click for previous page SCOMBR Thun 1 1983 FAO SPECIES IDENTIFICATION SHEETS FAMILY: SCOMBRIDAE FISHING AREA 51 (W. Indian Ocean) Thunnus alalunga (Bonnaterre, 1788) OTHER SCIENTIFIC NAMES STILL IN USE: Germo alalunga (Bonnaterre, 1788) Thunnus germo (Lacèpede, 1800) VERNACULAR NAMES: FAO: En – Albacore Fr – Germon Sp – Atún blanco (=Albacora) NATIONAL: DISTINCTIVE CHARACTERS: A large species with an elongate, fusiform body, deepest at a more pelvic fin posterior point than in other tunas (at, or only slightly anterior to, second dorsal fin rather than near middle of first dorsal fin base). Eyes rather large; gillrakers 25 to 31 on first arch. Two dorsal fins separated only by a narrow interspace, the second clearly lower than the first and followed by 7 to 9 finlets; pectoral fins remarkably long, usually 30% of fork length or longer, reaching well beyond origin of second dorsal fin (usually up to second dorsal finlet); 2 flaps (interpelvic process) between pelvic fins; anal fin followed by 7 or 8 finlets. Small scales on body; corselet of larger scales developed but not very distinct. Caudal peduncle very slender, bearing on each side a strong interpelvic lateral keel between 2 smaller keels. Liver striated on ventral surface. process Swimbladder present. Colour: back metallic dark blue, lower sides and belly whitish; a faint lateral iridescent blue band runs along sides in live fish; first dorsal fin deep yellow, second dorsal and anal fins light yellow, anal finlets dark; posterior margin of caudal fin white. DISTINGUISHING CHARACTERS OF SIMILAR SPECIES OCCURRING IN THE AREA: All other species of Thunnus: pectoral fins shorter, never reaching beyond posterior end of second dorsal fin base in adults (however, young specimens of T. alalunga, less than 30 cm, have pectoral fins about equal in length to similar-sized specimens of T. albacares and T. obesus); body deepest more anteriorly (at level of first dorsal fin origin); no white margin to caudal fin. Further distinguishing characters of other species of Thunnus are the following: T. albacares: no striations on ventral sur- finlets yellow, face of liver, and belly frequently crossed by black-edged about 20 broken, nearly vertical striations; also, second dorsal and anal fins greatly elongate in large adults; dorsal and anal finlets yellow, with a narrow black margin. T. obesus: dorsal and anal finlets bright T. albacares yellow, with distinct black margins (entire finlets dark in T. alalunga). T. maccoyii: pectoral fins very short, finlets yellow, never reaching the space between dorsal fins; black-edged second dorsal fin reddish brown; more gillrakers (31 to 40; 25 to 31 in T. alalunga). T. tongol: lower sides and belly with colourless, elongated, oval spots arranged in hori- zontal rows; swimbladder absent, ventral surface of liver not striated. T. obesus liver T. albacares, T. alalunga T. tonggol SIZE: T. maccoyii Maximum: 120 cm fork length; common to 100 cm. GEOGRAPHICAL DISTRIBUTION AND BEHAVIOUR: A cosmopolitan species, often extending into cool waters. In the Indian Ocean its range extends in a broad band, about 10°N to 30°S. It is found from South Africa to about 508 off the East T. tonggol African coast through the Seychelles to off the southern coast of Sri Lanka. Oceanic, the young often in large schools; found below the thermocline, particularly larger individuals, or at tempera- tures of 17° to 21° C. Feeds on many kinds of organisms, particularly fishes, squids and crustaceans. FAO Species Synopses No. 66 (W. Atlantic), No. 77 (as G. alalunga, E. Atlantic) and No. 52 (as T. germo, Indo-Pacific), and No. 109 (Atlantic). PRESENT FISHING GROUNDS: Oceanic waters, throughout its range. CATCHES, FISHING GEAR AND FORMS OF UTILIZATION: The catch from Fishing Area 51 totalled about 3 300 t in 1981 Caught with purse seines, longlines; also by trolling. Marketed mainly canned or frozen. SCOMBR Thun 3 1983 FAO SPECIES IDENTIFICATION SHEETS FAMILY: SCOMBRIDAE FISHING AREA 51 (W. Indian Ocean) Thunnus albacares (Bonnaterre, 1788) OTHER SCIENTIFIC NAMES STILL IN USE : Neothunnus macropterus (Temminck & Schlegel, 1844) Neothunnus albacora (Lowe, 1839) Thynnus argentivittatus (Cuvier, 1831) VERNACULAR NAMES: FAO: En - Yellowfin tuna Fr - Albacore (= Thon albacore, Area 31) Sp - Rabil NATIONAL: DISTINCTIVE CHARACTERS: A large species with an elongate, fusiform body, slightly compressed pelvic fin from side to side. Gillrakers 26 to 34 on first arch. Two dorsal fins, separated only by a narrow interspace, the second followed by 8 to 10 finlets; anal fin followed by 7 to 10 finlets; 2 flaps (interpelvic process) between pelvic fins; large specimens have very long second dorsal and anal fins, becoming well over 20% of fork length; pectoral fins moderately long, usually reaching beyond second dorsal fin origin but not beyond end of its base, usually 22 to 31% of fork length. Body with very small scales; corselet of larger scales developed but not very distinct. Caudal peduncle very slender, bearing on each side a strong lateral keel between 2 smaller keels. No striations on ventral surface of liver. Swimbladder present. interpelvic process Colour: back metallic dark blue changing through yellow to silver on belly; belly frequently crossed by about 20 broken, nearly vertical lines; dorsal and anal fins, and dorsal and anal finlets, bright yellow, the finlets with a narrow black border. DISTINGUISHING CHARACTERS OF SIMILAR SPECIES OCCURRING IN THE AREA: Thunnus obesus: striations present on ventral surface of liver; dorsal and anal fins never elongate. In specimens of similar size, T. obesus is generally heavier, deeper, and has a larger eye. T. alalunga: pectoral fins much longer in adults (but not in young up to 30 cm), usually reaching to second dorsal finlet (usually 30% of fork length or more), greatest body depth near origins of second dorsal and anal fins instead of more ante- riorly; a narrow white posterior margin to caudal T. obesus fin; striations present on ventral surfaces of liver. T. maccoyii: pectoral fins shorter, never reaching to interspace between dorsal fins; liver ventrally striated; also, restricted to southernmost part of area. T. tonggol: lower sides and belly with colour- less, elongated, oval spots arranged in horizontal rows; swim bladder absent. T. alalunga liver T. alalunga T. obesus T. albacares T. maccoyii SIZE: T. maccoyii Maximum: 195 cm fork length; common to 150 cm. GEOGRAPHICAL DISTRIBUTION AND BEHAVIOUR: A pantropical species. Known from the entire area north of 30°S except for the Rea Sea and the "Gulf". Oceanic, above and below the thermocline. Schools by size, also with other species. Peak T. tonggol spawning occurs during summer, in batches. Feeds on a wide variety of fishes, crustaceans, and cephalopods. FAO Species Synopses No. 69 (W. Atlantic) and No. 59 (Pacific as T. (Neothunnus) albacares), No. 76 (E. Atlantic as Neothunnus albacora), and No. 53 (Indian Ocean as Neothunnus macropterus) PRESENT FISHING GROUNDS: Open waters, throughout its range. CATCHES, FISHING GEAR AND FORMS OF UTILIZATION: The catch reported from Fishing Area 51 totalled about 27 000 t in 1981. Caught mainly with longiines and purse seines. Marketed mainly canned or frozen. SCOMBR Thun 4 1983 FAO SPECIES IDENTIFICATION SHEETS FAMILY: SCOMBRIDAE FISHING AREA 51 (W. Indian Ocean) Thunnus maccoyii (Castelnau, 1872) OTHER SCIENTIFIC NAMES STILL IN USE: Thunnus thynnus maccoyii (Castelnau, 1872) VERNACULAR NAMES: FAO: En - Southern bluefin tuna. Fr - Thon rouge du Sud Sp - Atún del Sur NATIONAL: DISTINCTIVE CHARACTERS: A very large species with a fusiform and rounded body (nearly circular in pelvic fin cross-section), very robust in front. Two dorsal fins separated only by a narrow interspace, the second higher than the first; 8 to 10 finlets present behind the second dorsal and 7 to 9 behind the anal fin; pectoral fins very short, less than 80% of head length, never reaching the interspace between the dorsal fins; 2 separate flaps (interpelvic process) between the pelvic fins; a well-developed, although not particularly conspicuous corselet; very small scales on rest of body. Caudal peduncle slender, with a strong lateral keel between 2 small keels located at the bases of the caudal fin lobes. Ventral surface of liver striated. Swimbladder present. interpelvic Colour: back dark blue or black, lower sides and belly silvery white process with colourless transverse lines alternated with rows of colourless dots (the latter dominate in older fish), visible only in fresh specimens; first dorsal fin yellow or bluish; anal fin and finlets dusky yellow edged with black; lateral keel yellow in adults. DISTINGUISHING CHARACTERS OF SIMILAR SPECIES deepest part OCCURRING IN THE AREA: of body Other species of Thunnus: fewer gillrakers, at most 33 on first arch (31 to 40 in T. maccoyii); pectoral fins longer, more than 80% of head length (or 23% of fork length) and reaching at least to space between dorsal fins. Further distinguishing characters of these T. alalunga species are the following: T. alalunga: pectoral fin usually reaching nearly to second dorsal finlet; caudal fin with a distal white margin; body depth greatest more posteriorly, near origin of second dorsal and anal fins. T. albacares: ventral surface of liver without striations; dorsal and anal fins bright yellow and becoming very elongate in large speci- mens; dorsal and anal finlets bright yellow with black margins; body frequently crossed by about T. albacares 20 broken, nearly vertical lines. (large adult) T. tonggol: lower sides and belly with colour less elongated, oval spots arranged in hori- zontal rows; ventral surface of liver without striations; swimbladder absent. liver T. maccoyii T. albacares, T. maccoyii T. tonggol SIZE: Maximum: 2000 cm fork length; common to 160 cm. GEOGRAPHICAL DISTRIBUTION AND BEHAVIOUR: Present only in the southernmost part of the area. Found T. tonggol throughout the southern Ocean mainly between 30° and 20°S. A pelagic schooling species associated with the West Wind Drift across the Indian Ocean.