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Facts about Hammerhead Sharks

[Phylum: Chordata] [Class: Chondrichthyes] [Order: Carcharhiniformes] [Family: Sphyrnidae]

Compared to the other shark species, one of the genus is instantly recognisable by the unconventional shape of its T-shaped head - like a hammer!

This guide contains fun and interesting facts about hammerhead sharks (Sphyrnidae), including where you can find them, what they eat, and how they reproduce.

Where Does the Hammerhead Shark Live?

Most of the hammerhead species prefer living in temperate and tropical oceanic environments, especially:

Often, the best place to see shoaling hammerheads is close to the surface as they cruise along continental shelves or gliding along the benthic zones of island coastlines.

Even so, most of the species prefer not to endure hot summer temperatures. As a result, they will conduct a mass migration away from the equator to find cooler water.

Hammerheads Behaviour and Characteristics

Having a white belly means this shark species blends into the background when viewed from below. Thus, most of the family Sphyrnidae use this means of camouflage when sneaking up on their prey. The upper sides have a light grey colouring with an olive green hue.

They have quite a small mouth for a large predatory fish, located on the underside of its head. Their teeth are very sharp, saw-like (serrated), and triangular in shape.

The lateral projections on the head (called cephalofoils) are the main reason for scientists to choose the somewhat funny fish names for hammerhead sharks.

Even though most hammerhead shark species have the same distinct hammer-like shape, the actual outline differs among the family Sphyrnidae.

For example:

The great hammerhead shark features a very distinct T-shaped cephalofoil. Whereas, a scalloped hammerhead has a rounded head containing a central notch, and the head of the smooth hammerhead is also rounded, but there it's not notched.

In general, the two outward extensions located on each side of the head serve several important functions for this distinctive group of sharks, including:

Pro Tip: Even though hammerhead eyes can produce almost 360 degrees of vision, they have a blind spot. They are unable to see straight ahead (e.g. directly in front of their nose).

Different Species of Hammerhead Shark

Having different length fins (compared to other sharks), and being able to tilt the dorsal fin, means hammerheads can swim in a sideways direction. Plus, an expansion in "wingspan" means they can also increase their swimming efficiency.

The Smallest and Biggest Hammerhead Species

Most of the known species range in size from one metre to six (6) metres long (20 feet). The biggest specimens can weigh up to 600 kilograms (1,000 pounds).

The scalloped bonnethead is the smallest species of hammerhead shark. Even when fully matured, they will grow to a maximum of ninety (90) centimetres (35 inches).

By comparison, the great hammerhead shark is the largest, growing to lengths that can measure in excess of six metres. It also happens to be the most aggressive specimen, even though recorded shark attacks on humans are scarce.

Fun Fact: Some hammerhead sharks have developed the ability to tan their skin while cruising in shallow water, from light to dark grey. Scientific studies are trying to determine how they tan without getting skin cancer.

What Do Hammerhead Sharks Eat?

Even though some species swim in schools during the daylight, they tend to search for seafloor-dwellers as solitary hunters when the sun starts to set.

As a natural carnivore, most prowling hammerheads hunt alone. They use the crescent-shaped mouth to rummage around the ocean floor searching for their favourite food source hidden under the sand - stingray fish!

Here's the thing:

Bonnethead sharks are the only known omnivore in the species that eat seagrass (including the gargantuan whale sharks). By comparison, others are cannibalistic in nature, meaning they will eat smaller hammerheads.

For the most part, the hammerhead shark will eat a healthy combination of small size fishes and bottom dwelling animals, including:

Despite being their favourite prey of choice, hammerheads have evolved a tolerance to the sharp sting of stingrays and it's not uncommon to see the barbs embedded in their skin.

How Do Hammerheads Reproduce?

Female hammerhead sharks are viviparous - meaning they do not lay eggs. They reproduce one time per year and the gestation period is around ten months.

After giving birth to a litter of about fifteen pups (up to 40 for great hammerheads), the live young are left to fend for themselves. The juveniles tend to have a more rounded head than the adult form.

Interesting Fact: In 2007, zoologists discovered a bonnet shark (shovelhead) capable of asexual reproduction. It took place through a process called "automictic parthenogenesis" where the female is able to fertilise her own egg and no male was involved in the reproductive act.

Threats and Predators

Other than human activities, the kings of the ocean have very few natural predators. In fact, hammerhead sharks can live up to thirty (30) years, and attacks by other species tend to be limited to large sharks, dolphins, and killer whales (orcas).

Even though most of the human interventions result from bycatch, shark fin traders also have a negative effect on their long term survival. Hammerhead meat is mostly unwanted, excluding Japan, Kenya, and Venezuela.

Important: The IUCN Red List of Threatened Species cites most of the hammerhead shark family Sphyrnidae as being either "Critically Endangered" (CR) or "Vulnerable" (VU). However, the bonnethead shark is listed as being "Largely Depleted" (LD).

Related Information and Help Guides

Note: The short video [3:57 seconds] presented by "BBC Earth" contains amazing footage of the complex mating rituals of hammerhead sharks - filmed in the Galapagos Islands.

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