Monday, July 25, 2011

Life of Pelagic Thresher Shark

Life of Sea | Pelagic Thresher Shark (Alopias pelagicus) | Pelagic Thresher Shark is the smallest shark from the thresher shark. It is primarily found an oceanic, epipelagic, or circumtropical species. Sometimes, You can see it near shore on beaches, near coral reefs, near dropoffs and in large lagoons, and on sea mounts.  In wild, they in warm and temperate offshore waters of the Pacific and Indian oceans, including the Mediterranean Sea. This species is abundant off the northeastern coast of Taiwan. In North American waters, this species is found off California and Mexico.  Another name of  Pelagic thresher shark is fox shark, fox-shark, foxtail, thresher, thrasher, sickletail, swingletail, and swiveltail.  Pelagic thresher shark can be distinguished with Common thresher shark by the dark, rather than white, color over the bases of its pectoral fins.
 
Pelagic thresher shark has lighter color than the other thresher species. Dorsal surface  is blue-gray. The sides of the body are a light blue-gray, with a white ventral surface. The gill and flank region may have a metallic silvery hue. Pelagic thresher shark is like other threshers. They have long upper caudal fin lobes. Pelagic thresher sharks  have dark patches of skin above the pectoral fin bases and  labial furrows. It is the difference with Common threshers. Additionally, Common threshers sharks have lack lateral cusplets on their teeth. Pelagic thresher sharks can be easily distinguished from the bigeye thresher by its smaller eyes and by the absence of deep horizontal grooves along the anterior dorsal surface.

Pelagic thresher sharks feed on fishes, especially herrings, flyingfishes , and mackerals. They also feed on pelagic squids. When they are feeding, they use their long strap-like upper caudal fin lobe to stun prey with sharp blows. Pelagic thresher sharks, like the other thresher species, sometimes swim in circles around a school of prey, narrowing the radius and tightening the school with their long upper caudal fin lobe. By condensing the school of fishes or squids, Pelagic thresher shark feed more easily on its prey. Their predators of the pelagic thresher are probably large predatory fish (including other sharks) and toothed whales.

Pelagic thresher sharks are able to elevate its body temperature. They have  a special circulatory system or known as the retia mirabilia.  Therefore, they can live in cool water. It also allows its muscles to function more efficiently for faster swimming. This circulatory system is also used by other lamniforme sharks such as the porbeagle, the makos, and the white shark.  Fins of Pelagic thresher sharks are used in the Asian shark fin trade. The hide is sometimes made into leather, and liver oil utilized for vitamin extraction. The oil of  the liver, known as squalene oil, is sometimes used in the manufacture of cosmetics, health foods, and high-grade machine oil. In addition, Pelagic thresher shark are considered prime game fish, and are targeted using rod and reel wherever they occur. The International Game Fish Association lists threshers as game fish, with the largest records having been caught from New Zealand waters, while light-tackle thresher records were taken off California.

Pelagic thresher sharks are rather harmless. They may avoid divers and swimmers in the water. For its size, the pelagic thresher has very small jaws and tiny teeth, indicating that it would not view humans as prey items. This species is currently being exploited by directed fisheries and is caught accidentally in various floating longline fisheries for tunas and swordfish. Fishing pressure may include being caught in its nursery areas. Fishing pressure combined with its very limited reproductive potential and other life history traits make the pelagic thresher extremely vulnerable. The pelagic thresher probably cannot support intensive exploitation. This species is currently not protected anywhere in the world. 

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