Author: Rafinesque, 1810
Field Marks:
Long, curving asymmetrical caudal fin, with dorsal lobe nearly or quite as long as rest of shark, short ventral lobe, long narrow pectoral fins, large to huge eyes.
Diagnostic Features:
Trunk cylindrical and moderately stout. Head short, much shorter than trunk; snout moderately long, pointed and conical, not greatly elongated, nor flattened and bladelike; mouth small and arcuate, ventral on head; teeth small to moderately large, compressed and bladelike, in less than 60 rows in either jaw; two rows of small to moderately large anterior teeth on each side of both jaws, the anteriors separated from the upper laterals by a row of small intermediate teeth or a gap; eyes moderately large to very large; gill openings short, not extending onto dorsal surface of head, last two pairs over pectoral fin bases; no gillrakers on internal gill slits. First dorsal fin large, high, erect and angular, second dorsal and anal fins minute, low and with pivoting bases, anal fin base behind second dorsal base; pectoral fins very long and narrow, longer than head in adults; pelvic fins very large, nearly or quite as large as first dorsal fin; caudal fin not lunate, upper lobe greatly elongated, about as long as rest of shark, lower lobe short but strong. Precaudal pits present, caudal peduncle slightly compressed and without keels.
Habitat, Distribution and Biology:
Threshers are large, active, strong-swimming sharks, ranging in habitat from coastal to epipelagic and deepwater epibenthic. They are found worldwide in tropical, subtropical and coldtemperate waters. These sharks are apparently specialized for feeding on small to moderately large schooling fishes and squids. Threshers swim in circles around a school of prey, narrowing the radius and bunching the school with their long, straplike caudal fins. The caudal fin is also used as a whip to stun and kill prey, and threshers are commonly tail-hooked on longlines after striking the bait with the caudal tip. The three species of this family broadly overlap in habitat and range, but differences in their structure, feeding habits and spatial distribution suggest that they reduce interspecific competition by partitioning their habitat and available prey to some extent. Alopias superciliosus, with its huge eyes, relatively large teeth, broad caudal fin, and preference for deeper water (coastally near the bottom), takes somewhat larger pelagic fishes (including small billfishes and lancetfishes) as well as bottom fishes; A. vulpinus, with smaller eyes and teeth, a narrower caudal fin, and preference for the surface, takes small peTagic fishes (including clupeids, needlefishes and mackerels) and squids, but also bonitos and bluefishes. The oceanic A. pelagicus is poorly known, but its even smaller teeth and very slender caudal fin suggest that it may take smaller prey than A. vulpinus or A. superciliosus.
Interest to Fisheries:
Thresher sharks form an important component of the oceanic shark fishery, particularly because of their high-quality meat which is utilized fresh, frozen, smoked and dried salted. Their fins are used for shark-fin soup, livers for vitamin extraction, and hides for leather. Sizeable pelagic thresher fisheries, utilizing floating longlines, have operated in the northwestern Indian Ocean, the central Pacific, and the western North Atlantic; recently an important pelagic gillnet thresher fishery has started off the California coast in the eastern Pacific. Threshers are also captured offshore and near shore with line gear (including rod and reel) and fixed bottom gillnets.