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Explorer's Guide
The Exterior of John G. Shedd Aquarium

The Explorer's Guide contains a treasure trove of aquatic science resources developed for use in K-12 classrooms. Back to Explorer's Guide.

Scalloped Hammerhead Shark Scientific Name: Sphyrna lewini
Scalloped hammerhead sharks have a T-shaped head with the eyes and nostrils located at the ends of the T-shape. Moving its head side to side while swimming allows the 14 foot scalloped hammerhead to scan all around and almost behind itself.

Region: Philippines

Taxon: Fish

The scalloped hammerhead shark has a T-shaped head with notches, giving it a scalloped appearance. The eyes and nostrils are located at the far ends of the heads. The pectoral fins or fins on the side of the body behind the gills and the caudal or tail fin have black tips. Most of the dorsal or back part of the body is grey/brown and fades to white near the ventral or stomach area. Like most sharks, the scalloped hammerhead shark exhibits countershading, which means the shark has a dark-colored back and a light-colored belly. When viewed from below, the hammerhead blends in with the brightness of the sunny waters above. Viewed from above, the shark blends in with the dark ocean bottom. Countershading camouflages the animal, allowing it to sneak up on unsuspecting prey.

Scalloped hammerhead sharks can be up to 14 feet (4.3 m) long and weigh as much as 334 pounds (152 kg).

These sharks swim along drop-offs near land in both shallow and deep water to depths of 916 feet (275 m). Scalloped hammerhead will swim close to the shore, sometimes entering bays and estuaries or areas where fresh and salt water mix. Huge schools or large groups of these sharks migrate away from the equator in the summer. Some schools of scalloped hammerheads remain in the same area all the time. These sharks can be found living alone, in pairs, or in schools, but while they are young they live in large schools.

Scalloped hammerhead sharks live in all the warm and moderately warm parts of all the Oceans.

This shark feeds on a wide variety of animals like eels, groupers, grunts, dolphinfish, other sharks, rays, squid, crabs, snails, cuttlefish, and even poisonous scorpionfish. The teeth of the scalloped hammerhead are razor-sharp and hooked, making it easier to grasp, cut and chop up its prey.

Scalloped hammerhead sharks are live-bearing or viviparous fish. Sharks don’t have a placenta like mammals, but they do have a uterus. Inside the uterus, each embryo is enclosed inside a separate membrane. The embryos attach to an egg yolk and leach nutrients from the yolk until birth. The babies or pups are born when they are old enough or large enough to survive on their own. Scalloped hammerheads bear litters of one to four pups or baby sharks. The gestation period lasts at least eight months, but can be as long as 16 months. When born, the pups are 17 to 22 inches (42 to 55 cm) long.

>A species or group of organisms that is in danger of extinction or disappearing from the face of the earth in the near future if its situation is not improved.

A species that can be found throughout its natural range but is declining in number and may become endangered in the absence of special protection efforts.

A species that is not declining in number but is of special concern because it is sensitive to pressure by particular human activities or natural events.

A species that is not declining in number and is not sensitive to pressures by human activities or natural events.

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Threats and Management
In near shore areas pups and juveniles live are often overfished. This leaves few young to grow to adulthood.

Because scalloped hammerhead sharks swim all over the world throughout many oceans, it is hard to track all of these sharks. Many of these sharks are often caught by fishers all over. A lack of information on population numbers makes it difficult to determine whether the high level of catches of scalloped hammerhead sharks is having an effect on their numbers in the ocean. Scientists believe their numbers are declining, but no one can prove this is true.

The fins that are cut off of the scalloped hammerhead shark are taken to markets and sold fresh, dried salted, smoked or frozen. If the whole shark is taken and not left as by-catch, fishers process the rest of the shark. The sandpapery skin is also sold. The liver is converted into oil or is used as vitamins. The rest the animal is smashed up and made into fish food.

Did You Know?
This is one of the most common large sharks in oceans around the world.

The odd-shaped head of the hammerhead shark is used for steering and balance. As the hammerhead swims, it moves it head from side to side, scanning the waters off to the sides and ahead for lurking prey. With its eyes and nostrils on the far ends of its head, this shark can view much more of the surrounding waters than just about any other animal.

Web Sites:
NOTE: The following Web sites are not maintained by the John G. Shedd Aquarium and will open in a new browser window.


Ichthyology at the Florida Museum of Natural History - Sharks:

Print Publications:
Dozier, T.A. 1977. Dangerous Sea Creatures. United States of America: Vineyard Books, Inc. 128p. ISBN# 0-913948-04-7.

Michael, S.W. 1993. Reef Sharks & Rays of the World. A guide to their identification, behavior, and ecology. Petaluma, California: Sea Challengers. 107p. ISBN# 0-930118-18-9.

Perrine, D. 1997. Mysteries of the Sea. Lincolnwood, Illinois: Publications International, Ltd. 312p. ISBN# 0-7853-2430-5.

Tricas, T.C., Deacon, K., Last, P., McCosker, J.E., Walker, T.I. and Taylor, L. 1997. Sharks & Rays. The Nature Company Guides. McMahons Point, Australia. 288p. ISBN# 0-7835-4940-7.

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Vocabulary Words

By-catch – The part of the fisher's catch which is returned to the sea either because it has no value to them. Fishing boats search the seas for target animals, like tuna, and discard anything else they accidentally catch—like sharks. The unwanted animals, called by-catch, dry out or suffocate on the deck, or get thrown back into the ocean all but dead.

Caudal – Having to do with the end or tail of an animal. The tail fin.

Countershading – A form of camouflage in which an animal has a dark-colored back and a light-colored belly. Using fish as an example, when viewed from below, a fish blends in with the brightness of the sunny waters above. Viewed from above, the animal blends in with the dark ocean bottom. Countershading camouflages the animal, allowing it to sneak up on unsuspecting prey or hide from predators.

Dorsal – The back of an animal. The large fin on the back of a shark; the fin that sticks out of the water when a shark swims near the surface.

Estuary – The end or mouth of a river that meets the ocean; where fresh and salt water mix.

Extinction – An organism that has not been present on the face of the earth for over 50 years.

Gestation – The period of development of the young in viviparous animals, from the time of fertilization of the egg until birth.

Organism – A living thing.

Overfishing – The excessive fishing or catching of aquatic (ocean or freshwater) animals to the point that the amount of animals being caught is greater than the amount of animals born. When more animals are caught than are being born, the aquatic environment is left depleted of the targeted animals.

Pectoral – The paired fins on the sides of a fish behind the gills.

Pup – A baby shark.

School – Many of the same fish swimming together.

Species – A group of organisms capable of breeding and producing fertile offspring; organisms that share the same gene pool.

Ventral – The belly of an animal.

Viviparous – A form of reproduction in which the young, or in this case pups, develop inside the mother. Each pup receives food from the mother’s blood through an umbilical cord. The pups are born fully developed and able to hunt and swim on their own. This form of reproduction is referred to as “live birth".

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Scalloped Hammerhead
Photo: Corbis

Scalloped Hammerhead
Copyright Peter Kragh/

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