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Neat to know ~ Creature of the month

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Caribbean Reef Shark at North Dry Rocks, Key Largo, 2021

Photo: Peter Kontakos, CC BY 2.0



There is a creature out there that was around long before the dinosaurs and that is still thriving today.  The shark, in all its many forms, has existed on the planet for some 400 million years.  To date, researchers have named around 500 species of shark.  They have been found in oceans all around the world, both in shallow waters and in the deep.  Their appearance and behavior have simultaneously fascinated and terrified humans for centuries.

Read on to discover more about these highly-evolved apex predators

Marine Marvels

– Sharks are at the top of the food chain making them what’s called, “apex predators.”  Their consumption of other creatures, particularly other smaller predators, is critical to the overall health and balance of the entire marine ecosystem.

– The sizes of sharks vary greatly.  The largest are whale sharks, which can be 40 feet in length (12.1 meters) and weigh up to 15 tons (13.6 metric tonnes).  Their mouths alone can be 4 feet (1.2 meters) in width!  These enormous creatures are gentle and graceful.  They glide through the sea with their mouths open, filter-feeding on plankton and fish eggs. 

20 million years ago lived the megadalon, a huge shark that would have made today’s whale sharks look miniature.  Scientists think that the megadalon was around 80 feet (24.4 meters) long, weighed 70 tons, and had a mouth that was 10 feet (3 meters) wide.  And, apparently, this would’ve been no gentle giant.  It had enormous teeth and a hefty appetite.  It most likely fed on dolphins, other sharks, and even humpback whales.

On the other end of the spectrum is the dwarf lantern shark, which can fit into a human hand. 

– Sharks have masses of teeth!  They lose those teeth regularly – some species lose some 30,000 teeth over their lifetimes – but new ones grow back as needed.  Most types of shark have several rows of teeth.  The powerful great white, for example, has jaws that can hold up to 300 teeth, arranged in seven rows.  Sharks’ teeth come in lots of different shapes and sizes, from triangular and pointed to jagged and serrated.

– Sharks usually feed on fish and other small sea creatures.  But if the opportunity arises, they might hunt mammals like seals.  Sharks are at the top of the food chain.  They “weed out” the sick and the weak and in this way help keep marine ecosystems healthy.  This includes coral reefs, where sharks keep populations of other predators under control so that the smaller fish, which take care of the reefs, can thrive.  Where shark numbers are dwindling, entire ecosystems have deteriorated, as the balance between prey and predator has been thrown off.

Contrary to some popular beliefs, sharks do not eat humans.  The chance of a person getting bitten by a shark is extremely slim — around one in 11.5 million.  Sharks might, however, lash out at a person if they feel threatened. 

– One characteristic that makes sharks such masterful predators is their speed.  Maybe you’ve heard of “aerodynamic,” meaning having a shape that allows for smooth movement through air.  But what about “hydrodynamic?”  “Hydro” comes from the Greek for “water.”  Sharks’ bodies are built for fast, effortless motion underwater, and this comes from their hydrodynamic design.  Their pointed heads and flat scales allow them to slice through water swiftly and quietly.  The fastest shark is the mako shark, which has been known to reach speeds in excess of 45 miles per hour.

– Sharks do not have bones.  Instead, their skeletons are made of cartilage, which is much more lightweight than bone.

– Sharks have a keen sense of sight, but they are most likely colorblind.

– Some sharks lay eggs and others give birth to live babies, called pups.  In either case, sharks do not reproduce at as high a rate as other fish.  They lay only a few eggs or give birth to a relatively small number of pups at a time.  Newborn sharks take years to reach reproductive age.

– The lifespan of sharks varies among species, but broadly speaking, they live for 20-50 years.  One extreme case is the Greenland shark, which is the longest-living vertebrate on Earth (vertebrates are animals with backbones inside their bodies).  These sharks inhabit the frigid polar waters of the Arctic and live for at least 250 years – but possibly for up to 500 years!  (To put this number into perspective, there might be a shark alive today that was born during the time of Medieval Europe!)

Extra Special Sharks

All sharks are remarkable.  Here are some interesting facts about a few of the hundreds of species that inhabit the world’s waters.

– Chain Catshark: This small shark communicates by glowing!  The fluorescent green light that flickers in patterns on its skin is, however, only noticeable when seen through a special blue filter light.

– Hammerhead Shark: The distinctive shape of this type of shark allows it to have a 350-degree scope of vision.

– Mako Shark: Not only is this shark the fastest of all sharks; it is also athletic and graceful.  It has been seen leaping 30 feet (9.1 meters) out of the water!

– Frilled shark: This is one of the rarest sharks.  It lives deep, deep below the surface of the sea – up to 1500 m down!  It can reach a length of almost 2 m.  These sharks have heaps of inward-curving teeth that resemble needles.  They are used for both catching and consuming large prey, which is often nearly as big as they are.

– Ornate Wobbegong:  These are so-called ambush predators, which means that they stay very still in one place and let their prey come to them.  When it’s close enough, they open their jaws and snap it up whole.  Large prey might remain in this shark’s mouth for several days before it is dead.

– Greenland Shark: As mentioned above, these cold-water sharks can live for centuries.  Their lifespans are so long, that they don’t exit “youth” and enter full adulthood until they are over 100 years old!


According to the IUCN, 143 shark species are currently endangered, and some are almost extinct.  This is largely due to their meat and in particular, their fins, being in high demand.  Some 100 million sharks are killed each year, largely as a result of being hunted for their fins, which are used in shark fin soup, a traditional delicacy in China that is said to have healing properties.

Habitat loss, climate change, and pollution are also causing shark populations to be on a sharp decline in many parts of the world.  The warming of the oceans, as well as the degradation of coastal lands due to building and development, have contributed greatly to the dying off of sharks.  Making the problem worse is the fact that sharks mature slowly and, as a result, reproduce slowly.  When they do have young, their broods are relatively small, compared to those of other fish.  Lots of sharks are killed before they have had a chance to reach adulthood and reproduce, causing their populations to shrink even faster.

Sources: wwf.org, “Sharks,” https://www.worldwildlife.org/species/sharknationalgeographic.com,” “Sharks,” https://www.nationalgeographic.com/animals/fish/facts/sharks-1; Signorelli, Laura, Museaum, “Ten interesting facts about sharks,” https://www.sea.museum/2020/01/16/ten-interesting-facts-about-sharks, February 10, 2020; Greenpeace.org, “10 Little-Known Shark Facts,” https://www.greenpeace.org/usa/10-little-known-shark-facts/, July 14, 2020; Panko, Ben, smithsonianmag.com, “More Than a Third of Shark Species Are Now Threatened with Extinction,” https://www.smithsonianmag.com/smart-news/more-one-third-shark-species-are-threatened-extinction-180978602/, September 8, 2021