Hammerhead sharks, recognizable by their distinctive, flattened head, belong to the family Sphyrnidae. The answer to whether they are carnivores is straightforward: the vast majority of hammerhead species are highly successful, active carnivores and apex predators in their marine habitats. Their body structure and sensory biology are specialized tools evolved for the detection and capture of other animals. However, nuances in the feeding habits across the nine recognized species challenge the strict carnivore label for one particular member of the family.
Defining the Hammerhead Diet
Hammerhead sharks primarily consume marine life. Their diet is largely composed of bony fish, including species like sea bass, grouper, and various schooling fish. They also routinely prey on cephalopods, such as squid and octopus, and crustaceans like crabs and shrimp.
The most defining and frequently targeted prey for larger species, like the Great Hammerhead, are stingrays and skates. These flattened relatives of sharks often bury themselves in the sandy seafloor, but they remain a preferred, high-energy meal. Great Hammerheads have even been observed with dozens of stingray barbs embedded in their bodies from successful, yet hazardous, hunting encounters.
Large hammerheads, such as the Great Hammerhead, also feed on smaller shark species. Researchers have determined that consuming a single, large prey item, like a 55-pound blacktip shark, can sustain a 250-pound hammerhead for up to three weeks. This preference for substantial meals highlights their opportunistic and energy-efficient approach to predation.
How the Cephalofoil Aids Hunting
The hammerhead’s head structure, known as the cephalofoil, is a sophisticated sensory and physical hunting apparatus. This broad shape acts like a wide antenna, maximizing the surface area available for specialized sensory organs. Hammerheads possess electroreceptors called the Ampullae of Lorenzini, which detect the faint electrical fields generated by living creatures.
The wide distribution of these pores across the cephalofoil significantly enhances the shark’s ability to “sweep” the ocean floor for prey. This increased sensitivity allows them to detect the weak bioelectric signals of animals, particularly stingrays, even when they are hidden under sand. This sensory advantage allows a hammerhead to detect cryptic prey from a much greater distance than other sharks.
The cephalofoil also aids in visual perception, as the eyes are positioned on the ends of the structure, providing superior binocular vision and depth perception. The head is also used as a physical tool once the prey is located. Larger hammerhead species have been observed using the wide margins of their cephalofoil to ram and pin stingrays to the substrate, incapacitating them before consumption.
Species Differences in Feeding Habits
While most hammerheads are carnivores, the family Sphyrnidae exhibits dietary variation among its members. Larger species, like the Scalloped and Great Hammerhead, are dedicated predators with broad, bladed teeth suited for capturing and shearing large fish and rays. Their size and hunting methods reinforce their classification as strict carnivores.
The smaller, more coastal Bonnethead shark (Sphyrna tiburo) presents a notable exception to the carnivorous rule. Although they primarily consume crustaceans like crabs and shrimp, they also ingest significant quantities of seagrass. For a long time, researchers believed this plant matter was consumed accidentally, offering no nutritional value.
However, recent studies have shown that the Bonnethead actively digests and assimilates nutrients from the seagrass. They possess the necessary enzymes to break down cellulose, a component of plant matter, and can successfully gain weight on a diet that is up to 90% seagrass. This confirmed ability to derive nutrition from both animal and plant sources technically classifies the Bonnethead shark as the first known omnivorous shark species.