Thresher Shark

Instantly recognizable by its extraordinarily long tail, the thresher shark is one of the ocean’s most remarkable predators. Their tails can be as long as their bodies. These sharks use their whip-like tails to herd, stun, and kill prey. This makes them unique among marine hunters. Thresher sharks are a larger group of sharks found in all temperate and tropical oceans worldwide.

Although thresher sharks have an intimidating size and appearance, they are non-threatening to humans and are far more at risk from us than we are from them. All three recognized species face population declines due to overfishing and bycatch, and they are now listed as vulnerable or endangered.

6 Thresher Shark Facts

• Tail weapon: These sharks use their tail to herd fish, stun them, and kill them. While their tails are often very aesthetically pleasing, they are not just there for looks.
• Non-threatening: Despite their unique hunting strategy, these sharks are non-threatening to humans. Very few shark bites are reported from the sharks in this family.
• Jumping skills: Thresher sharks can jump extremely high. They are known for their impressive breaching behavior, sometimes leaping several meters out of the water.
• Other potential species: While we know three species still exist, other species may also exist. For instance, a potential fourth species was located through DNA evidence but not documented otherwise.
• Low aggression: Despite being sharks (and somewhat scary-looking), these sharks are not very aggressive. This trait makes them prone to over-fishing.
• Slow reproduction: With small litters and late maturity, threshers struggle to recover from population declines.

Classification and Scientific Name

Thresher Sharks belong to a particular family of sharks, Alopiidae. Only one genus exists in this family, namely Alopias. This family belongs to the order Lamniformes, which are also known as mackerel sharks. They include some famous shark species, such as the great white and goblin sharks. Members of this order have eyes without nictitating membranes, a mouth that extends behind their eyes, and two dorsal fins. The name Alopias comes from a Greek word meaning “fox,” which refers to their cunning hunting techniques.

Types of Thresher Shark: The 3 Different Species

Currently, three species are widely accepted in this family. While other species may exist, they are not accepted by all experts. Therefore, we will only be discussing the three widely accepted species.

Pelagic thresher (Alopias pelagicus): The smallest of the thresher sharks, growing up to 10 feet. It lives in the subtropical waters of the Indian and Pacific Oceans, usually far from the shore. In 2018, this species was listed as endangered.

Bigeye thresher (Alopias superciliosus): Considered vulnerable to extinction due to its decreasing population. It has an extensive range and is found worldwide in tropical and subtropical seas. Its common name comes from its extremely large eyes, perfect for hunting in deep, dark waters.

Common thresher (Alopias vulpinus): This is the largest, and can reach up to 20 feet long and over 1,000 pounds. This species prefers slightly cooler temperatures than the other two, though it can be found worldwide. The common thresher is also considered vulnerable, as it does not reproduce quickly.

Appearance and Unique Features

One of the most distinguished features of a thresher shark is its long scythe-like tail, which may equal the rest of its body length. This tail is utilized to stun and kill prey, which the shark eats. Typically, this shark consumes small to medium schooling fish. Therefore, it swings its tail towards one of these schools to capture prey.

Compared to most sharks, this species has a relatively small mouth, and they are generally slender and streamlined. Its teeth size varies between species, though some have relatively small teeth.

This family of sharks varies in size depending on the exact species. The largest thresher can reach up to 20 ft and weigh over 1,000 pounds. However, the pelagic thresher can only reach 10 feet.

Typically, these sharks are very slender. Their dorsal fin is small compared to other sharks and extremely aerodynamic. Their coloration varies, and some may have stripes or other markings. Common threshers are usually dark green, pelagic threshers are blue, and bigeye threshers are brown. They swim with slow, eel-like undulations when cruising, but can accelerate explosively when hunting.

Behavior and Hunting

Although thresher sharks are typically solitary hunters, they may occasionally form loose aggregations where there is more prey. They are capable of long-distance travel and are highly migratory.

They hunt by herding schools of fish into tight balls. They will then stun or kill multiple fish at once, with a sudden flick of their tails. Their prey includes mackerel, bluefish, tuna, squid, and crustaceans. Sometimes, if they misjudge a swing of their tails, they can injure themselves because the tail strikes are so powerful

Distribution, Population, and Habitat

The thresher shark has a huge range. You can find these sharks just about anywhere outside of Arctic waters, which are too cold to survive. They usually prefer the open ocean. However, some species may wander close to the shore occasionally. Common threshers are the most common species to wander towards the continental shelf.

In warmer waters, bigeye and pelagic threshers are more common. However, common threshers prefer slightly cooler waters.

Currently, experts believe that 1,600 ft deep is this family’s limit. Still, video evidence has emerged in a few places putting thresher sharks lower than this. Therefore, many are currently rethinking how deep these sharks can go. Furthermore, thresher sharks are commonly seen outside of their range. For instance, bigeye was spotted in the Mediterranean.

The population numbers of all species of threshers are declining due to fishing pressure. Recovery is difficult once numbers fall, because they mature slowly and reproduce infrequently.

Predators and Prey

Thresher sharks eat mostly school fish that stay in the open water. These fish include bluefish, tuna, and mackerel. However, sometimes they wander into coastal waters, where they eat squid and cuttlefish. With that said, they aren’t very picky, so they will usually eat whatever they can get their hands on. For instance, these thresher sharks also eat seabirds and crustaceans.

These sharks do not have many predators, as they are typically the top carnivore. However, juvenile sharks are more likely to be eaten by other sharks. Humans are by far the largest threat.

Thresher sharks also play an important ecological role by controlling populations of fast-breeding prey species like squid and small fish.

Reproduction and Lifespan

According to researchers, thresher sharks do not have a breeding season. Instead, they breed throughout the year. As live-bearing sharks (ovoviviparous), fertilization and embryonic development occur internally.

The pup sharks are born unusually large, measuring up to 59 inches. Usually, their litters are small with only two to four. Once the young fish run through their yolk sac, they eat their mom’s unfertilized eggs, called oophagy. Gestation takes about 9 months.

Despite being born large, these sharks take a while to mature. Typically, it takes between 7 and 13 years for females to mature. Males mature around 8 to 14 years. However, because sharks mature based on their size, it may take them up to 20 to 30 years to mature if food isn’t readily available. These sharks have a slow reproductive rate, which makes them highly vulnerable to overfishing.

Human Interaction

These sharks are rarely encountered, as they prefer open waters and are very shy. They are not dangerous to humans. However, they remain popular game fish in the United States, South Africa, and Baja, Mexico.

These sharks are not regularly used for cooking. Their fins are valued for shark fin soup in some regions, which contributes to fishing pressure on the species. Thresher sharks are not a major commercial fishing species, but bycatch remains a problem.

Conservation Status

All three species of thresher shark are at risk:

• Common thresher: Vulnerable
• Bigeye thresher: Vulnerable
• Pelagic thresher: Endangered

Threats include:

• Bycatch in tuna and swordfish fisheries.
• Targeted fishing for sport or meat.
• Slow reproduction makes population recovery difficult.

Thresher sharks are listed under CITES Appendix II, meaning international trade is regulated, and some regions have introduced bans on targeted thresher fishing.

Comparison with Other Sharks

• Hammerhead shark: Unique head shape vs. thresher’s unique tail; hammerheads often hunt in groups, while threshers are solitary.
• Great white shark: Larger, more aggressive, and a known threat to humans.
• Mako shark: Faster, with shorter tails, and also migratory.