A shark with a scythe; a 1000 pound sharp-toothed creature with a weapon it can slash at 80 miles per hour even under water. Oh yes, it is real. This is the shark of many names: whiptail, sea fox, thrasher. Most commonly, perhaps, it goes by the name of “thresher.” Never heard of it? Neither had I, but now I cannot forget it even if I wanted to. This is no oceanic grim reaper though; the thresher shark is one of the most majestic and memorable creatures of the sea. Allow me to introduce you!
Why are thresher sharks important?
| Kingdom | Animalia |
| Phylum | Chordata |
| Class | Chondrichthyes |
| Order | Lamniformes |
| Family | Alopiidae |
| Genus | Alopias |
| Species | Vulpinus (Common) Superciliosus (Bigeye) Pelagicus (Pelagic) |
Thresher sharks are an extremely unique sight, with an amazing and incomparable tail fin that gives them a graceful and unmatched appearance in the ocean as it glides behind them. The long tail is part of why some people refer to them as fox sharks.
Thresher sharks are important for the same reason as all sharks: because of their position on the food chain. As predators, they control populations and weed out the weak, sick and dying. More importantly, perhaps, is that they influence their prey’s behavior. Most wildlife in the ocean has adapted its appearance, habits, and locations to avoid predation. Could life go on without them? Maybe, but that is a big risk and one we are not yet prepared for.
Where do thresher sharks live?
Thresher sharks live in temperate water around the planet and we believe them to be highly migratory. Although we only call one of the three species “pelagic” (simply meaning it likes the open ocean), all thresher sharks spend most of their time in the open ocean, though not typically deeper than 1600 feet. The common thresher tends to stick around continental shelves. Sometimes these sharks can be seen in shallower waters, but these are either eccentrics or they went there in pursuit of food that fled from deeper water. No thresher sharks can survive in freshwater.
How are thresher sharks unique?
2 reasons:
1. They breach
Thresher sharks are one of the few shark species who breach, or jump above the waters surface (another is the Mako). We do not know why thresher sharks jump, but have some theories based on research into marine mammals such as dolphins and whales in which breaching is far more prevalent.
We believe that these mammals breach for one of 3 reasons
1 communication
2 grooming
3 fun
In dolphins, for example, the breaching may be in order to communicate dominance, or who knows what else. Thresher sharks tend to be a solitary creature though, especially when compared to dolphins. Crocodiles are also less sociable, but we know males will splash as a form of communication, “head-slapping” to attract females or intimidate males. Perhaps when thresher sharks jump it means something to other sharks that we do not yet know.
They may otherwise breach in order to remove parasites or organisms such as barnacles that cling to their skin. The impact on landing may break the death grip these unwanted passengers have on the poor shark, or even scratch an otherwise obnoxious itch. Think about it, in the open ocean there is not much to rub against, so like your grandpa rubbing his back on the wall to get out an itch, sharks may be jumping for the same effect. What other option do they have?
Finally, perhaps they just find it amusing.
2. Their tail fins
So, how long are thresher sharks tails anyway?
Thresher sharks have tail fins almost as long as their actual body; in other words, half of the shark’s total length is just the tail fin. There are three living species of thresher shark: pelagic thresher, bigeye thresher, and common thresher. Each of these grows to different sizes and are listed largest to smallest below:
- An adult of the largest species (the common thresher) can reach a total measurement of up to 20 feet in length. 10 feet of this is their tail fin!
- Next up, the bigeye thresher shark grows up to around 16 feet, meaning an 8 foot tail fin
- Finally, the pelagic thresher comes in at about 10 feet long with a 5 foot tail.
What do thresher sharks eat?
They typically eat small deep-water schooling fish, such as bluefish and mackerel, but will also feed on cuttlefish, squid, and even birds. Killer whales and larger sharks in turn eat thresher sharks when they can.
How thresher sharks hunt:
They hunt with their tail in one of 2 ways:
- They charge at their prey and then come to a sudden stop, whipping their tail over their head like a scorpion. The event resembles a speeding bicyclist who jams the front brake and goes vertical. They stop by turning their pectoral fins to create drag and by tipping their head down.
- They swim alongside their prey and then come to a sudden stop, whipping their tail around to the side
After stunning or even killing the target fish with this attack, the shark moves in to feed. It does not always work, but when it does can kill or stun from 2 to 7 fish at once.
In 2010 Klemens Gann and Simon Oliver first recorded thresher sharks using their tails to whip at large schools of fish in the Philippines. Of 25 videos taken, 3 of these involved the shark swiping its tail sideways rather than over its head, and more were witnessed but not recorded on camera. Interestingly, in all of these cases they only used sideways strikes after successful overhead strikes.
In this study, the average thresher shark whipped its tail at a speed of 30 miles per hour, and the fastest strike recorded was 80 miles per hour. Oliver accurately compares their overhead strike to the motions of a trebuchet.
Are they dangerous? Relation to humans
They are as dangerous as any wild animal, and considering they can grow up to 20 feet long and 1300 pounds, I would recommend you not antagonize them.
That said, however, thresher sharks are not man eaters; as far as sharks go, these are the good guys. They are one of the least dangerous shark species toward humans, especially considering that their main prey includes smaller fish such as sardines, not human-sized seals like the great white would target.
Browsing the global shark attack files supports this view: there were no unprovoked attacks, and most incidents involved fishermen who had reeled one in. The only non-fisherman attack was a surfer who grabbed the shark, which then turned and bit him. So, again, they are dangerous if you provoke them, but comparatively of very little threat to humans.
Are thresher shark endangered?
Thresher sharks (all 3 species) are listed as vulnerable to extinction, meaning they are one step above endangered, and closer to extinction than to healthy population levels. Like many other sharks, they have a low rate of re-population. They can take 7 to 13 years to mature, and then gestate for 9-12 months to give birth to only 2-4 pups.
Thresher sharks are hunted for their meat, fins, skin, and oil. They also wind up as by-catch as victims of commercial fishing, especially mackerel fishermen who are targeting the same schools of fish as the sharks.
In certain areas such as the United States thresher sharks regulations offer some protection to sharks. However, because of their highly migratory nature these isolated measures are not enough for thresher sharks. International cooperation will be needed to keep their population stable.
Conclusion
The thresher shark is a very special part of our oceans, and in many ways is still very little understood. We do not know how many are left, we do not know why they jump. We are not sure of their distribution, as they have been found at greater depths than previously thought (seen by a deep sea camera following the BP oil spill) and in areas not previously suspected (the Mediterranean). Only in 2010 did anyone see a thresher shark actually using its tail to hunt, and this at first just a tethered bait trolled behind a research boat. Only in 2013 was other research published establishing that they conclusively use this tail to hunt in the wild. That is not so long ago as far as our knowledge of this natural world goes. We thought it to be true, but nobody knew for sure until very recently. Thresher sharks are a truly mysterious creature, and one worth studying to grow in our understanding of what they are, how they live, and what their role is in the greater ecosystem of this planet.