Sphyrna mokarran

Geographic Range

Great Hammerhead sharks are highly circumtropical and found throughout the Southwest Indian Ocean, along the Gulf of Mexico, the Florida coast and nearby Northwest Atlantic, and within the South China sea. These predators are observed within latitudes ranging between 40 degrees North to 35 degrees South and longitudes ranging between 180 degrees East to 180 degrees West.

• Biogeographic Regions
• neotropical neotropical
  • native native
• australian australian
  • native native
• oceanic islands oceanic islands
  • native native
• indian ocean
  • native native
• atlantic ocean atlantic ocean
  • native native
• pacific ocean pacific ocean
  • native native
• mediterranean sea
  • native native

• Other Geographic Terms
• cosmopolitan cosmopolitan

Habitat

These sharks inhabit both the pelagic and coastal regions in coral reefs, inland seas, lagoons, and bays in tropical and subtropical environments. As great hammerheads are seasonally migratory, they move polewards during the warmer months of the year. Generally, great hammerheads are more commonly observed over the continental shelves and relatively shallow waters both inshore and offshore. Additionally, they tend to prefer warmer temperatures of 20 degrees Celsius and higher. They are found between 1 to 300 meters depth, but most commonly prefer an average of around 80 meters.

• Habitat Regions
• temperate temperate
• tropical tropical
• saltwater or marine saltwater or marine

• Aquatic Biomes
• pelagic pelagic
• reef reef
• coastal coastal
• brackish water brackish water

Physical Description

The Great Hammerhead’s most notable feature is its wide, scalloped head, also known as its cephalofoil. It has a streamlined, fusiform body allowing for speed, and wide-set eyes for visual acuity. Its teeth are triangular and serrated, aiding in the successful capture and consumption of its prey. There are over 30 rows of teeth in the upper jaw alone, not including the midline. Body coloration is variable and ranges from brown to green, with many other hues such as gray or tan. Ventral coloration is white, as is typical in animals that display countershading. The dorsal fin is hooked, high, and long. These sharks can grow up to approximately 6 meters in length and over 227 kg. Claspers on the anal fin indicate the shark is male. Females are typically slightly larger than males.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Development

Great Hammerhead sharks engage in internal fertilization. Seminal fluid is transferred from the clasper into the female's cloaca, and sperm fertilize the eggs in the uterus. Embryos are initially sustained with yolk, then a connection between the uterine wall and yolk sac develops, and functions in a similar way as a placenta does. The young are born live and have flexible, soft heads. Upon being birthed, the young must immediately fend for themselves with instinctual predatory behaviors.

Reproduction

Mating occurs both near the sea bottom and close to the surface. Fertilization occurs internally, wherein the male shark’s claspers fertilize the female’s eggs through the cloaca. The species is viviparous, with embryos sustained on the yolk sack and about 20-40 eggs hatching inside the female and being subsequently sustained with nutrients via the placenta. The female sharks give live birth after a gestation period of about 11 months.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

The Great Hammerhead shark is unique in that it is reported to mate near the surface. Most other species of sharks mate on or near the ocean floor every 2 years, often during spring and summer. Sphyrna mokarran has a gestation period of 7 to 12 months, with 11 months being the average. While there is not sufficient research to substantiate a specific birth mass of the species, pup length at birth is between 50 and 70 centimeters. Females reach sexual maturity at 15 years of age, while males reach it sooner, at 6 years.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• viviparous viviparous

Within the first few minutes after birth, the shark pups will quickly swim away in search of food, becoming an independent predator almost immediately.

• Parental Investment
• no parental involvement

Lifespan/Longevity

The Great Hammerhead shark lives approximately 20 to 40 years of age. The oldest age ever recorded for an individual is 44 years. Age can be determined by carefully counting vertebral rings, while radiocarbon dating and marginal-increment analysis are used to validate the data. Because the of the species' extraordinarily elusive nature, the longest known and expected lifespans in captivity and the longest known lifespan in the wild are unknown. Based on data from similar species, it might be hypothesized that the Great Hammerhead's lifespan would be shortened in captivity due to extremely high levels of stress and aggression created by an inability to migrate seasonally and engage in natural reproductive behaviors.

Behavior

This species is typically solitary but has been noted to migrate in groups during warmer periods, specifically summer. Great Hammerheads move around every day and are found all over the world. There is avid interspecific competition for food and mates, as with many shark species.

• Key Behaviors
• natatorial natatorial
• motile motile
• nomadic nomadic
• migratory migratory
• solitary solitary
• territorial territorial

Home Range

This highly migratory shark is known to travel long distances each day; as such, the home range and territory size is indeterminate.

Communication and Perception

The species has a highly developed electrosensory system as granted by its Ampullae of Lorenzini wherein it is able to detect the electric fields of other animals; this is typically heavily relied upon at dusk in order to detect prey and also to navigate extensive distances. Additionally, the olfactory sense of this shark is indubitably keen, supplying it with the ability to smell blood and track prey from long distances away. Contributing to the said sense of smell are its large nostrils and hammer-shaped head which serve to provide a "stereoscopic" detection of scent. It auditory-detection senses are advanced , especially when picking up lower frequencies. Its lateral line system detects changes in pressure and turbulence, allowing it to effectively navigate in areas of little to no light. Being able to sense these vibrations enables successful predation.

• Communication Channels
• visual visual
• acoustic acoustic
• chemical chemical
• electric electric

• Other Communication Modes
• pheromones pheromones
• vibrations vibrations

• Perception Channels
• visual visual
• acoustic acoustic
• vibrations vibrations
• chemical chemical
• electric electric
• magnetic magnetic

Food Habits

The Great Hammerhead is a carnivore that feeds on invertebrates such as squid and octopus, bony fishes such as skates and rays, and other sharks, thereby engaging in cannibalism. Another well-known favorite of this shark is the stingray. Digested stingray remnants were discovered in the stomachs of over 80% of Great Hammerhead sharks caught off Natal, South Africa. There are few to no known instances of the shark consuming plant matter or detritus.

• Primary Diet
• carnivore carnivore
  • eats non-insect arthropods
  • molluscivore molluscivore
  • eats other marine invertebrates
  • scavenger scavenger
• omnivore omnivore

• Animal Foods
• birds
• mammals
• fish
• mollusks
• aquatic crustaceans
• other marine invertebrates

Predation

The Great Hammerhead Shark has placoid scales; the texture is rough and comparable to sandpaper. They serve to deter any possible predators and to injure prey. Its cartilagenous vertebral column and skeleton allow for maximum flexibility and speed. Due to the combination of these adaptations alongside the Great Hammerhead's position at the top of the food chain, these sharks are very rarely preyed upon. One of the only known predators is the killer whale, whose massive size and penchant to hunt in groups is highly successful, even when tracking down large sharks. Young and wounded sharks are sometimes preyed upon by bigger sharks.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Because sharks are apex/keystone predators, at the highest status in the food chain hierarchy, they serve to regulate populations of cephalopods, crustaceans, and more. Remoras are known to attach to these sharks, and the pilot fish Naucrates ductor is a noted mutualistic partner of Sphyrna mokarran . Naucrates ductor is protected by the shark and is able to eat the leftovers of the shark's meals. Furthermore, they eat parasites such as parasitic siphonostomatoid copepods Alebion elegans . The tapeworm Phoreiobothrium manirei is commonly found within the digestive tract of this shark. There are no known species used as hosts by Sphyrna mokarran .

• Ecosystem Impact
• keystone species keystone species

Economic Importance for Humans: Positive

Humans benefit at the expense of Sphyrna mokarran in that the prized fins of the shark are made into shark fin soup, a Chinese luxury food of an extremely high price. The hides of the Great Hammerhead are used as leather, as is typical for many shark species. Shark fatty oils harvested from the liver, specifically squalene, are used in vitamins, medicine, and health supplements. Sharks prey upon many weak and diseased fish, thereby allowing the lines of slow, sick fish to die out, while faster, healthier fish are able to reproduce and be harvested by fishermen. Great Hammerheads are commonly the victim of bycatch fisheries. This is especially prevalent with long-line fishing.

• Positive Impacts
• food food
• body parts are source of valuable material
• source of medicine or drug source of medicine or drug
• research and education
• controls pest population

Economic Importance for Humans: Negative

The Great Hammerhead shark is the most dangerous of the hammerheads and is more commonly in contact with humans than many other species of shark. This is because they prefer warm waters, a similarly desired environment for surfers, swimmers, and divers. This shark has been said to approach and rush toward divers, swimmers, and surfers when sudden movements are made. Even so, the majority of the demonstrated aggressive behavior of this shark is based on defense and competition. From 1580 to 2012, 37 hammerhead shark attacks have been reported; 17 of these attacks were unprovoked and none fatal. As this data refers only to the genus Sphyrna , it is interesting to note that only 1 attack has been reported as being orchestrated by Sphyrna mokarran . The reported attack was provoked, demonstrating that although Great Hammerheads are dangerous, they do not attack often and are typically provoked first.

• Negative Impacts
• injures humans
  • bites or stings

Conservation Status

The IUCN Red List lists Sphyrna mokarran as an endangered species due to fishing pressure and fin trade. Because the species breeds only once every 2 years, it is very vulnerable to overfishing. Even though the USA and Australia have embraced many bans to prevent shark finning, excessive illegal fishing and lack of implementation for other countries have resulted in a decreasing population trend of the Great Hammerhead shark.

Other Comments

An interesting facet of Sphyrna mokarran is its fondness for stingray consumption. The Great Hammerhead will search the sandy floor for stingrays, whose physical adaptations and cryptic appearance allow it to effectively camouflage. After sensing the vibrations of the creature, the shark will bite the pectoral fin or "wing" of the ray, immobilizing its prey before taking leisurely bites from its body. A Great Hammerhead found off the Florida coast had 96 stingray barbs lodged in its mouth.

An open source photo that could be used for this species account is found at

Additional Links

Encyclopedia of Life

Contributors

Clarissa Saunders (author), San Diego Mesa College, Paul Detwiler (editor), San Diego Mesa College, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Allen, T. 1999. The Shark Almanac . New York, New York: The Lyons Press.

Bray, R. 1996. "Phoreiobothrium manirei Caira, Healy & Swanson, 1996" (On-line). WoRMS World Register of Marine Species. Accessed February 04, 2016 at http://www.marinespecies.org/aphia.php?p=taxdetails&id=419263 .

Bright, M. 2000. The Private Life of Sharks . Mechanicsburg, PA: Stackpole Books.

Burgess, G. 2012. "

ISAF Statistics on Attacking Species of Shark

International Shark Attack File, Florida Museum of Natural History, University of Florida

Caira, J., C. Healy, J. Swanson. 1996.

A New Species of Phoreiobothrium (Cestoidea: Tetraphyllidea) from the Great Hammerhead Shark Sphyrna mokarran and Its Implications for the Evolution of the Onchobothriid Scolex

Denham, J., J. Stevens, C. Simpendorfer, M. Heupel, G. Cliff, A. Morgan, R. Graham, M. Ducrocq, N. Dulvy, M. Seisay, S. Valenti, F. Litvinov, P. Martins. 2007. "Sphyrna mokarran" (On-line).

The IUCN Red List of Threatened Species

Froese, E., D. Pauly. 2016. "Sphyrna mokarran (Rüppell, 1837) Great hammerhead" (On-line). FishBase. Accessed February 03, 2016 at http://www.fishbase.org/summary/SpeciesSummary.php?id=914 .

Hammerschlag, N., A. Gallagher, D. Lazarre, C. Slonim. 2011. Range extension of the Endangered great hammerhead sharak Sphyrna mokarran in the Northwest Atlantic: Preliminary data and significance for conservation. Endangered Species Research Endang. Species Res. , 13/2: 111-116.

Martin, A. 2003. "Biology of Sharks and Rays" (On-line). ReefQuest Centre for Shark Research. Accessed May 01, 2016 at http://www.elasmo-research.org/education/ecology/sandy-gt_hammerhead.htm .

Oldewage, W., M. Smale. 1993. Occurrence of piscine parasitic copepods (Crustacea) on sharks taken mainly off Cape Recife, South Africa. South African Journal of Marine Science , 13/1: 309-312.

Piercy, A., J. Carlson, M. Passerotti. 2010. Age and growth of the great hammerhead shark, Sphyrna mokarran, in the north-western Atlantic Ocean and Gulf of Mexico.

Marine and Freshwater Research

Snyderman, M. 1997. Shark: Endangered Predator of the Sea . San Diego, CA: Laurel Glen Publishing.

Stafford-Deitsch, J. 2000. Sharks of Florida, the Bahamas, the Caribbean and the Gulf of Mexico . Piccadilly, London: Trident Press Ltd.

van Dyck, C. 1993. Fish: An Enthusiast's Guide . Oxford, England: University of California Press.

2015. "Great Hammerhead Shark (Sphyrna Mokarran) - Office of Protected Resources - NOAA Fisheries" (On-line).

NOAA Fisheries: Office of Protected Resources

2013. "Great Hammerhead Sharks, Sphyrna mokarran" (On-line). MarineBio Conservation Society. Accessed February 04, 2016 at http://marinebio.org/species.asp?id=87 .

2016. "SHARKS' ROLE IN THE OCEANS" (On-line). SharkSavers WildAid. Accessed May 01, 2016 at http://www.sharksavers.org/en/education/the-value-of-sharks/sharks-role-in-the-ocean/ .

2000. "Sphyrna mokarran; Great Hammerhead Shark" (On-line). Encyclopedia of Life. Accessed April 27, 2016 at http://eol.org/pages/224168/details .