Sunday, July 24, 2011

Life of Common Thresher Shark

Life of Sea | Common Thresher Shark (Alopias vulpinus) | Common thresher shark  also called Thintail thresher. It is easy to recognize by its long caudal (tail) fin. The tail equals about half the total length of its body. This awesome shark also has a characteristic dorsal fin and pelvic fins. This shark is similar species with Bigeye thresher, Alopias superciliosus and Pelagic or Fine-tooth thresher, Alopias pelagicusBigeye thresher is named for its enormous eyes. It is much larger than those of the common thresher. Bigeye threshers are thought to navigate deep waters. Pelagic threshers are smaller than Common threseher sharks. Common threshers live inss both coastal and pelagic waters in tropical and temperate climates worldwide, from the surface to a depth of 550 m (1,800 ft). Common thresher shark will go to coastal areas when they are catching fish. The juvenile often found close inshore and in shallow bays.

Common thresher shark has a moderate size eye and a first dorsal fin free rear tip located ahead of the pelvic fins. The pectoral fins are falcate and narrow tipped. The sides above the pectoral-fin bases are marked with a white patch that extends forward from the abdominal area. Common thresher shark are usually dark brown and slate gray but can be almost completely black. They are white on their underside, but have dark spots near the pelvic fin and the caudal peduncle. The white color can extend above the pectoral fins onto the head. Common thresher shark have small, blade like, smooth edge-curved teeth. There are 20 teeth on either side of the upper jaw and 21 teeth on either side of the lower jaw. The two jaws have similar teeth with each successive tooth becoming increasingly oblique with outer margins increasingly deeply concave.

Another interesting fact is that Thresher sharks are observed commonly jumping out of the water. They also are considered harmless. The species is shy and difficult to approach. Common thresher sharks feed mostly on small schooling fish such as menhaden, herring, Atlantic saury, sand lance, and mackerel. Bluefish and butterfish are the most common meal. They also feed on bonito and squid. When they are hunting, Common thresher sharks will encircle schools of fish. Then they stun the prey with their tails. This is often done in groups and/or pairs. They have also been known to kill sea birds with their tails.

Common thresher sharks have valuable and commecial value, mainly their meat and fins. Their hides are used for leather and their liver oil can be processed for vitamins. They are often found in nets of mackerel fisherman. Threshers have been widely caught in offshore longlines by the former USSR, Japan, Taiwan, Spain, Brazil, Uruguay, USA and other countries. The northwestern Indian ocean and eastern Pacific are especially important fishing areas. A drift net fishery for the shark developed in southern California; however, the stock was rapidly overfished. It is classed as a game fish and sportsmen in the USA and South Africa fish them. They are often hooked on the upper lobe of the caudal fin. This occurs when the sharks try to stun live bait with their caudal fin. As the result, the Vulnerable global assessment considers this species as Near Threatened in the eastern central Pacific; Vulnerable in the northwest Atlantic and western central Atlantic; Vulnerable in the Mediterranean Sea; and Data Deficient in the Indo-west Pacific.

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