Sharks evolved over millions of years as an apex predator, yet are no match for humans

Megan Marples
CNNDigital
Published Sunday, July 11, 2021


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Sharks have called the Earth's oceans home for hundreds of millions of years and adapted to thrive in harsh environments.

While these top hunters of the deep blue have evolved to survive cold and dark climates, sharks are no match for the ultimate predator -- humans.

That's why Shark Week, running from July 11 through July 18, was launched 33 years ago by Discovery Channel to encourage shark conservation and educate the public on these underwater predators.

The world's shark and ray populations plummeted 70 per cent from 1970 to 2018, with overfishing as a primary cause, according to a 2019 study published in the journal Nature.

Of the 31 oceanic species of sharks and rays, 24, or over three-quarters, of the species are now threatened with extinction due to their steep drop in numbers, the study said.

With Hollywood blockbusters like "Jaws" and "The Meg" fanning the flames of fear and paranoia in humans, these underwater animals have suffered a serious image problem.

However, sharks play a crucial role in their environment and keep the animal kingdom in check.

Sharks balance the food chain

As sharks were killed off from overfishing in the Sea of Cortez, located between Baja California and the Mexican mainland, other creatures swooped in to take their place on the food chain.

Wahoo and hammerhead sharks, along with other fish species like marlin and swordfish, have seen a steep decline in population due to commercial and local fishing in the area.

Scientists believe the decline in sharks is one of the reasons the Humboldt squid now call the Baja home in greater numbers. The creature can grow up to 7 feet (2.1 meters) long and weigh over 100 pounds (45.4 kilograms).

The squid only live for a couple years, but they reproduce at a much faster rate than sharks.

Some sharks are partially warm-blooded

Despite having a reputation of being cold-blooded, some sharks -- like the great white and the salmon shark -- are able to internally regulate their temperature, according to a June study published by the British Ecological Society.

The study found endothermic fish, which are able to regulate their own body temperature, swam over one-and-a-half times faster than ectotherms, animals that rely on the outside temperature to regulate their body heat.

Researchers weren't able to make any conclusions on how the warm-bloodedness could be helpful to sharks, but they hypothesized that it could help them when searching for food or migrating.

Sharks can live for hundreds of years

Sharks tend to have one of the longest life spans of creatures in the animal kingdom.

Using radiocarbon dating to estimate how old Greenland sharks were for a 2016 study, researchers discovered the underwater creatures lived to be at least 272 years old, with the largest of the group clocking in at around 392 years old.

The animals don't reach maturity until the ripe age of 150 years old, and they are the longest-lived vertebrate known to humans.
Some can glow in the dark

A small number of sharks are bioluminescent and glow hundreds of feet below the ocean's surface, according to a February study published in Frontiers in Marine Science.

One of the sharks is the kitefin shark (Dalatias licha), which spans nearly 6 feet (1.8 meters). It's also the world's largest known bioluminescent shark.

Very little is known about sharks that glow because the sharks mostly roam in the deep sea, which begins over 656 feet (200 meters) below the ocean surface.


Researchers also discovered the southern lanternshark (Etmopterus granulosus) and blackbelly lanternshark (Etmopterus lucifer) have bioluminescent abilities.
They nearly went extinct millions of years ago

Despite having the reputation as an apex predator, sharks died off at alarming rates millions of years ago.

Over 90 per cent of open-ocean sharks disappeared from the planet around 19 million years ago, scientists said.

Researchers said they could not confirm what caused the near-mass extinction event, and it could have lasted from a single day to 100,000 years.

Based on current research, there was no climate or ecosystem crisis during this time, which leaves a gaping hole of knowledge for scientists to do more research on and unlock the mystery.




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