goback to main page

FAO Fisheries Circular No. 920 FIRM/C920

Rome, 1997

ISSN 0429-9329

Marine Resources Service,
Fishery Resources Division,
Fisheries Department,
FAO, Rome, Italy




The sub-order Scombroidei is usually referred to as tuna and tuna-like species, composed of tunas (sometimes referred to as true tunas), billfish, swordfish and other tuna-like species.

The tunas (Thunnini) include the most economically important species referred to as principal market tuna species because of their global economic importance and their international trade for canning and sashimi (raw fish is regarded as a delicacy in Japan and recently, in some other countries). In fact, the anatomy of tunas seems to have been purpose-designed for canning and loining. The tunas are sub-classified into four genera (Thunnus, Euthynnus, Katsuwonus and Auxis) with thirteen species all together.

Figure C1.1
Figure C1.2
Figure C1.3
From genera Thunnus, the principal market tunas are albacore (T. alalunga), bigeye tuna (T. obesus), northern and southern bluefin tuna (T. thynnus and T. maccoyii, respectively) and yellowfin tuna (T. albacares). Skipjack tuna (Katsuwonus pelamis) is the sixth principal market tuna species. They are all oceanic, capable of long migrations or movements, and constitute one or two stocks in each ocean. The global distribution and main fishing areas of these six main species are shown on maps in figures C1.1, C1.2, C1.3, C1.4 and C1.5 respectively large, good quality, fatty individuals of bluefin sold by fishermen for sashimi can reach prices sometimes even above US$ 200 per kg if they are properly handled after catching. Bigeye can also be well priced on the sashimi markets. Yellowfin are also very popular (over US$ 2 per kg) for sashimi, but their prices are much lower. For canning, albacore get the best prices due to its white meat, followed by yellowfin and skipjack (even well below US$ 1 per kg).

Figure C1.4 Figure C1.5
figure figure The relatively low prices of canning quality fish are compensated by very large catches, especially in the case of skipjack and yellowfin. Longtail tuna (T. tonggol) is another species of tuna that is becoming increasingly important for canning and is a subject of substantial international trade. The consumption of tuna and tuna-like species in forms different from canned products and sashimi is increasing.

The other tuna species are more neritic (living in water masses over the continental shelf). They include blackfin tuna (T. atlanticus), black skipjack (E. lineatus), kawakawa (E. affinis), little tunny (E.alletteratus) and bullet and frigate tuna (A. rochei and A. thazard, respectively).

The billfishes (Istiophoridae) include marlins (Makaira spp.), sailfish (Istiophorus spp.) and spearfish (Tetrapturus spp.). The swordfish include only one species (Xiphias gladius). With the exception of two spearfishes, all billfishes and swordfish have very wide geographical distributions but not all the species necessarily occur in all oceans.

Billfishes are mostly caught by longliners as by-catches and by sport fishermen who greatly value them. Swordfish are also targeted in certain regions. Other important tuna-like species include slender tuna (Allothunnus fallai), butterfly kingfish (Gasterochisma melampus), wahoo (Acanthocybium solandri), bonitos (Cybiosarda, Orcynopsis, Sarda), Spanish and king mackerels, seerfish and sierra (Scomberomorus step.). They represent a significant catch potential, especially for developing countries, and are now being caught mostly by artisanal and recreational fisheries. Slender tuna and butterfly kingfish (with a circumpolar distribution in the Southern Ocean) are now mostly caught as by-catches of the Japanese longline fishery targeting southern bluefin tuna. Most of the other species mentioned in this paragraph are shared by two or more countries and their stocks are likely to straddle across the 200-mile limit.

From the tuna and tuna-like species, the principal tuna market species, billfishes, swordfish, blackfin tuna, bullet and frigate tuna, little tunny and kawakawa, are classified according to the 1982 UN Convention on the Law of the Sea as highly migratory, regardless of the fact that some of them are neritic in distribution. Black skipjack, for example, is probably more oceanic than little tunny and kawakawa.


Tuna and tuna-like species are mostly caught with purse-seine, longline and pole-and-line all over the oceans (see in figures C1.1, C1.2, C1.3, C1.4 and C1.5). The purse-seine and pole-and-line methods are used to catch fish found close to the surface (e.g. skipjack and relatively small individuals of yellowfin, albacore and northern and southern bluefin tuna), whereas the longline method targets fish found at greater depths (e.g. large individuals of northern and southern bluefin tuna, bigeye tuna, yellowfin, albacore, billfish and swordfish). Billfish and swordfish are taken mostly as by-catches, though there are fisheries targeting swordfish. Most purse-seine and pole-and-line catches are canned, while longline catches, with the exception of those of albacore, are mainly sold on the sashimi market to be consumed raw, essentially in Japan. Other gear used are troll lines, handlines, driftnets, traps and harpoons. Natural or artificial fish aggregating devices (FADS) are often used in conjunction with purse-seining or hand-lining. Information on fishing vessels, flags and techniques by area are given in Table C1.1.

Table C1.1. Industrial tuna fisheries tuna wholly or partially on the high seas

Area Gear Principal flag Target species
N.E. Pacific troll USA, Canada albacore
S.E. Pacific longline Japan, Rep. of Korea, and
Taiwan (Province of China)
bigeye, albacore and yellowfin
E.C. Pacific purse seine Vanuatu, Venezuela, Mexico
and Panama
yellowfin and skipjack
W.C. & S.
longline Rep. of Korea, Taiwan
(Province of China) and
albacore, yellowfin and bigeye
  pole and
Japan skipjack
purse seine Japan, Taiwan (Province of
China), Rep. of Korea, USA,
Indonesia and Philippines
skipjack and yellowfin
E. Indian longline Japan, Taiwan (Province of
China) and Rep. of Korea
bluefin, bigeye and yellowfin
W.C. Indian purse seine France, Spain and Japan skipjack and yellowfin
  longline Taiwan (Province of China),
Rep. of Korea and Japan
bigeye and yellowfin
E. Atlantic purse seine France and Spain skipjack and yellowfin
  longline Japan, Rep. of Korea and
Taiwan (Province of China)
bluefin, bigeye, yellowfin
and albacore
C.W. Atlantic longline Japan bluefin

The tuna fisheries, especially those of distant water fishing nations (DWFN) are very dynamic. For example, in the early 1980s, many French and Spanish purse-seiners from the Atlantic shifted to the Indian Ocean, contributing to the doubling of the Indian Ocean catch in the 1980s. Some of these vessels have now moved back to the Atlantic.

Another example of the dynamic changes of which the industrial tuna fleets are capable is the cessation of operation of most US purse-seiners in the eastern Pacific because of incidental catches of dolphins. Some of these vessels from the eastern Pacific have moved into the western part of that Ocean. The Republic of Korea and Taiwan (Province of China) have also started substantial purse seine operations in the western Pacific.

More recently, small-scale longlining for high-quality fish for the sashimi market has become a frequently used method by vessels from China and Taiwan (Province of China), as well as by other developing nations. This phenomena is part of a more general trend of rapidly increasing importance of developing coastal countries (including island countries of the Indian Ocean and the Pacific) in tuna fishing. This results from the purchase of purse seiners and from the intensification of artisanal fisheries. Their catches may be still under-estimated, despite the fact that the rate of non reporting of catches in developing countries is being reduced.

The use of pole-and-line and large-scale longline methods has been generally declining, while purse seining is becoming more popular. This has resulted in increased catches of skipjack and of small to medium yellowfin, while catches of large yellowfin and the other principal tuna market species have remained relatively stable.


Figure C1.6
figure The global production of the principal tuna market species has tended to continuously increase, from below 0.5 million tons in the early 1950s to 3.1 million tons in 1994, the last year for which data are currently held by FAO (see Fig. C1.6). The increase during the last ten years for which the data are available was about 44 %. Historically, the largest proportion (about 64 % now) of principal market tuna species has been taken from the Pacific, with the Atlantic being the second largest provider of catch till the mid-1980s, when it was overtaken by the Indian Ocean, which now yields about 20% of the global tuna production. This resulted, at least partially, from the shift of some French and Spanish purse-seiners in the early 1980s from the Atlantic to the Indian Ocean.

Skipjack tuna accounts for the greatest proportion of the world catch of tunas (see Fig. C1.6). In 1994, nearly 1.5 million tons of skipjack were caught, representing about half of the catch of all principal tunas, and almost all is sold for canning. In the early 1980s, skipjack catches increased sharply as a result of expansion of fishing effort into the western tropical Pacific and the western Indian Ocean. The largest increases, in terms of tonnage, have been in the Pacific, especially the western tropical Pacific, followed by the western Indian Ocean and the eastern Atlantic.

Yellowfin is commercially the second most important species of tuna and, in 1994, accounted for about 1.1 million tons or 35% of the total catch (see Fig. C1.6). Yellowfin is the premier species for canning, but more and more of the catch is being sold in fresh fish markets (also some frozen fish), particularly in the United States and Latin America. Catches in the Atlantic have shown very little change over the last two decades, whereas in the Indian Ocean they increased due to the reasons just mentioned. In the Pacific, catches of yellowfin, like skipjack, increased consistently until 1976, when they stabilized. They did not rise again until the early 1980s, when large fleets of purse-seine vessels began to fish in the western tropical Pacific.

Figure C1.7
figure The third most important species in terms of catch volume is bigeye tuna (see Figure C1.7), which is similar in appearance to yellowfin. However, unlike yellowfin, bigeye tunas are primarily deep-water species, spending most of their lives in cold waters below the upper mixed layer of the ocean. Again, unlike yellowfin, they are captured mainly by longline gear. Their high fat content (for insulation from the cold water) make them desired for the Japanese sashimi market. The rapid increase in catches in the mid-1970s resulted from modifications of longline gear which enabled it to be used in much deeper water than previously, leading to the substantial increases in the catches.

World production of albacore over the past three decades has been fluctuating around 200 000 t (Fig. C1.7). In the Pacific, where most albacore are taken, catches have been widely fluctuating. In the last decade, large catches of small albacore were made by drift-net fisheries on the high seas in the southwestern and northeastern Pacific. Since the termination of these fisheries, the overall albacore catch in the Pacific has declined.

Northern and southern bluefin tuna contribute relatively little in terms of volume to the total catch of principal tunas (Fig. C1.7). In the 1980s, the catch of the first species declined significantly, before increasing in the 1990s due to higher reported catches in the Mediterranean Sea. The catches of southern bluefin decreased significantly in the 1980s, stabilizing more recently.

About 71 % of the skipjack, 63 % of the yellowfin, 42 % of the bigeye and 60 % of albacore were taken in the Pacific in 1994. Of the remaining catches of skipjack in 1994, the Indian Ocean catch was 1.5 times higher than that in the Atlantic, and the yellowfin catch in the Indian Ocean in 1994 was 1.7 times higher than that in the Atlantic. The 1994 bigeye and albacore catches in the Atlantic were 1.6 and 3.8 times higher than those in the Indian Ocean. The northern bluefin tuna is taken mainly in the Atlantic but also in the Pacific. The southern bluefin tuna is taken mainly in the Indian and Pacific Oceans.

Approximately 62 % of the 1994 catch of the principal market tuna species was taken by the traditional tuna fishing countries: Japan (625 944 t), Taiwan (Province of China) (353 754 t), USA (253 408 t), ), Spain (245 096 t), Republic of Korea (241 884 t) and France (193 543 t). In addition to traditional tuna fishing countries, Indonesia, the Philippines, Mexico, Maldives, Venezuela, Ecuador, Ghana, Solomon Islands, Sri Lanka, Brazil, Colombia, Panama, Iran, Oman, Pakistan, Portugal, Australia, New Zealand, China, India, Fiji, Comoros and Mauritius (ordered according to the magnitude of 1994 catches) contributed most to the 1994 catch. In fact, 1994 catches by Philippines exceeded those of France, and the 1994 Indonesian catches were not much smaller than those of France. This reflects a more general trend towards greater catch increases by non-traditional tuna fishing countries (mostly developing countries) than by traditional tuna fishing countries. The 1994 catches of each of the remaining tuna fishing countries were less than 5 000 t.

Particularly off Southeast Asia, in both the Indian and Pacific Oceans, tuna fisheries are growing, including the artisanal sector catching mostly small tunas, skipjack and yellowfin. This sector's growth was also significant in the entire Indian Ocean.

The catch of tunas and tuna-like species other than the principal tuna market species, also increased significantly from about 0.5 million tons in the early 1970s to 1.4 million tons in 1994 (Figure C1.6). Only about 11% of this catch is composed of billfishes and swordfish, taken mainly in the Pacific and Atlantic. In terms of volume of catches, according to FAO's statistics, the most important species of tuna and tuna-like species other the principal tuna market species are: Japanese Spanish mackerel (228 000 t), frigate and bullet tuna (212 000 t), kawakawa (179 000 t), narrow-barred Spanish mackerel (120 000 t), longtail tuna (101 000 t), swordfish (83 000 t), eastern Pacific bonito (57 000 t), seerfish ( 52 000 t), Indo-Pacific king mackerel (48 000 t) and Indo-Pacific blue marlin (28 000 t) .


Information on the status of tuna and tuna-like stocks is given in Table XVII. When considering this information, uncertainties in stock assessment need to be taken into account. The data on principal market tuna species are generally much better than for other species of tuna and tuna-like species because they have been studied for many years and more research effort is devoted to them. However, even for these species, significant uncertainties exist in the basic biological knowledge. For example, recent research indicates that southern bluefin tuna, one of the best studied tunas may live much longer than expected. On the data side, officially reported catches of northern bluefin tuna, another species in a critical state, may be significantly smaller than those actually taken, according to information from a special statistical programme recently introduced by the International Commission for the Conservation of Atlantic Tunas (ICCAT).

Generally, the principal market tuna species are highly resistant to exploitation due to very high fecundity, wide geographical distributions and adaptation for opportunistic behavior. Their superbly efficient metabolic system includes a circulatory system that allows them to retain or dissipate heat as required for peak biological performance and efficiency. The dynamics of tuna populations make them highly productive. With proper management, they are capable of sustaining very high yields relative to their biomass.

However, the species most desired for the sashimi market are heavily exploited, some being overexploited or even depleted. The temperate, long-lived species of bluefin are prone to overexploitation and only recover some time after reducing fishing effort. However, concerns over heavy exploitation are raised even for bigeye, another species highly desired for sashimi, which has a shorter life span. Significant uncertainties in the status of many billfish stocks also represent a serious conservation problem.

Short-lived tropical tuna species like skipjack and yellowfin are the most resistant to exploitation and still have potential for significant increases in their catches in some areas. Swordfish in the Indian Ocean may also have such a potential. The status of other tuna and tuna-like species is highly uncertain or simply unknown. Therefore, the intensification of their exploitation raises a concern.


Some States whose vessels fish tuna and tuna-like species cooperate regarding conservation and fisheries management within the framework of the Commission for the Conservation of Southern Bluefin Tuna (CCSBT), the Inter-American Tropical Tuna Commission (IATTC) in the eastern Pacific, the International Commission for the Conservation of Atlantic Tunas (ICCAT) and the Indian Ocean Tuna Commission (IOTC). CCCSBT, IATTC and ICCAT facilitate data collection, processing and stock assessment for their areas of competence, and in some cases may also cover adjacent areas if fish stocks are found to have an extended distribution. Many countries fishing tuna in the Mediterranean Sea (which is included in the area of competence of ICCAT) are not members of ICCAT but of the General Fisheries Council for the Mediterranean (GFCM). Therefore, ICCAT closely collaborates with GFCM regarding tuna and tuna-like species.

After becoming operational, IOTC will also facilitate the data collection and processing and the stock assessment for the Indian Ocean, taking over the technical responsibilities of the FAO/UNDP Indo-Pacific Tuna Programme (IPTP). With this transition underway, IPTP has already transferred the responsibility for data collection, processing and dissemination and other research for tuna and tuna-like species in the Pacific off Southeast Asia to the Southeast Asian Fishery Development Center (SEAFDEC).

The South Pacific Commission (SPC) fulfills similar technical functions, but its responsibilities do not extend to fisheries management. In the Eastern Pacific there is an established framework (i.e. IATTC) for tuna conservation and fisheries management. The South Pacific Forum Fisheries Agency (FFA) is involved in regulating access of tuna vessels of Distant-Water Fishing Nations (DWFN) in their area of competence. However, its Members are limited to South Pacific island nations, excluding DWFN's. Discussions are underway to create a tuna fishery body in the western and central Pacific. The potential problem with such a body is that the distribution of stocks of tuna and tuna-like species in the western and central Pacific is likely to extend beyond its potential area of competence. The establishment of a body covering the entire Pacific might be preferable from the technical point of view.

Generally, ocean-wide areas of competence of tuna fishery bodies seem appropriate, taking into account that tuna stocks with the exception of southern bluefin tuna are limited to one ocean. However, industrial tuna fleets are highly mobile and the principal tuna market species are intensively traded on the global scale. Also, tuna research, conservation and management problems are similar in all oceans. Therefore, there is a need for exchange of information and collaboration on the global scale regarding tuna fisheries, as well as some other species. An important example of such an collaboration is the formulation, in 1995, of the Agreement for the Implementation of the Provisions of the UN Convention on the Law of the Sea of 10 December 1982 Relating to the Conservation and Management of Straddling Fish Stocks and Highly Migratory Fish Stocks. The United Nations (UN) facilitated the conclusion of this Agreement, but the Food and Agriculture Organization (FAO), UN's specialized technical agency with responsibilities for various fisheries matters on the global scale, was actively involved, with technical advice, in reaching the Agreement.

After its ratification, the 1995 UN Agreement will become a new legal basis for conservation and fisheries management of tuna and tuna-like species, supplementing the 1982 UN Convention on the Law of the Sea. In 1995, the Code of Conduct of Responsible Fisheries was completed within the framework of FAO. Although not legally-binding, the Code provides a norm for all fisheries and related activities. The Agreement and the Code pose new requirements for conservation, fisheries management, technology and research for tuna and tuna-like species, which are likely to affect various sectors of the tuna industry (see below).

At present, the prime conservation problem for tuna and tuna-like species is the depletion of stocks of bluefin tuna. This concern has even been discussed outside of the framework of regional tuna institutions (i.e., within the context of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES)). Generally, for many tuna fishing fleets, there is no control on their capacity or actual fishing effort, nor their catches, creating a potentially serious problem. Despite this, serious overfishing has been largely avoided due to reduction in economic incentives, the lowering of prices as markets become saturated, and still existing possibilities for expansion on some species.

The overall yield from tuna and tuna-like species depends on the combination of fishing techniques as well as the overall fishing effort because different methods have differing abilities to target various age groups. Improvements in the long-term yield might be achieved in some cases (e.g. for albacore and yellowfin in the Atlantic and after stock recovery, the northern and southern bluefin tuna) by protecting small or immature fish and targeting older age-groups more precisely. Problems occur with compliance to the present size regulations (e.g., within the framework of ICCAT, especially for northern bluefin tuna in the Mediterranean Sea). Protection of small size fish may be ineffective for stocks with high natural mortality like skipjack, or may be locally ineffective in areas of intense migration.

Bio-economic interactions among fisheries need to be scientifically addressed for the resolution of fisheries management problems. Coordinated effort in this direction is being made. For example, FAO has initiated a Japanese-funded Trust Fund project: "Cooperative Research on Interactions of Pacific Tuna Fisheries". In 1995, the project sponsored the Second FAO Expert Consultation on Interactions of Pacific Tuna Fisheries.

Dolphins caught incidentally by purse-seiners targeting yellowfin in the eastern Pacific have been another area of concern. Research, management restrictions and monitoring have resulted in significantly reduced incidental mortality of dolphins. Many canneries have stopped accepting tuna that are caught with dolphins with implications for fishing operations in the eastern Pacific. The need to protect dolphins in the eastern Pacific may also lead to smaller catches of large yellowfin as these are usually associated with dolphins, resulting in sub-optimal tuna fishing.


Extrapolating the recent increases to catches of principal tuna market species, the annual catch of these species might increase slightly to over 4 million tons (i.e., by 875,000 t or 27 %) by year 2000. From the biological point of view, an annual catch of 3.9 million tons might be sustainable (coming from possible increases in catches of skipjack and yellowfin). That catch might require about 100 purse seiners (the most important fishing vessels from the catch volume point of view) in addition to the 450 large purse seiners which are currently catching about 4 500 to 5 000 t per year each. Even with recent rises in prices of canning-quality tuna, such an increase is unlikely. According to one prognosis, is it more realistic to expect an increase in the future to an annual catch of 3.5 million tons

Another factor affecting future catches will be the adoption and implementation of the provisions of:

(a) the 1995 UN Agreement for the Implementation of the Provisions of the UN Convention on the Law of the Sea of 10 December 19982 Relating to the Conservation and Management of Straddling Fish Stocks and Highly Migratory Fish Stocks, and
(b) the Code of Conduct of Responsible Fisheries.

These are likely to affect the traditional image of unrestricted fishing on the high-seas. If properly implemented, the Agreement and the Code may reduce the rate of catch increase or even the magnitude of present actual catches in the short term. However, in the long term,

they may result in larger sustainable catches due to better conservation and more rational management of tuna fisheries.