Hammerhead sharks are predators, but what they eat depends on the species. Great hammerheads take bony fishes, rays, and other sharks, scalloped and smooth hammerheads hunt squid and fish, and the small bonnethead eats crustaceans along with a surprising amount of seagrass. Scalloped hammerheads appear to forage at night, away from the islands where they school by day.
This guide is written by the scientists of the Marine Megafauna Foundation, whose work in the Galápagos and Florida brings them into regular contact with hammerheads, and draws on the published research, including Dr. Alex Hearn’s long-term tracking of scalloped hammerheads in the Eastern Tropical Pacific.
What do hammerhead sharks eat?
Hammerheads eat bony fishes (teleosts), squid and octopus (cephalopods), crustaceans, and other sharks and rays (elasmobranchs), but the relative importance of these prey groups differs among species. A 2018 review of the three large species found that great hammerheads (Sphyrna mokarran) “feed primarily on teleost fishes and other elasmobranchs, from small rays to large sharks”. Cephalopods, on the other hand, do not appear to be an important prey item for great hammerheads. Scalloped hammerheads (Sphyrna lewini), in contrast, take a mixture of fish, crustaceans, and cephalopods, with squid as a primary prey item, while smooth hammerheads (Sphyrna zygaena) feed largely on squid. The difference shows even in their teeth: the great hammerhead’s are more robust, which the reviewers suggest may be because they feed on elasmobranch prey.
The smaller species are less studied. The bonnethead (Sphyrna tiburo), an Endangered hammerhead that is among the most abundant and conspicuous animals in US seagrass meadows, eats mainly crustaceans plus seagrass. One study examined four hammerhead species sharing the same coastal waters: the scalloped bonnethead (Sphyrna corona), scoophead (Sphyrna media), bonnethead, and scalloped hammerhead. The first three, along with juvenile scalloped hammerheads, act as mid-level predators (mesopredators), whereas sub-adult scalloped hammerheads “could be considered top predators”. Each species’ diet overlapped more with others of its own kind than with its relatives, which suggests that competition is more likely within a species than between species. The species are compared in Types of Hammerhead Shark.
How do great hammerheads hunt stingrays?
Great hammerheads use the head itself as a weapon, slamming a ray into the seabed and pinning it there while they pivot to bite. The classic account comes from May 1988, when scientists at a sunken barge 12 kilometers (7.5 miles) east of North Bimini, in the Bahamas, watched a female estimated at 3 meters (10 feet) long chase a southern stingray. She closed the distance in about eight seconds and drove her head onto the middle of the ray’s back, “sending the ray into the bottom with great force”. The shark then held the ray down with the underside of its head, pivoted on top of it, and bit away the front edge of a pectoral fin, repeating the sequence until the ray was disabled. The observers knew of no earlier report of a shark using its head to restrain a ray while pivoting to bite. The same paper notes earlier finds of 54, about 50, and 96 stingray spines in and around the mouths of large great hammerheads.
Stingrays fleeing the hammerhead beat their fins 6.1 times a second on average, against 1.4 when flushed by divers, and many sheltered inside the wreck, which the authors suggest may provide an antipredatory refuge. A second Bimini account, of a great hammerhead killing a spotted eagle ray, is one of the few published natural predation events by great hammerheads. The head-pinning technique is now known as “pin and pivot”.
Great hammerheads have more than one method, though. Off Western Australia, one shark of about 3.5–4 meters (11–13 feet) sheared a 2–2.5-meter (7–8-foot) bottlenose wedgefish in half with its first bite. It used the force of its tail to twist and shear the body, a ray-hunting style that differs from previously recorded techniques. On tidal flats less than 1.5 meters (5 feet) deep in Florida, the Bahamas, and Palau, great hammerheads have been seen making up to 22 tight turns while gripping their prey, a behavior the researchers named “grasp-turning”. Whether the head’s shape evolved for this kind of prey handling is one of several competing ideas. Experiments on young scalloped hammerheads found the head gives a wider search area and sharper turns rather than a more sensitive electrical sense, a debate covered in the chapter on why hammerheads have a hammer.
Do great hammerheads eat other sharks?
Yes. Large great hammerheads are apex predators, and off eastern Australia other sharks and rays are their main prey. Researchers there measured chemical tracers (stable isotopes) in the tissues of great hammerheads 234–383 centimeters (7.7–12.6 feet) long, caught in bather-protection nets. Mixing models based on those tracers suggested that blacktip sharks and Australian cownose rays were the dominant prey over the previous year, while bony fishes, cephalopods, and crustaceans were not significant components of the diet. On a Florida tidal flat, one great hammerhead of about 3.65 meters (12 feet) caught a nurse shark roughly 0.9 meters (3 feet) long. It then held station facing into the current for 15 minutes with the prey’s tail still protruding from its jaws.
Their presence changes how other sharks behave. Drone footage along the southeast Florida coast shows adult blacktip sharks fleeing into the shallow water next to the beach when confronted or chased by a great hammerhead. To the authors’ knowledge, this is the first evidence of adult blacktips using shallow water as a refuge. In northern Australia, where rays are abundant on shallow sand flats year-round, isotopes and videos suggest that great hammerheads specialize on rays (batoids), which may explain why most of them stay within relatively small areas.
Young great hammerheads eat mostly fish. In the Arabian Gulf, bony fishes made up 93.8% of the diet of juveniles under three years old by a standard index of prey importance, led by the bartail flathead. Females, however, preferred rays to bony fishes in their second and third years. Adults in Florida appear to follow concentrations of fishes, although the tracking studies that show this did not measure what the sharks ate. Tagged great hammerheads arrived at Bahia Honda, a well-known tarpon prespawning site, significantly more often than chance would predict when tagged tarpon were present. Their seasonal habitat shifts may be driven by prey availability, as core use areas often matched reef-fish spawning aggregations. A 2026 accelerometer study of nine great hammerheads estimated a thermal optimum of 29.3 °C (84.7 °F), the temperature at which their measured activity performance peaks. The sharks still performed well across a relatively broad temperature range, which likely enables great hammerheads to take advantage of seasonal prey pulses during both summer and winter.
Do hammerhead sharks hunt at night?
Scalloped hammerheads appear to, at least in the Eastern Tropical Pacific. There, tracking suggests they forage offshore at night, away from the islands and seamounts where divers see them schooling by day. Much of that evidence comes from acoustic tracking led or co-authored by Dr. Alex Hearn, a professor at the Universidad San Francisco de Quito and its Galápagos Science Center. When his team tracked hammerheads at Wolf Island in the Galápagos, the sharks showed a significant preference for daylight hours at all sites around the island. One female, followed by boat in November 2008, moved offshore on each of three successive nights to an area 5.6 kilometers (3.5 miles) east of Wolf, returning before dawn. She dived to 100–300 meters (330–980 feet) as she headed out to the open ocean in the evening. Tellingly, none of the tagged hammerheads was ever seen feeding at the island, unlike the dolphins and Galápagos sharks there. Feeding, the team suggested, “simply takes place further offshore and not at the island itself”.
The same pattern holds across the region. At Malpelo Island, Colombia, tagged hammerheads were detected more often by day than by night. At Cocos Island, Costa Rica, most detections fell between dawn and dusk. At San Benedicto Island, in Mexico’s Revillagigedo National Park, detections dropped significantly at night, and the authors suggest the sharks’ preferred sites might be related to nearby offshore seamounts where they feed. A review of the Galápagos work by Hearn and colleagues describes “frequent nocturnal absences of several hours duration, beginning at dusk”, presumed to be foraging trips. The same review notes that hammerheads landed on mainland Ecuador appear to feed mainly on oceanic squid such as the jumbo squid (Dosidicus gigas). Young scalloped hammerheads keep similar hours: pups in Hawaii fed at all times of day, but more at night. Why the sharks gather by day, and how far they travel, is the subject of the chapter on schooling and migration.
Why do scalloped hammerheads dive so deep?
The leading explanation is that they hunt squid in deep, oxygen-poor water, although the tracking data cannot yet confirm it. In the Gulf of California, stomachs of scalloped hammerheads larger than 160 centimeters (5.2 feet) held mainly deep-water (mesopelagic) squids, jumbo squid, and mackerel, and four species of deep-water squid have been recovered from their stomachs. One female tagged at El Bajo Espíritu Santo seamount in 2004 dived to at least 980 meters (3,215 feet), the deepest her tag could measure. She also went below 250 meters (820 feet), into the low-oxygen layer, on at least 29 days. The authors proposed that she was pursuing prey such as deep-water squids, and that tolerating such water may give hammerheads access to prey “relatively free from competition” with other predators.
Tracking at Wolf Island by Ketchum, Hearn, and colleagues recorded similar behavior. Sharks heading offshore made “yo-yo” dives through the thermocline (the boundary between warm surface water and colder water below), deep enough to feed on jumbo squid, one of them to nearly 900 meters (about 2,900 feet). The authors stress, however, that the “data are limited and remain inconclusive”. Off Hawaii, a female carrying an archival tag for 180 days made 1,098 dives to 500 meters (1,640 feet) or deeper, and only 14 of them between 7 a.m. and 5 p.m. Among them was a dive to 1,240 meters (4,068 feet), reported in 2022 as a record for the species. The authors consider it possible that she met a rich prey source, or a predator, at about 750 meters (2,460 feet).
These dives are excursions rather than a way of life. In a global study of shark and ray diving co-authored by MMF scientists, 17 tagged adult scalloped hammerheads ranged from the surface to 971 meters (3,186 feet), yet the 16 with full depth records had a median depth of only 43.3 meters (142 feet). The species grouped with primarily piscivorous (fish-eating) sharks of warm waters.
How do scientists know what hammerheads eat?
Scientists combine stomach contents from fished sharks, chemical tracers in tissue, DNA in feces, and direct observation by divers, drones, and cameras. The chemical tracers are stable isotopes, different forms of carbon and nitrogen whose ratios pass from prey to predator. Those ratios record roughly where, and how high in the food web, a shark has been feeding over the previous months or years.
Isotope studies have been especially productive in the Eastern Pacific. In scalloped hammerheads landed at Manta, Ecuador, carbon values suggested foraging mainly in food webs sustained by bottom-growing macroalgae. The authors inferred that males remain in coastal areas during most of their life cycle, while females migrate offshore to oceanic islands and then return inshore. Scalloped and smooth hammerheads caught together off Ecuador had dietary niches (the range of prey each uses) of similar width. Their niches showed low overlap (0.25), suggesting they use different feeding areas even though the prey consumed is similar. Individual scalloped hammerheads also overlapped little with one another, pointing to individual foraging specialization. In the Galápagos, biopsies from large adult females at Darwin Island and juveniles in mangrove bays suggest the adults feed in the archipelago’s highly productive waters, consistent with a pattern of residence.
Climate shapes this picture. A four-year isotope study of the Galápagos aggregation suggests that hammerheads respond to climatic fluctuations, with La Niña “potentially benefiting their trophic needs as the overall marine productivity increased”. At Cocos Island, predicted counts of scalloped hammerheads, modeled from dive-guide logs, were 105.6% higher during strong La Niña conditions than during strong El Niño conditions. The authors think this shift likely reflects distributional change rather than population decline. What a warming ocean could mean for hammerheads is covered on MMF’s climate change page.
How does a hammerhead’s diet change as it grows?
Diet shifts with age in all three of the large hammerheads studied, generally from small coastal prey toward larger or offshore prey. In the Gulf of California, female scalloped hammerheads move offshore at a smaller size than males. Bottom-living (benthic) prey made up only 15.1% of the diet of females up to 160 centimeters (5.2 feet) long by a standard index, against 40.9% for males of similar size. The author contended that this move offshore helps young females grow faster to the larger size needed to carry embryos. In the Galápagos, sub-adult scalloped hammerheads had carbon and nitrogen isotope signatures that suggest feeding in oceanic and deeper waters, unlike both pups and adults.
Great hammerheads shift from fish toward rays. Two immature sharks in Queensland had isotope values suggestive of feeding on bony fishes, and a 225-centimeter (7.4-foot) female appeared to be partway through a shift from a fish-based juvenile diet to a benthic adult diet. Young smooth hammerheads off Pacific Mexico carry a different chemical record. Mercury isotope signatures in their muscle decreased with body length, reflecting increasing reliance on offshore mesopelagic prey with age. The authors estimate that the sharks use coastal resources for about two years before migrating offshore.
What do baby hammerhead sharks eat?
Scalloped hammerhead pups eat small shrimps and fishes in shallow nursery bays, and in Hawaii’s Kāne’ohe Bay, many of them appear not to get enough. An estimated 7,700 hammerheads are born in the bay each year. By day the pups form a loose school hovering about 1.5 meters (5 feet) off the bay floor, and at night they range over the bottom on what probably represent foraging excursions. Their most common prey are a single species of snapping shrimp and two species of goby. Yet only 41% of newborns with open umbilical scars had food in their stomachs, against 87.8% of older pups with healed scars. Even among those older pups, the median stomach content was only 0.22% of body weight, measured as dry weight.
Energy budgets explain why this matters. A typical 760-gram (1.7-pound) pup would need about 28.2 grams (1 ounce) of food, or 3.7% of its body weight, every day just to maintain its weight. Estimated daily rations in the bay, however, are only 2.12–3.54% of body weight. The researchers concluded that food is limiting and consumption may fall below maintenance for much of the year, and that “a significant percentage of pups in Kāne’ohe Bay may starve”.
Survival records point the same way. Only 7–15% of each year’s newborns remained in the bay to age one, a loss that combines natural deaths, fishing, and emigration. Early weight loss indicated that “malnutrition and starvation make a major contribution to this mortality”.
Part of the problem may be historical. A 2002 study set more recent estimates of about 3.6 per square meter for the pups’ key snapping shrimp against 14 in 1976–1978. The authors suggested that the earlier density may have been raised by nutrient enrichment from sewage, since most sewage discharge into the bay had been halted by 1978.
So why use a nursery with so little food? The Hawaii studies suggest the bay is more valuable as a refuge from predators than as a source of food. That conclusion runs against one of the most common hypotheses for why sharks use nursery areas. Elsewhere, juvenile scalloped hammerheads in northwest Florida feed on small fishes, mostly flounders and croakers, and shrimps. In the Galápagos, a team led by Yasuní Chiriboga-Paredes, with Hearn as senior author, identified a putative nursery in a mangrove-fringed bay on San Cristóbal Island. Pups, nurseries, and litter sizes are covered in Baby Hammerhead Sharks.
Do bonnethead sharks really eat seagrass?
Yes. Bonnetheads digest a substantial share of the seagrass they swallow, which makes them omnivores rather than strict carnivores. Earlier studies had found seagrass making up as much as 62.1% of the gut contents by mass. A 2021 paper, summarizing those diet studies, gives up to 62% in juveniles and up to 40% in adults, with the rest mainly crustaceans. To test whether the sharks were digesting the seagrass or simply passing it through, researchers fed captive bonnetheads a diet of 90% chemically labeled seagrass and 10% squid for three weeks. All the sharks gained weight, digested 50% of the seagrass organic matter, and incorporated seagrass carbon into their blood and tissues. That efficiency is comparable to juvenile green sea turtles, at 44.7%, and the authors called the bonnethead “the first species of shark ever to be shown to have an omnivorous digestive strategy”.
The test diet held more seagrass than wild adults normally eat, and the mechanism is still uncertain. A follow-up study could not detect cellulase activity, the enzymes that break down plant cellulose. It concluded that bonnetheads appear to be largely reliant on their own digestive processes, with a possible microbial role. Even so, citing population estimates of about 4.9 million bonnetheads along the US Atlantic and Gulf of Mexico coasts, the 2018 authors argue that the species’ role in seagrass meadows needs to be re-evaluated.
What do smooth hammerheads and winghead sharks eat?
Smooth hammerheads feed largely on squid, while the little evidence on winghead sharks points to fast-moving fish. Off southern Africa, inshore and oceanic cephalopods made up 55.81% and 21.31% of the wet mass of smooth hammerhead stomach contents. In the eastern Pacific, the diet is dominated by jumbo flying squid and Patagonian squid. Their major prey overall is cephalopods, mainly flying squid (ommastrephids), and small schooling fishes. Off Peru, juveniles from three nursery areas had significantly different diets and trophic niches. The authors therefore recommended managing each nursery area as a unique juvenile stock, a distinct group with its own management.
Smooth hammerheads occasionally attempt much larger prey. During an aerial survey 168 kilometers (104 miles) off Rio de Janeiro, Brazil, observers saw at least three smooth hammerheads of 3.0–3.5 meters (10–11.5 feet) pursuing about 100 pantropical spotted dolphins. Two sharks approached a lone dolphin, and a bloodstain on the surface suggested a successful attack. Stomach studies indicate that hammerheads rarely include dolphins in their diets, but the authors suggest the sharks could still be important in shaping the behavior of open-ocean dolphins.
The winghead shark (Eusphyra blochii), Critically Endangered and little studied, has been filmed by drone off Magnetic Island, Queensland, chasing down and eating a bony fish. It made rapid turns and repeated up-and-down adjustments of its head, behavior consistent with the idea that its wide head aids pursuit of agile fish.
What eats hammerhead sharks?
Other sharks, including adult hammerheads, prey on young hammerheads, and killer whales have been seen eating small smooth hammerheads. In Kāne’ohe Bay, pups have been found in the stomachs of adult hammerheads and blacktip sharks, and predation by adult males is probably high immediately after birth. In the Galápagos, a study co-authored by Hearn analyzed DNA in the feces of 107 juvenile blacktip sharks from 14 bays. Scalloped hammerhead DNA was the fourth most common prey taxon detected, at 11.7% by the study’s occurrence measure. DNA alone, however, cannot show whether the blacktips caught live hammerheads or scavenged them, or how large those hammerheads were. At offshore seamounts, larger sharks such as bull, tiger, and white sharks might occasionally prey on small scalloped hammerheads.
Killer whales also take hammerheads. In the Bay of Islands, New Zealand, in 2002, an adult male killer whale caught a smooth hammerhead about 1 meter (3 feet) long and shared it with an adult female. It was the first report of smooth hammerheads as killer whale prey. Adult hammerheads, though, have far more to fear from fishing: harvest is the major threat to each of the large species, as explained in Why Are Hammerhead Sharks Endangered? and on MMF’s overfishing page.
Why it matters for conservation
How hammerheads feed affects how easily they are caught. At Cocos Island, scalloped hammerheads spend the day inside a marine protected area that was then 22 kilometers (14 miles) in radius. The authors of a 2019 tracking study reasoned that the sharks may move in and out of it daily as they forage offshore at night. That pattern would increase their vulnerability to longline fishing, which generally operates from dusk to dawn. According to a 2014 review, hammerheads’ burst-swimming hunting style is thought to underlie highly disturbed blood chemistry after capture and at-vessel and post-release mortality of 60–80% when they are caught as bycatch. Great hammerheads tracked in Australia, with their reliance on shallow inshore habitats and small home ranges, may be particularly vulnerable to localized depletions.
Those same habits make protection workable. Because scalloped hammerheads aggregate at predictable islands and seamounts, well-placed marine protected areas make it feasible to protect them. Shark tracking across the Eastern Pacific, compiled in a 2022 review co-authored by Hearn, has already shaped protection in three countries. It enabled Mexico to create the Revillagigedo National Park, Colombia to enlarge the Malpelo Fauna and Flora Sanctuary, and Costa Rica to create a protective corridor between Cocos Island and the Las Gemelas seamounts. MMF’s research in the Galápagos helped secure the Hermandad Marine Reserve. MMF’s Dr. Chris Rohner leads the foundation’s part of a silky shark tracking study, led by Hearn, across the same offshore islands. In Florida, aerial and boat surveys for the Florida Manta Project have recorded hammerheads. To support this work, see MMF’s shark research in the Galápagos; for quick answers, see the hammerhead shark facts, the hammerhead overview, and the rest of The Complete Guide to Hammerhead Sharks.