Thresher Sharks are amazing sharks that belong to the family of Alopiidae. They are of three extant species, the common thresher, the bigeye thresher, and the pelagic thresher, all in genus Alopias. These sharks are famous for their unique tail fin and their unmistakable large pectoral fins.
Name Origin
Thresher sharks family and genus are from the word alopex which means “fox” in Greek. As a result, the long-tailed or common thresher shark (Alopias vulpinas) is also known as Fox Sharks. These sharks got their common name from their caudal fin, which can be as long as their entire body.
Distribution Range
Thresher sharks are oceanic species that inhabit tropical and cold-temperate waters worldwide. In the Atlantic ocean, thresher sharks range from Newfoundland to Cuba. From southern brazil, Norway to Argentina. British isles, to Ivory Coast and Ghana, including the Mediterranean sea.
Though you can find these sharks along the entire U.S. Atlantic coast, they are rare in the south of New England. In the Indo-Pacific region, you can find thresher sharks Off South Africa, Somalia, Tanzania, Maldives, Pakistan, Gulf of Aden, India, Sumatra, Sri Lanka, Republic of Korea, Australia, New Caledonia, and New Zealand.
In the eastern Pacific Ocean, they occur off the coast of British Columbia to central Baja California. Then, from Panama south to chile. You can also find Thresher sharks in the fanning islands, society islands, and Hawaiian islands.
Natural Habitat
Thresher sharks are pelagic species that inhabit both oceanic and coastal water. These sharks do not come to shore, although they wander close to the coast in search of prey. Adults of Thresher sharks are common over the continental shelf, while juveniles live in coastal bays and nearshore waters. These sharks inhabit waters of 1800 feet (550 m) in depth.
Appearance and Anatomy
Thresher sharks got their name from their long, thresher-like tail or caudal fins, which can be as long as the total length of their body. This tail is used as a weapon to stun their prey. Thresher sharks have a short head and a cone-shaped nose.
They have a small mouth and teeth that range in size from small to large. Among the three species of thresher sharks, Common thresher is the largest (Alopias vulpinus), which may reach a length of 20 ft (6.1 meters) and a mass of over 1,100 lb (500kilograms).
The bigeye thresher is the next in size, followed by the pelagic sharks (Alopias pelagicus) which is the smallest of the three species. These species are slender, with small dorsal fins and large recurved pectoral fins. Apart from the big eye thresher, the other two species have small eyes positioned to the forward of their head.
Thresher sharks coloration ranges from brownish, bluish, or purplish-grey dorsally with lighter shades ventrally.
Denticles
These sharks’ dermal denticles are overlapping and very small. The blades are horizontally small and have moderately long peduncles.
Behavior
Threshers sharks are solitary creatures. Segregation occurs in Indian oceans by depth and gender. Some species, however, do occasionally hunt in groups of two or three contrary to their solitary nature. All thresher species are highly migratory or have oceanodromous habits.
When thresher sharks are hunting schooling fish, they would usually whip the water with their tail, to stun the prey. They use their elongated tail to swat smaller fishes, before feeding on them. Sometimes, the thresher shark will resort to slicing the fish into two parts before eating.
These species are one of the few sharks known to jump out of the water entirely, using their elongated tail to propel them out. This behavior is known as “breaching.”
Hunting Behavior
Thresher sharks tend to be very athletic sharks. They are popular for slaying their prey with their huge tails and even more for their characteristic jumping skills. This jumping behavior is known as breaching, where they jump out of the water and into the air.
While hunting, these sharks lunch themselves with their whole body out of the water and perform wild turns. They also love to hunt schools of fish in the open ocean water and prefer mackerels, tuna, and sometimes some seabirds.
Feeding Habits
Thresher sharks majorly feed on pelagic schooling fish such as juvenile tuna, bluefish, and mackerel. They also feed on crabs, squid, crustaceans, seabirds, and cuttlefish.
Reproduction
There is no distinct breeding season observed for thresher sharks. Thresher sharks are ovoviviparous (Fertilization and embryonic development occur internally). This live-bearing mode of reproduction results in a small litter, usually two to four large, well-developed pups.
Young pups exhaust their yolk sacs while still inside their mother. They feast on the mother’s unfertilized eggs, a process which is known as Oophalagy. Thresher sharks have a prolonged growth rate.
Their males reach sexual maturity between seven and thirteen years of age while their females reach it between eight and fourteen years. These species may live up to 20 years or more.
Their gestation period lasts for about nine months, with birth occurring in the spring. In October 2013, a researcher took the first picture of a thresher shark giving birth off the coast of the Philippines.
Sensory System
These sharks have an extraordinary heat exchanger system which is called “endoderms.” It allows them to retain metabolic heat. This feature is unique to thresher sharks only.
Parasites
Nine species of copepods, genus nemesis, are known to parasitize thresher sharks. These parasites attach themselves to the gill filaments of thresher sharks, which can cause tissue damage to them.
Predators
Large sharks prey on young thresher sharks. But, when they mature, they do not have any predators.
Species of Thresher sharks
There are three extant species of threshers sharks, and they are Pelagic Thresher, Common Thresher, and Bigeye thresher. The three species are highly migratory and mostly inhabit the tropical and temperate regions across oceans.
Among the three species, only pelagic thresher has no record in the Atlantic ocean. All the same, they are often confused with Common thresher sharks, so there is a high chance their range is more extensive than thought.
The three thresher sharks look quite similar unless you pay close attention. They all have a slender torpedo-shaped muscular body and a unique tail. However, each individual has its unique difference, which we would be discussing in the next paragraph.
1. The Common Thresher (Alopias vulpinus)
This shark is the largest and the most common of the three species of thresher sharks. Common thresher sharks are much more like the Pelagic Thresher. Still, they are easy to differentiate through the white band that extends from the belly region over to the pectoral fins. They have a purplish-brown coloration, fading to bluish on the flanks.
Their pectoral fins curve to a point and sometimes have a white spot at the tip. When you take a closer look at Common threshers, you will notice a slight furrow at the corners of their mouth, which is one of the unique features of this species. Common thresher shark’s eyes are moderate in size and positioned forward of their head. They grow to about 16.4 feet (5 m) in length but can also reach a length of 21.3 ft (6.5 m).
Common thresher sharks are circumglobal, with a noted tolerance for cold waters. These species are especially vulnerable to fisheries exploitation because of their epipelagic habitat. It is within the range of many unregulated and under-reported longline fisheries and gillnets, in which they readily occur as bycatch.
Severe declines have occurred where these species have been heavily fished.
Analyses of pelagic longline CPUE (Catch Per Unit Effort) data from logbook reports covering the total species range in the northwest and western central Atlantic vary according to the period but suggest thresher sharks stocks declined by 63 – 80% within the period of 1986 – 2000.
Evidence showed that common thresher sharks are repeated targets by pelagic fisheries for swordfish and tuna in attempts to sustain catches, and exploitation is increasing in these areas.
The IUCN assessed the common thresher shark as “Vulnerable (VU)” in their Red List of Threatened Species.
2. The Bigeye Thresher (Alopias superciliosus)
Bigeye threshers have a deep metallic violet to purplish-brown coloration and creamy white color underneath. These sharks differs from the other two species by their enormous oblong eye.
Their eyes are taller than it is full and reaches around slightly to the top of their head. The top of the eye bulges out and has an upward orientation, giving them the ability to see straight up. The structure of their eyes is probably an adaptation for hunting from below in the low light.
These sharks pectoral fins are similar to that of common thresher, curved and end in a point. Bigeye threshers occur all over the subtropical regions of the seas. Still, there is no much data on their migratory patterns.
They are often swim in warmer surface waters over the continental shelf. Nevertheless, They also occur in the open ocean in a depth of over 2,362 feet (720 m). Bigeye thresher sharks are targets of fishing throughout its range. Hence, there are Significant reductions in thresher CPUE (Catch Per Unit Effort) in pelagic longline fisheries in the northwest Atlantic and the eastern Pacific.
The bigeyed thresher shark is also listed as “Vulnerable (VU)” in the IUCN Red List.
3. Pelagic Thresher Sharks (Alopias pelagicus)
Pelagic threshers are the smallest of the three species. Consequently, they have an average length of just about 9.8 feet (3 m). These sharks have a dark blue to grey coloration with a white underbelly.
You can differentiate Pelagic threshers with the dark coloring above their pectoral fins. Also, their pectoral fins are broader and straighter than those of the other species, though more rounded at the tips.
Pelagic threshers mostly occur in the open oceans in depths ranging from the surface to 492 feet (150 m). Still, they come close to shore, especially in places where the continental shelf is not very wide.
For example, there is the Coral Sea in the indo-pacific where you can find young pelagic sharks and adults near coral reef drop-offs and seamounts.
The most notable location for seeing pelagic threshers is Malapascua island in the Philippines. Pelagic sharks are especially vulnerable to fisheries exploitation (bycatch and target). Because their epipelagic habitat occurs within the range of many unregulated and under-reported longline and gillnet fisheries.
Although these species are reportedly relatively common in some coastal localities, current levels of exploitation in some areas are considered to be unsustainable. Overall, Scientists propose a high possibility of severe depletion of the global population of the pelagic thresher shark.
The IUCN listed the pelagic thresher shark as an “Endangered (EN)” species.
Interaction With Humans
Importance to humans
Humans fish Threshers sharks majorly for their meat and fins. They also use their hides for leather and their liver oil for vitamins. Thresher sharks are wildly caught in countries like Taiwan, Japan, Spain, Brazil, Uruguay, the USA, and other countries.
The northwestern Indian Ocean and eastern pacific are especially essential fishing areas. Sportspeople in the USA and South Africa consider Thresher sharks as excellent game fish. So, they make a great catch for game fisheries.
Dangers to Humans
Thresher sharks are considered harmless to humans. They are shy and difficult to approach. Divers who have encountered these sharks claim that they did not act aggressively. However, you should take some caution, considering their size.
Conservation Status
Like many shark breeds, thresher sharks often become entangled in fishing nets. These sharks are considered harmless to humans. Although they are uncommon in U.S. fish markets, people consume them in other countries. They are essential for their fins, meat, hide, and liver. Sportsmen also fish them as gamefish.
Thresher sharks abundance in U.S. Atlantic waters dropped clearly by about 67%. All the three extant species of thresher sharks are listed as Vulnerable (VU) globally in the IUCN Red List. This assessment is because of their rapidly declining populations. These downward trends are because of a combination of slow life history characteristics.
Thresher Sharks in Captivity
Like most other large sharks, thresher sharks do not do well in captivity. They require an ample swimming space to survive. There are no records of any thresher sharks in any aquarium.
Thresher Sharks Fun Facts at a Glance
These sharks are amazing unique species of shark. They have unusual behavior, anatomy, and history. Although they are prevalent because of their habitat, they do not pose any harm to humans.
Here are nine fun facts about them:
1. Thresher Sharks May Have an Undiscovered Species!
Only three extant species of thresher sharks are known, the common thresher, bigeye thresher, and pelagic thresher. However, scientists discovered a species of thresher sharks off the coast of Baja in 1995.
After several scientific analyses of its DNA, scientists found it to be a new species of thresher sharks potentially. However, there has only been one sample of this potential species so far.
2. They have a unique caudal fin
Thresher sharks have a long caudal fin that can be as long as the entire length of their body. These long tails give them several unique biological and behavioral capabilities.
3. These Sharks are Named After Foxes
Aristotle was the first person to ever write about thresher sharks. In his book Historia Animalia, he described thresher sharks as a highly intelligent and cunning shark that can bite through fishing lines to escape.
He also claims that they temporarily swallow their pups to protect them from predators. However, these two behavior is scientifically inaccurate. Yet, it earned them their name Alopex which means “Fox” in greek because people believe them to be highly intelligent.
4. Thresher Sharks are Pelagic Creatures
Although thresher sharks breed along the coastal waters and their juveniles stay in shallower water until maturity. These sharks still prefer deep, open oceans. They spend most of their lives at a depth of about 1,000 ft.
They migrate the open ocean waters spending summertime in the north and winter in the south. Thresher sharks prefer tropical and subtropical waters but will migrate into temperate waters to hunt.
5. Thresher Sharks are Amazing Hunters that Prefer to Prey on Schools of Fish
Thresher sharks are impressive hunters. They use their unique long tail to help trick and lure their prey. Once the prey comes to them, they attack the prey with their tail until its disabled. After that, they attack the prey with speed assault, taking bites until they consume the prey completely.
6. Thresher Sharks are Endothermic
These sharks are one of the few sharks with endothermic abilities. As a result, they have slow-oxidative muscles combined with blood vessel counter current exchange, which helps them regulate their blood pressure internally.
Being warm blooded allows them to monitor proteins in colder waters and help them more efficiently use their muscles. Their endothermic capabilities also made them quick swimmers and agile hunters.
7. Threshers Sharks are Active Swimmers
These sharks are energetic, active swimmers. They are one of the fastest sharks in the ocean that can swim at a top speed of 48.2 kph (30 mph). Thresher sharks can jump out of the water, a behavior known as breaching. They can swim so fast because of the combination of extra thrust from their long caudal fin.
Their endothermic capabilities band the presence of a strip of aerobic red muscle along their flanks that helps give them extra power and strength. Their bodies are also torpedo-shaped, which reduces the drag of the water against their bodies.
8. Thresher Sharks and the great white sharks are related
These sharks are lamniform, otherwise called Mackerel sharks. The mackerel shark family includes Basking sharks, Famous great white shark, and mako sharks. Thresher sharks are also believed to be related to the prehistoric terror, megalodon shark. All mackerel sharks can regulate their blood temperature. They have similar biological features like two dorsal fins, five-gill slits, anal fins, and a mouth that goes past their eyes.
9. There is an interesting myth about thresher sharks
There is a long-known myth that thresher sharks and swordfish work together to attack whales. Even more, this myth claims that thresher Sharks will swim in front of a whale and distract it by violently whipping its tail around.
Meanwhile, the swordfish will attack the whale with its sharp nose from the back, killing it. After that, both the thresher sharks and swordfish shares the feast. No one knows the origin of this myth. However, it is not true since neither swordfish nor thresher sharks can eat whales.
References
- “Discover Fishes: Alopias vulpinus, Thresher Shark”, Florida Museum.
- “Thresher Sharks, Alopias vulpinus“, The MarineBio Conservation Society.
- “Three species of Thresher Sharks”, Thresher Cove.
- “Thresher Shark”, Wikipedia (accessed April 28, 2020).