Duh Nuh, Duh Nuh, Duh Nuh, Duh Nuh,
Duh Nuh, SHARK WEEK!
It’s that time of year — a week long celebration dedicated to the most jaw-some fish in the sea… sharks! We’re starting the week off with a game of Fact or Fiction. Think you would mako good shark biologist? Let’s sea if you can sniff out the fishy misconceptions, below…
Sharks have 7 rows of teeth.
Female sharks have thick skin.
Sharks can smell a drop of blood from a mile away.
Sharks have decay-proof teeth.
All sharks are carnivores.
Sharks must keep swimming in order to breathe.
As elasmobranchs, sharks do not have bones.
Sharks are dangerous.
Finished sorting fact from fiction? Now lets sink our teeth into the truth…
1. Sharks have 7 rows of teeth.
FICTION: Although some sharks do have seven rows of teeth, most have around five. Bull sharks have a whopping 50 rows of teeth (which offsets the average number of teeth to around 15 rows)! All these teeth make it easy to rip through prey with one powerful bite. Unlike humans’ teeth, sharks’ are not attached to their gums via a root, making it easier for them to fall out (especially when they’re chomping into tough food!). No sweat, some sharks can replace teeth as quick as one day after a losing them.
2. Female sharks have thick skin.
FACT: In some species, females’ skin is up to twice as thick as their male counterparts’. The ladies need thick skin to protect them from bites that ensue during shark mating. During some shark’s finteresting mating process, males nip a female’s back, sides, and fins to get into position. So much for taking a gill out for a bite to eat before you clasper…
3. Sharks can smell a drop of blood from a mile away.
FICTION: This popular myth is greatly exaggerated. Despite was Hollywood may have you believe, sharks cannot smell one drop of blood from a mile away. Sharks actually have similar smell to that of other fishes — meaning they can detect chemical cues with potency between around one part per 25 million and one part per 10 billion. Some sharks can smell blood from about a quarter mile away, but humans aren’t intentionally on the menu. For example, lemon sharks, which have a heightened sense of smell, can detect tiny particles in the water from far away. However, they’re more interested in chomping down on mollusks, crustaceans, or bony fish, making the scent of human blood much less appetizing.
4. Sharks have decay-proof teeth.
FACT: 4/5 dentists would approve of sharks’ oral hygiene! Some shark teeth have been found to contain fluoroapatites, a natural fluoride. Unlike human teeth, which are coated with hydroxyapatite, shark teeth’s fluoroapatites coating makes them less water soluble. This advantageous trait topes the charts as the best way to prevent cavity-causing bacteria.
5. All sharks are carnivores.
FICTION: Lets face it, sharks are often portrayed as man-eating monsters. Despite the tails we often hear, not all sharks are strictly carnivores. Bonnethead sharks, for example, preefer a Paleo diet of meat and plants, and are the first shark to receive official designation as an ‘omnivores.’ Whale sharks and basking sharks ingest both phytoplankton and zooplankton and derive nutrition from plants, making them technically omnivores, as well.
6. Sharks must keep swimming in order to breathe.
FICTION: Not all sharks need to swim in order to breathe. Some sharks swim to pass oxygenated water over their lungs, allowing them to breathe, while others can manually facilitate this water movement. Yes, sharks need oxygen too. Sharks breathe by passing oxygen-rich water over their gills, where red blood cells take up the oxygen molecules and exchange CO2, similar to our respiratory process. Many highly-mobile sharks use their swimming motion to force water over their gill slits, as seen in mako sharks. Others, like nurse sharks, can pump water over their gills, allowing them to lie stationary on the seafloor. When these sedentary sharks open their mouth, the pharynx expands and flattens their gill slits, creating a vacuum-like motion that sucks water in. By then constricting their pharynx, these sharks force water over their gill slits, recreating the motion of the ocean, allowing them to breathe.
7. As elasmobranchs, sharks do not have bones.
FACT: Ding, ding, ding! That’s right, sharks are members of the Chondrichthyes class containing cartilaginous fish. Chondrichthyes is divided into two sub-classes, one of which is elasmobranchs. All members of the Chondrichthyes class lack calcified bones. This characteristic keeps sharks afloat: without a swim bladder, sharks’ lightweight skeletal system is essential to maintaining buoyancy in the water column.
8. Sharks are dangerous.
FICTION: Is the thought of spotting a shark fin is enough to send shivers down your spine? Easy tiger… this myth is total bull. Paparazzi may love a good shark bait story, but sharks are statistically very unlikely to kill you. Let’s put that into perspective…
Enax, Joachim, et al. “Structure, Composition, and Mechanical Properties of Shark Teeth.” Journal of Structural Biology, vol. 178, no. 3, 2012, pp. 290–299., doi:10.1016/j.jsb.2012.03.012.
Leigh, Samantha C., et al. “Seagrass Digestion by a Notorious ‘Carnivore.’” Proceedings of the Royal Society B: Biological Sciences, vol. 285, no. 1886, 2018, p. 20181583., doi:10.1098/rspb.2018.1583.
Rohner, Ca, et al. “Diet of Whale Sharks Rhincodon Typus Inferred from Stomach Content and Signature Fatty Acid Analyses.” Marine Ecology Progress Series, vol. 493, 2013, pp. 219–235., doi:10.3354/meps10500.