Hammerhead Sharks are a group of sharks popular among others because of the unusual structure of their head. As you may readily guess, these sharks head resemble a hammer-head which is how they come about their name.
Hammerhead sharks belong to the family of Sphyrnidae and are about 9 members in this group. These are lovely creatures occurring worldwide in warm waters on continental shelves and along coastlines. One unique thing about Hammerhead sharks is that they swim in schools during the day which is uncommon among other ocean sharks.
Kingdom – Animalia
Phylum – Chordata
Class – Chondrichthyes
Order – Carcharhiniformes
Family – Sphyrnidae
Hammerhead Sharks inhabit the tropical and temperate waters with a temperature of 20 degrees Celsius or higher worldwide. They also live in offshore waters reaching depths of about 80m and inshore water with shallow depths of less than 1m. These sharks live in lagoons, continental shelves, Island terraces, in deep water close to the shoreline and in the open ocean. More so, hammerhead sharks prefer to swim in school during the day. Most of their school are common in Galapagos Islands in Ecuador, Cocos Island off Costa Rica, near Malpelo Island in Colombia, off southern and eastern Africa and near Molokai in Hawaii.
How to Identify Hammerhead sharks
Hammerhead sharks are typically light grey with a greenish tint. They have white bellies that allow them to blend in the water when they want to sneak up on their prey. This white underside color serves also as camouflage when you view them from the bottom blending in with the color of the sunlight hitting the water.
Hammerhead sharks have lateral projections on their head that give them a hammer-like shape. There are high concentration of electrical receptors (ampullae of Lorenzini) on their head that enables them to detect prey anywhere even the ones hidden in the sand. They have unusually small mouth compared to other sharks. These sharks tend to swim in school during the day and prefer to be alone during late-night hunting.
Among the hammerhead sharks, the great hammerhead shark is the one that has the most unique features that can differentiate it from others which is its dorsal fin. Its first dorsal fin has the shape of a sickle and tall, arising from above the insertions of its pectoral fins. Its second dorsal fin is also large with a deepness in the rear margin. Dermal denticles cover the skin of Hammerhead sharks and closely placed together. Also, each of their denticles has a diamond shape with 3 – 5 horizontal ridges that lead to marginal teeth in their juvenile and about 5 – 6 horizontal ridges in their adults.
Hammer Sharks have strong serrated teeth with the shape of a triangle. Their teeth appear to be oblique towards the corners of their mouth. These sharks, on the upper jaw, have 17 teeth on each side and 2 – 3 teeth in the middle of their Jaw. While their lower jaw comprises of 16 – 17 teeth and 1 – 3 at the middle jaw.
The position of the eyes of Hammerhead sharks allows them to see 360-degree vision which means, these sharks can see below and above; every time. Hammerhead sharks’ head shape was at first thought to help them in taking sharp movement without losing their stability. However, research has found out that it is the unusual structure of their vertebra that enables them to turn sharply more often as it shifts and provide lift than their head shape.
Hammerhead Sharks growth rate and size
Hammerhead sharks have a fast growth rate and known to reach up to about 3.4 m in length and weigh about 230kg averagely. Female hammerhead sharks are usually larger compared to the males and would reach up to a maximum length of 20 feet. Hammerhead Sharks have a great life expectancy and would reach up to about 20 – 30 years before they die.
The shape of their head gives them an upper edge when it comes to catching their prey. Hammerhead sharks have wide eyes that give them a better visual range compared to other shark species. When they spread their specialized sensory organs over the hammer-shaped head, they get to scan the ocean well for food. One of their sensory organs called ampullae of Lorenzini enables them to detect electrical fields created by prey. Even more, the pores on Hammerhead sharks’ head lead to sensory tubes that detect electricity given off by other animals in the water.
Hammerhead Sharks Taxonomy
Hammerhead sharks are closely related to Carcharhinid sharks. Only their teeth are used as fossils. When scientists studied their DNA, they came about the conclusion that their ancestors must have lived in Miocene epoch about 20 million years ago. A research on the mitochondrial DNA of Hammerhead sharks showed Winghead shark like the one with the largest hammerhead of all the hammerhead sharks. This also suggests that the ancestors of the hammerhead sharks had a very large head.
Hammerhead Sharks Breeding/Reproduction
Hammerhead shark’s reproduction only occurs once in a year. There is a courtship behavior where the mating pair swim around in a rather violent manner before the female submits for mating. They exhibit a viviparous mode of reproduction, that is, they give birth to their young ones. Like most sharks, their fertilization is internal and it occurs by the male transferring its sperm to the female through their organs known as “Claspers”.
When the embryo is developing, the yolk sac sustains it, however, when the yolk sac is weak; it transforms into a structure analogous to a yolk sac placenta or pseudo placenta through which the young feed from its mother until birth. Once hammerhead sharks give birth to their baby sharks, they come together and swim towards temperate warm waters until they grow big enough to become independent.
Research in 2007 detected that bonnethead shark which is one of the hammerhead sharks is capable of asexual reproduction through parthenogenesis. This process is when the female ovum fuses with a polar body to form a zygote without having to mate with any male. Interestingly, the bonnethead shark is the first to do this among other sharks.
Hammerhead sharks prefer to mate near the sea bottom except for the great hammerhead sharks who prefers to mate close to the water surface. Hammerhead sharks breeding occurs once in a year and their gestation period is usually up to 11months. The females of Hammerhead sharks in Australian waters tend to give birth around December to January, while those in the northern hemisphere give birth around late spring close to summer. At birth, the pups weigh about 19.5 to 27.5 inches in total length. The baby hammerhead shark usually has a rounded head compared to when in adults when their head is more hammer-like in shape.
Hammerhead sharks eat a wide range of prey which includes fish (sea catfishes, tarpons, grunts, toad fishes, flatfishes and broker) including other sharks that are not as big as they are. They eat squid, crustaceans, octopuses, and stingrays which is especially their favorite.
This group of sharks typically swim along the ocean bottoms to stalk and catch their prey. And, their hammer-heads is an important weapon for hunting their prey, thus they use the head to pin down their prey and eat it when they the prey is still in shock and weak.
The Great hammerhead shark which is the largest of the hammerhead sharks tends to be more aggressive and sometimes indulges in cannibalism. It would eat other hammerhead sharks, even its own species. On the other hand, the bonnethead which is also one of the hammerhead sharks seems to be potentially omnivorous. This shark-like to feed on seagrass which on observation makes up half of its stomach content.
Hammerhead Sharks Predators
When Hammerhead sharks are still in the juvenile stage, they usually fall prey to sharks like bull sharks and tiger sharks. However, as adults because of their large size, they do not form prey to any sea creatures.
Hammerhead Sharks Parasites
These sharks have many parasites who rely on them to feed daily. They include Alebion carchariae, Eudactylina pollex, Kroyeria gemursa, Nesippus orientalis, Nemesis atlantica, and N. crypturus.
Hunting Behaviour of Hammerhead sharks
Hammerhead sharks are active predators that roam around the water in search of prey. They usually hunt at dusk or dawn. When they are in their hunting mode, they swing their head around to pick up any electrical signs their prey like stingrays might be producing.
Their favored prey stingrays like to bury themselves in the sand as a means to escape predators. Unfortunatley, hammerhead sharks can discover them through the help of their electroreceptors concentrating on the underside of their cephalofoil. Once hammerhead sharks can detect rays from the sand, their cephalofoil act as hydrofoil which enables them to turn around quickly and attacking the prey.
Hammerheads just like most other sharks rely on water temperature to sustain the core of their body temperature. Therefore, they migrate toward the south during winter and to the north during summer to keep their desired temperature range. They migrate using electroreception to reproduce and survive. These sharks give birth to pups in nurseries to keep them safe from predators.
The Different Species that make up the Hammerhead Group and Their Unique Features
As you have already read in this article, hammerhead sharks are a group of sharks and there are 9 species in this group. And, they include the following:
1. Sphyrna corona
This shark has a common name of scalloped bonnethead and it is currently listed as Endangered (EN) on the IUCN Red List.
2. Sphyrna lewini
The common name of this species is Scalloped hammerhead and currently, in the IUCN Red List assessment, it is a Critically Endangered (CR) species. This shark’s head is arched with a more pronounced center notch when you compare it with others. Also, it has two matching notches on each side that gives it, its unique appearance.
3. Sphyrna tiburo
The species whose common name is *Bonnethead and listed as Least Concern (LC). They are still extant worldwide. Bonnetheads differs from other hammerheads because of its rounded front and a head that resembles shovel more than a hammer.
4. Sphyrna tudes
The common name for this shark is Smalleye hammerhead. This species is Vulnerable (VU) on IUCN List.
5. Sphyrna media
This shark has a common name of Scoophead. It is Data Deficient (DD).
6. Sphyrna gilberti
This species has a common name of Carolina hammerhead shark and is yet to undergo any assessement.
7. Sphyrna zygaena
The common name for this shark is Smooth hammerhead and the IUCN assessed it as Vulnerable (VU) on their Red List. Smooth hammerhead sharks have a smooth (no notches) head that is slight, and broadly arched.
8. Sphyrna mokarran
This species is commonly known as the Great hammerhead listed as Critically Endangered (CR) on the IUCN Red List. It has a broad head that is nearly flat across the front when compared to others and with a single shallow notch in its center.
9. Eusphyra blochii
The common name for this shark is Winghead sharks and it is listed as Endangered (EN) on IUCN Red List.
Unique Trait about Hammerhead sharks
The position of their eyes is set to give them a wide visual range compared to most other sharks. They can scan the river at a 360-degree range.
Can Hammerhead sharks be kept as a pet?
No, they can’t. They require specialized skills and grow too big for most home aquariums. Moreover, keeping sharks as a pet is illegal in some countries.
Hammerhead Sharks and Human Interactions
When you consider the large size and the teeth structure of Hammerhead sharks, you will realize they can cause more harm than good to humans. These sharks are mildly aggressive. Some may shy away from humans until they feel threatened. However, there are still cases of those that attack humans immediately they enter the water without any form of provocation.
The Great hammerhead shark is one of the hammerhead sharks popular for its cannibalistic nature and has a bad reputation for attacking humans. Although it is hard to differentiate the hammerhead sharks from each other, one case of great hammerhead shark attacking humans has been confirmed and recorded.
On the part of humans, Great hammerhead sharks and scalloped hammerheads have been listed as Endangered on the IUCN List, also the smalleye hammerhead shark is already Vulnerable, all due to overfishing by humans. The overfishing of these sharks is a result of the high demand for their fins and expensive delicacy in Asian countries like China and Indian.
Scientists already expressed their concern about these sharks at the American Association for the Advancement of Science annual meeting in Boston. As such are now working on ways to protect them from going into extinction. The fishermen that harvest these sharks usually harvest them for their fins. After cutting off their fins, they throw them back into the river without any care in the world. This practice which is known as finning is very dangerous to sharks.
Population Size and Trend
Some Hammerheads are listed as endangered while some are listed as least concern. So, their population depends on the particular hammerhead shark you wish to know more about.
The Fossils of Hammerhead sharks show that they might have been existing earlier than Paleocene.
Natives of Hawaii believe sharks to be their gods, they assume sharks to be the protector of humans and also the cleaners of ocean life. They believe these sharks are their family members that have died in the past but now reincarnated to sharks. This is why they worship them. Although, they refer to some sharks as niuhi because they consider them as a man-eater. Examples of those sharks are tiger sharks, bull sharks, etc. In all, they consider hammerhead sharks as gods and highly respected among others.
They are often referred to by Natives of Hawaii as aumaka which could translate to “protector”. Many Hawaiians consider aumaka to be watching over them and protecting them from dangerous sharks like niuhi. Children of Hawaiian that are born with the animal sign are believed to be powerful warriors and are meant to sail the oceans for the rest of their lives.
Hammerhead sharks seldomly pass through Maui, however, the natives of the country believe that them swimming by is a sign that the gods which are the aumaka are watching over them and protecting their families. They also believe when hammerhead sharks pass by the ocean is clean and balanced.
Hammer heads sharks in Captivity
One of the hammerhead sharks which is the bonnethead is steady in public aquariums because it is easy to capture and relatively small in size, compared to others. This shark requires highly specialized skills to keep it. During the transfer of the bonnethead shark from one facility to another, it tends to be vulnerable and would often be found rubbing itself on the aquarium walls, bumping into rocks in the aquarium which may lead to severe injuries.
On the other hand, many cities in North America such as the Bahamas, New Jersey, Atlanta, Las Vegas, and Florida keep Scalloped head sharks and great hammerheads sharks in their public aquarium. However, in 2014 due to the heavy reduction in the population of scalloped head sharks, the population of them being kept in public aquariums reduced to about 15.
Why does hammerhead have such broadhead?
Although, scientists are not particularly sure why hammerhead sharks have such head, however, it is safe to assume that they evolved that way so that their head could serve as a lift when they are swimming. Another theory is that the shape of their head could make them more flexible and turn around easily with great speed.
Law and protection
Due to the endangerment hammerhead sharks are currently facing, they have been added to Appendix II of CITES (Convention on International Trade in Endangered Species) which bring them under licensing and regulation.
Why do hammerhead sharks swim Sideways?
Hammerhead sharks are popular sideway swimmers. They prefer to spend most of their time tilted to one side in a position that looks awkward, but the odd habit seems to be the less energy consuming way for them to swim. So, they swim sideways to save energy.
Sharks are known to use different types of body language to communicate with themselves or other prey. They stiffen or arch their bodies to exhibit threats to other sharks that may want to drag their prey with them. Also, they communicate by hitting the water body with their tail which is a form of discouragement towards other sharks like bull sharks roaming around the water.
Threat to Humans
Hammerhead sharks do not appear as threats to humans, however, there have been cases of the bigger hammerhead sharks like great hammerhead attacking humans.
Superstitions about sharks
Sharks have a bad reputation for being cannibalistic, however, not all of them are demons that eat humans. Out of all the hammerhead sharks, the great hammerhead shark is the only one to exhibit that trait due to its excessive aggressive nature, although this is due to the misidentification of humans as prey most times. The great hammerhead has only been implicated for only one serious attack on a human.
Often time, humans eat the meat of hammerhead sharks. Also, fisheries harvest their fins, teeth, and skin for various purposes. It is important to note that larger species of hammerhead sharks have high levels of mercury, therefore consumers should be careful. Many larger hammerheads sharks come as sport fish.
Amazing facts about hammerhead sharks
- The Great hammerhead shark is the biggest of all hammerhead sharks. It reaches a length of 4m and weighs about 230kg.
- Great hammerhead sharks exhibit cannibalistic behavior.
- Hammerhead sharks’ favorite preys are stingrays. Therefore, they often times have stingray barbs sticking out of their mouth.
- These sharks can detect their prey using electrical fields created by the prey.
- Hammerhead sharks head which referred to as Cephalofoil is an adaptation for hunting prey.
- Hammerhead sharks swim tilting toward their side to save energy.
- Mating of great hammerhead sharks occurs near the water surface, unlike other hammerhead sharks.
- The Great hammerhead shark which is the largest of the hammerhead sharks is critically endangered.
- When hammerhead sharks swim, their head moves from side to side.
- Hammerhead sharks’ head can serve as a weapon to attack their prey.
Hammerhead sharks are a group of sharks constituting of 9 member species. And, their unique traits lie on their odd heads that make people curious to know more about them. This article contains just about every information you need to know about these amazing creatures.
- “Hammerhead Shark”, Wikipedia (edited 28 February 2020), Wikipedia.
- IUCN Red List of threatened species
- “Hammerhead Shark”, National Geographic.
- “Great Hammerhead Shark (Sphyrna mokarran)“, Oceana.
- “Hammerhead sharks roll over and swim sideways to save energy”, New scientist.