Thresher Sharks – the Tail Whipper of Cocos Island

Photo courtesy from libutron – Tumblr

Thresher Shark (Alopias vulpinus)

Max. Length: 573 centimeters
Length at 1st Maturity: 207.3 centimeters
Weight: 348 kilograms
a value: 0.01880
b value: 2.519
Depth Range: 1 – 650 meters (3 – 2,145 feet)
Frequency: Threatened due to increasing demand for shark’s fin

Photo courtesy from

While Cocos island is known for hammerhead sharks, tiger sharks and whitetip reef sharks, thresher sharks is one of the lesser known shark species to thrive in this offshore Costa Rican Island.

If there is one easy identifying mark for thresher sharks, then it would definitely be their caudal fin which can grow longer than its body. But take note, it’s not both their caudal fins that are elongated. It is only the upper caudal fin that is highly developed while the lower caudal fin is in a normal size. Aside from their blue grey to brown body, you will notice that their eyes are big and their pectoral fins are curved with a white band on the base.

Pretending to be long

Back view of a thresher shark showing its elongated caudal fin. Photo courtesy from Scientific American Blogs

If you try to look at the data entered at the maximum length, then we can initially say that thresher sharks is a relatively huge species of cartilaginous fish. But actually it is not. As previously mentioned about their super elongated caudal fin, you can safely say that the actual body length is only half of its total length.

Let’s take the case of the data entered above. For example, you saw a 5 meter thresher shark in Cocos island. Divide that length into 2, which gives you 2.5 meters. That quotient will give you an estimate as to how long its actual body and how long its caudal fin. With this realization, you now know that they are not really big and long where various studies classify threshers only as a medium-sized shark.

Tail Smacking

Have you ever wondered what’s the purpose of their elongated caudal fin? Is it used to attract a mate? Kidding aside, just imagine a male thresher shark waving gloriously his caudal fin while passing by a female thresher shark then utter the words “wanna have some fun?“. If you are thinking what we are thinking, then you are partly right and wrong. Wrong in the sense that their tails are not used to attract mate. Right in the sense that they are going to have fun . . . fun while feeding.

Photo courtesy from

Yes, it’s known as tail smacking. They use their elongated caudal fin to stun and directly hit their prey. When thresher sharks are able to locate a group or school of fish, they first circle around them to try to concentrate the school in to a tight pack. After this, they will swiftly swim towards their prey. Just a few meters away before reaching their meal, thresher sharks suddenly stop while raising their body causing their tail to smack and hit their prey. After their prey has been stunned, they can easily consumed it with a single bite.


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IUCN Redlist of Threatened Species:

World Register of Marine Species:

Video courtesy from Animal Wire

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