The hammerhead shark (Sphyrna mokarran) is a fish that belongs to the Sphyrnidae family. It is characterized by its head with the appearance of a hammer, rectangular and straight, in relation to the major axis of its body..
It has a robust body, where a large curved dorsal fin stands out. Regarding its coloration, dorsally it can be from light gray to dark brown, a color that fades to the ventral area, which is white..
This shark, which can reach 6 meters, lives in warm and temperate waters around the world. Although it can be distributed in a diversity of habitats, it prefers the continental shelf and coastal areas.
The Sphyrna mokarran uses a method of getting around known as coiled swimming. In this, the shark turns to the side and continues swimming forward. This posture conserves energy and minimizes drag, saving nearly 10% on drag and movement cost..
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At birth, the baby hammerhead shark is between 60 and 70 centimeters long. In adulthood, their body length measures between 3.5 and 4 meters, although there are records of sharks of 6.1 meters.
Regarding the weight, this species can have from 200 to 500 kilograms. However, animals weighing up to 580 kilograms have been found.
The characteristic that distinguishes the Sphyrna mokarran It is the particular shape of its head, in the shape of a T. The width of the head occupies between 23 and 27% of the total length of the body. In this, the nostrils and eyes are at the ends, so, to have a global vision of the environment, the shark moves its head from side to side.
In the young, the front margin is slightly curved. When the animal is adult, it becomes almost straight, with a small notch in the center. In addition, it has a shallow rounded depression near each nostril.
As for the mouth, it is widely arched, with small labial grooves on the lower jaw. The corners of the mouth are behind the outer corners of the head.
Hammerhead shark teeth adapted to cut through the body of their prey. These are sharp, heavily serrated, and triangular in shape. Towards the corner of the mouth they are oriented obliquely.
There are 17 teeth on each side of the upper jaw. The midline or mandibular symphysis has two or three of these bony structures. Regarding the lower jaw, there are 16 or 17 teeth, 1-3 of which are located in the symphysis.
Those that are located in the anterior part are characterized by having jagged edges and long central cusps, while most of the posterior ones end in a point
This species has two dorsal fins. The first is very tall and heavily falcate. Its origin is located above the insertions of the pectoral fins. As for the second, it is large and tall, with a short inner margin, contrary to the posterior one, which is concave..
The anal fin is curved, with a deep posterior edge, where it is notched. In relation to the pectorals, they are wide, short and curved. Its shape is similar to a sickle, with concave rear edges. As for the pelvics, they are falcate, with sunken back margins.
The dorsal area of the Sphyrna mokarran It has a dark brown, olive or grayish hue, while the lower part is white. In adults, the fins do not present any color different from the rest of the body, but in youngsters the tip of the second dorsal fin may be dark.
The hammerhead shark has tiny pores, known as Lorenzini blisters, all over the ventral surface of the head. These work as highly sensitive electrical receptors, which capture the electrical signals emitted by the prey, even if they are buried in the sand..
The skin of this shark is covered by dermal denticles, which are superimposed along the entire length of the lateral and frontal margins. These are diamond-shaped, with horizontal ridges that vary in number depending on the size of the animal..
Thus, the small species can have between 3 and 5 crests, while the largest have 5 to 6.
The hammerhead shark is part of a unique group of elasmobranchs characterized by having a laterally expanded and dorsoventrally compressed head area. In addition, the chondrocranium is modified in the olfactory, rostral and optic regions.
Researchers hypothesize about the benefits of this hammer-shaped head for shark. One of these consists of the hydrodynamic lift at the front end of the animal. This increases maneuverability and makes it easier to chase your prey..
Also, it offers a higher resolution of the olfactory gradient, due to the wide distance between the two nostrils. Thus, the hammerhead shark can capture odors that are spatially separated, which implies greater olfactory acuity and a large sampling area..
Another theory is that it provides shark with improved binocular vision. The fact that the eyes are at both ends of the head, increases the anterior binocular vision and increases its visual field.
In turn, the extension of the surface of the head expands the electrosensory area in charge of receiving the electrical stimuli that some prey, such as stingrays, may emit, thus being able to have a greater capacity to detect and capture them..
Animal Kingdom.
Subkingdom: Bilateria.
Phylum: Chordate.
Subfilum: Vertebrate.
Superclass: Chondrichthyes.
Class: Chondrichthyes.
Subclass: Elasmobranchii.
Superorder: Euselachii.
Order: Carcharhiniformes.
Family: Sphyrnidae.
Species: Sphyrna mokarran.
The great hammerhead shark is distributed in tropical waters worldwide, between latitudes of 40 ° N and 37 ° S. In this way, it can be located along the Indian Ocean and in the Indo-Pacific, from French and New Polynesia Caledonia to the Ryukyu Islands in Japan.
In the eastern Pacific it lives from southern Baja California to Mexico and the southern area of Peru. In relation to the Atlantic Ocean, the populations range from North Carolina to Uruguay, including the Caribbean Sea and the Gulf of Mexico. In the eastern Atlantic region it is found from Morocco to the Mediterranean Sea and Senegal.
The habitat of Sphyrna mokarran it's very diverse. It can live both in coastal waters, less than 1 meter deep, and in the high seas, 80 meters from the surface. They are also found on coral reefs, on continental shelves, lagoons and in areas near islands..
This species, unlike other members of the Sphyrnidae family, generally does not form aggregations. On the contrary, it is nomadic and migrates within its tropical coastal-pelagic range..
In recent studies, data were revealed that confirm that the whale shark made a trip from the southern coast of Florida to the mid-Atlantic Ocean, off the coast of New Jersey. A journey of 1,200 kilometers made in 62 days.
Such evidence, related to long-distance migrations in a relatively short time, could indicate that the species may possibly carry out transoceanic mobilizations..
Researchers have observed the hammerhead shark at stops or precise locations in the Bahamas, which could indicate that these places are migratory paths used by this large fish..
In this sense, there are references to the displacements, during the summer season, of the populations located in the South China Sea and in Florida to the regions near the poles..
The great hammerhead shark is on the IUCN list of endangered species. The reason is the significant decrease that its population has been suffering throughout its geographical range..
This species is caught incidentally with longlines, hooks, fixed bottom nets, and bottom and pelagic trawls..
Also, it is hunted to market its fins, whose international prices are high, driven by the Asian market. This part of your body is the main ingredient in the famous Asian dish known as shark fin soup. In addition, your liver is used to extract an oil highly used in the pharmaceutical industry..
Its bycatch occurs in both artisanal and industrial fishing. In times past, the hammerhead shark was observed from Mauritania to Angola. However, evidence suggests that its population has declined to such low levels that it can be considered almost extinct..
The increase in hunting began in the 1970s, when a commercial network was established in The Gambia, encouraging local fishermen to fish for this shark, to export them to other countries..
The Sphyrna mokarran he is a summer migrant to KwaZulu-Natal, on the east coast of South Africa, where his capture has occurred frequently. However, in recent years this situation has decreased.
Bycatch occurs in bottom and pelagic longline and net fisheries throughout the Gulf of Mexico and the Northwest Atlantic. It is also caught as part of recreational fishing.
The meat is not the main objective of their hunting, but their fins, since they are sold at an excellent price. Because of this, fishing still occurs in some regions of the United States..
During the 1980s and early 1990s, off the coast of Belize, the hammerhead shark was fished with longlines. This has caused a drastic decrease in their population, as a result of overexploitation.
In the north of this country, cases of illegal fishing have increased. In addition, in the Great Barrier Reef, northeast of Australia, longlines are used to mitigate shark attacks. This leads to the death of large numbers of hammerhead sharks..
The Sphyrna mokarran male reaches sexual maturity when it weighs 51 kilograms and measures between 2.3 and 2.8 meters. As for the female, it is capable of reproducing from the moment that it has a length of 2.5 to 3 meters, with an approximate weight of 41 kilograms.
The vast majority of sharks breed on or near the bottom of the sea. However, the hammerhead shark mates in an area close to the surface. Mating occurs once every two years and the process begins when the male bites the female on her fins, until she accepts him as a mate..
This species has a viviparous mode of reproduction. Similar to other sharks, fertilization occurs internally. During copulation, the male introduces one of his two hemipenis into the female's cloaca, thus transferring the sperm to her..
Initially, embryos develop within a yolk sac. As soon as the yolk is used up, the sac is transformed into a structure known as a pseudo-placenta, similar to the placenta in mammals. Through this, the mother provides nutrients to the embryo for its development.
After eleven months of gestation, the young are born. The size of the litter can vary between 6 and 55 young, although generally it is usually 20 to 40. Newborns can measure from 60 to 70 centimeters. The head of the young person does not have the same hardness of the adult, in addition its margin is curved.
The hammerhead shark is an active predator that has a highly varied diet. This includes crabs, squid, lobsters, octopus, and bony fish, such as sardines, shad, sea catfish, grouper, toadfish, boxfish, and porcupines. You can also eat smaller sharks and elasmobranch fish.
In the Rangiroa Atoll region of French Polynesia, the Sphyrna mokarran opportunistically captures the gray reef shark (Carcharhinus amblyrhynchos), when it is exhausted, after having had a long chase of other fish.
However, the preferred food is the skate, such as the American whip ray (American dasyatis). In addition, they frequently hunt the cartilaginous guitarfish, which inhabit the seafloor of the eastern Pacific coasts..
Hunting for their prey occurs at dusk or dawn. For this, he swims above the depths of the ocean, moving his head from side to side at wide angles..
In locating its food, the hammerhead fish uses the Lorenzini blisters on the surface of its head. These allow it to capture the electrical waves emitted by some fish, such as rays, even though they are buried in the sand.
The particular shape of its head works like an airboat, making it easier for the shark to make quick turns. In this way, it can catch its prey more quickly despite its large size. Likewise, it could hit the line with the head, causing it to fall to the bottom..
Once there, if the animal tries to get up, the hammerhead shark gives it a second blow that sends it back to the sand, at which point the shark takes the opportunity to bite the pectoral fins of the ray..
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