Types of Hammerhead Shark: How Many Species, and How to Tell Them Apart

There are about ten species of hammerhead shark, grouped in two genera: Sphyrna, which holds all but one of them, and Eusphyra, whose only member is the winghead shark. The three large species most people picture, the scalloped, great, and smooth hammerheads, are told apart mainly by the shape of the front edge of the head and the size of the dorsal fin. The rest are smaller sharks of the coastal Americas, the little-known Carolina hammerhead, and the winghead of the Indo-West Pacific. This chapter of MMF’s guide to hammerhead sharks explains how to recognize each of them.

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.

How many species of hammerhead shark are there?

About ten, although the count has shifted as taxonomists have revised the family. A 2018 review of the large hammerheads states that “there are 10 species of hammerhead sharks”, nine of which are now assessed on the IUCN Red List. Other studies have used different totals: nine in a 2014 review and eight in a 2020 study.

The count moves for two reasons. First, genetic studies keep finding species that look identical to known ones: the Carolina hammerhead, formally named in 2013, was first detected as a separate genetic lineage hidden within the scalloped hammerhead. Second, some familiar species are probably more than one. The 2021 Red List assessment of the bonnethead describes it as likely a complex of three species, each confined to its own stretch of coast. If the assessors are right, the count will rise again.

As a group, hammerheads are young. They form the family Sphyrnidae within the ground sharks (order Carcharhiniformes) and diverged from the rest of that order around 10 to 20 million years ago, among the most recently of all living sharks. How the family came by its cephalofoil (the hammer-shaped head) is the subject of why hammerheads have a hammer.

What are the nine hammerhead species on the IUCN Red List?

The IUCN Red List assesses three large, wide-ranging hammerheads, four smaller species of the coastal Americas, the poorly known Carolina hammerhead, and the winghead shark. Sizes are maximum total lengths (snout tip to tail tip) from each species’ latest assessment unless a newer study gives a better figure. The size chapter works through the records, and the hammerhead facts page and the hammerhead overview give quick answers.

Eight of the nine sit in a threatened category and six are Critically Endangered; the exception is the Carolina hammerhead, for which there is inadequate information to assess its status. For the scalloped hammerhead, the 2019 assessment gives a slightly larger maximum of 4.2 m (14 ft) than the 4 m used in more recent work. Several small species have already disappeared from parts of their range. The scalloped bonnethead now appears to be absent from Mexico, the scoophead is no longer present in the Gulf of California, and neither is the bonnethead. The causes, and the protections now in place, are covered in why hammerhead sharks are endangered.

What is the difference between large and small hammerheads?

Size, range, and habitat: the large species are ocean-going sharks found worldwide, while the small species are coastal sharks with much narrower ranges. One common grouping puts large species above 1.5 m (5 ft) and smaller species below it. A 2006 genetic study summarized the contrast this way: four described species are small and occupy coastal habitat with restricted geographical range. The scalloped, great, and smooth hammerheads, by contrast, are larger, ocean-going, and more widely distributed.

The three large species have attracted most of the research and conservation attention. A 2018 review focused on them because they are the best studied of the hammerheads, heavily exploited in fisheries worldwide, and prized in the shark fin industry. The same review noted that the winghead and the Carolina hammerhead are also relatively large, but that “virtually no information exists on their biology”.

The four small species, the bonnethead, scalloped bonnethead, scoophead, and smalleye hammerhead, live in shallow water over the continental shelf. That habitat exposes them to coastal gillnets, longlines, and trawls throughout their ranges. The assessments of the scalloped bonnethead, scoophead, and smalleye hammerhead each cite a lack of refuge at depth among the reasons for their status.

Size also shapes how a species copes with fishing. The largest hammerheads are the slowest growing, whereas the bonnethead has “among the highest population growth rates calculated for sharks”. Even so, its assessment reports drastic inferred declines through much of its range, with numbers stable due to management only in the United States, the Bahamas, and Atlantic Mexico. High productivity, in other words, has not protected the bonnethead on its own; where it is holding steady, the assessment credits management.

How do you tell a scalloped, great, and smooth hammerhead apart?

Look first at the front edge of the head, then at the dorsal fin. The three large species are similar in build, and the front margin of the head is the trait most frequently used to tell them apart. On a great hammerhead, that edge is straight. On a scalloped hammerhead, it forms two rounded lobes separated at the midline by a prominent indentation, which smooth hammerheads lack; on a smooth hammerhead, it forms a single rounded lobe. The great hammerhead also has a much larger body and a disproportionately large, sickle-shaped dorsal fin, while the other two have smaller, curved dorsal fins.

Where scalloped and smooth hammerheads overlap, as they do in warm-temperate Australia, the rear fins help. Researchers confirming a scalloped hammerhead aggregation off Western Australia used the central indentation in the head plus two fin features. On a scalloped hammerhead, the base of the anal fin is noticeably larger than that of the second dorsal fin, and the second dorsal fin’s free rear tip nearly reaches the start of the upper tail lobe. On a smooth hammerhead, the two fin bases are of similar size and the second dorsal fin ends well ahead of the tail.

Is a bonnethead a hammerhead shark?

Yes. The bonnethead (Sphyrna tiburo) belongs to the same genus as the scalloped and great hammerheads; its head is simply the least expanded in the family. Bonnetheads are small, coastal hammerhead sharks with a broadly rounded, spade-like head and the least degree of lateral head expansion of all hammerhead species, reaching only 1.5 m (5 ft). They live over mud and sand, seagrass, coral reefs, estuaries, shallow bays, and channels on both coasts of the Americas.

Mature bonnetheads can also be sexed by the head. At sexual maturity, males develop a prominent bulge along the front margin of the head, which females, juveniles, and embryos lack. The bulge forms as cartilages inside the snout lengthen, in step with the growth of the male’s claspers (reproductive organs), and it was the first sexual difference in head shape reported for any shark species. The bonnethead’s diet is unusual too. In a feeding trial, captive bonnetheads digested seagrass, making it “the first species of shark ever to be shown to have an omnivorous digestive strategy”, as the feeding chapter describes.

“The bonnethead” may also be more than one species. Its 2021 Red List assessment treats it as likely a complex of three geographically discrete species: one in the United States, the Bahamas, and Atlantic Mexico; one from Belize south to Brazil; and one in the Eastern Pacific. A genetic study found significant differentiation between bonnetheads from Caribbean Panama and Belize and those elsewhere in the western Atlantic, though on preliminary evidence from mitochondrial DNA, which traces maternal ancestry. The three groups are faring very differently. The northern Atlantic group is stable due to management, whereas in the Eastern Pacific the bonnethead was last recorded in Mexico in 2006 and has not been encountered in Central America since the 1980s.

What is a winghead shark?

The winghead shark (Eusphyra blochii) is the only member of the second hammerhead genus, and its head is the most extreme in the family, extremely wide and narrow. It is a medium-sized hammerhead reaching 1.86 m (6 ft) that lives over the continental shelf of the tropical Indo-West Pacific, from the surface to 127 m (417 ft). There it favors shallow, turbid coastal areas and estuaries, often around large river mouths.

That head gives the winghead unusually wide forward vision. In a comparison of five shark species, it had the largest binocular overlap, the zone both eyes see at once, at 48°, more than four times that of the lemon (10°) and blacknose (11°) sharks. The authors concluded that binocular overlap has increased with lateral head expansion in hammerhead sharks, one of the ideas weighed in why hammerheads have a hammer.

The winghead once ranged from the northern Indian Ocean through South and Southeast Asia to New Guinea and northern Australia. Primarily because of fishing, it is now considered “possibly extinct” in northern Southeast Asia, from Thailand to Taiwan, and the 2025 Red List assessment lists it as Critically Endangered. However, it remains widespread along the coasts of New Guinea. In Australia, its declines are not suspected to be as severe, owing to reductions in fishing intensity, low catches, and an increase in marine protected areas. Since 2023, it has been listed on Appendix II of CITES, which requires exports to come from legal and sustainable fisheries.

A winghead caught by recreational fishers in Moreton Bay, Queensland, about 800 km (500 mi) south of its known range may mean the species had gone undetected there. Alternatively, it may be shifting south, as other sharks have along Australia’s east coast. The authors raise both possibilities; the second would fit the shifts described on the climate change page.

What is the Carolina hammerhead?

The Carolina hammerhead (Sphyrna gilberti) is a cryptic species: it looks almost identical to the scalloped hammerhead and was discovered through its DNA. In 2006, geneticists studying scalloped hammerheads found a deep split within their Atlantic samples. A third lineage, found in that sampling only between coastal North Carolina and Florida, carried a variant of a nuclear gene not found in any other scalloped hammerhead sampled. The authors took this as evidence of reproductive isolation and thus the occurrence of a cryptic species. Because earlier taxonomists had been unable to tell the two forms apart by eye, they concluded that “speciation was cryptic”.

Only one physical difference has been found, in the number of vertebrae. In a sample of eight juveniles, four from each lineage, those of the cryptic lineage had significantly fewer total vertebrae, an average of 171 against 194 in Atlantic scalloped hammerheads. The Red List assessment specifies a narrower count: the species can only be morphologically distinguished from the scalloped hammerhead by precaudal vertebral counts, that is, by counting the vertebrae ahead of the tail. A living Carolina hammerhead therefore cannot be told from a scalloped hammerhead in the water.

The species was formally named in 2013, and its full range, depth range, and maximum size remain unknown. Most specimens have been juveniles collected in shallow coastal bays or inlets, with confirmed records from Florida to North Carolina and possible occurrences in Panama and Brazil. A large genetic survey of western Atlantic scalloped hammerheads identified only three Carolina hammerheads, all in the western South Atlantic. The 2006 sampling suggested that it is less abundant than the scalloped hammerhead and therefore potentially more susceptible to fishery pressure.

How do scientists identify hammerhead species?

In the field, by head shape and fins; in the hand, by details such as the sensory pores on the underside of the head; and, increasingly, by DNA. Each method has limits. Because head shape changes significantly as a hammerhead grows, identification on that feature alone can go wrong, and a 2009 study of museum collections in Brazil found cephalofoils attributed to the wrong species. Its author proposed a check that holds from juvenile to adult: the pattern of pores under the head that lead to the ampullae of Lorenzini, the shark’s electrosensory organs. Together with head shape, that pattern was sufficient to identify accurately the four species the study examined, the most common hammerheads of the southwestern Atlantic.

Identification in the field is harder still. A 2017 study of hammerhead connectivity across northern Australia, Indonesia, and Papua New Guinea had to exclude a citizen-science dataset of more than 2,100 records. The dataset had placed hundreds of hammerheads in temperate waters where scalloped and great hammerheads do not commonly occur, and the authors judged these probably misidentifications between the great hammerhead and the smooth hammerhead. In Western Australia, drone footage of a scalloped hammerhead aggregation could not identify every shark to species, so researchers confirmed it from snorkelers’ photographs.

DNA settles cases the eye cannot. In August 2017, the refrigerated cargo ship Fu Yuan Yu Leng 999 was detained while crossing the Galápagos Marine Reserve with 7,639 sharks aboard. A team from the Universidad San Francisco de Quito that included Dr. Alex Hearn sequenced a gene from 929 of them and found 12 shark species. Among them were 122 scalloped hammerheads (13.1%) and 67 smooth hammerheads (7.2%). The threats chapter covers what that seizure revealed. A study co-authored by Hearn has also trained a deep-learning model to detect and track hammerheads in underwater video, a tool the authors suggest could help monitor their relative abundance in the wild.

Which hammerhead species live in the Galápagos and the Eastern Pacific?

The scalloped hammerhead dominates at the offshore islands, where it is one of four hammerheads on the reserve’s species list, and more species live along the mainland coast. Dr. Alex Hearn of the Universidad San Francisco de Quito has studied these hammerheads since his team began tagging them at Darwin and Wolf islands in 2006. His team also leads the silky shark tracking study in which MMF takes part. That list comes from a 2014 review of the reserve’s sharks and rays, led by Hearn, which names the scalloped, great, smooth, and bonnethead. The great hammerhead, however, was included only on the basis of plausible yet unconfirmed sightings.

The scalloped hammerhead is the species divers travel to see. In the review’s dive surveys, hammerhead and Galápagos sharks were by far the most commonly encountered sharks, with hammerheads schooling in large numbers at upstream current sites at Darwin and Wolf. Tracking at Wolf Island by Hearn’s team showed that these schools are mainly made up of females. MMF’s scientists meet the schools at Darwin Island, where they work with partners on the Galápagos Whale Shark Project. Visiting divers follow a protocol designed to avoid disturbing these shy sharks, and the schooling and diving chapters explain how the schools form and how to see them.

Along the mainland coast, the mix changes. Off Ecuador, smooth and scalloped hammerheads are landed together by the artisanal fleet. A study of both species from the port of Manta used stable isotopes, chemical signatures in body tissue that reflect diet. It found low overlap in their feeding niches, suggesting different feeding areas even though they eat similar prey. Farther south, young smooth hammerheads use nursery areas off northern Peru, one of the nurseries covered in baby hammerhead sharks. A diet study of four species sharing coastal waters included the scalloped bonnethead, which lives only in the Eastern Pacific. It found their trophic niches, the range of food and feeding roles each species occupies, more similar within species than among them, pointing to potentially different roles for each species in the food web.

Protection has followed. In 2014, the Eastern Pacific population of the scalloped hammerhead was listed as endangered under the US Endangered Species Act. MMF’s work in the Galápagos also helped secure the Hermandad Marine Reserve, an expansion covering 60,000 km² (23,000 square miles).

Which hammerhead species can you see in Florida?

South Florida’s coastal waters hold at least three hammerhead species, and in a long-running scientific survey the great hammerhead was caught far more often than the other two. The survey used drumlines, single baited hooks on a weighted line marked by a surface buoy, and caught 3,398 sharks of 15 species between 2009 and 2021 from Miami to the middle Florida Keys. Great hammerheads ranked fifth among all sharks caught, with 238 individuals, against 22 scalloped hammerheads and 11 bonnetheads. The largest shark in the entire survey was a 450 cm (15 ft) great hammerhead, close to the 4.55 m (15 ft) maximum in a recent tracking study in Queensland and Western Australia. The size chapter examines the “20-foot hammerhead”. The cryptic Carolina hammerhead has also been recorded in Florida.

Florida’s great hammerheads are not confined to Florida. Tagging showed return migrations of about 3,000 km (1,900 mi), seasonal residency, and annual returns to Bimini and to Jupiter, Florida, by many individuals. Jupiter lies at the northern end of the Palm Beach County coast, where MMF’s Florida Manta Project studies juvenile manta rays. The project’s aerial and boat surveys along the South Florida coast have recorded hammerheads on several occasions. Both great and scalloped hammerheads are prohibited species in Florida state waters. Even so, hammerheads have a relatively high rate of death after release because of the stress of capture, as the overfishing page explains.

Why it matters for conservation

Protection for hammerheads is written species by species, so it depends on being able to tell them apart. In 2013, the great and smooth hammerheads were each added to Appendix II of CITES based on their similarity to the scalloped hammerhead. The listing requires exports to be accompanied by permits showing that the shark parts come from legal and sustainable fisheries. A permit, however, is only as good as the ability to say which species is in a shipment.

Hidden species raise the stakes. The authors who discovered the Carolina hammerhead argued that effective management of large coastal sharks should incorporate the discovery, since a rarer species counted as a scalloped hammerhead can be overfished unnoticed.

Status also differs sharply among the large species. In a global analysis of half a century of abundance data for 18 oceanic shark and ray species, which we co-authored, the smooth hammerhead was the only species not to decrease. The scalloped and great hammerheads, by contrast, were among three oceanic sharks now classified as Critically Endangered. The same analysis found that hammerhead populations are rebuilding in the Northwest Atlantic, owing to strictly enforced quotas throughout their US range, evidence that well-enforced management works. The threats and protections for each species are set out in why hammerhead sharks are endangered and on MMF’s overfishing and climate change pages.

To help, support MMF’s shark research in the Galápagos, where MMF’s scientists work with Dr. Alex Hearn’s team to track sharks across the island reserves of the Eastern Tropical Pacific.