Thresher Shark
Thresher sharks are known for their unusually long tails, the top lobe of which can be as long as the rest of the body (nearly half the shark’s total length).
Class: Chondrichthyes
Order: Lamniformes
Family: Alopiidae
Genus: Alopias
Species: A. vulpinus (Common Thresher or Atlantic Thresher), A. pelagicus (Pelagic Thresher), A. superciliosus (Bigeye Thresher)
Common Names: Thresher Shark, Longtail Shark, Fox Shark
Thresher sharks feed on small and medium sized fish such as bluefish or mackerel, as well as squids and cuttlefish. Its unusual tail is used in its hunting technique – it slaps its prey with its tail in order to stun it, making it easier to catch and eat.
Thresher sharks mostly keep to themselves, and all three species are known to migrate over long distances. The common thresher and bigeye thresher are believed to inhabit oceans basically worldwide, except for the extreme northern and southern waters, while the pelagic thresher does not inhabit the Atlantic Ocean.
Threshers are one of the few sharks that engage in breaching– using their powerful tails, they can launch their entire bodies out of the water in spectacular leaps.
Threshers are ovoviviparous, meaning they give birth to live young. Their litters are usually small (two to four pups) and the sharks can measure up to 59 inches at birth, though much of that length is tail.
The three species of thresher shark are all similar in appearance, with a few differences that set them apart. All of them have short heads with cone shaped noses, small dorsal fins, and large pectoral and pelvic fins. Their most distinctive characteristic is their tail – the top lobe is extraordinarily long, comprising almost half of the shark’s total body length.
Common thresher sharks can grow up to 20 feet long, while pelagic threshers are smaller at around ten feet. In between is the bigeye thresher, which grows up to 16 feet. The bigeye thresher can be distinguished from the other species by its abnormally large eyes.
The common and pelagic threshers are very similar, but can be identified by differences in their coloration – common threshers have white areas above their pectoral and pelvic fins, while in pelagic threshers these areas are dark colored. The pelagic thresher also has a shorter snout.
The thresher shark was known to humans as far back as 300 BC, and was mentioned by the Greek philosopher Aristotle. At the time it was believed that threshers could bite through fishing lines and swallow their young to hide them from predators. While these tales are untrue, these “clever” behaviors gave rise to the shark’s nickname – the fox shark. Even the common thresher’s species name references this – “vulpinus” means fox.
While the bigeye thresher was determined to be separate from the common thresher as far back as 1840, the pelagic thresher’s status as a separate species would not be suggested until almost a hundred years later. Even then, there were doubts from scientists, until further scientific analysis in the 1990s showed that its closest relative is actually the bigeye thresher, and not the common thresher.
This analysis also suggested that there may be a fourth thresher shark species living off the Mexican coast of the Baja California peninsula. However, not much is known about this species, except that it seems to visually resemble the bigeye thresher.
The common and bigeye threshers are listed as Vulnerable, with the Pelagic thresher is listed as Endangered. All species are caught by game fishermen as well as commercial fisheries. Their skin is used to make leather, their fins are used to make shark fin soup, and their meat is consumed.
Thresher shark populations are declining in many areas. Though the process of “finning” a shark (removing its fins for shark fin soup) is illegal in the United States, it is still practiced in many countries and is harmful to shark populations. Overfishing is a serious threat to all thresher shark species.
References
Castro, Jose I. (2011). The Sharks of North America. New York, New York: Oxford University Press, Inc.
https://en.wikipedia.org/wiki/Thresher_shark
https://en.wikipedia.org/wiki/Bigeye_thresher
https://en.wikipedia.org/wiki/Pelagic_thresher
https://en.wikipedia.org/wiki/Common_thresher
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