FAO/SIDP Species Identification Sheets Thunnus obesus (Lowe, 1839) FAO Names EN - Bigeye tuna; FR - Thon obèse(=Patudo); SP - Patudo. Scientific Name with Reference Thynnus obesus Lowe, 1839, Proc.Zool.Soc.London, 7:78 (Madeira) Synonyms Thynnus sibi Temminck & Schlegel, 1844; Orcynus sibi Kitahara, 1897; Germo sibi Jordan & Snyder, 1901; Thunnus mebachi Kishinouye 1915; Parathunnus mebachi Kishinouye, 1923; Parathunnus sibi Jordan & Hubbs, 1925; Parathunnus obesus Jordan & Evermann, 1926; Germo obesus Fowler, 1936; Thunnus obesus Fraser-Brunner, 1950; Neothunnus obesus Postel, 1950; Parathunnus obesus mebachi Jones & Silas, 1961; Thunnus obesus sibi Jones & Silas, 1963a; Thunnus obesus mebachi Jones & Silas, 1964. Diagnostic Features A large species, deepest near middle of first dorsal fin base. Gillrakers 23 to 31 on first arch. Pectoral fins moderately long (22 to 31% of fork length) in large individuals (over 110 cm fork length), but very long (as long as in T. alalunga) in smaller individuals (though in fish shorter than 40 cm they may be very short).In fish longer than 30 cm, ventral surface of liver striated. Swimbladder present. Vertebrae 18 precaudal plus 21 caudal. Colour: lower sides and belly whitish; a lateral iridescent blue band runs along sides in live specimens; first dorsal fin deep yellow, second dorsal and anal fins light yellow, finlets bright yellow edged with black. Geographical Distribution Worldwide in tropical and subtropical waters of the Atlantic, Indian and Pacific oceans, but absent from the Mediterranean. Habitat and Biology Epipelagic and mesopelagic in oceanic waters, occurring from the surface to about 250 m depth. Temperature and thermocline depth seem to be the main environmental factors governing the vertical and horizontal distribution of bigeye tuna. Water temperatures in which the species has been found range from 13° to 29° C, but the optimum range lies between 17° and 22° C. This coincides with the temperature range of the permanent thermocline. In fact, in the tropical western and central Pacific, major concentrations of T. obesus are in occurrence of the species is closely related to seasonal and climatic changes in surface temperature and thermocline Juveniles and small adults of bigeye tuna school at the surface in mono-species groups or together with yellowfin tuna and/or skipjack. Schools may be associated with floating objects. In the eastern Pacific some spawning is recorded between 10° N and 10° S throughout the year, with a peak from April through September in the northern hemisphere and between January and March in the southern hemisphere. Kume (1967) found a correlation between the occurrence of sexually inactive bigeye tuna and a decrease of surface temperature below 23° or 24° C. Mature fish spawn at least twice a year; the number of eggs per spawning has been estimated at 2.9 million to 6.3 million. The food spectrum of bigeye tuna covers a variety of fish species, cephalopods and crustaceans, thus not diverging significantly from that of other similar-sized tunas. Feeding occurs in daytime as well as at night. The main predators are large billfish and toothed whales. Size Maximum fork length over 200 cm; common to 180 cm (corresponding to an age of at least 3 years). The all-tackle angling record for the Pacific is a 197.3 kg fish from off Cabo Blanco, Peru in 1957. This fish was 236 cm long but it was not specified whether this pertained to fork length or total length. For the Atlantic, the all-tackle angling record is a 170.3 kg fish with a fork length of 206 cm taken off Ocean City, Maryland, USA in 1977. Maturity seems to be attained at 100 to 130 cm fork length in the eastern Pacific and in the Indian Ocean, and at about 130 cm in the central Pacific. Interest to Fisheries Total production for Thunnus obesus. Total capture for Thunnus obesus. Catch statistics are reported by 17 countries for 14 fishing areas. Yearly catches of more than 10 000 metric tons are taken in Fishing Areas 34, 51, 61, 71) and 77 with more than two thirds of the total taken in the Pacific up to 1980. Among the countries reporting bigeye tuna catches Japan ranks first, followed by the Republic of Korea with much lower landings. The world catch increased from about 164 000 t in 1974 to 201 000 metric tons in 1980 reaching a peak of 214 000 t in 1977 (FAO, 1981). For 1981 a decrease to about 167 000 t was estimated (FAO, 1983). In the Indian Ocean, the bigeye tuna fishery was dominated by Japanese fleets up to the end of the sixties, but subsequently operations of vessels from the Republic of Korea became more important, and have accounted for more than 60% of the catch in the late seventies. The most important fishing gear, at least in the Pacific, are longlines, which comprise some 400 'baskets' (consisting of 5 branch lines, each with a baited hook) extending over up to 130 km. Species commonly used as bait include (frozen) Pacific saury (Cololabis saira), chub mackerel (Scomber japonicus), jack mackerel (Trachurus) and squid. Day- and night-time operations are common throughout the year, but there are seasonal variations in apparent abundance reflected in changes of fishing effort. In the seventies, deep longlines employing between 10 and 15 branch lines per basket were introduced. This new type of gear is theoretically capable of fishing down to 300 m depth, as compared to the usual 170 m reached by traditional longline gear. Catch rates increased for about 3 years and then declined to previous levels again, suggesting that only a portion of the bigeye resources are exploited. Bigeye tuna is exploited in increasing quantities as associated catch of the spring and summer pole-and-line fishery in the northwestern Pacific, and of the purse seine fishery in the eastern Pacific, both directed primarily at skipjack and yellowfin tuna. In Japan, its meat is highly priced and processed into sashimi in substitution for bluefin tuna. The total catch reported for this species to FAO for 1999 was 399 628 t. The countries with the largest catches were Japan (79 742 t) and Other nei (70 597 t). Local Names ARGENTINA : Ojos grandes, Patudo. BRAZIL : Albacora bandolim. CHILE : Atún de ojo grande. COLOMBIA : Atún. CUBA : Ojigrande. ECUADOR : Albacora, Atún ojo grande. FRANCE : Patudo, Thon aux grands yeux, Thon obèse, Thon ventru. GERMANY : Grossaugenthun. JAPAN : Bachi, Daruma, Darumeji, Mebachi, Mebuto. MARTINIQUE : Patudo, Thon obèse. NETHERLANDS : Storje, Grootoogtonijn. Aáhi o'opa, Aáhi tatumu. PERU : Atún ojo grande, Patudo;. POLAND : Opastun. PORTUGAL : Albacora-ôlho-grande, Atum patudo. SENEGAL : Thon obèse. SOUTH AFRICA : Bigeye tuna, Grootoog-tuna. SPAIN : Patudo. Bigeye tuna. USA : Bigeye tuna. Bolsheglazyj tunets. VENEZUELA : Atún ojo gordo. YUGOSLAVIA : Zutoperajni tunj. Literature Reference Mimura et al . (1936a, Indian Ocean); Alverson & Peterson (1963, Pacific); Fischer & Whitehead, eds (1974, Species identification Sheets, Eastern Indian Ocean/Western Central Pacific); Collette (1978, Species Identification Sheets, Western Central Atlantic; 1981, Species Identification Sheets, Eastern Central Atlantic); Calkins (1980, Pacific). Source of Information Collette, B.B. & C.E. Nauen, 1983. FAO species catalogue. Vol. 2. Scombrids of the world. An annotated and illustrated catalogue of tunas, mackerels, bonitos and related species known to date. FAO Fish. Synop., (125)Vol.2:137 p. The "Interest to Fisheries" section has been updated according to recent FAO fishery statistics.