Hammerhead sharks are not one uniform predator with a single menu. The family Sphyrnidae includes roughly nine recognized species, and their diets range from stingrays and other sharks to crabs, squid, bony fish, and even seagrass. The great hammerhead is an apex predator that routinely eats other sharks, while the smaller bonnethead digests plant material with surprising efficiency. What ties them together is a distinctive head shape that gives them a real edge in finding prey buried in sand or hiding in murky water.
The Great Hammerhead Eats Other Sharks
Among all hammerhead species, the great hammerhead (Sphyrna mokarran) sits at the top of the food chain. Research off eastern Australia using stable isotope analysis found that large great hammerheads are apex predators that rely primarily on other sharks and rays, with a particular preference for benthic species like the Australian cownose ray during the summer months.1PubMed. Resource use of great hammerhead sharks (Sphyrna mokarran) off eastern Australia Their isotopic signatures indicate they move across coastal, open-ocean, and bottom-dwelling food webs, meaning they are not locked into one type of habitat or one type of prey.
Off southern Florida, great hammerheads are known to target blacktip sharks that gather in large seasonal groups. A recent study examining the energetics of this behavior found that great hammerheads are unusual among sharks because they actively prefer large prey, including other shark species and big bony fish, rather than the smaller fish or invertebrates that most sharks eat.2PubMed. Energetic benefits of prey choice for a shark-eating shark Hunting a blacktip shark is risky and energy-intensive, but the caloric payoff of a single large meal appears to make the strategy worthwhile.
Great hammerheads also eat stingrays with what looks like a specialized technique. They use the wide, flat underside of their head to pin a ray against the seafloor before biting off pieces of the wing. Stingray spines have been found embedded in the mouths and jaws of great hammerheads without apparent harm, suggesting they tolerate the venom well. This combination of shark-hunting and ray-pinning makes the great hammerhead one of the most formidable predators on any reef.
Scalloped Hammerheads and Their Fish-Heavy Diet
The scalloped hammerhead (Sphyrna lewini) is probably the most studied member of the family, partly because it forms large schools and is commonly caught in fisheries. Its diet leans heavily toward bony fish and squid. DNA analysis of fecal samples from scalloped hammerheads in the Galápagos identified Thoburn’s mullet as the most common prey item.3Carolina Digital Repository. Elucidating the diet of sharks through DNA analysis of fecal matter Stomach content studies of juveniles in the Gulf of California found that carangid fishes (jacks) contributed the highest mercury levels among prey, while scombrid fishes (mackerels and tunas) were also significant diet components.4PubMed. Mercury and Selenium in Muscle and Target Organs of Scalloped Hammerhead Sharks Sphyrna lewini of the SE Gulf of California: Dietary Intake, Molar Ratios, Loads, and Human Health Risks
Scalloped hammerheads are also known for deep dives that take them well below the sunlit zone, where they feed on squid and deep-water fish. These dives can reach depths where the water is extremely cold, which requires physiological adaptations to keep their bodies functioning. Their deep-diving behavior expands their menu to include prey that shallower-swimming sharks cannot access.
Despite a similar trophic level to great hammerheads, scalloped hammerheads end up with a fairly different diet in practice. Isotope research in waters where both species coexist found low trophic niche overlap between the two, suggesting they use different individual foraging strategies even when living in the same area.5PubMed. Population and individual foraging patterns of two hammerhead sharks using carbon and nitrogen stable isotopes In other words, sharing a habitat does not mean sharing a plate.
The Bonnethead, a Shark That Eats Its Vegetables
The bonnethead (Sphyrna tiburo) is the smallest hammerhead, rarely exceeding about a meter in length, and it has the most surprising diet of the group. Bonnetheads live in shallow coastal waters thick with seagrass, and for years scientists noticed huge amounts of seagrass in their stomachs. The assumption was that the grass was swallowed incidentally while chasing crabs and shrimp hiding in the grass beds. That changed in 2018.
A controlled feeding study showed that bonnetheads actually digest seagrass with about 50% efficiency, similar to some sea turtles that are dedicated herbivores. Researchers fed captive bonnetheads a seagrass-heavy diet labeled with a carbon tracer and found the sharks assimilated seagrass carbon into their tissues. Enzyme assays also detected cellulose-degrading enzyme activity in the sharks’ hindguts.6PubMed Central. Seagrass digestion by a notorious ‘carnivore’ Seagrass had been recorded at up to about 62% of gut content mass in wild bonnetheads, which is an extraordinary proportion for any shark. The finding makes the bonnethead the first shark species confirmed to function as an omnivore.
Beyond seagrass, bonnetheads are avid crab eaters. Fecal DNA analysis identified the Atlantic blue crab as a primary prey item, with very little dietary overlap with other shark species in the same waters.3Carolina Digital Repository. Elucidating the diet of sharks through DNA analysis of fecal matter Their teeth reflect this preference: bonnetheads have flat, plate-like rear teeth built for crushing hard shells, quite different from the pointed teeth of their larger relatives. The bonnethead’s digestive tract also has molecular machinery for absorbing products of protein digestion, with peptide transporters identified throughout the esophagus, stomach, intestine, and other gut tissues.7PubMed Central. Molecular identification and functional characteristics of peptide transporters in the bonnethead shark (Sphyrna tiburo)
Smooth Hammerheads, Smalleye Hammerheads, and Other Species
The smooth hammerhead (Sphyrna zygaena) is a wide-ranging species found in temperate and tropical waters. Off southern Australia, stomach contents from smooth hammerheads revealed a broad diet dominated by benthic cephalopods, especially southern calamary. Other important prey included bottom-dwelling bony fish, crustaceans like western king prawns and red swimmer crabs, ommastrephid squids, cuttlefish, Australian anchovy, and southern sea garfish.8ICES Journal of Marine Science. A quantitative comparison of the diets of sympatric pelagic sharks in gulf and shelf ecosystems off southern Australia The variety of prey reflects the patchy seagrass and reef habitats that smooth hammerheads frequent in that region.
The smalleye hammerhead (Sphyrna tudes) is less studied, but fishers’ ecological knowledge from a tropical estuary in Brazil paints a useful picture. The most commonly reported food items were fish (about two-thirds of mentions), followed by crustaceans and other bottom-dwelling invertebrates. Among fish, catfish and Brazilian snapper were cited most often, along with mullets, mojarras, and soles.9SciELO – Scientific Electronic Library Online / Neotropical Ichthyology. Fishers’ ecological knowledge of smalleye hammerhead, Sphyrna tudes, in a tropical estuary These are mostly muddy-bottom and estuarine species, fitting the smalleye hammerhead’s preference for turbid coastal waters.
What stands out across all these species is that each hammerhead fills a somewhat different dietary niche, even when they share the same waters. Great hammerheads eat sharks and rays. Scalloped hammerheads eat fish and squid. Bonnetheads eat crabs and seagrass. Smooth hammerheads lean into cephalopods. The family as a whole covers an unusually wide range of prey types for a single shark lineage.
How the Hammer-Shaped Head Helps Find Food
The flattened, laterally expanded head of a hammerhead shark is not just for show. It plays a direct role in locating prey. All sharks can detect the weak electrical fields produced by living organisms buried in sand or hiding nearby, using specialized pores called ampullae of Lorenzini spread across the snout. In hammerheads, that snout is stretched out sideways, which means the electroreceptor pores are distributed over a much larger area.
Research comparing juvenile scalloped hammerheads with sandbar sharks (a conventional-headed species) found that the hammerhead’s head does not make it more sensitive to prey-simulating electric fields on a per-receptor basis. Instead, the wide head provides a greater lateral search area, increasing the probability of encountering prey during a sweep of the bottom. The head shape also enhances maneuverability, which helps in the final moments of capturing prey once it has been detected.10PubMed. Electroreception in juvenile scalloped hammerhead and sandbar sharks Think of it like scanning a metal detector across the beach: a wider detector head does not beep louder, but it covers more ground with each pass.
The head also gives hammerheads binocular vision with overlap in their forward visual field, and the nostrils are set far apart at the tips of the head, which may help them track scent gradients more precisely. For a species like the great hammerhead that pins stingrays against the bottom, the broad head doubles as a physical tool. For the bonnethead, whose head is more shovel-shaped, it helps sift through sandy or muddy substrate where crabs and shrimp hide. The head morphology is multipurpose, but the electroreceptor advantage is the one that has been tested most rigorously.
Diet Shifts as Hammerheads Grow Up
Young hammerheads do not eat the same things as adults. This is true across many shark species, but hammerheads show it particularly clearly because juveniles often live in completely different habitats than adults. Juvenile scalloped hammerheads, for example, tend to stay in shallow coastal nursery areas where they feed on small fish and invertebrates. A stable isotope study in the Galápagos found that juvenile scalloped hammerheads had isotope signatures consistent with coastal feeding, while adults showed a progressively more oceanic-associated diet.11PLOS ONE. Using stable isotopes analysis to understand ontogenetic trophic variations of the scalloped hammerhead shark at the Galapagos Marine Reserve All three maturity stages had a similar trophic level, meaning they eat at roughly the same position in the food chain, but the specific prey they eat shifts from nearshore to open-water species.
A separate study on smooth hammerheads using triple-element isotope analysis of vertebrae found consistent shifts in diet signatures, with early juveniles showing coastal-associated isotopes followed by a transition at around two and a half years of age toward increasingly oceanic habitat and prey.12Nature. First use of triple-element stable isotope analysis of elasmobranch vertebrae reveals strong ontogenetic shifts in smooth hammerhead sharks The vertebral record functions like a flight recorder, capturing dietary information laid down over the shark’s entire life, so researchers can track the transition from coastal juvenile to pelagic adult.
These shifts matter for conservation. If juvenile hammerheads depend on specific coastal nursery habitats for their early meals, then degradation of those habitats (through pollution, coastal development, or loss of seagrass beds) can hit a species before it ever reaches adulthood. Protecting nursery areas is, in effect, protecting the sharks’ early food supply.
Seasonal Movements Follow the Food
Hammerhead sharks do not stay in one place all year, and their movements are often timed to match prey availability. Tracking data on great hammerheads in the southeastern United States showed seasonal shifts between core use areas that corresponded to known locations of spawning aggregations for reef fish.13PubMed. Migratory patterns and seasonal habitat use of great hammerhead sharks (Sphyrna mokarran) in the southeastern United States When reef fish gather in large numbers to reproduce, great hammerheads show up. When those aggregations disperse, the sharks move on.
The Florida blacktip shark aggregation mentioned earlier is another example of this pattern. Every winter, blacktip sharks gather in warm shallow waters off southern Florida, and great hammerheads follow them there to feed.2PubMed. Energetic benefits of prey choice for a shark-eating shark These seasonal movements mean that a great hammerhead’s diet in January may look completely different from its diet in July, simply because different prey are available in different places at different times of year.
Scalloped hammerheads also show seasonal patterns. They form large schools around seamounts and oceanic islands, and the timing of these gatherings often aligns with productive upwelling events that boost prey abundance. The schooling behavior itself may serve multiple purposes including mating and navigation, but access to concentrated food resources during certain seasons is part of the picture.
Tooth Shape and Diet Across the Family
One way to read a shark’s diet is to look at its teeth. Across sharks more broadly, there is a statistically significant relationship between tooth shape and the type of prey a species eats. A study examining tooth morphology across dozens of shark species found that pointed teeth are associated with predation on large vertebrates and cephalopods, while flat, rounded teeth are associated with crushing hard-shelled prey like crabs and mollusks.14Cell Press (Current Biology). Dental disparity and morphological turnover in sharks across the Mesozoic-Cenozoic transition
Within hammerheads, this pattern plays out neatly. The great hammerhead has robust, triangular teeth with serrated edges, suitable for cutting through the tough skin of stingrays and other sharks. The scalloped hammerhead has narrower, more triangular teeth good for gripping slippery fish and squid. The bonnethead, with its flat crushing plates in the back of the jaw, is equipped for a diet that includes hard-shelled crabs and, as it turns out, a fair amount of seagrass. You can get a rough sense of what each species eats just by looking at its dental hardware.
Mercury in the Food Chain
Because hammerheads occupy high positions in their food webs, they accumulate contaminants from their prey. Mercury is the main concern. A study of smooth hammerheads caught off Baja California Sur, Mexico, found mercury concentrations in muscle tissue ranging from 0.005 to 1.93 micrograms per gram wet weight, with one specimen exceeding the international safety limit for human consumption of 1.0 microgram per gram.15PubMed. Mercury and selenium bioaccumulation in the smooth hammerhead shark, Sphyrna zygaena Linnaeus, from the Mexican Pacific Ocean Mercury levels in the fins were much lower.
Juvenile scalloped hammerheads in the Gulf of California showed average mercury levels in muscle ranging from 0.12 to 1.17 micrograms per gram wet weight, with the highest mercury contributions coming from the carangid fishes in their diet. More than 98% of the total mercury accumulated in the sharks ended up stored in muscle tissue.4PubMed. Mercury and Selenium in Muscle and Target Organs of Scalloped Hammerhead Sharks Sphyrna lewini of the SE Gulf of California: Dietary Intake, Molar Ratios, Loads, and Human Health Risks A broader study of four shark species in the same region, including the smooth hammerhead, found that all species exceeded the Mexican government’s mercury limit for human consumption.16PubMed. Bioaccumulation and biomagnification of total mercury in four exploited shark species in the Baja California Peninsula, Mexico
Selenium, which can offset some of mercury’s toxic effects in living tissue, was also found in hammerhead muscle and prey items. The ratio between selenium and mercury matters: when selenium levels are high relative to mercury, the health risk is considered somewhat lower. But the overall message from these studies is that hammerhead shark meat, like that of most large predatory sharks, carries meaningful mercury loads. For the sharks themselves, this is simply a consequence of eating high on the food chain. For people in regions where hammerhead is consumed, it is a food-safety issue worth paying attention to.
How Scientists Figure Out What Sharks Eat
Diet studies on sharks have historically relied on cutting open stomachs, which is exactly as crude as it sounds. The problem is that many sharks are caught with empty stomachs, and soft-bodied prey like squid digest quickly, biasing the results toward hard-to-digest items like fish bones and crab shells. Newer methods have changed the picture.
Stable isotope analysis, the technique behind many of the findings in this article, works by reading the chemical signatures left by food in a shark’s tissues. Different prey from different habitats leave distinct ratios of carbon, nitrogen, and sulfur isotopes in muscle, blood, and even vertebral cartilage. This approach reveals not just what a shark ate last week but what it has been eating over months or years, and whether its feeding ground was coastal or oceanic.1PubMed. Resource use of great hammerhead sharks (Sphyrna mokarran) off eastern Australia
DNA analysis of fecal matter is another advancement. Researchers can now identify prey species from fragments of genetic material in shark feces without ever needing to kill the animal. This method has been used to clarify bonnethead diets (confirming the prominence of blue crabs) and scalloped hammerhead diets (identifying Thoburn’s mullet as a key prey species in the Galápagos).3Carolina Digital Repository. Elucidating the diet of sharks through DNA analysis of fecal matter Because it is non-lethal, fecal DNA analysis is especially useful for studying endangered species like the scalloped hammerhead, where killing animals for stomach content analysis is ethically difficult to justify.
Fishers’ traditional ecological knowledge also fills gaps, particularly for species that are hard to study in the wild. Local fishers in Brazil provided detailed accounts of smalleye hammerhead diets that aligned well with the limited scientific data available, naming specific prey species and describing feeding behaviors that formal surveys had not captured.9SciELO – Scientific Electronic Library Online / Neotropical Ichthyology. Fishers’ ecological knowledge of smalleye hammerhead, Sphyrna tudes, in a tropical estuary The combination of all these methods gives a much fuller picture of hammerhead diets than any single approach could provide on its own.