Thresher shark is any of three species (kinds) of sharks that have a long, curved upper lobe of the caudal (tail) fin. This thresher—or whiplike—fin, from which the shark gets its name, can be as long as the rest of its body. Thresher sharks have a small pointed head. They are brown to purple in color on their back and lighter underneath. These sharks may grow to about 10 to 20 feet (3 to 6 meters) long.
Thresher sharks inhabit both coastal and pelagic (open ocean) waters, in both tropical and temperate seas. They are most commonly seen in water less than 650 feet (200 meters) deep, but they also have been found at depths of more than 1,600 feet (500 meters).
Thresher sharks eat such schooling fish as bluefish, herring, mackerel, and small tuna. They also feed on such cephalopods as squid. Thresher sharks use their long upper caudal fin like a whip, stunning their fish prey so they can be easily caught and eaten. These sharks may jump fully out of the water while hunting.
Thresher sharks are ovoviviparous—that is, the female carries the eggs within her body until they hatch. After eating up the yolk of their eggs, the shark embryos (developing young) eat unfertilized eggs produced by the mother, a process called oophagy. The young of ovoviviparous sharks then hatch from egg cases within the female and are born live. A female thresher shark has two to four pups per litter.
Thresher sharks are abundant in the world’s oceans, but they are vulnerable to overfishing. They are routinely targeted by both sport and commercial fisheries and fall victim to the fin trade. Their fins are used to make a popular Asian dish called shark fin soup. The sharks also are taken as bycatch—that is, they are caught accidentally by fishing crews who are fishing for other species. Thresher sharks are generally considered harmless to humans.
