15 Strange Shark Facts to Sink Your Teeth Into

Sharks never cease to captivate our imaginations. Strange, scary, beautiful, powerful, unique, special ... the long list of descriptors would dwarf a whale shark! Sharks have had hundreds of millions of years to evolve and dominate the sea as perfectly honed predators. The more we study them, the more surprises they reveal. Here are just a few fascinating facts about sharks around the world.

1. Hammerhead Sharks Have a 360-Degree Field of Vision

Hammerheads are standouts thanks to their curiously shaped heads. Scientists have been curious about the hammerheads' head shape—and its purpose—for a long time.

Because their eyes are placed on the very tip of the elongated head, they have particularly excellent binocular vision. Most sharks have eyes placed on the sides of their heads, rather than in the front, which means they don’t have very good stereo vision. Hammerheads, on the other hand, get a 360-degree view of the world.

The only place a hammerhead has a blind spot is directly above and below its head. The substantially improved binocular vision helps explain why these sharks evolved with such a unique profile.

2. Cookiecutter Sharks Steal Circular Chunks of Flesh From Living Prey

These sharks grow to less than 2 feet (0.6 meter) in length, yet have the largest teeth-relative-to-body size of any shark species. Why? Because they grab a bite on the go.

Cookiecutter sharks specialize in taking circular chunks out of living prey. In a way, it’s a smart strategy. They get a mouth full of food, and their prey lives on to become yet another meal in the future. It’s win-win, albeit a painful win for the victim.

The shark accomplishes the feat through a highly specialized mouth. It swims up to a victim and latches on like a sucker, with its suctorial lips forming a tight seal. Then its huge bottom teeth sink into the flesh while it twists its body to make a circular cut. Once a chunk of flesh is removed, the prey can escape.

Cookie cutter sharks aren’t picky eaters and will take a bite out of pretty much anything swimming in the sea. Everything from tuna to whales, seals and other shark species bear the circular tell-tale scars of cookiecutter shark bites. There has even been a documented attack on a human, when long-distance swimmer Mike Spalding had a plug of flesh bitten from his calf during a nighttime swim in Hawaii.

3. Shark Embryos in Eggs Can Sense When Danger Is Approaching

The most vulnerable time for a baby shark is probably when it's stuck inside an egg case without any ability to escape danger. Indeed, even embryos seem to know they’re in a dangerous situation locked inside a leathery pouch for any predator to feast upon. So they've come up with a survival strategy.

As shark embryos grow, the seal on the egg case starts to open, and at this point, predators can sense these developing fish through the electric fields emitted by their movement. But the embryos can also sense the movement of the approaching predator. When they do, the embryos freeze, and even stop breathing, in an effort to “hide” from predators and avoid detection. Researchers tested this by mimicking the electric field of predators, recording the embryos ceasing movement until the danger passed.

Scientists are using this knowledge as a lead for developing better shark repellants, noting that the embryos are less wary if the electric field never varies.

4. Tiger Shark Embryos Eat One Another in the Womb

For sand tiger sharks, life is never easy, not even in the womb. The females of this species have two uteri, and produce two pups at the end of each breeding season. But they start out the season with perhaps a dozen embryos. What happens?

The first tiny shark embryo to hatch will grow faster than its siblings, and when it reaches about 10 centimeters (4 inches) in size, it will begin to kill and eat its siblings. Once all the sibling embryos are consumed, the baby sand shark will start dining on its mother’s unfertilized eggs.

The strategy of ravenously feasting on current and future generations of siblings pays off by the time birth rolls around. From the moment these sharks hatch from a fertilized egg in the womb, the race is on to become the biggest the fastest. And you thought baby sharks in egg cases had it tough!

5. The Greenland Shark Is the Slowest-Moving Fish Ever Recorded

While the Greenland shark can rival the whale shark for size, with a maximum size of around 24 feet (7 meters) long and an average size of 8 to 14 feet (2 to 4 meters), it beats the whale shark (and every other fish) in another record: the slowest.

It’s no surprise, really, since these ectothermic animals primarily live in frigid waters. In a recent study, Greenland sharks were found to cruise at around 0.8 mph (1.3 kph). That’s less than one-third the average speed at which a human walks. When they turn on the speed, they max out at around 1.7 mph (2.7 kph). In other words, you could probably walk at about half your normal speed and still outpace a Greenland shark.

If they’re so slow, how do they manage to catch and eat seals, a prey item often found in their stomachs? Scientists think they use their great sense of smell to locate sleeping seals and make an ambush attack on the unsuspecting mammals.

6. The Rare Megamouth Shark Feeds on Krill

With a name like megamouth shark, you’d think this species would be the stuff of nightmares. And maybe it is—but only the nightmares of krill.

This large shark cruises through schools of krill, capturing food with its mega-sized mouth. It's one of three large filter-feeding sharks, including the basking shark and the much more famous whale shark.

This rarely spotted species is still a mystery to science. The first of its kind was only documented by humans in 1976. Luckily, a tiny piece of information about the life of the megamouth was put in place in 1990. Scientists caught a megamouth in a net and radio-tagged it before releasing it. They tracked the shark for two days and discovered it participates in vertical migration.

During the day, the shark hung out at depths of 450 to 500 feet (137 to 152 meters). At night, it migrated up to around 40 feet (12 meters) below the surface. The migration follows the movement of its food source, such as krill, which also makes a daily vertical migration. Megamouth sharks caught since the first sighting have had species of krill and other tiny prey in their stomachs.

There have been 41 megamouths caught since that first 1976 specimen, and with each encounter, we learn just a little bit more about this strange species.

7. Great White Sharks Can Go Weeks Without Eating

One shark species famous for its eating habits is the great white. This powerful predator is perfectly evolved to hunt down large prey, although the great white can go a long time between meals—reportedly as long as three months without eating, thanks to oil stored in their livers.

This is particularly useful for migration. For instance, females that feed off the coast of California will head out to an area known as White Shark Cafe, an area midway between Hawaii and California, during breeding season. Having plenty of oil stored in their liver helps them make this long journey through areas of ocean where little food can be found.

At the same time, claims that great whites regularly go weeks on end without eating are a bit of a stretch. Indeed, a 2013 study from the University of Tasmania showed great whites eat three or four times more than previously thought to sustain the high levels of energy they expend during hunting.

This new understanding of their activity level helps us better understand their crucial role in marine ecosystems, as the sharks are helping balance out larger populations of animals than previously suspected.

8. Some Shark Species Return to Their Birthplace to Reproduce

Sharks have a long memory, and where some shark species choose to give birth is proof they can hold on to information starting at a very young age.

A long-term study published in 2013 showed that at least some species of shark will return to where they were born to give birth, something called natal philopatry. It's the same behavior seen in many other animals, such as sea turtles that return to their birth beach to lay eggs, or albatrosses that return sometimes to within feet of where they were born to build nests for their own chicks.

The study tagged 2,000 baby sharks starting in 1995 and followed them for two decades.

“At least six females born in the 1993-1997 cohorts returned to give birth 14-17 years later, providing the first direct evidence of natal philopatry in the chondrichthyans. Long-term fidelity to specific nursery sites coupled with natal philopatry highlights the merits of emerging spatial and local conservation efforts for these threatened predators,” write the study authors.

For lemon sharks, this is particularly important information as they use mangrove forests as nurseries. Preserving mangrove habitat not only is key to protecting the future of this shark species, but of countless other species that need mangroves for protection, including humans.

9. Shark Skin Feels Like Sandpaper

You might expect a shark's skin to feel smooth, but it is not. Instead, it's rough, like sandpaper. Shark skin is covered with tiny teeth-like formations called placoid scales, or dermal denticles. Rays have the same thing. "Placoid scales are composed of a vascular (supplied with blood) inner core of pulp, a middle layer of dentine and a hard enamel-like outer layer of vitrodentine," explains the Australian Museum. They point back toward the tail and reduce friction when sharks are swimming. The scales do not grow in size, as happens with regular fish scales, but rather additional ones are added between the older scales.

10. Sharks Can Go Into a Trance

Sharks can enter a state known as "tonic immobility," which is a temporary state of inactivity. It happens when the animal is flipped over onto its back and becomes disoriented. Sensory pores located on the shark's snout detect and induce the state, causing it to relax and start breathing deeply and rhythmically, almost as if it's hypnotized.

Tonic immobility is helpful to researchers, as it allows them to subdue the shark, but its evolutionary purpose is not clearly understood. It might be a self-defense strategy, much like playing dead, though why an apex predator would want to do this is unclear. It could also be a hunting tactic. Shark Trust reported that in 1997, an orca in the Farallon Islands off California's coast was seen holding a white shark upside down for 15 minutes. "Whether intentional or not, the orca likely caused the shark to enter tonic immobility. Defenceless, the shark, suffocated. This also happened again in 2000."

11. Whale Sharks Have Unique Spot Patterns

Whale sharks are covered with white spots, but these vary significantly among animals. Researchers have discovered that each has a pattern that's as unique as a human's fingerprint is, making it possible to identify individual animals. To date, WWF has identified and catalogued 458 different whale sharks in waters around the Philippines.

12. Some Sharks Must Swim Continuously to Survive

The great white shark, the whale shark, and the mako shark rely on a form of breathing that requires them to swim with their mouths open. The faster they swim, the more water is pushed through their gills, oxygenating their bodies. If they stop moving, they don't receive that oxygen and they could die. This type of breathing is known as "obligate ram ventilation," but it does not apply to all shark species.

13. Some Sharks Use 'Spiracles' to Breathe

Certain species, such as nurse sharks and tiger sharks, do not have to keep swimming to receive oxygen. They rely on a method called "buccal pumping" to pull water into their mouths and over their gills. If they're buried in sand on the ocean floor or if their mouth is busy eating, they can switch their pumping method to "spiracles," which are respiratory openings located behind their eyes. These do the same job of pulling water to their gills.

14. Sharks Reproduce in Different Ways

As described above, not all baby sharks are born in the same way. Some come out of egg sacs that are laid outside the mother's body and left to take care of themselves upon hatching. These are known as oviparous (egg-laying) species. Others are viviparous (live-bearing) species, such as bull sharks, whitetip reef sharks, lemon sharks, hammerheads, and more. These lay eggs that hatch inside the mother's body and the babies are fed via a placenta. They are born in litters of anywhere from two to 20 pups.

15. Sharks Have a Sixth Sense

Sharks are successful predators thanks to electroreceptors, also known as "ampullae of lorenzini" located on the tips of their snouts, that allow them to detect electric fields nearby. Every other living thing emits tiny electrical fields, so admittedly those sharks are getting an unfair advantage when it comes to sniffing out prey. The pores on a shark's snout that house these electroreceptors are large enough to see with the human eye; they work best at close range, allowing a shark to move in for the kill or find fish that have buried in the sand. Scientists also think that the receptors may help sharks to follow water currents and might function as a sort of internal compass for navigating vast oceans.

Understanding more about sharks continuously reveals more about their crucial role in marine ecosystems, which also affect our own survival as a species. Studying sharks not only reveals more of these strange facts, but also reveals more about our reliance on them to keep our oceans in balance. Reversing the trend toward extinction of these ancient creatures has never been more important.