COMMON THRESHER SHARK Alopias vulpinus
Description: Common threshers are the largest
species of thresher shark; individuals 6–16 ft. long and weighing 510
lbs. are not uncommon, and they can grow upwards of 20 ft. long. The
body is solidly built and torpedo-shaped, with very long, falcate
(sickle-shaped) pectoral fins. The first dorsal and pelvic fins are
large, while the second dorsal and anal fins are tiny. The distinctive
upper caudal fin lobe is slender, bearing a moderate ventral notch near
the tip, and can be nearly as long as the rest of the body. The head is
fairly short and broad, with a strongly convex dorsal profile and a
pointed conical snout. The eyes are of medium size. The common thresher
is dark brown to gray to almost black above, with a metallic luster.
Dark spots are present around the pelvic fins and the caudal peduncle,
and there may be a white spot at the tip of the pectoral fins. The
underside is white, extending in a characteristic patch over the
pectoral fin bases to the "cheeks".
Habitat: Common threshers are inhabitants of both continental waters and the open ocean. They tend to be most abundant in proximity to land, particularly the juveniles which frequent near-coastal habitats such as bays. Most individuals are encountered near the surface, but this species has been recorded to at least a depth of 1,800 ft.
Feeding: The common thresher's diet is mostly composed of bony fishes, mostly small schooling forage fish such as mackerel, bluefish, and herring. Before striking, the sharks compact schools of prey by swimming around them and splashing the water with its tail, often in pairs or small groups. There are numerous accounts of common threshers using the long upper lobes of their tail fins to stun prey, and they are often snagged on longlines by their tails after presumably striking at the bait.