Sharks have evolved over millions of years as top predators, but they are no match for humans

(CNN) – Sharks have called Earth’s oceans their home for hundreds of millions of years and have adapted to thrive in harsh environments.

Although these great hunters of the blue depths have evolved to survive cold and dark climates, they are no match for the quintessential predator: humans.

That’s why Shark Week, which runs from July 11-18, was launched 33 years ago by the Discovery Channel to promote shark conservation and educate the public about these underwater predators.

The global populations of sharks and rays plummeted 70% between 1970 and 2018, with overfishing as the main cause, according to a 2019 study published in the journal Nature.

Of the 31 oceanic species of sharks and rays, 24, or more than three-quarters, are now in danger of extinction due to their sharp decline in numbers, according to the study.

With Hollywood blockbusters like “Jaws” and “The Meg” fanning the fire of fear and paranoia in humans, these underwater animals have suffered from a serious image problem. However, they play a crucial role in their environment and keep the animal kingdom in check.

Sharks balance the food chain

As sharks disappeared due to overfishing in the Sea of ​​Cortez, located between Baja California and the states of Sonora and Sinaloa, in Mexico, other creatures began to take their place in the food chain.

Wahoo and hammerhead sharks, along with other fish species such as marlin and swordfish, have experienced a sharp decline in population due to commercial and local fishing in the area.

Scientists believe that the decline of sharks is one of the reasons why the Humboldt squid now inhabits Baja California in greater numbers. This creature can be 2.1 meters long and weigh more than 45.4 kilos.

Squid only live a couple of years, but they reproduce at a much faster rate than sharks.

Some sharks are partially warm-blooded

Despite having a reputation for being cold-blooded, some sharks, such as the White shark and the salmon shark, are capable of internally regulating their temperature, according to a study published in June by the British Ecological Society.

The study found that endothermic fish, that is, that are capable of regulating their own body temperature, swam more than one and a half times faster than ectotherms, animals that depend on the outside temperature to regulate their body heat.

The researchers were unable to draw any conclusions about the usefulness of warm blood to sharks. However, they hypothesized that it could help them foraging for food or migrating.

Sharks can live for hundreds of years

Sharks tend to have one of the longest lives in the animal kingdom.

A group of researchers used radiocarbon dating to estimate the age of Greenland sharks in a 2016 study. In the study they found that the underwater creatures lived at least 272 years, and that the oldest of the group was about 392 years old.

Animals do not reach maturity until the ripe old age of 150, and they are the longest-lived vertebrates known to humans.

Some may glow in the dark

A small number are bioluminescent, glowing hundreds of meters below the ocean’s surface, study shows Posted in February in Frontiers in Marine Science.

One of these sharks is the kitefin shark (Dalatias licha), also called carocho, which measures almost 1.8 meters, which makes it the largest known bioluminescent shark in the world.

Very little is known about shining sharks because most of them move in the deep sea, which begins more than 200 meters below the ocean’s surface.

The researchers also discovered that the southern lantern shark (Etmopterus granulosus) and the black-bellied lantern shark (Etmopterus lucifer) have bioluminescent capabilities.

They were on the verge of extinction millions of years ago

Despite having a reputation for being a supreme predator, sharks became extinct at an alarming rate millions of years ago.

According to scientists, more than 90% of open ocean sharks disappeared from the planet about 19 million years ago.

Investigators said they couldn’t confirm what caused the near mass extinction event, and that it could have lasted from a single day to 100,000 years.

According to current research, there was no climate or ecosystem crisis during this time. That leaves a knowledge gap for scientists to continue investigating and unraveling the mystery.