Being among the most popular shark species, the appearance of the great hammerhead shark (Sphyrna mokarran) can never be mistaken. Of course, with the flat head crossing its body, this shark has an apparent hammerhead shape. Anyone who encounters this shark wouldn’t have a hard time recognizing it.
Although there are 10 known hammerhead sharks, the great hammerhead shark is the largest of all. Among the hammerhead sharks, nine including the great hammerhead is in the same genus Sphyrna. While the oddball belongs to a separate genus Eusphyra and turns out to be the only member of its genus.
The great hammerhead shark differs from other hammerheads with the shape of its hammer, otherwise known as cephalofoil. It has a front margin that is almost straight as opposed to the arched of other hammerheads. Another thing is the shark’s first dorsal fin that is tall and shaped like a sickle.
This shark is an apex predator that occurs worldwide in tropical and warm temperate waters, inhabiting coastal areas and continental shelf. Great hammerhead sharks do swim to shallow inshore waters and encounter humans, especially divers quite often. Therefore, observation of this shark species shows it has amazing characteristics that will make your day!
Unique Adaptations of the Great Hammerhead Shark
This shark has eyes set wide for a greater visual range than most other shark species. The highly specialized sensory organs of this shark can spread across its flat hammerhead. Thus enabling the shark to scan the sea thoroughly for food. Also, the great hammerhead shark has a concentration of the ampullae of Lorenzini which helps it detect low electrical fields created by prey animals. And, because the great hammerhead shark has ampullae with increased sensitivity, it can find stingray believed to be its favorite meal even while buried in the sand.
Another important adaptation of the great hammerhead shark is its “rolled swimming” practice. On observation, this shark will tend to assume a swimming position which involves tilting to its side. Hence, achieving lift with its very large dorsal fin, referred to as rolled swimming. A 2016 study showed that the essence of this practice is to reduce drag and conserve energy.
The great hammerhead shark can spend up to 90% of its time swimming in this position. And, this technique may save approximately 10% in drag and, of course, the cost of movement.
Scientific Classification
The valid scientific name of the great hammerhead shark is Sphyrna mokarran. This shark belongs to the family Sphyrnidae and order Carcharhiniformes under the class Chondrichthyes.
Note that before the great hammerhead shark finally settled for the species name, there were other names used to describe this species which may appear in earlier texts.
Habitat and Distribution
The great hammerhead shark inhabits both the tropical and temperate waters around the world. They can be found in offshore waters reaching depths of 260 feet (80 m) and inshore waters at shallower depths of less than 3.3 feet (1 m). This shark inhabits continental shelves, lagoons, island terraces, the open ocean, deep water close to the shoreline and they tend to favor coral reefs.
Having been found in the Atlantic, Pacific, and Indian Oceans, the great hammerhead shark has a worldwide distribution, thus occurs as follows.
In the Atlantic Ocean
The great hammerhead shark occurs from North Carolina to Uruguay including the Caribbean sea and the Gulf of Mexico, then from Morocco to Senegal, and the Mediterranean Sea.
In the Pacific Ocean
This shark occurs from the Ryukyu Islands toward, New Caledonia, Australia, and French Polynesia, then from southern Baja California to Peru.
Great hammerhead sharks are migratory species, as such, they tend to move toward the poles during summer as documented in populations off Florida and in the South China Sea.
Description and Appearance
Body and Cephalofoil
Just like other hammerhead sharks, the great hammerhead shark has a streamlined body with an expanded caphalofoil. However, particular to the adult great hammerhead shark is the cephalofoil which has an almost straight margin with pronounced lateral and medial indentations. The width of the cephalofoil measures up to 23 – 27% of the total body length.
Dentition
This shark has strongly serrated teeth that are triangular in shape and appearing to be more oblique toward the corners of the mouth. On the upper jaw, there are 17 teeth on either side with 2 – 3 teeth in the midline of the jaw (symphysis). While the lower jaw contains 16 – 17 teeth with 1 – 3 teeth at the symphysis.
Fins
The most distinct fin of the great hammerhead shark is its first dorsal fin which is very tall and sickle-shaped, originating above the insertions of the pectoral fins. Similarly, the second dorsal fin is relatively large with a deep notch in the rear margin, this description also fits the anal fin. The pelvic fin has concave rear margins with the shape of a sickle.
Dermal Denticles
Covering the skin of the great hammerhead shark are dermal denticles closely placed together. Each denticle has the shape of a diamond with about 3 – 5 horizontal ridges leading to marginal teeth in juvenile hammerhead, while in adults, 5 – 6 horizontal ridges.
Coloration
On the upper part of the great hammerhead shark is a distinct color of dark brown, to light gray, to olive, however, this color fades to white toward the underside. While the tip of the second dorsal fin in juveniles may be dark, in adults, the fins are not marked.
Growth Size
An average adult great hammerhead shark will measure around 11 feet (3.4 m) in length and weigh over 510lb (230 kg). The female great hammerheads grow larger than the males, as such can reach a maximum length of 20 feet (6.1 m) which is the highest on record. A pregnant female specimen with up to 55 near-natal pups and 14 feet (4.4 m) in length recorded the heaviest ever caught with weight 1280lb (580 kg). This individual was caught off Boca Grande, Florida, in 2006.
Typical Behavior of the Great Hammerhead
Great hammerhead sharks are solitary species given wide distance by other reef sharks for safety. These sharks are nomadic predators which means they roam about in search of prey. On observation, these sharks tend to respond agonistically to confrontations, thus, they tend to drop their pectoral fins and swim in a jerky or stiff manner.
Hunting and Feeding Behavior
This shark species is an active predator that roam the water searching for prey. The great hammerhead will mainly hunt at dawn or dusk. While hunting, this shark swings its head across a wide-angle to pick up electrical signatures of stingrays which usually bury themselves in the sand. They do this with the help of electroreceptors concentrating on the underside of the cephalofoil.
Once this shark detects a ray, the cephalofoil acts as a hydrofoil, thus, enabling it to turn around very fast while striking at the prey. Observation of this shark species shows that its cephalofoil mostly function to handle prey. As a result, the great hammerhead shark has been seen striking a southern stingray from above with a heavy blow, subsequently pinning it to the seafloor with its head. Then, it turned to take a strong bite at each side of the pectoral fin disc of the ray, hence fully incapacitating the ray. Picking up the ray in its jaws, the great hammerhead shark with rapid shaking of the head tore the ray apart.
A similar incident occurred with a spotted eagle ray observed in open water as the shark took a heavy bite on one of the ray’s pectoral fin, consequently disabling it. Then, pinning the ray on the seafloor took it in its jaws from the head. These observations suggest that the great hammerhead shark tries to incapacitate rays with the first bite.
Food Materials
The great hammerhead shark has a wide variety of diet which includes the favorite prey rays and skates, most especially stingrays.
Other diets of this shark include invertebrates such as squid, octopus, lobster, and crabs. Bony fishes such as sea catfishes, sardines, tarpons, croaker, grunts, porcupine fishes, toad fishes, box fishes, groupers, and flatfishes.
The great hammerhead also feeds on smaller shark species such as smoothhounds and opportunistically on grey reef sharks that got exhausted from chasing mates.
Mating and Reproduction
The great hammerhead shark is a viviparous species. But, in this case, the developing embryos make use of the yolk from the yolk sac at first. However, as they use up their yolk supply, the yolk sac tends to transform into a structure compared to a mammalian placenta. Thus, the embryos now attach to the mother by the placenta structure as the gestation lasts.
Mating of great hammerheads occurs close to the water surface unlike most other sharks that prefer to mate near the sea bottom. The mating pair swim around each other as they ascend to the surface where mating finally occurs.
Breeding occurs once, in two years and gestation lasting for 11 months. The female sharks in the Northern Hemisphere gives birth during late spring toward summer. While the ones inhabiting Australian waters give birth from December to January. The great hammerhead delivers litters of up to 55 pups, although, more commonly 20 to 40 pups litter.
At birth, the baby shark measures 19.5 to 27.5 inches (50 to 70 cm) in length. The males mature at 7.5 to 9.2 feet (2.3 to 2.8 m) while the females mature at 8.2 to 9.8 feet (2.5 to 3.0 m). With their rounded frontal margin, the juvenile great hammerhead shark differs from the adult.
How Long Does the Great Hammerhead Shark Live?
A great hammerhead will typically live up to 20 – 30 years. Though the largest female ever caught, that is the case at Boca Grande, California, was estimated to be around the age of 40 – 50 years.
The Predators of Great Hammerheads
A juvenile great hammerhead shark is prey to large predators as the bull shark (Carcharhinus leucas). As this shark reaches the adult stage, it will no longer have any major predator. Of course, except for the killer whales which may hunt any hammerhead not considering the age.
On the other hand, there are several parasites of the great hammerhead. These includes copepods such as Nesippus orientalis, N. crypturus, Alebion carchariae, A. elegans, Eudactylina pollex, Nemesis atlantica, and Kroyeria gemursa.
The Great Hammerhead and Human Interactions
Considering the size and teeth structure of the great hammerhead shark, it can cause serious harm to humans. This shark has a relative temperament. As such, there are reports of divers underwater suggesting that the great hammerhead shark tends to shy away from humans. Or, still do not react to their presence. Also, there are still reports of this shark species approaching divers closely and even charging towards them as they first enter the water.
The great hammerhead shark has a reputation for aggression and maybe the most dangerous of all hammerheads. There are several shark attacks on humans by hammerhead sharks. But due to the difficulty in differentiating them, it is not certain how many the great hammerhead shark is responsible for. Although, it has been confirmed to be responsible for only one attack.
On the side of humans, the great hammerhead is globally captured as a target and bycatch in commercial and small-scale fisheries. This involves the use of gillnets, pelagic longlines, and trawls. Although these catches are not mainly for the meat as people rarely consume it. But, the fins are of high demand and used for shark fin soup. Other uses include a skin for leather, liver oil for vitamins, and carcass for fishmeal.
Threats and Conservation
The major threat to the population of great hammerheads is overfishing by humans. Moreover, this shark is not naturally abundant due to the long cycle of reproduction. It is quite difficult to assess the conservation status of this species. This is because of the fact that most fisheries group it together with other hammerheads.
In all, the IUCN assessed this species globally as “Critically Endangered (CR)”. There are conservations already in place to protect the great hammerhead in nature.
10 Amazing Great Hammerhead Shark Facts in a Glance
1. Immune to Stingray and Catfish Venom
The great hammerhead hunts stingrays and catfish as meals, nevertheless, it usually does not go unscathed. This is because the stingray and catfish leave their barbs sticking out of the shark’s mouth. However, the shark seems unbothered as it can carry a lot of them while feeling great. Hence, suggesting their immunity to the venom of stingray and catfish.
2. Largest of All Hammerhead Species
The genus Sphyrna has nine species of hammerheads in it including the great hammerhead. But of all these species, the great hammerhead is the largest. This shark grows around 11 feet as an adult and weighs 510lb.
3. Believed to be Cannibalistic
There are speculations that the great hammerhead may feed on its own species in worst-case scenarios.
4. Swims Most Times By Its Side
The great hammerhead shark swims the majority of the time by its side while lifting itself with the dorsal fin. This practice is known as “Rolled Swimming”, and it is an adaptation for energy conservation and reducing drag.
5. The Hammerhead (Cephalofoil) is an Adaptation for Hunting
From tracking of prey to hunt it down, the Cephalofoil of the great hammerhead shark plays important roles. The underside of the Cephalofoil has active electroreceptors that help the shark track down its prey. This follows the detection of electrical fields produced by the prey. More so, it acts as hydrofoil giving the shark quick action in water as it attacks its prey.
6. The Great Hammerhead Tries to Incapacitate Rays with the First Bite
Of the times observed hunting rays, the great hammerhead tends to bite rays first on their pectoral fins. Thus disabling them before taking them in its jaws and sawing them apart.
7. Mating Occurs Near the Water Surface
Courtship involves the mating partner swimming around each other toward the water surface where mating finally takes place. Mating involves the male depositing sperm into the female through his claspers.
8. Great Hammerheads May Cause Severe Injury to Humans
While it is unlikely that great hammerheads would attack humans unprovoked, it is better to take caution near this shark. Of course, their large size and teeth arrangements suggest severe damage in case of an attack.
9. Stingray is the Great Hammerhead’s Favorite Meal
Stingrays are very flat sea creatures that can hide in the sand on the seafloor as camouflage in an attempt to escape predation. But, quite, unfortunately, the great hammerhead can detect their presence often and would always attack them, because they are the favorite prey.
10. The Great Hammerhead Shark (Sphyrna mokarran) is Critically Endangered
The IUCN – International Union for Conservation of Nature in their Red List of threatened species assessed the great hammerhead shark as Critically Endangered (CR). This is a call for concern to save this species.
Conclusion
The great hammerhead is a popular shark species with common human encounters, especially by divers. This is because this shark approaches shallow inshore waters where humans can sight them. Thus, this page contains all the information and facts you need to know about this shark.
A common concern about this shark species is its conservation status which shows that there is a massive decline in its natural population. This calls for more conservation actions to save this species.
Further Reading
- “Great Hammerhead”, Wikipedia (edited 29 January 2020), Wikipedia. Online here
- “Sphyrna mokarran (Great Hammerhead)”, IUCN Red List of threatened species. Online here
- “Great Hammerhead Shark – Sphyrna mokarran“, Oceana. Online here
- “Hammerhead Shark Study Shows Cascade of Evolution Affected Size, Head Shape”. ScienceDaily. 2010. Accessed June 30, 2012. Online here.