38 Fun Facts About Hammerhead Shark

Besides keeping water flowing over its gills, why must a hammerhead keep swimming?

It sinks if it stops: a hammerhead is heavier than water, so it stays up only by the lift its fins generate as it moves.

What is the technical name for the hammerhead's flattened, T-shaped head?

Cephalofoil: it was long assumed to work as a steering wing, but tests on young hammerheads found they do not roll into their turns as a winged craft would.

Which hammerhead has the widest head for its size, as much as half its body length across?

The winghead is named for it: the narrow, wing-like blades of its head stretch as wide as half its body length, far beyond any other hammerhead's.

What is the bonnethead's main prey, cracked open with flat teeth at the back of its jaws?

Blue crabs: the bonnethead sweeps its head over the seabed to find them, seizes them with small sharp front teeth and crushes the shells with broad molars.

A 2009 study found that a hammerhead's wide-set eyes give it better what than sharks with ordinary heads?

Binocular vision: the wider the hammer, the more the two eyes' fields overlap in front, and the widest-headed species tested had nearly four times the overlap of a lemon shark.

The sensory pores spread across a hammerhead's wide head detect what from prey hidden under the sand?

Electric fields: the pores, called ampullae of Lorenzini, pick up the faint electricity every living animal gives off, and a wider head sweeps more seabed at once.

Which are the hammerheads' closest relatives?

The requiem sharks, the family of the bull and lemon sharks: hammerheads are thought to descend from a requiem-shark ancestor, which is why researchers use lemon sharks as their plain-headed comparison.

When do great hammerheads do most of their hunting?

At dusk: in the fading light they swing their heads in wide arcs just above the bottom as they search for a meal.

How does the front of a great hammerhead's head differ from a scalloped hammerhead's?

Nearly straight, not arched: the great hammerhead's hammer is almost square-fronted, while the scalloped species has a curved front edge with the scallop-like lobes that give it its name.

What is the great hammerhead's favourite prey?

Stingrays are the great hammerhead's favourite prey; it sweeps its head over the sand to sense rays buried there, and venomous barbs lodged in its mouth do not seem to trouble it.

How does a great hammerhead subdue its favourite prey?

Pins it with its head: the shark presses its catch down with the hammer and takes a disabling bite from each side before it can escape.

Where do young scalloped hammerheads spend their first years, out of reach of bigger sharks?

Shallow coastal bays: the nurseries shelter pups from predators, but they also put the young within easy reach of inshore fishing nets.

A 2016 study found great hammerheads spend up to 90% of their time doing what to save energy?

Swimming on their side: a 2016 study of tagged great hammerheads found 'rolled swimming' up to 90% of the time, using the tall dorsal fin as a lift surface and cutting drag by about 10%.

Unlike most sharks, where have great hammerheads been observed mating?

Near the surface: most sharks mate on or close to the sea floor, which makes the great hammerhead's habit of rising to the top of the water to couple an oddity.

Which hammerhead prefers cool temperate seas to the tropics favoured by its relatives?

The smooth hammerhead ranges as far as the British Isles and New Zealand, and because swimmers are scarcer in such cool water, it rarely crosses paths with people.

How do hammerhead embryos get nourishment in the later stages of gestation?

Through a yolk-sac placenta: once the embryos use up their yolk, the empty sac attaches to the wall of the womb and works like a mammal's placenta until birth.

What happens to most great hammerheads that fishing crews hook by accident?

They die on the line: great hammerheads tire quickly and are unusually fragile once hooked, so even catch-and-release fishing poses a real threat to them.

In 2007, a zoo's bonnethead gave science its first proof that sharks can do what?

Reproduce asexually: the pup was born in 2001 to a female that had not been near a male hammerhead for three years, and DNA tests published in 2007 found no trace of a father.

Which food can make up more than half of what is in a bonnethead's stomach?

Seagrass can exceed 60 per cent of a bonnethead's gut contents, and feeding tests showed the sharks digest about half of it, the first proof of an omnivorous shark.

The bonnethead is the only shark known to differ between males and females in what?

The shape of its head: males grow a bulge along the front edge as they mature, at the same time as their claspers lengthen, while females keep an evenly rounded outline.

Which shark was shown in 2022 to be an omnivore, digesting floating seaweed along with its usual prey?

The whale shark: tissue chemistry showed it takes real nourishment from the sargassum it swallows while filter-feeding, making the biggest fish also the biggest omnivore.

What unusual social behaviour do some hammerheads show by day?

Swimming in large schools: scalloped hammerheads gather over reefs and seamounts by day, mostly females, then split up after dark to hunt alone in open water.

In 2014 NOAA listed four scalloped hammerhead populations for protection under which law?

The US Endangered Species Act: after a 2011 petition from two conservation groups, NOAA listed two populations as endangered and two as threatened in July 2014.

How did the IUCN classify the great hammerhead in its 2019 assessment?

Critically Endangered (CR): the assessment found steep declines worldwide, driven above all by demand for the species' large fins.

What does the International Shark Attack File record about hammerheads and people?

A few bites and no deaths: for all their fearsome looks, hammerheads have fewer than twenty unprovoked attacks to their name in over four centuries of records, none of them fatal.

Which city is the world's largest shark fin trade market?

Hong Kong is the hub of a trade in which hammerhead fins rank among the most highly rated of all for shark fin soup, prized by traders for their large size.

How does a hammerhead's pale belly help it hunt?

It hides the shark from below: seen against the bright surface, a white underside melts into the light, a camouflage called countershading that lets it close in on prey unseen.

Hammerheads were added to Appendix II of which convention in March 2013?

CITES: the vote put hammerheads on Appendix II alongside the oceanic whitetip and the porbeagle, so their fins and meat can cross borders only under permit.

What do bonnetheads follow on their long daily and seasonal travels?

Warm water: bonnetheads prefer seas above 21°C, so as winter sets in they move toward the equator, travelling long distances every day to stay in the warmth.

In Hawaiian tradition, families who honoured the hammerhead as their 'aumakua saw the shark as what?

A guardian ancestor: such families would never hunt or eat sharks, believing that departed relatives had taken the animal's form.

The Hawaiian name for the hammerhead, mano kihikihi, describes the shark as what?

Angular: kihikihi means cornered or zigzag, a fair description of the head, and Hawaiians used the same word for the cornered gold coins of California's gold rush.

Apart from its prized fins, a great hammerhead's liver oil is sold to make what?

Vitamins: the fins are what fishers want, the meat is rarely eaten, and the rest of the shark ends up as liver-oil supplements, leather and fishmeal.

Where on the family tree does the widest-headed hammerhead sit?

On its oldest branch: DNA studies place the widest hammer on the first lineage to split off, so the earliest hammerheads probably had big hammers that later species reduced.

Why are most hammerhead species considered harmless to people?

They are too small: most species are fairly small, and it is the great hammerhead, at up to six metres and fiercer than its relatives, that calls for the most caution.

What is the typical lifespan of a great hammerhead?

20 to 30 years is the expected span, and females bear young only every second year, so a population that is overfished takes a long time to recover.

In tests, how did young hammerheads turn compared with a plain-headed shark?

More sharply: the hammerheads bent their bodies further into each turn than the other shark could, a flexibility that may come from the shape of the body in cross-section.

According to National Geographic, what do hammerheads do in summer?

They favour warm tropical coasts and continental shelves the rest of the year.

A 2009 study found hammerheads swing their heads more than other sharks to offset what?

A blind spot dead ahead: eyes set at the ends of the hammer leave a gap just in front of the snout, so the sharks sweep their heads from side to side as they swim to cover it.