| Name | Hammerhead sharks | Diet | Carnivorous |
| Scientific name | Sphyrnidae | Weight | 3–580 kilograms (6.6–1,300 pounds) |
| Pronunciation | ha-mr-hed shaark | Length | 0.9–6.0 meters (35.4–236.4 inches) |
| Classification | Chondrichthyes, Carcharhiniformes, Sphyrnidae | Location | Worldwide |
The Hammerhead Shark
The hammerhead sharks are among the most recognizable shark species in the world.
They’re unmissable, thanks to their flattened head that extends laterally to the sides, giving it a unique T-shaped appearance.
The shape of the hammerhead or cephalofoil varies for the different species of hammerhead sharks.
Hammerhead sharks live in both temperate and tropical waters worldwide.
They’re prolific predators, and their mallet-shaped head gives them an edge in finding prey in the water around them.
Some species of hammerhead sharks also use their heads as tools to pin down prey, among other uses.
The hammerhead shark’s cephalofoil is not its only fascinating feature.
In this article, we’ll explore all the interesting facts about this unique family of sharks.
Taxonomy and Classification
The common name, hammerhead sharks, applies to all shark species in the Sphyrnidae family.
This family has nine species of shark, split into two genera.
Eight species are in the Sphyrna genus, while the winghead shark is placed separately in the Eusphyra genus.
Hammerhead sharks belong to the order Carcharhiniformes, the largest order of sharks commonly referred to as ground sharks.
Their closest relatives are the requiem sharks (family Carcharhinidae), with species such as the bull, spinner, blacktip, and copper sharks.
The great hammerhead shark (S. mokarran) is the biggest of all the nine hammerhead species.
Other species of hammerhead sharks include the
- Winghead shark (E. blochii)
- Smooth hammerhead (S. zygaena)
- Scalloped hammerhead (S. lewini)
- Carolina hammerhead (S. gilberti).
- Bonnethead (S. tiburon)
- Scoophead shark (S. media)
- Small-eye hammerhead (S. tudes)
- Scalloped bonnethead (S. corona).
Like other shark species, hammerhead sharks have been around for several million years.
Although they’re among the most recently evolved shark family, the hammerhead sharks have been around since the Early Miocene Epoch (about 23 million to 5.3 million years ago).
Some scientists think they might even be older, dating back to the Eocene Epoch.
The winghead shark is considered the oldest member of this family.
The hammer of this hammerhead species is larger than that of any other species.
This suggests that the extinct members of this family had significantly bigger hammers, and the size of their heads reduced proportionately as they evolved.
The hammer-like shape may have evolved as an adaptation to enhance the shark’s vision and other sensory functions.
Physical Characteristics
Hammerhead sharks are among the strangest-looking sharks.
Their most distinctive feature is their flattened hammer or shovel-shaped head, also known as a cephalofoil.
The rest of the hammerhead shark’s body looks like that of other shark species with extra-tall, pointed dorsal fins.
The cephalofoil extends from the side of their head to form a wing-like structure.
The size and shape of this mallet-shaped head varies for the different species.
While some species, like the winghead shark and great hammerhead shark, have a cephalofoil bigger than their bodies, other species, such as the bonnethead and scooped shark, have relatively small hammers compared to the rest of their bodies.
Some species, like the great hammerhead shark, have a distinct T-shape hammer.
That of the scalloped hammerhead is more rounded and has a central notch, while the smooth hammerhead has no notch at all.
The overall body size of hammerhead sharks also varies by species.
Most species are small, except the great hammerhead shark, which can grow to a length of up to 20 feet (six meters).
Other species have an average size of about three to six feet (1 to 2 meters).
The smallest species in the family, the bonnethead shark (S. corona), is only 90 centimeters (35 inches) long.
The heaviest hammerhead shark on record weighed about 991 pounds (450 kilograms).
The mouth of the hammerhead shark is positioned on the underside of their head and is small compared to other shark species.
The coloration of hammerhead sharks varies, but they’re mainly gray to brown colored with a greenish tint on their dorsal side, while the underside is typically light-colored.
Habitat and Distribution
Hammerheads are adaptable sharks found in a wide range of environments.
In places where these sharks are found, their habitats extend from far offshore environments to the continental shelf near the shorelines.
Species that live far offshore can reach depths of up to 300 meters, but they are more commonly found in shallow coastal areas with depths of about 80 meters.
They mainly live in temperate and tropical waters worldwide.
The distribution and range of the hammerhead shark depend on the species.
The great hammerhead shark, for instance, lives in parts of the Atlantic Ocean, with a range that includes the Gulf of Mexico, the Caribbean, and oceanic habitats off the coasts of South America and West Africa.
On the other hand, the scalloped hammerhead is found in tropical and warm temperature waters of the Pacific Ocean, especially near the eastern Pacific and the Indo-Pacific Ocean.
Smooth hammerheads and bonnetheads live in the Atlantic Ocean, and the winghead shark is found in the Indo-Pacific region.
Behavior and Social Structure
Hammerhead sharks are predators known to patrol the sea actively.
They are flexible and are renowned for their ability to make sharp turns to catch prey without losing stability.
In the past, it was assumed that the shape of the shark’s head made them extra-flexible this way.
However, more recent findings suggest that hammerhead sharks have a unique vertebrae structure that allows them to make sharp turns.
The shape of the head does provide some lift during complex maneuvers.
Another factor that influences their agility is the length of their fins.
Hammerhead sharks have long dorsal fins that can tilt to the side to reduce drag and increase their swim efficiency.
Hammerhead sharks are most active during the twilight and dark hours of the day, which means they are crepuscular or nocturnal.
Most species of hammerheads are solitary.
However, a few species, such as scalloped hammerhead and smooth hammerhead, may form large schools that consist of numerous individuals.
These schools are often segregated by sex or age.
Larger hammerheads, like the great hammerhead shark, live and hunt alone most of the year and will only interact with other hammerheads during the mating season.
These solitary sharks patrol vast areas of the ocean, migrating over long distances of up to 756 miles (1,200 kilometers) all alone.
They’re particularly aggressive and have been known to cannibalize smaller members of their own species.
Other species of hammerheads migrate seasonally in mass, too, moving to cooler waters during summer and seeking warmer waters in winter.
Diet and Feeding
Hammerhead sharks have a predominantly carnivorous diet.
They are aggressive predators with a varied diet that includes fish, rays, smaller sharks, squids, and crustaceans.
Stingrays are the favorite prey of most hammerhead shark species.
The positioning of their mouth (underneath their head) makes it particularly easy for them to hunt rays, skates, and other sea-floor dwellers.
The hammerhead shark’s unique head is a specialized adaptation that is very helpful when hunting prey.
With each eye on the edge of their laterally compressed heads, hammerheads have a wide field of vision and improved anterior depth perception.
Their heads also have specialized electro-receptors known as the ampullae of Lorenzini.
This sensory organ, which is spread across its broad snout, can detect electrical signals given off by the body of prey species, including those buried under the substrate.
Hammerheads can also utilize their head as a weapon for hunting prey directly.
When a hammerhead finds a ray or any other type of prey in the sand, it can use its head to pin it down or hit it.
This stuns the prey and makes it easier for the shark to eat.
Species of hammerheads that prey actively on stingrays have developed a tolerance to the toxic sting of the rays.
The dentition of the hammerheads varies for the different species.
For instance, the giant hammerhead has numerous sharp and serrated teeth in its jaws.
Others, like the bonnethead, have blunt, flat teeth better adapted to crushing hard-bodied prey such as crabs and shrimps.
Bonnetheads also feed on seagrass, making up to half of the diet of some individuals.
This means they’re omnivorous and one of the few sharks with this feeding habit.
Reproduction and Life Cycle
Hammerhead sharks mate about once a year.
Their typical mating season varies from one species to the other.
Mating rituals typically involve the male actively pursuing the female and nipping at her pectoral fins.
Fertilization is internal, with the male transferring sperm into the female’s body using a pair of organs known as claspers.
There has been at least one case of a hammerhead shark reproducing without mating this way.
In 2007, a bonnethead shark produced pups asexually without a male through a process known as automictic parthenogenesis.
Hammerhead sharks carry their pups in their body and give birth to live young.
The pups develop in eggs within the female’s body and take nourishment from the egg yolk.
However, when the yolk is exhausted, the yolk sac transforms into a pseudo-placenta, which connects to the mother’s body.
Similar to the placenta of mammals, the yolk sac placenta allows the hammerhead pups to take nourishment from the mother.
In contrast to other shark species that are ovoviviparous, the hammerhead shark earns its reputation as viviparous for this reason.
Most hammerhead sharks give birth to about 12 to 15 pups after an 11-month gestation period.
However, the great hammerhead shark can have litters of up to 40 pups at once.
The pups are fully independent at birth, and the hammerhead does not provide any form of parental care.
In fact, great hammerhead sharks can be quite aggressive and may cannibalize their own young.
The baby sharks swim to shallow and warmer waters where they live and are young until they’re old enough to venture out to the open sea.
Hammerheads reach maturity between the ages of five to 15 years, depending on the species.
The average lifespan of this shark is about 30 years, but some individuals may live for up to 44 years in the right conditions.
Ecological Role and Interactions
Hammerhead sharks are active predators.
Their main prey are stingrays, fish, and cephalopods, but they may occasionally prey on shelled animals like crustaceans.
Hammerheads are among the few predator species that can prey on stingrays.
These rays have incredibly sharp barbs that can deliver a dangerous toxin and leave a painful wound.
Hammerheads possess immunity to ray stings, and researchers have found many with stingray barbs embedded in their skin.
This makes them an important predator species that helps regulate the population of stingrays and prevent overpopulation of these prey within their ecosystem.
The feeding activities of large shark species like the hammerhead also provide food for smaller carnivores and scavengers in their ecosystem that feed on their leftovers.
Although hammerhead sharks (especially the larger species) are apex predators themselves, smaller hammerhead sharks are prey for larger sharks, killer whales, and other marine predators.
Thus, they contribute to the aquatic food web and aid the circulation of nutrients within their environments.
Conservation Status and Threats
Currently, human activities are depleting hammerhead shark populations.
Many countries target and kill these sharks for their fins to make shark fin soup.
Various sharks’ fins go into making this soup, but chefs commonly target the hammerhead shark because its fins are larger and richer in liver oil than those of other shark species.
Often, fishers slice off only the fins and dump the rest of the shark’s body back into the ocean.
Even in areas where commercial fisheries don’t target hammerheads directly, gillnets can still catch these sharks as bycatch.
Other threats faced by hammerhead sharks include habitat degradation, overfishing of their typical prey species, and climate change.
Due to these threats, most hammerhead sharks are currently at risk of extinction.
Experts classify species like the winghead shark and bonnethead as Endangered, while they list the smooth hammerhead as Vulnerable.
Other species, such as the great hammerhead, smalleye hammerhead, scooped shark, scalloped hammerhead, and scalloped bonnethead, are critically endangered.
Many countries impose fishing regulations to limit hammerhead shark catches, while others ban them outright.
Promoting education, awareness, and sustainable fishing practices in commercial fishers will be crucial to hammerhead sharks’ long-term conservation and survival.
Unfortunately, efforts to protect hammerhead species from extinction have been largely ineffective so far, and their numbers continue to drop alarmingly.
Unique Adaptations and Survival Strategies
The hammer-shaped head (cephalofoil) of this shark family is their most distinctive adaptation.
Experts believe the bizarre head shape of the hammerhead serves various purposes, from enhancing sensory function to boosting maneuverability.
The position of the shark’s eyes at the ends of the cephalofoil expands their field of vision so they can spot prey and potential predators easily.
However, this unique eye positioning also means the hammerhead sharks can’t see directly in front of them.
Fortunately, they have electroreceptors known as the Ampullae of Lorenzini on their snout, which helps detect prey beyond their field of vision.
Although all sharks have this specialized sensory organ, the hammerhead’s broad head allows for more space for the electroreceptors, improving their ability to detect prey significantly.
The hammerhead’s flattened head also improves its stability and maneuverability in the water, so it can make sharper turns and quick movement while hunting prey.
Cultural Significance and Human Interactions
The hammerhead shark is one of the most recognizable shark species.
It is particularly famous with indigenous and coastal communities in regions where this shark is abundant.
For instance, Islanders living in the Torres Strait commonly represent the hammerhead shark in totems and other cultural artifacts.
In Hawaii, people regard sharks as the sea gods, holding both positive and negative reputations.
In this region, people consider hammerhead sharks as protectors of the sea and hold them in high regard.
Local cultures in this region consider them protectors and widely respect them.
Most hammerhead sharks are too small to pose significant threats to humans.
However, bigger species like the giant hammerhead shark are potentially dangerous because of their size and aggressive personality.
Public aquariums often keep smaller species like the bonnethead and scalloped hammerhead, and have successfully bred them in the past.
Future Prospects and Research
As a vulnerable animal at risk of extinction, scientists are actively studying hammerhead shark populations with the hope of devising measures to protect existing populations.
There’s a growing need to understand this shark species’ population structure and genetic diversity.
This will help determine the health of existing populations or even identify distinct subpopulations of hammerheads.
Another potentially fascinating study area for this species is their ability to reproduce through automictic parthenogenesis.
This occurs when a female’s ovum fuses with a polar body to form a zygote, producing young without mating with a male.
The bonnethead shark stands as the first species to reproduce in this manner, establishing itself as a crucial link in researching this unique trait among hammerheads and other shark species.
Conclusion
Sharks from the hammerhead family inhabit warm, temperate, and tropical waters around the world.
Most species of this shark are relatively small, but some, like the great hammerhead shark, can grow quite big.
Hammerhead sharks stand out because of their distinctive T-shaped heads, which enhance their sensory skills and maneuverability.
Human activities such as overfishing put this fish family at risk, and their population is currently at an all-time low.
Fragile species require us to treat them with utmost care and respect to guarantee their survival and recovery.
Sources:
- https://en.wikipedia.org/wiki/Hammerhead_shark#
- https://www.britannica.com/animal/hammerhead-shark
- https://oceana.org/marine-life/great-hammerhead-shark/
- https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/sphyrna-mokarran/
- https://theconversation.com/why-do-hammerhead-sharks-have-hammer-shaped-heads-184372
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