The sub-order Scombroidei is comprises are composed of tuna (or true tuna), billfish, swordfish and other tuna-like species ranging mostly throughout the tropical and temperate zones of the world. Many species are extremely valuable commercially. Top quality northern and southern bluefin tuna for sashimi (raw fish) reaches 200 US dollars per kilogram. Many species are extensively used for canning. Due to spectacular fighting ability, some species, especially billfishes, are among the world's most sought-after gamefish. The demand for tuna and tuna-like species is expected to continue to increase in the future while most traditional target species are already fully or overexploited.
The tuna (Thunnini) comprises 13 species and 4 genera: Auxis, Euthynnus, Katsuwonus, and Thunnus. The most commercially valuable Tuna species belong to the genus Thunnus. The northern bluefin tuna (Thunnus thynnus) exist in the Pacific and Atlantic oceans, from 70° N to 0° N (See map). The southern bluefin tuna (T. maccoyii) is found in the Atlantic and Pacific oceans from 10° S to 60° S. The bigeye tuna (T. obesus), yellowfin tuna (T. albacares), and albacore (T. alalunga) are found all over the three oceans between 40-55° N and 40-45° S. The skipjack (Katsuwonus pelamis), of relatively lower value, is also distributed in the three oceans from 50° -60° N to 50° S. The above species are usually referred to as the principal market tuna species. They can undertake long range migrations (although skipjack and yellowfin tunas may do so to a lesser extent) and are considered as highly migratory by the Law of the Sea. Under heavy exploitation, however, it has been argued that only a minor part of the population might get a chance to migrate, especially for skipjack and yellowfin.
Map 6: Distribution of Northern and Southern Bluefin tuna and related fisheries (from Bartoo, 1987. Courtesy US-NMFS)
| Distribution of Northern and Southern Bluefin tuna and related fisheries (Legend: yellow = longline fisheries; pink= surface fisheries) |
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Map 7: Distribution of Bigeye tuna and related fisheries (from Bartoo, 1987. Courtesy US-NMFS)
| Distribution of Bigeye tuna and related fisheries (Legend: yellow = longline fisheries; pink= surface fisheries) |
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Map 8: Distribution of Yellowfin tuna and related fisheries fisheries (from Bartoo, 1987. Courtesy US-NMFS)
| Distribution of Yellowfin tuna and related fisheries (Legend: yellow = longline fisheries; pink= surface fisheries) |
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Map 9: Distribution of Albacore tuna and related fisheries (from Bartoo, 1987. Courtesy US-NMFS)
| Distribution of Albacore and related fisheries (Legend: yellow = longline fisheries; pink= surface fisheries) |
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Map 10: Distribution of Skipjack tuna and related fisheries (from Bartoo, 1987. Courtesy US-NMFS)
| Distribution of Skipjack and related fisheries (Legend: yellow = longline fisheries) |
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Two other oceanic species of lower value occur in the Southern Ocean with a circumpolar distribution between 15° S and 50° S: the slender tuna (Allothunnus fallai) and the butterfly kingfish (Gasterochisma melampus). Despite their lower value they represent a significant potential and are now caught as by-catch in the Japanese southern bluefin fishery.
The billfish (Istiophoridae) includes marlins (Makaira spp.), sailfish (Istiophorus spp.), and spearfish (Tetrapturus spp.). The swordfish (Xiphiidae) includes only one species (Xiphias gladius). With the exception of two spearfish, all billfish and swordfish species have very wide geographical distribution, but not necessarily do all species occur in all the oceans. All the billfish and swordfish species are excellent sea food and also extremely valuable for game fishing (Map).
Map 11: Distribution of Marlins and related fisheries
| Distribution of Marlins and related fisheries (Legend: yellow = longline fisheries; pink= surface fisheries) |
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Other important species are of a more neritic character, living closer to shelves, around islands and archipelagos. In this category are found less commercially valuable species of the Thunnus genus such as the longtail tuna (T. tongol) and blackfin tuna (T. atlanticus). The first species occurs in the eastern Indian Ocean, in Southeast Asia, and Australia (20° N to 35-40° S). The second species is encountered in the western Atlantic (40 ° N to 25° S). Other tuna-like species of importance to fisheries include Acanthocybium solandri (Wahoo), Auxis spp. (bullet and frigate tunas), Euthynnus spp. (kawakawa, black skipjack and little tunny), Cybiosarda, Orcynopsis, Sarda (bonito), and Scomberomorus spp. (Spanish and king mackerels, seerfish, sierra).
Tuna and tuna-like species are commercially caught all over the world, either close to the surface using pole-and-line and purse-seines (Map) or in deep waters with longlines (Map). The first two methods are used for fish found close to the water surface (e.g., skipjack and relatively small yellowfin, albacore and northern and southern bluefin tuna), whereas the last method aims at fish being deeper in the sea (e.g., large northern and southern bluefin tuna, bigeye tuna, yellowfin, albacore, billfish and swordfish). The last two species are taken mostly as by-catch. The other gears used are troll lines, hand-lines, driftnets, traps and harpoons. Natural or artificial fish aggregating devices (FADs) are often used in conjunction with purse-seining or hand-lining.
Map 12: Distribution of surface fisheries for tuna (pole-and-line and purse seining)
| Distribution of surface fisheries for tuna (pole-and-line and purse seining) |
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Map 13: Distribution of deep-sea fishing for tuna (long-lining)
| Distribution of deep-sea fishing for tuna (long-lining) |
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1 Source: Garcia S.M. and J. Majkowski (1990): The state of high seas resources. In: Kurobayash T.. And E.L. Miles (Eds.). The law of the sea in the 1990s: a framework for further international cooperation . Law of the Sea Institute. Honolulu, Hawai