The great hammerhead is the largest of the nine hammerhead shark species, capable of reaching 20 feet in length and weighing close to 1,000 pounds. It’s found in warm coastal and tropical waters worldwide and is instantly recognizable by its wide, flat head, which stretches out like the top of a capital T. Despite its impressive size and striking appearance, this shark is critically threatened by overfishing and is currently classified as endangered.
Size and Physical Features
Great hammerheads typically max out at 18 to 20 feet long. The world record specimen, caught off Sarasota, Florida, weighed 991 pounds, though the species averages over 500 pounds. Females tend to be slightly larger than males. In Australian waters, males reach sexual maturity at about 7.4 feet and 113 pounds, while females mature at around 6.9 feet and 90 pounds, meaning these sharks spend years growing before they can reproduce.
The feature that defines this species is its hammer-shaped head, technically called a cephalofoil. The great hammerhead’s version is distinct from other hammerhead species: it has a nearly straight front edge with a small notch in the center, giving it a clean T-shape. The scalloped hammerhead, by comparison, has a curved front edge with multiple indentations. This difference in head shape is the quickest way to tell the two species apart.
What the Hammer-Shaped Head Actually Does
The wide, flattened head isn’t just for show. It likely evolved to boost sensory perception rather than vision specifically. The broad surface spreads out the shark’s electroreceptors, tiny pores that detect the weak electrical fields generated by other animals’ muscles and heartbeats. This gives the great hammerhead a wider “scanning area” as it sweeps its head back and forth across the seafloor, almost like a metal detector.
The head shape also improves stereo-olfaction, the ability to detect which direction a scent is coming from by comparing the strength of the smell reaching each widely separated nostril. Surprisingly little is known about how the placement of its eyes at the far ends of the hammer affects its vision. Researchers still haven’t fully mapped the hammerhead’s visual field or determined how the shark integrates information from two eyes that face in very different directions.
A Stingray Specialist
Great hammerheads eat a range of prey, but stingrays are their signature meal. Research from James Cook University tracked more than 30 great hammerheads over four years in Australia’s Great Barrier Reef and found the sharks stayed remarkably local, patrolling shallow coral reef flats and mudflats to hunt juvenile stingrays. The researchers described the species as “really reliant on stingrays,” and this dietary preference is what keeps great hammerheads close to shore rather than roaming open ocean.
The hammer-shaped head plays a direct role in hunting rays. Great hammerheads use the flat underside of their head to pin stingrays against the seafloor, immobilizing them before biting off chunks of the ray’s disc-shaped body. Stingray spines have been found embedded in the mouths and heads of great hammerheads, with some individuals carrying dozens of old spine fragments, evidence of a lifetime spent wrestling dangerous prey.
Staying Warm in Cold Water
Hammerhead sharks are warm-water animals, but they sometimes dive into deep, cold water where temperatures drop to around 40°F. Research from the University of Hawaiʻi revealed a remarkable adaptation: scalloped hammerheads (a close relative) essentially hold their breath during deep dives by closing their gill slits. Since gills act as natural radiators that would rapidly cool the blood, sealing them off allows the shark to keep its muscles warm and functional during hunts in frigid depths. Computer modeling confirmed that without this gill-closing behavior, the sharks’ body temperature would plummet too quickly for them to hunt effectively. The muscles stayed warm throughout the dive but cooled rapidly as the sharks reopened their gills near the surface.
Reproduction
Great hammerheads give birth to live young after an 11-month gestation period. Litter sizes vary widely, from 6 to 33 pups, with each newborn measuring about 26 inches long. This is relatively large for a shark pup, but the species’ slow reproductive rate is a serious vulnerability. Females don’t mature until they’re nearly seven feet long, which takes several years, and they don’t breed every year. Combined with the large investment of an 11-month pregnancy, the population simply can’t bounce back quickly from heavy losses.
Where Great Hammerheads Live
Great hammerheads inhabit tropical and warm temperate waters in the Atlantic, Pacific, and Indian Oceans. They favor continental shelves and coastlines, often cruising over shallow flats, coral reefs, and mudflats where their stingray prey is abundant. They are also found around oceanic islands and occasionally venture into deeper offshore waters. Tracking data consistently shows that many individuals are more residential than expected, staying in a relatively limited home range rather than undertaking long open-ocean migrations.
Conservation Status
The great hammerhead is listed as endangered on the IUCN Red List. The primary threat is fishing, both targeted and incidental. Hammerhead fins are among the most valuable in the shark fin trade, commanding high prices for shark fin soup. Because hammerhead meat is often considered unpalatable, many of these sharks are “finned,” meaning their fins are removed and the rest of the body is discarded at sea.
The numbers paint a grim picture. Great hammerhead populations in the eastern Atlantic have declined by roughly 80%. In West Africa, landings have effectively collapsed. The species faces intense fishing pressure at every life stage: juveniles are caught in nearshore fisheries, and adults are taken by both shelf-based and high-seas fleets operating across international waters. Their habit of staying in shallow coastal areas, combined with their large fins, makes them especially easy targets.
Risk to Humans
Great hammerheads are large predators, but they pose very little danger to people. The International Shark Attack File, the world’s most comprehensive database of shark encounters (covering incidents from the 1500s to the present with over 6,800 investigations), attributes very few unprovoked bites to hammerhead species overall. Divers who encounter great hammerheads in the wild generally describe them as cautious and quick to swim away. The far greater danger runs in the opposite direction: humans kill vastly more great hammerheads each year than these sharks have ever harmed people across recorded history.