With its unusually long tail, thresher sharks are one of the most easily distinguishable of all sharks in the ocean. The upper lobe of the thresher shark’s tail fin accounts for half of the shark’s total length – its tail is as long as the entire rest of the shark’s body!
The three kinds of Thresher Sarks are the Common Thresher, Pelagic Thresher, and Bigeye Thresher. All three species are migratory and are found in tropical to temperate regions across the oceans. Of the three species, only the Pelagic Thresher is not recorded in the Atlantic Ocean, however it is often confused with the Common Thresher, so it is quite possible its range may be larger than thought.
The three Thresher Species look very similar at first glance. They all have a slender torpedo-shaped muscular body and an uncommonly long tail. Meanwhile at the other end, the Thresher Shark’s snout is short and the jaws are quite small. But fish beware! Their many teeth have sharp blade-like curved edges that are perfect for snatching their slippery prey. The pectoral fins of thresher sharks are long and the dorsal fin is relatively small for the rest of its body.
The Common Thresher (Alopias vulpinus)
The Common Thresher (Alopias vulpinus) is the largest and most common of the three species. It regularly reaches lengths up to 5 m but can grow as large as 6.5 m. species is purplish brown to grey on top, fading to more blueish on the sides and white underneath. The common thresher, often confused with the pelagic thresher, can be distinguished by the white band that extends from the belly over the pectoral fins. The pectoral fins curve to a point and sometimes have a white spot at the tip. If you get a close look at the common thresher’s smile, you will see furrows at the corners of its mouth, another characteristic totally unique to this species. The eyes of the common thresher are moderately sized and positioned forward on its head.
The Bigeye Thresher (Alopias superciliosus)
The Bigeye Thresher (Alopias superciliosus) average around 3 to 4m long but can grow up to 5m. In colouring they are deep metallic violet to purplish brown and creamy white underneath. Bigeye threshers are easily distinguished from the other 2 species by their enormous (up to 10 cm across) oblong eye. The eye is taller than it is wide and reaches around slightly to the top of the head. The top of the eye bulges out and can be oriented upward giving this thresher the ability to see straight up. This bizarre eye is likely an adaptation for hunting from below in the low light.
The pectoral fins of the bigeye thresher are similar to the common thresher, curved and end in a point. Bigeye threshers are found all over the subtropical regions of the oceans, but little is known about their migratory patterns. They are most often seen in the warmer surface waters over the continental shelf but are also found in the open ocean and have been tracked to depths over 720 m.
The Pelagic Thresher (Alopias pelagicus)
The Pelagic Thresher (Alopias pelagicus) is the smallest of the 3 species, averaging around 3m in total length but can grow up to 3.8 m. Pelagic threshers are dark blue to grey on the top and sides with a white underbelly. This species can be distinguished from the common thresher by the dark coloring above its pectoral fins. Also its pectoral fins are straighter and broader than those of the other species and are rounded at the tips.
Pelagic threshers are most often found in the open ocean in depths ranging from the surface to 150m, but they are also known to come close to shore especially in areas where the continental shelf is not very wide. One such area is the Coral Sea in the Indo-Pacific, here juveniles and adult pelagic threshers are can be spotted near coral reef drop offs and seamounts. The most notable (and reliable) location for seeing pelagic threshers is at Malapascua Island in the Philippines.