transshipments must be monitored by observers, and as a rule, regional fisheries management organisations prohibit transhipping at sea by purse seiners, although exceptions are permitted in archipelagic and territorial waters of some member countries of WCPFC.
Yellowfin is often caught on conjunction with fishing for other target species. In the Western and Central Pacific Ocean tuna purse seine fishery, roughly 15 to 20 percent of the catch is yellowfin, as vessels are also fishing for skipjack and opportunistically may capture yellowfin as well. Most longliners in the WCPO target albacore or higher value bigeye tuna, but also capture yellowfin tuna during fishing activities. In contrast, Indian Ocean yellowfin tuna is a target species for both purse seine and longline fleets.
Employment on vessels catching yellowfin tuna varies with the type of gear, size and country of origin of vessel, length of fishing trips, from small local boats operated by only a few fishers on day trips, to large industrial purse seiners and longliners crewed by 15-40 members. Distant water longliners may be away from shore for more than a year. Typically, flag state regulations require the skipper and other technical positions to be filled by people from the flag country of the owners, e.g., Japan, USA, Taiwan and Korea. Deck positions are filled by nationals of lower wage countries in order to lessen crewing costs. In most developing countries, however, the crew of domestic vessels are from the home country, e.g., India, Indonesia, Philippines, Vietnam and some Pacific Islands.
Economic pressures to contain fishing costs create conditions in which some fishing vessels operate without due regard to compliance with international safety and crewing standards. At the worst, cases have been documented in the Western and Central Pacific and Indian Oceans of illegal fishing vessels operated outside laws and social norms, using forced labour and abandoning crew in foreign ports. In ports, transactional sex (e.g., for money, food, fish, alcohol) happens; sexual abuse of fellow crew at sea and of children during port visits have been reported. The fisheries for yellowfin tuna are not any more affected than some other fisheries, nor immune from these problems.
Almost all at-sea workers on vessels catching yellowfin tuna are men and some boys (under 18 years). In Fiji in 2001, only 3% of people in the harvesting sector were women, compared to a majority of women in the processing sector.
In the environmental campaigns that promote tuna pole-and-line fishing and oppose purse seine and associated-FAD fishing, several social as well as environment benefits of pole-and-line have been noted. These include enhanced employment opportunities for local crews because of the increased labour requirements of pole-and-line. These same benefits result in added costs, however, and this coupled with the requirement for live bait severely limits the potential for pole-and-line fishing to adequately supply the world market. Handline fishing for large yellowfin tuna in some locations, e.g., southern Philippines and Indonesia, offers the opportunity to supply export and domestic markets as long as transportation is available to those markets.
SCIENTIFIC AND MANAGEMENT SERVICES
The Oceanic Fisheries Programme (OFP) of the Secretariat of the Pacific Community provides scientific advice to the Western and Central Pacific Fisheries Commission. This includes catch and effort data compilation and publication of an annual yearbook, and the provision of regular stock assessments and management advice to members of the Commission.
In the Western and Central Pacific Ocean, the Pacific Island Regional Fisheries Observers arrangement (including US South Pacific Tuna Treaty observers, Forum Fisheries Agency observers, observers for the Parties to the Nauru Agreement for MSC chain of custody requirements) and national observers in some cases) coordinates fisheries observers employed by countries and regional bodies to help scientific data gathering and compliance with conservation and management measures. For the Parties to the Nauru Agreement, trained independent observers oversee the Marine Stewardship Council chain of custody system. Industrial purse seine fishing generally has 100% observer coverage (levels may be lower in Indonesia, Vietnam, Philippines) with other fishing types are covered at lower levels. Around 600 professional observers from Pacific Island countries are employed, including women observers and coordinators in some countries; observer management standards have been developed and applied.
PORTS, PROCESSING AND OTHER LAND BASED FACILITIES
The siting of tuna processing facilities in the Pacific islands of the Western and Central Pacific Ocean is closely linked to fishery access. Hence most onshore processing development has taken place in countries with significant tuna resources, e.g. Papua New Guinea, Solomon Islands, and Marshall Islands.
Land-based employment faces the same cost pressures as at-sea employment. Several small island countries in the Western and Central Pacific and Indian Oceans have benefited from the creation of thousands of jobs in processing factories, ports and in indirect jobs supplying these enterprises. On the negative side, ports and factories servicing tuna industries can bring with them a range of environmental and social problems. Industrial tuna processing affects different groups of people in distinct ways, depending on whether they live near the facilities and can take advantage of or suffer the effects. Government definitions of “development” have been slow to include an assessment of working conditions, health and environmental consequences of tuna-based development, but this is beginning to change. Governments of coastal states that have secured and retained local canneries against the cost pressures, view these as a means to secure more of the benefits of their large tuna resources.
Unskilled and skilled women and men are engaged in canneries in the Pacific, Asia and Indian Ocean countries, including those canning yellowfin tuna. Unskilled labourers are on low wages, a fact that attracts processors to a particular location in the first place. Whereas men's work spans loading and unloading and the more physically-demanding tasks, women work primarily on the processing lines. Migrant women and men, often from minority ethnic groups, have been found working in some canneries in the Philippines and Thailand, where human trafficking is finally being addressed as part of the crack-down on IUU fishing. Canneries in other countries, for example PNG and Solomon Islands, overall, have been upholding international conventions pertaining to human rights that they have ratified. In addition to the direct jobs created in the canneries, as many as 2.5 times this number of indirect jobs are estimated (PNG) to also be created.
Canneries prefer to engage women processors because they are considered more skillful than men at cleaning and cutting the fish. Worldwide, tuna canneries are large-scale employers of female workers in unskilled, production-level positions, particularly skinning and loining. At least 70% of workers in PNG canneries are female; 80-90% of whom are employed in production lines. In many canneries, women are paid lower wages than are the men employees for similar work. Workers often lack job continuity and security, and the right to form collective bargaining unions. In some locations, communities are negatively affected by the women’s cannery jobs if the women live away from home and their communal obligations and child rearing fall on unemployed men and older people.
At present, canning companies are not considered likely to automate most of the processing jobs. This is partly because of the desire to retain jobs in the Western and Central Pacific and Indian Ocean countries. Consequently there has been a lack of research and development undertaken to mechanize certain processes. This is compounded by the perceived difficulties in installing and maintaining high technology automation in relatively remote locations where many tuna processing factories are located.
GUIDE TO FURTHER READING
Note: Details of all sources are given in References below.
For tuna fishing and processing technology, see Mike McCoy and colleagues (2015) (Western and Central Pacific Ocean), Liam Campling and Martin Doherty (2007), and Amanda Hamilton and colleagues (2011b); for Pakistan see Muhammad Moazzam and Rab Nawaz (2014). For a guide to on-board processing of tuna for the sashimi market, see Michel Blanc and colleagues (2005).
For the types of products and markets Makoto Peter Miyake and colleagues (2010), and for value-added and byproducts, see INFOFISH (2007), and Shri Sreekanth G.B. and colleagues (2010).
For common names, see FishBase (www.fishbase.org), and Makato Peter Miyake and colleagues (2010) for USA names. For nutritional information, see NOAA FishWatch Pacific Yellowfin Tuna Table of Nutrition; Peter Nichols and colleagues (1998), and Australian Fishfiles (http://www.fishfiles.com.au/knowing/species/finfish/tuna-billfish/Pages/Yellowfin-Tuna.aspx).
For information on mercury in yellowfin tuna, see Maureen Kumar and colleagues (2004) (Fiji), Gary Myers and colleagues (2007) (Seychelles), and the Codex Alimentarius Commission, (2014). For information on mercury and selenium, see John Kaneko and Nicholas Ralston (2007) and Joanna Burger and Michael Gochfeld (2011).
For trade and markets, see Makato Peter Miyake and colleagues (2010), Mike McCoy and colleagues (2015), and Liam Campling 2015.
For employment in tuna supply chains, see Amanda Hamilton and colleagues (2011b) (global), and Robert Gillett (2009) (Pacific Island countries), Robert Gillett (2011) (pole-and-line fishing). For labour problems on vessels, see Eve de Coning (2011); and for legal instruments relevant to seafarers on fishing vessels, see the International Collective in Support of Fish Workers site (http://legal.icsf.net/icsflegal/). For women fishers, see Patricia Tuara Demmke (2006). For information on the Pacific Island Fisheries Regional Observers, see http://www.spc.int/oceanfish/en/ofpsection/fisheries-monitoring/observers.
For processing factories labour and other local issues, see Kate Barclay and Ian Cartwright (2008), Elizabeth Havice and Kristen Reed (2012), Parris (2010), and Olha Krushelnytska (2015). For gender information, see Patricia Tuara Demmke (2006), Amanda Hamilton and colleagues (2011a), Nancy Sullivan and Vina Ram-Bidesi (2007), Eve de Coning (2011). For the outlook for factory automation, see Mike McCoy and colleagues (2015).
- Barclay, K & I Cartwright. 2008. Capturing Wealth from Tuna: Case Studies from the Pacific. Asia Pacific Press, ANU Canberra.
- Blanc, M, A Desurmont & S Beverly. 2005. Onboard handling of sashimi-grade tuna a practical guide for crew members. Secretariat for the Pacific Community, Noumea, 25 p.
- Burger, J & M Gochfeld. 2011 Mercury and selenium levels in 19 species of saltwater fish from New Jersey as a function of species, size, and season. Science of the Total Environment, 409:1418-1429.
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All fishing gears have some level of environmental effect. Under the FAO Code of Conduct for Responsible Fishing, the fishing sector is expected to reduce its effects to the minimum possible in ways that are also compatible with its own sustained existence. For yellowfin tuna caught in surface and deep waters by a wide variety of fishing methods, bycatch is one of the most observable effects of fishing on the environment. This is especially the case when yellowfin tuna are caught by longline, gillnet and by purse seining on floating objects, including fish aggregating devices (FADs). Air and water pollution from fishing vessels and fish processing are other environmental concerns.
Environmental variation also has an effect on the abundance and distribution of yellowfin tuna. As the ocean warms and becomes more acidic due to increased emissions of carbon dioxide (CO2), the distribution and catchability of yellowfin tuna stocks are expected to become even more variable.
EFFECTS OF YELLOWFIN FISHING ON OTHER SPECIES
Yellowfin tuna are caught by purse-seine nets, longline, pole-and-line and troll line in the Western and Central Pacific Ocean (WCPO), and by gill nets, longline, purse seine, pole-and-line, handline and troll line in the Indian Ocean (IO) (see Production). These gears do not come into contact with the seafloor and so do not directly affect the benthic environment.
Nevertheless, longline fishing for yellowfin, albacore and bigeye tuna has a substantial bycatch of non-tuna species. Varying by area of the WCPO, the main fish bycatch species include sharks (especially blue shark which may be a target species), billfish, pelagic stingrays, and moonfish or opah (Lampris guttatus).
Sharks are not always caught as bycatch. Sometimes, they are targeted for their fins and meat because longline crews often take the opportunity to top up their incomes through sales of shark fins. Tens of thousands of sharks are caught (and usually finned) each year in the WCPO and IO. As a result, catches of many shark species have experienced steep declines in recent years, most likely due to high fishing mortality.
In the WCPO about a dozen species of shark have been identified as common bycatch: blue shark (Prionace glauca), silky shark (Carcharhinus falciformis), oceanic whitetip shark (Carcharhinus longimanus), mako sharks (Isurus spp), thresher sharks (Alopias spp), porbeagle shark (Lamna nasus), winghead hammerhead (Eusphyra blochii), scalloped hammerhead (Sphyrna corona), great hammerhead (Sphyrna mokarran) and smooth hammerhead (Sphyrna zygaena). In the IO, shark catches have been recorded only recently and refer mainly to retained catch.
Conversely, sharks cause considerable damage to tuna on hooks in the longline fishery, and reduce the value of the tuna catch.
Changing the types of hooks used on longlines and their positions in the water column, replacing wire traces with nylon leaders, and improved shark handling practices, are being used or investigated to 1) reduce the catch of sharks, 2) improve condition of sharks on landing and survival upon release, and 3) enhance the catch of target species.
Longline catches of seabirds, marine mammals and turtles are significant in some areas.
Gill nets, which are used extensively in the IO, are of greatest concern for bycatch among the surface fisheries for yellowfin tuna. Gillnet fishing is poorly monitored. The proportion of non-tuna species in the purse-seine catch is relatively low, whether the nets are set around FADs (1.6%) or on free-swimming schools not associated with FADs (0.4%). In the WCPO surface fisheries, the bycatch of non-tuna species includes mainly silky shark, mackerel scad, mahi mahi, frigate mackerel, oceanic triggerfish and rainbow runner. The bycatch of juvenile bigeye tuna is of concern in the tropical purse-seine fishery. The bycatch from pole-and-line and troll fisheries is minimal. However, when pole-and-line fishing was much more common than it is today, localized depletion of stocks of the small pelagic fish species used as live bait was of concern to some Pacific countries.
The Western and Central Pacific Fisheries Commission (WCPFC) and the Indian Ocean Tuna Commission (IOTC) have conservation measures for bycatch mitigation and monitoring. Specific conservation and management measures address bycatch issues for sea turtles, sharks (including finning), sea birds, cetaceans, other finfish and reporting provisions to support bycatch research and monitoring. The International Seafood Sustainability Foundation (ISSF) conducts regionally specific bycatch mitigation training workshops for purse-seine vessel skippers and publishes guidebooks for purse-seine skippers and observers, and for longline skippers (http://www.issfguidebooks.org/downloadable-guides/)
IMPACTS ON AIR AND WATER
Purse-seine and longline vessels rely on fossil fuel and thus their exhaust fumes and refrigerant gases contribute to greenhouse gas (GHG) emissions and global warming. The estimated total carbon footprint of tuna caught by purse seine (all species) was approximately 1,530 kg CO2 per tonne of tuna landed (2009 estimate). The GHG emissions associated with catching tuna by purse-seine vessels, storing the fish on board, and delivering whole fish to processing plants are three times greater than the emissions stemming from the processing, packaging and transport of the resulting products. The amount of fuel used to catch a tonne of tuna is greater for longline vessels than for purse-seine vessels. The carbon footprint of longline tuna products is increased further if air freight is used to deliver sashimi-grade tuna and other fresh tuna products to markets because GHG emissions are much higher for airfreight than for sea freight.
The most significant environmental effects from catching juvenile yellowfin tuna in surface fisheries are point-source impacts from canning. Many of the countries that process and export canned tuna are developing countries: Thailand, Seychelles, Mauritius, Kenya, Indonesia (IO) and Philippines, Indonesia, Papua New Guinea, Fiji, American Samoa (WCPO). In these low-cost countries, the processing (‘canning’ or ‘loining’) facilities undertake the labour-intensive activities while the actual canning may also be done there or in higher-cost countries such as Spain and Germany. The amount of factory waste has increased significantly in low-cost countries, which generally have less capacity to regulate environmental impacts. As a result, in the vicinity of the factories, local access to coastal food resources, and quality of life, may be affected.
Another environmental effect of fish processing is the high consumption of water for transporting fish and offal around the plant in flume systems, for cleaning plant and equipment, for washing raw materials and product, and for de-icing and thawing.
EFFECTS OF ENVIRONMENT ON YELLOWFIN
Ocean conditions have pronounced effects on the distribution and abundance of tropical tuna. While these effects are best documented for skipjack tuna, they also occur for yellowfin tuna.
In the WCPO, the most conspicuous of these effects are due to the El Niño Southern Oscillation (ENSO) in the WCPO. ENSO is a swing between warmer (El Niño) and cooler (La Niña) ocean conditions across much of the tropical Pacific, that also affects the depth of the thermocline and the extent of the upper mixed layer. It occurs on irregular cycles (2-7 years) due to interactions between the atmosphere and the ocean. Changes in ocean currents and temperatures linked to ENSO are likely to influence where and when yellowfin tuna spawn, and how larvae, juveniles and their prey are dispersed or retained in areas conducive to their growth and survival. El Niño events appear to be favourable to yellowfin tuna recruitment because the main yellowfin tuna spawning grounds in the WCPO are associated with the warm pool, which expands during such events.
Annually, the IO has two distinct monsoon seasons that cause seasonal changes to oceanic and coastal waters, including in the depth of the thermocline and position of convergence zones. In turn, these changes affect the distribution of yellowfin tuna and its vulnerability to fishing gears. Yellowfin tuna is caught in greater numbers where the thermocline is shallow. In addition, year to year variation in the seasonal pattern of changes is large and associated with the Indian Ocean Dipole, a climate oscillation (on irregular cycles of 4-5 years) between a warmer (positive) and a cooler (negative) state. Indices measuring the state of the Indian Ocean Dipole are better predictors of warm and cold events in the Western Indian Ocean than are ENSO events, although ENSO events also appear to have an influence, especially if intense.
A complex relationship exists between the Indian Ocean Dipole and the yellowfin-tuna catches of purse-seines and longlines, including differences across sub-regions of the IO. In the western IO, the distribution and longline catches of yellowfin tuna are influenced by the Indian Ocean Dipole. With a period of about 4 years. High sea surface temperatures (>29.5 °C) tend to be related to low primary production and decreased catch rates during positive Indian Ocean Dipole events. Especially in the Arabian Sea and around Madagascar, increased yellowfin tuna catch rates occur in association with negative Indian Ocean Dipole events, along with lower sea surface temperature and high primary production.
EFFECTS OF CLIMATE CHANGE ON YELLOWFIN
Increased GHG emissions are expected to increase sea surface temperatures (SST), stratification of the water column and the pH of seawater, and alter the strength of major currents and counter currents. In the WCPO, SST and the average extent of the warm pool are expected to progressively resemble present-day El Niño conditions. Modelling of the projected effects of changes to the WCPO on yellowfin tuna has yet to be completed. However, such effects are expected to be somewhat similar to the projections that have been made for skipjack tuna. In the shorter term (by 2035), increases in catches may occur in the central and eastern areas of the region. However, by the end of the century, decreased catches are expected in the EEZs of all Pacific Island countries and territories except French Polynesia and Cook Islands.
In the WCPO, the prime yellowfin tuna fishing grounds are expected to move progressively eastward along the equator, and towards higher latitudes. Where yellowfin tuna remains within its preferred temperature range, catch rates of surface schools may increase as the water column becomes more stratified due to increasing SST and decreasing salinity resulting from the projected increases in in rainfall in equatorial regions.
GUIDE TO FURTHER READING
Note: Details of all sources are given in References below.
For preliminary estimates of the impact of tuna fishing on non-tuna species, see Ana Justel-Rubio & Victor Restrepo (2015). For bycatch of longlines, see Victor Restrepo and colleagues (2014. For bycatch on longlines in the WCPO, see Shelton Harley and colleagues (2010).
For sharks and longline fishing, see Mike McCoy & Robert Gillett (2005), Shelley Clarke, (2011), Shelley Clarke and colleagues (2011) and (2014) and Tim Lawson (2011) for the WCPO, David Ardill and colleagues (2011) for the IO. Makoto Peter Miyake and others (2010) reported on shark damage to tuna on longlines. The WCPFC’s Conservation and Management Measure (CMM) 2010-07 lists shark species of concern. For information on fishing gear modifications to reduce longline shark catch and bycatch see Don Bromhead and others (2013), Pew Marine Environment Group (2011), and Peter Ward and others (2007).
For longline catches of seabirds, mammals and sea turtles, see Shelley Clarke and colleagues (2014). For remarks on surface fisheries for yellowfin tuna catches and gill nets, see ISSF (2014a). For purse-seine catch information for the WCPO, see Shelton Harley and colleagues (2010). On baitfish for pole and line fishing in Solomon Islands and Fiji, see Steve Blaber and others (1993); for Maldives see R. Charles Anderson (1997). For bycatch conservation and monitoring measures of the WCPFC, see https://www.wcpfc.int/conservation-and-management-measures, for IOTC see http://www.iotc.org/cmms; for a recent compendium of measures, see ISSF (2014b). For ISSF skippers' and observers' guides, see http://www.issfguidebooks.org/downloadable-guides/.
Peter Tyedmers and Robert Parker (2011) provide a preliminary assessment of the impacts of bigeye tuna fishing and supply chain on air and water. The report from UNEP (2000) provided information on the environment impacts of tuna processing.
For information on tuna fish processing, see Makoto Peter Miyake and others (2010), Amanda Hamilton and others (2011), Elizabeth Havice & Kristen Reed (2012), Patricia Tuara (2006), Nancy Sullivan & Vina Ram-Bidesi (2007), Kate Barclay & Ian Cartwright (2007), and UNEP (2000).
For the effects of the environment and oceanography (including the ENSO in the WCPO) on yellowfin tuna distribution and biology, see Patrick Lehodey and others (2003), (1997) and (2011), Janice Lough and others (2011), Alexandre Ganachaud and others (2011) for the WCPO; and, for the IO, Francis Marsac (2001, 2014), Frederic Ménard and others (2007), Kathleen Miller (2007), and Ana Corbineau and others (2008), and Kuo-Wei Lan and colleagues (2013).
For the effects of climate change on yellowfin tuna stocks and the supporting ecosystem in the WCPO see Alexandre Ganachaud and others (2011), Patrick Lehodey and others (2011), (2013), Johann Bell and others (2013), Janice Lough and others (2011), and Robert Le Borgne and others (2011).
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- Havice, E & K Reed. 2012. Fishing for development? Tuna resource access and industrial change in Papua New Guinea. Journal of Agrarian Change, 12:413-435.
- ISSF (International Seafood Sustainability Foundation). 2014a. Tuna Stock Status Update: Status of the world fisheries for tuna. ISSF Technical Report 2014-09. International Seafood Sustainability Foundation, Washington, D.C., USA.
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The yellowfin tuna is a large, elongate fish with a round and tapered body. Its body is deepest at the first dorsal fin. Some large specimens have very long second dorsal and anal fins, which can be more than 20% of fork length (FL). The pectoral fins are moderately long, usually reaching beyond the origin of the second dorsal fin but not beyond the end of its base. The back is metallic dark blue in colour, changing to yellow and then to silver on belly, which is frequently crossed, at juvenile sizes by about 20 broken, nearly vertical lines. These lines disappear in adults. The second dorsal and anal fins, and dorsal and anal finlets, are bright yellow. The finlets may have a narrow black border. There is a strong lateral keel on the caudal peduncle. Yellowfin tuna has 26-34 gill rakers on the first gill arch.
Yellowfin tuna has a swim bladder. When inflated, the swimbladder is about half the length of the body cavity whereas, in bigeye tuna, the swimbladder reaches most of the length of the body cavity.
Yellowfin tuna is similar in appearance to bigeye tuna, but can be distinguished using several external features (body markings, body shape, head and eye shape, pectoral and caudal fin characteristics, finlet coloration) and internal features (liver shape, swimbladder size). Juveniles of yellowfin and bigeye tuna are more difficult to distinguish than are adults.
Together with the other species of tropical tuna, yellowfin 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. Yellowfin tuna spends most of its foraging time above the thermocline. As it grows, yellowfin tuna is able to capture larger prey, within the limits of the sizes available. As an oceanic predator spending considerable time in the surface layers, especially when young, yellowfin tuna also consumes prey (eggs, invertebrate and fish plankton) exported from reef ecosystems.
Predators of yellowfin tuna include other tunas, including other yellowfin tuna, pelagic sharks, sailfish, marlins, and toothed whales including dolphins.
HABITAT AND DISTRIBUTION
Yellowfin tuna mainly inhabit tropical and subtropical waters of the Atlantic, Indian and Pacific oceans, but can occur up to 40oN and 40oS. It is found predominately in tropical coastal and open ocean ecoregions, in waters from the surface to the mixed layer depth that varies with place and season. Yellowfin tuna does not occur over shallow coastal shelves (ocean depths less than about 50 m). [See slide show for yellowfin tuna distribution map]. In the Pacific, most of the population occurs from 20oN to 20oS.
Yellowfin tuna tolerates a wide range of environmental conditions. Water temperature and oxygen levels have a major influence on the habitats yellowfin tuna occupies. Like other tuna, the blood circulation of yellowfin has a heat exchanger system that can sustain muscle temperature significantly above that of the water. This specialized anatomy gives yellowfin tuna enhanced swimming efficiency and the ability to live within a relatively wide range of temperatures. Yellowfin tuna regulates its body temperature in response to muscle temperature changes, moving into cooler or warmer waters as required. As a result, yellowfin can feed in both sunlit surface waters and in deeper, cooler nutrient-rich layers of the ocean.
Yellowfin tuna have been found in water temperatures of 18o to 31oC, but most commonly live between 20o to 30oC. Yellowfin tuna spend less than 10% of their time at depths where oxygen (O2) levels are < 4.3 mg/l (3.3 mg/l, 65% saturation). As a result of temperature preferences and tolerances, juvenile and adult yellowfin usually remain in depths in which temperatures are within 8oC of that of the surface water although occasionally they dive to around 1000 m. In the Indian Ocean, the main swimming depth for adult yellowfin tuna caught by longline is from 80 m to 200 m.
Yellowfin tuna can be highly migratory, and long-distance movements of thousands of nautical miles have been recorded. However, the vast majority of recorded movements of tagged yellowfin tuna have been much shorter. For example, the median lifetime displacement for yellowfin tuna in the Western and Central Pacific Ocean (WCPO) is 337-380 nm.
Although tagging data indicate that yellowfin tuna in the WCPO are a single stock, sub-regional biological differences are possible and need further investigation. In the IO, tagging data support the assumption that yellowfin tuna comprises a single stock.
GROWTH, REPRODUCTION AND DIET
Yellowfin tuna growth is complex, and goes through several stages over its life. A juvenile yellowfin tuna grows quickly to about 40 cm FL and is first caught in surface commercial fisheries when only several months old. Growth slows between 40 and 70 cm and then accelerates again between 70 and 100 cm FL, probably during sexual maturation. Older fish live in deeper colder waters. Growth rate plateaus and declines with size. Young yellowfin tuna may grow more slowly in the equatorial waters of Indonesia and the Philippines than in the wider area of the Western and Central Pacific Ocean. The estimated average maximum size is 180 cm and 100 kg. Tag-and-release information, indicates that yellowfin live for at least six years.
Yellowfin tuna reaches sexual maturity at a length of 95-120 cm FL and an age of 2 to 3.5 years. However, in exceptional circumstances, it can become mature at 50- 60 cm FL and an age of 12 -15 months. Spawning can take place all year-round, but is most frequent during the summer months in each hemisphere. Yellowfin tuna are multiple batch (serial) spawners, i.e. they spawn eggs and sperm into the water column almost every day over the spawning period. Average batch fecundity (egg production per spawning event) is 2.2 million in the Western Pacific.
Extensive sampling of tuna stomachs has shown that the diet of yellowfin tuna is diverse, comprising a variety of surface-dwelling and deeper-dwelling fish species, pelagic crustaceans and squid. The diet also changes with age. In the Western and Central Pacific Ocean, juvenile yellowfin tuna (< 45 cm) consume mainly anchovies (Engraulidae), other small surface-dwelling fish (including reef-associated fish during their pelagic phase) and planktonic crustaceans. Subadult (45-120 cm) and adult (>120 cm) yellowfin prey on scombrid fishes (including juvenile skipjack tuna), pelagic-stages of reef fish, squid and deeper-dwelling fish.
Guide to Further Reading
Note: Details of all sources are given below in References.
For description of yellowfin tuna, see Bruce Collette (2001). 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; also see David Itano (2005). See also for Kurt Schaefer (1999) on physical differences, including extent of swim bladder.
For ecosystem role, with an emphasis on the Western and Central Pacific Ocean (WCPO), see John Sibert and colleagues (2006) and Valerie Allain and colleagues (2012); and, on predators, FishBase.
For habitat and distribution, see Gabriel Reygondeau and colleagues (2012) for ecoregions, Makoto Peter Miyake and colleagues (2010), and FAO yellowfin tuna distribution map (link). For stock structure, see WCPFC (2012) and, for IO, Adam Langley and colleagues (2009).
For environmental and habitat information, see Paul Sund and colleagues (1981), and Patrick Lehodey and colleagues (2011). For temperature, oxygen, and depth distribution information, see Richard Brill and colleagues (1999), Li Ming Song and colleagues (2008), and Kurt Schaefer and colleagues (2011). For WCPO yellowfin tuna displacements, see John Sibert and John Hampton (2003).
For growth, see Alain Fonteneau and Didier Gascuel (2008), Alain Fonteneau and Emmanuel Chassot (2013), Adam Langley and colleagues (2011), Patrick Lehodey and Bruno Leroy (1999).
For reproduction, see Kurt Schaefer (1996, 1998), Patrick Lehodey and Bruno Leroy (1999), David Itano (2000) For diet, in WCPO see Arnaud Bertrand and colleagues (2002), Valerie Allain and colleagues (2012); in Indian Ocean see Michel Potier and colleagues (2004); and, more generally, FishBase.
- Allain, V, E Fernandez, SD Hoyle, S Caillot, J Jurado-Molina, S Andréfouët, & SJ Nicol. 2012. Interaction between coastal and oceanic ecosystems of the western and central Pacific Ocean through predator-prey relationship studies. PLoS ONE. 7 (5)
- Bertrand, A, F-X Bard & E Josse. 2002. Tuna food habits related to the micronekton distribution in French Polynesia. Marine Biology 140:1023-1037.
- Brill, RW, BA Block, CH Boggs, KA Bigelow, EV Freund & DJ Marcinek. 1999. Horizontal movements and depth distribution of large adult yellowfin tuna (Thunnus albacares) near the Hawaiian Islands, recorded using ultrasonic telemetry: implications for the physiological ecology of pelagic fishes. Marine Biology 133:395-408.
- 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.
- Fonteneau, A. and D. Gascuel. 2008. Growth rates and apparent growth curves, for yellowfin, skipjack and bigeye tagged and recovered in the Indian Ocean during the IOTTP. IOTC-2008-WPTDA-08.
- Fonteneau, A. and E. Chassot. 2013. An Overview of Yellowfin Tuna Growth in the Atlantic Ocean: Von Bertalanffy or Multistanza Growth? ICCAT, SCRS/2012/045 Collect. Vol. Sci. Pap. ICCAT, 69(5):2059-2075.
- Itano, DG. 2000. The reproductive biology of yellowfin tuna (Thunnus albacares) in Hawaiian waters and the western tropical Pacific Ocean: Project summary. SOEST 00-01, JIMAR Contribution 00-328.
- Itano, D. 2005. A handbook for the identification of yellowfin and bigeye tunas in fresh condition (v2). Western and Central Fisheries Commission. Fishing Technology Working Group. December 2005. 25 p.
- Langley, A, M Herrera, J-P Hallier & J Million. 2009. Stock assessment of yellowfin tuna in the Indian Ocean using MULTIFAN-CL. Indian Ocean Tuna Commission, 11th Session of the Working Party on Tropical Tunas, 10-23 October 2009, Kenya. Working paper 10. 66p.
- Langley, A, S Hoyle, & J Hampton. 2011. Stock assessment of yellowfin tuna in the Western Central Pacific Ocean. Western & Central Pacific Fisheries Commission 7th Scientific Committee Regular Session, 9-17 August 2011, Pohnpei, Federated States of Micronesia, Paper SA-WP-03 (Revision 1-03 August 2011). 135 p.
- Lehodey, P & Leroy, B. 1999. Age and growth of yellowfin tuna (Thunnus albacares) from the Western and Central Pacific Ocean as indicated by daily growth increments and tagging data. Working Paper YFT-2, Standing Committee on Tuna and Billfish, 16-23 June, 1999, Tahiti.
- Lehodey, P, J Hampton, RW Brill, S Nicol, I Senina, B Calmettes, HO Pörtner, L Bopp, T Ilyina, JD Bell, & J Sibert. 2011. Vulnerability of oceanic fisheries in the tropical Pacific to climate change. Pp 433-492, in JD Bell, JE Johnson & AJ Hobday (eds), Vulnerability of Tropical Pacific Fisheries and Aquaculture to Climate Change. Secretariat of the Pacific Community, Noumea, New Caledonia.
- 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.
- Potier, M, F Marsac, V Lucas, R Sabatié, J-P Hallier & F Ménard. 2004. Feeding Partitioning among Tuna Taken in Surface and Mid-water Layers: The Case of Yellowfin (Thunnus albacares) and Bigeye (T. obesus) in the Western Tropical Indian Ocean. Western Indian Ocean Journal of Marine Science 3(1):51-62.
- Reygondeau, G, O Maury, G Beaugrand, JM Fromentin, A Fonteneau & P Cury. 2012. Biogeography of tuna and billfish communities. Journal of Biogeography, 39:114-129.
- Schaefer, K. 1996. Spawning time, frequency, and batch fecundity of yellowfin tuna, Thunnus albacares, near Clipperton Atoll in the eastern Pacific Ocean. Fish. Bull. 94:98-112.
- Schaefer, K. 1998. Reproductive biology of yellowfin tuna (Thunnus albacares) in the eastern Pacific Ocean. Inter-Am.Trop. Tuna Comm. Bull. 21:205-221.
- 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, & BA Block. 2011. Movement, behaviour and habitat utilization of yellowfin tuna (Thunnus albacares) in the Pacific Ocean off Baja California, Mexico, determined from archival tag data analyses, including unscented Kalman filtering. Fisheries Research 112 (2011): 22-37.
- Sibert, J & J Hampton. 2003. Mobility of tropical tunas and the implications for fisheries management. Marine Policy 27:87-95.
- Sibert, J, J Hampton, P Kleiber & M Maunder. 2006. Biomass, size, and trophic status of top predators in the Pacific Ocean. Science 314:1773-1776.
- Song, LM, Y Zhang, LX Xu, WX Jiang & JQ Wang. 2008. Environmental preferences of longlining for yellowfin tuna (Thunnus albacares) in the tropical high seas of the Indian Ocean. Fisheries Oceanography 17:239-253.
- Sund, PN, M Blackburn M & F Williams. 1981. Tunas and their environment in the Pacific Ocean: A review. Oceanography Marine Biology: An Annual Review 19, 443-512.
- WCPFC (Western and Central Pacific Fisheries Commission). 2012. Summary Report of the Scientific Committee, the Commission for the Conservation and Management of Highly Migratory Fish Stocks in the Western and Central Pacific Ocean. 7th Regular Session, 9-17 August 2011, Kolonia, Pohnpei, Federated States of Micronesia. 211p.
- Quick Facts: Patricia Kailola and Meryl Williams
- Sustainability: Meryl Williams and Patricia Kailola
- Production: Patricia Kailola, Tarlochan Singh and Meryl Williams
- Supply Chains and Markets: Patricia Kailola, Tarlochan Singh and Meryl Williams
- Environment and Climate: Patricia Kailola, Johann Bell and Meryl Williams
- Biology: Patricia Kailola, Johann Bell and Meryl Williams
INFORMATION PROVIDED BY THE FOLLOWING PEOPLE
- John Hampton, Secretariat for the Pacific Community (SPC)
- Johann D. Bell, SPC (Pacific Island consumption patterns, climate change)
- Lindsay Chapman, SPC (Pacific Island consumption patterns)
- Simon Hoyle, SPC
- Peter Williams, SPC
- Peter Nichols, CSIRO, Australia (nutrition)
- Indian Ocean Tuna Commission Secretariat (Indian Ocean material)
- Miguel Herrera (IOTC)
- Fishbase team
Drafts of the presentations were reviewed by the following:
- Sustainability - Johann Bell (SPC, Conservation International - CI)
- Production - Johann Bell (SPC, CI), Peter Williams (SPC), Miguel Herrera (IOTC, Organizacion de Productores Asociados de Grandes Atuneros Congeladores - OPAGAC)
- Supply Chains and Markets - Antony Lewis, Mike McCoy, Shri Sreekanth G.B., Peter Nichols (nutrition)
- Environment and Climate - Johann Bell (SPC, CI), Ming-An Lee (IO climate)
- Biology - Johann Bell (SPC, CI), Simon Nicol (SPC), Bruno Leroy (SPC)
PHOTOGRAPHS AND GRAPHICS
- Secretariat for the Pacific Community
- Johann Bell, SPC
- International Seafood Sustainability Foundation (ISSF)
- David Itano, ISSF, personal
- Food and Agriculture Organization (FAO) Fisheries and Aquaculture Department (figures, maps)
- Antony Lewis
- Shri Sreekanth G.B.
- Warren Scomi, SPC
- Gabriel Reygondeau, Institut de Recherche pour le Developpement (IRD)
- Wikimedia Commons
FUNDING AND SUPPORT
Funding to prepare the yellowfin tuna profiles was provided by the International Seafood Sustainability Foundation (iss-foundation.org), the Asian Fisheries Society (www.asianfisheriessociety.org), and the personal time of Johann Bell. In-kind support has been provided by the host organizations of those who provided information and reviewed drafts.