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Author: Nakamura, 1935

Field Marks:
Long dorsal caudal lobe nearly as long as rest of shark, relatively small eyes, straight, broad-tipped pectoral fins, white colour of abdomen not extending over pectoral fin bases.

Diagnostic Features:
Eyes moderately large in adults, very large only in newborn and fetuses, with orbits not expanded onto dorsal surface of head; dorsal profile of head convex and forehead moderately convex in lateral view; space between dorsal edges of eyes broadly convex; snout moderately long, conical; an inconspicuous horizontal groove on each side of head above gills; labial furrows absent; teeth small, over 29 rows in either jaw. Pectoral fins not falcate, straight and broad-tipped; terminal lobe of caudal fin very small. White colour of abdomen not extending over pectoral fin bases.

Geographical Distribution:
Oceanic and wideranging in the Indo-Pacific. Indian Ocean: South Africa, Red Sea, Arabian Sea (off Somalia, between Oman and India, and off Pakistan). Western North Pacific: China, Japan (southeastern Honshu). Western South Pacific: Australia (northwestern coast), New Caledonia, Tahiti. Central Pacific: Hawaiian Islands. Eastern Pacific: Mouth of Gulf of California to Galapagos Islands.

Habitat and Biology:
Primarily an oceanic, epipelagic, circumtropical species, but sometimes caught near shore, ranging in depth from the surface to at least 152 m. A little-known, active, strong-swimming species. Ovoviviparous, with at least two young; apparently a uterine cannibal like other species of Alopias. Presumably feeds on small fishes and squid but no details are known. Harmless to people.

Size:
This is quite evidently a smaller species than A. superciliosus or A. vulpinus. Maximum total length at least 330 cm, with males adolescent at 192 cm and adult at 276 cm; females may be immature (or adolescent) up to 277 cm, but adults range from 264 to 330 cm (Gohar and Mazhar, 1964, had an adult female 3 m long); size at birth about 96 cm.

Interest to Fisheries:
This species has been mainly exploited by the longline fishery in the northwestern Indian Ocean (primarily by the USSR) but it also fished in the Central Pacific and probably elsewhere. Utilized for its meat (for human consumption), liver oil for vitamin extraction, hides for leather, and fins for shark-fin soup.

Remarks:
Nakamura (1935, p. 3) described Alopias pelagicus from three large specimens 285 to 330 cm total length, one of which he illustrated (pl. 1, fig. 2). He also included a separate description (p. 5) and illustration (pl. 3) of at least one fetus (the one illustrated being about 97 cm long) under the name A. pelagicus. Nakamura did not designate type material and did not indicate if one of the three large specimens was the mother of the illustrated fetus or if the latter was separately obtained. Although the large pelagicus specimen illustrated by Nakamura appears to be the same species as the one termed A. pelagicus by Bass, d'Aubrey and Kistnasamy (1975b), the illustrated fetus may be A. vulpinus (recognizable by its small eyes, broad head with a strongly convex dorsal profile, short snout, presence of labial furrows, and falcate pectoral fins). I do not know if designated types exist for A. pelagicus, and if there is a holotype for the species. The name A. pelagicus is tentatively assigned here to the species recognized as pelagicus by Bass, d'Aubrey and Kistnasamy (1975b), with the cautionary note that Nakamura's type specimens (or specimen), if extant, might be based in whole or part on A. vulpinus.

Alopias pelagicus has commonly been mistaken for A. vulpinus. For example, Gohar and Mazhar (1964, Red Sea), Kato, Springer and Wagner (1967, Eastern Pacific), Fourmanoir and Laboute (1976, New Caledonia), Johnson (1978, Tahiti), and Faughnan (1980, Hawaiian Islands) have all published illustrations of this species under the name A. vulpinus. This species may be more wide-ranging than the present sparse records show, primarily because it has been misidentified as A. vulpinus in the literature.

Type material:
Holotype: Uncertain. Type Locality: off Taiwan (Province of China), specimens examined in Suo, Taiwan (24° 36'N, 52'E) fish market.

Pelagic thresher (Alopias pelagicus)