Understanding the mechanics of hammerhead sharks reveals how their distinct head shape gives them an edge in the wild. Discover how their unique features help them thrive.

Key Insights

Great white sharks exude confidence, standing as the apex predator of the seas. Tiger and bull sharks are no less impressive, silent hunters that captivate on screen and strike fear in those on the beach. White tips and threshers are fierce as well, but not as notorious as their larger, more intimidating cousins. Meanwhile, hammerheads are often overlooked. With their small mouths and modest teeth, they aren't much of a threat to humans. Their odd, hammer-shaped heads and wide-set eyes often make them seem almost comical, not to mention their reputation among divers and surfers as harmless.

Shark Photo Collection

Hammerheads may not always get the attention they deserve, but they are undeniably fascinating. There are nine different types of hammerhead sharks, though only four species are commonly found: the great hammerhead, scalloped hammerhead, smooth hammerhead, and bonnethead. Of these, all except the bonnethead are considered capable of posing a threat to humans, though incidents are rare. Since 1580, there have only been 38 documented attacks on humans, 16 of which were unprovoked, and none have resulted in fatalities [source: ISAF]. Generally, hammerheads are not aggressive, and the few unprovoked attacks are likely the result of surprise or fear.

Hammerhead sharks can be found in temperate and tropical seas across the globe. Some species, like the great hammerhead, prefer the depths, while others stay closer to the coast. They tend to gravitate toward cooler waters, migrating in schools toward the poles during warmer months. These sharks are targeted both commercially and recreationally for their skins and meat. Additionally, like many sharks, they are victims of finning, where their fins are removed and sold as an ingredient in shark fin soup in Asia. Shark finning is widely regarded as inhumane and is banned in U.S. waters.

This article will delve into the distinctive physical features of the hammerhead shark and explore the various theories surrounding the purpose of their unique head shape. We'll also examine their mating behaviors, hunting techniques, dietary preferences, and the species that travel in schools.

The Hammerhead Shark's Journey

Hammerhead sharks vary significantly in size depending on the species. Scalloped hammerheads typically grow between 5 and 10 feet (1.5 to 3 meters) in length and weigh from 175 to 225 pounds (80 to 100 kg). Smooth hammerheads can be a bit larger, but the great hammerhead is by far the largest. These predators can reach up to 18 feet (5 meters) in length and weigh as much as 800 pounds (360 kg). The bonnethead is the smallest of the four main hammerhead species, averaging feet (1 meter) long and weighing about 20 pounds (9 kg) [source: Florida Museum of Natural History].

In addition to their unique head shape, hammerheads have a tall dorsal fin that rises above the surface of the water in shallow areas. Their coloration is typically grayish-brown or olive on top, with lighter bellies, much like other shark species.

The hammerhead’s mouth is relatively small compared to other large sharks, and it doesn't open very wide. Inside, you'll find small teeth that are sharp and heavily serrated at the front, but larger and flatter at the back. These back teeth are used to grind down tougher prey like shellfish. Scalloped, smooth, and great hammerheads generally feed on bony fish, smaller sharks, shellfish, and their preferred meal — stingrays. Bonnetheads, however, eat bony fish, shrimp, seagrass, and primarily feed on crustaceans such as blue crabs.

While hammerheads typically hunt alone, scalloped hammerheads exhibit an interesting behavior: they form schools. The exact reason for this behavior is still unclear, but there are a few theories. Small fish often school to protect themselves from predators, but since the scalloped hammerhead is a large shark, this likely isn’t the reason. Another theory is that schooling fish surround their prey, but since hammerheads are solitary hunters, this doesn't apply either. Most researchers believe scalloped hammerheads gather in schools simply because they enjoy socializing with one another.

Male scalloped hammerheads are significantly outnumbered by females, with a ratio of 6-to-1, making them quite picky when choosing a mate. Their ideal partner? The bigger, the better. The larger the female, the more pups she can carry, which makes her all the more desirable. In a school of hammerheads, the largest females are usually positioned in the center. The males swim toward the center, select a female, and mate with her right there in broad daylight. Older, larger females can give birth to up to 40 pups, while younger and smaller sharks may have only around 12. After carrying the pups inside for 8 to 10 months, they are born in shallow waters. At birth, the pups measure about 18 inches long and have soft hammers that bend towards the tail, easing the birth process for the mother. These soft hammers harden as the shark matures.

In the next section, we'll explore several theories behind the hammerhead's distinct hammer-shaped head.

Unique Traits of the Hammerhead Shark

The unique hammer-shaped head of these ocean predators is known as a 'cephalofoil,' and it exhibits subtle differences across various hammerhead species. The great hammerhead features a broad, nearly flat cephalofoil with a shallow notch in the center. The scalloped hammerhead's cephalofoil is more curved, with a prominent notch in the center flanked by two smaller notches on each side, creating a scalloped effect. The smooth hammerhead has a simple, smooth cephalofoil, slightly arched with no notches. The bonnethead's cephalofoil is notably different—it's rounded at the front and more closely resembles a shovel than a hammer.

But why do these sharks have such a peculiar head shape? While researchers are not completely certain about the exact reason for this evolutionary trait, they have proposed several theories, some of which are supported by research. One idea is that the hammerhead's cephalofoil acts as a lift, similar to the wing of an airplane. However, studies suggest that although hammerheads are more maneuverable than other sharks, this is likely due to their increased flexibility rather than the shape of their cephalofoil, which allows them to turn and pivot more swiftly.

Another theory proposes that the hammerhead's cephalofoil helps it trap prey. A favorite meal for these sharks is the stingray. Once a ray is located, the hammerhead uses its cephalofoil to pin the ray to the ocean floor before beginning to eat it. This behavior has been observed in the wild, though it's likely a learned behavior rather than the primary function of the cephalofoil.

The most plausible explanation is that the cephalofoil enhances the hammerhead's ability to detect prey. Like all sharks, hammerheads have electrical sensors in their heads and noses called ampullae of Lorenzini, named after the researcher Stephan Lorenzini. These sensors detect weak electrical signals emitted by other marine life. Since hammerheads have wide, flat heads, their ampullae are distributed over a larger surface area, allowing them to cover more ground and detect prey more easily. This theory is supported by the hammerhead's tendency to patrol the ocean floor and its ability to locate camouflaged stingrays buried in the sand.

For more articles on sharks and hammers, feel free to explore the links on the following page.