Hammerhead sharks are recognizable predators, distinguished by their uniquely shaped heads. This distinctive “hammer” or cephalofoil provides a wide field of vision, aiding in their predatory success. They inhabit marine environments globally, intriguing scientists and the public with their unusual appearance and ecological roles.
Identifying the Hammerhead Species
The hammerhead family, Sphyrnidae, encompasses ten recognized species. These species are categorized into two genera: Sphyrna, which includes nine species, and Eusphyra, containing a single species. While all share the characteristic hammer-shaped head, subtle variations in its morphology distinguish each type.
The ten species are:
Great Hammerhead
Scalloped Hammerhead
Smooth Hammerhead
Bonnethead
Winghead Shark
Smalleye Hammerhead
Scoophead
Scalloped Bonnethead
Whitefin Hammerhead
Carolina Hammerhead
Distinctive Features of Each Species
The Great Hammerhead (Sphyrna mokarran) is the largest species, reaching up to 20 feet in length. Its cephalofoil is notably wide with a nearly straight front edge, featuring a prominent median indentation. This characteristic straight edge helps differentiate it from other large hammerheads.
The Scalloped Hammerhead (Sphyrna lewini) has a distinct central indentation on its head, along with two additional indentations on either side, giving it a “scalloped” appearance. This species can reach up to 11 feet long.
The Smooth Hammerhead (Sphyrna zygaena) is the second largest hammerhead, growing up to 16 feet. Its cephalofoil has a smoothly curved front margin without the central indentation seen in other species, which gives it its name. This head shape provides depth perception and a wide field of view.
The Bonnethead (Sphyrna tiburo) is one of the smallest hammerheads, reaching 3 to 4 feet in length. Its head is shovel-shaped or bonnet-shaped, smooth and rounded without notches. Male and female bonnetheads exhibit different head shapes, with adult males developing a distinct bulge in the middle of their hammer.
The Winghead Shark (Eusphyra blochii) has an elongated, wing-shaped cephalofoil. This medium-sized shark can reach about 6 feet in length.
The Smalleye Hammerhead (Sphyrna tudes) is a smaller species, around 4 to 5 feet long. It is often called the “golden hammerhead” due to its bright gold or orange-yellow coloration, which comes from its diet of shrimp and sea catfish.
The Scoophead (Sphyrna media) is another smaller hammerhead, reaching about 5 feet. It has a broad, mallet-shaped head with an arched front margin and weak indentations, appearing similar to the scalloped bonnethead.
The Scalloped Bonnethead (Sphyrna corona) is one of the rarest and smallest, around 3 feet long, with a rounded head that has scalloped edges.
The Whitefin Hammerhead (Sphyrna couardi) can grow over 9 feet long and is characterized by a broad head with narrower blades compared to some other species. Its name is a misnomer, as its fins are not white; the name may refer to the absence of dark fin tips seen in other sharks.
The Carolina Hammerhead (Sphyrna gilberti) was only formally described in 2013. It is almost identical in appearance to the scalloped hammerhead but is genetically distinct and has fewer vertebrae.
Global Habitats and Distribution
Hammerhead sharks are widely distributed throughout tropical and warm temperate marine waters worldwide. They are found in coastal areas, including shallow lagoons and coral reefs, as well as over continental shelves. Some species also venture into deeper pelagic (open ocean) waters.
Different species exhibit specific habitat preferences. For instance, the Great Hammerhead prefers warm, tropical waters near coral reefs and continental shelves, and can be found in depths up to 300 meters. Scalloped Hammerheads inhabit coastal warm temperate and tropical seas globally, often near continental and insular shelves, and form large schools.
Smooth Hammerheads, while widely distributed, prefer temperate waters and migrate poleward in summer, sometimes forming schools. Bonnetheads are abundant in shallow coastal waters, estuaries, and bays, often over sandy and muddy bottoms. The Smalleye Hammerhead prefers shallow, muddy areas off the east coast of South America.
Conservation Status
Many hammerhead shark species face conservation challenges, with more than half listed as threatened. Primary threats include overfishing for their fins and meat, habitat degradation, and bycatch in commercial fisheries. Their fins are valued in the global shark fin trade due to their large size and high cartilage content.
Conservation organizations, such as the IUCN Red List, assess the status of these species. The Great Hammerhead, Scalloped Hammerhead, Smalleye Hammerhead, Scalloped Bonnethead, and Scoophead are classified as Critically Endangered. The Smooth Hammerhead and Winghead Shark are listed as Vulnerable or Endangered, respectively. Bonnethead sharks are listed as Endangered.
High mortality rates from fishing, combined with their late sexual maturity and infrequent reproduction, hinder population recovery. Protecting these predators is important for maintaining healthy marine ecosystems.