Latin name

Alopias vulpinus

Other name

Atlantic thresher

Identification

The common thresher is characterized by a highly elongated upper caudal fin blade that can be as long as the body. They have a stocky, torpedo-shaped body and a short, broad head with a conical, pointed snout. There are 5 pairs of short gill slits, the last two slits being above the long and narrow pectoral fins. The mouth is small and arched. There are 32-53 upper and 25-50 lower rows of teeth in the mouth. Teeth are small, without serrations. The eyes are small. The third eyelid is missing. The skin is covered with small, overlapping placoid scales, each bearing 3 ridges. The posterior margin of the scales ends in 3-5 marginal denticles. 

Threshers are excellent swimmers. It's not uncommon for them to jump completely out of the water. They have a band of aerobic muscles on the sides of their bodies that can contract forcefully for long periods of time. In addition, their circulatory system is modified to retain metabolic heat energy. There is a mechanism that acts as a countercurrent heat exchanger. This structure is a band of red muscle along each side that is closely connected to blood vessels. Metabolic heat is transferred from this band of muscle through the blood vessels to the interior of the shark's body to maintain and regulate body temperature. The internal body temperature is on average 2°C higher than the surrounding seawater, although individual differences are possible. This species lacks the ocular rete mirabile, which protects the eyes and brain from temperature changes.

Features of fish fins

Dorsal spines (total): 0; Anal spines: 0.

The long sickle-shaped pectoral fins taper to narrow, pointed tips. The first dorsal fin is quite high and closer to the base of the pectoral fins. The pelvic fins are about the same size as the first dorsal fin, and males have thin, long pterygopodia. The second dorsal and anal fins are tiny. A crescent-shaped dorsal and ventral notch is present in front of the caudal fin. There is a small ventral notch near the edge of the upper lobe. The lower lobe is short but well developed.

Fish colouring

The coloration of the dorsal surface of the body of the Common Thrasher is metallic purplish brown to gray, the sides are bluish, and the belly is white. The white coloration extends to the base of the pectoral and pelvic fins - this distinguishes these sharks from similar pelagic sharks that do not have spots at the base of the fins. The tips of the pectoral fins may be white.

Distribution

The range of these sharks includes temperate and tropical waters around the world. In the western Atlantic, they are common from Newfoundland to the Gulf of Mexico, although they rarely occur off New England, and from Venezuela to Argentina. In the eastern Atlantic, they occur from the North Sea and British Isles to Ghana, including Madeira, the Azores, and the Mediterranean, and from Angola to South Africa. In the Indo-Pacific, fox sharks are found from Tanzania to India, the Maldives, off Japan, Korea, southeastern China, Sumatra, the east coast of Australia and New Zealand. They are also caught around many Pacific islands, including New Caledonia, the Society Islands, Tabuaeran and Hawaii. In the eastern Pacific, they have been observed in coastal waters from British Columbia to Chile, including the Gulf of California.

Habitat

Subtropical marine pelagic-oceanic oceanodromous, with a habitat depth range of 0 to 650 m, usually 0 to 200 m. Although these sharks are occasionally seen offshore, they are primarily pelagic and prefer to stay offshore, venturing down to depths of 550 m. Young sharks are more likely to be found in shallow waters close to shore.

Size

It is the largest member of the family, reaching a length of 7.6 meters and a weight of 510 kg.

Behavior

Common thresher make seasonal migrations, following warm water masses to high latitudes. In the eastern Pacific, males make longer migrations than females, reaching Vancouver Island in late summer and early fall. Young sharks prefer to stay in natural nursery areas. There are probably separate populations with different life cycles in the eastern Pacific and western Indian Oceans. There are no interoceanic migrations. In the northwestern Indian Ocean, territorial and vertical segregation by sex occurs from January to May when pups are born. Mitochondrial DNA analysis revealed significant regional genetic variation in fox sharks living in different oceans. This fact supports the hypothesis that sharks from different habitats do not interbreed despite migration.

Food and feeding habits

They are active predators. They beaten their prey with the upper blade of the caudal fin. 

97% of their diet consists of bony fish, mostly small and gregarious, such as bluefish mackerel, herring, sargans and lanternfish. Before attacking, sharks circle the school and seal it with tail strikes. They sometimes hunt in pairs or small groups. They can also prey on large individual fish such as sawfish, as well as squid and other pelagic invertebrates.

Reproduction

They reproduce by oviparity. Mating occurs in the summer, usually in July and August, and parturition occurs from March to June. Pregnancy lasts 9 months. Fertilization and embryonic development occur intrauterine. After the yolk sac is emptied, the embryo begins to feed on unfertilized eggs (intrauterine oophagy). The teeth of the embryo are peg-shaped and are not functional because they are covered by soft tissue. As they develop, they become more similar in shape to adult shark teeth and "erupt" just before birth. In the eastern Pacific, the litter size ranges from 2 to 4 (rarely 6) newborns, and in the eastern Atlantic from 3 to 7.

The length of the newborns is 114-160 cm and is directly related to the size of the mother. Juvenile sharks grow 50 cm per year, while adults grow only 10 cm. Age of sexual maturity depends on habitat. In the Northeast Pacific, males mature at 3.3 meters, or 5 years old, and females mature at 2.6-4.5 meters, or 7 years old. Life span is at least 15 years, with a maximum of about 45-50 years.

Fishing

It is commercially fished in Japan, Spain, the United States, Brazil, Uruguay, Mexico and Taiwan. They are harvested with longlines, pelagic nets and gill nets. The meat, especially the fins, is highly prized. It is eaten fresh, dried, salted and smoked. The skin is dressed and the liver fat is used to produce vitamins.

Relationship with a person

Despite their large size, common sea foxes are considered harmless. They are fearful and swim away immediately when humans appear. Divers report that they are difficult to approach.