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10 things you didn’t know about sharks

There are more than 400 known species of sharks inhabiting our planet’s marine ecosystems but detailed knowledge about most sharks is considerably lacking. Biologists often encounter barriers to studying sharks in captivity and in the wild due to factors such as their large size, relatively low demand in commercial markets, fast speeds, and wide habitat ranges. Because of this lack of general knowledge about these animals, misunderstandings arise and sensationalized stories are created out of fear. Admittedly, large fish with big, pointy teeth capable of swimming quickly can be intimidating but not all sharks fall into this narrow stereotype. To get in the Shark Week spirit this year, we’ve compiled ten surprising facts about these ancient and diverse creatures.

  1. The most primitive living shark is the frilled shark, named for its large frill-like gill slits encircling its head. This rare shark usually inhabits deep, cold waters and is shaped much like an eel.
  2. Where did the name “dogfish” come from? In the past, it was thought to originate from a time when the prefix “dog” was used to denote plants or animals unfit for human consumption. However, it turns out that the prefix was generally only used for inedible plants. These sharks were named simply because their actions mirrored that of dogs: they bite.
  3. Lanternsharks usually have bioluminescent skin organs called “photophores” on their sides or undersides that allow them to “light up like lanterns.” This bioluminescence allows the sharks to blend in with the light coming from the surface of the ocean (a process known as “counterillumination) and makes it difficult for predators below to spot them when looking up.
  4. The whale shark is the only species in the family Rhincodontidae and is the largest fish in the world, measuring about 5-10 meters. But fear not: these sharks are gentle giants and are only known to consume various plankton species, small fish, and crustaceans.
Denticules_cutanés_du_requin_citron_Negaprion_brevirostris_vus_au_microscope_électronique_à_balayage
Dermal denticles of a lemon shark viewed through a scanning electron microscope. Image by Pascal Deynat/Odontobase. CC BY-SA 3.0 via Wikimedia Commons.
  1. Sharks are largely known for the frightening-looking teeth in their mouths, but their entire bodies are actually covered in tiny dermal denticles: tooth-like scales that vary widely in shape between shark species. You definitely would not want to rub a shark the wrong way…
  2. Averaging 20-30 miles per hour (32-48 kilometers per hour), the shortfin mako is recognized as the fastest shark species. Its fast speed makes it an excellent apex predator capable of feeding on other quick-moving species such as sharks, swordfish, and bluefish.
  3. On the opposite end of the spectrum, the slowest moving shark species is the Greenland shark. Most individuals inspected in this species are also thought to be blind due to common eye infections caused by parasitic copepods. However, these seemingly sluggish and nearly blind sharks have been noted (through stomach content evaluation) to prey on fast-moving and agile seals and squid. While it has been suggested that the Greenland sharks wait undetected before ambushing unsuspecting prey, their ability to capture such fast-moving species still remains quite a mystery.
  4. Sharks have a sixth sense: electroreception. Minute gel-filled electroreceptor organs called “ampullae of Lorenzini” cover the head of sharks, particularly in the snout area. These organs enable the sharks to detect weak electric fields at short ranges, allowing them to detect animals – predator or prey – in the dark or hidden out of view.
  5. Some sharks take sibling competition to a whole new level in a process known as “oophagy”. Species that are oophagous are born live instead of in egg cases and are characterized by large embryos that feed directly on eggs in the uterus. In the early stages, these embryos have small yolk sacs that are quickly consumed. The embryos then develop a “precocious dentition” that allow it to feed on other ovulated eggs in the mother’s uterus.
  6. Lastly, the great white shark. Although most people think of these sharks as voracious predators, some larger individuals can actually be scavengers. In an effort to save energy, it has been suggested that great whites will occasionally opt to feed passively on large whale carcasses than engage in active predation.

Featured image credit: A whale shark in the Georgia Aquarium by Zac Wolf. CC BY-SA 2.5 via Wikimedia Commons.

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