Bonnethead Shark

• Maximum length1.5 m (4.9 ft); most adults 0.8–1.2 m
• WeightUp to about 11 kg (24 lb)
• LifespanAbout 12 years; large females to 17–18
• Depth rangeSurface to 80 m (260 ft), usually under 25 m
• DietBlue crabs, shrimp, molluscs, small fish and seagrass
• IUCN statusEndangered (assessed 2019)

How to recognise a bonnethead shark

Look at the front edge of the head. Every other member of the hammerhead family carries notches, scallops or a straight chopped-off margin across the leading edge of its cephalofoil; the bonnethead's is one smooth, unbroken curve, so the head reads as a rounded spade or a garden trowel rather than a hammer. Seen from above it is wider than it is long, with the eyes set at the outer corners and the nostrils running along the front margin.

The body behind it is a plain little shark: grey to greyish-brown on the back, occasionally with a scattering of faint dark spots, and dull white underneath. The first dorsal fin is tall and hooked, the second much smaller, and the fins have no bright markings at all, which is itself a useful clue on a coast where juvenile blacktips and Atlantic sharpnose sharks carry obvious pale or dark fin edges.

Open the mouth and the identification becomes certain. The front teeth are small, sharp and cusped for gripping, but the rear teeth flatten into broad, pavement-like molars built to crush shell. No other hammerhead has that arrangement. Adult males are also the only sharks in the family with an obvious bulge on the front of the head, a swelling of the cephalofoil cartilage that appears at maturity; females keep the plain, evenly rounded outline all their lives.

How big do bonnethead sharks get?

The largest reliably measured bonnetheads are about 1.5 m (4.9 ft) in total length and weigh roughly 11 kg (24 lb). Those are exceptional animals. On a Florida or Texas flat the sharks you actually see run 80 cm to 1.2 m, and a shark of a metre weighs only three or four kilograms: this is a species you can lift with one hand.

Females are the larger sex, as in most sharks. Males mature at around 52 to 75 cm and rarely exceed 1.1 m; females mature at roughly 84 to 90 cm and account for every record-sized individual. Newborn pups measure 30 to 40 cm, so a bonnethead is already a quarter of its adult length on the day it is born.

One correction to the older literature is worth making here. The bonnethead is often called the smallest hammerhead, and it is not: the scalloped bonnethead of the eastern Pacific tops out near 92 cm, comfortably smaller. What the bonnethead really is, among the ten or so species in the family, is the smallest one that most people will ever encounter alive.

Where bonnethead sharks live

Bonnetheads are warm-water animals of the shelf edge inward, and in practice that means the shallowest water a shark can occupy. They are found over seagrass beds, sand and mud bottoms, in estuaries, bays, tidal creeks and channel edges, usually between the surface and 25 m and only occasionally as deep as 80 m. Water below about 21 °C empties them out entirely.

The Atlantic and Gulf range runs from North Carolina south through Florida, around the Gulf coasts of Alabama, Louisiana and Texas, and on to Mexico and Belize. Summer wandering carries a few animals as far north as Rhode Island; every autumn they retreat, and the sharks that spend July in North Carolina and South Carolina winter off Florida.

Older accounts extend the range down the Pacific coast from California to Peru and across the Caribbean to Brazil, and the map above still reflects that. Genetics has since broken the bonnethead into several species. The animals from Belize south through Panama, Colombia and Trinidad to Brazil were described in 2024 as a separate shark, Sphyrna alleni, and the eastern Pacific populations from Ecuador and Peru northward belong to further lineages still under revision. Sphyrna tiburo in the strict sense is a western Atlantic shark.

What bonnethead sharks eat

The centre of the bonnethead's diet is the blue crab. Add shrimp, mantis shrimp, small bivalves and snails, octopus, and small bottom fish such as gobies and pinfish, and you have almost the whole list. It is a crushing predator, not a chasing one: the shark quarters the flat with its head close to the bottom, sweeping the ampullae of Lorenzini spread across that broad cephalofoil over the sand until a buried crab's muscle activity gives it away, then pins the animal and works it back to the molars.

Then there is the seagrass. Stomach contents from Florida Bay and the Gulf routinely come back more than half seagrass by mass, which for decades was written off as accidental swallowing, or explained as a cushion against crab shell. In 2018 a feeding trial at the University of California and Florida International University settled it: bonnetheads fed a labelled seagrass diet digested and assimilated around half of the plant's organic matter, put on weight, and carried gut enzymes able to break down plant carbohydrate.

That makes the bonnethead the only shark demonstrated to be genuinely omnivorous rather than a filter feeder straining plankton. It matters ecologically as well as biologically: a shark this abundant, moving nutrients between seagrass meadows and the creatures that eat it, behaves partly like a grazer in a system where no one expected one.

Behaviour, senses and movement

Bonnetheads are sociable in a loose way. The usual sight is a group of three to fifteen animals moving with the tide over a flat, though aggregations of several hundred have been recorded on migration, and males, females and juveniles often travel apart. Within a group they space themselves out rather than school tightly, and the small dominance displays seen in larger hammerheads are muted.

The cephalofoil does three jobs at once. It spreads the electroreceptive pores over a much wider search area, it widens the nostrils' sampling of the water, and it gives the eyes, sitting at the tips, a broad field of view with genuine binocular overlap in front. It also provides lift, but less than in the big hammerheads: swimming studies show the bonnethead relies more on its pectoral fins to hold depth than a scalloped hammerhead of the same shape does, because its head is proportionally far smaller.

One claim from older shark writing should be dropped. Bonnetheads are sometimes said to signal their position to each other by releasing cerebrospinal fluid. No study has ever demonstrated this, and there is no known anatomy that would allow it; what bonnetheads do use, like every shark, is smell, hearing, the lateral line and electroreception. Their real communication is postural.

Movement is dictated by temperature. Populations shift south and offshore as autumn water cools and return with spring warming, a pattern tight enough that fishery surveys can predict arrival dates within a fortnight.

Reproduction and lifespan

Bonnetheads are viviparous: the embryos use up their yolk in the first weeks, after which the empty yolk sac fuses to the wall of the uterus and becomes a placenta that feeds them directly, exactly as in other requiem-type sharks. What sets the species apart is the timetable. Gestation lasts only about four and a half to five months, the shortest pregnancy recorded in any shark, and a female can breed every year rather than every second or third.

Litters run from 4 to 16 pups, most often 6 to 12, and the pups arrive in late summer and early autumn in shallow, sheltered bays and creeks where adults are scarce. Males are mature at around two years old, females at two to three. Recorded ages reach about 12 years, with the largest females estimated at 17 to 18; by shark standards this is a fast, short life, closer to a bony fish than to the decades most species need (see how long sharks live).

The bonnethead also wrote a footnote into reproductive biology. In 2001 a female held for three years at the Henry Doorly Zoo in Omaha, Nebraska, with no male present, gave birth to a single pup. Genetic testing published in 2007 found no paternal DNA: the first confirmed case of parthenogenesis, virgin birth, in any shark, and the reason biologists now check for it routinely in captive elasmobranchs (more on how sharks reproduce).

Are bonnethead sharks dangerous to people?

No. The SharkSider database holds no incident attributed to this species, and neither the International Shark Attack File nor any regional record links a bonnethead to an unprovoked bite. The animal is simply not equipped for it: an adult mouth is a few centimetres across, set on the underside of a head the size of a paperback, and the back half of the jaw is paved with crushing plates rather than cutting teeth.

In practice bonnetheads and people share the same water constantly. They are among the commonest sharks on Gulf and south Atlantic flats, they are caught in enormous numbers on light tackle, and wading anglers regularly find one working the same sandbar they are standing on. The shark's reaction to a person is to leave. The only injuries on record come from handling: a hooked bonnethead thrashes, and the small front teeth and the rough skin can open a hand. Support the body, keep fingers away from the mouth, and use pliers on the hook. Treat any shark you release as a fish worth returning in good condition, not as a trophy.

The SharkSider database has no incident attributed to this species. The database draws on the International Shark Attack File, the Global Shark Attack File and verified local reports, and is updated weekly.

Conservation status

The IUCN Red List assessed the bonnethead as Endangered in 2019, an unusually severe listing for a shark that anyone in Florida can still catch in an afternoon. The rating is driven by the wider picture rather than by the United States: across the Caribbean, Central America and Brazil the species is taken heavily in artisanal gillnets and has vanished or become scarce in areas where it was once ordinary, and the modelled global decline exceeds fifty per cent over three generations.

The North American picture is better. In United States federal waters the bonnethead is managed within the Atlantic small coastal shark complex, which has been assessed as neither overfished nor experiencing overfishing, with quotas, size rules and a long fishery-independent survey record. Recreational catch is large but mostly released.

Since November 2023 the species also carries international trade controls: the whole family Sphyrnidae was added to CITES Appendix II, so exports of bonnethead fins, meat and specimens now require permits and proof of legal, sustainable sourcing. The remaining pressures are shrimp-trawl bycatch, gillnetting in nursery bays, and the steady loss of the seagrass this shark feeds and breeds over. The 2024 split of the Caribbean and Brazilian populations into Sphyrna alleni also means the next assessment will have to be rewritten for a smaller, more northern species, which will change what the numbers mean (see why sharks are endangered and how the IUCN Red List works).

Similar species and close relatives

Within the family, the closest animals to the bonnethead are the other small-headed species. Sphyrna alleni, described in 2024 from Belize to Brazil, was part of the bonnethead until genetics and vertebral counts separated it; its cephalofoil is more pointed in front with lobed rear margins. The scalloped bonnethead of the eastern Pacific is smaller still and has a notched, distinctly scalloped head. The smalleye hammerhead of muddy South American coasts is closer in size to a bonnethead than to a great hammerhead, and turns golden from the shrimp it eats.

The larger relatives are unmistakable side by side: the scalloped hammerhead and Carolina hammerhead have a notched, wing-like head and reach three metres or more, the smooth hammerhead has a broad head with no central notch, and the great hammerhead has an almost straight-edged head and a towering first dorsal fin.

On the flats themselves the real confusion is with a shark from another family. The Atlantic sharpnose shares the bonnethead's size, habitat and grey-brown colour, but has an ordinary pointed snout and white spots along the flanks. Anything with a flattened head, however small, is a hammerhead.

• Scalloped Bonnetheadspecies profile
• Carolina Hammerheadspecies profile
• Scalloped Hammerhead Sharkspecies profile
• Smooth Hammerheadspecies profile
• Great Hammerhead Sharkspecies profile
• Atlantic Sharpnose Sharkspecies 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 July 26, 2022 · Last updated September 22, 2026 · No incident attributed to this species in the SharkSider attack database, which is updated weekly.