Did You Know That Sharks Have Different Personalities? Plus 9 Other Facts

Trees first appeared on Earth during the Devonian period, around 385 million years ago, and dinosaurs about 100 million years later, between 250 to 200 million years ago. But you might be surprised to learn that sharks were present on our planet far before both.

Many people still have misconceptions about sharks as mindless killing machines. This simply is not true. Sharks, though their bite can do significant damage, are fascinating creatures with incredible behaviors and senses that many people cannot even conceive of. If you want to change your views on sharks and better appreciate these misunderstood animals, take a look at these 10 interesting shark facts.

1. Sharks Show Diverse Personalities

Humans don’t tend to come in contact with sharks as much as we do cats or dogs, both animals we have observed having personalities firsthand. Most people are probably happy about this, considering the widespread fear of sharks. But sharks are actually much more varied than people give them credit for.

Several studies, including a 2016 study published in The Journal of Fish Biology, found that sharks have individual personalities, just like people or pets! Different sharks and different species may display:

• Boldness and willingness to take risks
• Docility and gentleness
• Various levels of stress reactivity
• Different social behavior – great white sharks like to be alone, while lemon sharks are often found in schools

According to Kelly Link, the Associate Curator of Fish and Invertebrates at the Georgia Aquarium, sharks are so fascinating because there is such a wide variation between species and between individual sharks themselves. Link and her team manage the Ocean Voyager, the largest exhibit at the aquarium. She has come into contact with sharks several times through daily animal care, which includes all the feeding, cleaning, and diving to maintain the habitat.

As an example, she reflects on three female zebra shark sisters in the shark and ray encounter program. Link explains, “One was super impatient and would do anything for food, so we had to start by feeding her. The next would nudge her way to the feeder when it was close to her turn, but would veer around guests when they wanted to touch her. The last one was super chill, had no issues with guests touching her, and would patiently wait her turn to eat.” For other sharks, people have observed that whale sharks are “gentle giants,” oceanic whitetip sharks are “curious and confident,” and scalloped hammerheads are “timid and sensitive.”

2. Some Sharks Can “Walk” on Land

All creatures must eventually adapt and evolve to changing environments to ensure the longevity of their species. Sharks are no different. The epaulette shark has several adaptations that allow for easier movement and “walking,” both on land and under the sea.

This shark, usually found in the Great Barrier Reef or around Australia and New Guinea, has specialized pectoral and pelvic fins. The fins provide an expanded range of motion that functions somewhat like feet. As a result, epaulette sharks can propel themselves on the ocean floor or in tidal pools on land. This allows these sharks to hunt and find prey that other sharks cannot reach.

But that’s not all. Epaulette sharks can actually slow down their breathing and how much of blood that goes to the brain. By doing this, these sharks limit potential damage from being out of the water. They can survive out of water for an estimated one to three hours at a time.

3. Sharks Have Multiple Ways to Reproduce

Not every shark gives birth the same way. In fact, says Link, “sharks have multiple ways to reproduce.” She breaks this down into three distinct ways:

• Oviparous: Sharks that reproduce in this way lay eggs, often called “mermaid purses.” The eggs eventually hatch live young.
  • Types of oviparous sharks: Horn shark, small-spotted catshark, zebra shark
• Viviparous: The sharks, Link explains, “have live, placental birth.” Up to 50-60% of sharks are viviparous, with some estimates suggesting as high as 70%.
  • Types of viviparous sharks: Bull shark, hammerhead shark, Caribbean reef shark
• Ovoviviparous: In this case, the sharks do have eggs. Unlike oviparous sharks, in ovoviviparous sharks, the egg develops inside the womb, and then the sharks give birth to live young.
  • Types of ovoviviparous sharks: Great white shark, nurse shark, thresher shark

4. Shark Skin is Actually More Tooth-Like

What if, instead of soft skin, you had teeth all over your body? For sharks, this is a reality. Their rough-feeling skin is composed of dermal denticles. Also known as placoid scales, these denticles actually contain the same material as human teeth.

“Essentially, shark skin is made of modified microscopic teeth,” Link explains. Each dermal denticle has:

• A central cavity with pulp and blood flow
• Dentine
• Enameloid (a hard, mineral-rich tissue that protects teeth from damage)

Dermal denticles are extremely helpful to sharks’ survival and play many roles. “Denticles can protect from predators and parasites, protect from abrasions, and reduce drag when swimming, making the sharks more hydrodynamic,” Link says.

All sharks are covered in dermal denticles. But not all denticles are the same, says Link: “Different sharks have different-shaped and sized denticles, based on their needs.” For example, sharks that are fast and predatory have thinner denticles to help them move more efficiently in the water. Rare sharks like the bramble shark have more jagged, “thorn-like” denticles that may help protect it from predators.

5. Some Shark Species Glow in the Dark

Bioluminescence is when an animal or organism produces light through a chemical process. Animals may use bioluminescence for a variety of reasons, including scaring off predators, luring prey, attracting a mate, or even camouflaging. An estimated 57 shark species are bioluminescent and can light up in shining blues and greens.

The kitefin shark is the largest known bioluminescent vertebrate. Studying kitefin sharks, alongside lantern sharks, helped researchers better understand what causes this phenomenon. Unlike other bioluminescent creatures, these sharks do not have luciferin in their skin. Instead, researchers found that melatonin and other hormones give the sharks their shimmering shine.

6. Flipping a Shark Puts It Into a Trance

When flipped upside down, sharks enter a natural state of paralysis known as tonic immobility that can last up to 15 minutes. Researchers don’t know exactly why this happens, but tonic immobility has been potentially linked to:

• Mating rituals
• “Playing dead” to avoid predators
• Fear or shock
• Pain relief

Regardless, sharks are at their most vulnerable during tonic immobility. Though rare, killer whales have been known to induce tonic immobility in sharks to kill and eat them.

7. Sharks Can Reproduce without Males

Bonnethead sharks, hammerheads, and zebra sharks have all been known to reproduce young through a process called parthenogenesis. Essentially, these sharks can give birth without having to involve males. Parthenogenesis has been observed in sharks both in and outside of captivity. Many scientists believe that sharks may reproduce through automatic parthenogenesis as a survival mechanism if they cannot find a mate.

Note: Parthenogenesis is not unique to sharks. It has also been observed in certain birds, reptiles, insects, and fish.

8. Not All Sharks Have to Swim Constantly

When you visit an aquarium, you might wonder why some sharks are seemingly always swimming and others, like nurse sharks, can rest comfortably on the bottom of the tank. This has to do with how sharks breathe and whether they are ram ventilators or buccal pumpers.

“Zebra sharks and nurse sharks are buccal pumpers, meaning they can pump water over their gills themselves,” Link shares. These sharks can pull water through their mouths and over their gills. This lets them rest motionless on the ocean floor, sometimes for hours at a time.

Others, “like white sharks and blue sharks, do need to continue swimming because they breathe through ram ventilation,” she adds. Ram ventilators have to swim to breathe because the forward motion propels water over the gills. If they stop swimming, it can be fatal.

9. Some Sharks Can Heat Their Bodies

Temperatures can heavily fluctuate under the sea. Deep ocean water is typically colder. This aligns with the fact that many sharks are ectothermic, or cold-blooded. They cannot regulate their temperature. As Link explains, “Their body temperature changes based on the temperature of the water surrounding them.”

However, certain sharks, like white sharks or salmon sharks, are endothermic, or warm-blooded. Says Link, “These sharks use a counter-current heat exchange system to transfer heat from muscles to warm their bodies, allowing them to swim in much colder water than other sharks.” Salmon sharks have been known to reach temperatures up to 60.1 degrees Fahrenheit!

10. At Least One Shark Species is Semi-Omnivorous

Jaws terrified a generation. Suddenly, people found themselves terrified that getting in the water meant they’d be eaten by a bloodthirsty shark. But you don’t need to worry. While many sharks do have a diet that is largely meat-based, sharks do not actually set out to eat humans. Several sharks, including the basking shark and whale shark, are planktivorous, meaning they mostly eat plankton. However, these sharks will also eat some small sea creatures like squid or jellyfish.

Diet sets bonnethead sharks apart from other sharks. Bonnethead sharks do eat a variety of prey, including crustaceans and bony fish. But a 2018 study from researcher Samantha C. Leigh found that:

• Bonnethead sharks could fully digest seagrass and get nutritional value from it.
• These sharks could subsist on a diet that was 90% seagrass. In fact, in bonnethead sharks found in nature, up to 62.1% of their gut content mass was linked to seagrass.
• Enzymes found in the bonnethead sharks’ stomachs could be responsible for why they seem to be the only sharks able to consume seagrass.