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Alopias pelagicus:   (click for more)

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Synonyms
Other Combinations:  Alopias vulpinus (not Bonnaterre, 1788).
FAO Names
En - Pelagic thresher, Fr - Renard pélagique, Sp - Zorro pelágico.
3Alpha Code: PTH     Taxonomic Code: 1060600602
Scientific Name with Original Description
Alopias pelagicus  Nakamura, 1935, Mem. Fac. Sci. Agric. Taihoku Imp. Univ. ,14(1): 2, 3, pl. 1, fig. 1. Syntypes: Three large individuals mentioned and measured, these 270, 285, and 330 cm TL, and a large female specimen illustrated but of uncertain size; also foetus 96.5 cm (Nakamura, ibid., 5, pl. 3), probably referable to Alopias vulpinus; all from Suô fish market, Taiwan (Province of China). Whereabouts of syntypes uncertain according to Eschmeyer (1998, Cat. Fish.: CD-ROM).
Diagnostic Features
fieldmarks: Long upper caudal lobe nearly as long as rest of shark, relatively small eyes, very narrow head with arched dorsal profile, straight broad-tipped 'oceanic' pectoral fins, first dorsal fin somewhat closer to pectoral-fin bases than pelvic-fin bases, very slender caudal-fin tip, body colour deep blue or grey above, white below, white colour of abdomen not extending over pectoral-fin bases.

Head narrow in dorsal and ventral views, with a convex, arched dorsolateral profile. Snout moderately long, conical. Eyes moderately large in adults but very large in newborn and foetuses, not expanded onto dorsal surface of head and without a vertical, binocular field of view; interorbital space broadly convex. Labial furrows absent.  Teeth very small, in 41 to 45/37 to 38 rows (total for both jaws 75 to 86 rows); posterior tooth rows 5 to 11; symphysial and intermediate tooth rows usually present.  Weak nuchal grooves present above branchial region.  Pectoral fins of "macroceanic" type with straight and very broad tips.  Claspers moderately slender and not whip-like.  First dorsal-fin midbase about equidistant between pectoral and pelvic-fin bases or closer to pectoral-fin bases. Caudal tip very slender with very narrow terminal lobe.  Ribs of monospondylous precaudal vertebrae fused ventrally to form a canal extending nearly to the occiput. Total vertebral count 453 to 477. Intestinal valve count 37 to 40.  Body deep blue to grey on upper surface with sides silvery and underside white, white colour of abdomen not extending over pectoral-fin bases; no white dot on upper pectoral-fin tips. 
Geographical Distribution

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Oceanic and wide-ranging in the Indo-Pacific. Indian Ocean: South Africa (KwaZulu-Natal), Red Sea, Gulf of Aden, Arabian Sea (off Somalia, between Oman and India, and off Pakistan), Australia (northwest Western Australia), Western North Pacific: China, Taiwan (Province of China), Japan (southeastern Honshu). Western South Pacific: New Caledonia, eastern Micronesia, Tahiti. Central Pacific: Hawaiian Islands, equatorial waters north of Howland and Baker, Phoenix and Palmyra Islands. Eastern Pacific: USA (California) and Mexico (Baja California, Gulf of California), equatorial waters northwest of French Polynesia, and off Galapagos Islands.
Habitat and Biology
Primarily an oceanic, epipelagic, circumtropical species, but sometimes caught near shore on beaches with a narrow continental shelf,ranging in depth from the surface to at least 152 m. Sometimes seen by divers near coral reefs, near dropoffs and in large lagoons, and on sea mounts.

A little-known, active, strong-swimming species, probably migratory but with movements little-known. In the eastern North Pacific there is a possible population centre off central Baja California, which tends to shift northward (along with other oceanic sharks) during strong El Niño events.Behaviour and sociobiology is poorly known. Michael (1993) has seen this species repeatedly leap (breach) out of the water.


Ovoviviparous, with uterine cannibalism as in other species of Alopias. Embryos subsist on their yolk-sacs up to about 12 cm, after which they become oophagous, feeding on unfertilized eggs. No evidence of adelphophagy (embryo-eating) was reported by Liu et al. (1999), who examined 233 embryos from 167 pregnant females. Litter size is two, with one foetus per uterus and with sex ratio 1:1. Gestation period uncertain because females give birth all year long without a definite birth season. Liu et al. suggest that the gestation period may be less than a year as with A. vulpinus, but because most adult females were pregnant throughout the year there may be an annual cycle with no resting period between pregnancies. Pupping may also occur in winter in the Gulf of Aden (R. Bonfil, pers. comm.).  This species presumably feeds on small fishes and squid but no details are known.

Vertebral growth rings are laid annually in vertebral centra; females mature at about 8 or 9 years old and males at about 6 to 9 years old, with up to 16 growth rings for females and 14 for males for a minimal age of 14 to 16 years old and a maximum age estimated from von Bertalanffy growth curves as 20 years for males and 29 years for females. Assuming birth of two young every year a female might produce about 40 young during her lifetime. This species has unusually large young, with the largest known foetus 43% of the length of the largest adult female. The large size of the young may help to reduce postnatal predation (presumably by other large sharks), but the relatively small size of the adults combined with the low fecundity imposed by large foetal size may in turn require annual breeding.
Size
Maximum total length at least 365 cm. Size at birth uncertain but presumably between about 130 and 160 cm and possibly up to 190 cm. The largest term foetus examined by Liu et al. (1999) off Taiwan (Province of China) was 158 cm and their smallest specimen was 190 cm long and a year old; a freeliving specimen from the western Indian Ocean that was examined by the author was 137 cm long. A term or near-term foetus 96.5 cm long attributed to this species by Nakamura (1935) is probably Alopias vulpinus. Off Taiwan (Province of China) males were immature at about 174 to 283 cm, adolescent at about 239 to 305 cm, and adult at 259 to 323 cm; onset of maturity was at about 267 cm, with 50% mature at 267 to 276 cm. Females from Taiwan (Province of China) were immature at 176 to 294 cm, adolescent at 253 to 321 cm, and adult at 265 to about 365 cm; onset of maturity was at about 273 cm, with 50% mature at 282 to 292 cm. Elsewhere males were adolescent at 192 to 318 cm and adult at 276 cm, while females were immature or adolescent at 277 to 233 cm, adult at 264 to 330 cm, while pregnant females were 264 to about 300 cm. This is apparently a smaller species than Alopias superciliosus or A. vulpinus. Length-weight equations are given by Liu et al. (1999) for Taiwanese specimens: Females: W(kg) = 4.61 x 10-5 TL(cm)2.494 (n = 230) Males: W(kg) = 3.98 x 10-5 TL(cm)2.52 (n = 230)
Interest to Fisheries
This species was formerly exploited by the longline fishery in the northwestern Indian Ocean (primarily by the former USSR), but it is also fished in the Central Pacific. It is an important catch off Taiwan (Province of China) with about 222 t landed yearly. Also caught by shark fishermen in the Red Sea and Gulf of Aden (R. Bonfil, pers. comm.).
Utilized for its meat (for human consumption), liver oil for vitamin-A extraction, hides for leather, and fins for shark-fin soup.Apparently seldom caught by anglers, but listed as a record fish along with other threshers by the International Game Fish Association. It is rarely caught by anti-shark nets off KwaZulu-Natal, South Africa.

Conservation Status : The conservation status of this shark is uncertain, but Liu et al. (1999) considered it extremely vulnerable to overexploitation and in need of close monitoring because of its very low fecundity and relatively high age at maturation.
Local Names
Widespread : Pelagic thresher .
Japan : Nitara .
Mozambique : Zorro pelagico .
Remarks
Nakamura (1935) described A. pelagicus from three large specimens 270 to 330 cm TL , for which he presented measurements. He also gave an illustration (pl. 1, fig. 2) of a large female specimen, one-twentieth life size. It is uncertain if the specimen illustrated is one of the three large individuals described, as scaling up the drawing (204 mm long) gives a size of 408 cm. He also included a separate description (p. 5) and illustration (pl. 3) of a foetus 96.5 cm long as A. pelagicus. All of these specimens are apparently syntypes of A. pelagicus. Nakamura did not designate types for A. pelagicus and did not indicate if one of the three large specimens measured or the large female illustrated was the mother of the illustrated foetus or if the latter was separately obtained.

The large A. pelagicus specimen illustrated by Nakamura is apparently conspecific with A. pelagicus of Bass, D'Aubrey and Kistnasamy (1975a), Compagno (1984), and Last and Stevens (1994), as shown by its fin shapes, fin positions, colour pattern (including lacking a white patch over its pectoral base), oblique teeth, and possibly by lacking labial furrows. However, the illustrated foetus is apparently A. vulpinus and is recognizable by its small eyes, broad head with a strongly convex dorsal profile, short snout, presence of labial furrows, and falcate pectoral fins. Compagno (1984) and Eschmeyer (1998) were unable to provide information on whether or not the syntypes of this species still exist or for that matter if they were even preserved and deposited in a research collection. Nakamura only mentioned that the specimens were drawn by him from life. It may be necessary to designate a neotype for A. pelagicus based on Taiwan (Province of China) material. The name A. pelagicus is used here in the sense of Bass, D'Aubrey and Kistnasamy (1975a), Compagno (1984), and Last and Stevens (1994), who served to revise the concept of this species by restricting it to the species represented by Nakamura's illustrated adult.

Alopias pelagicus has commonly been mistaken for A. vulpinus. For example, Gohar and Mazhar (1964, Red Sea), Kato, Springer andWagner (1967, eastern Pacific), Fourmanoir and Laboute (1976, New Caledonia), Johnson (1978, Tahiti), and Faughnan (1980, Hawaiian Islands) all published illustrations of this species under the name A. vulpinus. This species is probably more wide-ranging than present records show, although it has not been found in the Atlantic Ocean nor Mediterranean Sea and may be absent there.
Threat to humans: Harmless to people, seldom encountered by divers and not kept in aquaria as far as is known. Divers have viewed and photographed this shark on coral reefs and seamounts in the Gulf of California and the Red Sea, Indonesia and Micronesia, but it is not a regular subject of ecotouristic diving. According to Michael (1993) it is shy and difficult to approach underwater.
Source of Information
Sharks of the world An annotated and illustrated catalogue of shark species known to date. Volume 2 Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Leonard J.V. Compagno 2001.  FAO Species Catalogue for Fishery Purposes. No. 1, Vol. 2. Rome, FAO. 2001. p.269.
Bibliography
Bass, D'Aubrey & Kistnasamy, 1975
Compagno, 1984, 1990a, b
Eitner, 1995
Faughnan, 1980
Fourmanoir & Laboute, 1976
Gohar & Mazhar, 1964
Hanan, AuHolts & Coan, 1993
J. Crow (pers. comm.)
Johnson, 1978
Kato, Springer & Wagner, 1967
Last & Stevens, 1994
Liu  et al.,  1999. 
Michael, 1993
Nakamura, 1935
Otakea & Mizue, 1981
R. Bonfil (pers. comm.)
S. Kato (pers. comm.)
S.P. Applegate (pers. comm.)
Villavicencio-Garaysar, Estrada-Agüero & Downton-Hoffman, 1997
 
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