Thresher Shark (Alopias vulpinus) is characterized
by its large upper caudal fin. This tail fin may often be
50 percent of the total length of the shark. It has a short
snout and large eyes placed forward on the head. The second
dorsal fin is much smaller than the first. The thresher is
a strong swimmer and can leap clear of the water. The jaws
are small with small, curved sharp teeth without basal cusps
or serrations. Color varies from brown to black with metallic
hues from above and irregular white markings on the underside.
In Canadian waters sizes have ranged from 10.8 to 18 feet
(3.3 to 5.5 meters) long. The maximum size recorded for this
species is 20 feet (6.1 meters), however they generally are
between 10 to 16.5 feet (2 to 5 meters) in length.
The name "Thresher Shark" is derived from the method
it uses to seize its prey. The shark whips its tail on schools
of fish stunning them and quickly returns to eat its catch.
Common threshers have a countershaded body, dark blue-gray
above and white underneath. It has small jaws, but can use
its tail to corral and even kill fish. The first dorsal fin
is much, much bigger than the second; the pectoral fins are
curved. Like other mackerel sharks, it has an anal fin, 5
gill slits, 2 dorsal fins, no fin spines, mouth behind the
eyes, and no nictitating eyelids. It is a very strong swimmer
and can even leap out of the water. It is mostly nocturnal
(most active at night).
The thresher shark, an oceanic and coastal species, inhabits
tropical and cold -temperate waters worldwide. It is most
common in temperate waters. In the Atlantic Ocean, it ranges
from Newfoundland to Cuba and southern Brazil to Argentina,
and from Norway and British Isles to Ghana and Ivory Coast,
including the Mediterranean Sea. Although it is found along
the entire U.S. Atlantic coast, it is rare south of New England.
In the Indo-Pacific region, it is found off South Africa,
Tanzania, Somalia, Maldives, Chagos Archipelago, Gulf of Aden
, Pakistan, India, Sri Lanka, Sumatra, Japan , Republic of
Korea, Australia, New Zealand, and New Caledonia. The thresher
shark is also found in the Society Islands, Fanning Islands,
and Hawaiian Islands. In the eastern Pacific Ocean it occurs
off the coast of British Columbia to central Baja California,
Panama south to Chile.
The thresher shark is a pelagic species inhabiting both coastal
and oceanic waters. It is most commonly observed far from
shore, although it wanders close to the coast in search of
food. Adults are common over the continental shelf, while
juveniles reside in coastal bays and near shore waters. It's
mostly seen on the surface but it inhabits waters to 1,800
feet (550 m) in depth. Thresher sharks are observed infrequently
jumping out of the water. Threshers are considered a highly
migratory species in the U.S. by the National Marine Fisheries
Service for fishery management purposes.