Great Hammerhead Shark

• Maximum length6.1 m (20 ft); most adults 3.5–4.5 m
• WeightUp to 580 kg (1,280 lb); typically about 230 kg
• Lifespan40–45 years
• Depth range1–300 m (3–980 ft)
• DietStingrays and other rays, bony fish, sharks, squid
• IUCN statusCritically Endangered (assessed 2018)

How to recognise a great hammerhead

You can identify a great hammerhead from a hundred metres away by the first dorsal fin. It is enormously tall, strongly curved backwards and pointed, and on a big animal it rises well clear of the surface when the shark cruises a sand flat. No other hammerhead carries a fin like it. The second dorsal and the anal fin are also high, with deeply notched rear edges, and the rear margin of each pelvic fin is concave, a detail that separates the species from the scalloped hammerhead, whose pelvic fins are straight-edged.

The head confirms it. Seen from above, the front of the cephalofoil is nearly straight across, with one shallow notch at the midline and none at the sides; adults lose the slight scalloping that pups show. The head is wide, about a quarter of the body length, but not as wide as in the winghead. Colour is a uniform grey-brown to olive above and white below, with no fin markings.

The teeth are the most heavily built in the family: 17 on each side of the upper jaw and 16 or 17 below, triangular, strongly serrated and angled toward the corners of the mouth, a cutting dentition made for rays and sharks rather than the slim fish-catching teeth of the scalloped hammerhead. Sharks of the same size in the same water, such as the bull shark, have rounded snouts and are never confused with it.

How big do great hammerheads get?

The great hammerhead is the giant of its family. The largest length in the literature is 6.1 m (20 ft), a figure repeated by FishBase and the Florida Museum, though sharks over 5 m are seen rarely and most measured adults fall between 3.5 and 4.5 m. The old claim of 20 ft is consistent with the biggest females; nothing credible exceeds it.

Weight follows length steeply. A 4 m shark weighs around 230 kg (500 lb); the all-tackle record, a female taken at Boca Grande, Florida, in May 2006, measured about 4.3 m and weighed 580 kg (1,280 lb), her mass swollen by a litter of 55 pups near term. That single catch is why so many pages quote 580 kg as the species maximum; a non-pregnant shark of the same length would be lighter.

Females grow larger than males. Males mature at 2.3 to 2.8 m and females at 2.5 to 3 m; pups are born at 50 to 70 cm (20 to 28 in). Growth is quick for a big shark in the first years and slows after maturity, so a 5 m female is likely thirty years old or more. The size bar below shows the largest published length next to a 1.8 m diver.

Where great hammerheads live

Great hammerheads live in warm water around the world, roughly between 40°N and 37°S, in all three oceans and the Mediterranean, where they are now very rare. They use the whole width of the continental shelf: reef edges, lagoon passes, sand flats a metre deep where they hunt rays, and the shelf edge to about 300 m. They cross open water between islands, but are almost never found far from a shelf.

The best-known populations are in the western Atlantic. Around Florida the species follows migrating tarpon and cownose rays into Boca Grande Pass and the Keys each spring, and in winter it gathers on the sand flats of South Bimini in the Bahamas, where dive operators have logged the same tagged individuals returning for a decade. It ranges through the Gulf of Mexico to Texas and south along Brazil. In the Indo-Pacific it is widespread from the Red Sea and Arabian Gulf across to northern Australia, where the Queensland and Northern Territory coasts hold some of the last healthy numbers.

Temperature drives its movements. Tagged sharks off Florida move north into the Carolinas in summer and back to the Keys and Bahamas as the water cools below about 22 °C; Australian sharks make the same seasonal shift along the east coast. The map and the country list below show where SharkSider readers can expect to encounter it.

What great hammerheads eat and how they hunt

Ask any guide in the Florida Keys what great hammerheads eat and the answer is stingrays, and the stomach data agree. Southern stingrays, cownose rays, eagle rays, guitarfish and skates are the core of the diet, followed by groupers, tarpon, jacks, sea catfish, flatfish, squid, crabs and other sharks, including blacktips, scalloped hammerheads and, now and then, smaller great hammerheads. Stingray spines do the shark no lasting harm: one individual was found with 96 spines lodged in its mouth and throat.

The hunt has been filmed at Bimini. The shark sweeps the sand in a slow zigzag with its head close to the bottom, using the electroreceptors under the cephalofoil like a metal detector to find a buried ray. When it strikes it does not bite first; it drives the ray to the bottom and pins it with the leading edge of its head, then pivots to bite off a pectoral wing. With one wing gone the ray cannot swim and is eaten at leisure.

Feeding peaks at dawn and dusk. Tarpon exhausted by anglers at Boca Grande are taken at the surface, and hooked fish of any kind draw the species from a distance, which is why great hammerheads are so often seen by fishermen and so seldom by swimmers. A shark of this size does not need to feed every day; a large ray is digested over several days.

Behaviour, senses and the sideways swim

Unlike the scalloped hammerhead, the great hammerhead is a loner. Divers at Bimini see several on the same flat in winter, but they arrive and leave separately, and there is no schooling anywhere in its range. Encounters between individuals are settled by size, and a big female will displace a smaller one from a bait with a lateral display of the head.

The oddest thing about its behaviour was only measured in 2016. Sharks fitted with motion tags off Belize and Australia swam rolled onto their sides, 50 to 75 degrees from upright, for up to 90 per cent of the time. Rolled over, the huge first dorsal fin works as a second pectoral fin and adds lift, and the models suggest it cuts the cost of swimming by about a tenth. It explains the tilted posture in so many underwater photographs.

The head gives it senses that a pointed-nosed shark lacks. The eyes, set at the ends of the cephalofoil, give a 360-degree view in the vertical plane and good binocular overlap ahead; the nostrils, set wide apart, let the shark compare the timing of a scent reaching each side and turn toward it; and the underside of the head carries thousands of ampullae of Lorenzini. Satellite tags have shown individuals covering more than 1,000 km along the Australian and American coasts within a season.

Reproduction and lifespan

Great hammerheads are viviparous with a yolk-sac placenta. Once an embryo has used up its yolk, the empty sac fuses with the wall of the uterus and passes oxygen and nutrients from the mother's blood through a cord attached between the pectoral fins, the arrangement found in other hammerheads and in requiem sharks. Gestation lasts about 11 months and litters run from 6 to 42 pups, with the 55 carried by the Boca Grande record female the largest known. Newborns measure between 50 and 70 cm.

Mating has been described only once in the scientific literature, from a pair seen near the surface off the Bahamas, and both sexes carry scars from courtship bites. Birth takes place in late spring and summer in shallow coastal water, and although the species has no tightly defined nurseries like the scalloped hammerhead, young sharks are landed on inshore flats and in estuaries across the tropics. A female breeds only every second year, since she must recover condition after an 11-month pregnancy.

Vertebral ageing of sharks from the Gulf of Mexico and the western Atlantic found males maturing at about 6 years and females at about 8, with the oldest female in the sample 44 years old. Growth studies in Australia point to similar ages. A lifespan of 40 years or more, late maturity and a two-year cycle add up to one of the slowest-reproducing sharks in tropical waters (how long sharks live).

How dangerous are great hammerheads to people?

On paper the great hammerhead has everything a dangerous shark needs: a 4 m body, serrated cutting teeth and a habit of coming close to fishermen. In practice it hardly ever bites anyone. The SharkSider database contains one record attributed to the species: a spearfisher off Fort Lauderdale, Florida, who received a laceration to a toe from a 2.4 m great hammerhead in July 2003. It was not fatal, and there is no death attributed to the species anywhere in the file.

The database also holds around 50 incidents recorded only as "hammerhead", most of them in the USA and Australia, and a share of those will have been great hammerheads, since this is the species that approaches boats and divers most boldly. Nearly all involve hooked or speared sharks, kayak anglers or spearfishers carrying fish; the shark wants the catch, not the person. Unprovoked bites on swimmers are almost unknown.

Divers at Bimini feed and photograph great hammerheads at arm's length every winter without injury. The animals are pushy around bait but not aggressive, and the sensible rules are the ordinary ones: do not carry speared fish on your belt, do not swim near anglers landing sharks, and follow the advice on what to do in a shark encounter. Records by region are on the Florida and Australia pages.

Great Hammerhead Shark incidents in the SharkSider database

• Records attributed1
• Fatal0 (0%)
• Years covered2003–2003
• Since 20001 incidents, 0 fatal
• Most common activityDiving & spearfishing
• Most recordsUSA (1)

The six most recent records attributed to the great hammerhead shark

• July 2003 · Fort Lauderdale, Broward County, Florida, USASpearfishing — Laceration to toeRecorded as: 8' great hammerhead shark · not fatal

Records are matched on the shark named in each report (“great hammerhead”), so they include incidents where the species was reported rather than confirmed. Full records by country on the shark attacks pages.

Conservation status

The IUCN assessed the great hammerhead as Critically Endangered in 2018, estimating a global decline of more than 80 per cent over three generations, roughly 70 years. In the north-west Atlantic, where data are best, the population fell steeply from the 1980s to the mid-2000s and has since levelled off at a low point; in the Indian Ocean, West Africa and South-east Asia there is no sign of recovery.

The fins are the problem. A great hammerhead's first dorsal is among the most valuable single fins in the trade, and the species is taken on longlines, in gillnets and by artisanal fisheries throughout its range, and its low-value meat meant many were finned at sea until finning bans spread. Even released sharks fare badly: great hammerheads are among the most stress-sensitive of all sharks on a hook, with more than half dying after capture in some longline studies, and they are also killed in the bather-protection nets and drumlines of Queensland and New South Wales (see bycatch).

International trade in the species has needed CITES Appendix II permits since 2014, and it is on Appendix II of the Convention on Migratory Species. Florida banned all harvest of great, scalloped and smooth hammerheads in state waters in 2012, the Bahamas closed its waters to shark fishing in 2011 and Australia has restricted hammerhead landings in its northern fisheries under its CITES obligations. As with all threatened sharks, biology sets the pace: a shark that breeds every second year from the age of eight cannot absorb the fishing pressure it faces.

Similar species and close relatives

Nine other hammerheads share the family Sphyrnidae with the great hammerhead, and most are told apart by the head. The scalloped hammerhead, the species that overlaps with it most, has notches at the sides of the head, a lower dorsal fin and straight pelvic fins, and it schools where the great hammerhead roams alone. The smooth hammerhead reaches a similar 4 to 5 m but lacks the central notch and prefers cooler water. The winghead has a head half as wide as its body is long, and the little bonnethead and scoophead have rounded, spade-shaped heads without notches. The general hammerhead shark page compares them side by side.

Beyond the family, the great hammerhead shares its ray-hunting niche with the bull shark and the tiger shark, which use the same flats and passes and are the species most likely to be confused with it in a poor photograph taken from a boat.

• Scalloped Hammerhead Sharkspecies profile
• Smooth Hammerheadspecies profile
• Carolina Hammerheadspecies profile
• Winghead Sharkspecies profile
• Bonnethead Sharkspecies profile
• Smalleye Hammerheadspecies profile

Written and reviewed by

SharkSider Editorial Team

A small team focused on researching sharks and making marine biology easy to understand. Every page is reviewed against current species records and the SharkSider attack database, and updated when new incidents or research appear.

Published November 13, 2022 · Last updated September 22, 2026 · 1 incident attributed to the great hammerhead shark in the SharkSider attack database (0 fatal), updated weekly.