Among the most magnificent expressions of "shark-ness" must be the great hammerhead. Biggest of its kind—that is, the biggest of all hammerheads—this mighty beast commonly grows to 3.5 to 4.3 metres (11.5 to 14 feet) in length, but exceptional specimens are thought to reach at least 6.1 metres (20 feet) and may weigh more than a half-ton. The sight of its tall scythe of a dorsal fin slicing the water off a beachfront is an intimidating one, though this superlative shark—potentially dangerous by virtue of its size alone—rarely bothers people.
It rarely bothers people, sure, but the great hammerhead—found worldwide in tropical, subtropical, and lower-latitude temperate waters and classified as Critically Endangered—is very bothersome if you're a smaller shark, a ray, or a skate. Bothersome's too low-key an adjective, actually: Try "terrifying." For great hammerheads are something of elasmobranch specialists as predators, and formidable ones, too, capable of dispatching good-sized prey at least up to a quarter of their own size.
A study published in the Journal of Fish Biology last year (and lately highlighted by the affiliated Florida International University) shed some light on why great hammerheads might so commonly set their sights on other sharks as food. After all, wouldn't it be easier to snap up a snapper or munch on a mullet than go after a comparatively large, toothy cousin?
Well, it's not that great hammerheads won't eat bony fish: They will indeed, and they'll also sometimes chow down on squid and crustaceans. But at multiple locations where their dietary preferences have been investigated, these apex predators commonly show a definite lean toward the elasmobranch end of the marine pantry, and not just in terms of the stingrays, cownose rays, and other batoids that are arguably its best-known fodder.
The 2025 paper, based on Florida-based Ph.D research by Erin Spencer under the mentorship of renowned FIU shark ecologist Yannis Papastamatiou, suggests that consuming other sharks yields major energetic benefits to great hammerheads. Scarfing a blacktip shark—a prized great-hammerhead prey item—once every three weeks or so might keep a hammerhead happy and satiated for a couple of months, whereas it might have to successfully catch one or two bony fish a day over the same period to meet its metabolic needs. Hence, perhaps, the value of passing up smaller fish in favour of going after sharky targets, delivering as they do a bigger bang for the buck.
It's not only blacktip sharks, either: Great hammerheads have been recorded preying on a variety of other shark species, especially various other carcharhinids (requiem sharks), among them dusky sharks, grey reef sharks, and lemon sharks. But nurse sharks have also landed on its dinner plate, and it's likely that just about any smaller shark the great hammerhead can catch and overpower is fair game.
Despite their large-to-huge size, great hammerheads are well known for cruising into surprisingly shallow waters, from tideflats to the swash zone right off sandy beaches. In such shallows, they employ a variety of specialised hunting behaviours that capitalise upon their explosive speed and exceptional manoeuvrability. That manoeuvrability stems from the species' standout flexure and also links to its unique swimming style: Great hammerheads appear to spend a lot of time cruising at a tilt, a unique, hydrodynamically efficient "rolling" orientation in which that swordlike dorsal fin acts in concert with the pectorals to enhance lift.
As spelled out in a 2016 Marine & Freshwater Behaviour & Physiology article, great hammerheads hunting rays and other sharks in shallow-water tidal flats employ a number of rather sophisticated methods. These include the "pin-and-pivot" attack, where the hammerhead immobilises the victim against the seafloor with its flat-edged "hammer" (aka cephalofoil); and the "grasp-turn," where, with jaws on its prize, it makes many tight spirals that may help keep prey secure and manoeuvre it into swallowing position.
By restricting escape options, the limited water column of shallows can give the agile and swift great hammerhead using such tactics a predatory advantage. But there's a limit to this. A 2020 Journal of Fish Biology study analysing drone footage of great hammerheads hunting blacktip sharks off southeastern Florida—where blacktips congregate in large numbers during the winter, shadowed by hungry great hammerheads—suggested blacktips may beeline for shore when pursued. The observed predatory attempts saw the great hammerheads' dorsal and upper tail (caudal) fins breaking the sea surface—thus perhaps degrading the predators' ability to generate lift and forward thrust—while the fleeing blacktips remained fully submerged. Such foiled hammerheads consistently executed a U-turn and returned to deeper waters.
An Instagram post from March by Evan Parness showing drone footage of a great hammerhead hunting Florida blacktips noted that the latter will even beach themselves in an effort to evade their sphyrnid pursuers.
More elasmobranch-focused than many other species though they may be, great hammerheads are far from the only shark-eating sharks out there. Indeed, great-hammerhead pups and juveniles are vulnerable to any number of other sharks, blacktips included (a taste for revenge?). Large sharks with more generalist diets, including tiger, bull, and great white sharks, represent a potential threat to most other, smaller sharks. White sharks, for example, have been documented consuming everything from smoothhounds, soupfins, and dogfishes to dusky sharks, sandbar sharks, bronze whalers, tiger sharks, and threshers. A good-sized great white (or perhaps a mako) was the suspected macropredator that gulped down a tagged 2.23-meter (7-foot) porbeagle researchers were tracking off Bermuda.
The presence of these large apex-level sharks may influence the spatial patterns of smaller, mesopredatory sharks. Bronze whalers, for example, seem to steer clear to some extent of great whites off South Africa, increasing in areas where the latter has decreased. And when tiger sharks seasonally show up at East Island in the northwestern Hawaiian Islands to hunt albatross fledglings, Galapagos and gray-reef sharks use different habitats (perhaps mainly to avoid competition with tigers in the case of the former, and probably to escape becoming tiger-shark chow in the case of the latter).
As the abundance of footage showing great hammerheads chasing and parting schools of blacktips demonstrate, drones have certainly demonstrated real potential over the past decade or so in documenting otherwise rarely observed shark-predation events. Another case in point? This recent video from Western Australia's Ningaloo Reef captured by Francesca DeWeerdt, which shows a tiger shark preying on one of that generalist predator's favourite foods: a sea turtle.
Top header image: Shutterstock
Sharks
Sharks
Predator vs Prey
