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Of all shark species the hammerhead shark is one of the most unusual. In this article we will discuss everything you ever wanted to know about this amazing creature from its unusual head shape to its diet and expected lifespan. If there is anything you have ever wanted to know about the hammerhead shark this is the place to find it.
What is the Hammerhead Shark?
The hammerhead shark is a member of the subclass Elasmobranchii, a subsection of the Chondrichthytes order that encompasses sharks. More specifically the hammerhead shark is a member of the order Carcharhiniformes, this particular order includes over 270 species of sharks. Carcharhiniformes are a group of sharks that include more species than any other order and are recognized as being “ground sharks.” Members of the ground shark Carcharhiniformes order include a number of commonly recognized species including the blue shark, sandbar shark and of course, the hammerhead shark.
Identifying Carcharhiniformes Sharks
Sharks within the Carcharhiniformes order are recognized by a specific set of characteristics. These characteristics include the presence of two dorsal fins, an anal fin, five gill slits and a nictitating membrane. The nictitating membrane is a translucent membrane that protects the eye while also providing adequate moisture and allowing the shark to see through it. This membrane is often recognized as a third eyelid and can not only be found in sharks but also in birds, amphibians and reptiles as well. Uniquely birds are able to actively control their nictitating membrane where sharks cannot and the appearance of the membrane is a reflex.
There are currently eight known families of Carcharhiniformes sharks; however, there is a dispute over the classification of all eight of these families as Carcharhiniformes. Scientists currently question whether all eight of these species are actually all descended from a similar ancestor and this question seems to indicate that sometime in the near future the Carcharhiniformes order will be revised. Currently the eight families of shark included in this order are: carcharhinidae or requiem sharks, hemigaleidae or weasel sharks, leptocharidar or barbeled houndsharks, proscyliidae or finback cat sharks, pseudotriakidae or false cat sharks, scyliorhinidae or cat sharks, Sphyrnidae or hammerhead sharks and tiakidae or hound sharks.
The Family Sphyrnidae
All hammerhead sharks are a group of sharks that fall in to the family Sphyrnidae. The majority of hammerhead sharks are designated in the Sohyrna genus; however, there is a species of hammerhead called the winghead shark that has its own genus – Eusphyra. There are currently only two recognized genera of hammerhead shark. Within the nine genera of hammerhead sharks there are currently nine recognized species which include the: winghead shark, scalloped bonnethead, whitefin hammerhead, scalloped hammerhead, scoophead, great hammerhead, bonnethead, smalleye hammerhead and smooth hammerhead.
The Physical Appearance of the Hammerhead
There are a number of hammerhead species which means that there is quite a bit of variation when it comes to the physical appearance of this shark but there are some characteristics that seem to be constant. The majority of hammerhead sharks are light grey in color and have a somewhat green color to them but they also feature light white bellies. Like many sharks with light under bellies the hammerhead is able to move along the bottom of the ocean and blend in with its surroundings in order to hunt prey. Since there is such considerable diversity among hammerhead species there is also considerable difference in the weight and length of each species. In general however, hammerheads grow to be anywhere from 3 to 20 feet in length and can weight anywhere from 500 to 1,000 pounds!
The Hammer Shaped Head
The most commonly recognized feature of the hammerhead shark is obviously the hammer shape to its head which is thought to have evolved as a way to enhance the eyesight of this group of sharks. The positioning of the eyes at the ends of the hammer shaped head provides the animal with a 360 degree field of vision in addition to providing binocular vision. The extremely versatile field of vision of the hammerhead shark allows for this creature to not only see around itself but to also view above and below itself as well. The most accepted explanation of the strange shaped head of the hammerhead shark is the adaptation of sensory function.
Sharks are well-known for the sensory pores which are distributed over their snout. These pores, scientifically named the ampullae of Lorenzini, serve to receive electrical signals through the water to help the shark locate prey. While most sharks have a concentration of these unique pores on their smaller snouts, the hammerhead has a much larger head and the pores are more spaced out providing a wider area of electroreceptory sensors thereby improving hunting skills.
Over the past few years there have been a number of ideas as to why the hammerhead has such a uniquely shaped head, these have ranged from making it easier for the shark to move through the tighter areas to helping the shark to find food more effectively. The most accepted explanation of the hammer shaped head currently is the wide distribution of electrosensory receptors.
Video: Hammerhead Sharks in The Wild
Want to take a swim with the sharks? (Without getting hurt of course!). Watch the two-minute video from National Geographic showing how they can whip their bodies around and see with panoramic vision.
Behavior of the Hammerhead Shark
Hunting Habits of the Hammerhead
As feeders the hammerhead shark species tend to hunt the majority of their prey along the bottom of the ocean. This type of hunting is believed to be the reason why these sharks have such small mouths. A large portion of the hammerhead’s lifetime is spent hunting but unlike most other shark species, the hammerhead is known for schooling behavior. Most sharks hunt independently and while the hammerhead will hunt independently at night-time, it tends to prefer schooling during the day. When schooling hammerheads can reach groups as large as 100 sharks.
Reproduction of the Hammerhead
Reproductive behavior of the hammerhead shark is seen only once every year and after gestation the female hammerhead gives birth to live young. Unfortunately for the female hammerhead the process of breeding is often a violent one in which she is bitten by the male of the species until she relents to the mating request. On average the hammerhead shark female gives birth to 12 to 15 pups in a single birthing session. The exception to this litter size is the Great Hammerhead that births 20 to 40 pups per litter. The hammerhead shark is not a nurturing species and after the birth of thee pups the females of the species leave their young to fend for themselves. As young small pups the hammerhead youngsters will move in a closely knit group to an area of warmer water where they will continue to stick together until they are large enough to defend themselves against predation.
While the majority of hammerhead sharks reproduce sexually, in 2007 the bonnethead shark was found to be capable of asexual reproduction. This finding was a particularly significant discovery since prior to 2007 no shark had ever been known to reproduce in such a manner. The bonnethead shark can asexually reproduce through automictic parthenogenesis, a process in which the egg of the female fuses with a polar body that is found within the ovum.
Diet of the Hammerhead
The hammerhead shark is a species of shark that is not particularly picky about its diet and they have been known to eat an incredible variety of foods. One of the favorite sources of nutrition for the hammerhead is stingrays; however, they are also fond of fish, octopi, crustaceans and other hammerhead sharks. Stingrays are believed to be the favorite food source for this shark due to their bottom hunting behavior. Hammerheads commonly patrol the bottom of the sea in an attempt to find food; this is believed to be a much more convenient hunting method due to their smaller mouths. Where most shark species have rather large mouths in comparison to the rest of their body, the hammerhead has a rather small mouth that sits underneath the hammer shaped head. The hammer shaped head of this shark species not only determines their hunting and feeding method but it also assists in the capturing of prey. As the hammerhead spots and tracks down prey it relies upon its large head to hold down prey while it eats.
Of all of the various hammerhead species, the great hammerhead shark is the most aggressive. In addition to having increased levels of aggression this type of hammerhead shark is also one of the largest of the hammerhead species making them a particular threat. The great hammerhead feeds on a similar diet to other hammerhead sharks but are much more aggressive hunters; these sharks are also known to pose a threat to humans.
The Hammerhead Shark and Humans
There are three species of hammerhead shark that are noted for being particularly dangerous to human beings. While it is often stated that sharks do not intentionally hunt human prey, these hammerheads are aggressive and when they do attack humans, whether out of confusion or intention, they inflict a significant amount of damage. The three most dangerous hammerhead species to humans include the great hammerhead, the scalloped hammerhead and the smooth hammerhead. Both the great and the scalloped hammerheads are considered to be endangered and have been since 2008. It is not fear of these sharks that causes them to find a place on the International Union for Conservation of Nature‘s endangered species list, but rather overfishing and hunting. These sharks are particularly in demand for their fins that are purchased in many foreign cultures as a delicacy that offers a number of health benefits in holistic medicine. Often these sharks are captured, have their fins removed, and are re-released in to the ocean where they inevitably perish.
While these hammerhead species may be some of the most aggressive of hammerhead sharks there is certainly no excuse for the behavior of fishermen who have driven two of the three species mentioned above to the verge of extinction. The various shark populations have managed to survive and evolve from the time of the dinosaurs and it is inexcusable that the human race be the cause of extinction for these amazingly versatile creatures.
Revering the Shark
In one area in particular the shark is revered as being a god of the sea. While many cultures choose to focus on the potential for shark attacks and the unconventional appearance of these creatures, Hawaii does not. The native Hawaiian culture believes the shark to be protectors of the human race, cleaners of the ocean – removing excessive ocean life, and overall gods of the sea. It is their belief that sharks are the reincarnation of relatives who have passed away. Hammerheads are not too common around the Hawaiian Islands but when they are seen they are considered to be a good omen and a sign that the ocean is well-balanced and in harmony. The hammerhead shark in particular is seen as being one of the most protective sharks to the human race and is well-respected for being able to protect families from the man-eating sharks. While many sharks are revered there are a small few sharks that are respected for their “man-eating” reputation including the great white shark, the bull shark and the tiger shark.
While the Hawaiian people respect the status of man-eating sharks in addition to the protective sharks, it is illegal to fish any species of shark in Hawaii. Fishing for or hurting sharks in any way is seen as an interference not only to the Hawaiian way of life and against their spiritual beliefs but it is also an interference with the natural balance of the ecosystem. Anyone caught attempting to catch or harm a shark in Hawaii faces felony charges.
The Lifespan of the Hammerhead Shark
The hammerhead shark like many sharks tend to live longer lives when they are not kept in captivity, this lifespan ranges from 20 to 30 years. Sharks, unlike some other animals do not experience longer life spans in captivity. There is some disagreement as to why sharks do not thrive in captivity but the most commonly held belief is that they are not only difficult to transport but they are also difficult to care for due to their unique requirements. While larger species of sharks have been known to survive for period of time in captivity they are generally re-released in to the wild before they show signs of degradation that often accompany captive living.
The Natural Habitat of the Hammerhead Shark
While the hammerhead shark does not thrive in captivity it is a widespread species when it comes to living in the wild. Hammerheads prefer to swim in the warm waters that run along coastlines and prefer to live in the mesopelagic zone of the ocean at around 260 feet in-depth. When it comes to distribution around the globe, the hammerhead can be found in a band that crosses the entire world covering all tropical and sub-tropical waters. This band of hammerhead territory covers territory from the upper North American continent to the base of the South American continent and stretches worldwide. The hammerhead is known to migrate during the summer to cooler areas of the ocean but still remain within the banded area described above.
What is known About the Evolution of Hammerhead Sharks?
When it comes to tracking the evolution of any shark species the process is somewhat inaccurate due to the fact that sharks do not have mineralized bones that get left behind when they die and settle to the bottom of the ocean. Most species of shark are identified by their teeth since the remains of sharks rarely fossilize. Identifying species of shark by their teeth these days is a much easier process than trying to identify extinct or previous species of shark since common day sharks can be identified from shark marine biologist research. To the best accuracy, it is believed that the hammerhead is closely related to the carcharhinid sharks that were around during the mid-tertiary period sue to similarities in tooth structure. These similarities in tooth structure however, make it difficult for researchers to determine when the hammerhead shark actually first appeared.
What is believed to be the most accurate “family tree” of the hammerhead shark to date was created by Andrew Martin and utilized mitochondrial DNA to create the phylogenetic tree tracing the history of this unique shark species. Using this DNA Martin established that the earliest branch of the hammerhead shark family was the winghead shark. This finding seems to suggest that the earlier species of hammerheads had significantly large “hammers” in comparison to the more recently evolved hammerhead species.
Should We Fear the Hammerhead?
Like any other species of animal the hammerhead should be respected for its ability to inflict damage upon the human race. With that said; however, these sharks rarely attack human beings and those that do rarely result in fatalities. The hammerhead shark, just like any other species of shark plays a significant role in maintaining a healthy and balanced ocean ecosystem. Without the hammerhead shark it is quite possible that many oceanic species would no longer be kept in check and the result would be potentially disastrous for a number of plants and other organisms that thrive within today’s oceans. When asked if we should fear the hammerhead, the question should perhaps be posed: should the hammerhead fear us because after all only one of the two creatures in the statement is currently looking at extinction of a handful of their species.
Have you ever encountered a Hammerhead shark?