Are Hammerhead Sharks Dangerous and Do They Attack Humans?

There are over 440 species of shark in the world, but the hammerhead shark stands out because of the bizarre shape of its head.

There are nine types of hammerhead shark. The great hammerhead shark is the largest of them all, and can grow up 20 feet, although this is very rare. On average, they grow up to 13 feet. Bonnethead hammerheads are the smallest species, growing to around five feet.

Hammerheads are found worldwide in tropical seas, and most typically around coastal reefs, however they are known to seasonally migrate into open ocean.

Their habitat, combined with their size, means they could cause significant damage to a human. But do they actually pose any threat to us?

Do they attack humans?

Jonathan Davis, a Texas-based marine biologist and shark expert, told Newsweek that it is isn't unusual for humans to encounter a hammerhead in shallow water, as this is where they commonly live.

However, this does not mean they are a threat to humans.

According to the International Shark Attack File, which is the world's only scientifically documented database of all known shark attacks, there have been 16 incidents between humans and hammerhead sharks since 1900.

And of those, there have been 0 deaths.

Most attacks took place off the eastern coast of Florida, with one off the coast of California, another off Australia and two off Pacific islands.

"I would not classify hammerheads as a danger to humans and would definitely put their 'attack' rate as very rare," he said.

A stock photo shows a Great Hammerhead shark, which is the largest species of hammerhead. Carlos Grillo/Getty Images

James Lea, chief executive officer of ocean conservation organization the Save Our Seas Foundation, told Newsweek that humans are actually a far greater threat to the sharks then they are to humans. He said that overfishing has left seven of the nine hammerhead shark species either endangered or critically endangered.

When human and hammerhead encounters that do happen, it is unlikely the sharks purposefully target us as prey. "Confusion with prey or curiosity are the most commonly suggested reasons, with most sharks moving on when realizing we aren't suitable prey," Lea said.

Why are their heads shaped like that?

The ancestors of hammerhead sharks appeared on Earth around 20 million years ago. According to research published by scientists at the University of Colorado in 2010, the first ancient hammerheads were as big as the largest on Earth today. Over time, divergent evolution saw it split into different species, with some getting smaller and its hammer-like head changing in shape and size.

Hammerheads are some of the most highly adapted shark species. The peculiar shape of its head sets them apart from other sharks in hunting skill, navigation ability and swimming efficiency.

With their eyes positioned out to the side, they get 360 degree vision and depth perception, both in the front and behind.

"Their heads also maximize the surface area for their electroreceptive pores, allowing them to home in on prey hidden beneath the sand like a metal detector," Lea said. "They can even use the hammer to physically pin down prey, or as a 'handbrake' to perform a pinpoint 180 degree turn."

Lea said that different species of hammerhead sharks also show a myriad of other fascinating behaviours.

"Scalloped hammerheads are a social species and can school in their thousands, Bonnetheads can digest plant material and even interpret the earth's magnetic field to navigate, while great hammerheads spend most of their time swimming 50 degree rolled to their side," he said.

How do they hunt and what do they eat?

While it has many advantages, the hammer-shaped head does not lend well to being a high speed ambush predator. This is why their success lies in its ability to locate prey such as stingrays in the sand that would likely go undetected by a generically shaped shark.

Hammerheads have relatively small mouths that face downwards. They use this positioning to grab food like fish, shellfish, squid, octopus, shrimp and stingrays.

Why don't hammerhead sharks often attack humans?

The shape of a hammerhead's head may explain why they leave us alone.

Davis said that the outward extensions of its head are "amazingly sensitive," and able to detect bioelectric fields, which includes those given off by humans. This means they are likely able to tell when we are in the water nearby. And, with their preferred meals consisting of stingrays, other sharks, bony fish and crustaceans, humans are not on their menu.

A stock photo shows a herd of Hammerhead sharks swimming. Their unique heads set them apart from other shark species. Eladio Arvelo/Getty Images

Davis said their "high efficiency" on how they detect prey likely contributes to their ability to discern between a human foot or leg and a stingray. He said that this would lend itself even more into the fact that none of the 17 human encounters were fatal.

Overall, Davis said the hammerhead shark is one of the most unique shark species to ever exist.

However, Davis said that as a result of their novelty they are often caught and handled for show. "As a negative effect of their high sensitivity, they have a relatively low survival rate after human encounters involving boats, beaches, and stress," he said. "It is highly encouraged to keep hammerheads in the water when caught and released as quickly and safely as possible for the human and the shark to minimize stress and increase survivability."